CIMMYT

OPEC Fund for international development

Smart Mechanization – Smart

Small Farmer Engineering report of the FertiKit

Project manager: Ir. Jelle Van Loon

Project engineer & author: Louis Gabarra

2014

This report goes through the process of designing a kit to enable a variable rate application of granular fertilizer depending on the real-time input received from a nitrogeN-sensor

(GreenSeeker®). The project focuses on the integration of the tool for small- and medium-scale farmers working in conservation agriculture conditions in Mexico.

I Contents

II Table of Figures .............................................................................................................................. 3

II. Introduction .................................................................................................................................. 6

III Progress report ............................................................................................................................... 8

III.1 Development of the technological kit for installation on agricultural equipment ................ 8

III.1.1 State of the art of the principal components of the technological kit ........................... 8

III.1.1.1 Nitrogen sensors...................................................................................................... 9

III.1.1.2 Dispensers and variable rate application fertilizer meters ................................... 12

III.1.1.3 Hardware and data flow controllers ..................................................................... 16

III.1.1.4 General configuration of the technological kit ..................................................... 17

III.1.2 Design and development of practical solutions for tailor-made equipment ............... 17

III.1.2.1 Choice of N-sensor ................................................................................................ 17

III.1.2.2 Solution for the dispenser and VRA fertilizer meter ............................................. 18

III.1.2.3 Design of Hardware and data flow controllers ..................................................... 19

III.1.2.4 Adaptation of the system to be used with two GreenSeeker sensors and two

electric actuators (4-wheel tractor prototype) ........................................................................ 29

III.1.2.5 Use of data and database structure ...................................................................... 32

III.1.2.6 Linking the NDVI to the linear electric actuator .................................................... 34

III.1.3 Proposed prototypes .................................................................................................... 49

III.1.3.1 Conceptualization and presentation of prototype designs ................................... 49

III.1.3.2 Photos of the FertiKit ............................................................................................ 50

Structural .......................................................................................................................... 51

III.1.3.3 aspects to consider for the integration of the GreenSeeker® ............................... 51

III.1.3.4 Aspects to consider for the integration of Microprocessors ................................ 52

III.2 Evaluation and opportunity of the FertiKit ........................................................................... 52

III.2.1 Evaluation on field ........................................................................................................ 52

III.2.2 Generation of maps ...................................................................................................... 53

III.2.3 Possible improvements ................................................................................................. 54

III.2.3.1 Add components for better real-time evaluation and interpretation .................. 54

III.2.3.2 Sensor to detect the fall of material ..................................................................... 57

III.2.3.3 Integrate the real-time sensed speed of tractor ................................................... 58

III.3 Possible Return on Investment ................................................................................................. 59

IV Conclusion .................................................................................................................................... 60

V Bibliography .................................................................................................................................. 61

II Table of Figures

Figure 1. Automated worm screw in fertilizer bin (adapted from Jorgenson, 1988) ............. 14

Figure 2. Traction activated worm screw with sliding door Type A (adapted from Jorgenson,

1988) ........................................................................................................................... 14

Figure 3. Traction activated worm screw with sliding door Type A (adapted from Jorgenson,

1988) ........................................................................................................................... 15

Figure 4. Conveyer belt with automated sliding door (adapted from Jorgenson, 1988) ........ 15

Figure 5. Automated sliding fluted roller (adapted from Jorgenson, 1988) ........................... 15

Figure 6. Fluted roller with automated sliding door (adapted from Jorgenson, 1988) .......... 16

Figure 7. Schematic representation of the main components of the technological VRA kit or

FertiKit ......................................................................................................................... 17

Figure 8. An electric actuator in closed position, when activated the rod on the top will

move outwards luted roller with automated sliding door (adapted from Jorgenson,

1988) ........................................................................................................................... 18

Figure 9. The proposed VRA dispenser with its components - A) fluted roller box, B)Electric

actuator; the red arrow represents the linear movement performed in real-time by

B, while the purple arrow is the movement of the roller generated by the operation

traction. The striped arrow represents the trajectory of the fertilizer passing through

the fluted roller box. Finally the blue marked area indicates one of the grooves in

the fluted roller where the fertilizer is caught (adapted from Jorgenson, 1988) ....... 19

Figure 10. Components of the FertiKit for the 2-wheel tractor machinery with (A) the electric

actuator FA-PO-35-12-6’’® (Firgelli Automation Technologies In.) – Factsheets in

Annexe 4, (B) the GreenSeeker® (NTech Industries Incorporation, Ukiah,CA, EUA)

sensors are used to measure crop canopy reflectance and calculate Normalized

Difference Vegetative Index (NDVI)- Factsheets in Annexe 3, (C) the control box, and

(D) the battery- factsheets in Annexe 6 ...................................................................... 20

Figure 11. Control box of the two wheel tractor with (A) the board with relays to control the

linear electric actuator (B) the communication board compatible with Bluetooth and

(C) the process board .................................................................................................. 20

Figure 12. Pictorial diagram of the FertiKit for the two wheel tractor prototype .................. 21

Figure 13. Communication Diagram between the operator (Via Cellphone or Laptop) and the

FertiKit for the 2-wheel tractor ................................................................................... 22

Figure 14. Diagram of the process of the NDVI from the GreenSeeker (Main) ...................... 23

Figure 15. Interruption diagram of the process of the NDVI from the GreenSeeker ............. 24

Figure 16. Main communication diagram ............................................................................... 24

Figure 17. Interruption communication diagram .................................................................... 25

Figure 18. Drawing showing the GreenSeeker reading in a zone without any plant. In this

case the value returned by the sensor will be “ERROR” or a NDVI < 0.2 with (A) the

value returned by the GreenSeeker, (B) Sensor GreenSeeker, (C) the plant, and (D)

the area sensed by the sensor .................................................................................... 26

Figure 19. Drawing showing an option of the way output can be grouped. In this case, the

time” Tmeas” has been defined to be one second, what corresponds to 3 values. The

value that will be processed, to provide a recommendation of the amount of N

fertilizer to apply, will be the “AVERAGE” of the 3 values. Here the average will be

defined to be 0.6. The value 0.6 is the value that will be considered for the

recommendation of N fertilizer application for the distance “d”. Errors will not be

considered in the average with (A) the corresponding value returned by the

GreenSeeker, (B) the sensor GreenSeeker reading the status of the corresponding

area, (C) the area the sensor GreenSeeker is reading and (D)the plants. ................. 27

Figure 20. Components of the FertiKit for the 4-wheel tractor prototype with (A) the electric

actuator #1 FA-PO-35-12-6’’® (Firgelli Automation Technologies In.), (B) the Sensor

GreenSeeker® #1 (NTech Industries Incorporation, Ukiah,CA, EUA), (C) Battery #1,

(D) the electric actuator #2 FA-PO-35-12-6’’® (Firgelli Automation Technologies In.),

(E) the control box, (F) the sensor GreenSeeker® #1 (NTech Industries Incorporation,

Ukiah,CA, EUA), and (G) the battery #2. ..................................................................... 29

Figure 21. Pictorial diagram of the 4-wheel tractor prototype ............................................... 31

Communication diagram Figure 22. Communication diagram between the operator (via

cellphone or laptop) and the FertiKit for the 4-wheel tractor .................................... 32

Figure 23. Simplified schema of the intermediate memory (Buffer) that will enable to ensure

that the electric actuator’s position will be adjusted at the right time. The buffer can

receive data from the sensor while sending another data to the electric actuator. . 33

Figure 24. Drawing of the 2 and 4-wheel tractor where we can see how is defined the

distance “d” between the sensor and the applicator ................................................. 38

Figure 25. Picture of the gear box’s wheel tractor implement established for the calibration

..................................................................................................................................... 41

Figure 26. Graph showing the relation between the amount of fertilizer applied and the

position of the applicator in configuration "Y" ........................................................... 41

Figure 27. Scheme of the general transmission train for the 4-wheel tractor implement. .... 42

Figure 28. Graph comparing theoretical and traditional calibration. ..................................... 45

Figure 29.Scheme of the general transmission on train for 2-wheel tractor .......................... 46

Figure 30. Graph showing the relation between the amount of fertilizer applied and the

position of the applicator ............................................................................................ 48

Figure 31. An illustration of the proposed 2-wheel tractor prototype. A) N-sensor with its

mounting structure, B) fertilizer bin of the planter implement pulled by the tractor,

C) the 2-wheel tractor, D) position of one of the electric actuator of the VRA

dispensers ................................................................................................................... 49

Figure 32. An illustration of the proposed four wheel tractor prototype. A) N-sensor with its

mounting structure, B) fertilizer bin of the planter implement pulled by the tractor,

C) the four-wheel tractor, D) position of two electric actuators of the VRA dispensers

..................................................................................................................................... 50

Figure 27. Figure 33. An illustration of the proposed two wheel tractor prototype. A) N-

sensor with its mounting structure, B) fertilizer bin of the planter implement pulled

by the tractor, C) the two-wheel tractor, D) position of one of the electric actuator of

the VRA dispensers ..................................................................................................... 50

Figure 34. Close-up of one of the VRA-dispensers to be constructed, with A) the electric

actuator, B) the fluted roller and C) the connection between these two components.

..................................................................................................................................... 50

Figure 35. Structure in the front of the four wheel tractor to be constructed to sustain (A)

the control box, (B) the battery and (C) the GreenSeeker®. On the left, Louis Gabarra

is showing the flexibility of the system, being able to adjust the position of the

sensors to fit to different configurations (such as the height of the plant or bed’s

width) .......................................................................................................................... 51

Figure 36. A) Picture of the FertiKit integrated to the two wheel tractor for a test on field

with corn B) Picture of the variable rate application of fertilizer. The picture has

been taken after fertilizing with the 2-wheel tractor integrated with the FertiKit .... 52

Figure 37. Picture of the bed made of textile in order to simulate a wide range of NDVI (from

0.12 the red color to 0.86 the black color). This ensures repeatability of the test. ... 53

Figure 38. Photo (retrieved from MSO System) with (A) the connection cable from the

sensor to the system, (B) the sensor to detect the fall of material, (C) the piepe

where the material fall from the N applicator (top) to the incorporation into the soil

(bottom) ...................................................................................................................... 57

Figure 39. Louis Gabarra testing the capacitive sensor designed with (A) the granular

fertilizer being applied, (B) the fertilizer pipe and (C) the capacitive sensor designed

to detect the fall of material. ...................................................................................... 58

Figure 40. Graph showing the possible ROI for the FertiKit for the 2-wheel tractor (700 USD)

and 4-wheel tractor (1300 USD). For the calculation it has been assumed that the

average application is 300 Kg/Ha with possible savings of 10%. It corresponds to 22

USD per hectare. One cycle can be divided in several farmers due to the modular

conception of the add-on Fertikit. ............................................................................. 59

II. Introduction

Recently farmers have been significantly affected by changing climate (Ozor & Cynthia, 2010) and

increasing scarcity of natural resources (Klare, 2012). Lack of resources vital for farming such as

water (FAO, 2008) and fossil fuels (White & College, 2008) has caused an increase in production

costs with no relief in sight (Briggeman & Mickelsen, 2013). In particular, production of synthetic

nitrogen fertilizers requires a great deal of fossil fuel; therefore the price of fossil fuels and of

fertilizers is closely tied and fertilizer prices have been increasing. This has a large effect on the cost

of production, as fertilizer application constitutes a significant amount (up to 30%) of a farmers

input costs (FIRA, 2007). Despite the high costs of fertilizers, worldwide nitrogen application

efficiency is only 33% (B. Raun & Johnson, 1999). In addition to raising the costs of production, in-

efficient nitrogen application has severely negative impacts on the environment (McMcKagues,

Reid, & Simpson, 2005). Therefore, increasing the efficiency of nitrogen application is desirable

from many perspectives.

In addition to rising costs of inputs the farming community is facing another serious challenge: an

aging population. Young people perceive farming as drudgery, with low profits and little room for

innovation. As a result young, innovative people are leaving rural areas for what they see as better

opportunities in the cities (Sjoberg & Schreiner, 2008). For young people the gap between their

aspirations and what agriculture is offering gives rise to increasing disinterest in the field (Van Loon

& Cortés, 2014); in order to attract young people farming needs to incorporate innovative and

exciting technology (Blackmore, Stout, Wang, & Runov, 2005). Mechatronic integration with

tractors has the potential to offer such opportunities (Blackmore, 2009). Nevertheless, due to the

high initial investment, mechatronics is recognized to be cost effective for large-scale farmers only

(Jacques, 2013), rendering these technologies in-accessible for small-scale farmers. By integrating

mechatronics and agriculture in a way such that the technologies are accessible to small- and

medium-scale farmers, both declining farmer income and lack of on-farm innovation opportunities

could be addressed. Advances in technology are improving the price-performance ratio of these

technologies, making them more price accessible (Sistler, 1987); these technological advances need

only to be integrated into agricultural production systems.

This project aims to provide a variable rate fertilizer applicator with consideration of real-time

nitrogen-sensor values. It was focused on smallholder farmers in Mexico through the MasAgro

innovation networks with advanced mechanical solutions for progressive improvement of farming

techniques and smart mechanization within the scope of conservation agriculture principles (1). This (1)

Conservation agriculture (CA) aims to enhance soil properties focusing on minimizing soil tillage and leaving the

crop residue behind for soil rehabilitation, in combination with traffic control and crop rotation.

kit can be incorporated or complement commonly used farming machinery and will assist

smallholder farmers in decision making concerning fertilizer use. The proposed technological kit,

FertiKit, is therefore conceived as an add-on kit providing farmers an advanced but user-friendly

and financially accessible solution which aids in efficient fertilizer usage. To make this kit more

widely accessible, two different prototypes were designed and tested using the FertiKit; one

powered by a two-wheel tractor and the other by a four-wheel tractor.

III Progress report

The structural prototype work is being done in several a mechanical workshops. As for support on

initial development of the needed electronics, several meetings with CINVESTAV1 were held. The

response was limited, so a private company Cosas de Ingenieria2 was invited to facilitate the

development process of the automated components. A list of relevant collaborators on this project

is presented in Table 1.

Table 1. List of relevant partners of the Innovation Platform at present

Partner Role Status

Sembradora TIMS Mechanical supprt Active

CINVESTAV Initial support for automated processes Active

Cosas De Ingeniería Electronical support Active

(1) CINVESTAV - Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional or Center for

Research and Advanced Studies of the National Polytechnic Institute - http://www.cinvestav.mx/

(2) Cosas de Ingenieria – www.cosasdeingenieria.com – More detailed information of interactions is available upon

request

III.1 Development of the technological kit for installation on agricultural equipment

III.1.1 State of the art of the principal components of the technological kit

A comprehensive review of existing relevant technology was performed to identify priorities and

plan for attainable and potential pathways within the project’s scope. Here we present a review of

the ‘state-of-the-art’ concerning the principal components necessary to realize a real-time

automated system (referred to as the technological kit) for precision in situ fertilization. Specific

aims and choices followed from this in-depth study.

Variable rate application (VRA) of nitrogen fertilizers in real-time requires certain key components,

listed below.

- Nitrogen-sensors

- Fertilizer dispensers and VRA fertilizer meters

- Hardware and data flow controllers

For each components a broad array of options are available, but choices should be made focusing

on feasibility and/or constraints of small-scale farmers (SSF).

III.1.1.1 Nitrogen sensors

Nitrogen (N) sensors, are tools that assesses the amount of Nitrogen present in a plant at a given

moment. For this project, we required contact-free and non-destructive detection of N in a field

setting. In general, field-based N-sensors do not directly detect the N present in the plant. Indeed,

the color, or ‘greenness’ of the plant is used as an indicator of N status. Nitrogen is a building block

of chlorophyll, which is vital for plant photosynthesis and therefore plant growth. Since the majority

of the functional N in a plant is allocated to chlorophyll (Clevers & Kooistra, 2012) which gives plants

it’s green color, a lack of greenness can be interpreted as an N deficiency (Evans, 1983). As a result,

N-sensors are also called chlorophyll or green meters. NitrogeN-sensors take advantage of the

correlation between color and N-status by using Vegetation Indices (VI). VIs are ratios of reflectance

measurements of different spectral bands. The following table presents several types of VIs.

Table 2. Different vegetation indices (Vis), their specific characteristics and use if applicable

Vegetation Index Observations Example of

receptive sensor References

Normalized Difference Vegetation Index (NDVI)

Commonly used Highly non-linear

Saturating for highly vegetated areas

GreenSeeker

(Kanke, Raun, Solie, Stone, & Taylor, 2012; Rouse, Haas, Schell, &

Deering, 1973; Trimble, 2014b; Ünsalan & Boyer,

2004)

Red Edge Inflection Point (REIP)

Sensitive to noise Narrow spectrum range

OptRX (AgLeader, 2013; Guyot,

Baret, & Major, 1988; Kanke et al., 2012)

Nitrogen Balance Index (NBI)

Ratio of two indices - Chlorophyll/flavonol

Multiplex (Force A., 2014; Zhang, Tremblay, & Zhu, 2012)

GreenNDVI/RedNDVI Similar to NDVI

(Moges et al., 2004)

CI590 - Chlorophyll Index High sensitivity to canopy N

status Crop Circle

(Jones & Vaughan, 2010; Scientific Holland., 2014)

Ration Vegetation Index (Simple ratio)

Low detail in satellite images

(Nikolaos G Silleos & Alexandridis, 1996;

Vaiopoulos, Skianis, & Nikolakopoulos, 2004)

Perpendicular Vegetation Index

High efficiency at removing soil effect

(Jones & Vaughan, 2010; Wiegand, Richardson,

Escobar, & Gerbermann, 1991)

Soil Adjusted Vegetation Index (SAVI)

Adjustment factor varies with vegetation density

(Huete, 1988; Qi,

Chehbouni, Huete, Kerr, & Sorooshian, 1994)

For a more thorough review of VIs, their origins and implications please refer to (Jones & Vaughan,

2010; N.G. Silleos, Alexandridis, Gitas, & Perakis, 2006). For a review of vegetation indices with

improved performance on satellite images such as the Atmospherically Resistant Vegetation Index

(ARVI) and the Aerosol Free Vegetation Index (AFRI), the reader is referred to (Liu, Liang, Kuo, Lin, &

Huang, 2004).

Since VIs are calculated using reflectance measurements and calibrated with algorithms on

chlorophylls counts (Gitelson & Merzlyak, 1997), each of these indices has their own limitations.

III.1.1.1.1 Passive and active sensors

An N-sensor can be either passive or active. Passive sensors do not have a power source only work

when an auxiliary source provides the stimulus. Factors such as light intensity, solar position or sky

turbidity can significantly affect the sensor’s output, which makes it difficult to extract a reliable

recommendation in outdoor applications. Active sensors on the other hand, generate a signal (i.e.

laser, ultrasound, etc.) which is ‘rebounded’ back to the sensor by the measured object. The

difference between the emitted and received signal is interpreted (NASA, 2012). These sensors

have the advantage of being unaffected by environmental conditions, and thus provide more

reliable readings (Natural Resources Canada, 2014).

III.1.1.1.2 Site specific versus remote sensing

N-sensors can be used as Site-Specific Crop Management (SSCM) monitoring tools or as satellite

remote sensing tools. Both methods provide sensor-based solutions to observe, measure and

respond to inter- and intra-field variability in crops, but each has a different time utility and

recommended use. In general, satellite images can cover large areas at once with decent precision.

Nevertheless, it usually requires various measurements to absorb environmental effects and the

attainable resolution is still not very accurate for work on plant level (Osgood, 2012). As a result,

from the moment the first image is made it takes up to 10 days to produce reliable readings of the

scanned area. On the other hand, the availability of geopositional data, complementary to the VI

measurements, is an advantage since it provides essential information for mapping purposes. An

example of a satellite based NDVI application is the MasAgro GreenSat, which is being used for in-

season NDVI scans of huge areas in the Mexican Republic (MasAgro, 2014). Due to the large area

needed for accurate sensor operation, these satellite technologies are not feasible in small-scale

farming operations where fields may be less than 1 hectare.

The counterpart to these satellite sensors are the far more user-friendly and cheaper N-sensors

which offer the advantage of potential integration into handheld tools or farm machinery. They lose

the ability to analyze large areas but instead offer flexible, independent and local data on specific

plant N status (cf. SSCM). Options are plentiful for these systems, but price ranges vary

considerably. In Table 3, an overview of a series of commercially available SSCM N-sensors is

presented.

Table 3. Overview of a series of currently available SSCM-type N-sensors Sensor VI. Estimated installation price is for complete system. Sensors are listed in order from highest to lowest price.

Sensor VI used Installation

Estimated price for complete

system in USD

Reference Provider1

Multiplex NBI Anywhere on

tractor 35,000 (Force A., 2014)

Yara N-sensor NDVI Top of tractor 30,000 (YARA, 2014)

Isaria REIP Boom system on

tractor 30,000

(Fritzmeier, 2014)

Crop Circle NDVI Handheld 17,500 (Scientific

Holland, 2014)

Crop SPEC NDVI Anywhere on

tractor 10,000 (Topcon, 2014)

OptRx Crop Sensor

REIP Anywhere on

tractor 7,500 (AgLeader, 2013)

SPAD 502 NDVI Handheld 5,662 (Hegedus et al.,

2014)

GreenSeeker® Handheld

NDVI Handheld or mounted on

tractor 5,500 (Trimble, 2014a)

Pocket GreenSeeker®

Handheld NDVI Handheld 550 (Trimble, 2014c)

1Prices are based on personal communication with providers and website information

III.1.1.2 Dispensers and variable rate application fertilizer meters

III.1.1.2.1 Liquid/Gas versus granular fertilizers

When talking about dispensers or fertilizer meters which control the dose of fertilizer applied, one

should first consider the different physical states of commercial fertilizers. Usually fertilizer are

generically described by their N-P-K ratio(1) and can be in Gas, liquid or solid solution. Custom ratios

can be made by mixing fertilizers. In general gas and liquid fertilizer mixes are more homogenous

and the ratios are therefore applied to the field more precisely, especially when using variable

rates. However, in order to vary both the ratio and the rate of the liquid/gas fertilizer, a

sophisticated installation is required with many components including flow meters, pumps and

pressure gauges as well as a solid sealing system for all tubing, plugs and nozzles involved.

(1)3Ammonium nitrate (33-00-00) and urea (46-00-00) contain only N-fertilizer. Other commercial formulas combine

N, P and K , for example 12-8-16 which contains 12% nitrogen, 8% phosphorus and 16 % potassium.

In addition to the high initial investment costs(2), the complexity of the system would require an

advanced knowledge and specific maintenance care, two aspects that might cause serious issues for

the low resource farmer. As such, even though these systems have been implemented successful in

large-scale farmers, this option is not feasible for medium- to small-scale farmers.

Dry or granular fertilizer, on the other hand, is far more accessible and used worldwide, mainly

because of the ease of transport, storage and lower cost (FAO & IFA, 2000; FAO, 2006; Janssen &

Myers, 2011). More so, granular fertilizer formulas are a lot more practical to handle on field, even

more so now that pre-mixed bulk recipes are readily available on the market (FAO, 2006). Often,

ease of application is achieved at the expense of precision. Broadcast application results in un-

uniform distribution and generates losses due to lack of incorporation in the soil. Conservation

agricultural practices provide however the perfect conditions for a mechanical VRA band

fertilization, where seed and/or fertilizer due to the retained crop residues on the topsoil are placed

under the residue into a minimal strip into the soil.

In conclusion a granular fertilizer dispenser is flexible and precise, has a low initial investment cost,

is easy to operate and maintain comparing to gas and liquid installation. It is therefore the most

appropriate option for incorporation into a VRA fertilizer system for small and medium-scale

farmers. We have therefore preliminarily excluded liquid fertilizer systems from this project.

III.1.1.2.2 Dispensing Systems

When considering dispensing systems, the goal was to find an automated system which would

ensure the correct dosage for the correct plant in the correct place within the context of CA

systems. An initial overview of possible designs and solutions is presented, each one with its

drawbacks and advantages (Forouzanmehr & Loghavi, 2012; Jorgenson, 1988).

Small- and medium-scale farmers have specific considerations which must be taken into account

when choosing a dispenser. Firstly, the system must be simple to install and repair as expert

services may not always be available or affordable. Secondly, if the electronic system does fail, the

dispenser must continue to function as a constant rate applicator. Thirdly, the system must respond

quickly to input received in order to adjust rates with plant-wise precision. As fertilizers are

corrosive susbstances, the dispenser materials must be resistant to chemical and environmental

weathering. Additionally, the dispenser must be resistant to mechanical strain in order to avoid

frequent replacements. Finally, the overall cost is one of the most important considerations since

this determines at what acreage the system is profitable and will ultimately determine the viability

off the system for small-holder farmers (Babcock & Pautsch, 1998).

(2)From 30 000 up to 120 000 USD depending on the brand, provider, sensor and size

III.1.1.2.2.1 Automated worm screw in fertilizer bin Type A

A worm screw positioned in the fertilizer bin moves at

different speeds to adjust the amount of fertilizer that is

being pushed through the bin openings (Figure 1). This

system has the advantage of having a fast response

time, but high precision can be difficult to achieve.

Nevertheless, since these implements are widely

available commercially, they are cheap. There are

disadvantages: this system is located inside the fertilizer

bin and as such maintenance and cleaning could pose a

problem. Additionally, an auxiliary motor would be

needed in order for the screw to operate independently

from the tractor speed.

III.1.1.2.2.2 Traction activated worm screw with sliding door Type B

Another option is a worm screw which is activated by the traction of the machine in combination

with a small gate at the bottom of the bin which is

operated in real-time to achieve VRA of the

fertilizer (Figure 2). If the fertilizer feed to the

gates can be constant, precision can be improved

since control of the openings has been added, but

lag time with the opening and closing of the

smaller gates could become a problem. If not

handled with care, obstruction under the worm

screw and the closing gates can occur which

would damage either the fertilizers prills or the

mechanism.

Figure 1. Automated worm screw in fertilizer bin (adapted from Jorgenson, 1988)

Figure 2. Traction activated worm screw with sliding door Type A (adapted from Jorgenson, 1988)

III.1.1.2.2.3 Traction activated worm screw with sliding door Type C conveyer belt with

automated sliding door

This is the same system as the one described above,

but the gates are located at the end of the bins (Figure

3). The same maintenance and cleaning issues occur as

the above two options, and when many exits are

needed, this can become an expensive and complex

system, having to combine serial screws which move

simultaneously.

III.1.1.2.2.4 Conveyer belt with automated sliding door

Another option is a conveyer belt type dispenser

moved by the tractor operating speed in

combination with a motorized sliding door (Figure

4). The main problem would be the construction

cost, since this is not easily adaptable to readily

available fertilizer bins it would require many

customized components such as rollers and belts.

III.1.1.2.2.5 Automated sliding fluted roller

Commercially available fluted rollers are widely used in

mechanic constant rate fertilizer applications. Nevertheless, an

auxiliary system would have to be added to incorporate a VRA

mechanism (Figure 5). Opening and closing of the system

would require a great deal of friction, and good pressure

control would be needed. An advantage would be easy

incorporation into currently available machines and when

working correctly very high precision could be achieved.

Figure 3. Traction activated worm screw with sliding door Type A (adapted from Jorgenson, 1988)

Figure 4. Conveyer belt with automated sliding door (adapted from Jorgenson, 1988)

Figure 5. Automated sliding fluted roller (adapted from Jorgenson, 1988)

III.1.1.2.2.6 Fluted roller with vertical or horizontal automated sliding door

Using the same constant rate fluted rollers

mechanism, a sliding door (either vertical or

horizontal) could be added to avoid direct

interference with the calibration system (Figure

6). This would require less strength and would be

easy to install, but once again obstruction could

occur.

III.1.1.3 Hardware and data flow controllers

Previous sections described how sensors measure the greenness of the plant and how fertilizer

dispensers adjust the rate of fertilizer applied; these two independent systems need to be linked.

To do this, a set of hardware controllers needs to be chosen that interprets input signals and

creates an output. In order to assist in precision crop management it is preferable that the on-the-

go data can be stored for later analysis and even visualized on the spot for added control by the

operator.

III.1.1.3.1 Microprocessors

To control the dispenser systems a microprocessor will be needed, which will enable the system to

know the position of the dispenser at any time. Another microprocessor inside the preselected

hardware has to handle the data coming from the N-sensors and translate this into a signal which

will signal the other processor to open or close the fertilizer feed of the dispenser. Data loggers

normally are used for instant data storage but are usually rather expensive. Therefore the option of

incorporating a USB connection to the hardware is considered.

Several existing options were found, three are presented here:

1 - Building-block preset structure like the Waspmote (Libelium, 2014)

2- Open-source microcontroller boards like Arduino UNO (Arduino, 2014)

3 - Fully programmable digital single controller like a dsPIC microchip (Microchip, 2005)

The first option is more appropriate for many parameters in a certain location, and it allows you to

configure what sensors and components to be added on (i.e. customized Wi-Fi weather stations or

water quality monitors). The Arduino system fits this project’s goals because it is open-source and

very flexible. The dsPIC microchips can be completely custom tailored, but this option requires

advanced programming knowledge.

Figure 6. Fluted roller with automated sliding door (adapted from Jorgenson, 1988)

III.1.1.4 General configuration of the technological kit

After review of the necessary components, an overview is given in Figure 7 on the general structure

of the proposed technological kit. For easier reference, in the future this technological add-on kit

will be referred to as FertiKit. This is a tentative visualization; future versions might have extra

components, depending on the added value and economic feasibility of installation on the actual

prototypes.

Figure 7. Schematic representation of the main components of the technological VRA kit or FertiKit

III.1.2 Design and development of practical solutions for tailor-made equipment

The current state of the art of existing solutions for each essential component presented in the

previous section helps to inform design and development choices of the actual FertiKit. Initial

investment costs and the added value by changing to VRA from uniform rate application are the

main considerations governing which tool is economically viable for small- to medium-scale

farmers. Therefore the solutions aim to be the cheapest, most flexible and most user-friendly (i.e.

simple structure, few electronics and easy to clean or replace). Secondary considerations are the

feasibility of installation in existing machinery and the timeframe of this project. This implies also

that certain solutions are opted for because of previous experience or work with this equipment

within CIMMYT and direct collaborators.

III.1.2.1 Choice of N-sensor

As seen in Table 3, pricewise the obvious choice for an N-sensor is the Pocket GreenSeeker®

Handheld sensor (Trimble, 2014c), which at 550 USD per unit is by far the cheapest available.

Additionally, there is strong evidence that the use of spectral radiance including Normalized

Difference Vegetative Index (NDVI), improves nitrogen use efficiency (Bruinsma, 2009; Del Corso,

Lollato, Macnack, Mullock, & Raun, 2013; W. R. Raun et al., 2005; Stone, Solie, Whitney, & Raun,

1996; Zillmann, Graeffa, Linka, Batchelorb, & Claupeina, 2006). The Pocket Sensors lack some

precision in comparison to the other sensors; however, even with the reduced precision, the cost of

the sensor and robustness of N fertilizer algorithms compensate for this lack of precision (Crain,

Ortiz-Monasterio, & Raun, 20112). Additionally CIMMYT, together with Oklahoma State

University(1), has been active in the development of this implement and is still performing research

to improve algorithms to infer a plant N status based on its greenness readings.

(1)Oklahoma State Univesity (http://go.okstate.edu/) and its involvement in the development of the GreenSeeker®

units (http://npk.okstate.edu/green-seeker-sensor)

III.1.2.2 Solution for the dispenser and VRA fertilizer meter

In choosing a dispensing system one must consider the following criteria: this system must be

reliable, minimize chances of obstruction, be easy to install and detach when maintenance is to be

performed, but at the same time be powerful, speedy and controllable with precision. In light of the

last criterion, the logical solution is to add an auxiliary system. This would provide control and

operability while the standard fertilizer meter is driven by the traction has to be always in

synchronization with the operation speed. From past CIMMYT experience we know that the most

efficient option for uniform rate application a fluted roller meter (Figure 8). A linear movement

parallel to the axis of rotation can reduce or increase the amount of groove volume available to

capture and dispense fertilizer. This volume can be adjusted during operation using a mechanism

that pushes or pulls the fluted roller more or less into the fertilizer deposition orifice allowing

control of fertilizer volume distribution. To control this lateral movement an independent piston-

like rod can be installed which has enough force and speed for real-time manipulation of the fluted

roller position. To avoid complex installation and wiring issues an electric cylinder or actuator was

chosen (Figure 8) over hydraulic pistons (need for

hydraulic valves and cables) or secondary motors (heavy

and expensive). Additionally, the electric actuator is

small enough to be integrated easily on farm

implements, has sufficient loading capacity (50 kg

strength), and has satisfactory precision and speed

(about 2 inches per second). The electric actuator

therefore fulfills the FertiKit’s requirements

(Automation world, 2012; Design, 2000; Thomson,

2010).The proposed configuration is presented in Figure

9.

Figure 8. An electric actuator in closed position, when activated the rod on the top will move outwards luted roller with automated sliding door (adapted from Jorgenson, 1988)

An additional benefit of using an electric actuator is that its position at any time can be registered

by a potentiometer and consequently can be monitored and controlled by a microprocessor,

making the link between the N-sensor output and the linear adjustment of the fluted rollers volume

much less complex.

III.1.2.3 Design of Hardware and data flow controllers

This section will describe the electronic processing of the N-sensor output. First the process for one

sensor and one fertilizer applicator is described. Adaption for 2 sensors and 2 applicators is then

described. Finally, we describe the manner of saving and processing the data.

Figure 9. The proposed VRA dispenser with its components - A) fluted roller box, B)Electric actuator; the red arrow represents the linear movement performed in real-time by B, while the purple arrow is the movement of the roller generated by the operation traction. The striped arrow represents the trajectory of the fertilizer passing through the fluted roller box. Finally the blue marked area indicates one of the grooves in the fluted roller where the fertilizer is caught (adapted from Jorgenson, 1988)

III.1.2.3.1 FertiKit’s structure for the 2-wheel tractor prototype

Figure 10. Components of the FertiKit for the 2-wheel tractor machinery with (A) the electric actuator FA-PO-35-12-6’’® (Firgelli Automation Technologies In.) – Factsheets in Annexe 4, (B) the GreenSeeker® (NTech Industries Incorporation, Ukiah,CA, EUA) sensors are used to measure crop canopy reflectance and calculate Normalized Difference Vegetative Index (NDVI)- Factsheets in Annexe 3, (C) the control box, and (D) the battery- factsheets in Annexe 6

Control box ’s component

Figure 11. Control box of the two wheel tractor with (A) the board with relays to control the linear electric actuator (B) the communication board compatible with Bluetooth and (C) the process board

(A)

(B)

(C)

(D)

(A)

(B)

(C)

Schematics diagrams of the FertiKit

Figure 12. Pictorial diagram of the FertiKit for the two wheel tractor prototype

Communication Diagram of the FertiKit

The goals of the communication are to display in real-time the actuator’s position and NDVI output

from the GreenSeeker®. This will enable the operator to change the variables required to calibrate

the system, and to be able to analyze data post-operation. Bluetooth communication protocol was

chosen because it is widely used, wireless, user friendly and economic(Mahmoud & Al-Awami,

2003). The communication can be established on Android, Linux, Windows and IOS using

HyperTerminals(1).

The communication using the Terminal (protocol Bluetooth) was tested and used with Windows

(XCTU(2)) and Android (Blue Term(3)).

(1) HyperTerminal is a program that you can use to connect to other computers, Telnet sites, bulletin board systems

(BBSs), online services, and host computers, using either a modem, a null modem cable, or a TCP/IP (Winsock)

connection (Hilgraeve, 2014; Microsoft, 2005)

(2) XCTU is a free multi-platform application designed to enable developers to interact with Digi RF modules

through a simple-to-use graphical interface. It includes new tools that make it easy to set-up, configure and test

XBee® RF modules (Digi, 2014).

(3)

The Blue Term App is simply put a Serial Terminal for your Android Phone or Tablet. It provides many of the

basic features you have come to expect from a standard Serial Terminal on a PC. The big difference is that it is on

your Phone or Tablet, and that it is designed specifically to work with Bluetooth to Serial devices. It doesn’t

emulate web terminal, SSH, or other options that you might find on the drop down menu in TeraTerm or

Hyperterminal (Dattilo, 2014).

Figure 13. Communication Diagram between the operator (Via Cellphone or Laptop) and the FertiKit for the 2-wheel tractor

Flow diagrams - Codingboard process

Figure 14. Diagram of the process of the NDVI from the GreenSeeker (Main)

Figure 15. Interruption diagram of the process of the NDVI from the GreenSeeker

Flow diagrams - Codingboard communication

Figure 16. Main communication diagram

Figure 17. Interruption communication diagram

III.1.2.3.2 Processing of NDVI (“ERROR” and grouping values)

The N-sensor (GreenSeeker) has a maximum read speed of 3 measurements per second. It is

possible for some measurements to register as errors and there must be a system in place to

manage these values to avoid misinterpretation. For example, if the sensor is reading bare soil the

value returned by the sensor can be either an error or a NDVI < 0.2 (Digi, 2014). Therefore, if the

NDVI returns an error, it is assumed there is no plant and therefore no need to apply fertilizer. The

system is therefore designed to completely close the fertilizer applicator in the case of an error

reading or a reading below 0.2.

Important: Closing the applicator when the sensor returns errors or values under 0.2 will ensure the

applicator is closed when the operator leaves the field.

Value

= ERROR (A)

(B)

(C)

(D)

Figure 18. Drawing showing the GreenSeeker reading in a zone without any plant. In this case the value returned by the sensor will be “ERROR” or a NDVI < 0.2 with (A) the value returned by the GreenSeeker, (B) Sensor GreenSeeker, (C) the plant, and (D) the area sensed by the sensor

Tractor movement and time to process (Tp) must be considered in relation to the sensor readings:

1) Information could be lost preventing to ensure the application of the right quantity on the

right plant.

2) The reading of the sensor is not continuous (1/300 HZ 3 readings per second) whereas

the application of fertilizer is. Without additional processing, the rate of fertilizer to be

applied between readings would be undefined.

3) The sensor takes 1 reading every 300 ms, but the time necessary to process the information

is 500 ms; therefore not every sensor reading can be processed.

4) If the actuator were instructed to move every 500 ms, the electric actuator, the battery and

the applicator of fertilizer would be over solicited.

Considering the above limitations, it is preferable to process the GreenSeeker output by grouping

values and taking the average of that group.

The number of values (NDVI) that will be grouped can be adjusted by the operator before the

operation. The variable to adjust is defined as “Tmeas” (time of measurement), corresponding to

the time the sensor is configured to generate an average for a group of values.

Conditions:

The minimum value for “Tmeas” is 500 ms (“Tp”).

“ERROR” will not be included in average calculations. In the example presented in the

drawing below, the “AVERAGE” would be 0.6.

If all the values returned by the sensor are “ERROR”, the program will consider the quantity

of fertilizer to apply equal to zero.

Figure 19. Drawing showing an option of the way output can be grouped. In this case, the time” Tmeas” has been defined to be one second, what corresponds to 3 values. The value that will be processed, to provide a recommendation of the amount of N fertilizer to apply, will be the “AVERAGE” of the 3 values. Here the average will be defined to be 0.6. The value 0.6 is the value that will be considered for the recommendation of N fertilizer application for the distance “d”. Errors will not be considered in the average with (A) the corresponding value returned by the GreenSeeker, (B) the sensor GreenSeeker reading the status of the corresponding area, (C) the area the sensor GreenSeeker is reading and (D)the plants.

III.1.2.3.3 Position of the electric actuator feedback

Different options are available to control the position of the actuator:

Incorporated potentiometer of the sensor(1)

External positions sensors(2)

Intern positions sensors (3)

Manual calibration(4)

(1) Incorporated potentiometer of the sensor: Some linear actuators come with a potentiometer incorporated.

For the prototype conception, linear actuators (with incorporated potentiometer) of two providers have been

tried (From Accele and Firgelli) (2)

External positions sensors: This option refers to add different positions sensors along the stalk of the linear

actuator such as photoelectric, capacitive, inductive, and ultrasonic. (3)

Intern positions sensors: It refers to add an positioN-sensors inside the motor of the electric linear actuator. (4)

Manual calibration of the sensor can be done taking as references the two extreme positions of the electric

actuator (max. and min.). Moving from one position to the other, the sensor will be calibrated taking as a

reference the voltage necessary to travel the distance between the extremes.

Value #1

= ERROR

Value #3

= ERROR

Value #2

= 0.6

Distance “d”

(A)

(B)

(C)

(D)

Table 4. Comparative table of the different options to calibrate the position of the linear electric actuator (potentiometer)

Options for potentiometers

Advantages Disadvantage

Incorporated potentiometer of the

sensor

No need extra components No need external procedure

Reliability and precision(1) Maintenance(1) Increase cost(2)

External positions sensors Easy to install and maintain

Possibility to configure the precision

Increment the inventory (2) Subject to external

degradations

Intern positions sensors Possibility to configure the precision Protected from external degradation

Require to open and modify the actuator(3)

Increment the inventory (2)

Manual calibration

No sensor needed Reliability(4)

Adaptable to every linear actuators Lowest cost

No sensor to return the position during the use(5)

To provide a low cost, user friendly and robust solution ensuring compatibility with a wide range of

electric actuators, the manual calibration has been chosen to return the position of the actuator in

real-time.

(1) We performed a test with two different actuators (Accele & Firgelli) to explore the differences in precision and

behavior. This variability in the characteristics of the incorporated potentiometer affects the flexibility regarding the

electric actuator to use. As such, the system would be programmed for specifics actuators only. (2)

Increasing inventory tends to raise the possibility of fails, the total cost, and the amount of providers

(complicating the purchase of material) (3)

When opening components such as the electric linear actuator some damages can be incurred, which can affect

the entire system. (4)

The test has been realized offering a 0.5 mm precision regarding the real position and the value returned (5)

The value returned depends on the initial calibration and the voltage applied. It may require recalibrating it

during the use.

III.1.2.4 Adaptation of the system to be used with two GreenSeeker sensors and two electric

actuators (4-wheel tractor prototype)

This system will utilize two sensor-VRA combinations – the groups will operate independently but

calibration and control of the processed values will be accessible through the same Bluetooth

communication flow (scheme below).

III.1.2.4.1 Components

Figure 20. Components of the FertiKit for the 4-wheel tractor prototype with (A) the electric actuator #1 FA-PO-35-12-6’’® (Firgelli Automation Technologies In.), (B) the Sensor GreenSeeker® #1 (NTech Industries Incorporation, Ukiah,CA, EUA), (C) Battery #1, (D) the electric actuator #2 FA-PO-35-12-6’’® (Firgelli Automation Technologies In.), (E) the control box, (F) the sensor GreenSeeker® #1 (NTech Industries Incorporation, Ukiah,CA, EUA), and (G) the battery #2.

(A) (D)

(E)

(B) (F)

(G) (C)

III.1.2.4.2 Control box’s components

The control box of the 4-wheel tractor prototype has two levels and 5 boards as shown in the

following pictures.

Figure 24. Microprocessors card for the 4 wheel tractor with (A) the process board sensor (B) the communication board (C) the relay board electric actuator (D) the process board Sensor 2 and (E) the relay board electric actuator 2

(A)

(B)

(C)

(D) (E)

III.1.2.4.3 Diagram of the FertiKit for the 4-wheel tractor prototype

Figure 21. Pictorial diagram of the 4-wheel tractor prototype

Communication diagram

Figure 22. Communication diagram between the operator (via cellphone or laptop) and the FertiKit for the 4-wheel tractor

III.1.2.5 Use of data and database structure

III.1.2.5.1 Possible use of data

For better understandings of field variability the producer will be able to analyze the data collected

during the operation on field. The

data can be used to generate a map

(Figure 20). In this case the map

was created by classifying different

zones according to NDVI readings.

For visual interpretation, the value

of the NDVI could be related to a

color (for example green for areas

with high NDVI and red for areas

with low NDVI).

III.1.2.5.2 Intermediate memory (Buffer)

It’s important to have an intermediate memory in order to control when the data generated by the

GreenSeeker is processed. The time the buffer will ‘keep’ the information is directly related to the

time necessary for the tractor to travel the distance between the sensor and the fertilizer

applicator. Since the linear electric actuator and the GreenSeeker work on different areas of the

field at the same time, this buffer will ensure that the adjusted rate of fertilizer will be applied on

the correct part of the field. A simplified scheme of the buffer function is shown in the drawing

below.

Figure 23. Simplified schema of the intermediate memory (Buffer) that will enable to ensure that the electric actuator’s position will be adjusted at the right time. The buffer can receive data from the sensor while sending another data to the electric actuator.

NDVI received and processed

Buffer

GreenSeeker generating NDVI

Linear electric actuator receiving

instruction

Order sent to the motor

Data waiting to be sent to the motors (time Tv

defined by the operator)

Figure 20. Map made with NDVI range of values. The darkest color signifies the highest NDVI measured and the lightest indicates the lowest NDVI values (Verhulst & Govaerts, 2010)

After establishing the communication between the GreenSeeker® and the linear electric actuator

we defined and calibrated the relationship between the NDVI of the GreenSeeker® and the position

of the applicator of fertilizer (actioned by the linear electric actuator). The following section will

describe the formula used to translate the NDVI output into a recommendation of the amount of N

fertilizer to apply.

III.1.2.6 Linking the NDVI to the linear electric actuator

In this section, three aspects will be reviewed:

1) Formula to convert the NDVI provided by the GreenSeeker® into a recommendation of kg

N/ha for maize

2) Synchronization considering the speed of the tractor and the distance from the sensor to

the application point

3) Calibrating the relation between the recommendation of kg N/ha (“X”) and the position of

the actuator

III.1.2.6.1 Formula to convert the NDVI provided by the GreenSeeker® into a recommendation of

kg N/ha for maize

The formula to relate the NDVI reading to fertilizer application recommendation has been defined

for maize in the El Batan* region of Mexico by Dr.Ivan Ortiz-Monasterio (Ortiz-Manasterio, 2014)

using the in-season method of determination (Lukina et al., 2001; Solie, Monroe, Raun, & Stone,

2012; Tubaña et al., 2008).

*Trials occurred in the research center of CIMMYT in El Batan - Latitude / Longitude: N 19 ° 31 ' 52 '', W 98 ° 50 '

50 ''- Elevation: 7448 feet - City: Texcoco - State: ESTADO DE MEXICO (Wunderground, 2014).

General formula obtained for corn in El Batan

X = (0.012 ∗ 𝑌𝑚𝑎𝑥 ∗ (

𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙𝐺𝐷𝐷𝑠𝑢𝑚 )

1.2516

𝑁𝑈𝐸) ∗ (

𝑁𝐷𝑉𝐼𝑟𝑠

𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙− 1)

Equation 1 Formula relating the NDVI measured on field (NDVIreal) to the recommendation of N fertilizer to apply in kg/ha (X)

III.1.2.6.2 Variables:

“X” is the recommended amount of fertilizer to apply to the plant in kg N/ha(1)

“NDVIreal” is the NDVI of the plant measured in real-time with the GreenSeeker®

“NDVIrs” is the NDVI of the Nitrogen Rich Strip(2)

“NUE” is the Nitrogen Use Efficiency(3)

“GDDsum” (Growing Degree Days)(4)

“Ymax” is the maximum yield possible to reach depending on the region and the crop

(1) The dose of nitrogen fertilizer (urea) to apply is commonly established in kg N/ha (Tubaña et al.,

2008). For the variable rate application in real-time, the kg N/ha will be converted in the

corresponding proportional rate to apply for the specific area sensed by the GreenSeeker®. (2) It is hard to detect N deficiencies in actively growing crops without comparing the crop to crops

with sufficient N. The easiest way to do that is to create strips with guaranteed sufficient N, applied

at non-limiting but also non-excessive amounts. These plants are known as the Nitrogen Rich Strip

(B. Raun et al., 2010).

(3) “NUE” (Nitrogen Use Efficiency) has been established (B. Raun & Johnson, 1999) that the

worldwide value for the NUE is about 33% using the following formula:

Equation 2 NUE formula defined by Girma, Holtz, Tubaña, Solie, & Raun in 2011

(4) “GDDsum” (Cumulative Growing degree days) is a measurement of heat units since planting

above a prescribed base. The formula of the GDD for one specific day called “d” is defined by:

𝐺𝐷𝐷 =𝑇𝑚𝑎𝑥{𝑑} − 𝑇𝑚𝑖𝑛{𝑑}

2− 10

Equation 3 GDD formula defined for a specific day “d” by McMaster & Wilhelmb in 1997

Where:

“Tmax{d}” is the maximum temperature recorded in the day d*

“Tmin{d}” is the minimum temperature recorded in the day d*

*Both variables have a maximum value equal to 30 and a minimum value equal to 10. In case values

are out of the interval [10 ; 30], they will be adjusted to fit in it as shown in the following example.

Example: if Tmax{d}=36 and Tmin{d}=5 then define the values the Tmaxadj{d}=30 and

Tminadj{d}=10 Where Tmaxadj{d} and Tminadj{d} are the values adjusted to fit in the interval (will

only be adjusted if required).

The general formula of the GDD is:

𝑮𝑫𝑫 =𝑻𝒎𝒂𝒙𝒂𝒅𝒋{𝒅} − 𝑻𝒎𝒊𝒏𝒂𝒅𝒋{𝒅}

𝟐− 𝟏𝟎

Equation 4 GDD formula taken into account the limit regarding the range of temperatures

The GDDsum is defined cumulative growing degree days from one day after planting to the day of

the operation. The formula of GDDsum is:

𝑮𝑫𝑫𝒔𝒖𝒎 = ∑ (𝑻𝒎𝒂𝒙𝒂𝒅𝒋{𝒅} − 𝑻𝒎𝒊𝒏𝒂𝒅𝒋{𝒅}

𝟐

𝒅𝟐

𝒅=𝒅𝟏+𝟏

− 𝟏𝟎)

Equation 5 GDDsum formula to consider integrating in the calibration of the system

Where:

“d1” is the planting date

“d2” is the date of the operation

The process to obtain historical temperatures required to calculate GDDsum is described in Annex

2.

III.1.2.6.3 Conditions

The formula has 4 conditions:

First condition:

If,

10000000 ∗ (𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙

𝐺𝐷𝐷𝑠𝑢𝑚)

1.2516

> 𝑌𝑚𝑎𝑥

Then, X = 0

Second condition:

If,

10000000 ∗ (𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙

𝐺𝐷𝐷𝑠𝑢𝑚)

1.2516

∗𝑁𝐷𝑉𝐼𝑟𝑠

𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙> 𝑌𝑚𝑎𝑥

Then,

X = (0.012

𝑁𝑈𝐸) ∗ (𝑌𝑚𝑎𝑥 − 10000000 ∗ (

𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙

𝐺𝐷𝐷𝑠𝑢𝑚)

1.2516

)

Third condition:

If, 𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙 > 𝑁𝐷𝑉𝐼𝑟𝑠

Then, X = 0

Fourth condition

If, 𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙 < 0.2

Or 𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙 = "𝐸𝑟𝑟𝑜𝑟"

Then,

X = 0

𝑁𝐷𝑉𝐼𝑟𝑒𝑎𝑙 = "𝐸𝑟𝑟𝑜𝑟"

III.1.2.6.4 Synchronization between the program and the mechanical aspects

This part will describe how the system will take into account the distance between the sensor and

the fertilizer applicator in order to place the fertilizer on the right field section at the appropriate

time.

Definition of the time “Tv” to be considered by the operator to ensure the

synchronization

The distance from the sensor to the applicator can differ from one machine to another. For

example, in the case of the two prototypes presented for 2- and 4-wheel tractors, this distance

(“d”) will differ (see drawing below).

Figure 24. Drawing of the 2 and 4-wheel tractor where we can see how is defined the distance “d” between the sensor and the applicator

In addition to the distance between the sensor and the applicator, the velocity “v” at which the

tractor is traveling must also be taken into consideration. In the prototype presented here the

‘d’=5.95

meters for

the 4 wheel

tractor

‘d’=2.80 meters

for the 2 wheel

tractor

velocity will have to be defined by the operator before beginning field operations. In the future,

prototypes could include a speed meter to ensure the reliability and enable real-time adjustments

according to instantaneous speeds.

The formula to consider is:

𝒗 =𝒅

𝑻𝒕𝒐𝒕

𝐓𝐭𝐨𝐭 =𝐝

𝐯

Where

“Ttot” is the total time to consider between the reading of the sensor and the fertilizer

application into the soil

“d” is the distance between the sensor and the place where the fertilizer is incorporated

“v” is the speed of the tractor in m s-1

Definition of “d”

The operator use a flexible tape measurer to determine the distance between the lens of the

GreenSeeker® and the point of fertilizer incorporation (refer to Figure 25).

Definition of “v”

The speed of the tractor during the operation has to be fixed before going on field. As mentioned

above, the possible variation on field won’t be considered.

Definition of “Ttot”

First we define the average time for the fertilizer to fall along the hose from the applicator to the

soil is defined by “Tfa”.

We define “Tav” as the time available for the system to get the electric actuator in the position

from the measurement of the GreenSeeker®. It’s defined by:

𝑻𝒂𝒗 = 𝑻𝒕𝒐𝒕 − 𝑻𝒇𝒂

And,

𝑻𝒗 = 𝑻𝒂𝒗 − 𝑻𝒑

Where:

“Tp” is the time to process the readings of the sensor, its value is 500ms.

“Tv” is the variable time that will have to be defined by the operator during the

calibration of the system to ensure that the fertilizer will be applied in the right place.

Then the general formula to determine “Tv” is:

𝑻𝒗 = 𝑻𝒕𝒐𝒕 − 𝑻𝒇𝒂 − 𝑻𝒑 =𝒅

𝒗− 𝑻𝒇𝒂 − 𝑻𝒑

𝑻𝒗 =𝒅

𝒗− 𝑻𝒇𝒂 − 𝟓𝟎𝟎𝒎𝒔

Equation 6 Definition of the time “Tv” to be considered by the oeprator

III.1.2.6.5 Calibration of the VRA dispenser

Once the NDVI value has been converted into an N application rate, it will be necessary to link this

quantity to the position of the electric actuator. The relation will depend on the characteristics of

the applicator and the transmission between the traction wheel and the rotating axis of the

fertilizer applicator. Therefore each specific N applicator will need calibration.

In this section we will review the method to calibrate the N applicator of the 2- and 4-wheel

tractors. The purpose of the calibration is to ensure a reliable procedure which will provide

reproducible results (Iglesias, Paneque, & Shkiliova, 1999).

The importance of this calibration cannot be over-emphasized (Price, Beumer, Graham, & Hausler,

1997). This report will review two different methods to calibrate a machine, one traditional and the

other theoretical (Alberta, 2014; Riethmuller, 2006). Results from both calibrations are compared in

order to evaluate the reliability of the theoretical method. The theoretical method offers the

possibility of predicting relationships using simpler experiments (Roux and al., 1999).

Both calibrations will be set up for a fixed configuration of the gear box, transforming the speed of

the tractor to the angular velocity of the axis controlling the application of fertilizer. The theoretical

calibration will enable predication of the quantity applied in any configuration and tractor speed

whereas the traditional method of calibration will need to be repeated for each new configuration

of the great box.

Calibration of the 4-wheel tractor prototype 1.

The configuration of the gear box for both the theoretical and

traditional calibrations of the N applicator of the 4-wheel tractor are

shown in Figure 25. The following calibration will refer to this

configuration; any change will require re-calibrations.

Traditional calibration of the 4-wheel tractor prototype

In Annex 1 the traditional method of calibration is presented; the

results are presented in Figure 26. On the graph is the formula

linking the position of the applicator to the quantity of fertilizer

applied in kg/ha in “Y configuration”.

The general formula linking the fertilizer application and the position of the linear actuator is:

𝒚 = 𝒂𝒙

The equation is

𝒚 = 𝟐𝟑. 𝟒𝟗𝟏𝒙

Where

Entrance

of the

gear box

Exit

of the

gear box

Figure 25. Picture of the gear box’s wheel tractor implement established for the calibration

Figure 26. Graph showing the relation between the amount of fertilizer applied and the position of the applicator in configuration "Y"

23.491 is the specific value for the applicator and the gear box configuration used during the

calibration

“y” is the quantity of fertilizer applied

“x“ is the position of the actuator

Theoretical calibration of the 4-wheel tractor prototype

The theoretical method uses the kinematic study of the characteristics of the specific gear train of

the 4-wheel tractor implement.

where

“𝜔1” 𝑖𝑠 𝑡ℎ𝑒 𝑎𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑤ℎ𝑒𝑒𝑙 in rad.s-1. It depends on the speed of

the tractor.

“𝜔2”, “𝜔3”, “𝜔4” and “𝜔5” are intermediate 𝑎𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡is 𝑜𝑓 𝑡ℎ𝑒 transmission train in

rad.s-1.

“𝜔6” 𝑖𝑠 𝑡ℎ𝑒 𝑎𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 of the axis controlling the application of fertilizer in rad.s-1.

“Zn” are the number of teeth of the driven gearwheels.

“Zn’” are the number of teeth of the drive gearwheels.

Figure 27. Scheme of the general transmission train for the 4-wheel tractor implement.

“Z4’” and “Z5” are the number of teeth of the gearwheel inside the gear box. These values

depend on the configuration of the gear box. The gear box can be configured to obtain the

final transmission required. The range offered by the gear box depends on the design of the

implement.

with,

ω1 = 2 ∗ π/(P𝑟𝑒𝑎𝑙

V𝑡𝑟𝑎𝑐𝑡𝑜𝑟)(1)

Where:

“Preal” the perimeter of the traction wheel.

“Vtractor” is the linear speed of the tractor

“Preal/Vtractor” is the time necessary for the traction wheel to perform one revolution

(1)ω1 can also be calculated directly with tachometer

Basic transmission ratio of the gear box

Using Willis method (Paul, 1979; Uicker, Pennock, & Shigley, 2003) for finding the kinematic solution of the gear train, it was found that the mechanism was governed by:

𝑅 =ω6

ω1

= (−1)0 ∗∏ Z𝑖𝑖

∏ Z𝑗𝑗

Equation 7 Willis formula to define the basic transmission ratio of the gear box

Where:

“R” is the basic transmission ratio of the gear train.

“n” is the the amount of external contacts

“Zi” Number of teeth of the drive gearwheels

“Zj” Number of teeth of the driven gearwheels

Results for the kinematic solution of the gear train

For the calibration of the 4-wheel tractor in the configuration of the established gear box, the value

for R is:

𝑅 =𝑍1′

𝑍2

∗𝑍2′

𝑍3

∗𝑍3′

𝑍4

∗𝑍4′

𝑍5

∗𝑍5′

𝑍6

=12

32∗

18

30∗

24

18∗

20

18∗

32

18= 0.6

The speed of the tractor during the operation is defined to be 8 km/h(1) equivalent to 2.22 m s-1. The

“Preal” is therefore 1,935 m(2)

So,

ω1 = 2 ∗ π/(P𝑟𝑒𝑎𝑙

V𝑡𝑟𝑎𝑐𝑡𝑜𝑟) = 2 ∗ π/(

1.935

2.22) = 7.2 rad s—1

And,

ω6 = ω1 ∗ 𝑅 = 7.2 ∗ 0.6 = 4.32 rad s—1

The N applicator was evaluated in 10 different positions, with three measurements in each position.

Ten revolutions were used to determine the amount of fertilizer applied per revolution. Ten

revolutions of the fluted roll fertilizer applicator (ω6=10*2π) corresponds to:

ω1 = ω6

𝑅 = 20π/0.6 = 104.7 rad

So, the traction wheel gave 104.7 revolutions, what corresponds to a distance run of:

D𝑟𝑢𝑛 =ω1

2π∗ P𝑟𝑒𝑎𝑙 =

104.7

2π∗ 1.9 = 31.6 meters

And the corresponding amount of beds in one hectare:

𝑩𝒆𝒅𝒔 =𝟏𝟎𝟎

𝑾𝑰𝑫𝑻𝑯 𝒃𝒆𝒅∗

𝟏𝟎𝟎

𝑫𝒓𝒖𝒏=

𝟏𝟎𝟎

𝟎. 𝟕𝟓∗

𝟏𝟎𝟎

𝟑𝟏. 𝟔= 𝟒𝟐𝟏. 𝟗

The calibration table is presented below.

Table 5. Results of the test of one N applicator in 10 positions rotating 10 times the fertilization axis and the corresponding amount of fertilizer in Kg/ha. 3 measurements have been done for every positions.

Applicator position

Measurement # 1 in g

Measurement # 2 in g

Measurement # 3 in g

Average in g

Equivalent in kg/ha

1 2 4 3 3 1

2 36 35 40 37 16

3 49 45 47 47 31

4 85 88 85 86 42

5 108 115 110 111 50

6 156 160 167 161 68

7 201 199 191 197 83

8 243 251 238 244 103

9 284 269 272 275 116

10 286 281 291 286 120

Comparison between the theoretical and traditional method for calibration

The results obtained with the traditional and with the theoretical are considered equivalent. The 2-

wheel tractor was therefore calibrated using the theoretical method.

Figure 28. Graph comparing theoretical and traditional calibration.

Calibration of the 2-wheel tractor 2.

The 2-wheel tractor implement was calibrated using the theoretical method previously established

in the 4-wheel tractor.

General transmission train for the 2-wheel tractor implement

“𝜔1” 𝑖𝑠 𝑡ℎ𝑒 𝑎𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑟𝑎𝑐𝑡𝑖𝑜𝑛 𝑤ℎ𝑒𝑒𝑙 in rad.s-1. It depends on the speed of

the tractor

“𝜔2” and “𝜔3” are intermediate 𝑎𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡is 𝑜𝑓 𝑡ℎ𝑒 transmission train in rad.s-1.

“𝜔4” 𝑖𝑠 𝑡ℎ𝑒 𝑎𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 of the axis controlling the application of fertilizer in rad.s-1.

“Zn” are the number of teeth of the driven gearwheels.

“Zn’” are the number of teeth of the drive gearwheels.

With,

ω1 = 2 ∗ π/(P𝑟𝑒𝑎𝑙

V𝑡𝑟𝑎𝑐𝑡𝑜𝑟)(1)

Where

Figure 26.

Figure 29.Scheme of the general transmission on train for 2-wheel tractor

“Preal” the perimeter of the traction wheel.

“Vtractor” is the linear speed of the tractor

“Preal/Vtractor” is the time necessary for the traction wheel to perform one revolution

Results of the theoretical calibration of the 2-wheel tractor

For the calibration of the 2-wheel tractor in the configuration of the transmission established, the

value for R is:

𝑹 =𝒁𝟏′

𝒁𝟐

∗𝒁𝟐′

𝒁𝟑

∗𝒁𝟑′

𝒁𝟒

=𝟐𝟒

𝟏𝟒∗

𝟏𝟔

𝟏𝟔∗

𝟏𝟔

𝟏𝟒= 𝟐

And,

𝑷𝒓𝒆𝒂𝒍 = 𝝅 ∗ (√𝑷𝒆𝒙𝒕

𝝅− 𝑪𝒓) = 𝝅 ∗ (√

𝟐𝝅 ∗ 𝟎. 𝟗𝟎

𝝅− 𝟎. 𝟎𝟐) = 𝟐. 𝟖 𝒎𝒆𝒕𝒆𝒓𝒔

Equation 8 “Preal” of the two wheel tractor

The speed of the tractor during the operation is defined to be 4km/h equivalent to 1.1m.s-1.

So,

ω1 = 2 ∗ π/(P𝑟𝑒𝑎𝑙

V𝑡𝑟𝑎𝑐𝑡𝑜𝑟) = 2 ∗ π/(

2.8

1.1) = 2.5 rad.s—1

And,

ω4 = ω1 ∗ 2 = 2.5 ∗ 2 = 5 rad.s—1

According the following formulas, 10 revolutions of the fluted roll N applicator (ω4=10*2π)

corresponds to 1 rad rotation of the traction wheel corresponding to a theoretical passage of Drun =

0.5 meters of the implement.

ω1 = ω4

R=

20π

2.5= 25.132 rad

D𝑟𝑢𝑛 =ω1

2π∗ P𝑟𝑒𝑎𝑙 =

25.1

2π∗ 2.8 = 11.2 meters

The corresponding amount of beds in one hectare is defined by:

𝑩𝒆𝒅𝒔 =𝟏𝟎𝟎

𝑾𝑰𝑫𝑻𝑯 𝒃𝒆𝒅∗

𝟏𝟎𝟎

𝑫𝒓𝒖𝒏=

𝟏𝟎𝟎

𝟎. 𝟗∗

𝟏𝟎𝟎

𝟏𝟏. 𝟐= 𝟗𝟗𝟐

We obtain the following graph for the two wheel tractor in the transmission train set up for the

trials:

Figure 30. Graph showing the relation between the amount of fertilizer applied and the position of the applicator

III.1.3 Proposed prototypes

III.1.3.1 Conceptualization and presentation of prototype designs

The N-sensor(s) will need to be attached in front of tractor, reading the plant N status and sending

this information through the microcontroller to the various fertilizer dispensers, which are

integrated into the fertilizer/planter implement that is pulled by the tractor.

(C)

(B)

(A

)

(D

)

Figure 31. An illustration of the proposed 2-wheel tractor prototype. A) N-sensor with its mounting structure, B) fertilizer bin of the planter implement pulled by the tractor, C) the 2-wheel tractor, D) position of one of the electric actuator of the VRA dispensers

III.1.3.2 Photos of the FertiKit

Figure 27. Figure 33. An illustration of the proposed two wheel tractor prototype. A) N-sensor with its mounting structure, B) fertilizer bin of the planter implement pulled by the tractor, C) the two-wheel tractor, D) position of one of the electric actuator of the VRA dispensers

(A

)

(B)

(C)

(D

)

Figure 32. An illustration of the proposed four wheel tractor prototype. A) N-sensor with its mounting structure, B) fertilizer bin of the planter implement pulled by the tractor, C) the four-wheel tractor, D) position of two electric actuators of the VRA dispensers

(B)

(C)

(A

)

Figure 34. Close-up of one of the VRA-dispensers to be constructed, with A) the electric actuator, B) the fluted roller and C) the connection between these two components.

III.1.3.3 Structural aspects to consider for the integration of the GreenSeeker®

The flexibility regarding the orientation and the height of the GreenSeeker® is important in order to

accommodate the height of the plant and the bed’s width.

In general, three aspects are important to consider for the structure carrying the GreenSeeker®:

1) The distance from the sensor to the tractor has been defined to be between 70 cm and 80

cm. This distance enables an optimal balance between allowing time for processing and

minimizing vibrations that could affect the readings.

2) The orientation of the sensor has to be adjustable to ensure that the light from the sensor

will hit the plant with the required angle.

3) In the case of the 4-wheel tractor, the distance between the two N-sensors corresponds to

the bed’s width. This can vary from 70-90 cm.

Figure 35. Structure in the front of the four wheel tractor to be constructed to sustain (A) the control box, (B) the battery and (C) the GreenSeeker®. On the left, Louis Gabarra is showing the flexibility of the system, being able to adjust the position of the sensors to fit to different configurations (such as the height of the plant or bed’s width)

(A)

(C)

(B)

Figure 36. A) Picture of the FertiKit integrated to the two wheel tractor for a test on field with corn B) Picture of the variable rate application of fertilizer. The picture has been taken after fertilizing with the 2-wheel tractor integrated with the FertiKit

III.1.3.4 Aspects to consider for the integration of Microprocessors

All the microprocessors will be grouped in one electromagnetism proof box. In order to limit the

vibration of the box, the box will be located in the front of the tractor, on the same structure as the

GreenSeeker® as close as possible to the engine of the tractor. It’s necessary to have the box close

to the GreenSeeker® to ensure a proper communication between the GreenSeeker® and the

microprocessors.

III.2 Evaluation and opportunity of the FertiKit

III.2.1 Evaluation on field

.

Figure 37. Picture of the bed made of textile in order to simulate a wide range of NDVI (from 0.12 the red color to 0.86 the black color). This ensures repeatability of the test.

III.2.2 Generation of maps

Tests has been done with different colored textiles to simulate the whole range of NDVI between

0.1 and 0.9 (see picture).

Table 6. Example of the map that can be generated with the FertiKit Database. The operator will be able to have a historical record of the NDVI measured with the quantity of fertilizer applied year after year

III.2.3 Possible improvements

- Implement table in the algorithms instead of formulas to reduce the time to process data

- Change of general components to increase the speed of the communication and reduce cost

(protocols of communication and sensors)

- Design one customized board per prototype instead of the five cards needed at the moment

(commercial boards have been used for the microprocessors resulting in high arrangement

complexity; it was made with time and costs in mind rather than reduced complexity

- Communication via Bluetooth between the N applicators and the GreenSeeker® removing

the crossing cable along the tractor and implement

III.2.3.1 Add components for better real-time evaluation and interpretation

III.2.3.1.1 Add an interface (Tablet PC, cell phone, PC, PLC)

The system, as it has been developed, can display in real-time the information being processed on a

smart phone or PC and will keep the information in a database for post-operation processing.

However, integrated hardware and software could be developed to process the data in real-time

(i.e. real-time mapping) and to display diverse indicators (such as errors and results).

Possible benefits

Adding a customized integrated hardware and software system which provides a complete and

user-friendly analysis of the operation would be to:

Increase the interest and understanding of the operation for the operator

Enable perception of a wide range of possible fails (regarding the process of the data of

the application)

Enable processing of data in real-time and providing understandable analysis to the

operator (such a mapping)

Bed made of textile

Measurements NDVI 87 85 85 84 85 12 18 13 14 15 76 78 76 75 76 46 48 46 45 46 32 35 32 31 33 Error Error

Average calculated

Map generated

76 47 41 33 33

Soil

86 60 15 56

260 Kg/Ha 280 Kg/Ha 300 Kg/Ha 300 Kg/Ha0 Kg/Ha 200 Kg/Ha 0 Kg/Ha 230 Kg/Ha 80 Kg/Ha

Reduce the time to interpret data for the operator

Possible Hardware

Different options are available to display information to users

PLC

PC

Tablet PC

Below, a table comparing the different options.

Table 7. Comparison between PLC, PC and Tablet PC

Characteristics PLC PC TABLET PC Antivirus No needed Needed

System updates No needed Needed

Electromagnetic interference (EMI)

Very good (no moving parts) Critical (magnet present in the hardware)

Contamination Very good (no moving parts) Critical (hard disk drives, fan, design) No fan and easy to protect

Vibration Very good (no moving parts) Critical (hard disk drives, fan) No fan

Serviceability /Maintenance External devices can be replaced with ease while the system is in operation

Only USB or other external peripheral devices can be replaced while running

Easy to replace the controller (modular design)

Difficult access to spare parts Spare parts with long-term availability

Response time As long the real-time processing is more important than the information processing, the PLC is in favor.

Hardware integration

PLC would have limited storage and processing capabilities. An advanced high-resolution imaging system

While the PLC can interface with a many different devices and perform complex operations, it still needs a PC to handle

memory-demanding tasks and make connections to other devices in the

system

The images/results can be stored, analyzed, compared, and possibly archived

PC is equipped with a more open and flexible array of interfaces, such as USB, FireW ire, serial, wireless Ethernet

Programming

PLC mixes scan-based and event-driven program execution PC software is typically event-driven

PLCs are programmed using languages specified in IEC 61131-3 (ladder logic,

instruction list, etc.),

PC-based controls can use programming languages such as C/C++/.NET. .

Performance VS cost

PLCs, however, typically start at a lower price point and can get more expensive

than a PC when high performance is needed

The initial cost of a PC might be higher, but it provides a very powerful system

and the cost only increases incrementally when more performance is required.

Cheaper than PC

PC-based solution may be more cost-effective

-

Expandability vs cost

The cost of a PLC is typically lower for applications where these items are not

important because of the optimized nature of PLCs, but the cost ramps up

steeply when a lot of additional devices are needed (

When no additional functions are needed and expandability is low, PCs tend to have a higher cost than PLCs, but PC cost does not increase

much when increasing expandability

Environment VS cost the standard PLC costs much less to

operate in rough environments compared to the PC

Adding components to make a PC more robust significantly increases the cost

Reboot time The reboot time of PLC is minor compared to a PC

Reliability PLC that runs doesn't crash, you can't guarantee this with a PC

References: (Bosch Group, 2011; HP, 2014; TechRadar, 2014)

III.2.3.2 Sensor to detect the fall of material

In order to obtain the feedback regarding the quantity of fertilizer applied corresponding to a

specific zone, a sensor could be added to the system. It would be placed into the fertilizer tube

going from the N-applicator to the point of incorporation into the soil. The displacement of fertilizer

is assured by gravity.

Possible sensor

Photoelectric

Capacitive

Inductive

Ultrasonic ((Bosch Group, 2011)– Refer to Annex 7 for properties)

Conception of a sensor to detect the fall of fertilizer into the fertilizer pipe

(A)

(B)

(C)

Figure 38. Photo (retrieved from MSO System) with (A) the connection cable from the sensor to the system, (B) the sensor to detect the fall of material, (C) the piepe where the material fall from the N applicator (top) to the incorporation into the soil (bottom)

.

III.2.3.3 Integrate the real-time sensed speed of tractor

Depending on the speed of the tractor, the time between the reading of the GreenSeeker® and the

time to incorporate the corresponding amount of fertilizer may vary. It’s corresponds to the time to

travel the distance “d” previously described in “III.1.2.5.2 Synchronization between the program

and the mechanical aspects”. It would ensure the synchronization for different speeds of the

tractor. An efficient tool to obtain the speed of the tractor can be a tachometer (instrument

measuring the rotation speed). A specific model’s factsheets is presented in Annex 5.

(B)

(A)

(C)

Figure 39. Louis Gabarra testing the capacitive sensor designed with (A) the granular fertilizer being applied, (B) the fertilizer pipe and (C) the capacitive sensor designed to detect the fall of material.

III.3 Possible Return on Investment

Figure 40. Graph showing the possible ROI for the FertiKit for the 2-wheel tractor (700 USD) and 4-wheel tractor (1300 USD). For the calculation it has been assumed that the average application is 300 Kg/Ha with possible savings of 10%. It corresponds to 22 USD per hectare. One cycle can be divided in several farmers due to the modular conception of the add-on Fertikit.

IV Conclusion

The FertiKit has been successfully integrated with a 2- and 4-wheel tractor, enabling a variable rate application in real-time of granular N fertilizer using the pocket Handheld GreenSeeker®. This integration enables the mapping of NDVI status and its respective dose of N fertilizer applied, giving farmers access to better understanding of their field over years. The flexibility of the FertiKit allows for easy integration with machines commonly used in conservation agriculture. Before testing the prototypes on cropped fields, the different components need to be assessed and fine-tuned. Further, an extensive trail should be elaborated to check the viability of the different configurations and prototypes. After that, guided trails at different locations will have to be performed with farmers. This is essential to understand how the FertiKit needs to be adjusted to their specific needs and capabilities. Eventually, a socio-economic study will be required, focusing efforts on lowering the cost and improving efficiency for optimal benefits to farmers.

This project has shown the possibility to provide small and medium-scale farmers a highly efficient tool for precision agriculture. It fulfills the requirements imposed by the current situation bringing benefits to farmers, environment, and offer new expertise to agriculture (i.e. mechatronics). It is relatively affordable, demonstrating that precision agriculture using a sensing system can be cost effective for small-scale farmers. The project has been realized with local partners only, which consolidates the possibility of providing tailor-made efficient and economical solutions for agriculture while boosting different sectors of local economy.

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Annex 1 Traditional calibration of the four wheel tractor

Material needed for the calibration VRA dispenser:

One weighing machine with a precision of 1 gram

Plastic bags

One flexible tape meter of 10 meters minimum

One rigid ruler

One implement fully equipped for fertilization (traction wheel, transmission, N applicator)

The calibration of machinery for agriculture is usually made on 50 meters. In order to simulate that

passage with stopped machine*, it will be necessary to define how many revolutions will be

required to give to the wheel to simulate the 50 meters passage. Below is described the method to

establish this relation depending on the characteristics of the tractor’s drive wheel.

*The calibration has been done with a stopped machine and rotating manually the drive wheel to

simulate the movement of the tractor

Simulation of the 50 meters passage

To calculate the amount of revolutions to give to the traction wheel, this is important to define

properly the relation between the tire and the distance run (Riethmuller, 2006). To establish this

relation, “Preal” has to be defined.

- With the flexible tape meter, measure the external perimeter of the wheel. The distance

measured will be called Pext*

Figure 44. Drive wheel of the 4-wheel tractor implement with the external perimeter represented with the blue stripped line

As we can see on the Figure 45, the

wheel has crampons (very common

in agriculture. It’s important to

subtract the crampons depth to the

external perimeter in order to have

the real correlation between the

wheel revolution and the distance

the tractor would move forward

- With the rigid ruler, measure the crampon’s depth

Figure 45. View of the drive wheel with the rigid ruler for the measurement of the crampons’ depth

The crampons depth will be called “Cr”.

- With two measurements obtained before, Pext and Cr, follow the succeeding operations:

Rext is the radius of the wheel still considering the crampons and Pext the corresponding

perimeter. The relation is defined by:

𝑷𝒆𝒙𝒕 = 𝝅 ∗ 𝑹𝒆𝒙𝒕𝟐

Rreal is the radius of the wheel without the crampon and Preal is the corresponding

perimeter. The relation is defined by:

𝑷𝒓𝒆𝒂𝒍 = 𝝅 ∗ 𝑹𝒆𝒙𝒕𝟐 𝑹𝒆𝒙𝒕 = √𝑷𝒆𝒙𝒕

𝝅

With,

𝑹𝒓𝒆𝒂𝒍 = 𝑹𝒆𝒙𝒕 − 𝑪𝒓

Then,

𝑷𝒓𝒆𝒂𝒍 = 𝝅 ∗ (√𝑷𝒆𝒙𝒕

𝝅− 𝑪𝒓) = 𝟏. 𝟗𝟑𝟓𝟕𝟓 𝒎𝒆𝒕𝒆𝒓𝒔

Equation 9 Formula to define the “Preal”

REV will be defined as the amount of revolutions required to give to the wheel to simulate

the 50 meters distance.

𝑹𝑬𝑽 =𝟓𝟎

𝑷𝒓𝒆𝒂𝒍= 𝟐𝟓. 𝟖𝟐 𝒓𝒆𝒗𝒐𝒍𝒖𝒕𝒊𝒐𝒏𝒔

Crampon’s depth

Rigid ruler

Equation 10 Formula to know how many rotations should be given to the traction wheel to simulate the 50 meters distance to run for a proper calibration

In order to facilitate the experiment, we will round up REV (=25.83 revolutions) to

REVround (=26 revolutions) and consider the distance (“D”) for the further operations. D

will be defined as:

𝑫 = 𝑹𝑬𝑽𝒓𝒐𝒖𝒏𝒅 ∗ 𝑷𝒓𝒆𝒂𝒍 = 𝟐𝟔 ∗ 𝟏. 𝟗𝟑𝟓𝟕𝟓 = 𝟓𝟎. 𝟑 𝒎𝒆𝒕𝒆𝒓𝒔

Equation 11 Formula to define the distance that will be run for the calibration after rounding up the amount of revolution calculated.

- Summarize of results to simulate the 50 meters passage

Table 8 Results obtained to define the amount of revolutions to give to the traction wheel to simulate the 50 meters passage

Pext (measured)

Cr (measured)

Preal (calculated)

REV (calculated)

REVround Distance run

simulated

2.03* 0.015 1.9 25.8 26 50.3

*All distances are in meter.

Calibration of the applicator

After determining the amount of revolutions to give to the drive wheel to cover the 50 meters,

different positions of the applicators must be defined. The different positions of the applicator all

refer to a different amount of fertilizer applied.

- Using the meter (flexible or rigid depending on the applicator’s design), define different

positions on the N applicator with a pen in order to establish a relation between the

position of the applicator and the quantity of fertilizer applied. In the case of the fluted roll

chose, 10 different positions have been set up. The range of the applicator is 5 cm long.

Then, the 10 different measurements will refer to 0.5 cm displacement of the applicator.

Once the different positions of the applicator have been defined, the system is ready to be

calibrated. For every position of the applicator, we will realize measurements of the amount of

fertilizer applied. For reliability matter, 3 measurements for each position are required.

To evaluate applicators regarding the amount of fertilizer applied depending on the applicator, we

will choose 2 positions (positions 2 and 10) to test on every applicator and compare the quantity

collected for both positions. Applicators presenting discrepancy will be discarded.

Realize to table 9 as shown below.

Table 9 Correlation between the positions of the N applicator to an equivalent in cm.

Position of the

applicator Equivalent

in cm

0 0

1 0.5

2 1

3 1.5

4 2

5 2.5

6 3

7 3.5

8 4

9 4.5

10 5

- Place plastic bags in applicators’ exits

- Move the applicator in the chosen position(1)

Figure 46. Picture of the test of every applicator to ensure that they deliver, in a given position, the same amount of fertilizer

- Remove and weight every plastic bags

- Realize two times more the operation 6. To 8.

(1)For every chosen position of the applicator the operations 6. To 9. will have to be realized 3

times. The two positions randomly chosen for the operation are the position 2 and the position

10.

- Realize the table 10 as shown below.

Drive wheel Applicators

of fertilizer

Plastic bags

Operator rotating the drive

wheel

Table 10. Results of the test of 8 N applicators to compare the amount applied in the different positions.

Positions of the

applicator Measurements

Measurements of the amount of fertilizer in g for the 8 N applicators Average

(in g) 1 2 3 4 5 6 7 8

2

#1 55 52 51 55 49 53 50 49 52

#2 50 51 56 48 54 52 51 54 52

#3 56 48 50 54 54 56 53 50 53

10

#1 461 460 456 458 472 459 457 458 460

#2 457 464 449 462 462 456 453 454 457

#3 459 458 449 465 465 462 460 461 460

- Analyze results of the table, if one applicator’s result presents a significant difference with

the other quantity, it would be preferable to avoid working with it.

- Choose one applicator to continue the calibration in every position.

- Realize the operation 6. To 9. in the 10 positions for the applicator chosen.

- Realize the table as shown below.

Table 11. Results in g for one specific applicator in the 10 different positions with its equivalent in Kg/ha for 0.75m wide beds with one row of corn or 1.5m wide beds with 2 rows of corn.

Applicator's position

Measurement # 1

Measurement # 2

Measurement # 3

Average in g

Equivalent in Kg/ha*

1 5 4 4 4 1

2 55 60 58 58 15

3 84 78 80 81 21

4 140 141 136 139 37

5 185 180 186 184 49

6 244 250 240 245 65

7 318 315 310 314 83

8 376 376 380 377 100

9 429 424 424 426 113

10 461 460 456 459 122

*Refer to Definition the equivalent in Kg/ha from a linear measurement in g along a distance run

“Drun”.

From a linear measurement of N fertilizer in g to the equivalent in Kg/ha

This value depends on the width of the bed and how many rows of corn are on the bed, below are

the operations to follow to determine this value (MSO - Technik, 2014). In this case, the calibration

has been done on the 4-wheel tractor to work on 1.50 m wide beds with 2 rows of corn and on

0.75m wide beds with one row of corn. The equivalent in Kg/ha is the same for both bed width

(2*0.75 = 1.5). At this stage, it’s important to remember that the measurement has been done for a

simulated distance “Drun” of 50.3 meters. The following calculation will be made considering the

0.75m wide bed with one row of corn. One hectare is equivalent to 100 m X 100 m (width*length).

“Beds” is defined to be the amount of 0.75 wide * 50.3 long beds in one hectare.

So, to obtain the value of Beds, the formula is:

𝑩𝒆𝒅𝒔 =𝟏𝟎𝟎

𝑾𝑰𝑫𝑻𝑯 𝒃𝒆𝒅∗

𝟏𝟎𝟎

𝑫𝒓𝒖𝒏=

𝟏𝟎𝟎

𝟎. 𝟕𝟓∗

𝟏𝟎𝟎

𝟓𝟎. 𝟑= 𝟐𝟔𝟓

Equation 12 Formula to define “Beds” (Riethmuller, 2006). It’s the amount of 0.75 wide * 50.3 long beds in one hectare.

The formula to have the equivalent of fertilizer in Kg/ha (“EQha”) from the average collected in g on

the 50.33 meters plot (“AVE”) is:

𝑬𝑸𝒉𝒂 = 𝑩𝒆𝒅𝒔 ∗ 𝑨𝑽𝑬

For the position 1 of the applicator (refer to the table above),

𝑬𝑸𝒉𝒂 = 𝟐𝟔𝟓 ∗ 𝟒 = 𝟏𝟎𝟓𝟗. 𝟔𝟒 𝒈 = 𝟏. 𝟎𝟓𝟗 𝒌𝒈 𝟏 𝒌𝒈

“Y” configuration (combining 2 N applicators)

For better precision, the system can be used putting together two applicators. It will increase the

variation possible for every application. This configuration to put together two applicators will be

called “configuration Y”. One electric actuator will control the 2 N applicators as show one the

picture.

Figure 47. Picture of the configuration “Y” where two N applicators are put together to combine their respective amount in one only exit (B). The electric actuator (C) is controlling the two applicators ((A) &

(D))

Then the relation would be as shown in the following table.

Table 12. Relation between the applicator’s positions and the correlated value in Kg/ha applied using the “configuration Y” 0.75m wide beds with one row of corn or 1.5m wide beds with 2 rows of corn.

Applicator's position

Equivalent in Kg/ha

Equivalent in Kg/ha

using the "Y"

1 1 2

2 15 30

3 22 44

4 37 74

(B)

(A)

(D)

(C)

5 49 98

6 65 130

7 84 168

8 101 202

9 114 228

10 122 244

Once we obtain the table, it will possible to generate a graph and a formula illustrating the

performance of the applicator.

Figure 48. Graph showing the relation between the amount of fertilizer applied and the position of the applicator in configuration "Y"

In order to have a proportional relation we will generate the average linear curve as shown in the

following graph. It will enable to generate a formula (y=ax), such as the one that appears on the

graph.

Figure 49. Graph showing the relation between the amount of fertilizer applied and the position of the applicator in

configuration "Y"

0

50

100

150

200

250

0 2 4 6 8 10

Qu

anti

ty a

pp

lied

in K

g/h

a

Position of the applicator

y = 23,491x

0

50

100

150

200

250

0 2 4 6 8 10

Qu

anti

ty a

pp

lied

in K

g/h

a

Position of the applicator

On the graph is the formula linking the position of the applicator to the quantity of fertilizer applied

in Kg/ha in “Y configuration”.

The formula is:

𝒚 = 𝟐𝟑. 𝟒𝟗𝟏𝒙

Where

23.491 is the specific value for the applicator and the gear box configuration used during the

calibration.

“y” is the quantity of fertilizer applied.

“x“ is the position of the actuator.

The general formula linking the nitrogen application and the position of the linear actuator is:

𝒚 = 𝒂𝒙

Annex 2- Historical of temperature to calculate the GDDsum

Description of the process to get the information (historical of temperature) required to calculate

the GDDsum

1. Go on the page www.wunderground.com

2. On the webpage, look for the region where the operation is made. In the case of “el

Batan*” the link is http://www.wunderground.com/personal-weather-

station/dashboard?ID=IESTADOD2#history/tdata/s20130526/e20140527/myear)

Figure 50. Screen capture #1 corresponding to the information of “El Batan” on the website wunderground.com

3. Select the “Custom” mode to generate a table from the day after the date of

seeding to the date of the operation. In this case, the seeding date is the 05/26 and

the date of the operation is 08/27. Then, click on “View”

Figure 51. Screen capture #2 showing how to choose the value of the beginning of the historical

4. The following table will be generated (make sure that the tab called “table” has

been selected as shown on the screen capture). Then click on “Download”.

Figure 52. Screen capture #3 of the historical after choosing the date and clicking on “View”

5. All the information will be displayed in a new tab (after clicking on “Download”, a

new tab appears as shown in the screen capture #4). Then copy paste all the

information (pressing “ctrl + a” and then “ctrl+c”) in a excel document as shown in

screen capture #5)

Figure 53. Screen capture #4 of the new tab after clicking on “Download” and selecting all the data with “ctrl + a”

Figure 54. Screen capture #5 of the excel document where all the information from the screen capture #4 has been copy

pasted

6. In the screen capture #5, all information has been copy paste in the column A only.

It will be necessary to separate all the value in different column in order to be able

to process the information as shown below.

6.1. Select the column A

Figure 55. Screen capture #6 of the excel document where the column A has been selected

6.2. Then go to “Data” and click on “text to column”

Figure 56. Screen capture #7 of the excel document showing how to access to the “Convert Text to Columns Wizard”

6.3. Choose the file type that best describes the data, it’s “delimited”. And then

press “Next”

Figure 57. Screen capture #8 of the excel document with the “Convert Text to Columns Wizard” open and with “Delimited”

selected as the file type that best describes the data

6.4. Choose “Commas” as the delimiter and then click “Finish”

Figure 58. Screen capture #9 of the excel document with the “Convert Text to Columns Wizard” open and with “Comma”

selected to be the delimiter

6.5. Then, the excel document will appears as shown in the Screen capture #10. All

value are in different column.

Figure 59. Screen capture #10 of the excel document where all the data has been separated in different column

7. In the screen capture #10, all information required is now available. Add a column

between the columns “D” and “E” and name it GDD. Then, in E2 write the following

formula:

= (𝐼𝐹(𝐵2 > 30,30, 𝐼𝐹(𝐵2 < 10,10, 𝐵2)) + 𝐼𝐹(𝐷2 > 30,30, 𝐼𝐹(𝐷2

< 10,10, 𝐷2)))/2 − 10

Figure 60. Screen capture #11 of the excel document after inserting a column between the column “D” and “E” and adding

the formula “ =(IF(B2>30,30,IF(B2<10,10,B2))+IF(D2>30,30,IF(D2<10,10,D2)))/2-10 “ in the cell E2.

8. Drag down the value until the date of the operation and add a total of the sum of every GDD

(GDDsum). The value obtained is the GDDsum be incorporated in the formula.

Figure 61. Screen capture #11 of the excel document where the formula of the GDD has been dragged down and that the

GDDsum added at the bottom of the column.

` Figure 62. Screen capture #12 of the excel document showing the final result for the GDDsum

Annex 3–Factsheets of the N-sensor GreenSeeker®

Figure 63. Infogram of the GreenSeeker® Handheld by Trimble with an explanation of major components, and operating

range and recommendations (Riethmuller, 2006)

Annex 4–Factsheets of the Actuator FIRGELLI

Visit http://www.firgelliauto.com/product_info.php?cPath=70&products_id=54 for more details

Annex 5–Factsheets of the tachometer to consider for a second phase of the

project

Annex 6–Factsheets of the battery

Annex 7 –Properties of the SeedEctor sensor

Visit http://www.mso-technik.de/docs/Seedector-De-2013-low.pdf for more details