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E. Gabellini, P. Ferrandino, M. ZuffranoBETA (Italian Society for sugar beet research)Via Conca, 75 - 44030 Malborghetto di Boara (FE) - Italy

IntroductionAcquaFacile (AF, literally: “EasyWater”), is a Decision Support System (DSS) irrigation software (www.betaitalia.it) developed by BETA and based on the Hargreaves equation (Hargreaves and Samani, 1982). It features reduced Kc’s, compared to the reference ones (FAO, 1998), and includes the contribution to ET from the shallow water-table. AF works on both spring and autumn beets, with different parameters.The dissemination of the software “AcquaFacile” on autumn beet in South Italy was preceded by an intensive work to tune the program algorithms. In this regard, an important reference was the previous calibration work by INEA (National Institute for Agricultural Economy) on the Hargreaves formula (imple-mented into AF), as well as on the Penman-Monteith formula (INEA, 2001).According to Graph. 1, the value of the fixed term in the Hargreaves formula, 0,0023, brings to a curve that overestimates ET consumptions, compared with the Penman-Monteith’s reference formula.

A reduction of this term to 0,0019 results in a better correlation between the two formulas (R2 = 0,9878), as shown in Graph. 2. Both functions assume the aspect of Graph. 3, where their alignment is evident.

A comparison of crop evapotranspiration between Hargreaves modified and Penman-Monteith formulas in drip-irrigated autumn sugar beet (Beta vulgaris L.) in ItalyKey words: Sugar beet; Irrigation; Evapotranspiration.

Sowing: 02/11/2004 - Harvest: 02/08/2005

Tab.1 - Comparison among irrigation systems. Foggia, 2004-2005.

TreatmentsRoot yield (t/ha)

Sugar content

(%)

Raw sugar (t/ha)

K % gp mmol

Na% gp mmol

Alpha N% gp mmol

Juicepurity (%)

Grossincome (e/ha)

Semi-rigid pipe positioned on soil surface

74,6 17,1 12,8 5,2 1,2 2,3 92,1 3.699

Flexible tape positioned on soil surface

71,7 17,0 12,2 5,8 1,0 2,6 91,6 3.543

Flexible tape buried in the soil (sub-irrigation)

66,1 17,9 11,8 5,7 1,4 3,2 91,3 3.414

Rainfed (ctrl) 29,4 22,3 6,5 6,6 2,1 5,3 90,3 1.866

Mean 60,4 18,6 10,8 5,8 1,4 3,4 91,3 3.130

LSD 5% 5,57 1,19 0,83 0,78 0,36 0,68 0,96 251,31

MethodsIn the cropping year 2004-2005, in South Italy (Foggia province) BETA tested three different drip irrigation systems: • Semi-rigid pipe - Naan TIF, Ø16 mm, thickness 32 mil. with in-line drippers

of 2 l/h at 1,013 bar, pitch 40 cm, placed on soil surface every other inter-row (90 cm distance).

• Flexible tape - Toro mod. Aquatraxx, Ø16 mm, thickness 6 mil., pressed drippers of 1,16 l/h at 0,7 bar, pitch 30 cm, placed on soil surface every other inter-row (90 cm distance).

• Flexible tape - Toro mod. Acquatraxx, Ø16 mm, thickness 15 mil., pressed drippers of 1,16 l/h a 0,7 bar, pitch 30 cm, buried in the soil at a 45 cm depth (sub-irrigation), at a 1,35 m distance between the lines. Tape positioning was performed during soil tillage by a tractor-mounted tool.

A strip-plot design at 6 replications was adopted in the trial, with a common rainfed control (ctrl). Root samples on 13,5 m² plot areas were collected during the harvest campaign, weighted and analysed for the major yield and quality traits. A parallel study was carried out in order to compare reference evapotranspi-ration (ETo) and the water balance as calculated by the AF software and by the Penman-Monteith equation.

ResultsThe results (Table 1) show a significant yield difference between irrigated and rainfed crop. In particular, the irrigated plots showed a weight increase of 100-150% and a lower sugar content (-5° as average), although it always remained above 17°. The juice purity (JP), though with lower sugar-content values, was always higher in irrigated plots, thanks to the lower concentration of impurities, especially of nitrogen and sodium. The most interesting data are linked to the sub-irrigation system. In fact, in this case high yields were realised at much lower costs, thanks to the multi-year depreciation involved by this system (Graph. 5).

The correlation coefficients are significant and explain more than 90% of the total variability. In the investigated year, the close resemblance between his-torical and the year’s ET data suggests that the former might be used as a common references within the calculations of water balance. This occurrence needs to be confirmed in future research. As for a practical application, considering the evapotranspiration during the growing season 2005, we obtain the following cumulated deficit for the period March 10 - July 10:• AcquaFacile 2005 (AF 2005) = 271• Historical AcquaFacile (historical AF) = 288• Penman-Monteith 2005 (PM 2005) = 287The progress of cumulated deficit during the crop cycle is shown in Graph. 8.

Graph. 1 - Source: INEA, 2001.

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5

4

3

2

1

01 101 201 301

ETo (Harg 0.0023)

ETo (Pen-Mon)

mm

day

1

day

Graph. 2 - Source: INEA, 2001.

5

4

3

2

1

0

Penm

an-M

onte

ith

300025002000150010005000

y = 0.0019x

R2 = 0.9878

Graph. 3 - Source: INEA, 2001.

5

4

3

2

1

01 101 201 301

ETo (Harg 0.0019)

ETo (Pen-Mon)

mm

day

1

day

Comparison of ETo formulas

A comparison between the two formulas, over the period January-July, on a ten-days scale, showed the following patterns:

1. ETo calculated with Penman-Monteith (PM) vs. AF (Hargreaves formula) using historical weather data. (Graph. 6)

2. ETo calculated with Penman-Monteith (PM) vs. AF (Hargreaves formula) using year 2005 weather data. (Graph. 7)

The data resulting from the study of the above correlations are confirmed by the fact that, also in this case, the cumulated deficit calculated with ‘’historical AF’’ corresponds to that calculated with PM, with a difference of only 1 mm in 4 months.

ConclusionThe trial confirmed the technical-economical effectiveness of sub-irrigation.As for the AcquaFacile software, the reduction of the fixed term in the Har-greaves formula meant a significant correlation of the ETo with the Penman-Monteith formula. This enables to use this software also in areas that are not equipped with automatic weather stations.

ReferencesFAO, 1998. Crop evapotranspiration – Guidelines for computing crop water requirements, FAO Irrigation and drainage Paper n. 56, Rome.Hargreaves, G.H., Samani, Z.A., 1982. Estimating potential evapotranspira-tion, Tech Note, J. Irrig. and Drain. Eng., ASCE 108, 225-230.INEA, 2001. Constitution of an agro-meteorological data bank within SIGRIA: resources, problems and methods, Rome

70

60

50

40

30

20

10

0

AF

wit

h hi

stor

ical

tem

p. (

Har

gr.)

Penman-Monteith

0 10 20 30 40 50 60 70

y = 0.8908x + 6.5422

R2 = 0.93

Graph. 6 - Correlation between ETo (mm) calculated with the formula of Penman-Monteith and with AcquaFacile (Hargreaves on historical temp.) in the period january-july.

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40

30

20

10

0

AF

wit

h te

mp.

of 2

005

(Har

gr.)

Penman-Monteith

0 10 20 30 40 50 60 70

y = 0.8461x + 5.9655

R2 = 0.92

Graph. 7 - Correlation between ETo (mm) calculated with the formula of Penman-Monteith and with AcquaFacile (Hargreaves on temp. of 2005) in the period january-july.

Dripping lines buried in the soil.

mm

Semi-rigid types on soil surface.

AF the irrigation software by BETA

350

300

250

200

150

100

50

0

Rai

nfal

l (m

m)

Dates10/3 25/3 9/4 24/4 9/5 24/5 8/6

40

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25

20

15

10

5

0

Cum

ulat

ed E

To a

nd w

ater

defi

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(m

m)

23/6 8/7

Rain2005 AFHistorical AFPM

Graph. 8 - Time-course of precipitations and of cumulated ETo with the three systems.

1.000

800

600

400

200

0Semi-rigid pipe positioned on soil surface

Flexible tape positioned on soil surface

Flexible tape buried in the soil (sub-irrigation)

E/h

a

Graph. 5 - Total costs of irrigation according to different seasonal volumes and irrigation systems.

1500 m3

2400 m3

3500 m3