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Production

Agricultural Extension ServiceThe University of Tennessee

PB1616

Plant Nutrition

& Fertilizers

ForGreenhouse

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Table of Contents

Plant Nutrition: The Basics______________________________________________________________ Fertilizer Salts ______________________________________________________________________ pH__________________________________________________________________________________ Factors Affecting Media Solution pH__________________________________________________ Water Quality/Alkalinity__________________________________________________________ Media Components _______________________________________________________________ Fertilizers Applied________________________________________________________________Fertilization and Fertilizers______________________________________________________________ Water-Soluble Fertilizers_____________________________________________________________ Slow-Release Fertilizers______________________________________________________________ Fertilizer Labels_____________________________________________________________________ Nutrient Analysis_________________________________________________________________ Nitrogen Form____________________________________________________________________ Potential Acidity/Basicity_________________________________________________________ Proper Dilution Rate______________________________________________________________ Fertilizer Injectors____________________________________________________________________ Multiple Injectors_________________________________________________________________ Injector Accuracy and Calibration_________________________________________________Starting a Fertilization Program__________________________________________________________ Pre-plant Nutrition Programs_________________________________________________________ Post-plant Nutrition Programs________________________________________________________ Nitrogen__________________________________________________________________________ Phosphorus______________________________________________________________________ Potassium________________________________________________________________________ Calcium and Magnesium__________________________________________________________ Micronutrients___________________________________________________________________Appendices: Fertilizer Calculations_______________________________________________________________ Conversion of Units__________________________________________________________________

336567777788889910101111121213131313

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Plant Nutrition: The Basics

Fertilizer SaltsFertilizers are salts. Salts are chemical

compounds that contain one positivelycharged ion (cation) bonded to one nega-tively charged ion (anion). When a salt isplaced into water, the two ions separate anddissolve. An example of a fertilizer salt is

Plant Nutrition & FertilizersFor Greenhouse Production

James E. Faust, Assistant ProfessorElizabeth Will, Graduate Student

Ornamental Horticulture and Landscape Design

calcium nitrate, which contains one calciumcation and a nitrate anion. Other ex-amples include: ammonium phosphate,magnesium sulfate, potassium nitrateand ammonium nitrate.

Fertilizer concentration (or saltiness) of asolution can be determined by measuringthe ability of a solution to conduct an elec-trical signal (electrical conductivity). Electri-cal conductivity meters, often called soluble

CALCIUM NITRATE

Ca++

NO-3

Ca++ NO3-

NO3-

Ca++

This publication is one of three in a series that covers the basics of developing anutritional program for producing container-grown plants in greenhouses. A completenutrition program encompasses the fertilizers, media and water used. The first sectionin Plant Nutrition and Fertilizers for Greenhouse Production develops backgroundinformation about plant nutrition that growers need to understand before discussingwhich fertilizers to use. The second section covers the range of fertilizers that growerscan choose from.

The second publication in the series, Irrigation Water Quality for GreenhouseProduction (PB 1617), examines the effect of water quality on a greenhouse nutritionalprogram. The third publication, Growing Media for Greenhouse Production (PB 1618),describes the important physical and chemical properties of growing media, mediatesting procedures and interpretation of test results. The objective of this series of publi-cations is to provide basic information that will allow greenhouse operators to develop anutritional program for their specific business.

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salts meters, measure the concentration ofsalts/ions in solution; therefore, a growercan always measure the amount of fertilizerbeing applied to a crop. However, electricalconductivity meters do not specificallymeasure which specific salts are in solution.For example, an electrical conductivity

55 carbon atoms60 hydrogen atoms5 oxygen atoms4 nitrogen atoms1 magnesium atom

Therefore, for the plant to build onechlorophyll molecule, the leaves must takein carbon dioxide, for the carbon and oxy-gen; the roots must take in water, for thehydrogen and oxygen; and the roots musttake up nitrogen and magnesium providedfrom the fertilizer applied.

meter can not tell the difference betweentable salt (sodium chloride), which is dan-gerous to plants, and potassium nitrate,which is useful for plants.

Ions dissolved in water are taken upthrough the roots and distributed within theplant. Plants actually expend energy to takeup most ions, however, calcium is thoughtto only come along for the ride, i.e., plantsdon’t actively take up calcium, it just comesinto the root with the water.

Once inside the plant, ions are recom-bined into compounds useful for plant

0

1 2

3 0

1 2

3

growth. The most common example of plantmetabolism involves photosynthesis, duringwhich water (hydrogen and oxygen) is com-bined with carbon dioxide (carbon and oxygen)to form starch or sugars (carbon, hydrogen andoxygen). Another example is the chlorophyllmolecule shown below that contains:

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Mobile Immobile

Sulfur Copper

Nitrogen

Phosphorus

Calcium

Iron

Manganese

Zinc

Potassium

Molybdenum

Magnesium

Table 1. Mobility of individual nutrientswithin plants.

Once inside the plant, some nutrientscan be mobilized to support new growingtissues, while other nutrients are fixed inolder plant tissues. This fact helps us todiagnose some plant nutrient deficiencies.For example, if a plant is deficient in animmobile nutrient, then deficiency symp-toms (yellowing/chlorosis) occur in the newgrowth, since the older tissues “hold” on tothe immobile nutrients. In contrast, defi-ciencies of mobile nutrients typically occur

in the older leaves, since the mobile nutrientsmove from the old leaves to the new leaves.

Plants require different amounts of eachnutrient. Carbon, hydrogen and oxygen arerequired in the greatest amounts; however,these are taken up by the plant in the formof water and carbon dioxide. Nitrogen,phosphorus, potassium, calcium, magne-sium and sulfur are required in large

amounts, thus are called macronutrients.Iron, manganese, copper, zinc, boron, chlo-ride, molybdenum are required in relativelysmall amounts, thus are called micronutri-ents, or minors.

pHpH is a measure of the concentration of

hydrogen (H+) ions, sometimes called pro-tons. The greater the H+ ion concentration,the more acid the solution, hence a lower pH.

pH controls the uptake of nutrients. Ifthe pH is not in the desired range, indi-vidual nutrients can not be taken up, creat-

Boron

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ing a nutrient deficiency, or the nutrient canbe taken up too readily, resulting in a nutri-ent toxicity. These nutrient imbalances willoccur even when proper amounts of nutri-ents are applied to the media, if the pH istoo high or too low. The figure below demon-strates the availability of nutrients to plantsat different media pH. Nitrogen and potas-sium are readily available at a wide pHrange. Although phosphorus is more readilyavailable at a low pH, phosphorus problemsare not commonly observed in greenhousecrops. Calcium and magnesium are morereadily available at a higher pH. At a low pH,the minor nutrients (iron, manganese,boron, zinc and copper) are readily avail-able. Minor nutrient toxicities are relativelycommon at a low pH (<5.8), while deficien-cies frequently occur at a high pH (>6.5)

Factors affecting media solution pH:1. Water Quality/Alkalinity: Alkalinity isone measure of the quality of waterused for irrigation. Alkalinity is the measureof the concentration of bicarbonates andcarbonates in water which determine thewater’s capacity to neutralize acids. In other

100

80

60

40

20

0C,H,O N,P,K, et al...

Perc

e nta

g eo f

P la n

t Dr y

We i

g ht

from solution. This process effectivelydecreases the H+ ion concentration inthe media and thus increases the mediasolution pH.

The reverse situation can also occur.Very pure water (low bicarbonates) cancause media solution pH to decreaseover time. The pH drops, because theremay not be enough bicarbonates toabsorb excess hydrogen ions. Thus, theH+ concentration in the media increases.

The most common solution for purewater sources is to increase the amountof pulverized dolomitic limestone incor-porated into the media prior to trans-planting plants into the media. Anothersolution is to top-dress containers withthe limestone. Finally, bicarbonate canbe added to irrigation water in the formof potassium bicarbonate to improve thebuffering capacity of the media solution(i.e., reduce pH fluctuation).

Water quality issues are covered inmore depth in Irrigation Water Quality forGreenhouse Production (PB 1617).2. Media Components. Peat tends to beacidic. Pulverized dolomitic limestone(CaMg(CO3)2) is incorporated into mostamended media to adjust the starting pHto ~6.0. Coarser grades of dolomitic

0

Perc

enta

g ein

P la n

t Tis

s ue

5

4

3

2

1

N P K Ca Mg S Fe Mn B Zn Cu Mo

words, irrigating with bicarbonates inwater is equivalent to applying lime witheach irrigation. The bicarbonates reactwith hydrogen ions and remove them

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limestone change the media pH more as a constant liquid fertilizer (CLF) program.A specific fertilizer program must be devel-oped around the irrigation water, media andcrops grown. Following is a typical CLFprogram:

200 ppm N from 20-10-20 Peat-LiteSpecial applied each irrigation for one week.

200 ppm N from 15-0-15 applied eachirrigation the following week.

100 ppm Mg from Epsom salts (magne-sium sulfate) applied once.

Repeat.The 20-10-20 Peat-Lite Special supplies

nitrogen, phosphorus, potassium and minornutrients. The 15-0-15 fertilizer suppliesnitrogen, potassium, calcium and minornutrients. The epsom salts supply magne-sium and sulfur. Rotating these three prod-ucts provides all essential nutrients re-quired for plant growth. Recently availableare water-soluble fertilizers that supply allessential nutrients in one fertilizer. Ex-amples include 15-5-15 Cal-Mag Specialand 13-2-13 Plug Special.

Slow-Release FertilizersSlow-release, or controlled-release,

fertilizers are usually used when crops aregrown outdoors. Slow-release fertilizers arebeneficial because they create less environ-mental pollution, e.g., fertilizer run-off,

slowly, and thus are not often used inpeat-based media. A relatively new, butpopular media component, coconut coir,is less acidic than peat, so less limestoneneeds to be used.

The role of media in a greenhousenutritional program is covered in moredepth in Growing Media Quality forGreenhouse Production (PB 1618).

Fertilizers are catego-rized into one of two groups: acid-residueor alkaline-residue. The fertilizers them-selves are not acidic or alkaline, but theyreact with microorganisms in the mediaand plant roots to affect media solutionpH. Fertilizers with ample ammonium orurea tend to acidify the media, i.e., lowerthe pH. Fertilizers with ample nitrates tendto raise the pH of the media solution slowlyover time.

Fertilizers and Fertilization

Water-Soluble FertilizersMost greenhouse fertilization programs

rely on water-soluble fertilizers to providemost of the nutrients required for plantgrowth. Water-soluble fertilizers are oftenapplied at each irrigation. This is referred to

3. Fertilizers Applied.

H H

HH

H

H

H

H

H H

HHH

+

Bicarbonate

HH

H

H

H

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when sprinker irrigation is used, and theycontinue to supply nutrients during rainyweather. Slow-release fertilizers are mar-keted based on the time of release, for ex-ample, 3- to 4-month longevity. The actualfertilizer release rate is determined by thetemperature and water content of the media.Therefore, the actual effective release time ofthe fertilizer may vary from the labeled time.

Slow-release fertilizers can be incorpo-rated into the media prior to filling thecontainers or top-dressed after planting.Slow-release fertilizers are often incorpo-rated into the media for garden mum pro-duction as an insurance policy againstrainy weather.

Fertilizer LabelsThis section will discuss information that

is critical to understand as you develop anutritional program for containerized green-house crops. A useful place to start whendiscussing fertilizers is the fertilizer labelitself. These labels contain several veryuseful pieces of important information for allgrowers.

Nutrient Analysis. The fertilizer analy-sis indicates the percentage of a particularnutrient contained within the fertilizer (on apercent weight basis). The fertilizer analysistypically refers to the percentage of nitrogen(N), phosphate (P2O5) and potash (K2O)contained in a given fertilizer. A balancedfertilizer should provide nutrients inamounts relative to plant requirements.Since nitrogen and potassium are used inrelatively similar amounts (on a weightbasis), a fertilizer should have a nitrogen topotassium ratio of approximately 1:1. Phos-phorus is required to a lesser degree, so thenitrogen-to-phosphorus ratio should beapproximately 2:1 to 4:1. Therefore, a 2:1:2(N-P2O5-K2O) is suitable for most green-house crops. An example of this type offertilizer is 20-10-20. While 20-20-20 is stillcommonly used, 20-10-20 is preferred, sincethe N-P2O5-K2O ratio is closer to thatrequired by plants. The extra phosphorus

provided by 20-20-20 is usually wasted, thuscreating potential environmental concerns.

Nitrogen Form. Nitrogen is provided inthree different forms: nitrate-nitrogen (NO3),ammoniacal-nitrogen (NH4) and urea-nitro-gen. The nitrogen form affects plant growthand media solution pH. Ammoniacal nitro-gen, sometimes called ammonium, tends tocontribute to “lush” plant growth, for ex-ample, greater leaf expansion and stemelongation, whereas nitrate nitrogen pro-duces a “hard” or well-toned and compactplant. High ammonium can be toxic toplants during cold, cloudy growing condi-tions. Therefore, ammonium and ureashould make up <40 percent of the nitrogenduring winter months. “Dark-Weather” or“Finisher” fertilizers tend to have high ni-trate and low ammonium nitrogen.

The following equation demonstrateshow to calculate the percentage of the totalnitrogen that is in the ammoniacal form.Note: When calculating the percentagenitrate versus ammonium, assume urea willbreak down to ammonium.

% N in ammonium form = (% Ammo-nium + % Urea) ÷ % Total N X 100

For example, a 15-5-15 label indicatesthe following nitrogen breakdown:

Total Nitrogen (N)……15% 1.20 % Ammoniacal Nitrogen 11.75 % Nitrate Nitrogen 2.05 % Urea Nitrogen (2.05% Urea + 1.20% Ammonium) ÷

15% Total N X 100 = 21.7% N in ammoniumform

Potential Acidity or Basicity. Thepotential acidity or basicity indicates howthe fertilizer will affect media solution pH. Afertilizer label will indicate that the fertilizerhas either a potential acidity or a potentialbasicity. The potential acidity refers to thefertilizer’s tendency to cause the media pHto decrease, while the potential basicityrefers to the fertilizer’s tendency to cause amedia pH increase. The larger the number,the greater the tendency for the media pH tobe affected by the fertilizer (Table 2). Fertiliz-ers high in ammonium cause the pH to

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decrease (become more acidic), while fertiliz-ers high in nitrate cause the pH to increase(become more basic or alkaline).

Several trends are apparent in Table 2.Fertilizers with a considerable percentage ofthe nitrogen in the ammonium form tend toleave an acid residue in the media, indicatedby the potential acidity. Fertilizers that havelow ammonium, and thus high nitrate formof nitrogen, tend to leave an alkaline, resi-due indicated by the potential basicity. Thehigh-ammonium fertilizers tend to have verylittle or no calcium or magnesium, while thelow-ammonium, alkaline-residue fertilizerscontain higher levels of calcium or magnesium.

Proper Dilution Rate. The proper dilu-tion rate is indicated on the fertilizer labeland can be tested with a soluble salts meter.The soluble salts concentration of the fertil-izer solution increases as the amount offertilizer increases. For example, 20-10-20Peat Lite Special will have an electricalconductivity (EC) of 0.33 mmhos/cm forevery 50 ppm of nitrogen. Therefore, afertilizer mixed to provide 250 ppm nitrogenwill have an EC of 1.65 mmhos/cm [(250 ÷50) ¥ 0.33]. Note: Each fertilizer has a differ-ent soluble salts to nitrogen relationship, sothe specific fertilizer label must be examined.

Fertilizer InjectorsInjectors mix precise volumes of concen-

trated fertilizer solution and water together.Injectors or proportioners are commonlyavailable in a mixing range of 1:16 to 1:200.For example, 1:100 injection ratio indicatesthat one gallon of concentrated fertilizer willproduce 100 gallons of final fertilizer solu-tion. Injectors allow growers to have asmaller stock tank and mix their fertilizerstock solutions less frequently. However, notall fertilizers can be mixed together. Calciumand magnesium fertilizers typically can notbe mixed with phosphate and sulfate fertiliz-ers while concentrated. A solid precipitatewill form in the bottom of the stock tank ifthe fertilizers are not compatible. Once theindividual fertilizers are diluted to their final

concentration, then all fertilizers are com-patible and thus can be mixed together.

Multiple Injectors. Multiple injectorsor multiple-headed injectors can be used toinject incompatible stock solutions. If sepa-rate injectors are plumbed serially, i.e., oneafter the other, then fertilizer stock solutionscan be mixed at the same concentration asif one injector is being used. For example,one head can inject calcium nitrate, whilethe other head injects magnesium sulfate.However, if two injector heads are placedinto one stock solution, then the final con-centration delivered to the plants will betwice the desired concentration, unlessproper dilution occurs, e.g., mix the stocksolution for 100 ppm N if 200 ppm is desired.

Injector Accuracy and Calibration.It is very common for injectors to lose cali-bration accuracy over time. Growers shouldtest the calibration accuracy with a solublesalts meter every time a new batch of fertil-izer is mixed. If a soluble salts meter is notavailable, then Calibration Method #2 canbe performed.

Calibration Method 1. Use a solublesalts/electrical conductivity (EC) meter todetermine concentration of fertilizer comingfrom the end of the hose. The EC of thewater must be subtracted from the EC offertilizer solution. The correct EC for agiven concentration is usually found onthe fertilizer label.

Calibration Method 2. Place the siphoninto a known volume of solution, e.g., aquart or a gallon. Turn the water on throughthe injector and fill up a large container,such as a 20- or 40-gallon garbage can.When the siphon has removed all of thesolution from the small container, turn offthe water. If using a Hozon Injector (1:16),then one gallon of stock solution shouldempty into 16 gallons final solution. If a 1:100injector is used, then one quart of stocksolution should fill 25 gallons of final solution.

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21-5-20 0 0 0 40 418 -20-10-20 0 0 0 38 393 -20-8-70 0 1 1 39 379 -15-15-15 0 0 0 52 261 -17-17-17 0 0 0 51 218 -15-16-17 0 0 0 47 215 -15-16-17 0 0 0 30 165 -20-5-30 0 0 0 56 153 -17-5-24 0 2 3 31 125 -20-5-30 0 1 0 54 118 -17-4-28 0 1 2 31 105 -20-5-30 0 0 0 54 100 -15-11-29 0 0 0 43 91 -15-5-25 0 1 0 28 76 -15-10-30 0 0 0 39 76 -20-0-20 5 0 0 25 40 -21-0-20 6 0 0 48 15 -20-0-20 7 0 0 69 0 -16-4-12 0 0 0 38 - 7317-0-17 4 2 0 20 - 7515-5-15 5 2 0 28 - 13513-2-13 6 3 0 11 - 20014-0-14 6 3 0 8 - 22015-0-15 11 0 0 13 - 31915-0-15 11 0 0 13 - 420

Potential Acidity Potential Basicity Ca Mg S NH4 (%) (%) (%) (%)

21-7-7 acid 0 0 0 90 1700 -24-9-9 0 0 10 50 822 -20-2-20 0 0 0 69 800 -20-18-18 0 0 1 73 710 -24-7-15 0 1 1 58 612 -20-18-20 0 0 1 69 610 -20-20-20 0 0 0 69 583 -20-9-20 0 0 1 42 510 -20-20-20 0 0 0 69 474 -16-17-17 0 1 1 44 440 -20-10-20 0 0 0 40 422 -

Table 2. The fertilizer analysis for the percentage (weight basis) of Ca, Mg, S and ammo-nium (NH4) provided in several commercially-blended fertilizers. Also, the potential acidity or

basicity are listed for each fertilizer.

Fertilizer(N-P2O5-K2O)

(lbs. Calciumcarbonate equiva-

lent per ton)

(lbs. Calciumcarbonate equiva-

lent per ton)

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Table 3 provides assistance in calcu-lating the amount of fertilizer to mix to makedifferent stock solutions using differentinjection ratios.

To use this chart:•Select your injector’s ratio setting acrossthe top of the columns.•Select percentage of nitrogen (N) formulaused in left column.•Read across and down to find ounce re-quired per gallon of concentrate.•Multiply this amount by the number ofgallons of concentrate used in your fertilizerstock tank.

The table is based on 100 ppm N. For150 ppm, multiply amounts to be used by1.5; for 200 ppm, multiply amounts to beused by 2, etc.

Starting a Fertilization Program

Nutrients can be placed into the mediaprior to planting, i.e., a pre-plant nutritionprogram, and during plant growth, i.e., apost-plant nutrition program. Do not forgetthat irrigation water can also be a signifi-cant source of plant nutrients, especiallycalcium and magnesium.

Despite considerable gardening advice tothe contrary, specific nutrients do not pro-

Table 3. A quick chart to determine the number of ounces of fertilizer required per gallonof stock tank solution based on the percentage of nitrogen in the fertilizer and the injection

ratio. See Appendix A for more specific calculations.

Ounces of fertilizer to make 100 ppm nitrogen

% Nat an injector ratio of:

1:16 1:50 1:100 1:200

10 2:1615 1:4420 1:0825 0.8630 0.72

6.75 4.53.38 2.72.25

13.5 9.06.75 5.4 4.5

27.018.013.510.8 9.0

Note: Acid injection is discussed in Irrigation WaterQuality for Greenhouse Production.

mote rooting or flowering! Specifically, phos-phorus does not promote rooting and potas-sium does not promote flowering. Excessnitrogen can potentially reduce floweringand produce excessive vegetative growth.

Pre-Plant Nutrition ProgramsNutrients can be supplied in limited

quantities, while the media components arebeing mixed. Calcium and magnesium areprovided when dolomitic limestone is usedto adjust the starting pH. Phosphorus andsulfur are provided with superphosphateplus gypsum (calcium and sulfur). (Singlephosphate is 50 percent gypsum by weight).Iron, manganese, zinc, copper, boron andmolybdenum are provided with micronutri-ent formulations (e.g., Micromax orEsmigram). Nitrogen and potassium areprovided with potassium nitrate.

Typical pre-plant recipe for 1 cubic yardof soilless media:

Dolomitic limestone 10 lbs.Treble Superphosphate 2.25 lbs.Gypsum 1.5 lbs.Micromax 1.25 lbs.Potassium Nitrate 1 lb.

(The additional nitrogen and potassiumwill last ~1 to 2 weeks.)

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Post-Plant Nutrition ProgramsMost small to medium-sized commercial

greenhouses use commercially blendedfertilizers for convenience and dependability;however, for some growers it is economicalto buy individual fertilizers and mix themtogether. Table 4 shows some of the com-mon ingredients in a variety of differentcommercial fertilizers.

Following are some important notesabout each of the essential plant nutrients:

Nitrogen (N)Sources: ammonium nitrate, urea,

calcium nitrate, potassium nitrate, magne-sium nitrate.

The concentration applied is determined bythe amount of leaching. For example, in aconstant liquid feed program using a sub-irrigation system (0 percent leaching) 100 ppmN may produce adequate growth, while 300ppm N may be needed if overhead irrigationresults in 25 percent leaching.

Crop requirements:Bedding Plants LightNew Guinea Impatiens LightGeranium ModeratePoinsettias Moderate to heavy

Chrysanthemums Heavy

Plug Special X X X X 13-2-13Cal-Mag Special X X X X 14-0-14High Calcium Spec. X X X 15-0-15Pansy Special X X X X X 15-2-20Poinsettia Spec. X X X 22-8-20Poinsettia Finish. X X X 15-11-29Pot Mum Special 1 X X X 5-11-29Geranium Spec. 15-15-15 X X XPlant Starter X X 15-50-5Fern Special X X X 18-24-18General Purpose X X X 20-10-20All Purpose X X X 20-20-20

Table 4. Some common ingredients found in a variety of commercially blended fertilizers.Note: Each fertilizer may contain several other ingredients not listed below.

CommercialSources

Urea AmmoniumNitrate

CalciumNitrate

PotassiumNitrate

MagnesiumNitrate

AmmoniumPhosphate

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Phosphorus (P)Sources: Ammonium phosphate, urea

phosphateA nitrogen-to-phosphate (P2O5) ratio of

2:1 is acceptable for most crops. Fertilizerswith high concentrations of ammoniumphosphate, such as 9-45-15, appear topromote stem stretching.

Potassium (K)Sources: Potassium nitrate, potassium

sulfateA nitrogen-to-potash (K2O) ratio of 1:1 is

acceptable for most crops.

Calcium (Ca) and Magnesium (Mg)Sources: Dolomitic limestone, irrigation

water, calcium nitrate, magnesium sulfate(Epsom salts), magnesium nitrate.

Calcium and magnesium provided bydolomitic limestone are released slowly overseveral months. These two nutrients canhave an antagonistic relationship (i.e., theycompete within the plant), thus a Ca:Mgratio of 3:1 to 5:1 is desirable. Calcium andmagnesium are commonly found in irriga-tion water, especially high alkalinity water.Calcium and magnesium deficiencies aremost common when the pH is low (less than5.8). Calcium and magnesium fertilizers cannot be mixed in the concentrated form withphosphate or sulfate fertilizers, thus cal-cium and magnesium are frequently omittedfrom commercial fertilizers. A few relativelynew fertilizers contain calcium and magne-sium along with the nitrogen, phosphorus

and potassium. These fertilizers often listfive numbers in the analysis. These num-bers represent N, P2O5, K2O, Ca and Mg,respectively. For example, (15-5-15-5-2, 14-0-14-6-3, 13-2-13-6-3). Note: Epsom saltsare 10 percent magnesium by weight.

MicronutrientsMicronutrients are sold in different

formulations; for example, Micromax,Esmigran and Soluble Trace Element Mixcontain only inorganic sources, while Com-pound 111 contains chelated sources. Che-lated forms are superior in that the micro-nutrients are more soluble, therefore morereadily available to the plant. Consequently,chelated micronutrients are applied at lowerrates. Compound 111 and STEM are labeledfor use in constant liquid feed programs.The rates are based on adding a certainamount of micronutrient mix per 100 ppmof N used in the fertilization program.

Micronutrient deficiencies are closelyrelated to media pH. High pH (greater than 6.5)can produce deficiencies, while low pH (lessthan 5.8) can cause toxicities. Adjusting themedia pH is the best solution to avoid micro-nutrient toxicities or deficiencies.

Table 5. The micronutrient concentration (ppm) to be applied with each 100 ppm nitrogen.

Soluble Trace 0.25 0.27 0.15 0.11 0.05 0.001 Element Mix (STEM)Compound 111 0.25 0.13 0.012 0.019 0.04 0.004

Fertilizer

Micronutrient ppm at 100 ppm N liquid feed

Iron(Fe)

Manganese(Mn)

Zinc(Zn)

Copper(Cu)

Boron(B)

Molybdenum(Mo)

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Appendices:

A. Fertilizer calculations1. Calculating the parts per million for

a fertilizer solution:Actual ppm = pounds fertilizer X %N X

Z ÷ gallons stock ÷ proportioner ratio

For N, Ca, Mg, Fe, Z=1200For Phosphorus (P), Z= 528For Potassium (K), Z= 996

Example 1: Calculate the concentration(ppm) of nitrogen applied when 1 pound of15-0-15 is mixed into a 5 gallonstock tankand a 1:16 proportioner is used.

1 lb. Fert. X 15%N X 1200 ÷ 5 gal. stock ÷16 proportioner = 225 ppm nitrogen.

Example 2: Calculate the concentration(ppm) of potassium applied when 1 pound of15-0-15 is mixed into a 5 gallon stock tankand a 1:16 proportioner is used.

1 lb. Fert X 15%K ¥ 996 ÷ 5 gal. stock ÷16 proportioner = 187 ppm potassium

Example 3: Calculate the concentration(ppm) of calcium applied when 1 pound of15-0-15 is mixed into a 5 gallon stock tankand a 1:16 proportioner is used. (Note fromTable 2, 15-0-15 contains 11% calcium).Also note that the irrigation water has 15ppm calcium.

1 X 11 X 1200 ÷ 5 ÷ 16 = 165 ppm cal-cium from fertilizer plus and additional 15ppm calcium from the irrigation water = 180ppm calcium applied

2. Calculating the amount of fertilizerto add to a stock tank:

lbs. of fert. = desired ppm X gal. stocksoln. X proportioner ratio ÷ %N ÷ Z

Example 1: How many pounds of 21-5-20fertilizer should one add to a 20 gallon stocktank in order to irrigate with 200 ppm Nusing a 1:100 injector?

200 ppm N X 20 gal. X 100 (injector ratio)÷ 21%N ÷ 1200 = 15.9 pounds of fertilizer(21-5-20) added to a 20-gallon stock tankwill produce 200 ppm N when injected at a1:100 ratio.

B: Conversion of Units Liquid

1 ounces = 29.6 milliliters = 2 table spoons

8 ounces = 1 cup2 cups = 1 pint2 pints = 1 quart4 quarts = 1 gallon10 liters = 2.64 gallons1 gallon= 128 ounces = 3.785 liters =

8.34 pounds of water1 gallon concentrate per 100 gallons

of spray = 2.5 tablespoons per gallon

Dry Weight1 ounce = 28.35 grams1 pound = 454 grams = 16 ounces1 tablespoon = 3 teaspoons1 ppm = 1 milligram per 1 kilogram

or 1 milliliter per liter or 1 milligram per liter

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A State Partner in the Cooperative Extension SystemThe Agricultural Extension Service offers its programs to all eligible persons

regardless of race, color, national origin, sex or disability and is an Equal Opportunity Employer.COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS The University of Tennessee Institute of Agriculture, U.S. Department of Agriculture,

and county governments cooperating in furtherance of Acts of May 8 and June 30, 1914. Agricultural Extension Service

Billy G. Hicks, Dean

PB1616-1M-2/99 E12-2015-00-104-99