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Developing and Implementing a Fertilizer Program...6 Nutrient Requirements of a Typical Crop Time...

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1/18/2017 1 Developing and Implementing a Fertilizer Program Marc van Iersel Supplying nutrients Pre-plant mixed with substrate components before planting Post-plant applied to substrate with the irrigation water (fertigation) top-dressing CRFs
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Page 1: Developing and Implementing a Fertilizer Program...6 Nutrient Requirements of a Typical Crop Time Nutrients Crop needs CRF supply Nutrients in the water • Calcium and magnesium may

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Developing and Implementing a Fertilizer Program

Marc van Iersel

Supplying nutrients

• Pre-plant• mixed with substrate

components before planting

• Post-plant• applied to substrate with the

irrigation water (fertigation)• top-dressing CRFs

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Dolomitic limestone• Ca & Mg• 10-15 lbs/yd3

• Limestone at 3 lbs/yd3 will increase pH 0.3 to 0.5 units

• Used to adjust substrate pH

Preplant Fertilization

(when no pH shift is desired)Gypsum• Ca and S• 5 lbs/yd3

Epsom salts• Mg and S• 1 lb/yd3

Preplant Fertilization

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• Calcium Nitrate (15.5-0-0-18)

• 1 lb/yd3

Potassium Nitrate(13-0-44)

1 lb/yd3

• Phosphorus• 0 - 44 - 0 (triple superphosphate)• 2.25 lbs/yd3

Preplant Fertilization: N,P, K

Preplant Fertilization

These normally do NOT supply amplenutrients for a crop

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• Micronutrients• (Fe, Mn, Zn, Cu, B, Mo)

• Normally supplied as a mixture (about 1 - 1.5 lbs/yd3)

Preplant Fertilization

Preplant fertilization

• Controlled-release fertilizers (osmocote, nutricote, polyon) can be incorporated

• Match release time with:

• Type of crop

• Expected temperature

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Controlled-Release Fertilizers (osmocote)

70

43o 52o 61o 70o 79o 88o

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Nutrient Requirements of a Typical Crop

Time

Nut

rient

s

Crop needs

CRF supply

Nutrients in the water

• Calcium and magnesium may be present in substantial amounts (hard water)

• Iron, chloride, and sulfur are less common

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Post-planting fertilization

• Fertigation is the most common approach• Applying water-soluble fertilizer with the

irrigation water

• Top-dressing controlled released fertilizer

• Foliar applications to correct deficiencies

Fertigation

• Continuous liquid feed (fertilizer is injected into the water at each irrigation)

• Weekly or twice weekly (better suited for some smaller growers)

• Either way, use an injector

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Injectors

• Designed for specific range of flow

• Need maintenance

• Check calibration

http://extension.uga.edu/publications/detail.cfm?number=B1237

Fertilizer ConcentrationBased on Nitrogen

• 50 - 250 ppm continuous feed• 150 - 400 ppm weekly • 1/2 rate when using a closed system• 150 ppm good starting point for most

crops (fertigation)

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Fertilizer Calculations (FertCalc)

https://www.ces.ncsu.edu/depts/hort/floriculture/software/fertcalc1/FERTCALC.htm

Checking the fertilizer rate

• Avoid costly mistakes due to measurement errors or malfunctioning injectors

• Check the concentration of your fertilizer solution

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Concentration of the fertilizer solution

• Three things you need to know

• the EC of your irrigation water

• the EC of the fertilizer solution

• the EC of a 100 ppm N fertilizer solution

Monitoring your fertilizer solution

• EC meter

• pH meter

• calibration solutions

Insert picture here

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Electrical Conductivity (EC)

• A measure of the total amount of soluble salts (mainly the macronutrients: N, P, K, Ca, S, and Mg)

• EC meters start at about $60, calibration solutions are cheap

Electrical Conductivity Units

• 1 mMho = 1 mMho/cm = 1 mSiemens = 1 mS = 1 mS/cm = 1 dS/m = 1,000 µS = 1,000 µS/cm

• Range needed: 0 - 8 mS/cm

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If you want to use 150 ppm nitrogen, the EC of your fertilizer solution should be 0.93 mmhos/cm higher than the EC of your water(1 mmhos/cm = 1 mS/cm = 1 mS = 1 dS/m = 1000 µmho/cm)

Example

• Irrigation water EC: 0.46 mmhos/cm

• Fertilizer solution EC: 1.70 mmhos/cm

• The fertilizer increased the EC by 1.70 - 0.46 = 1.24 mmhos/cm

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The concentration is 200 ppm N

Spreadsheet available at http://hortphys.uga.edu/

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26 52 105 210 420ppm nitrogen

Choose for optimal quality,not maximum growth

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Choosing a Fertilizer

• Proper nutrient ratio:• Many crops do well with N:P:K ratio of 2:1:2

• Does the fertilizer contain Ca? If not, incorporate adequate amounts in the substrate (or use calcium nitrate occasionally)

• Does the fertilizer contain micronutrients?

• Sulfur normally not listed in the analysis (may be provided as ammonium and/or magnesium sulfate, do not rely on Cu, Mn, or Zn sulfate)

Choosing a Fertilizer

• Some of the micronutrients need to be chelated (Fe, often others as well)

• Store fertilizer solution in the dark

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Do NOT store your fertilizer like this!

Choosing a Fertilizer

• What form of nitrogen?• Ammonium: lush growth, large leaf area, tall

plants (because of high P)

• Urea: breaks down into ammonium

• Nitrate: hardening-off, compact growth (sometimes used later in production) (low P)

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Nitrogen Source

• 3 forms - ammonium, urea, nitrate• 40% ammonium + urea generally safe

• ammonium + urea decrease substrate pH

• nitrate increases substrate pH

• Optimal form of nitrogen depends on substrate pH (water quality)

• Example label(5.99 +1.89) / 20 x 100% =39% ammonium

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Ammonium toxicity

Deformed leaves may become chlorotic/necrotic

Necrotic root tips (orange/brown)

Fertilizers and substrate pH

• Different fertilizers affect substrate pH differently

• Ammonium lowers pH

• Nitrate increases pH

• Potential acidity/basicity is a rough indicator of how a fertilizer may affect pH

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Potential acidity/basicity

Potential acidity: indicates a likely DECREASE in substrate pH

Potential basicity: indicates a likely INCREASE in substrate pH

Alternating fertilizers may help to stabilize pH [e.g. 20-10-20 (acidity = 410 lbs/ton) and 13-0-44 (basicity = 520 lbs/ton)]

Potential acidity/basicity

• Actual pH (acidity) of fertilizer matters too!

• Some fertilizers are very acidic

• Typically Ca-containing fertilizers• 15-5-15 Cal-Mag

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pH

• Tells you how acid or alkaline the water or growing medium is

• This determines the availability of micronutrients (Fe, Mg, Mn, B)

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pH

• Depends on:• Substrate• Fertilizer• Water• Species

• Acid injection may be needed

Alkalinity Calculations (Alk_Calc)

https://extension.unh.edu/Agric/AGGHFL/alk_calc.cfm

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Iron toxicityin marigold

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pH meters• Start at about $60• Two calibration solutions needed• First calibrate at pH 7 then at pH 4

Calibration

• At least once a week. If you do not calibrate your meters, there is no need to collect any samples either.

• You will get bad information and will make the wrong decisions.

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Recirculating systems

• Many high-wire vegetables

• Subirrigation

• Cut flowers

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Measuring individual nutrients?

• Difficult

• Use analytical lab

• Hard to interpret

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Low Concentrations Do Not Indicate Deficiencies

Slide courtesy of Bruce Bugbee, data from Kennedy Space Center

(PP

M)

Time (days)

Choosing a Fertilizer• Solubility is important:

• Use a fertilizer specifically developed for fertigation

• Check maximum solubility

• Dissolve stock solution in hot water

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Developing a Nutritional Program• Take different nutrient sources into

account (substrate, water, fertilizer)

• Different crops may have different needs (place crops accordingly)

• By monitoring pH and EC, you can assure that nutrients are available in ample amounts

• Solution AND substrate

Thank you


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