developing and implementing a fertilizer program...6 nutrient requirements of a typical crop time...
TRANSCRIPT
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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