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 1
Preplant Fertilization Dolomitic limestone Ca & Mg 10-15 lbs/yd 3 Limestone at 3 lbs/yd 3 will increase ph 0.3 to 0.5 units Used to adjust substrate ph Preplant Fertilization (when no ph shift is desired) Gypsum Epsom salts Ca and S Mg and S 5 lbs/yd 3 1 lb/yd 3 2
Preplant Fertilization: N,P, K Calcium Nitrate (15.5-0-0-18) 1 lb/yd 3 Phosphorus Potassium Nitrate (13-0-44) 1 lb/yd 3 0-44 - 0 (triple superphosphate) 2.25 lbs/yd 3 Preplant Fertilization These normally do NOT supply ample nutrients for a crop 3
Preplant Fertilization Micronutrients (Fe, Mn, Zn, Cu, B, Mo) Normally supplied as a mixture (about 1-1.5 lbs/yd 3 ) Preplant fertilization Controlled-release fertilizers (osmocote, nutricote, polyon) can be incorporated Match release time with: Type of crop Expected temperature 4
Controlled-Release Fertilizers (osmocote) 70 43 o 52 o 61 o 70 o 79 o 88 o 5
Nutrient Requirements of a Typical Crop CRF supply Crop needs Nutrients Time Nutrients in the water Calcium and magnesium may be present in substantial amounts (hard water) Iron, chloride, and sulfur are less common 6
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 7
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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 Concentration Based 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) 9
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 10
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 Insert picture here ph meter calibration solutions 11
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 12
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 13
The concentration is 200 ppm N Spreadsheet available at http://hortphys.uga.edu/ 14
Choose for optimal quality, not maximum growth 26 52 105 210 420 ppm nitrogen 15
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 16
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) 17
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 18
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 19
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 20
ph Tells you how acid or alkaline the water or growing medium is This determines the availability of micronutrients (Fe, Mg, Mn, B) 21
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 22
Iron toxicity in marigold 23
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. 24
Recirculating systems Many high-wire vegetables Subirrigation Cut flowers 25
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Measuring individual nutrients? Difficult Use analytical lab Hard to interpret 28
Low Concentrations Do Not Indicate Deficiencies (PPM) Time (days) Slide courtesy of Bruce Bugbee, data from Kennedy Space Center Choosing a Fertilizer Solubility is important: Use a fertilizer specifically developed for fertigation Check maximum solubility Dissolve stock solution in hot water 29
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 30