Greenhouse Plant Nutrition 1. Start with water quality analysis Rosa E. Raudales, Ph.D. Assistant Professor and Extension Specialist rosa@uconn.edu Phone: (860) 486-6043 www.greenhouse.uconn.edu Se habla Español! 1 Water quality Alkalinity Factors: 1. Alkalinity 2. Electrical conductivity (EC) 3. Specific ions 4. ph Alkalinity: is the neutralizing capacity of a solution (acid-buffering capacity). Think of dissolved limestone Bicarbonates: [HCO - 3 (Ca, Mg, Na)] Carbonates: [CO 3 (Ca, Mg, Na)] Alkalinity is a stronger base than ph For example: A 1L container irrigated with 1L of water per week, for 15 weeks. Water quality: ph 9 and alkalinity of 200 ppm CaCO 3. Factor Quantity Meqs of base added to the pot ph 9.0 0.15 base Alkalinity 200 ppm CaCO 3 60 base Limestone (CaCO 3 ) 5 lb/yd 3, 3 kg/m 3 60 base Water ph added only a little base, whereas the alkalinity added the same as limestone. Alkalinity: Dissolved limestone Alkalinity: is the neutralizing capacity of a solution. Grower A Grower B ph 9.3 8.3 Alkalinity (CaCO3 mg/l) 71 310 Sulfuric acid (35%, fl. oz.) 15.8 68.6 Bailey and Bilderback, NCSU (1997)
Electrical Conductivity (EC) EC is a measurement of the ability of a solution to move electric charge. Total concentration of salts in the solution. Ions that contribute to EC: Use the EC as an indicator: Target EC is determined by the crop EC Nutrient Solution 1.8 ms/cm In water: Ca, Mg, SO 4, Na, Cl, HCO 3 - In fertilizers: NO 3 -, NH 4+, PO 4, K, Ca, Mg, SO 4, Cl EC- fertilizer 1.3 ms/cm EC-irrigation water 0.5 ms/cm 9 High salts can be toxic to crops Onsite measuring High EC is an indicator of high concentration of salts in water. But which salts? If EC >0.5 Element ppm (mg/l) Sodium (Na) < 50 Chloride (Cl) < 70 Sulfur (S) < 120 Boron < 0.5 Fluoride < 1.0 ph and EC: can be measured with the same meter. Alkalinity: titration kit. Can not be measured directly with ph meter. 2. Know the plants requirements What is ph? Plants species differ in their response to media ph Iron Inefficient General Iron efficient H O H H + H O _ Petunia group: ph 5.4-6.2 General group: ph 5.8-6.4 Geranium group: ph 6.0-6.6 H 2 O Water H + Acid OH - Base
ph of the growing media affects: Nutrient solubility Plant health: Excessive toxicity Insufficient deficiency Iron-inefficient plants: Petunia Group This group of plants show Fe-deficiency when grown in high medium-ph. Deficiencies ph > 6.4 Optimum ph: 5.4 a 6.0 Azaleas, bacopa, calibrachoa, dianthus, nemesia, pansy, petunia, rhododendron, snapdragons, verbena, vincas, etc Iron-efficient plants: Geranium Group These group of plants uptake Fe and Mn very efficient. ph <6.0 toxicity Optimum ph: 6.0 to 6.6 Geraniums (seed and zonal), marigolds, lisianthus, New Guinea impatiens, etc. General Group: ph neutral Optimum ph: 5.8-6.2 Chrysanthemums, impatiens, osteos, poinsettias, coleus, Ivy geranium, most plants. Plants sensitivity to EC in substrate 3. Match the fertilizers to water quality and crops needs Sensitive to high EC of the substrate: Example: Heliotrope, New Guinea Impatiens, ferns, plugs and seedlings Sensitive to low EC of the substrate (Grow better with high EC): Examples: Petunias, Chrysanthemums Maintaining a moderate EC in the substrate will be good for all crops.
Fertilizer labels P in fertilizers N-P 2 O 5 -K 2 O N-P 2 O 5 -K 2 O Conversion: - P 2 O 5 to P x 0.44 - K 2 O to K x 0.83 20-10-20 = 20-4.4-16.6 N-P-K 20-10-20 N-P 2 O 5 -K 2 O = 20-4.4-16.6 N-P-K The % of elements absorbed by the plant are: 4-0.5-4 (equivalent to 20-2.5-20 N-P-K) Fertilizers like 20-10-20 (20-4.4-16.6) are too high in P. Plants are efficient taking up P and P in runoff is an environmental contaminant. High P results in leaf expansion and stretched plants. Harvey Lang, Univ. Texas A&M Common fertilizers in greenhouses N-P 2 O 5 -K 2 O 13-2-13 is a common fertilizer for plugs. 15-5-15 or 17-4-17 are typical proportions used to finish crops with enough P to sustain plant growth and promote flowering. More P will only go in the run-off. N in the label Nitrogen form: Nitrate, ammonium or urea. In this label: 8/20 = 40% N ammonium 12/20 = 60% N-nitrate Water-Soluble Fertilizers Are classified as acidic, neutral or basic. The ph of the fertilizer solution DOES NOT indicate the tendency of fertilizers to raise or lower medium-ph. Nitrogen form affects medium-ph Nitrogen form Formula Acid/Base effect Ammonium-N NH + 4 Strongly acidic Nitrate-N NO - 3 Weakly basic Urea-N CO(NH 2 ) 2 Weakly acid
N in the label Nitrogen form: Nitrate, ammonium or urea. In this label: 8/20 = 40% N ammonium 12/20 = 60% N-nitrate N-P 2 O 5 -K 2 O Acidity or basicity of fertilizers (NH 4 -N + Urea-N) / N Total Fertilizer Reaction (A=acid, B=base) 21-7-7 100% A 1560 20-10-20 40% A 429 17-5-17 20% B 0 15-0-15 13% B 420 Acidity or basicity of fertilizers Product Name Potential Acidity (A) / Basicity (B) (CCE/ton) Nitrogen NH4-N Urea-N NO3-N 21-7-7 1580 A 54.6 45.4 0.0 20-10-20 Peat-Lite Special 415 A 40.5 0.0 59.5 21-5-20 Multi Purpose 390 A 34.8 5.2 60.0 20-20-20 General Purpose 532 A 20.5 52.0 27.5 13-2-13 Plug & Bedding Plant 335 B 0.0 6.9 93.1 Special 15-0-15 Peat-Lite Dark Weather 221 B 13.3 0.0 86.7 15-5-15 Cal-Mag Special 131 B 7.3 14.0 78.7 17-3-17 Peat-Lite Neutral Cal-Mag 27 B 23.5 0.0 76.5 Matching Fertilizer to Water Alkalinity Alkalinity (mg/l CaCO 3 ) % Acidic nitrogen (ammonium + urea)/total N Commercial fertilizer blend Reaction potential (A/B) 50 13% 15-0-15 B 420 100 20% 17-5-17 B 0 200* 40% 20-10-20 A 40 300* 100% 21-7-7 A 1560 Goal: Balance water alkalinity and fertilizer to sustain the desired ph. Dealing with high alkalinity and salts 1. Use alternative water source for sensitive crops. Matching Fertilizer to Water Alkalinity: Go to: www.backpocketgrower.com Tools> Fertilizer ph 2. Inject an acid to neutralize the alkalinity to ph 6.0 (under this level you will acidify the crop and risk burning it). (https://extension.unh.edu/agric/agghfl/alk_calc.cfm) 3. Fertilize with a neutral fertilizer at a high rate: >200 ppm with high leaching fraction 21-5-20 (acid) + 15-0-14+Mg (basic) (or 15-0-20) (high in + charges to compete with Na+) Alternate with fertilizers with high K (14-5-38)
Don t forget the micronutrients Peat-lite (high concentration of micros) vs. general (low concentration of micros) General vs Peat-Lite Fertilizers Micronutrient concentration at 200ppm N Fertilizer Fe Mn Zn Cu B Mo General Use (20-20-20, 15-0.5 0.1 0.1 0.05 0.05 0.03 16-17, 21-7-7) Peat-Lite (20-10-20, 17-5-17, 13-2-13) 1.0 0.4 0.4 0.3 0.2 0.08 How much fertilizer to add? EC of the fertilizer (ms/cm) 50 ppm N 100 ppm N 150 ppm N 200 ppm N 14-0-14 0.33 0.65 0.98 1.30 13-2-13 0.34 0.68 1.02 1.36 12-4-12 0.32 0.64 0.96 1.28 14-4-14 0.35 0.70 1.05 1.40 Additional notes about WSF 1. Monitor, monitor, monitor ph and EC of growing media at least every other week (See handout). 2. Have in your arsenal a couple of fertilizer to help you push the ph in either side. 17-5-17 0.34 0.69 1.05 1.35 20-10-20 0.33 0.65 0.98 1.30 20-20-20 0.20 0.40 0.60 0.80 46 Controlled Release Fertilizes CRF: For Production or Retail? Production: CRF incorporated in growing media + WSF during the production cycle. Retail: Production with WSF and then top-dressed with CRF with short longevity before sale or incorporate with longer longevity.
Controlled Release Fertilizers After 42 days in production, using WSF (200 ppm) and/or CRF for production provided marketable plant quality. Controlled Release Fertilizers At consumer phase, high rates of CRF (10 lbs/yd 3 ) had greater plant quality than WSF (200 ppm in production) or low CRF (6 lbs/yd 3 ) 84 days after planting Oliveira et al. (2016) HortTechnology 26(2):164-175 Oliveira et al. (2016) HortTechnology 26(2):164-175 Chrysanthemums Helen Chrysanthemums Helen 250 ppm 20-10-20 11 lbs/y 3 9-month Osmocote After 10 weeks, CRF-only plants were the smallest; however, plants that received CRF plus four or six weeks of WSF were the same size as WSF plants. Catlin N, Mattson N (2014) Greenhouse Grower: July 2014 8 lbs/y 3 CRF + WSF 52 Catlin N, Mattson N (2014) Greenhouse Grower: July 2014 53 Pros & Cons of Fertilizers Steps Water Soluble Fertilizers Slow/ Controlled Release Fertilizers Good under protected structures that Good when rain cannot be isolated prevent exposure to rain (nursery) (greenhouses) Easy to adjust the concentration to Required a nutrient release curve and match it to the crops needs. match it to the crop s needs. Needs to be applied directly in the Less pollution and cost, compared to container (i.e. drip irrigation, hose, applying water soluble fertilizers with sub-irrigation). sprinklers. Easy to leach if the EC levels are high. Harder to leach if the EC is high. Requires an injector. Crops can be irrigated only with water, o need to have an equipment. Controlled-release fertilizers can be used as a starter fertilizers and combined with water soluble fertilizers. 1. Check water quality (alkalinity and EC). 2. Match fertilizer to crop needs and water quality. 3. Trust no-one! Test new batches of growing media. 4. Monitor ph and EC of the growing media. 5. Switch temporary to an acid or basic fertilizer.
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