1. Managing and Amending Soils for Productive Yields in High Tunnels Carl Rosen Department of Soil, Water, & Climate University of Minnesota 2009 Regents of the University of Minnesota

2. Topics Considerations before planting Site selection Yield potential in a high tunnel Satisfying nutrient needs Preplant amendments Importance of soil testing Nutrient management Without fertigation Nutrient sources organic and controlled release With fertigation Nutrient sources & timing of application 2009 Regents of the University of Minnesota

3. Site Selection Ideal soil is a well-drained sandy loam to silt loam Medium to high organic matter levels (3.5 to 6%) Consider growing green manure crops before planting/establishing the tunnel Sorgum-sudan Rye or oats Legumes such as field peas, clover 2009 Regents of the University of Minnesota

4. Improving Soil Physical Properties Compost addition 1-2 lbs compost per sq. ft. Use good quality compost Beware of herbicide residuals 2009 Regents of the University of Minnesota

5. Yield Potential & Nutrient Needs Yields in a high tunnel can be 2 to 4 times the yield obtained in the field Higher yields will require more nutrients, but knowing how much to apply is a challenge Lack of nutrients deficiencies Excessive nutrients salt build up Both situations affect yield and quality 2009 Regents of the University of Minnesota

6. Book Values for Tomatoes N P K Plant Part -------- lb per ton F.W. ------------ Fruit 3.4 0.4 6.0 Vines 2.6 0.4 3.4 Total 6.0 0.8 9.4 A 50 ton yield/A would require: 300 lbs N/A 40 lbs P/A (92 lbs P2O5) 470 lbs K/A (564 lbs K2O) 2009 Regents of the University of Minnesota

7. Satisfying Nutrient Demand in a High Tunnel System Release of nutrients from the soil Importance of good preparation Addition of fertilizer Preplant During the growing season fertigation 2009 Regents of the University of Minnesota

8. Amendments Before Planting Have soil tested before applying amendments pH, OM, nitrate-N, P, K, Ca, Mg, micronutrients, soluble salts Retest yearly, especially if problems are occurring 2009 Regents of the University of Minnesota

9. Soluble Salts (EC) Based on saturated paste: < 2 mmhos/cm (dS/m) - no problems 3-4 some plants affected 5-7 many plants affected >8 only salt tolerant plants survive Most soils in Minnesota have low salts, but salts may accumulate with excessive fertigation 2009 Regents of the University of Minnesota

10. Soil pH Acceptable range: 5.5-7.5 Adjust before planting Acid soils use calcitic or dolomitic limestone Alkaline soils use compost, sphagnum peat, elemental sulfur 2009 Regents of the University of Minnesota

11. Phosphorus and Micronutrients Base P application on soil test level Greater than 41 ppm is considered very high for most vegetables/fruit Incorporate before planting if soil test indicates a need Potassium phosphate, DAP, MAP Numerous micronutrient sources Composted manure Use starter solutions high in P for transplants 2009 Regents of the University of Minnesota

12. Nitrogen and Potassium A portion should be applied before planting Base K fertilizer application on soil test most can be applied preplant Greater than160 ppm is considered very high for most vegetables/fruit potassium chloride (0-0-60) potassium sulfate (0-0-50) potassium magnesium sulfate (0-0-22); acceptable organic source For soluble N sources, apply about 1/3 1/2 of the required N before planting urea (46-0-0) ammonium nitrate (34-0-0) calcium nitrate (15.5-0-0) potassium nitrate (13-0-44) composted manure (variable) 2009 Regents of the University of Minnesota

13. Nutrient Management Without Fertigation Organic systems Composted manure Type of compost Moisture content Crops grown To supply equivalent of 100 lbs available N/A: Dairy manure compost: 2700 lbs/1000 sq. ft. Poultry manure compost: 900 lbs/1000 sq. ft. Incorporate 6 to 8 inches into soil 2009 Regents of the University of Minnesota

14. Nutrient Management Without Fertigation Use legume cover crops Warm season cover crops can be planted later in the season 2009 Regents of the University of Minnesota

15. Nutrient Management Without Fertigation Conventional system Composted manure Soluble fertilizers Controlled release N fertilizers Coated urea Osmocote Be sure that release rate is fast enough for the crop being grown For most vegetables 50 to 70 day release is needed Temperatures are warmer in a high tunnel faster release 2009 Regents of the University of Minnesota

16. Nutrient Management With Fertigation Injection of one or more nutrients into the irrigation water Review the Minnesota Chemigation/Fertigation Permit Application and Safety Requirements www.mda.state.mn.us Submit the Minnesota Chemigation/Fertigation Permit Application to MDA Main requirement is to have recommended anti-pollution and safety devices 2009 Regents of the University of Minnesota

17. Nutrient Management With Fertigation Primarily used for nitrogen and potassium Urea-ammonium nitrate (28%N) (liquid) Calcium nitrate (15.5% N) Potassium nitrate (13% N; 44% K2O) Potassium chloride (60%; K2O) Blends eg. 20-20-20 Soluble sources of organic fertilizers are available, but are expensive and may cause clogging Some fish emulsions have been successfully used 2009 Regents of the University of Minnesota

18. Solubility of Common Fertilizers Material Composition Salt index Solubility %N %P2O5 %K2O lbs/gal H20 Calcium nitrate1 15.5 0 0 53 8.5 Potassium nitrate 13.0 0 44 73 1.1 Ammonium nitrate 33.5 0 0 105 9.8 Urea 46.0 0 0 75 6.5 Ammonium sulfate2 21.0 0 0 69 5.9 Potassium chloride 0.0 0 60 116 2.3 Potassium sulfate2 0.0 0 50 46 0.6 Diammonium phosphate2 18.0 46 0 30 3.6 1May cause clogging if irrigation water is high in bicarbonates 2Not recommended for use with calcium nitrate or if irrigation water is high in calcium 2009 Regents of the University of Minnesota

19. Mixes to Avoid Phosphorus compounds with calcium or iron Calcium with sulfate and bicarbonate To avoid precipitation problems two stock tanks should be used, one for calcium nitrate and iron chelate and the other for the remaining fertilizers Alternatively apply P fertilizer preplant 2009 Regents of the University of Minnesota

20. Rate and Timing of Application Preparing soils and applying preplant nutrients is still important - compost or fertilizer About 2/3 of N and K needs can be applied through fertigation Timing is not as critical as rate Once per month Once per week Every time there is an irrigation event 2009 Regents of the University of Minnesota

21. Fertigation Use a batch loading fertigation approach Inject total volume of nutrient during an irrigation event Total volume of fertilizer for batch loading depends on the area of the irrigated zone and the desired nutrient rate The injection rate does not need to be precisely controlled The injector should apply the chemical solution in a time period that does not result in over-irrigation, otherwise leaching will occur 2009 Regents of the University of Minnesota

22. Meeting the Demands for Crops with Different Requirements Fertigate crops at different times Allows for varying rates to be applied Fertigate to meet the demands of the crop needing the lowest amount of nutrients Make up difference with preplant fertilizer 2009 Regents of the University of Minnesota

23. Determining the Rate of N and K to Apply Most conventional recommendations are based on lbs N or K2O/A Ounces per linear feet of row is more practical for high tunnels Based on 4ft spacing between rows 100 linear ft = 400 sq. ft. 2009 Regents of the University of Minnesota

24. N and K Fertigation Schedule for Tomatoes - lb/A basis Days after Planting Daily N Weekly N Seasonal N Daily K2O Weekly K2O Seasonal K2O ----------------------------------------- lb/A--- ---------------------------------------------- Preplant ---- ---- 50.0 ---- ----- 100.0 0- 21 0.5 3.5 61.5 1.0 7.0 121.0 22- 49 0.7 4.9 81.1 1.4 9.8 160.2 50- 70 1.0 7.0 102.1 2.0 14.0 202.2 71- 91 1.1 7.7 125.2 2.2 15.4 248.4 92-112 1.0 7.0 146.2 2.0 14.0 290.4 2009 Regents of the University of Minnesota

25. N and K Fertigation Schedule for Tomatoes oz per 100 ft basis Days after Planting Daily N Weekly N Seasonal N Daily K2O Weekly K2O Seasonal K2O --------------------------------- oz/100 linear row ft -------------------------------------- Preplant ---- ---- 7.3 ---- ----- 14.7 0- 21 0.07 0.50 9.0 0.15 1.1 17.8 22- 49 0.10 0.70 11.9 0.21 1.5 23.5 50- 70 0.15 1.05 15.0 0.29 2.0 29.7 71- 91 0.16 1.12 18.4 0.32 2.2 36.5 92-112 0.15 1.05 21.5 0.29 2.0 42.6 1 assumes 4 ft spacing between rows; lb/A X 0.147 = oz/100 linear ft of row. lbs/A x 0.147 = oz/100 linear ft of row 2009 Regents of the University of Minnesota

26. Calculating the Rate of Fertilizer to Inject Example for urea-ammonium nitrate (28%) Area to fertilize 200 linear feet (800 sq. ft.) Liquid (28% N) 3 lbs N/gallon Recommendation is 10 lbs N/A 10/3 = 3.33 gallons/A 3.33 gal * 800/43560 * 128 oz/gal = 7.8 fl oz Use similar approach for granular except conversion to lbs product rather than fl. oz. is made 2009 Regents of the University of Minnesota

27. Amount of UAN Solution for Various N Rates per Acre N Rates lbs/ac 1 2 3 4 6 8 10 28% 0.33 0.67 1.00 1.33 2.00 2.67 3.33 Gallons/ac 28% fl. 0.39 0.78 1.16 1.55 2.32 3.10 3.88 oz/100 linear ft of row1 1Assumes a between row spacing of 4 ft. 2009 Regents of the University of Minnesota

28. Summary Soil test before planting Incorporate compost if needed to improve soil physical and chemical properties If needed adjust acid soil pH with lime Incorporate P and micronutrients before planting based on a soil test For organic production use composted manure before planting 2009 Regents of the University of Minnesota

29. Summary For conventional systems, use fertigation with soluble N and K sources or use controlled release fertilizers A portion of the N and K can be applied before planting Total rate applied is more important than timing Use the tables provided to estimate amounts of nutrient required on a linear foot basis 2009 Regents of the University of Minnesota