Advanced topics in soil fertility

1. 2014 Fresh Fruit and Vegetable Conference January 20th, 2014 Advanced topics in soil fertility Matt Ruark Dept. of Soil Science UW-Madison UW-Extension

2. outline • Irrigation • Delivery • Salt issues • Cover crops

3. Fertilizer guidelines • Nitrogen

4. Fertilizer guidelines • Phosphorus

5. Fertilizer guidelines • Potassium

6. Fertilizer guidelines Cucumber • Low: Boron, Molybdenum • Medium: Copper, Manganese, Zinc Tomato • Medium: Manganese, Molybdenum, Zinc • High: Boron, Cooper, Sulfur

7. Movement of ions from soil to roots • Root interception • Root comes in contact with nutrient • Mass flow • Nutrient moves with water • Diffusion • Nutrient moves via diffusion

8. root tip H2PO4- Mn2+ H2PO4- Zn2+ Zn2+ H2PO4- mycorrhizae Root interception– roots obtain nutrients by physically contacting nutrients in soil solution or on soil surfaces; - roots contact ~1% of soil volume; - mycorrhizal infection of root increase root-soil contact

9. root tip Ca2+ NO3- NO3- Ca2+ Mass flow– dissolved nutrients move to the root in soil water that is flowing towards the roots

10. Diffusion– nutrients move from higher concentration • in the bulk soil solution to lower concentration at the root; • In the time it takes NO3- to diffuse 1 cm, K+ diffuses 0.2 cm, • and H2PO4- diffuses 0.02 cm root tip NO3- NO3- NO3- NO3- NO3- NO3-

11. Principal ways in which ions move from soil to the roots of corn

12. Fertigation calculations

13. Where to start • Deciding on when to apply N fertilizer: • Evenly throughout year, or staggered to adjust to plant uptake • Perfect timing relative to uptake is difficult, need to predict ahead. • From Rosen et al. (2004): “In general, the frequency of application is not as important as the total rate applied.” • Monthly, weekly, every time you irrigate • You do the math. • If multiple crops in high-tunnel: • Fertigate each crop separately – if able. • Apply fertigation based on lowest N demand crop and adjust by crop with preplant N.

14. Adjusting to multiple crops under irrigation line Crop need = 100 lb/ac N Crop need = 150 lb/ac N Fertigation = 70 lb/ac N Fertigation = 70 lb/ac N Preplant N = 30 lb/ac N Preplant N= 80 lb/ac N Crop need = 200 lb/ac N Fertigation = 70 lb/ac N Preplant N = 130 lb/ac N

15. What to put through irrigation line? • Water soluble N (e.g. UAN) and K (e.g. KCl) • Calcium nitrate can precipitate if water is high in bicarbonates – form calcium carbonate and clog • If water is high in Ca concentration, do not recommend use of ammonium sulfate or potassium sulfate. • P and micros? • Only if compatible with irrigation water; irrigation water needs to be below pH of 6.5 • P can precipitate with Al or Ca • Apply calcium nitrate separately than P

16. Fertilizer calculations • Area fertigated • Nitrogen rate in volume units • Area: width × length • Linear feet × (row spacing × # of rows) = ft2 • 12 in = 1 ft; 1 acre = 43,560 ft2

17. Fertilizer calculations Convert N need (lb) to product volume (gal) • Need to know concentration of fertilizer in liquid (e.g. UAN = 3 lb of N per gallon) • Or know density • UAN = 28% N = 0.28 N per lb of UAN • 1 gallon of UAN = 10.6 lb of UAN • (0.28 lb-N/lb-UAN) × (10.6 lb-UAN/1 gal-UAN) • 3 lb-N / gal-UAN

18. Fertilizer calculations • Fertilize 400 linear feet of row, with 4 foot spacing • Calculation = 1600 ft2 = 0.037 acre • Need to apply 10 lb/ac of N using 28% UAN • Calculation = 10 lb-N/ac × (1 gallon-UAN / 3 lb-N) = 3.3 gallons per acre of UAN 3.3 gal-UAN/ac × 0.037 ac = 0.12 gal-UAN (15 fl. oz) 1 gallon = 4 quarts = 128 fl. oz = 3.8 liters

19. Avoiding salt buildup in high tunnels:the maine approach

20. Univ. Maine recommendations • Year 1: Routine Soil sampling (pH, OM, P, K) • Year 2&3: Basic high tunnel test • Nitrogen carry over • Fine tune soil fertility • Monitor salt buildup • If EC>4 (slurry method) • Uncover to natural rainfall • Flush by flooding or heavy irrigation • Rules of thumb: 6” of water cuts salt concentration by 50%, 12” of water cuts salt by 80% • Move hoop house http://anlab.umesci.maine.edu/soillab_files/under/hoop-soil-mgt.pdf

21. Univ. Maine recommendations • Year 3 and beyond • Monitor water-soluble nutrient levels (Saturated media extract, SME) • Measure of nutrients in soil solution, but not reserve • If EC>4 • Uncover or flood irrigate • Add peat moss (dilutes salt concentration, adds organic matter to increase water retention) • http://www.soiltest.uconn.edu/factsheets/InterpSMEGreenMedia.pdf http://anlab.umesci.maine.edu/soillab_files/under/hoop-soil-mgt.pdf

22. Soluble salts testing - Wisconsin • Measure the electrical conductivity (EC) in a 1:2 soil-to-water slurry (10 g soil: 20 mL water) • Measured with a conductivity meter • Sandy soils • Low = 0-0.25 dS/m; Medium = 0.26-0.75 • High >0.75 dS/m • Siltysoils • Low = 0-0.40 dS/m; Medium = 0.41-1.05 • High >1.05 dS/m

23. Cover crops

25. Corn response to nitrogen, Janesville 2010 Stute and Shelley, unpublished

26. Pictures taken October 1, 2013

27. October 29, 2013 October 1, 2013

31. 2013 Radish - Sheboygan

32. Radish N uptake – Sheboygan Co. Total N uptake = 121 lb/ac

33. 2012 soil nitrate (PPNT & PSNT)

34. 2013 Soil Nitrate (PPNT & PSNT)

35. 2013 Radish - Sheboygan

36. Cover crops • For erosion control • Rye – survives winter • Oats or spring barley – winter kill • For N additions • Red clover – survives winter • Berseem or crimson clover – winter kill • For N uptake • Grasses • Radish – but no N credit yet confirmed

37. Thank youQuestions?Comments?Concerns?