Fertilizer Sources: Proper Selection and Management

1. Fertilizer Sources: Proper Selection and Management T. Scott MurrellNorthcentral DirectorPotash & Phosphate Institute2006 Dale F. LeikamAssociate ProfessorKansas State University

2. Questions to be addressed: N sources for corn • How does corn take up and use nitrate? • How does corn take up and use ammonium? • Is there an optimum NH4+:NO3- ratio? • How do N forms react prior to plant uptake? • How do these reactions impact phosphorus management?

3. Corn root: horizontal cross section Casparian strip Stele Endodermis Root hair Xylem Phloem Pericycle Cortex Epidermis Russell, 1977 Zea mays root cross-section, mature root

4. Cell wall Plasmodesmata Corn root cross section Cytoplasm Vacuole Russell, 1977 Zea mays root cross-section, mature root

5. Symplasmic pathway: transport of nutrients through the cytoplasm From rootepidermisand cortex To xylem Marschner, 2002 Zea mays root cross-section, mature root

6. Getting nutrients into the symplasmic pathway Proton-ATPase pump(requires energy - ATP)Moves H+ “uphill” againstthe electrical potential gradient andthe chemical potential gradient (pH) Nitrate, phosphate, chloride:co-transport via aproton pump Vacuole Cytoplasm ATP H+ H+ Anion pH 7.3-7.6 pH 5.5 -120 to -180 mV Cell wall Tonoplast Plasmamembrane Marschner, 2002

7. Getting nutrients into the symplasmic pathway Cations (except K)Uniport Uniport:“downhill” of electrical potential gradient,but energy is still neededto maintain the gradients Vacuole Cytoplasm Cation -120 to -180 mV Cell wall Tonoplast Plasmamembrane Marschner, 2002

8. A comparison of ammonium and nitrate assimilation Marschner, 2002

9. Early corn growth and ammonium/nitrate ratios Totalconcentration(mM) 5 5.0 4 1.0 3 Dry weight (g plant-1) 2 0.2 1 0 NH4+ 100 75 50 25 0 0 25 50 75 100 NO3- Proportion of N form Marschner, 2002

10. Ammonium and nitrate: rhizosphere pH differences pH Acid NH4+ NO3- H+ OH- or HCO3- Basic Marschner, 2002

11. Wheat – 2wks Corn – 8 wks old Scale NO3-N NH4-N NO3-N NH4-N 200 kg N per ha Rōmheld

12. Effect of Nitrogen form on Rhizosphere pH 1:1 8.0 NO3- Soy NO3- Corn 7.5 7.0 6.5 Rhizosphere pH 6.0 5.5 5.0 NH4+ Soy NH4+ Corn 4.5 4.0 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 Bulk soil pH Riley and Barber, 1971; Soon and Miller, 1977

13. Why is there a need for both ammonium and nitrate? • Rhizosphere pH control • If rhizosphere pH drops too much, ammonium uptake becomes restricted, favoring nitrate uptake • Reverse occurs if pH increases too much from nitrate uptake • Carbon allocation and energy regulation • Less photosynthate is needed for nitrate assimilation • Nitrate has lower energy storage costs since it can be stored “as is” • So the presence of both ions helps the plant regulate rhizosphere pH, energy expenditures, and carbon allocation

14. Rhizosphere pH affects P uptake by corn • 11 day old corn • Ammonium source reduced rhizosphere pH and increased P uptake Oneida L Buford SiL 6 5 4 Wendigo SL Total P uptake, mg P (g DM)-1 3 MCP + CaCl2 2 MCP + Ca(NO3)2 1 MCP + (NH4)2SO4 0 3 4 5 6 7 8 9 Rhizosphere pH Soon and Miller, 1977

15. Starter fertilizer: NH4+ and P should be placed together 60 20-40 lb P/acre 20-40 lb P/acre + 10 lb N, mixed 20-40 lb P/acre + 10 lb N, separate 40 Percent of the plant Pcoming from the band Occurs regardlessof P soil test level 20 0 0 400 800 1200 1600 2000 Phosphate added to bulk soil, lb P2O5/acre Miller and Ohlrogge, 1958

16. Common phosphate fertilizers with ammonium • Monoammonium phosphate (MAP) • NH4H2PO4 • pH of 0.1M solution is 4.0 • H2PO4-↔ HPO42- + H+ • Diammonium phosphate (DAP) • (NH4)2HPO4 • pH of 0.1M solution is 7.8 • HPO42-↔ H2PO4- + OH- • Ammonium polyphosphate (APP) • pH 6.0 – 6.5 • Hydrolysis reaction Photos courtesy of Agrium Sauchelli, 1965

17. Nitrification: Converts ammonium to nitrate Important components of the reaction: • Requires oxygen • Reaction is acid-forming Step 1: conversion to nitrite by the Nitrosomonas bacteria 2NH4+ + 3O2→ 2NO2- + 4H+ Step 2: conversion to nitrate by the Nitrobacter bacteria 2NO2- + O2→ 2NO3- Havlin et al., 2005 Nitrosomonas (Natl. Inst. Res. Environ.)

18. Reaction of anhydrous ammonia • Reaction of ammonia with water is base-forming • Reaction is reversible at a higher pH • Nitrification can acidify the band that was initially higher in pH Ammonia hydrolysis (splits water): NH3 + H2O NH4+ + OH- Nitrification Sauchelli, 1964

19. Measured pH changes after ammonia injection 1 day 3 weeks 10 weeks 3.5 in. < 5.1 Laboratory experiment:Walla Walla SiL Initial pH = 5.5 CEC = 17 meq/100gN rate was equivalent to 107 lb N/acre at 20 in. spacing 5.1 – 6.0 pHscale 6.1 – 7.0 7.1 – 8.0 > 8.0 Cochran, 1975

20. 0 6.1 6.7 6.7 6.4 6.7 5.8 6.7 5.5 10 0 6.2 6.8 6.8 5.6 5.9 6.8 6.5 10 Acidification patterns in soil after knifed ammonia(ridge-slot plant system) 30 in. 30 in. 2 months after an early May application 14 months after an early May application Webster clay loam Robbins and Voss, 1989

21. Implications of soil acidification after ammonia applications In reduced tillage systems with knifed ammonia applications, apply in the same zones each time • The pH increases help reverse acidity resulting from nitrification from the previous applications • Keeps subsurface acidity from spreading to other areas Robbins and Voss, 1989

22. Effects of ammonia concentration on nitrification pH right after application 300 9 8 250 7 pH after 14 days 200 6 5 Nitrate N (ppm) pH 150 4 100 3 [NO3-] after 14 days 2 50 1 0 0 0 200 400 600 800 Ammonia (NH3-N ppm) Eno et al., 1955

23. Recommendations based on ammonia reactions • Ammonia is the preferred source for: • Fall applications (sustained soil temp. below 50oF) • Spring pre-plant applications on sandy soils • Ammonia should be injected 6-10 in. deep on friable, moist soil to avoid: • Volatilization losses • Injury to seedlings

24. Reaction of urea Urea hydrolysis at pH 6.5 – 8.0 • Acid-consuming • pH will not increase above 9.3 urease CO(NH2)2 + H+ + 2H2O → 2NH4+ + HCO3- Urea hydrolysis at pH < 6.5 urease CO(NH2)2 + 2H+ + 2H2O → 2NH4+ + H2CO3 Koelliker and Kissel, 1988

25. Volatilization of ammonia The reaction NH4↔ NH3 + H+ is driven by: • Difference in NH3 activity between where the fertilizer was applied and the surrounding air (windy conditions) • Higher pH • Higher temperature • Lower CEC (maintains a higher solution NH4 concentration) • Loss of CO2, which causes the pH to increase • Contact with crop residues, which contain urease Koelliker and Kissel, 1988

26. Phosphorus form affects urea volatilization Total N was kept constant at 117 lb N/acreP rate was kept constant at 132 lb P2O5/acre Fan and Mackenzie, 1993

27. Practical suggestions for urea use • Avoid using as a preplant application on sandy soils • Avoid contact with the seed • Within 2 days: • Incorporate to a depth of 2 to 4 inches or • Receive or apply 0.25 to 0.5 in. of precipitation • Other considerations for no-till • Consider surface bands to reduce contact with urease • If also applying P, band MAP or TSP with the urea at the surface

28. Summary • N nutrition affects the pH of the soil surrounding the root and P uptake. Ammonium forms should be placed with P. • When ammonia is formed, nitrification can be delayed • In reduced tillage systems, acidification from nitrification needs to be controlled, possibly through the use of N fertilizers that are initially base-forming, repetitively banded in the same location • Phosphorus can be a good product to co-apply with ammonium banded near the seed • Phosphorus can be a good product to co-apply with urea banded at the surface

29. References Anghinoni, I. and S.A. Barber. 1980b. Predicting the most efficient phosphorus placement for corn. Soil Sci. Soc. Am. J. 44:1016-1020. Barber, S.A. 1984. Soil nutrient bioavailability: A mechanistic approach. Wiley Interscience, New York, NY. Barber, S.A. 1978. Growth and nutrient uptake of soybean roots under field conditions. Agron. J. 70:457-461. Cochran, V.L., F.E. Koehler, and R.I. Papendick. 1975. Straw placement: Its effect on nitrification of anhydrous ammonia. Agron. J. 67:537-540. Edwards, J.H. and S.A. Barber. 1976. Phosphorus uptake rate of soybean roots as influenced by plant age, root trimming, and solution P concentration. Agron. J. 68:973-975. Eno, C.F., W.G. Blue, and J.M. Good, Jr. 1955. The effect of anhydrous ammonia on nematodes, fungi, bacteria, and nitrification in some Florida soils. Agron. J. 19:55-58. Fan, M.X. and A.F. Mackenzie. 1993. Urea and phosphate interactions in fertilizer microsites: Ammonia volatilization and pH changes. Soil Sci. Soc. Am. J. 57:839-845. Havlin, J.L., J.D. Beaton, S.L. Tisdale, and W.L. Nelson. 2005. Soil fertility and fertilizers: An introduction to nutrient management. 7th ed. Pearson Prentice Hall, Upper Saddle River, NJ. Koelliker, J.K. and D.E. Kissel. 1988. Chemical equilibria affecting ammonia volatilization. p.37-52. In B.R. Bock and D.E. Kissel (ed.) Ammonia volatilization from urea fertilizers. Bull. Y-206. Natl. Fert. Development Center, TVA, Muscle Shoals, AL. Marschner, H.M. 2002. Mineral nutrition of higher plants. 2nd ed. Academic Press, New York, NY. Mengel, D.B. and S.A. Barber. 1974. Rate of nutrient uptake per unit of corn root under field conditions. Agron. J. 66:399-402. Borkert, C.M. and S.A. Barber. 1985b. Predicting the most efficient phosphorus placement for soybeans. Soil Sci. Soc. Am. J. 49:901-904. Miller, H.H. and A.J. Ohlrogge. 1958. Principles of nutrient uptake from fertilizer bands. I. Effect of placement of nitrogen fertilizer on the uptake of band-placed phosphorus at different soil phosphorus levels. Agron. J. 50:95-97. Riley, D. and S.A. Barber. 1971. Effect of ammonium and nitrate fertilization on phosphorus uptake as related to root-induced pH changes at the root-soil interface. Soil Sci. Soc. Am. Proc. 35:301-306. Robbins, S.G. and R.D. Voss. 1989. Acidic zones from ammonia application in conservation tillage systems. Soil Sci. Soc. Am. J. 53:1256-1263. Russell, R.S. 1977. Plant root systems: Their function and interaction with the soil. McGraw-Hill, New York, NY. Sauchelli, V. 1965. Phosphates in agriculture. Reinhold Publishing Co., New York, NY. Sauchelli, V. 1964. Nitrogen: Chemical and physical properties. p.10-17. In V. Sauchelli (ed.) Fertilizer nitrogen: It’s chemistry and technology. ACS Monograph Ser. 161. Reinhold Publishing Co., New York, NY. Soon, Y.K. and M.H. Miller. 1977. Changes in the rhizosphere due to NH4+ and NO3- fertilization and phosphorus uptake by corn seedlings (Zea mays L.). Soil Sci. Soc. Am. J. 41:77-80.

30. Corn root: longitudinal cross section Xylemtransports ions andwater to otherareas in the plant Maturationzone Phloemtransports products ofphotosynthesis to the roots Elongationzone EndodermisEncases the steleand acts as a barrier Meristematiczone Root capcells ahead of theapical meristem Mucigel

31. Nutrient influx by roots • Ions are not simply absorbed according to their ratios in solution • Ions with this characteristic influx pattern require energy to be absorbed • H2PO4-, HPO42-, NO3- • K+, NH4+ • Maximum influx is reached at higher solution concentrations (Imax) 22-23 day old soybean roots 3.0 Imax 2.5 2.0 1.5 Influx, 10-14 lb P2O5 / (in s) 1.0 0.5 0.0 0 1 2 3 4 5 -0.5 Solution P, 10-6 lb P2O5/gal Barber, 1984; Edwards and Barber, 1976

32. 10-3 lb P2O5 per pot 100 3.6 75 0.9 Relative dry matter yield (%) 50 Corn 25 Soybean 0 0 20 40 60 80 100 Fertilized soil fraction (%) Anghinoni and Barber, 1980; Borkert and Barber, 1985b

33. P influx varies with plant age: The case for starter 5 Corn Corn can take in Pat a high rate early(per unit of root)but not later 4 3 Influx, 10-5 lb P2O5 / (in. day) 2 1 Soybean 0 0 20 40 60 80 100 120 -1 Plant age, days Barber, 1978; Mengel and Barber, 1974