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Phosphorus Nutrition of Wheat. Photo courtesy of the USDA-ARS. Outline: P Nutrition of Wheat. What are the nutrient requirements of wheat throughout the season? Why is P needed early in the season? Why is placing P near the seed important? How can I be sure there are adequate supplies of P?

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Phosphorus Nutrition of Wheat


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    1. Phosphorus Nutritionof Wheat

    2. Photo courtesy of the USDA-ARS Outline:P Nutrition of Wheat • What are the nutrient requirements of wheat throughout the season? • Why is P needed early in the season? • Why is placing P near the seed important? • How can I be sure there are adequate supplies of P? • What are some good strategies for managing P?

    3. 0.38 bu/A/yr 45 U.S. 40 35 Canada 30 Wheat yield, bu/A 0.31 bu/A/yr 25 20 15 10 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year What have the trends been in wheat yield? NASS; Statistics Canada

    4. What are the nutrient requirements of wheat throughout the season? Photo courtesy of the USDA-ARS

    5. Plants take up P as: • Primary orthophosphate ion: H2PO4- (pH < 7.0) • Secondary orthophosphate ion: HPO4= (pH > 8.0) • The form most common is a function of soil pH – both equally present at neutral Solution P

    6. 38 bu/A spring wheat 140 120 K2O 100 N 80 Nutrient uptake, lb/A 60 40 P2O5 20 0 tillering flag leaf harvest heading anthesis early milk soft dough emergence Growth stage How much N, P, and K does wheat take up? Johnston et al., 1999

    7. 38 bu/A spring wheat 120 Grain Straw 100 80 Nutrient content, lb/A Crop Removal 0.5 – 0.6lb P2O5/bu 60 40 20 0 N P2O5 K2O How are nutrients distributed in the plant? Johnston et al., 1999

    8. 90 bu/A irrigated spring wheat 60 50 Grain 40 80 Cumulative P uptake,lb P2O5/A Head 30 20 Stem 9 10 8 Leaves 0 3 139 319 499 679 859 1039 1219 1399 1579 1759 GDD* Haun** 1.8 4.5 7.0 10.2 11.5 14.0 15.0 16.0 * Growing degree days ** Haun growth stage How is P distributedin the plant? Percent at physiological maturity: Miller et al., 1994

    9. 300 36 % Unfertilized Fertilized with MAP 250 39 % 200 43 % Total P uptake, mg 150 100 50 46 % 0 4 weeks heading soft dough mature Stage of growth What percent of the Pin the plant comes from fertilizer? Mitchell, 1957

    10. Why is P neededearly in theseason?

    11. Photo courtesy of the USDA NRCS Early season P nutritionis critical • Early season P deficiencylimits yield potential • Critical period:first 5 to 6 weeks • P has major impacts ontillering and rooting • Wheat absorbs only 15%of total P uptake in firsttwo weeks of growth • Small amount but critical for optimum yield • Reserves can support later growth • Later season P stress has much lower impact oncrop production

    12. FourthleafL4 FifthleafL5 ThirdleafL3 SecondtillerT2 FirsttillerT1 SecondleafL2 FirstleafL1 ColeoptiletillerT0 Nodal roots Seed Seminal roots Wheat Plant Wheat tillers • Wheat producestwo kinds of stems (culms): • Main stem • Variable number of tillers • Tillering is not a random event • Follows a very strict pattern • Tillers initiated vary greatlyin vigor and potentialfor grain production Goos and Johnson, 1996; Klepper et al., 1982

    13. Mainstem SecondtillerT2 60 FirsttillerT1 50 40 Percent of final yield 30 20 10 0 Main stem T1 + T2 Other Contribution of tillersto yield Spring WheatEmbden, ND – 46 bu/A Goos and Johnson, 1996

    14. 100 90 80 lb P2O5 /A placed with the seed 70 60 0 Percent initiation 50 30 40 30 20 10 0 T0 T1 T2 T3 T4 ST Tillers Phosphorus increases tiller initiation Hettinger, NDOlsen P = 10 ppm Goos and Johnson, 1996

    15. Why is placing Pnear the seedimportant?

    16. Impact of a Cool Spring on Spring Wheat’s Emergence Both sides received fall-banded 70-30-10-10 10 lb of starterP2O5 with seed No starter P

    17. Crown 0 Rooted soil volume 2 First seminal pair Depth, in. 4 6 Primary root 8 6 4 2 0 2 4 6 Distance from the seed row, in. Root development:1-2 leaf stage Winter wheat Veseth et al., 1986

    18. Crown 0 Second seminal pair First crown root 2 First seminal pair Depth, in. 4 6 8 6 4 2 0 2 4 6 Distance from the seed row, in. Root development:4 leaf stage, 1 tiller Winter wheat Veseth et al., 1986

    19. The inability of P to moveto absorbing roots Lower Pconcentration Diffusion Plant root Higher Pconcentration The primarycause oflow, shortterm uptakeof Pfertilizer:

    20. Root 0.12” 0.5” P diffusion zone Distance between roots Spring wheat rootsat 38 days • Based on average root density in surface 6” 5% of soil volume can contribute P to the plant

    21. Root Spring wheat rootsat 94 days • Based on average root density in surface 6” 0.13” 0.24” Distance between roots P diffusion zone 26% of soil volume can contribute P to the plant

    22. Control 20 lb P2O5/A applied with the seed as 10-34-0 2.0 1.6 T1 + T2 tiller initiation,number/plant 1.2 0.8 0.4 0.0 95-1 95-2 96-1 96-2 96-3 95-3 96-4 95-4 Year – site: Olsen P, ppm: 6 7 8 9 10 13 13 16 Is P near the seed important at higher soil test P levels? Goos and Johnson, personal communication

    23. Control 70 20 lb P2O5/A applied with the seed as 10-34-0 60 50 40 Spring wheat yield, bu/A 30 20 10 0 Year – site: 95-1 95-2 96-1 96-2 96-3 95-3 96-4 95-4 Olsen P, ppm: 6 7 8 9 10 13 13 16 Is P near the seed important at higher soil test P levels? Goos and Johnson, 2001

    24. Photos courtesy of the USDA NRCS How can Ibe surethere areadequatesuppliesof P?

    25. What information does a P soil test provide? • An index of the amountof plant-available P inthe soil • This index must becalibrated to yieldresponse: • Examine responses to Padditions at various soil test levels • Conduct studies across a wide rangeof soil test levels and environmental conditions

    26. 80 Watertown Site 1995Olsen P = 5.0 ppm 70 60 50 Winter wheat yield, bu/A 40 30 39 bu/A 20 X 100 = 53.4% % relative yield for this site-year: 10 73 bu/A 0 0 20 40 60 80 100 Fertilizer P, lb P2O5/A How is a soil test calibrated to yield response? Gelderman et al., 1995

    27. 4 Hauberg (Irr.) 19 Tullis (Irr.) 12 Riley (Irr.) 5 SIDC (Irr.) 6 Kent (Irr.) 3 Hauberg (dry-Fallow) 4 Hauberg (dry-Stub.) Crop responses at various soil test levels Soil test P(ppm) 105 90 75 Spring wheat yield, bu/A 60 45 30 0 20 40 60 80 100 P2O5 rate, lb/A Henry and Gares, 1993

    28. Average level of yield response is related to soil test P Henry and Gares, 1993

    29. 90 80 70 60 50 Yield increase, % 40 r = - 0.68 30 20 10 0 -10 -20 0 10 20 30 40 50 60 Soil test P, ppm Average level of yield response is related tosoil test P • As soil test levels increase, the magnitude of yield response to added P decreases Mitchell, 1932

    30. 100 80 Several sitesand years 60 Winter wheat relative yield, % 40 Watertown 1995 20 Critical level = 16 ppm 0 0 5 10 15 20 25 30 35 Olsen P, ppm How is a soil test calibrated to yield response? 120 Gelderman et al., 1996

    31. Accuracy in response predictions is limited Gelderman et al., 1996

    32. 100 90 one site-year 80 Relative yield, % 70 60 50 Prairie soils 40 10 30 40 50 60 70 0 20 Norwest P, ppm Examples of Pcalibration data • Calibration curve indicates which soil test levels tend to limit yields • Data based on P responses observed across several sites and years McKenzie et al., 1995

    33. Spring wheat, Northern Great Plains 100 90 80 70 Relative yield, % 60 Winter wheat, Kansas 50 40 30 0 5 10 15 20 25 30 Olsen P soil test level, ppm Examples of Pcalibration data PPI, PKMAN Ver. 1.0

    34. Good Fair Poor What are the best uses for soil test P information? • Estimating average probabilities of crop response • Examining changes in levels over time • Estimating average relative yield response • Estimating a specific probability of response for a given site and year • Estimating a specific relative yield response at a given site and year

    35. Photos courtesy of the USDA NRCS What are somegood strategies for managing P?

    36. Relative yield, % Soil test P level Approaches to P fertilization • Sufficiency approach:Apply P to maximizenet returns to fertilizationin the year of application • Strategy: fertilize onlywhen there is a goodchance that a profitableyield response will be realized • Soil test levels kept in lower,responsive ranges • Normally adopted on land leasedfor short periods of time or when cash flow is limited

    37. Relative yield, % Soil test P level Approaches to P fertilization • Build and maintenanceapproach:Remove P as ayield-limiting variable • Strategy: apply extra P(more than expectedcrop removal) to buildsoil tests to levels thatare not yield-limiting • Soil test levels kept in higher,non-responsive ranges • Normally adopted on owned land or land leased for longer periods of time

    38. Can annual fertilizer applications match higher fertility? Amount broadcastinitially, lb P2O5/A Olsen soil testat end of 5-yr: 42 15 ppm 160 40 80 8 ppm 38 0 36 5 ppm Wheat yield, bu/A 34 32 30 28 0 10 20 30 40 Annual seed-placed P2O5, lb/A Wager et al., 1986

    39. 17 bu:35% increase 64.8 70 60 54.8 5 bu:12% increase Winter wheatyield, bu/A 46.7 50 47.9 42.3 40 41.7 30 6 bu:40% increase 20.4 20 17.0 10 14.6 40 0 20 110 P2O5 rate,lb/A 0 55 N rate, lb/A 0 How do N and P interact? Grant et al., 1985; Grant et al., 1986

    40. 9.00 $8.60 8.00 7.00 $6.82 Net returnto Pfertilization,$/A $6.68 6.00 $5.60 5.00 $5.26 4.00 $4.76 $4.28 3.00 $3.69 2.00 $2.96 1.00 $5.00 0.00 $4.00 Winter wheatprice, $/bu $0.22 $0.27 $3.00 P2O5 price, $/lb $0.32 How do crop and nutrient prices impact profit? 110 lb N/A40 lb P2O5/A Grant et al., 1985; Grant et al., 1986

    41. Does P fertilizer form influence crop response? • Research evaluating crop response to MAP, DAP and APP have found all sources give equal crop response • In addition, no agronomic differences have been found between dry and liquid sources • The only exception is rock phosphate which provides limited crop response due to low P solubility Fixen, 1989; Leikam, 1990

    42. How much is saved the first year if P is applied below recommended rates? * $0.25/lb P2O5

    43. How much is saved the first year if P is applied below recommended rates? * $0.25/lb P2O5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term

    44. How much is saved the first year if P is applied below recommended rates? * $0.25/lb P2O5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term

    45. How much is saved the first year if P is applied below recommended rates? * $0.25/lb P2O5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term *** $4.00/bu wheat

    46. What does it cost the first yearif P is applied aboverecommended rates? (one-year lease) * $0.25/lb P2O5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term *** $4.00/bu wheat

    47. Solution P Labile P Non-labile P What happens to fertilizer P after I apply it? • Solution P: • 10 to 30 % of applied P • Immediately available • Labile P: • 70 to 90% of applied P • Future supply • Metastable Ca-phosphates

    48. What does it cost the first yearif P is applied aboverecommended rates? (five-year lease) * 10% real interest rate (after inflation rate has been subtracted), compounded annually

    49. What does it cost the first yearif P is applied aboverecommended rates? (five-year lease) * 10% real interest rate (after inflation rate has been subtracted), compounded annually ** 30% of applied P not recovered after five years (30% depreciable base with five-year economic life, straight line depreciation, $0.25/lb P2O5)

    50. What does it cost the first yearif P is applied aboverecommended rates? (five-year lease) * 10% real interest rate (after inflation rate has been subtracted), compounded annually ** 30% of applied P not recovered after five years (30% depreciable base with five-year economic life, straight line depreciation, $0.25/lb P2O5)