1. Phosphorus Nutrition of Wheat

2. Outline: P Nutrition of Wheat 1.What are the nutrient requirements of wheat throughout the season? 2.Why is P needed early in the season? 3.Why is placing P near the seed important? 4.How can I be sure there are adequate supplies of P? 5.What are some good strategies for managing P? Photo courtesy of the USDA-ARS

3. 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. How much N, P, and K does wheat take up? 0 20 40 60 80 100 120 140 emergence tillering flag leaf heading anthesis early milk soft dough harvest Nutrient uptake, lb/A N K2OK2O P2O5P2O5 38 bu/A spring wheat Growth stage Johnston et al., 1999

7. How are nutrients distributed in the plant? GrainStraw 0 20 40 60 80 100 120 NP2O5P2O5 K2OK2O Nutrient content, lb/A Crop Removal 0.5 – 0.6 lb P 2 O 5 /bu 38 bu/A spring wheat Johnston et al., 1999

8. How is P distributed in the plant? Miller et al., 1994 Percent at physiological maturity: 16.01.815.07.010.211.514.04.5 Haun** 80 9 8 3 0 10 20 30 40 50 60 13931949967985910391219139915791759 GDD* Leaves Stem Head Grain Cumulative P uptake, lb P 2 O 5 /A 90 bu/A irrigated spring wheat * Growing degree days** Haun growth stage

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

10. Why is P needed early in the season?

11. Early season P nutrition is critical Early season P deficiency limits yield potential –Critical period: first 5 to 6 weeks –P has major impacts on tillering and rooting Wheat absorbs only 15% of total P uptake in first two weeks of growth –Small amount but critical for optimum yield –Reserves can support later growth Later season P stress has much lower impact on crop production Photo courtesy of the USDA NRCS

12. Wheat tillers Wheat produces two kinds of stems (culms): –Main stem –Variable number of tillers Tillering is not a random event Follows a very strict pattern Tillers initiated vary greatly in vigor and potential for grain production Wheat Plant Nodal roots Seminal roots Seed Coleoptile tiller T0 Second tiller T2 Second leaf L2 Fourth leaf L4 Fifth leaf L5 Third leaf L3 First leaf L1 First tiller T1 Goos and Johnson, 1996; Klepper et al., 1982

13. Contribution of tillers to yield Goos and Johnson, 1996 0 10 20 30 40 50 60 Main stemT1 + T2Other Percent of final yield Second tiller T2 Main stem First tiller T1 Spring Wheat Embden, ND – 46 bu/A

14. Phosphorus increases tiller initiation Goos and Johnson, 1996 0 10 20 30 40 50 60 70 80 90 100 T0T1T2T3T4ST Percent initiation 0 30 lb P 2 O 5 /A placed with the seed Tillers Hettinger, ND Olsen P = 10 ppm

15. Why is placing P near the seed important?

16. 10 lb of starter P 2 O 5 with seed No starter P Impact of a Cool Spring on Spring Wheat ’ s Emergence Both sides received fall-banded 70-30-10-10

17. Root development: 1-2 leaf stage Winter wheat Veseth et al., 1986 0 2 4 6 8 0246246 Distance from the seed row, in. Depth, in. Primary root First seminal pair Crown Rooted soil volume

18. Root development: 4 leaf stage, 1 tiller 0 2 4 6 8 0246246 Distance from the seed row, in. Depth, in. Crown Second seminal pair First crown root First seminal pair Winter wheat Veseth et al., 1986

19. The primary cause of low, short term uptake of P fertilizer: The inability of P to move to absorbing roots Plant root Higher P concentration Lower P concentration Diffusion

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

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

22. Is P near the seed important at higher soil test P levels? Year – site: 95-195-296-196-296-395-396-495-4 T1 + T2 tiller initiation, number/plant 0.0 0.4 0.8 1.2 1.6 2.0 Control 20 lb P 2 O 5 /A applied with the seed as 10-34-0 Olsen P, ppm:691013 1687 Goos and Johnson, personal communication

23. Is P near the seed important at higher soil test P levels? Goos and Johnson, 2001 95-195-296-196-296-395-396-495-4 Spring wheat yield, bu/A 0 10 20 30 40 50 60 70 Control Olsen P, ppm: 691013 1687 Year – site: 20 lb P 2 O 5 /A applied with the seed as 10-34-0

24. How can I be sure there are adequate supplies of P? Photos courtesy of the USDA NRCS

25. What information does a P soil test provide? An index of the amount of plant-available P in the soil This index must be calibrated to yield response: –Examine responses to P additions at various soil test levels –Conduct studies across a wide range of soil test levels and environmental conditions

26. How is a soil test calibrated to yield response? Gelderman et al., 1995 % relative yield for this site-year: 39 bu/A 73 bu/A X 100 = 53.4% Watertown Site 1995 Olsen P = 5.0 ppm 0 10 20 30 40 50 60 70 80 020406080100 Fertilizer P, lb P 2 O 5 /A Winter wheat yield, bu/A

27. Crop responses at various soil test levels 020406080100 30 45 60 75 90 105 P 2 O 5 rate, lb/A Spring wheat yield, bu/A Soil test P (ppm) 4 Hauberg (Irr.) 19 Tullis (Irr.) 12 Riley (Irr.) 5 SIDC (Irr.) 6 Kent (Irr.) 3 Hauberg (dry-Fallow) 4 Hauberg (dry-Stub.) Henry and Gares, 1993

28. Average level of yield response is related to soil test P Soil typeSoil test P Yield Increase (ppm)(%) Hauberg (dry)393 Hauberg (Irr.)443 Hauberg (S)465 SIDC565 Kent617 Riley1227 Tullis195 Henry and Gares, 1993

29. Average level of yield response is related to soil test P As soil test levels increase, the magnitude of yield response to added P decreases Mitchell, 1932 90 Yield increase, % r = - 0.68 0102030405060 Soil test P, ppm 80 70 60 50 40 30 20 10 0 -10 -20

30. How is a soil test calibrated to yield response? 120 Gelderman et al., 1996

31. Accuracy in response predictions is limited Winter wheat study site PhosphorusIdealWatertown rate4.5 ppm5.0 ppm (lb P 2 O 5 /A)------------ (bu/A) ----------- 03339 253249 503445 753156 1003273 Responsive?NoYes Gelderman et al., 1996

32. Examples of P calibration 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. Examples of P calibration data PPI, PKMAN Ver. 1.0 30 40 50 60 70 80 90 100 051015202530 Olsen P soil test level, ppm Relative yield, % Winter wheat, Kansas Spring wheat, Northern Great Plains

34. 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 Good Fair Poor

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

36. Approaches to P fertilization Sufficiency approach: Apply P to maximize net returns to fertilization in the year of application –Strategy: fertilize only when there is a good chance that a profitable yield response will be realized –Soil test levels kept in lower, responsive ranges –Normally adopted on land leased for short periods of time or when cash flow is limited Relative yield, % Soil test P level

37. Approaches to P fertilization Build and maintenance approach: Remove P as a yield-limiting variable –Strategy: apply extra P (more than expected crop removal) to build soil tests to levels that are 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 Relative yield, % Soil test P level

38. Can annual fertilizer applications match higher fertility? Annual seed-placed P 2 O 5, lb/A 010203040 28 30 32 34 36 38 40 42 Wheat yield, bu/A 5 ppm 8 ppm 15 ppm Amount broadcast initially, lb P 2 O 5 /A 160 80 0 Olsen soil test at end of 5-yr: Wager et al., 1986

39. N rate, lb/A P 2 O 5 rate,lb/A Winter wheat yield, bu/A 110 55 0 0 20 40 0 10 20 30 40 50 60 70 How do N and P interact? Grant et al., 1985; Grant et al., 1986 64.8 54.8 47.9 46.7 42.3 41.7 20.4 17.0 14.6 6 bu: 40% increase 5 bu: 12% increase 17 bu: 35% increase

40. $0.22 $0.27 $0.32 $3.00 $4.00 $5.00 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 P 2 O 5 price, $/lb Winter wheat price, $/bu Net return to P fertilization, $/A How do crop and nutrient prices impact profit? $8.60 $6.82 $5.60 $6.68 $5.26 $4.28 $4.76 $3.69 $2.96 110 lb N/A 40 lb P 2 O 5 /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? If you cut the rate by: *Fertilizer cost savings: (lb P 2 O 5 /A)($/A) 51.25 102.50 205.00 4010.00 * $0.25/lb P 2 O 5

43. How much is saved the first year if P is applied below recommended rates? If you cut the rate by: *Fertilizer cost savings: **Interest on money saved: (lb P 2 O 5 /A)----------- ($/A) ------------- 51.250.13 102.500.25 205.000.50 4010.001.00 * $0.25/lb P 2 O 5 ** 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? If you cut the rate by: *Fertilizer cost savings: **Interest on money saved: Total savings (fertilizer cost + interest) (lb P 2 O 5 /A)-------------------- ($/A) ------------------------ 51.250.131.38 102.500.252.75 205.000.505.50 4010.001.0011.00 * $0.25/lb P 2 O 5 ** 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? If you cut the rate by: *Fertilizer cost savings: **Interest on money saved: Total savings (fertilizer cost + interest) ***Maximum allowable yield reduction (lb P 2 O 5 /A)-------------------- ($/A) ------------------------(bu/A) 51.250.131.38(0.3) 102.500.252.75(0.7) 205.000.505.50(1.4) 4010.001.0011.00(2.8) * $0.25/lb P 2 O 5 ** 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 year if P is applied above recommended rates? (one-year lease) If you over- apply by: *The lost principle is: **The lost interest is: Total cost (principle + interest) ***Yield equivalent of total cost (lb P 2 O 5 /A)-------------------- ($/A) ------------------------(bu/A) 5(1.25)(0.13)(1.38)(0.3) 10(2.50)(0.25)(2.75)(0.7) 20(5.00)(0.50)(5.50)(1.4) 40(10.00)(1.00)(11.00)(2.8) * $0.25/lb P 2 O 5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term *** $4.00/bu wheat

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

48. What does it cost the first year if P is applied above recommended rates? (five-year lease) If you over- apply by: *The lost interest is: (lb P 2 O 5 /A) ($/A) 5(0.13) 10(0.25) 20(0.50) 40(1.00) * 10% real interest rate (after inflation rate has been subtracted), compounded annually

49. What does it cost the first year if P is applied above recommended rates? (five-year lease) If you over- apply by: *The lost interest is: **The depreciation is: (lb P 2 O 5 /A)----------- ($/A) ----------- 5(0.13)(0.08) 10(0.25)(0.15) 20(0.50)(0.30) 40(1.00)(0.60) * 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 P 2 O 5 )

50. What does it cost the first year if P is applied above recommended rates? (five-year lease) If you over- apply by: *The lost interest is: **The depreciation is: Total cost: (interest plus depreciation) (lb P 2 O 5 /A)---------------------- ($/A) --------------------------- 5(0.13)(0.08)(0.21) 10(0.25)(0.15)(0.40) 20(0.50)(0.30)(0.80) 40(1.00)(0.60)(1.60) * 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 P 2 O 5 )

51. What does it cost the first year if P is applied above recommended rates? (five-year lease) If you over- apply by: *The lost interest is: **The depreciation is: Total cost: (interest plus depreciation) ***Yield equivalent of total loss (lb P 2 O 5 /A)---------------------- ($/A) ---------------------------(bu/A) 5(0.13)(0.08)(0.21)(0.05) 10(0.25)(0.15)(0.40)(0.1) 20(0.50)(0.30)(0.80)(0.2) 40(1.00)(0.60)(1.60)(0.4) * 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 P 2 O 5 ) *** $4.00/bu wheat

52. Over-applying vs. under- applying (five-year lease) If you over- apply by: Yield equivalent of total loss: If you under- apply by: Maximum allowable yield reduction (lb P 2 O 5 /A)(bu/A)(lb P 2 O 5 /A)(bu/A) 5(0.05)5(0.3) 10(0.1)10(0.7) 20(0.2)20(1.4) 40(0.4)40(2.8) * 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 P 2 O 5 ) *** $4.00/bu wheat

53. Summary P nutrition is critical to reaching the attainable yield potential of wheat Early in the season when the wheat plant is “deciding” to initiate tillers, P must be positionally available P deficiencies earlier in the season are more detrimental than those occurring later P nutrition must be part of a management strategy that considers the importance of other nutrients Land ownership/rental and cash flow have a large impact on the approaches taken to managing soil fertility

54. For more information, contact: International Plant Nutrition Institute (IPNI) 655 Engineering Drive, Suite 110 Norcross, GA 30092-2604 Phone: 770-447-0335; Fax: 770-448-0439 www.ipni.net Reference 06128