Phosphorus Nutrition of Wheat

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

What have the trends been in wheat yield? NASS; Statistics Canada

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

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

How much N, P, and K does wheat take up? 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

How are nutrients distributed in the plant? GrainStraw 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

How is P distributed in the plant? Miller et al., 1994 Percent at physiological maturity: Haun** 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

What percent of the P in the plant comes from fertilizer? Mitchell, weeksheadingsoft doughmature Total P uptake, mg Unfertilized Fertilized with MAP 46 % 43 % 36 % 39 % Stage of growth

Why is P needed early in the season?

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

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

Contribution of tillers to yield Goos and Johnson, Main stemT1 + T2Other Percent of final yield Second tiller T2 Main stem First tiller T1 Spring Wheat Embden, ND – 46 bu/A

Phosphorus increases tiller initiation Goos and Johnson, T0T1T2T3T4ST Percent initiation 0 30 lb P 2 O 5 /A placed with the seed Tillers Hettinger, ND Olsen P = 10 ppm

Why is placing P near the seed important?

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

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

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

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

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

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

Is P near the seed important at higher soil test P levels? Year – site: T1 + T2 tiller initiation, number/plant Control 20 lb P 2 O 5 /A applied with the seed as Olsen P, ppm: Goos and Johnson, personal communication

Is P near the seed important at higher soil test P levels? Goos and Johnson, Spring wheat yield, bu/A Control Olsen P, ppm: Year – site: 20 lb P 2 O 5 /A applied with the seed as

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

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

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 Fertilizer P, lb P 2 O 5 /A Winter wheat yield, bu/A

Crop responses at various soil test levels 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

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

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, Yield increase, % r = Soil test P, ppm

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

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

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

Examples of P calibration data PPI, PKMAN Ver Olsen P soil test level, ppm Relative yield, % Winter wheat, Kansas Spring wheat, Northern Great Plains

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

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

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

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

Can annual fertilizer applications match higher fertility? Annual seed-placed P 2 O 5, lb/A Wheat yield, bu/A 5 ppm 8 ppm 15 ppm Amount broadcast initially, lb P 2 O 5 /A Olsen soil test at end of 5-yr: Wager et al., 1986

N rate, lb/A P 2 O 5 rate,lb/A Winter wheat yield, bu/A How do N and P interact? Grant et al., 1985; Grant et al., bu: 40% increase 5 bu: 12% increase 17 bu: 35% increase

$0.22 $0.27 $0.32 $3.00 $4.00 $ 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 $ lb N/A 40 lb P 2 O 5 /A Grant et al., 1985; Grant et al., 1986

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

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) * $0.25/lb P 2 O 5

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) * $0.25/lb P 2 O 5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term

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) * $0.25/lb P 2 O 5 ** 10% real interest rate (after inflation rate has been subtracted), compounded annually, 12 month term

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) (0.3) (0.7) (1.4) (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

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

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

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

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) (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 )

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) (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 )

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

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

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

For more information, contact: International Plant Nutrition Institute (IPNI) 655 Engineering Drive, Suite 110 Norcross, GA Phone: ; Fax: Reference 06128