Phosphorus Nutrition of Soybean Outline P Nutrition of

Phosphorus Nutrition of Soybean

Outline – P Nutrition of Soybean • • P uptake by above-ground plant tissue Soybean root morphology P influx by roots Yields and soil test P levels P placement P timing P and soybean pests/diseases

P Uptake by Above. Ground Plant Tissue • Examining uptake throughout the season

Aerial accumulation (lb/acre) Nutrient Uptake by 80 bu/A Soybeans 450 400 N 350 P 2 O 5 K 2 O 300 250 200 150 100 50 0 0 20 40 60 80 100 Days after planting Source: Henderson and Kamprath, 1970 120 140 160

Soybean P Uptake 100 90 % of total uptake 80 Total P uptake: 12 – 24 lb P 2 O 5/A 70 Beans 60 50 Pods 40 Stems Petioles 30 20 Leaves 10 0 0 28 V 1 Source: Hanway and Weber, 1971 56 V 10 84 R 4 Petioles (fallen) Leaves (fallen) 112 R 6 R 7 Days after emergence Growth stage (inferred)

Soybean Phosphorus Derived from Fertilizer Soybean plant fraction P derived from fertilizer (%) Leaves (and petioles? ) 36 Stems 20 Pods 25 Beans 16 Source: Ham and Caldwell, 1978

% of P derived from fertilizer Soybean Phosphorus Content Derived from Fertilizer Soil P level 60 Low 50 40 Medium 30 High 20 10 0 20 40 60 80 Days after planting Source: Bureau et al. , 1953 100 120

Soybean Root Morphology • Establishing a background for discussions of P placement

Soybean Root Growth 6 in. • Phase 1 (1 st month after planting) – Rapid vegetative top growth – Downward taproot growth – Development of horizontal laterals in upper soil profile Source: Mitchell and Russell, 1971

Soybean Root Growth • Phase 2 (2 – 2. 5 months after planting) – High rates of top growth (from flowering through pod formation) – More laterals develop in upper soil profile – Some laterals begin to turn downward 6 in. Source: Mitchell and Russell, 1971; Raper and Barber, 1970

Soybean Root Morphology • Left side: single soybean plant grown in isolated plot – Primary lateral roots branch from taproot within upper 15 cm (6 in. ) – Below 15 cm (depth of cultivation), taproot degenerated to a root with a diameter similar to primary laterals but with less branching Source: Raper and Barber, 1970 (approx. 10 wk. after planting)

Soybean Root Morphology • Right side: soybean grown in 30 in. rows – Primary lateral roots branch from taproot within upper 15 cm (6 in. ) – Near center of rows (45 cm or 18 in. ), laterals angle down sharply as they encounter root zone of neighboring plant (approx. 10 wk. after planting) Source: Raper and Barber, 1970

Soybean Root Growth • Phase 3 (Seed set to maturity) – Continued rapid rates of downward extension of laterals – Laterals penetrated deeper than the tap root Source: Mitchell and Russell, 1971 Depth of sample (in. ) Root dry weight at the following days after planting: 31 67 80 102 ------- (grams) ------- 0 - 3 0. 24 2. 60 3. 10 4. 23 3 - 6 0. 04 0. 26 0. 73 0. 52 6 - 9 0. 01 0. 07 0. 12 0. 08 9 - 12 0. 01 0. 04 0. 07 0. 04 12 - 18 -- 0. 05 0. 10 0. 04 18 - 24 -- 0. 03 0. 10 0. 08 24 - 36 -- 0. 07 0. 08 0. 07 36 - 48 -- -- 0. 06 48 - 72 -- -- -- 0. 03

Portion of total root length in P-treated volume Roots Proliferate in Zones of Higher P Concentration 0. 8 Soybean 0. 7 Corn 0. 6 0. 5 0. 4 0. 3 0. 2 0. 1 0 Source: Borkert and Barber, 1985 1: 1 0 0. 1 0. 2 0. 3 0. 4 0. 5 P treated soil portion, % 0. 6

Effects of P or Mycorrhizae on Soybean Shoot Dry Weight 3. 0 Non- mycorrhizal DM Non-mycorrhizal infection Mycorrhizal DM Mycorrhizal infection 2. 5 100 80 2. 0 60 1. 5 40 1. 0 20 0. 5 0 Source: Lambert et al. 1979 Initial Bray 1 soil test P = 8 ppm 0 115 345 Applied P rate, lb P 2 O 5/A 920 0 % of root colonized Shoot dry weight, grams Greenhouse study

Management Factors Affecting Soybean Root Morphology • Cultivar choice – Root angle – Root elongation rate • Planting date – Soil temperature – Soil moisture – Photoperiod – Quantity of radiation Source: Coale and Grove, 1986 • Tillage – Soil moisture – Soil temperature – Soil bulk density – Soil aeration • Soil fertility – Plant dry matter distribution – Root proliferation • Irrigation – Soil moisture profile

P Influx by Roots • Examining how quickly roots can absorb P

Nutrient Influx by Roots – H 2 PO 4 -, HPO 42– K+ • Maximum influx is reached at higher solution concentrations (Imax) Sources: Barber, 1984; Edwards and Barber, 1976 22 -23 day old soybean roots Influx, 10 -14 lb P 2 O 5 / (in 2 s) • Ions are not simply absorbed according to their ratios in solution • Ions with this characteristic influx pattern require energy to be absorbed 3. 0 Imax 2. 5 2. 0 1. 5 1. 0 0. 5 0. 0 -0. 5 0 1 2 3 4 Solution P, 10 -6 lb P 2 O 5/gal 5

Nutrient Influx Depends on Both P and K Fertility Low P limits P diffusion and energy for P uptake Low P limits energy for K uptake Influx, 10 -13 lb / (in 2 s) P 2 O 5 influx by soybean roots 10. 0 9. 0 8. 0 7. 0 6. 0 5. 0 4. 0 3. 0 2. 0 1. 0 0. 0 K 2 O influx by soybean roots 55 ppm Bray P-1 11 ppm Bray P-1 50 70 90 11 ppm Bray P-1 130 150 50 70 Soil test K, ppm Source: Hallmark and Barber, 1984 90 110 130 150

Influx, 10 -5 lb P 2 O 5 / (in. day) P Influx Varies with Plant Age 5 Corn 4 3 2 1 Soybean 0 0 -1 Sources: Barber, 1978; Mengel and Barber, 1974 20 40 60 80 Plant age, days 100 120

Yields and Soil Test P Levels • Examining how production level is related to soil test P level

Relative grain yield, % Soil Test P Calibration Data 100 80 60 40 Corn 20 0 0 10 20 30 40 50 60 70 80 0 Soybean 10 20 30 40 50 60 70 80 Soil test Bray P-1, ppm Source: Mallarino, 1999

Comparisons of Soil Test P Calibration Data 120 Relative yield, % 100 80 60 40 20 MO IL AR KY MS AL 0 0 5 10 15 20 25 30 35 40 Bray P-1 soil test level, ppm Source: Snyder, 2000

P placement • Broadcast and banded applications

Nutrient Placement Considerations Source: Anghinoni and Barber, 1980 Conceptual model (nutrient deficient soil) High nutrient rate Dry matter yield • Banding: – Less soil volume fertilized – Smaller portion of fertilizer is “tied up” – Roots proliferate where N and P are found – Rate may be too low to maximize yield • Fewer roots exposed to supply • Increase in influx rate by roots may not compensate for fewer total number of roots near P supplies Low nutrient rate 0 20 40 60 80 100 Fertilized soil fraction, %

Starter vs. Broadcast: Irrigated Zone Source: Rehm, 1986 Range in average yields: 50 - 71 bu/A 25 Soybean yield response, % • 3 of 10 site-years responded significantly • p. H: 7. 6 – 8. 1 • Olsen P: 5. 6 – 10. 7 ppm • Calcareous soil • Band placement: 2 in. below 2 In. to the side (2 x 2) 20 Broadcast 15 2 x 2 Band 10 5 0 0 -5 20 40 60 P 2 O 5 rate, lb/A 80 100

Starter vs. Broadcast: Dryland Zone Yield response, % 60 50 1 in. below 40 1 in. x 1 in. 30 With seed 20 Spring broadcast 10 Fall broadcast 0 -10 0 25 50 75 P rate, lb P 2 O 5/A Source: Bullen et al. , 1983 100 125

Starter vs. broadcast: Temperate Rain Fed Zone • 20 site-years at research stations Source: Borges and Mallarino, 2000 13. 1 11. 6 3. 9 Starter 3. 9 Broadcast Averaged over all sites Starter 14 12 10 8 6 4 2 0 Broadcast • 9 sites tested Very Low to Low (6 to 15 ppm Bray P-1) • 7 of the 9 sites (78%) (6 to 11 ppm Bray P-1) showed significant responses to P • P placement did not influence soybean yield Yield response, % • 4 – 29 ppm Bray P-1 Averaged over responsive sites

Bray P-1: 3. 5 ppm NH 4 OAc K: 150 ppm 14. 0 band broadcast + w/seed 15 4 10 0 4 10 P 2 O 5: 18 46 60 78 106 K 2 O: 12 30 35 42 10 7. 2 5. 0 5 0 Source: Ham et al. , 1973 19. 6 w/seed Yield response, % 20 19. 9 broadcast + band Comparison of Placement Combinations and Rates N: 5

Deep Banding vs. Broadcast • 20 site-years at research stations • No-till systems • 0 – 6 in. soil samples: – 4 – 29 ppm Bray P 1 – p. H 5. 9 – 7. 1 • Significant responses to P occurred on 7 sites ranging from 6 – 11 ppm Bray P 1 – Average response at these sites: 4. 6 bu/A – 5 of the 7 sites showed no differences in placement Source: Borges and Mallarino, 2000 Range in average yields: 26 – 63 bu/A 30 in. 6 - 8 in. 30 in.

Deep Banding vs. Broadcast • 11 site-years on farmer fields • No-till systems • 0 – 6 in. soil samples: Range in average yields: 37 – 58 bu/A 7. 5 in. – 5 – 34 ppm Bray P 1 – p. H 5. 8 – 7. 5 • Across all site-years, there was a slight (1 bu/A) advantage to P fertilization, and no difference between placement methods Source: Borges and Mallarino, 2000 6 - 8 in. 30 in.

Considerations for Placement • Banding is expected to be superior when soil test levels are low and only smaller rates of P are applied • Broadcast applications may be superior to banded applications when rainfall or irrigation keeps moisture in the upper part of the soil profile • Placement of bands directly below the seed may be better than other band placements • Band broadcast applications used together may be better than either one applied on its own

P Timing • Comparing fresh and residual effects of fertilization

Annual vs. Biennial: Broadcast Applications • Corn/soybean rotation • Long no-till history • P timing (0 -46 -0) – Every 2 -yr. 80 lb P 2 O 5/A – Every yr. 40 lb P 2 O 5/A • 2 of 4 site-years showed no timing differences • 1 site (18 ppm Bray P 1): annual > biennial by 3 bu/A • 1 site (37 ppm Bray P 1): biennial > annual by 3 bu/A Source: Buah et al. , 2000 Range in average yields: 24 – 48 bu/A 30 in.

Annual vs. Biennial: Broadcast Applications • Corn/soybean rotation • Long no-till history • P timing – Every 2 yr. (0, 30, 80, 160 lb P 2 O 5/A) – Every yr. (0, 15, 40, 80 lb P 2 O 5/A) – Direct > residual 2 out of 3 years – 2 bu/A average response – Bray P-1: 6 – 14 ppm Source: Buah et al. , 2000 Range in average yields: 37 – 46 bu/A 10 in.

Annual vs. Biennial: Starter Applications • Corn/soybean rotation • Long no-till history • P timing (0 -46 -0) Range in average yields: 24 – 48 bu/A – Every 2 -yr. 80 lb P 2 O 5/A – Every yr. 40 lb P 2 O 5/A • 2 of 4 site-years showed no timing differences • 1 site (18 ppm Bray P 1): annual > biennial by 6 % • 1 site (37 ppm Bray P 1): biennial > annual by 13 % Source: Buah et al. , 2000 30 in. 3 - 4 in. 2 in. 30 in.

Annual vs. Biennial: Starter Applications • Corn/soybean rotation • Long no-till history • P timing – Every 2 yr. (0, 30, 80, 160 lb P 2 O 5/A) – Every yr. (0, 15, 40, 80 lb P 2 O 5/A) – Annual > biennial 2 out of 3 years – 2 bu/A average response – Bray P-1: 6 – 14 ppm Source: Buah et al. , 2000 Range in average yields: 37 – 46 bu/A 10 in. 4 in. 30 in.

% of yield attained with 600 lb P 2 O 5/A applied initially, and 67. 5 lb P 2 O 5/A applied annually Residual effect of a single, large application of P 0 lb P 2 O 5 applied initially 67. 5 lb P 2 O 5/A applied annually 120 110 100 90 80 70 600 lb P 2 O 5 applied initially 0 lb P 2 O 5/A applied annually 60 50 40 1975 1980 1985 1990 Year Source: Dodd and Mallarino, 2005 1995 2000

Timing Considerations • Cases where annual applications may be better than biennial applications in no-till systems: – Soils with lower soil test levels – Soybeans planted in narrower rows • Other tillage systems need to be investigated • Single, larger applications of P can have significant residual value – Builds soil test levels – Can be performed when economics of larger applications are favorable – Allows P to be omitted in times of unfavorable economic conditions

Phosphorus and soybean pests/diseases

Nutrition and Foliar Diseases: Asian Rust Rate N P 2 O 5 Upper extent Lesion Type of Overall K 2 O of rust lesions density pustule rating (lb/A) 80 0 0 upper third heavy sporulating susceptible 0 61 0 upper third medium sporulating mod. susceptible 0 0 32 upper third medium sporulating mod. susceptible 80 184 0 upper third heavy sporulating susceptible 27 61 32 middle third medium non-sporulating mod. resistant Source: Piccio and Fanje, 1980

SMV incidence, % Nutrition and Diseases: Soybean mosaic virus 50 45 40 35 30 25 20 15 10 5 0 K 2 O P 2 O 5 N Total N + P 2 O 5 + K 2 O, at equal rates 0 25 50 75 100 Nutrient rate, lb/A Source: Pacumbaba et al. , 1997 125 150

Nutrition and Nematodes: Soybean cyst nematode (SCN) 18 16 14 12 10 8 6 4 2 0 30 25 Yield response 20 15 10 5 0 0 -0 30 -30 60 -60 90 -90 120 -120 Fertilizer mixture (P 2 O 5 - K 2 O), lb/A C/C Source: Howard et al. , 1998 S/S C/S Yield response, % Cysts / 100 cc Cultivar highly susceptible to SCN races 3 and 4

Nutrition and Nematodes: Soybean cyst nematode (SCN) 18 16 14 12 10 8 6 4 2 0 30 25 20 Yield response 15 10 5 0 0 -0 30 -30 60 -60 90 -90 120 -120 Fertilizer mixture (P 2 O 5 - K 2 O), lb/A C/C Source: Howard et al. , 1998 S/S C/S Yield response, % Cysts / 100 cc Cultivar resistant to SCN races 3 and 4

Conclusions • At harvest, most of the P in the above-ground portion of soybean is in the grain • At lower soil test levels, more of the P taken up by the plant comes from applied P • In the first month after planting, root development is primarily characterized by elongation of the taproot • In subsequent months, soybean develops much of its root system near the soil surface • Compared to corn, the rate of P influx by soybean roots is about 4 times slower in the first 20 days • P proliferates soybean roots when present in concentrated zones • Mycorrhizae can increase soybean growth at low soil test P levels, even when P is applied

Conclusions • Soil test calibration data provide a biological evaluation of chemical tests • Average calibration relationships can be similar across large geographies • Placement of bands directly below the seed may be better than other band placements • Band broadcast applications used together may be better than either one applied on its own • Annual applications appear to be superior to biennial applications when plant spacing is narrower and soil tests are low • P can help reduce the incidence and or severity of some soybean diseases

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