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

Nutrient Uptake by 80 bu/A Soybeans Source: Henderson and Kamprath, 1970

Soybean P Uptake Days after emergence Growth stage (inferred) % of total uptake V1V6V10R4R6R7 Beans Pods Stems Petioles Petioles (fallen) Leaves Leaves (fallen) Total P uptake: 12 – 24 lb P 2 O 5 /A Source: Hanway and Weber, 1971

Soybean Phosphorus Derived from Fertilizer Soybean plant fractionP derived from fertilizer (%) Leaves (and petioles?)36 Stems20 Pods25 Beans16 Source: Ham and Caldwell, 1978

Soybean Phosphorus Content Derived from Fertilizer Days after planting % of P derived from fertilizer Soil P level Low Medium High Source: Bureau et al., 1953

Soybean Root Morphology Establishing a background for discussions of P placement

Soybean Root Growth Phase 1 (1st month after planting) –Rapid vegetative top growth –Downward taproot growth –Development of horizontal laterals in upper soil profile 6 in. 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 (approx. 10 wk. after planting) Source: Raper and Barber, 1970

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 Depth of Root dry weight at the following days after planting: sample (in.) (grams) Source: Mitchell and Russell, 1971

Roots Proliferate in Zones of Higher P Concentration P treated soil portion, % Portion of total root length in P-treated volume Soybean Corn 1:1 Source: Borkert and Barber, 1985

Effects of P or Mycorrhizae on Soybean Shoot Dry Weight Source: Lambert et al Greenhouse study Applied P rate, lb P 2 O 5 /A Shoot dry weight, grams % of root colonized Non- mycorrhizal DMMycorrhizal DM Non-mycorrhizal infectionMycorrhizal infection Initial Bray 1 soil test P = 8 ppm

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

P Influx by Roots Examining how quickly roots can absorb P

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 –H 2 PO 4 -, HPO 4 2- –K+–K+ Maximum influx is reached at higher solution concentrations (I max ) day old soybean roots Solution P, lb P 2 O 5 /gal Influx, lb P 2 O 5 / (in 2 s) I max Sources: Barber, 1984; Edwards and Barber, 1976

Nutrient Influx Depends on Both P and K Fertility Soil test K, ppm Influx, lb / (in 2 s) P 2 O 5 influx by soybean rootsK 2 O influx by soybean roots 11 ppm Bray P-1 55 ppm Bray P-1 11 ppm Bray P-1 55 ppm Bray P-1 Low P limits P diffusion and energy for P uptake Low P limits energy for K uptake Source: Hallmark and Barber, 1984

P Influx Varies with Plant Age Plant age, days Influx, lb P 2 O 5 / (in. day) Corn Soybean Sources: Barber, 1978; Mengel and Barber, 1974

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

Soil Test P Calibration Data Source: Mallarino, 1999

Comparisons of Soil Test P Calibration Data Bray P-1 soil test level, ppm Relative yield, % MOILAR KYMSAL Source: Snyder, 2000

P placement Broadcast and banded applications

Nutrient Placement Considerations 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 Fertilized soil fraction, % Conceptual model (nutrient deficient soil) Low nutrient rate High nutrient rate Dry matter yield Source: Anghinoni and Barber, 1980

Starter vs. Broadcast: Irrigated Zone 3 of 10 site-years responded significantly pH: 7.6 – 8.1 Olsen P: 5.6 – 10.7 ppm Calcareous soil Band placement: 2 in. below 2 In. to the side (2x2) P 2 O 5 rate, lb/A Soybean yield response, % Broadcast 2x2 Band Range in average yields: bu/A Source: Rehm, 1986

Starter vs. Broadcast: Dryland Zone P rate, lb P 2 O 5 /A Yield response, % Source: Bullen et al., in. below 1 in. x 1 in. With seed Spring broadcast Fall broadcast

Starter vs. broadcast: Temperate Rain Fed Zone 20 site-years at research stations 4 – 29 ppm Bray P-1 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 Broadcast Starter Broadcast Starter Yield response, % Averaged over all sites Averaged over responsive sites Source: Borges and Mallarino, 2000

Comparison of Placement Combinations and Rates w/seed band broadcastbroadcast + w/seed broadcast + band Source: Ham et al., 1973 N: P2O5:P2O5: K 2 O: Yield response, % Bray P-1: 3.5 ppm NH 4 OAc K: 150 ppm

Deep Banding vs. Broadcast 20 site-years at research stations No-till systems 0 – 6 in. soil samples: –4 – 29 ppm Bray P1 –pH 5.9 – 7.1 Significant responses to P occurred on 7 sites ranging from 6 – 11 ppm Bray P1 –Average response at these sites: 4.6 bu/A –5 of the 7 sites showed no differences in placement 30 in. Range in average yields: 26 – 63 bu/A in. Source: Borges and Mallarino, 2000

Deep Banding vs. Broadcast 11 site-years on farmer fields No-till systems 0 – 6 in. soil samples: –5 – 34 ppm Bray P1 –pH 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 30 in. 7.5 in in. Range in average yields: 37 – 58 bu/A Source: Borges and Mallarino, 2000

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 and 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 P1): annual > biennial by 3 bu/A 1 site (37 ppm Bray P1): biennial > annual by 3 bu/A 30 in. Range in average yields: 24 – 48 bu/A Source: Buah et al., 2000

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 10 in. Range in average yields: 37 – 46 bu/A Source: Buah et al., 2000

Annual vs. Biennial: Starter 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 P1): annual > biennial by 6 % 1 site (37 ppm Bray P1): biennial > annual by 13 % 30 in. Range in average yields: 24 – 48 bu/A 2 in in. Source: Buah et al., 2000

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 10 in. Range in average yields: 37 – 46 bu/A 30 in. 4 in. Source: Buah et al., 2000

Residual effect of a single, large application of P Year % of yield attained with 600 lb P 2 O 5 /A applied initially, and 67.5 lb P 2 O 5 /A applied annually 0 lb P 2 O 5 applied initially 67.5 lb P 2 O 5 /A applied annually 600 lb P 2 O 5 applied initially 0 lb P 2 O 5 /A applied annually Source: Dodd and Mallarino, 2005

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 RateUpper extentLesionType ofOverall NP2O5P2O5 K2OK2Oof rust lesionsdensitypustulerating (lb/A) 8000upper thirdheavysporulatingsusceptible 0610upper thirdmediumsporulatingmod. susceptible 0032upper thirdmediumsporulatingmod. susceptible upper thirdheavysporulatingsusceptible middle thirdmediumnon-sporulatingmod. resistant Source: Piccio and Fanje, 1980

Nutrition and Diseases: Soybean mosaic virus K2OK2O P2O5P2O5 Total N + P 2 O 5 + K 2 O, at equal rates N Source: Pacumbaba et al., Nutrient rate, lb/A SMV incidence, %

Nutrition and Nematodes: Soybean cyst nematode (SCN) Fertilizer mixture (P 2 O 5 - K 2 O), lb/A Cysts / 100cc Yield response, % C/CS/SC/SYield response Cultivar highly susceptible to SCN races 3 and 4 Source: Howard et al., 1998 Yield response

Nutrition and Nematodes: Soybean cyst nematode (SCN) Source: Howard et al., Fertilizer mixture (P 2 O 5 - K 2 O), lb/A Cysts / 100cc Yield response, % C/CS/SC/SYield response Cultivar resistant to SCN races 3 and 4 Yield response

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 and 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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