Phosphate Sorption Implications on Phosphate Soil Tests and Uptake by Corn
1990
Kuo, S.
Phosphate sorption greatly affects P availability in soils. This greenhouse study was conducted to determine the influence of the quantity of P added and P sorption capacity on P soil tests and P accumulation by corn (Zea mays L.). Seven soils with varying contents of amorphous Al oxide were treated with 0 to 4 mmol P kg⁻¹, incubated for 9 wk, and planted with corn in pot culture after uniform fertilization with N and K. Corn plants were harvested 4 wk after sowing. The dry-matter yields, P concentration in the plants, as well as sodium bicarbonate extractable P (NaHCO₃-P) and sodium acetate extractable P (NaOAc-P) were determined. The P-sorption capacities of the soils were closely related to their amorphous Al oxide contents, and the average affinity coefficient was close to the intrinsic equilibrium constant for the formation of neutral surface species. While increasing in proportion to the amounts of P added, the concentration of NaHCO₃-P and NaOAc-P decreased as the P-sorption capacities of the soils increased. Both soil tests were a function of the fraction of P coverage on soil surfaces (Θ), defined as the ratio of the amount of P sorbed to the P-sorption capacity. As with the soil tests, the plant P concentration and P uptake were all highly correlated with Θ. The quantity of P added and P-sorption capacities of the soils affected the plant P concentration, dry-matter yield, and P uptake in the same manner as they did the soil tests. As a single measurement, Θ was more successful than the two soil tests in predicting P accumulation and P uptake by the plants.
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