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Anion Exchange and Mehlich-III Phosphorus in Humaquepts Varying in Clay Content

Zheng, Zhiming, Simard, Régis R., Parent, Léon E.
Soil Science Society of America journal 2003 v.67 no.4 pp. 1287-1295
Glycine max, Hordeum vulgare, Humaquepts, anion exchange, barley, clay, clay fraction, coarse-textured soils, crops, fine-textured soils, growth chambers, mineral content, phosphorus, phosphorus fertilizers, risk, sand, soil texture, soybeans, surface water
Soil-test P is not only used for fertilizer recommendations but also as a component to predict risk of P transfer from soils to surface waters. The changes in soil-test P following P application are often related to soil texture. This study assessed the changes in anion-exchange membrane P (AEM-P) and Mehlich-III extractable P (M3P) in Humaquepts varying in clay content. Five soils from loamy sand to "heavy" clay received 0 (P0), 10 (P10), 20 (P20), or 40 (P40) mg P kg-1 per each simulated growth season were successively cropped with barley (Hordeum vulgare L.) and soybean (Glycine max L. Merr.) in a growth chamber experiment. There were clay content mineral fertilizer P (MFP) interactive effects on soil AEM-P, M3P contents and plant P uptake. The AEM-P paralleled clay content and MFP rate. The average increase in M3P at P10 and P20 over P0 was smaller on clayey than on coarse-textured soils. The converse trend was true at P40 over P10 and P20. The increase in M3P per unit MFP addition in excess of plant uptake decreased linearly with the increase in clay at P10 and P20 but not at P40. There was a quadratic plateau relationship between AEM-P and M3P contents with a turning point at 4.2 μg AEM-P cm-2 or 93.0 mg M3P kg-1 Plant P uptake was more closely related to AEM-P than M3P in all soils, suggesting AEM-P is a more reliable indicator of labile P than M3P in Humaquepts for the tested crops, particularly in fine-textured soils. Clay content has a large influence on changes in AEM-P and M3P following MFP additions to Humaquepts.