Phosphorous Sorption and Desorption Characteristics of Soil as Affected by Organic Residues

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Abstract
The influence of seven organic residues on sorption and desorption of P by a high P‐fixing soil was determined after 30, 75, and 150 days of incubation. After incubating for 30 days, all residues decreased the amount of P sorbed by the soil, resulting in higher equilibrium solution P levels. However, after incubating for either 75 or 150 days, the P content of the organic residues had a marked influence on sorption of added P and desorption of sorbed P. The critical value of P in organic residues which resulted in no tie‐up of soil P was 0.3%. Sawdust, wheat straw, and cornstalks which contained < 0.3% P decreased labile soil P and increased sorption by soil after incubating for 75 or 150 days. Alfalfa (Medicago sativa), barley (Hordeum vulgare), beans (Phaseolus vulgaris), and poultry manure that contained P in excess of 0.3% decreased sorption of P. The results suggest that P fertilizer rates estimated from sorption isotherms may need to be modified following addition of organic residues.

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