Effect of aggregation on phosphate sorption-desorption behaviour of soils under various land use patterns of Eastern India

The present experiment was conducted to study whether aggregation had any influence on phosphorus (P) adsorption-desorption behaviour of soils under four land uses of eastern India. The highest amount of P sorbed at any amount of P addition was recorded in the smallest size aggregate, i.e. 0.10–0.05 mm and the least in the largest size aggregate (>2.0 mm). The per cent P sorbed of added P decreased with increase in the level of P addition irrespective of size of aggregates. Sorption isotherms were described by Langmuir and Freundlich adsorption equations. Larger size aggregates had lesser buffering capacity and bonding energy indicating higher solution P concentration for plant absorption than the smaller size aggregates, but would not sustain solution P concentration for longer period of time. The amounts of P desorbed also increased with increase in added P concentration and the proportions of P desorbed of sorbed P increased with increase in the fineness of aggregates. The results thus indicated that weakly aggregated soil would release more P than the well aggregated soil. In a particular size aggregate, the proportion of P release to sorbed P increased up to a limit of P addition (200 mg P kg⁻¹) and thereafter decreased steadily.