Soil management effects on phosphorus sorption and external P requirement in oxisols of Malawi

Oxisols are one of the major soils of Malawi and they are high in P sorption. Conservation agriculture has been practiced on this soil for some years now but soil management effects on P sorption and external P requirement (EPR) of Oxisols in Malawi have not, however, been determined. Soil management effects on P sorption and EPR of Oxisols in Malawi were therefore determined in the present study. The effects studied were conventional tillage (CT), no-tillage (NT) and crop rotation (CR). The soils differed considerably in their sorption characteristics, with the sorption maxima ranging from 413 to 345 mg P kg-1. Differences in sorption maxima and affinity due to soil management effects were statistically significantly (P ≤ 0.05). The sorption affinity (b) values ranged from 0.48 to 0.72 dm3 mg-1 and differences due to soil management effects were statistically significant (P ≤ 0.05) only between conventional tillage (CT) and no tillage (NT) or crop rotation (CR). The sorption affinity due to NT was not statistically significant from that of CR. The b values were the highest in soils that had been subjected to CT.