Direct and residual effects of p sources on cassava in Sierra Leone

Abstract

Direct, residual and cumulative effects of various P sources and rates were investigated on Njala upland soils using cassava as an indicator crop. The utilization index (UI) of ‘cocoa’ cassava was not significantly affected by source or rate of P. No significant direct effect of P sources and rates on fresh tuber yield was observed when compared with the control. The largest yield of 16 tons/ha occurred at 52.8 kg P/ha of P from urea ammonium phosphate. Increasing rates of P resulted in an increase in soil available P. Residual effects of P sources and rates signifi‐. cantly increased fresh tuber yield when triple superphosphate and urea ammonium P were the P sources.