Efficiency of P utilization by sunflower grown on residual P fertility

A greenhouse experiment was conducted to study the residual effects of P and poultry manure (PM) applied to soybean in a soybean-sunflower cropping sequence. P removal by sunflower increased with increasing levels of residual P. The residual P level of 12 mg kg−1, along with 2.0 g kg−1 of PM, resulted in a saving of inorganic P fertilizer for sunflower of approximately 30%. The percentage of P derived from freshly applied fertilizer (%Pdff) by sunflower decreased significantly with an increased level of residual P. The calcareous and acid soils showed a higher %Pdff compared with non-calcareous soils. P uptake from the soil increased with the residual P level and PM. The percentage utilization of freshly applied P also increased with residual P fertility.