The availability of soil and fertilizer phosphorus to wheat and rape at different water regimes

Abstract

The uptake of native phosphorus and band-applied fertilizer phosphorus was studied for wheat (Triticum vulgare L. Oxley) and rape (Brassica napus L. Dwarf Essex) at two water regimes in a pot experiment. Soils were cracking clays known to differ in phosphorus availability. Both crops responded to fertilizer on Cecilvale (low available phosphorus), but not on Waco soil (high available phosphorus), and wheat also responded on Mywybilla soil (intermediate phosphorus). Fertilizer uptake was in the order: Cecilvale > Mywybilla > Waco for wheat and Cecilvale > Waco for rape. Crops recovered generally twice as much native phosphorus from each soil with the wet than with the dry regime. There was no effect of water regime on uptake of fertilizer phosphorus by wheat on any soil. Water regime did not increase fertilizer uptake by rape from Waco soil, although it did increase uptake on Cecilvale soil. Favourable fertilizer response under arid conditions appears to be due to a reduction in accessibility of native soil phosphorus due to the stunted root system, but no reduction in the availability of fertilizer phosphorus.