WHEAT GROWTH FROM PHOSPHORUS FERTILIZERS AS AFFECTED BY TIME AND METHOD OF APPLICATION IN SOIL WITH AN ACIDIC SUBSURFACE LAYER

Using soils with an acidic subsurface layer, three glasshouse experime nts were carried out to evaluate the effect of placement method and ap plication rate of triple superphosphate (TSP) and North Carolina phosp hate rock (NCPR) on dry matter (DM) yields. Time of application of NCP R on DM yield response of wheat was also studied. For Experiment 1, so il was collected in depth intervals of 0.2; 4-6; 6-8; and 8-10 cm from a red earth (chromic luvisol). The treatments included two P sources (TSP and NCPR), three placement methods (broadcast, banded or mixed in to the subsurface layer, 6-8 cm), and six application rates. In this P deficient soil with an acidic subsurface layer, there was relatively little effect of application method of TSP on wheat yield responses. T he maximum dry matter yield responses for broadcast, band and mix appl ication methods was 30, 42 and 50%, respectively. Responses to NCPR br oadcast, band and mix methods were 20, 9 and 44%, respectively. Mixing NCPR into to acidic subsurface layer produced yields similar to those from TSP although a higher application rate of P as NCPR was needed t o achieve this outcome. Treatments for Experiments 2 and 3 were time o f application of NCPR (0 and 30 days before sowing) and rate of applic ation of NCPR (0 and 40 mg P/pot). In Experiment 2 (same soil as Exper iment 1) application of NCPR prior to sowing, resulted in higher Coldw ell P concentration than when applied at sowing, but time of applicati on had no effect on final DM yields. Experiment 3 used a red podzolic (chromic luvisol) soil which had a lower P-status, was more acid and h ad a lower exchangeable Ca2+ concentration than the red earth. Applica tion of NCPR prior to sowing resulted in lower DM yield than when it w as applied prior to sowing.