Response of wheat to deep placement of nitrogen and phosphorus fertilizers on a soil high in phosphorus in the surface layer

Abstract

Wheat was grown in a series of field experimenls on a sandy red-brown earth that was well supplied with phosphorus in the top 10 cm, and deficient in nitrogen. Nitrogen (0-60 kg ha-') as ammonium sulfate or urea, and/or phosphorus (0-100 kg ha-1) as triple superphosphate were applied at various depths down to 30 cm. In one experiment the response to fertilizer placement was examined under dryland and irrigated conditions. The dry weights and the concentrations of nitrogen and phosphorus in the plants were determined, and in one experiment root lengths were also measured. In none of the experiments did placement of fertilizers at depth increase grain yields to a greater extent than placement at 5 cm. While the concentrations of nitrogen and phosphorus in the plants were increased by the application of nitrogen and phosphorus fertilizers respectively, the depth at which the fertilizers were placed was immaterial. Application of phosphorus fertilizer increased root length, but only at the site of placement. Irrigation increased yields, but there was no interaction with depth of fertilizer placement. The soil disturbance (ripping) associated with deep placement of the fertilizers affected shoot growth in all experiments, but the effects were not consistent. Ripping had no effect on root length. Residual effects of the fertilizer treatments on growth and composition of the wheat were small. Deep placement of fertilizer is not recommended for wheat where the nutrient content of the topsoil is high and the topsoil remains wet during the early part of the season.