Rate and timing of nitrogen fertilizer applications on wheat grown under dryland and supplementary irrigation

Abstract

Field experiments were carried out at the University of Sydney Farm, to examine nitrogen fertilizer application strategies for increasing N uptake and productivity of wheat (Triticum aestivum L.) grown on a red-brown earth (Natrixeralf) in Australia, under dryland and supplementary irrigation. Increasing N rate increased shoot dry matter and N uptake consistently but grain yield response was greatly dependent on soil moisture or rainfall in the post-heading period. Water availability at this time determined kernel weight and hence grain yield, even when sufficient grain number had been established. Split application of N increased N uptake most, when the second dose was applied at tillering. On the other hand, delayed applications to the time of heading or anthesis resulted in a relatively lower uptake of N even with supplementary irrigation. The effect of a single pre-sowing application was similar to that applied at sowing or early tillering. We conclude that a split application of N is important for increasing N uptake when the second dose is applied during tillering rather than at heading or anthesis.