Effects of time of urea application on combine-sown Calrose rice in south-east Australia. I. Crop response and N uptake

Abstract

Urea (50 kg N ha-1) was applied at one of four times (before the first flush, before permanent flood, after permanent flood and at panicle initiation) to Calrose rice growing on an alkaline grey clay soil. Plant N uptake was highly correlated with dry matter production (r2=0.90) and with grain yield (r2 = 0.95). Efficiency of fertilisation and grain yield were highest when urea was applied either before permanent flood (56 kg grain (kg N) -1, 6.4 t ha-1) or at panicle initiation (47 kg grain (kg N)-1, 6.0 t ha-1), and these efficiencies are among the highest that have been recorded in rice. Significantly lower yields were obtained when the fertiliser was applied at sowing or after permanent flood, largely due to lower panicle densities. Fertilisation at sowing did not produce significantly more grain than the control, despite an early vegetative response. This is in contrast with previous findings on a more fertile acid red-brown earth, and suggests that soil properties may be an important consideration in predicting optimum fertilisation strategies.