Recovery of nitrogen fertiliser by drill-sown rice crops using best management practice: a 15N-labelled urea study

Context. Optimising nitrogen (N) management strategies for drill-sown rice crops is essential for minimising input costs for growers and reducing the environmental impact of rice production. Aims. The study aimed to determine the recovery of fertiliser-N in drill-sown Australian rice crops, following current N fertiliser recommendations where two-thirds of the N is applied at sowing (pre-flood) and one-third at panicle initiation. Methods. N-15-labelled urea was used to quantify N recovery by field-grown rice crops on a Sodosol and a Vertosol, and to determine the contributions of fertiliser-N applied pre-flood vs that applied at panicle initiation to total N fertiliser recovery on the Vertosol. Results. Recovery of N-15 fertiliser in grain + straw was similar to 50% of applied N on both soils, with a further 20% recovered from roots and soil to a depth of 30 cm. Recovery of N fertiliser applied at panicle initiation (59%) was significantly higher than of N fertiliser applied pre-flood (43%), likely due to the presence of actively growing roots and higher plant N demand. Crops that received N fertiliser took up more native soil N than unfertilised crops on the Vertosol; hence, apparent fertiliser N recoveries were 10-15% higher than N fertiliser recovery determined using N-15-labelled urea. Conclusions. The recovery of 50% of fertiliser-N in aboveground plant material indicates that N fertiliser use efficiency in drill-sown rice is similar to that of dryland cereal crops in Australia when best management practice guidelines for N fertiliser use are followed.