NITROGEN ACCUMULATION AND REMOBILIZATION IN WHEAT OF N-15-UREA APPLIED TO A DUPLEX SOIL AT SEEDING

Accumulation and remobilisation of N-15-labelled urea by wheat grown on a duplex soil at East Beverley, Western Australia, was investigated. N-15-urea was applied to microplots in a field experiment at 5.2 g N/m2 at seeding. The microplots were sampled at tillering, stem elongation, anthesis, and maturity. A maximum of 10.6 g N/m2 was accumulated by anthesis and no additional N was accumulated to maturity. Most N uptake occurred between tillering and stem elongation when plant N increased by 7 g/m2. Nitrogen loss of about 1.2 g/m2 occurred after anthesis. Post-anthesis remobilisation from the vegetative plant parts accounted for 69% of the N measured in the heads. Remobilisation from the straw of the mainstem and tiller 1, respectively, was 68 and 71% of the N measured in the heads. The balance of about 0.7 and 0.4 g N/m2 for the mainstem and tiller 1 was presumably obtained from tiller 2 and 3, from which losses were 0.4 and 0.6 g N/m2, respectively. Recovery of N-15-labelled urea in the plant was 39% and the apparent efficiency of utilisation of the N fertiliser applied at seeding was 50%. These low recoveries in the plant indicate a need to improve N utilisation by wheat in duplex soils.