PRESOWING NITROGEN-FERTILIZER MANAGEMENT FOR AERIAL-SOWN RICE ON PUDDLED SOIL

Presowing nitrogen (N) fertiliser management for aerial-sown rice was investigated for 2 soil cultivation methods, conventional cultivation and puddling, in the Coleambally Irrigation Area of New South Wales. T wo N sources, urea and anhydrous ammonia (NH3, ColdFlo), were used. Ur ea was applied at 3 depths (0, 7, 17 cm) and NH3 at 2 depths (7, 17 cm ). These 5 treatments were compared with an unfertilised control and w ith a novel method of applying NH3 in the same operation as puddling. Urea was applied at 60 kg N/ha; the application rate of NH3 appeared t o be higher than the intended rate of 60 kg N/ha. The site was respons ive to N: agronomic efficiency of the urea-fertilised treatments avera ged 39 kg grain yield increase/kg applied N. Dry matter yield, N uptak e, and grain yield were similar on conventionally cultivated and puddl ed soil. There were no significant interactions between cultivation an d N treatments in their effects on crop growth or N uptake. Applicatio n depth of fertiliser also had no significant effect on crop performan ce. Applying NH3 in the same operation as puddling was as effective as other methods of applying N, with the advantage of allowing soil prep aration and fertiliser application to be completed in 1 pass. Urea lab elled with N-15 was applied at depths of 0, 5, and 15 cm to microplots at a rate of 60 kg N/ha. Recoveries of N-15 in plants and soil were s imilar for both methods of soil cultivation and for different N applic ation depths, consistent with results from the large plots described a bove. There was no interaction between soil cultivation and urea appli cation depth treatments. Recovery of applied N-15 averaged 32% in the plant shoots and 24% in the top 30 cm of the soil. Recoveries of N-15 from presowing urea application have not previously been reported for aerial-sown rice in New South Wales. The results suggest that puddling can be readily integrated into the rice management system without cha nging current fertiliser practices. However, soil N uptake was very hi gh, accounting for around 90% of the plant N uptake in the urea-fertil ised treatments. Therefore, extrapolation of the results of the treatm ent comparisons to other sites with lower available N should only be d one with caution.