Effects of timing and placement of urea on aerial-sown semi-dwarf rice in south-east Australia

Abstract

Three field experiments over two seasons and on two soil types studied the effects of placement and time of nitrogen fertilizer (N) application on yield and N uptake of aerial-sown semi-dwarf rice. Grain yield and apparent N fertilizer recovery were greatest when fertilizer was drilled into the soil, with no significant difference between 3 cm and 7 cm depth. Placement onto wet soil resulted in significantly lower grain yield and total N uptake than placement onto dry soil or incorporation into the soil. Reducing the time of application before flooding from 15 days to 1 day significantly improved the efficiency of fertilizer use. Delaying the time of application from before flooding to soon after flooding produced much lower grain yield and agronomic efficiency. Further delaying the application time from soon after flooding to around mid-tillering increased the yield response and agronomic efficiency. The results demonstrated that urea should be drilled into the soil as soon as possible before flooding rather than broadcasting onto the soil surface before flooding or into the floodwater after flooding.