Nitrogen timing and rate effects on growth and grain yield of delayed permanent-water rice in south-eastern Australia

Abstract

The need for continual improvement in water productivity of rice farming has led to the development of delayed permanent (continuous) water (DPW) irrigation practice for drill-sown rice in south-eastern Australia. Current rice-growing practices have the crop flooded for most, or all, of its growing period, whereas DPW has reduced the period of flooding during the vegetative phase, resulting in significant water savings. The changed water-management practice required nitrogen (N) management practices to be investigated, because traditional N application timings and rates may no longer be suitable. Six experiments were conducted over three rice-growing seasons, 2010–11, 2011–12 and 2012–13, on two soil types in south-eastern Australia. Nitrogen applications at sowing, early tillering, mid-tillering and pre-PW were investigated at different rates and split-timing combinations. In the third season, three current commercial semi-dwarf rice varieties, Reiziq, Sherpa and Langi, were investigated for their growth and grain yield using different N treatments under DPW management. Nitrogen applied with the seed at sowing increased vegetative plant growth but did not increase grain yield, whereas N applied at early tillering had no significant impact on plant growth or grain yield. Nitrogen applied at mid-tillering often increased plant growth but did not lead to increased grain yield over treatments that received all N before PW application at 18–22 days before panicle initiation. When rice is managed under DPW, all N should be applied in one application, before the application of PW. The results from this research show that applying 100 kg N ha–1 before PW for rice grown under DPW was the best N-management option for the experimental fields. All three varieties grew and yielded well under the practice of DPW and responded similarly to N application rates and timings.