Improving the Water Use Efficiency of Rice - Final Report

Abstract

The cost of irrigation water accounts for 20-30% of the total variable costs of rice production in the Murrumbidgee and Murray Valleys. Rice production consumes a substantial proportion of the available supply of irrigation water. Any agronomic/water management practice that has the potential to reduce water use should be investigated. Research in the Burdekin River Irrigation Area indicated that crop water use of rice grown on raised beds was 32% less than when grown using conventional permanent flood. Whilst recognising that there are likely to be agronomic constraints to rice production on raised beds in the Riverina, investigations into potential water savings, were investigated in this project. The project evaluated the water use efficiency of rice grown on a raised bed layout on two of the principal soil types used for rice production (four experiments). This layout was compared with the now traditional aerial sown fully ponded flat layout. The opportunity to explore water management options on the raised bed layout was also undertaken in three of the experiments. Water use was quantified and agronomic performance of the rice crop monitored. Maintaining water in the furrows all season reduced grain yield by an average of 10% (range 7-20). In three of the four experiments harvest index was lower where water was maintained only in the furrows. Moisture stress during panicle development and grain filling may have contributed to this result. Although sterility was not measured, no affected panicles were observed. Water use, where water was maintained in the furrows, was reduced by 14% (range 7-18). Water use efficiency increased on two occasions but decreased on one. Efficiencies for the two irrigation layouts by water management treatments of most interest (water maintained in the furrows; fully ponded flat) ranged only from 7.1 to 8.1 kg/ha/mm of water used by the crop. Despite an apparently similar soil type across the experimental areas, considerable variation in water use between plots with the same water management was measured. When attempting to measure water use in ‘small plots’ it is recommended that there be a minimum of four replications and/ or differences in water management between treatments be substantial. This project demonstrated that rice can be successfully grown on the raised bed layout (yields > 10 t/ha). Reductions in water use will not be as substantial as those reported from Queensland. Where water ‘subs’ readily to the centre of the raised bed grain yield, water use and water use efficiency are all likely to be similar to the traditional fully ponded flat layout.