Quantifying the water budget of irrigated rice in the Shepparton Irrigation Region, Australia

A field trial was conducted in south-eastern Australia to test the applicability of the United Nations Food and Agriculture Organization (FAO) standard procedures for calculating rice evapotranspiration (ET) and to quantify deep percolation losses under an irrigated rice field. Two sites were measured, site A which was in its fourth consecutive season for growing rice and site B which was in its first season of growing rice. Good agreement between in-field lysimeter and field water balance measurements of rice water requirements was found at both sites. From in-field lysimeter measurements of ET, it was concluded that FAO standard procedures for calculating rice ET were appropriate for south-eastern Australia. Half of the measured deep percolation at site B occurred within the first 24 h of ponding. These initial deep percolation losses occurred through soil cracks. A total of 382 +/- 74 mm of deep percolation was measured at this site. Measured deep percolation was less at site A (121 +/- 74 mm). The difference in deep percolation between sites was attributed to higher soil moisture content at site A prior to initial irrigation.