Water use and crop coefficients in sprinkler irrigated rice

Field experiments were carried out during the years 2002, 2004, 2005 and 2006 to analyze water-soil-atmosphere interactions in sprinkler irrigated rice. The research was carried out in Sardinia (39° 59' N; 8° 40' E, at altitude 15 m). The cultivars used in the experiments, respectively in 2002 and in 2004-2005-2006, were Irat 212 and Eurosis. In each year cultivars were subjected to the same crop management. Irrigation was applied since the emergence with the sprinkler method, taking into account the loss of water from 'Class A' pan evaporation. Soil water content was monitored at 0.10 m intervals until l.00-m depth using a 'Diviner 2000' (Sentek). In 2002 seven irrigation scheduling treatments were compared. In 2004, 2005, 2006 irrigation treatments provided for optimal soil water conditions during the growing season.In 2002 the results highlighted: 1) 0-0.20 m depth was the most important layer for crop water uptake and the best correlated layer with rice rough yield; 2) the positive relationship between yield and water supply was significant until 6500 m3ha-1of water applied. Further seasonal irrigation volumes did not increase significantly yield.In 2004, 2005 and 2006 the analysis of the soil water balance at different crop phenological stages allowed to estimate crop coefficients (Kc) using the Penman-Monteith equation and the 'Class A' pan evaporation (Kcev).Kc varied over the three-year period on average from 0.90 to l.07 and 0.97, respectively for the emergence-end of tillering, end of tillering-heading and heading-maturing periods, while crop coefficients as a ratio between maximum crop evapotranspiration (ETc) and Epan, Kcev ranged from 0.78 to 0.92 and 0.81 for the same time period