Lateral Seepage, Deep Percolation, Runoff, and the Efficiencies of Water Use and Application in Irrigated Rice in Kooshkak Region in Fars Province, I. R. Iran

Due to continuous flooding, irrigation management of rice (oryza sativa l.) is very important, particularly in semiarid and arid regions where water is scarce. rice plantations in i. r. iran are located mainly in the humid; north, however, it is also grown in arid and semiaridareas of the country, including the fars province, in the south. in this province, nearly 55000 ha of rice is grown under irrigated conditions. therefore, research on proper irrigation managementhas significant impacts on crop and water use efficiency production. the present research was conducted in kooshkak agricultural research station of shiraz university in 1997 and 1998 to determine lateral seepage, deep percolation, runoff, irrigation application efficiency and water use efficiency for irrigated rice. the cultivar used was a short season local cultivar, namely champa-kamfiroozi, commonly planted by most of the farmers in the studied area. for measuring deep percolation, a pair of cylindrical shape iysimeters, with a 56 em diameter and a100 em height, were used in three locations in the rice field. in each pair, one of the iysimeters was bottom-less to allow for deep percolation. thus, difference in water used in the two iysimeters was due to deep percolation. for measuring the inflow and outflow of water, 90 degree triangular weirs were used in the entrance and exit of the experimental plot, respectively.the difference between total water used in the field (measured by weirs) and actual evapotranspiration (measured by iysimeter) was considered as sum of lateral seepage and deep percolation. subtraction of deep percolation from this sum showed lateral seepage. the amountsof daily deep percolation and lateral seepage were 3.4 mm and 0.19 m dol mol in 1997, respectively. these amounts were 3.5 mm and 0.22 rrr'd mol in 1998, respectively. surface runoff which was the main source of water loss was 6.15 and 8.30 mm dol in 1997 and 1998,respectively. in order to investigate the effect of reusing surface runoff, application efficiency was calculated for both cases of runoff reuse and without reuse. in 1997, irrigation application efficiency with runoff reuse was 49.6% while its value was 30.8% without runoff reuse. for1998, these values were 46.6 and 31.5%, respectively. the results showed an increase of 15% to 19% in irrigation application efficiency due to the consideration of runoff to be reused for the two years. water use efficiency for rice grain was 2.9 and 2.5 kg mm' of water in 1997 and 1998, respectively.