Changes in seasonal evapotranspiration, soil water content, and crop coefficients in sugarcane, cassava, and maize fields in Northeast Thailand

This study was performed to examine seasonal changes in evapotranspiration (ET), soil water content, and crop coefficients (K-c) for sugarcane, cassava, and maize fields in Northeast Thailand. ET rates during the rainy season varied between 2 and 6 mm per day but remained around I mm per day in the dry season. The normal dry season ET was much greater than the water loss from the top 0.5 m of soil, suggesting that capillary rise from deeper soil layers provides significant amounts of water to the upper soil layer. The K-c for sugarcane and cassava reached growing season peaks of approximately 1.10 and 1.20, respectively, in June. The maximum K-c for the maize field was approximately 1.20. Although the ET estimated by the Hargreaves equation exceeded the FAO reference ET value for this region, the values had a high correlation when the Hargreaves ET was calculated using solar radiation measurements. (C) 2004 Elsevier B.V. All rights reserved.