Assessment of maize evapotranspiration, water requirements and productivity using weather data in Coimbatore’s semiarid climate

Accurately estimating crop water use is crucial for efficient water management in conservation agriculture, especially in Coimbatore's semiarid climate. This study assessed maize water use and productivity over three growing seasons (2023-2024) at AC&RI, Coimbatore. Irrigation applied each season varied between 500.8mm and 554.1 mm, averaging 535.8 mm, while total water supply ranged from 810.6 to 985.3 mm. Actual evapotranspiration (ETa) was estimated using locally developed crop coefficient curves (Lkc) and FAO crop coefficients. Water productivity for maize was calculated based on these estimates. Daily ETa for maize ranged from 0.9mm to 8.2 mm. Other than the different seasons, ETa varied from 342.6 to 372 mm, averaging 355.6 mm with the Lkc curve. By FAO Kc, ETa ranged from 400.8mm to 479.1 mm, with an average of 444.2 mm. The irrigation requirement ranged from 579.6mm to 672.7 mm, with an average of 629.5 mm using LKc. Using FAO Kc, the range was 637.8mm to 762.9 mm, with an average of 718 mm. Crop water use efficiency (CWUE) ranged from 0.8 and 0.9 kg/m³, with an average of 0.9 kg/m³. The evapotranspiration water use efficiency (ETWUE) ranged from 2.0 to 2.1 kg/m³, with an average of 2.1 kg/m³. The irrigation water use efficiency (IWUE) varied across seasons, averaging 1.4 kg/m³. Strong correlations were observed between CWUE, IWUE, and the amount of seasonal irrigation (R² = 0.98 and 0.99, respectively). CWUE and ETWUE strongly correlated with IWUE (R² = 0.98 and 0.75, respectively). These findings suggest that maize irrigation in Coimbatore's semiarid regions should be tailored to local conditions to enhance water productivity.