Determining the water production function, root distribution and crop water stress index of maize and validation of CERES maize crop growth model under Çukurova

DC Abstract This study was carried out to determine yield-water relationships or production function of the first crop maize, effects of the limited water on yield and yield components, and to establish an irrigation scheduling program for maize using the crop water stress index (CWSI) determined from the observed data of the infrared thermometer and porometer, and to test and validate the CERES-Maize growth model under Çukurova region conditions. Experimental site was located at the Research Field of the Agricultural Structures and Irrigation Department (altitude 20 m sea level above, 36° 59' N, 35° 18' E) on Clayey Mutlu Soil Series. TTM-815 hybrid corn variety was used in this study. Irrigation management treatments were created as 100 %, 80 %, 60 %, 40 %, 20 % and 0 % replenishment of water depleted in the 120 cm soil profile from the 100 % replenishment treatment in every ten days. Iioo treatment plots were irrigated 6 and 7 times in 1993 and 1994, respectively, and a total of 752 mm to 823 mm of irrigation water were applied Iioo irrigation treatment, İn which water use was determined as 999 mm and 1052 mm in 1993 and 1994, respectively. Grain yield obtained from the above mentioned irrigation treatment was 1001.5 kg/da in the first year and 1003.4 kg/da in the second year of the experiment. Significant relationships between grain yield (Y) vs seasonal irrigation (I), and grain yield vs water use (ET) were found in the first year as Y = -0.00191 I2 + 2.9 I - 139.34 (r2 = 0.98 **) and Y = 1.623 ET - 500.45 (r2 = 0.88 **). Corresponding relations for the second year were as Y = -0.0012 I2 + 1.9 I + 222.49 (r2 = 0.97 **) and Y = 1.042 ET - 14.10 (r2 = 0.88 **), respectively. The yield response factor (ky) ranged between 1.08-1.61. Irrigation water use efficiency (IWUE) and water use efficiency (WUEet) were found to be between 1.0-2.43 kg/da-mm and 0.22-1.25 kg/da-mm, respectively for the treatments studied. As crop water stress increased, leaf area index (LAI), dry matter, plant height, numbers of leaves per plant, ear length, ear yield, number of kernels per ear, number of ears per plant, grain yield per plant and number of kernels per plant decreased. In this study, the yield reduction threshold CWSI values were determined using the infrared thermometer (IRT) and porometer readings. These threshold values of crop water stress index for IRT and porometer were 0. 19 and 0.26, respectively. As crop water stress increased, rooting was observed in the deeper soil profile. It was found that roots of maize concentrated in the first 40 cm soil profile. Effective root depth for maize was determined as 100 cm. It was observed that CERES-Maize growth model was sensitive to the irrigation water use efficiency and at soil water contents of field capacity and the permanent wilting point. But the model did not exactly estimate the yield and the yield components obtained from some irrigation treatments.