Water Balance Analysis and Development of Crop Coefficients for Drip Irrigated Greenhouse Chile Pepper.

Limited water supplies in arid regions are putting constraint on agriculture. To sustain agriculture in arid regions, efficient irrigation scheduling must be implemented. For proper irrigation scheduling, accurate, point and continuous measurements are necessary using nondestructive sensors. However, soil and site specific calibration of sensors are required. The objectives of this study were to: (1) calibrate two capacitance sensors, hydra probes and 5TM, and one TDR CS616 sensor in a greenhouse study; (2) compute water balance for drip irrigated chile pepper; and (3) develop crop coefficients for the growing seasons of 2011 and 2013. Three water treatments were (1) control where water was applied at the surface using two drip emitters, (2) partial rootzone drying vertical (PRDv) where subsurface irrigation was applied at 20 cm depth, and (3) partial rootzone drying compartment (PRDc) where roots were divided into two compartments and irrigation was applied to one of the compartments on an alternate day cycle for 15 days. Sensor generated volumetric water contents were correlated with the gravimetrically determined volumetric water content and new coefficients were developed for each sensor using a nonlinear optimization program. Site specific calibration equations improved the precision of water content estimates more than manufacturer’s equation indicating that sensors must be calibrated prior to use for determining soil water balance and scheduling irrigation. The crop ET values calculated from water balance were used to develop crop coefficients for drip irrigated greenhouse chile pepper for both years and  were also related to the growing degree days. The maximum values of crop coefficients were about 1.4 from control and PRDv treatments during 2013. The 2011 growing season was shorter and maximum crop coefficients were closer to one. Crop coefficients can be used to schedule irrigation and reduce water loss in water-limited areas.