LOW COST PVC HYDRAULIC WEIGHING LYSIMETER FOR MEASUREMENT OF CROP EVAPOTRANSPIRATION

Lysimeters are used for measurement of crop evapotranspiration (ET_c), which in turn is used for effective crop water management. Though weighing type lysimeters with sophisticated electronic or mechanical weighing systems are the best devices for measurement of ET_c, they are quite expensive. Therefore, a study was undertaken at the Indian Institute of Technology Kharagpur to develop a low cost weighing type lysimeter. The developed lysimeter consisted of a circular PVC (Polyvinyl Chloride) tank of 1 m diameter and 0.60 m height and an insulated heliflex PVC pipe of 10 cm diameter, serving as the load cell. Two adjacent holes were made on this pipe, which were fitted with two tubes; one was connected to a manometer and the other was used to fill the heliflex pipe with water. The lysimeter was used to determine the crop coefficients of a chili crop (Capsicum annuum L). Daily reference evapotranspiration (ET_o) was computed using the FAO Penman-Monteith method. Crop coefficients (K_c) were estimated at different growth stages of chili crop, using the lysimeter measured actual ET and the estimated ET_o. The K_c values for initial, crop development and reproductive stages were found to be 0.41, 0.72 and 0.78 respectively. The performance of the lysimeter was evaluated by comparing the ET_c measured through manometric deflection of the hydraulic weighing lysimeter, with that of measured ET_c using soil moisture data recorded by neutron probe. The regression analysis between the two methods of measurement of crop evapotranspiration gave a correlation coefficient of 0.93, indicating potential for the low cost PVC hydraulic weighing lysimeter’s use in the developing and under developed countries. The sensitivity of the lysimeter for 5° manometer angle was found to be 0.45 mm of water.