LOW COST PVC HYDRAULIC WEIGHING LYSIMETER FOR MEASUREMENT OF CROP EVAPOTRANSPIRATION

Abstract

Lysimeters are used for measurement of crop evapotranspiration (ETc), 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 ETc, 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 (ETo) was computed using the FAO Penman-Monteith method. Crop coefficients (Kc) were estimated at different growth stages of chili crop, using the lysimeter measured actual ET and the estimated ETo. The Kc 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 ETc measured through manometric deflection of the hydraulic weighing lysimeter, with that of measured ETc 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.