DESIGN, CONSTRUCTION AND TESTING OF A LYSIMETER FOR A STUDY OF EVAPOTRANSPIRATION OF DIFFERENT CROPS

This paper describes the design and construction of a set of lysimeter s, consisting of four field tanks. each with one cubic meter effective volume. The field tanks are made of a galvanized sheet. Water supply and drainage collection, control and measurement works are in a separa te access chamber of size 2.4 x 1.9 X 3 m. The lysimeter has two modes of use. In the first mode, irrigation water is supplied to the soil s urface. In the other mode, water is supplied to the soil surface. In t he other mode, water is supplied from the bottom part at any desired d epth. A mariotte principle is used to maintain a constant supply head at this depth. The water supply tank and constant head supply cylinder need refilling every 10 days or so. The cost of construction approxim ated to US$ 2270. The design may be useful in other countries. The lys imeter was tested by experimenting with lentil crop (Lens culinaris). The performance was found satisfactory. Due to unusually high rainfall during 23-26 days after emergence, the crop suffered from stunted gro wth. The highest water use index of the crop was found to be 5.13 kg/h a mm in the tank which was irrigated at 21 days' interval. Total water required for this treatment was 180 mm for 98 days after emergence.