Studies On Measurement Principle And Design Method Of New Electric Weighing Lysimeters

Studies on water balance in farmlands and water flow in soil-plant-atmospheric continuum lay a solid basis for highly efficient agricultural water use. Of all components of water balance in farmlands, evapotranspiration, capillary rise from a water table and deep percolation are difficult to determine. It is significant to measure precisely these components for quantifying soil water balance and evaluation water resources.The thesis described the measurement principle and design of new electric weighing lysimeters. According to operating patterns of weighing sensors, the new lysimeters were classified into two categories: fixed weighing lysimeter and suspended weighing lysimeter. With tensile sensors or manometric sensors, the lysimeters converted soil mass into electric signals and stored the signals in data acquisition system, resulting in a high precision. The lysimeters overcame the problems of current lysimeters which need artificial complicated calculations. The fixed lysimeters were cylindrical with a surface of 1.6 m2, a depth of 1.265 m, and an accuracy of 35 g (equivalent to 0.022 mm water depth). The suspended lysimeters were cubic with a surface of 0.4 m2, a depth of 0.8 m, and an accuracy of 20 g (equivalent to 0.05 mm water depth). The lysimeters used outer containers to separate it from the surrounding soil mass, decreased the disturbance of the soil in the field. The lysimeters were low-cost and convenient for maintenance.The lysimeters will play an important role in studies of water movement in soil-plant-atmospheric continnum, laying out reasonable irrigation schedule, saving agricultural water, and creating favorable environment for crop growth. The lysimeters provide technical support and service for evapotranspiration and crop water use investigation in China.