The Instrument Developed To Measure Reference Crop Evapotranspiration And Applied In Irrigation Forecast

The present measuring and computing methods of crop water requirements have lots of defects when were applied to Chinese peasants, such as a high cost of instruments, a trouble maintenance, a complicate calculating formula, or required parameters are plethora and difficult acquirement. Therefore, it is difficult in applying to agricultural irrigation for the peasants in China who are generally at a low level of economy and culture. A simple instrument for measuring crop evapotranspiration is developed by the technology of biological membrane, according to the definition of reference crop evapotranspiration(ET0), the evaporation mechanism of soil and the transpiration mechanism of plant. The instrument can simulate the physical procedure of soil evaporation and plant transpiration when the moisture in soil is adequate.The instrument is a physical simulating model of vegetation transpiration. The water in the instrument enter the stuff in the vessel through the ports in the vessel, then uplift to the surface of the stuff by the capillary force. This delivery process simulates moisture from soil to leaves through roots, stems. Then the moisture of the stuff surface evaporate into the space between the stuff and biological membrane, disperse to the atmosphere subsequently through the pores in the film. This delivery process simulates the transpiration of air pores in the leaves. That is moisture turn into vapour on the surface of diachyma cells around substomatic chambers or in the intercellular space, and then diffuse to the atmosphere through substomatic chambers and air holes.The instrument is developed according to the evaporation mechanism of soil and the transpiration mechanism of plant, and so it can simulate the physical procedure of soil evaporation of stable phase and plant transpiration supplied water adequately. The instrument can measure reference crop evapotranspiration for the water in instrument goes up to the surface of the stuff by the capillary force to supply evaporate last and fully. The evaporation intensity of the instrument is determined only by the meteorological conditions, and it is indifferent to the water level of the instrument. Therefore, the principle of the instrument conforms to the definition of reference crop evapotranspiration, that is water feed sufficiently and evapotranspiration intensity is relative only to the meteorological conditions. The relationship between the variation of water level and ET0 is linear, so the ET0 could be computed directly by the variation of water level.Field tests ware executed to verify the performances of the instrument at the period of winter wheat and summer corn. The testing data were analysed by two methods. The first is specific value flexure method, that is the quotient of the water table variation and ET0 was studied by day serial. The second method is accumulating flexure method, that is daily water table variation and ET0 were added day by day, and then the relationship between the two cumulative values was studied. The specific value flexures certify that the water table variation in the instrument is indifferent to its water table. The accumulating flexures testify that the relationship between the variation of water level and ET0 is linear, which is simple multiple relation. The relative coefficients are close to one. The instrument applied in practice proofed that the instrument can guide peasants when and how much to irrigate. The precision of the instrument can satisfy the requirement of irrigation prediction.The instrument can be operated and maintained simply. Peasants can afford to buy the instrument easily. Therefore, The instrument will have some prospect in market place.