Comparing Different Methods Of Calculating Crop Evapotranspiration & Study On Limited Irrigation Forecasting

Water scarcity is seriously constricting the continuing development of agriculture, thereare amplitude areas of arid and semi-arid in our country, and that limited irrigation can guidethe way of water allocating during crop growing stages and different crops in those areas. Thispaper will study on this and forecasting of irrigation under limited water supply.Considering of different meteorologic data in different regions, five methods(namelyPenman-Monteith method, Radiation method, Blaney-Griddle method, Penman method andHargraves method)of calculating reference Evapotranspiration (ET₀) proposed by FAO areused, and FAO Penman-Monteith method is raked as the criterion to revise other four methods,thus educing the revised formulae in studied region.The results show that among four revised formulae, three have linear relation withPenman-Monteith ET₀ result except Blaney-Griddle method has exponential relation withPenman-Monteith method. The revised Radiation method formula has the best resultcompared with Penman-Monteith formula, the average relative error is 3%, moreover,Hargaves method requiring the least data in calculating ET₀, so this method has the highactual application value; The following are penman method; The worst is the Blaney-Griddlemethod, the average relative error is 10%.Based on the different methods of calculating reference evapotranspiration, three kindsof main functions of forecasting system are accomplished, namely Calculating referenceevapotranspiration, Allocating limited water to crops and crop grow stages and Irrigationforecasting function. In designing stage, VB integrated design environment is used. Thewhole system has the characteristic of friendly interface, reasoned structure and simple way ofoperation.