Establishment of new Criteria for Irrigation Scheduling

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Recentry, it has been proposed that irrigation scheduling should be done based on the moisture condition in the plant instead of the soil moisture condition. A purpose of this study is to establish new criteria for irrigation scheduling. The results obtained ate shown as follows :(1) Index of the leaf temperatureThe leaf-air temperature difference is recommended as a simple index for irrigation scheduling as the results obtained from the experiments in the different places that leaf temperature decreases with increased evaporativity and with high soil moisture.(2) Index of the evapotranspirationA new method to estimate evapotranspiration as functions of solar radiation, mean air temperature and mean wind velocity using the data of leaf temperature is proposed. It was recognized that the relation between the Penman's potential evapotranspiration and the estimated values by the proposed method was linearly correlated with high correlation coefficient of 0.98.(3) Index of the moisture in the soil and plantAs the results of simulation and experiment, the typical variations of solar radiation, leaf temperature, leaf water potential, stomata resistance, matric potential, osmotic potential and transpiration rate with time were obtained with plant water stress under the different irrigation conditions.