Experimental Study On The Optimum Point And Suitable Control Limit Of Soil Moisture Of Rice

Rice is the most important crop in our country. In the increasingly serious water shortage situation, the main way to solve the problem of water shortage is changing the rice irrigation methods from the traditional full irrigation to non-sufficient irrigation. In the technology system of non-sufficient irrigation, the determinations of the optimum point and the suitable limit of soil moisture of rice can provide a theoretical basis to moisture control in water-saving irrigation, and also have important practical significance by developing a water-saving irrigation system of rice.By analyzing the observational data achieved during the field test at the irrigation and water conservancy Experiment Station in Huaiyin District of Huaian, the optimum point and the suitable limit of soil moisture of rice under the conditions of water-saving irrigation were studied and achieved the following two outcomes:(1) The optimum point of soil moisture (optimum soil moisture) of early growth stage, growth medium and late growth stage of rice was determined as18.03%,15.78%and18.17%, accounting for about50%of saturated soil moisture (respectively accounting for53.32%,46.67%and53.72%of saturated soil moisture). Under the condition of the transpiration of each growth stage is not less than80%of the corresponding period’s maximum transpiration, the following results were obtained: the upper limit of soil moisture of each growth stage for rice irrigation separately were24.64%,18.83%and22.42%;the lower limit of soil moisture of each growth stage for rice irrigation separately were11.57%,12.43%and13.98%;the corresponding irrigation quota of each growth stage were48.8m3/mu,23.9m3/mu and31.5m3/mu。(2) In the case of the affection on crop output was less than5%of each growth stage, the suitable limit of soil moisture of rice was determined. The suitable limit of soil moisture of early growth stage, growth medium and late growth stage of rice respectively were41.6%-55.9%,40.5%-54.4%and45.7%-55.0%of saturated soil moisture. The optimum point of each growth stage was just about at the mid-point of the suitable limit of soil moisture.