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Xingjiang is area with a characteristic of "drought oasis, irrigated agriculture Automatic drip irrigation can significantly improve water use efficiency, crop quality and increase the farmers’ income.In order to exert the advantages of the automatic drip irrigation system, it’s a important task to research the rule of soil moisture content change and forecast soil moisture. Therefore this paper researched on the rules of soil moisture content variation under automatic drip irrigation cotton filed and forecast soil moisture.This paper used soil moisture content data from cotton filed with automatic drip irrigation system National Agriculture Science and Technology Park in Shihezi Xinjiang between2009 & 2010, analyzed the law of soil moisture variation, and the craft of soil moisture content of cotton to carry on the summary, established the law of soil subsidize coefficient and cotton birth time coefficient between fitting relationship, and through the fitting relationship established based on subsidize coefficient method of soil moisture forecast model, and through the field measured data, the model test, get the following conclusions:(1) in vertical direction, soil moisture content in cotton birth period over time and indented change; From the soil moisture content changes with time perspective, acuteness degree of soil is divided into three layers, the lost-voice layer (0-20cm), active layer (20cm-60cm) and relatively stable layer (60cm-100cm); Moisture content increased with depth variations, namely the relationship will decrease the biggest change surface soils,80-100cm at present the minimum; soil changes The change in seedling stage of soil moisture in cotton, relatively stable bolls changes in the cotton flower intensifies, the biggest change in the period of the lower, the moisture changes during the cotton reduced gradually.(2) in horizontal direction, from the different distances from the dropper, with different positions for the size of soil moisture content is different in different depth 20cm; at 0-20cm is cotton lines> ditch> middle membrane; 20-40cm is cotton lines> ditch> middle membrane; 40-60cm ditch> cotton lines> middle membrane; 60-80cm middle membrane> ditch> cotton lines:80-100cm is middle membrane> cotton lines> ditch.(3) 2009 and 2010 average moisture content is consistent with the change of time, are slow fade in seedling changes, cotton bolls and spend the bell period of dramatic changes of soil moisture in cotton, the change is lower period moisture content decreased gradually; And two years of moisture content change also has difference, such as the change of soil moisture in 2010 in time axis is the 2009 back after a week results, and on June 25th 2009 before the moisture content is greater than 2010 after 2010, the water due to the larger than soil moisture content, so its soil-moisture content in 2009 is higher, variation amplitude is bigger also.(4) Through the formula K=(lnw1-lnw2)/(t2-t1) established in midst of Nol cotton filed.,2009 the soil moisture content, and to subsidize retreat coefficient on the depth of the coefficient of variation analysis, it is concluded that the direction of soil moisture subsidize coefficient increases with the decrease of the soil depth, and the inverse relation in 0-20cm soil retreat coefficient variation amplitude is the largest, the variation from 0.1 to 0.27, overall 80-100cm layer soil subsidize coefficients were below 0.1.(5) On soil moisture content and cotton on the relationship between birth time coefficient fitting, (0-100cm) fitting of the soil for:formula LnK=14.867 x2+-16.216 x-7.9426, its R2at 0.8184, with better fitting relationship.(6) Combined with subsidise coefficient of soil moisture balance equation in 2009 and 2010,2 # 0 within the field on the soil moisture content 100cm at present, the results show that the prediction respectively relative error range 12.81% and veracity-11.14%0.18%.Its show that this method can forcast soil-moisture well.
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