Study On Soil Moisture Content Forecasting Of Drip Irrigation Cotton Field

【Objective】Using statistical analysis method, by monitoring soil moisture of cotton field and contrasting reference value of the optimum soil field capacity to determine soil moisture change rules and optimum monitor location of soil moisture and to establish the forecast model of soil moisture and to provide a scientific basis for making the optimized irrigation scheduling and realizing precision irrigation and automatic irrigation.【Methods】The field experiments of three irrigation levels(220m3/667m2,260 m3/667m2,300 m3/667m2) were been set up. The first time of irrigation was in June 20 and an irrigation cycle was eight days. By collecting soil samples of three soil layers(0-20 cm, 20-40 cm and 40-60cm) in perpendicular to the drip irrigation belt0 cm, 10 cm and 20 cmevery ten days and using drying method to measure soil mass water content to study soil moisture change rules during the growth period of cotton; using CPN503 DRneutron probe to monitor soil volumetric water content and t-Verify method to determine the optimum monitor location of soil moisture; after the first time irrigation and raining every time, to monitor soil moisture of 30 cm in perpendicular to the drip irrigation belt and of 50 cm between two cotton, to calculate the soil regression coefficient K and establish the forecast model of soil moisture; by observe the agronomic traits and yield to determine the effect of the irrigation volume on the agronomic traits and yield of cotton.【Results】1. The soil moisture was increase first, then decrease with the soil depth increase in range of 0-120 cm. In the vertical direction, soil moisture of 0-20 cm was radical changes and.that of 60-120 cm was relative stable. In horizontal direction, from the middle to the edge of membrane, soil moisture of 0-20 cm soil layer and 20-60 cm soil layer were decrease and increase respectively. Soil moisture of 60-120 cm soil layer did not obviously change. Before and after irrigation, soil moisture inside membrane that was perpendicular to drip irrigation belt20-30 cm changed greatly. 2. For planting patterns 20cm+40cm+20cm+65cm, 30 cm from the water dropper no matter in horizontal or in vertical direction was the best monitor point. 3. Calculate and verify the soil regression coefficient K was calculated and verified. The forecast model of soil moisture was established.【conclusions】1. For planting patterns 20cm+40cm+20cm+65cm, it has good effect that the neutron probe to monitor soil moisture was installed in 30 cm from the water dropper no matter in horizontal or in vertical direction. 2. The soil regression coefficient K is calculated. The soil moisture is decrease in growth period of cotton. Furthermore, decreasing range of soil moisture is unceasingly increase. 3. After irrigation, soil moisture shows a phenomenon of periodic fluctuation somewhat and its periodicity is coincide with irrigation frequency. Because water requirement of cotton reduces after boll opening period, the fluctuation of soil moisture becomes slow.