| Drip irrigation under mulch is a advanced technique combined by the trickle irrigation technique and the polyethylene film planting technique, which have the advantages of saving water, enhancing yields, upgrading quality and high utility. Compared with conventional irrigation and cultivation mode, the soil moisture and thermal environment, water requirement pattern are changed by drip irrigation under mulch. The field experiment study for cotton and corn was conducted in Xiaobakou Irrigation Experiment Station in Minqin country, Gansu province. The main results are as follows:(1) Applying the theory of soil-water flow system in ground water, the mechanism of water-saving and product-enhancing for drip irrigation under mulch were analysised. It was found: 1 )The film restrained evaporation surface intensity and had obvious function of rising and keeping moisture, 2)The drip irrigation could supply water according to growing requirement and augment of water conflux intensity around crop root, it also had strongly controllable operation and wasted fewer water.(2) The distinction of soil-water flow system and benefits of water-saving and product-enhancing for different planting pattern were analysised. "1 pipe irrigation 3 lines of crop" was better than "1 pipe irrigation 4 lines of crop" in WUE, yields and elements of product for better water environment. In the most ration of water supplying, yield of crop was enhanced when irrigation ration was increased no matter what planting pattern was applied.(3) Compared with bare soil, income of net radiation declined, apparent heat weakened and latent heat exchange were almost disappeared on the soil surface with film. Soil temperature decreases with depth increasing. The upper layer soil temperature rapidly rise or fell, while the under layer soil temperature slowly changed. The temperature daily variation could be characterized by three measurements at 8:00,14:00 and 20:00,which separately represents the lowest temperature, the highest temperature and the midst temperature. The highest temperature, the maximum temperature fluctuation, and temperature in the every time of day in the upper layer soil all occurred under the middle of the mulch, which was followed in turn by the side and clearance of the mulch. For different soil depths, the amplitude of temperature daily variation can be approximated asan exponential function of the depth; which correlation coefficient is above 0.90.(4) In 2001, the average daily ET of cotton in the whole growth season is 1.75mm/d, the total ET is 307.48mm,and the average crop coefficient (kc) is 0.39 under deficient irrigation . In 2002, the average daily ET of cotton in whole growth season is 1.94mm,the total ET is 337.04mm,and the average crop coefficient (kc) is 0.43 under sufficient irrigation.(5) The synthetic draft curve was conducted by crop coefficient and relative soil moisture. The correlation in crop coefficient and relative water content takes on uniform trend comparing to the soil water deficient degree. In the whole growth season of cotton, the high correlation coefficient occurred in the period of seeding, which was declined in the period of blooming and flowering, whereas it was raised in the late period of cotton. The relationship established between Kc and meteorological data indicated that crop coefficient (Kc) increases as wind speed increases, or net radiation or relative humidity declines.
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