Characteristics Of Salt And Water Movement And Numerical Simulation In Greenhouse Soil Under Different Irrigation Frequencies

The secondary salinization had become bottleneck of agricultural sustainable development in china. One of solutions to reduce secondary salinization was searching suitable irrigation frequency.One-dimensional soil column and two-dimensional soil box tests were studied to explore effect of different irrigation frequencies on movement of moisture and saltand characteristics of major saltions in greenhouse soil under one-dimension and two-dimension condition.In order to provide theoretical basis for effective prevention of greenhouse soil, HYDRUS-1D model was applied to simulate the dynamic of moisture and salt under different irrigation. The main results were as following:(1)Changes of soil moisture in profile under different irrigation was mainly in 0-20cm soil layer in one dimension.30 cm and 40 cm layer were the transition layerof soil moisture. Improving irrigation frequency could increase soil moisture of top soil layer to 36%. The 5d/time treatment was not conductive to moisture storage. Leaching of major salt ions under 5d/time treatment was better than others, but its mass center depth was 23.71cm which could cause rising of salt. Except Na+,the leach rate of Ca2+, NO3- and SO42- under 5d/time was better than other treatments, and which of NO3-reached 65.68%.(2) Changes of soil moisture intwo dimensionunder different irrigation were mainly concentrated in irrigation area as the center, radius area within 40 cm. The soil moistrue of top soil layer under 5d/time treatment was higher than others with 27%, however moisture of soil profile under 5d/time treatment was relatively low. Improving irrigation frequency could expand the range of desalination in horizontal and vertical direction. It was showed that preferential flow easily appeared in 20-30cm from irrigation area. The leach rate of Na+and SO42- under high5d/time treatment was higher than 15d/time treatment. The leach rate of Ca2+, NO3- showed opposite rule.(3) The soil moisture of different depth simulated by HYDRUS-1D modelwere in good agreement with the measured value, but the simulated value of soil moisturewas higher than measured value. RMSEwas 0.0176cm3/cm3,0.0174cm3/cm3 and 0.0172cm3/cm3 for 5d/time, lOd/time and 15d/time treatment respctively. Soil salt simulated value and measured value showed that saltsimulated valuewas relatively close to the measured value in soil 20-40 cm layer,but soil salt simulated value and measured valuewere biasedin 0-20 cm and 40-50 cm soil layer.RMSEwas 0.239g/kg, 0.169g/kg and 0.093g/kg for 5d/time, lOd/time and 15d/time treatment respctively. The RMSEbetween simulated value and measured value under different irrigation frequencies were low. HYDRUS-1D model could describe the distribution of soil water and salt under different irrigation frequencies.