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| DOI：10.13522/j.cnki.ggps.2020089 |
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| The Effects of Water Pressure in Moist-tube and Nitrogen Application on Movement of Water and Nitrogen in Soil |
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GUO Hanxiao, SHEN Lixia*, FAN Yao, NIU Shuang, YANG Mei, SUN Xuelan, LIU Ronghao
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College of Water Resources Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
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| Abstract: |
| 【Background】Moist-tube irrigation is a new technology to deliver water and fertilizer to the root zone through a semipermeable membrane tube continuously from a line source. The movement of water and nitrogen in soil is a parameter for designing the micro-tube irrigation systems but is poorly studied.【Objective】 The purpose of this paper is to bridge this gap. We experimentally investigated the movement and distribution of water and urea in soil under moist-tube irrigation operated under different water pressures.【Method】The experiment was conducted in a laboratory, and we compared two water pressures: 1.0 m and 1.5 m, and three urea concentrations: 0, 500 and 1 000 mg/L. Overall, we had six treatments. In each treatment, we measured the cumulative infiltration and advancing distance of the wetting fronts. After 132 h of onset of the experiment, we measured the distribution of soil moisture, ammonium and nitrate contents in the wetted soil, which were used to analyze the impact of the water pressure and the urea concentration.【Result】Adding urea impeded water outflow from the moist-tube and the cumulative infiltration in all treatments increased linearly with time. Among all treatments, the maximum accumulated infiltration at the end of the experiment was 10.55 L, achieved when the pressure head and 1.5 m in the absence of urea addition. Increasing urea concentration coupled with a decrease in water pressure slowed down the advance of the wetting fronts. Compared with the water pressure 1 m, the water pressure 1.5 m increased soil moisture, ammonium and nitrate content in the soil. The peak of ammonium content in the soil changed with time and treatments. After 132 h of infiltration at water pressure 1.0 m, the ammonium and nitrate contents in soil under addition of urea at 100 mg/L concentration were lower than that under 500 mg/L concentration, while when the water pressure increased to1.5 m, the ammonium and nitrate contents in soil under 1 000 mg/L concentration were higher than that under 500 mg/L concentration. 【Conclusion】 Increasing water pressure increased significantly water infiltration rate, advance of the wetting front, soil moisture, and ammonium and nitrate contents in the soil, but the increase depended on the urea concentration. Increasing fertilizer concentration above a critical value could reduce decomposition and transformation of the urea in soil. |
| Key words: moist-tube irrigation; liquid concentration of urea fertilizer; pressure head; cumulative infiltration; soil moisture content; ammonium nitrogen; nitrate nitrogen |
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