Experimental Investigation On Water And Nitrogen Migrations Under Multi Water Storage Pit Irrigation

China is a water-deficient country, especially in the north hillock regions. Drought and soil erosion problems are more serious in these areas. Aiming at these problems, Professor Sun Xihuan proposes a new irrigation method water storage pit irrigation. It is mainly applied to the orchard irrigation. Its biggest advantage is to get water-saving irrigation and water conservation organically together. Proved by tests, it has good water retention, water and soil conservation effect. After more than10years of research, the method has been successfully to the field from the indoor simulation test. It has made some achievements in evaporation and infiltration, but at the initial stage in nutrient distribution and migration. And multi water storage pit irrigation is closer to the actual condition of the field. Therefore, the research is particularly important that the distribution and transport characteristics of water and nitrogen in soil under the condition of multi water storage pit irrigation.In this paper, based on the indoor simulation test, combined with the solute transport and soil water dynamics theory, the test data are analyzed, in order to explore the water and nitrogen distribution and migration rule in soil under multi water storage pit irrigation. The experiment design of three factors three levels on soil water and nitrogen transport effects, respectively is the soil bulk density (1.3,1.4,1.47g/cm3), fertilizer solution concentration (700,900,11OOmg/L), irrigation amount (9,11,13L). The main conclusions are as follows:(1) Under the condition of multi water storage pit infiltration, it’s free infiltration before water at the baffle (zero flux plane). At the beginning, wetting front radial advance distance is greater than the vertical distance. After a period of time, the vertical advance distance under the common action of matrix potential and gravitational potential is greater than the radial distance of only matrix potential role. The shape of the wetting pattern is irregular ellipsoid with the storage pit axle at the center. After the moisture migrating to the baffle, water infiltration gets into the intersection of infiltration, with the vertical advance beginning, at the end of the distribution tending to be uniform. Soil moisture distribution in the vertical direction is high in the middle, low on both sides, and in the30cm-60cm depth water content reaches its peak; with the radial distance increasing in radial distribution, moisture content decreases gradually.(2) In moist soil, the smaller the bulk density, the wetting front advances farther; reaching a certain cumulative infiltration volume requires shorter time, cumulative infiltration volume curve is steeper, the infiltration rate is higher; the smaller the bulk density, water content is more little, so the water easily go to a more distant migration. Fertilizer solution concentration is greater, wetting front advances farther; on cumulative infiltration volume and infiltration rate of the impact is not great; the moisture content influence is not big. Different irrigation amount in free infiltration stage, wetting front, cumulative infiltration and infiltration rate is basically the same; the greater the amount of irrigation, water content is larger.(3) Nitrate nitrogen with negative charge is less susceptible to soil colloid adsorption, keeping consistent with moisture migration in soil. Convection is mechanism of nitrate solute transport. Under the condition of multi pit, nitrate nitrogen in soil of vertical distribution is low content of middle, upper and lower content of high. The vertical distance20-80cm of nitrate nitrogen content are smaller than the background values, while5cm and85cm are high; in the radial direction, before35cm, nitrate nitrogen content change not quite, to the45cm baffle suddenly increase. Nitrate nitrogen accumulates in the moist boundary formation, in the baffle at the cumulative maximum. Ammonium nitrogen with positive charge, is easily adsorbed by soil colloid. Therefore the ammonium nitrogen lags in water transport. Diffusion is mechanism of ammonium nitrogen solute transport. Ammonium nitrogen vertical distribution presents the content increases first and then decreases, but still higher than the background value; ammonium nitrogen declines on the whole with radial distance increasing, but still higher than the background value, only smaller than the background value at the baffle45cm. (4) The larger the bulk density, the content of nitrate nitrogen is lower and ammonium nitrogen higher, because of the charge they took and soil colloid particles adsorption on. Fertilizer solution concentration higher, nitrate content is higher, and ammonium nitrogen content is greater, too. This is mainly because of the different content of irrigation nitrogen. The greater the water amount, nitrate nitrogen content is smaller, and ammonium nitrogen content is higher. The excess irrigation amount has caused the general assembly of nitrate nitrogen, while ammonium nitrogen is easily adsorbed by soil colloid particles and accumulated without the moisture migration.(5) Comparing the changes in water content chart, nitrate nitrogen and ammonium nitrogen content variation diagram in different radial r=30cm and r=40cm,It’s obvious that due to the r=40cm is closer to the baffle, or simulated zero flux plane, the content of r=40cm tends to be more gentle. This is because after reached the baffle moisture will be redistributed, so the water in the soil box distributes more uniform. This reflects the baffle’s role, namely zero flux plane will make water distribution tends to be uniform, nitrate nitrogen and ammonium nitrogen also redistributes. That explains the multi water storage pit has better effect on water retention and fertilizer retention...