Study On The Characteristics About The Transport Of Water And Nitrogen And Influential Factors Of Bubbled-Root Irrigation

To improve the water and fertilizer utilization efficiency under water and fertilizer integration of bubbled-root irrigation. In this paper, the soil bulk density, soil initial moisture content, the concentration of fertilizer solution and the level of emitter spacing were established,and the simulation experiment of water and fertilizer infiltration was carried out with the soil box. The effects of various factors on the infiltration capacity, wetting front migration, soil moisture,ammonium nitrogen and nitrate nitrogen were investigated. The main research results are as follows:(1) The cumulative infiltration of fertilizer solution concentration, initial moisture content,soil bulk density and emitter spacing under the condition of bubbled-root irrigation fertilizer infiltration is consistent with Kostiakov infiltration model. A mathematical model is established,which is based on the cumulative infiltration as the dependent variable. With decreasing of soil bulk density, initial moisture content, and the increase of the fertilizer concentration, the cumulative infiltration amount is gradually increased. Under the condition of one-way irrigation,the cumulative infiltration amount is smaller than that of free infiltration. Moreover, the smaller the emitter spacing, the smaller the cumulative infiltration amount.(2) Under the condition of fertilizer concentration, initial water content and soil bulk density,there is a significant power function relationship between the infiltration distance and infiltration time. Wetting front migration prediction model is established by taking the migration distance of the wetting front as the dependent variable, the infiltration time and the influencing factors as independent variables,and after verification, the model has high reliability.The same infiltration condition, the anisotropic wetting front distance is accompanied by a decrease in soil bulk density,increases the initial soil water content and fertilizer concentration and showed a gradual increase trend. With the increase of the spacing of the emitter, the vertical distance of the wetting front in the position of the emitter is gradually reduced, which is greater than that under the same conditions. The wetting distance at the interface is reduced with the increase of the emitter spacing.At the end of the irrigation, the smaller the soil bulk density, the higher the soil initial water content and the concentration of fertilizer, the greater the corresponding soil moisture content at the same node at the end of irrigation. With the redistribution, wetting body becomes larger and the moisture distribution is much more uniform.(3) The distribution of ammonium nitrogen and nitrate nitrogen in the moisturizing infiltration of moisturizing fertilizer is affected by fertilizer concentration, initial water content,soil bulk density, emitter spacing and time and space. Based on the characteristics of ammonium nitrogen, and then the distribution stage end of irrigation, ammonium nitrogen distribution mainly concentrated in the soil near the emitter outlet.For nitrate nitrogen,it is not easy to be moved by soil, which is similar to water in wet body. At the end of irrigation, the contents of ammonium nitrogen and nitrate in the same node at the same end of the wet body showed an increasing phenomenon with the decrease of soil bulk density and the increase of fertilizer concentration. The average, change and rate of change of ammonium nitrogen and nitrate nitrogen in the wet body also showed similar trends. With the decrease of soil bulk density and the increase of fertilizer concentration, the initial water content of soil increased, and the distribution area of nitrate nitrogen in wetting body increased. The contents of ammonium nitrogen and nitrate nitrogen in the same node at the interface of wetting are increased with the decrease of the distance between the emitter. The average fraction of nitrate nitrogen in moisturizing body is within 3 days of redistribution, and the average value does not change, and the distribution range became more uniform. Redistribution for 5 days until the redistribution is carried out for 20 days, and the content of ammonium nitrogen in the wetted body decreased greatly. The content of ammonium nitrogen in the wetted body is close to the soil background value, which is about 20 days. At the beginning of the redistribution of 5 days, the nitrate nitrogen mass fraction increased significantly until the redistribution of 15 days, and the content of nitrate nitrogen in wet body reached the maximum value. At the beginning of the redistribution of 20 days, the nitrate content is lower than that of the redistribution of 15 days, the closer to the soil surface, the slower the decrease of nitrate nitrogen.(4) On the basis of Hydrus-3D software, this paper simulated the water infiltration characteristics under the condition of bubbled-root irrigation, and compared the simulation results with the measured values. The results show that Hydrus-3D software can simulate the soil water infiltration characteristics of bubbled-root irrigation.