The Study Of The Effect Derived From Re-watering’s Movement On Nitrogen In Horizontal Earth Column

Agricultural irrigation in all aspects of research, especially water movement has matured, meanwhile lots of research on the aspect of nutrient migration law has been carried out. But the research on the nutrient migration law and re-watering nutrient migration law in the two different conditions of precipitation time and precipitation volume after irrigation is imperfect is just located at the very beginning stage. Therefore, the research on the water and nitrogen migration law; in condition of different water application and different re-watering; possesses theoretical and practical significance.In this thesis, the method of laboratory experiments combining with theoretical analysis is adopted. The laboratory experiments carries out from3different aspects:different bulk density (1.3g/cm3,1.4g/cm3,1.5g/cm3), different irrigation volume (1.8L,2.6L,3.4L), different re-watering volume (0.3L,0.6L,0.9L,1.2L) and different re-watering time (1day after irrigation,3days after irrigation,5days after irrigation,7days after irrigation).And on the basis of the results from these experiments, some conclusions of distribution law of water and nitrogen under different effects are drawn. (1) In the earth column experiments, along with the increase of soil bulk density, the infiltration rate decreases, and finally stabilizes.(2) Under the conditions of different bulk density, the trends of soil moisture distribution are almost same. In the front of the wet body, the moisture content is relative higher than the other parts of it. Along with the increase of distance, the moist content decreases gradually. And at the edge of the wet body, the moist content decreases more rapidly along with the increase of distance.(3) Along with the increase of soil bulk density, nitrate nitrogen accumulation decreases in the tail of the wetting front. As time passes by, the content of nitrate nitrogen increases gradually along with the increase of soil column depth, and the nitrate nitrogen content increases rapidly at the end of wetting front.(4) With the different soil bulk density, the content of ammonium nitrogen in the earth column quickly decreases with depth increase. And at the front of the wet body, this content increases with the increase of soil bulk density. Otherwise in the middle of the wet body, this content decreases with the increase of soil bulk density. Finally, in the end of wet body the change trends of this content is accorded with that of soil bulk density.(5) After re-watering, the moisture content distribution trend remains unchanged, but the moisture content of the whole earth column increases, meanwhile in the rear of the wet body, the greater the re-water volume is, the greater the moisture content is. (6) After the different volume of irrigation, in the same time and same depth of different earth column, the ammonium nitrogen content increases along with the increase of irrigation volume. In the different time after the same irrigation volume, the general distribution trend of ammonium nitrogen content in the earth column is that following the increase of depth, the nitrogen decrease occurs. Along with the time elapse after the irrigation, ammonium nitrogen migrates to deeper place in earth columns and its migration speed is slower than that of water in the same earth column. The longer the time interval between irrigation and re-watering is, and the more volume of re-watering is applied, the greater effect on the ammonium nitrogen content distribution is shown. Accompanied by the time elapse after re-watering, in the same depth of different earth column, the ammonium nitrogen content accumulates gradually at the rear of wet body.(7) Under the situation of different volume of re-watering, the occurrence of the phenomenon of the ammonium nitrogen content decrease at the front-end of wet body is accompanied by the volume increase of re-watering. In the same time, in the middle and rear section of the wet body, the ammonium nitrogen content increases along with the volume increase of re-watering. At the edge of the wetting front, the nitrate nitrogen concentration increases along with the increase volume of re-watering.As the re-watering time goes by, great amount of nitrate nitrogen migrate to the more deeper position in the earth column accompanied by water.