| Water shortage and poor fertility are two key factors of limiting the agricultural development in the arid and semi-arid area. The limited supplement irrigation and the application of fertilizer are the important ways to improve the agricultural productivity and water use efficiency. Controlled alternate irrigation is a new method for saving water. Many researches showed less or no yields losses for controlled alternate irrigation when compared with traditional irrigation, but amount of irrigation water used was decreased by 30 % to 50 %. Research about how to apply fertilizer under this new irrigation method was fewer. Some studies pointed out alternate irrigation with fertilization in the un-irrigated furrow (AIFUF) was a better special coupling between irrigation water and fertilizer. To better understand the movement of water and nutrients under this irrigation model will be helpful for reasonable management of water and fertilizer in order to save water and fertilizer. This will play an important role in properly using agricultural resources, avoiding destroy environment and ecosystem, improving the sustainable development of arid agriculture. There are two parts in the paper. â…°) The micro-plot (with rainproof) experiments, summer maize as tested crop, was used to study the movement and the distribution of water and nutrients in the soil profile under AIFUF and the effect of mulching on the movement and distribution of water and nutrients; â…±) The indoor simulation experiments were used to analyze the percolation and horizontal diffusion of water and nutrients and the rule of water infiltration under the treatment of AIFUF. The main results were as followings: (1) The yield was significantly increased for alternate irrigation when compared with traditional irrigation under the same amount of irrigation water; less yields decreased or yields maintained for alternate irrigation but half of irrigation water was saved. At the same time, alternate irrigation greatly improved irrigation efficiency. Irrigation efficiency was related to the amount of irrigation water, the irrigation efficiency at low amount of irrigation was higher than that at high amount of irrigation. AIFUF increased the photosynthesis rate, transpiration rate and Pn/Tr at the same amount irrigation water. Also, AIFUF maintained maize root activity in the later stage and increased the uptake and accumulation of nitrogen at low irrigation water. The recovery of nitrogen fertilizer of AIFUF at low or moderate amount irrigation water increased by 92 % ~ 100 % when compared with traditional irrigation; however, at high amount irrigation water decreased by 22%. (2) The effect of AIFUF was related with the amount of irrigation water. At low and moderate amounts of irrigation water (<600 m3/hm2), there were great difference of water content and nutrient content between irrigation furrow and fertilization furrow; the effect of AIFUF on root activity, uptake of nutrients and control of metabolism was great and the effect of saving water was rather significant. When the amount of irrigation water is higher than 600 m3/hm2, the efficiency of alternate irrigation decreased. (3) Regardless of the amount of irrigation water,at the first time,there was great difference of water content and nutrients between irrigation furrow and fertilization furrow in the 0-60 cm profile under AIFUF, below the 60 cm profile the difference was small. At the second time, the water content difference decreased at topsoil layer (0-40 cm) at low amount irrigation water; at the low layer, there was great difference between irrigation furrow and fertilization furrow. At high amount irrigation water (600~900 m3/hm2), the difference between irrigation and fertilization decreased steadily even disappeared. As for the distribution of nitrate in the profile, there was a difference of nitrate content at 0-60 cm profile between irrigation and fertilization furrow at low amount of irrigation but it was smaller than that at high amount of irrigation. It was showed there was severe leaching occurred in the irrigation furrow at high amount of irrigation water. So it should be controlled of the amount of irrigation water under alternate irrigation, the optimal irrigation rate should be below 600 m3/hm2. (4) The accumulation of residual nitrate in the 0-100 cm profile under AIFUF was 40-50 kg/hm2 higher than the traditional irrigation after maize harvesting at different irrigation rate. The residual nitrate would be available fertilizer for the next winter wheat. Through the analyses of soil moisture, nitrate and ammonium spatial variance in the treatment of AIFUF, results showed the variance of the three index at low irrigation rate was smaller than those at high irrigation rate, i.e. the distribution of soil moisture, nitrate and ammonium at low irrigation rate was more even than high amount of irrigation water. (5)Preventing from the effect of rain by using a rainproof, straw and plastic-film mulching decreased the evaporation, and improved the fallow efficiency and increased the water storage in the 0-60 cm profile when applied fallow tillage. When grown corn, straw mulching increased the water storage, however, plastic-film mulching increased the expense of water. Both straw mulching and plastic-film improved the grain yield compared with no mulching. The effect of straw mulching on grain yield was not significant, but plastic-filmmulching increased the yield by 130 % and the water use efficiency was twice as much as no mulching. Different mulching materials had different effect on the distribution of water and nitrate in the profile. Compared with bare land, the nitrate content in the 0-20 cm layer after straw mulching reduced; but increased after plastic-film mulching. Compared to fallow, growing corn decreased significantly the nitrate content in the profile. (6) The results of simulation experiments showed, both the vertical movement and horizontal movement existed under AIFUF. The wetting fronts of two directions increased with time. The infiltration rate decreased with time according to the water content of soil tested and the environment temperature. We used polynomial function to model the dynamics change of wetting fronts, including vertical and horizontal direction. Through the function, we could estimated the maximum distance of vertical movement achieved was 78.0 cm at 20 h after irrigation, and the maximum distance of horizontal diffusion was 34.6 cm 19 h after irrigation. To some extent, it was benefit for the irrigation in field. As far as nutrients movement concerned, the movement of nutrients was mainly downward in irrigation area; these trend in fertilization area was slightly and the regime of movement was limited, only 10 cm approximately. So AIFUF could reduce the chance of fertilizer leaching in fertilization area. The distribution of nutrients in profile had great difference between KNO3 experiment and Urea experiment. The causes of the difference were the processes of urea hydrolyzation and ammonium nitrification. In addition, there existed the process of nutrients in fertilization area diffused to the irrigation area. It had been studied the movement of water and nutrients at different irrigation rate under AIFUF; nevertheless, there still have some problems to be solved, for example the optimal ratio of fertilizer and irrigation water.
|
PDF Full Text Request