| Inner Mongolia Hetao irrigation district is the typical district of soil salinization. Due to the inappropriate irrigation and fertilization for a long time, a large amount of fertilizer was leached into groundwater with the irrigation,rainfall and autumn irrigation. This phenomenon made the agricultural non-point pollution become particularly serious. It threatens the safety of the Yellow River water quality seriously. It has become the limiting factor which restricts the agricultural sustainable development of the region. Therefore, it should be adjust the local fertilization model rationally to solve this problem, which could improve the fertilizer use efficiency, restrict the leaching losses of fertilizer effectively and provide the theory basis for reducing the agricultural non-point source pollution further. Based on the current situation of agricultural production in irrigation district, this research selected the slight salinity cultivated land as research object. The cropping mode is that wheat interplant maize. Only setting up a water stress, apply the "3414" implementation scheme of nitrogen and phosphorus. Decide whether the fertilizer level is reasonable from the point of soil-plant system. Firstly, analyze the change law of crop yield, water and fertilizer use efficiency and nitrogen transport and balance under the condition of applying nitrogen and phosphorus. Secondly, build the model of critical N dilution curve and evaluate the fertilization level based on the accumulation and waning of crop plant nitrogen and the N nutrition index. Meanwhile, reveal the nitrogen leaching rule during the process of soil nitrogen residual, irrigation and the autumn irrigation with the different conditions of applying nitrogen and phosphorus. Build the correlation relationship between the soil enzyme activities of soil urease, alkaline phosphatase, catalase, sucrase and the fertilization. Take the four kinds of the soil enzyme activities as the soil enzymology indexes to evaluate the fertilizer level. Finally, put forward the best pattern of applying nitrogen and phosphorus based on the soil-plant system in the salinity and water saving irrigation district. The concrete conclusion is as follows:(1) The production effect of wheat intercrop maize with the condition of applying nitrogen and phosphorus:The yield of wheat intercropping maize and the fertilizer of nitrogen and phosphorus meet the quadratic regression model. The nitrogen, phosphorus fertilizer and their interaction effect have a obvious significance to the yield. That shows nitrogen and phosphorus interaction effect>nitrogen>phosphorus. When the fertilization level is low, nitrogen and phosphorus show the collaborative role well. After reaching the limit value of yield, they show the invalid and antagonistic effect.(2) The influence of applying nitrogen and phosphorus on the water and fertilizer use efficiency of wheat intercrop maize:When one of the factors in nitrogen and phosphorus meets the crop demand, the surplus factor and the WUE would show a quadratic parabolic trend. Applying the nitrogen and phosphorus properly could increase the consumption of soil pondage and improve the soil water use efficiency of crop. The nitrogen use efficiency shows a trend of decrease with the increase of nitrogen application. Applying the phosphorus properly could increase the nitrogen accumulation of crop effectively and increase the nitrogen use efficiency. The excessive phosphorus restricts the nitrogen uptake of crop and decrease the nitrogen use efficiency. The nitrogen agronomy efficiency and the PFPN also show a similar rule. The rule of phosphorus use efficiency is similar to the nitrogen. So, the low use efficiency of nitrogen and phosphorus has a great relationship with the disproportionate of applying nitrogen and phosphorus.(3) The research on the nitrogen uptake, transport and balance of wheat intercrop maize with applying nitrogen and phosphorus:The changing law with time of nitrogen uptake of aboveground plant could be simulated by Logistic model and it could reach significant level. It shows the nitrogen uptake would increase with the increase of nitrogen application. Within a certain extent, increasing the phosphorus application could improve the nitrogen uptake of plant. The excessive phosphorus would restrict the nitrogen uptake. Applying nitrogen and phosphorus properly could coordinate the supply-demand balance between the soil N supplying capacity and the nitrogen uptake demand of plant. In a certain range of nitrogen, increasing the nitrogen application could increase the transportation amount, transportation rate and transportation contribution rate. The excessive nitrogen would lead to a trend of decrease. Applying the phosphorus properly could increase the transportation amount, transportation rate and transportation contribution rate. Coordinate the relationship between the nitrogen transshipment before flower and the nitrogen assimilation after flower. Distribute the nitrogen uptake reasonably in the whole growth period of maize. The nitrogen surplus in the whole growth period of crop shows a trend of increase with the increase of nitrogen application.(4) Based on the critical nitrogen fertilization diagnosis crop aboveground research: the amount of plant dry matter weight of maize and wheat interplanting overground along with the change of time curve fitting Logistic equation, and the fitting results are good, show the (slow-fast-slow) S type’curve; Establishing the critical nitrogen dilution curve model of wheat and maize interplanting in Inner Mongolia hetao irrigation area, wheat(Nc=4.50W-0.47),maize(Nc=34.295W-0.3579), This model can be used as nitrogen nutrition diagnosis curve of wheat and maize interplanting in Inner Mongolia hetao irrigation area; the nitrogen deficiency value derived from the wheat and maize interplanting critical nitrogen concentration dilution curve model can better solve the problem of quantitative nitrogen rate, also can be used for monitoring the fertilizer levels in Inner Mongolia hetao irrigation area, nitrogen nutrition index can be used to diagnose plant nitrogen nutrition of wheat and maize interplanting, better describing the effect of nitrogen shortage restrictions on nitrogen uptake by plant and nitrogen excess supply, it has better relationship with the nitrogen deficiency value, the middle nitrogen level deficiency value close to zero, nitrogen nutrition index is closing to1, indicating that middle nitrogen level can well coordinate the soil nitrogen supply and the relationship of the crop nitrogen uptaking, it can be used as the recommended fertilizer rate for wheat and maize interplanting in Inner Mongolia hetao irrigation area.(5) Research on nitrogen leaching losses in soil profile of the field:After the crops harvesting, the NO3--N residue in0～120cm soil profile increases with the increasing of nitrogen application rate, when the application rate of nitrogen exceeding the N2P2level, soil NO3--N residue increased significantly; Excessive nitrogen and unbalanced fertilization, leading to a nitrate accumulation peak in80～120cm soil layer of wheat belt, while that in60～80cm soil layer of maize belt, nitrate pollution caused by the nitrogen application rate to the environment is greater than the crop biomass contributes; In the farmland ecosystem of Inner Mongolia hetao irrigation area, the leaching amount of each water irrigation of wheat and maize interplanting is small, Nitrogen leaching occurs mainly after the autumn irrigation, the leaching amount increases with the increasing of N application rate, the more N application rate, the more NO3--N leaching rate, also its higher in the maize belt than the wheat belt, the total leakage rate of wheat is3.0%～31.5%,while that of maize is5.2%～25.2%;under the condition of middle nitrogen level, with a certain amount of phosphate fertilizer, can cut farmland NO3--N leaching effectively, middle phosphate treatment compared with other phosphate treatments, the NO3--N leaching of wheat belt decreasing19.0%～24.8%,while that of maize decreasing12.6%～18.0%. Above all, reasonable phosphate fertilizer can coordinate to soil nutrient supply, increases the crop absorption of NO3--N, also can control the deep soil NO3--N accumulation and NO3--N leaching of autumn irrigation.(6) With the increasing of nitrogen phosphorus fertilizer application rate, the activity of urease, phosphatase and catalase in farmland soil showed the trend of first rise and then drop, the invertase activity keep increasing, certain amount of phosphate fertilizer can effectively increase the activity of urease, phosphatase, catalase and sucrase in the soil; Nitrogen application rate has significant correlation with the activity of catalase, urease, alkaline phosphatase and invertase, the application rate of phosphoric fertilizer has a significant correlation with alkaline phosphatase only, also the four soil enzyme activity has a significant correlation. Above all, the four soil enzyme activity can use as an evaluation index for whether the nitrogen and phosphorus application rate is reasonable or not. |
