Research On Mechanism Of Water And Nitrogen Transport And Efficient Utilization In Crop Rootzone Under Water-Saving Irrigation

Low efficiency of water and fertilizer is a main problem faced by agricultural production. How to improve the efficiency of water and fertilizer and adjust environment of water and fertilizer are urgent need to solve the key issues in developing water saving agriculture in dry areas of North China. Advanced water-saving technology were widely studied and applied considering optimal allocation of limited water in crop growth stages, such as controlled roots-divided alternative irrigation and regulated deficit irrigation could improve indeed irrigation water use efficiency and crop growth soil water situation. Many scholars have paied more and more attention to the efficiency of water and nutrient. So the research on transport of water and nitrogen efficient utilization mechanism in crop rootzone soil under water-saving irrigation has theory and realistic meaning in fair use water and fertilizer resources and water-saving and fertilizer-saving. The transport and utilization of water and nitrogen in rootzone soil was studied and systematic analyzed by pot and field experiments about maize and wheat under water-saving irrigation condition. After studying I have preliminarily obtained some major research results as follows:(1) The transport and utilization of water and nitrogen in rootzone soil was studied of controlled roots-divided alternative irrigation. Results showed that, Soil NO₃^--N content were positively correlated with amount of nitrogen application, Soil NO₃^--N content in both rootzone of alternative irrigation was evenly distributed, and the soil NO₃^--N accumulation in dry side was significantly greater than wet side of fixed irrigation. The NO₃^--N residues in upper soil of alternative irrigation was approximately equal with them of convention irrigation, while the residues in lower soil of alternative irrigation were much than them of convention irrigation. The WUE of alternative irrigation were 1.16～1.03 times it of convention irrigation, the irrigation amount of alternative irrigation is 0.75 times it of conventional irrigation, water-saving effects of alternative irrigation was evident.(2) Effects of alternative furrow irrigation on transport and accumulation of water and nitrogen in maize rootzone soil were investigated. The results showed that, The maximal accumulated NO₃^--N of low water and high nitrogen was gained in the whole profile at harvest time, which was 1.2 times of that of high water and high nitrogen. The accumulation of NO₃^--N of low water and low nitrogen was 1.27 times of that of low nitrogen and high water. NH4+-N contents in the soil of 0～30 cm reached a peak, and the contents basically did not change below 30 cm soil after fertilizing. Soil water accumulation and distribution was not obviously affected by the level of nitrogen. The treatment of high water reduced the accumulation of NO₃^--N in root zone, which lead to leaching and reduced nitrogen fertilizer use efficiency. The best coupling form of alternative furrow irrigation was treatment of low water and high nitrogen.(3) Transport and utilization mechanism of water and nitrogen in spring maize rootzone soil were studied about separate furrow irrigation and nitrogen application in deffrent rootzone (fertilizing in the irrigated furrow (FII) and unirrigated furrow (FIU)). Results showed that high water of FII was more easily lead NO₃^--N leaching, the content of NO₃^--N was basically equal in the profile of treatment of high water of FII at harvest time. The treatment of high nitrogen and low water of FIU had maximum grain yield of 9953 kg·hm^-2 and highest grain irrigation water use efficiency (IWUE) of 6.70 kg·m^-3, compared with IWUE of treatment of high nitrogen and high water of FII, it raised by 72.68%.The best form of water and nitrogen space coupling was treatment of high nitrogen and low water of FIU.(4) Transport and utilization of water and nitrogen in spring maize rootzone soil was studied about different furrow mode and nitrogen rate under rain canopy. The results showed that, the treatment of CAFI, middle water and low nitrogen rate reached the highest yield, which was 1.06 times it of CAFI, high water and high nitrogen. Maize average yield of CAFI could reach 9317 kg·hm^-2, it was respectively 1.05 times of CFI and 1.16 times of FFI under the same condition of water and nitrogen. The average WUE of CAFI was 3.39 kg·m^-3,it of CFI took the second place; it of FFI reached the minimum value of 2.94 kg·m^-3. Nitrogen cumulant of CAFI was the maximum,nitrogen cumulant of CFI took the second place, and it of FFI was less 26 kg·hm^-2 than CAFI. NO₃^--N contour of CAFI in rootzone soil was similar to that of CFI under the same condition of irrigation quality and nitrogen rate, and NO₃^--N content in furrow profile was along the symmetry of ridge center.(5) The effect of regulated deficit irrigation and nitrogen nutrition on availability of water and nitrogen in maize rootzone was studied. The results showed that, NO₃^--N content in middle and lower soil layer of regulated deficit irrigation lies between the treatment of low and high water of normal irrigation, there was a positive correlation between the content of NO₃^--N in middle and lower soil layer and N rate at end of the heading stage. N rate and deficit period had a notably significant effect on accumulation of dry matter and total nitrogen. Water deficit at jointing stage affected mostly dry matter accumulation. The treatment of high nitrogen and deficit water at seedling stage had the maximum WUE. The best coupling treatment was deficit water in heading stage and low nitrogen.(6) The effect of regulated deficit irrigation and nitrogen nutrition on physiological characteristics of maize was studied. The results showed that, water deficit led to lower chlorophyll content; nitrogen rate and chlorophyll content was positively relevant. Water deficit would increase the proline content; the nitrogen apply would slightly reduce the proline content. Water deficit reduced root activity; compensation effect of root activity was obvious after water covered. Deficit irrigation could increase MDA and soluble sugar content, while decrease POD and SOD content. Nitrogen could ensure soluble sugar, SOD and POD at a higher level before heading date. The treatment of deficit irrigation in seedling stage had better compensation effect of biochemistry; deficit irrigation in jointing stage had less compensation effect. The treatments of high nitrogen were not suitable to be irrigated deficit in the heading stage. The best handling combination was deficit irrigation in seedling stage with low nitrogen.(7) Spring wheat population utilization of water and nitrogen in Shiyang River was studied about regulated deficit irrigation and nitrogen rate. The results showed that nitrogen rate and irrigation in jointing and heading stage impacted on spring wheat yield remarkably. With nitrogen rate (168 kg·hm^-2), irrigation (90 mm) in jointing stage, and irrigation (70 mm) in heading stage, spring wheat production is higher. The impact of nitrogen rate on nitrogen accumulation of grain yield and dry matter were significant; nitrogen accumulation of grain came to maximum when nitrogen rate (168 kg·hm^-2) and irrigation (90 mm) were applied. The optimal model of irrigation and nitrogen rate of spring wheat in Shiyang River Basin were nitrogen rate(168 kg·hm^-2), irrigation(90 mm) in jointing stage and irrigation(60 mm) in tillering,heading,filling and jointing stage.(8) Utilization mechanism and transfer of water and nitrogen was studied about regulated deficit irrigation in Shiyang River. The results showed that NO₃^--N accumulation in root soil was mainly concentrated in the 0～40 cm profile before the jointing stage and the accumulation was about 550 kg·hm^-2. NO₃^--N was leaching in the rootzone soil of high water treatment from 62 days after sowing, the NO₃^--N accumulation of high water treatment was 0.76 times of that of lower treatment in the profile. The residual of NO₃^--N was in sequence of lower water>low water>middle water>high water at harvest time. Supplementary irrigation amount of 360～280 mm in the whole growth period could guarantee yield and water use efficiency on the condition of deficit water resources.