Effects Of Nitrogen And Water Saving On Growth,Yield And Water And Nitrogen Use Efficiency Of Spring Wheat And Post-wheat Multiple Cropping Rapeseed In Yellow Irrigation Area Of Ningxia

In view of the extensive management mode of spring wheat planting in the yellow irrigation area of Ningxia,the low water resource use efficiency caused by unreasonable fertilization and irrigation,as well as the problem of soil nitrogen leaching caused by exposed land during the wheat recreation period,and the problems of soil nitrogen leaching caused by rainfall,the effects of nitrogen reduction and water conservation on the microclimate of spring wheat canopy and its growth,yield and water nitrogen use efficiency,and the effects of replanting rapeseed after wheat on rainfall during the summer leisure period and the absorption and utilization of residual nitrogen in the wheat season,while improving the water and nitrogen utilization efficiency of spring wheat.The yield of spring wheat is guaranteed,in order to provide a basis for formulating reasonable irrigation and nitrogen application technical measures suitable for the growth and development of spring wheat in the yellow irrigation area of Ningxia,with high yield and stable yield.In 2021～2022,spring wheat experiment and replanting rapeseed experiment will be carried out in the experimental farm of Ningxia University,and the spring wheat experimental irrigation quota is set at three levels:conventional irrigation W1(400 mm),water saving 20%W2(320 mm)and water saving 40%W3(240 mm).The three nitrogen fertilizer levels,namely 0,202.5 and 270 kg·hm-2,were expressed as no nitrogen fertilizer(N0),25%reduction of nitrogen fertilizer(N2)and conventional nitrogen application(N1),respectively.The effects of different fertilization and irrigation quotas on the growth,yield and water and nitrogen use efficiency of spring wheat under micro-spray irrigation were studied.and to study the absorption and utilization of residual nitrogen in wheat season and rainfall during the summer leisure period,as well as the changes of soil nitrogen after turning green manure rape back into the field.The main findings are as follows:(1)Compared with conventional irrigation treatment,20%water saving has no obvious effect on the microclimate of spring wheat farmland,and the 20%water saving treatment keeps the canopy of spring wheat with lower air temperature and high relative humidity than conventional irrigation treatment and 40%water saving treatment,which is more conducive to the growth and development of spring wheat in the whole growth period,reduces the influence of dry hot wind on the growth and development of spring wheat to a certain extent,and is conducive to improving water use efficiency.(2)Compared with conventional irrigation,the 20%water saving did not reduce the plant height and leaf area of spring wheat,there was no significant difference from the conventional irrigation treatment,and the 20%water saving also increased the accumulation of dry matter in the aboveground.Compared with conventional nitrogen application,nitrogen reduction did not reduce the plant height and leaf area of spring wheat,and significantly increased the SPAD value and aerial dry matter quality of spring wheat.Nitrogen reduction treatment also significantly improved the net photosynthetic rate,transpiration rate and flag leaf stomatal conductance of spring wheat.In the late growth stage of spring wheat,the stem intensity of the 20%nitrogen reduction and water saving treatment was significantly higher than that of conventional irrigation and 40%water saving treatment,which reduced the risk of lodging of spring wheat in the late growth stage.(3)During the ripening period,the total nitrogen content was maximized under the treatment of 20%nitrogen reduction and water saving,and the nitrogen reduction did not reduce the total nitrogen content of spring wheat.The total nitrogen content of spring wheat increased first and then decreased with the decrease of irrigation quota under the same nitrogen application level,and the total nitrogen content of conventional irrigation and 20%water saving treatment was significantly higher than that of water saving by 40%,and the nitrogen accumulation was up to 20%nitrogen reduction and water saving treatment,which was 268.82 kg·hm-2.The nitrogen reduction treatment did not reduce the total nitrogen content in the seed and shell+panicle shaft of the plant,and there was no significant difference from the conventional nitrogen application treatment.The distribution ratio in the treated grain was 62.8%with 20%water saving,which was not significantly different from conventional irrigation and 40%water saving.Water saving of 20%is more conducive to the transfer of nitrogen from stem+leaves to the grain.(4)The soil volume and moisture content in the later stage of spring wheat growth period decreased significantly compared with the previous period.Under different irrigation quotas of the same nitrogen level,the highest soil volume moisture content was conventional irrigation treatment,and the lowest was water-saving 40%treatment.Soil moisture in different soil layers increased to varying degrees before and after irrigation,and the increase in soil moisture in conventional irrigation treatment was the most obvious.The soil moisture transport variation was mainly above 60 cm soil layer,and the most obvious change was 0-20 cm soil layer.Compared with conventional nitrogen application and conventional irrigation treatment,nitrogen reduction and water saving by 20%treatment have a better effect on promoting the absorption and utilization of surface soil water in spring wheat after irrigation,and the effect of reducing water infiltration to the deep layer is more obvious.(5)The seasonal nitrogen application rate of wheat increased,and the biomass of green manure rape reached 679.34～2110.13 kg·hm-2.The residual nitrogen in wheat season could improve the water use efficiency and irrigation water use efficiency of rapeseed,and the residual nitrogen fertilizer increased the irrigation water use efficiency of green manure rapeseed by 1.07～1.80 kg·hm-2.The water use efficiency increased by 0.22～1.36 kg·hm-2.Compared with before planting,planting green manure rapeseed in summer increased the soil storage water of 0100 cm soil layer.The accumulation of mineralized nitrogen in the surface layer of 0-20 cm after rapeseed harvest decreased by 2.56～35.13 kg·hm-2 compared with before planting.The accumulation of mineral nitrogen in the surface layer of 0-20 cm after rapeseed was returned to the field increased by 45.02～78.08 kg·hm-2 compared with before planting.(6)The nitrogen surplus was significantly higher than that of nitrogen reduction and no nitrogen application.Under nitrogen application,the nitrogen surplus was at least 20%water saving,which was manifested as a decrease in irrigation quota and then increased.The 20%water saving treatment at the level of nitrogen reduction has obvious positive effects on improving crop nitrogen uptake and reducing soil residual nitrogen.The nitrogen reduction and water saving by 20%significantly increased the grain yield of spring wheat,which was 5516.67 kg·hm-2,followed by conventional irrigation treatment at the level of 25%nitrogen reduction,which increased by 13.36%and 6.16%,respectively,compared with conventional nitrogen application conventional irrigation treatment.Nitrogen reduction and water saving by 20%significantly increased the protein and soluble sugar content of spring wheat grain.The agronomic efficiency,nitrogen fertilizer partial productivity and nitrogen utilization rate of nitrogen fertilizer treated with 20%water saving were all shown that nitrogen reduction level was better than that of conventional nitrogen application.At the same time,the water use efficiency of 20%water-saving irrigation treatment was 1.43 kg·m-3 under the nitrogen reduction level,which was 31.19%and 21.19%higher than that of conventional irrigation and 40%water-saving treatment.