Effect Of Intercropping Cover Crop And Water-Nitrogen Regulation On Yield,Quality Of Silage Maize And Soil Environment

Silage maize（Zea mays L.）is the main forage crop in the arid oasis area of Hexi Corridor.However,the shortage of water resources,excessive application of nitrogen fertilizer and declining soil quality in this area seriously restrict its agricultural production and sustainable development.Therefore,how to realize the efficient utilization of water and nitrogen under the limited water and fertilizer resources,and to synchronously improve the farmland soil environment is the key technical bottleneck of silage maize production in this area.In this study,a 2-year silage maize intercropping with leguminous cover crops of field experiment conducted from 2021to 2022 under various drip fertigation conditions,including the red clover（TP,Trifolium pretense L.）,common vetch（VS,Vicia sativa L.）and the hairy vetch（VV,Vicia villosa Roth）three leguminous cover crops,120 kg N hm^-2（N1）and 180 kg N hm^-2（N2）two nitrogen application rates as well as 75%crop evapotranspiration（ETc,W1）and 100%ETc（W2）two irrigation levels.No-cover crop under 180 kg N hm^-2and 100%ETc was used as control（None）.For exploring the influence of intercropping leguminous cover crops and water-nitrogen regulation on silage maize yield,quality and soil environment,suitable water-nitrogen regulation strategies are recommended in the Hexi Corridor by using the principal component analysis（PCA）and entropy weight coefficient（EV）of multiple index decision analysis（TOPSIS）.The main results are presented as follows:（1）Leguminous cover crops varieties had no significant effect on plant height and stem diameter（P>0.05）.However,the stem strength of VV under W2N2 was significantly higher than that of TP and VS（P<0.05）,increasing by 12.1%-16.1%and15.6%-18.0%,respectively.During the silking period of silage maize,the intercellular carbon dioxide（CO₂）concentration of silage maize leaves under TP and VV treatment increased by 9.5%-9.7%and 19.4%-28.5%compared with the control treatment.（P<0.05）.During the silage maize filling period,the net photosynthesis rate of silage maize under VV increased by 17.3%-33.3%compared with the control treatment.Thus,it can be seen that cover crops could improve the agronomic properties of silage maize and enhance the leaves photosynthetic characteristics.（2）Under the same water and nitrogen application condition,the hay yield of silage maize intercropping with three legume cover crops was not significantly different（P>0.05）.The systematic hay yield under VV was significantly higher than under the control treatment,increasing by 13.2%-26.7%.There were no significant differences in silage maize starch content under three leguminous cover crops（P>0.05）.Under VV treatment,the intercropping system hay yield of W2N1 had no significant differences with W2N2（P>0.05）,however,W2N1 improved water use efficiency by 10.4%-15.2%,nitrogen productivity by 33.3%-39.8%compared to W2N2（P<0.05）.Accordingly,with the hairy vetch as a cover crop,the W2N1 did not significantly reduce the intercropping system yield,and concurrently improved the water and nitrogen utilization efficiency.（3）There was no significant difference in soil p H and conductivity between the three leguminous cover crops and the control treatment（P>0.05）,however,soil total nitrogen under the intercropping VV significantly increased by 18.0%-18.6%（P<0.05）.Under W2N2,VV,PT and VS treatment significantly reduced soil wind erosion by 50.5%-56.4%,41.6%-44.7%and 40.3%-42.6%,respectively（P<0.05）.Under various water and nitrogen regulation strategies,the degree of soil wind erosion inhibition showed that W2N2>W2N2>W1N1>W1N2>W1N1.It is thus clear that intercropping leguminous cover crops,especially the hairy vetch,could improve soil environment.（4）Using TOPSIS model to evaluate the yield,quality and soil environmental benefits of silage maize,results showed that the three cover crops scored in yield,quality and soil environment were VV>TP>VS,TP>VV>VS and VV>TP>VS,respectively.Obviously,the hairy vetch as a cover crop is more suitable for intercropping with silage maize than red clover and common vetch.Further,under the hairy vetch,red clover and common vetch as cover crops intercropping with silage maize,the W2N1,W2N2 and W1N2 were strongly recommended to the silage maize production and soil environment improvement,respectively.It is concluded that 100%ETc and 120 kg N hm^-2could effectively increase forage yield,promote nutritional quality,enhance water and nitrogen utilization efficiency and simultaneously improve the soil environment under silage maize intercropping hairy vetch system.