Effect Of Conservation Tillage Practices On Summer Maize Yield And Water And Nitrogen Use Efficiency

Maize is the most widely grown food crop in China,and its yield is directly related to the nation’s food security.Grain filling is a critical process if a high grain yield is to be achieved.Poor inferior kernel grain filling is a challenge that limits summer maize yield.In order to increase yield,farmers resort to excessive irrigation and nitrogen application and frequent tillage practices,leading to various economic and environmental problems such as decreased soil quality,low fertilizer utilization,and increased carbon emissions from farmland.In addition,limited water resources,uneven interannual rainfall distribution and severe evaporation losses（1500 mm）in the Loess Plateau region make soil water an important factor limiting the sustainability of agriculture in the region.In order to reveal the effect and mechanism of conservation tillage practices on improving the photosynthesis of summer maize in semi-arid loess plateau rainfed agriculture affecting grain filling of inferior kernel to increase yield and water and nitrogen use efficiency,a 2 year（2019–2020）field experiment supported by the Ministry of Education was conducted at the Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas（34°20 0 N,108°230 E,521 m）,Yangling,Shaanxi Province,with Zheng dan 958 maize as the experimental crop.Under 3 tillage practices included reduced tillage（RT）,no tillage（NT）,and conventional tillage（CT）and 3 coverage measures included ridge-furrow with plastic film mulching（RFM）,straw mulching（SM）and no mulching（NM）,total 6 treatments.We studied soil water,soil nutrients,root system morphology,dry matter accumulation,photosynthesis,grain filling of inferior kernels and grain yield of summer maize.The main findings are as follows:（1）Reduced tillage and NT can improve soil water content and root systems,improve photosynthesis and grain filling of inferior kernels.Under RT and NT treatment,the final 100-kernel weight of maize and maximum and mean grain filling rates were higher than CT and increased soil water content at the jointing stage,the silking stage and grain filling stage in comparison with CT,increased root system morphology of maize and dry matter accumulation,net photosynthetic rate,transpiration efficiency,and stomatal conductance in comparison with CT,and they also decreased intercellular CO₂ concentration,and they increased chlorophyll content,above-ground dry matter accumulation,evapotranspiration of maize.Ultimately,RT and NT increased grain yield by 17%and 14%,respectively.Considering the optimal water retention effect,RT is an effective tillage method suitable for rain-fed agriculture in the semi-arid loess plateau.（2）SM and RFM significantly increased soil water content,root system morphology and nutrient uptake,which correspondingly enhances yield of maize and water and nitrogen use efficiency.SM and RFM significantly increased soil water content by 23.8%and 15.2%,respectively;increased plant nitrogen uptake by 37.6%and 11.3%（P<0.05）;increased grain nitrogen uptake,aboveground dry matter accumulation and evaportranspiration of summer maize;improved grain yield of summer maize by 16.8%and 9.2%and water use efficiency by 13.0%and 9.1%（P<0.05）,respectively.（3）RT,NT and SM can increase soil carbon and nitrogen content.Compared with NM,RFM significantly increased soil temperature by 0.5～1.0°C at 5 cm soil depth and increased soil temperature by 0.2～0.7°C at 10 cm soil depth,accelerated decomposition of soil organic carbon,enhanced soil respiration rate by 33.2%（P<0.05）;SM decreased soil temperature by 0.2～1.5°C at 5 cm soil depth and decreased soil temperature by0.5～1.0°C at 10 cm soil depth,increased soil organic carbon content and decreased soil respiration rate.RT、NT and straw mulching increased soil organic carbon content,decreased soil respiration rate by 30.0%,18.4%and 44.0%,respectively.RFM significantly decreased soil nitrate nitrogen content of furrow.RT,NT and SM significantly increased soil nitrate nitrogen content in the 0～60 cm soil depth,but significantly reduced soil nitrate nitrogen content in the deep soil（P<0.05）.Considerate significant effect of increasing yield of summer maize and soil water and decreasing carbon emission,straw mulching is an effective mulching method suitable for rainfed agriculture on the semi-arid loess plateau,China.