| The Loess Plateau is the main rainfed farmland area in China.The low temperature in early spring and uneven precipitation are the main factors limiting the spring maize yield,water and fertilizer use efficiency in this area.Different surface mulching and nutrient management techniques are used to further improve crop yields and resource utilization efficiency,maintain the stability and sustainability of soil ecosystems,all of which play an essential part in ensuring regional food security and promoting green agricultural development.Controlled-release nitrogen fertilizer is promising since the N release rate could synchronize crop nitrogen demand,thereby increasing crop yield and nutrient use efficiency.In this study,dry-land mulching maize in the Loess Plateau was chosen as the research object.Surface mulching:including no mulching(NM),plastic film mulching(FM)and straw mulching(SM)and nitrogen application:no N application(N0),conventional N application with urea(NU),and optimized N application with controlled-release urea and common urea at a ratio of 1:2(NC)were the two factors,to investigate the potential improvement of production efficiency and possible mechanism from spring maize yield,dry matter and nitrogen accumulation,temporal-spatial distribution of root system,water uptake and utilization and the soil microbial community structure and diversity.A microplot experiment was set up to investigate the uptake and utilization of residual NO3–-N by maize.The objective of this study was to provide a scientific basis for guaranteeing stable and high yield and nitrogen efficiency with eco-development sustainability.The main conclusions of this study were showed as follows:(1)Both plastic film mulching(FM)and straw mulching(SM)markedly paccelerated plant growth and flowing,and increased grain yield.The optimized N application with plastic film mulching(FMNC)had the most significant effect on increasing yield.The FM and SM were effective at increasing leaf area index(LAI),chlorophyll content(SPAD)and radiation interception during the vegetative growth period,improving the amounts of accumulated dry matter,leading to greater grain yield and N accumulation.Compared to the no mulching treatment(NM),the FM and SM treatments increased the mean yield by6.3%?27.9%and 2.6%?8.9%,respectively.N application significantly increased maize grain yield.Compared to the conventional N application treatment(NU),the optimized N application treatment(NC)increased the mean grain yield by 4.6%and 12.4%in 2016 and2017,no difference was observed in 2018.The FMNC treatment had the highest grain yield with 14.9,14.8 and 16.7 t ha-1 in 2016,2017 and 2018.The FMNC treatment significantly increased the economic benefits by increasing grain yield and decreasing the cost of topdressing,with the highest economic benefits(1.76×104 yuan/ha–1 and 1.75×104 yuan/ha–1)in 2016 and 2017.(2)The NC treatment changed the characteristics of root growth,promoted the growth of fine root in deep soil in the late growth stage.The NC treatment was effective at improving the growth of root in the upper soil layer during the R1,R3 and R5 stages,delaying the root aging in the deep soil layer during the R5 stage.Compared to the NU treatment,the NC treatment significantly increased the root length density by 52.1%?119.4%and 24.2%?63.2%in the 0-100 cm soil layer in 2016 and 2017,respectively.The root length density,root weight density and root surface area density in the upper soil layer during the R1 stage and the whole soil layer during the R3 and R5 stages had significant positive correlation with the maize grain yield.(3)Both the FM and SM treatments improved the soil water content of the upper soil layer in the early growth stage,increased the water consumption of the deep soil layer in the later growth stage,and significantly improved the water use efficiency(WUE).The effect of FM was better than the SM.Compared to the NM treatment,the FM and SM treatments increased the mean soil water content in 0-20 cm soil layer by 11.2%?22.7%and2.29%?8.2%at V6 stage,respectively.Compared to the NM treatment on the average of N application,the FM increased the WUE by 28.5%and 25.4%,and the SM increased by 16.0%and 17.5%,respectively,in 2016 and 2017.No difference was observed in 2018.The NC treatment increased deep soil water consummation in the later growth stage,and improved WUE.Compared to the FMNU treatment,the FMNC increased mean soil water content in100-200 cm soil layer by 1.3%?6.8%and 0.4%?2.6%in 2017 and 2018.Compared to the NU treatment on the average of surface mulching,the NC treatment increased the WUE by3.7%,19.8%and 3.9%,respectively,in 2016,2017 and 2018.The FMNC treatment obtained the highest WUE with 38.1,38.8 and 38.9 kg ha-1mm-1.(4)The optimized N application with plastic film mulching(FMNC)and straw mulching(SMNC)treatments increased maize N uptake and translocation before R1 stage,and the N uptake after R1 stage,therefore,increased N use efficiency and reduced NO3–-N accumulation.Compared to the optimized N application with no mulching treatment(NMNC),the FMNC increased PFP by 28.8%,21.2%and 8.9%,the SMNC increased PFP by 6.3%,2.5%and 3.0%,respectively,in 2016,2017 and 2018.Under NC fertilization,the residual of NO3–-N with FM decreased by 59.6%and 87.2%;the SM decreased by 53.6%and 61.9%,in the 0-100 and 100-200 cm soil layer,compared to the NM treatment,respectively.Under NU fertilization,the FM decreased residual NO3–-N by 58.6%and73.7%,in the 0-100 and 100-200 cm soil layer compared to the NM treatment,respectively;the SM decreased it by 49.9%in 0-100 cm soil layer,and increased it by 18.4%in 100-200cm soil layer.(5)Both surface mulching and N application increased residual NO3–-N uptake and use efficiency by maize,and used the residual NO3–-N in the upper soil layer much more effectively than that in the deeper soil layer.The effect of FM was better than the SM treatment.The FMNU treatment increased the use efficiency by 20.20%and 16.99%with NO3–-N in 20-50 cm and 50-80 cm soil layer,respectively.On the average of N application,the FM,SM and NM use efficiency with NO3–-N in 20-50 cm soil layer increased by 25.1%,28.2%and 25.7%,compared to that with NO3–-N in 50-80 cm soil layer.On the average of surface mulching,the use efficiency of N0 and NU with NO3–-N in 20-50 cm soil layer increased by 31.2%and 22.6%,compared to that with NO3–-N in 50-80 cm soil layer.The N application and surface mulching had significant interaction on the NO3–-N use efficiency,and decreased the downward distance of residual NO3–-N.Therefore,plastic film mulching and N application increased the absorption and utilization of accumulated residual NO3–-N by maize in dryland farming on the Loess Plateau,avoid its migration to deeper soil and reduce the loss of NO3–-N.(6)Surface mulching and N application affected microbial community diversity and community composition,as well as microbial symbiosis.Compared to the NM treatment,the FM decreased soil SOM DOC,MBC and MBN content,increased the relative abundance of Actinobacteria and Firmicutes,promoted the alpha diversity with soil bacteria,and improved the competition and cooperation among species.The SM increased soil SOM,DOC,MBC and MBN content,increased the relative abundance of Bacteroidetes,decreased the relative abundance of Actinobacteria,and reduced the competition and cooperation among species.Surface mulching and N application had no significant effect on fungal alpha diversity.Compared to the N0 treatment,the NU significantly decreased the bacteria alpha diversity,increased the relative abundance of Proteobacteria,promoted the competition and cooperation between bacteria and fungi,and improved the complexity of microbial networks,niches and access to nutrients.The results of this study indicated that optimized N application with plastic film mulching treatment could better meet the N demand of spring maize in this area,promoted root growth into deep soil and utilized water effectively,improved the absorption and utilization of residual NO3–-N,reduced the loss of NO3–-N accumulation and downward migration in soil profile,therefore,increased grain yield,water and nitrogen use efficiency and economic benefits.The optimized N application with plastic film mulching treatment also increased the competition and cooperation among soil microbes,and improved sources of available nutrients.Therefore,the optimized N application with plastic film mulching might be an effective way to promote the sustainable production of maize in the Loess Plateau. |
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