Effects Of Fertilization And Supplementary Irrigation On Water And Nitrogen Utilization Of Winter Wheat Under The Ridge-furrow Mulching System In Semiarid Region

The Loess Plateau region of the northwest China is rich in heat and light resources that have high potential for increasing crop yields.However,water scarcity and soil infertile limit the yield potential of crops in this region.In recent years,ridge-furrow mulching system as a prospective rainwater harvesting system,has been widely used to improve crop productivity in this region.However,there is a lack of systematic research on the effect of ridge-furrow mulching system on water and nitrogen utilization of winter wheat under different fertilizer application rates and supplementary irrigation modes,which not only restricts the exploitation of yield potential of winter wheat,but also aggravates the waste of resources and environmental risks.To address the above problems,a 4-year（2016–2020）field experiment of winter wheat was conducted in ridge-furrow mulching system（traditional flat planting used as the control）in a typical dry farming area in southern Ningxia.Four fertilizer application rates(High:N 270+P₂O₅ 180 kg ha^-1;Medium:N 180+P₂O₅ 120 kg ha^-1;Low:N 90+P₂O₅ 60 kg ha^-1;None:N 0+P₂O₅ 0 kg ha^-1)and the ridge-furrow mulching system combined with supplemental irrigation（RI）and border irrigation（BI as the control）under medium fertilizer application rate were set to analysis the effects of ridge-furrow mulching system on soil water use,dry matter accumulation and root morphology of winter wheat,nitrate nitrogen residue,N₂O emission and related denitrifying bacterial community,yield and nitrogen uptake.The results obtained in this study suggest a scientific basis for the efficient use of water and nitrogen in dry farming fields and sustainable high and stable wheat yields.The main findings are as follows:（1）Ridge-furrow mulching system improved soil moisture statusRidge-furrow mulching system significantly improved the soil water content of 0–200cm soil layer by 6.5%,2.7%,3.2%and 2.4%under high,medium,low and no fertilization,respectively in the early growth stage of winter wheat,and maintaining this improvement until maturity in wet and normal years,and the improvement varied with the amount of precipitation at that stage.At late growing stage,increased fertilizer application effectively promoted soil water uptake and utilization in wheat under ridge-furrow mulching system,and the difference of soil water content among different fertilization treatments were higher than that in flat planting.Under ridge-furrow mulching system,the soil water content of0–200 cm soil was reduced on average by 5.2%,8.0%and 12.3%under low,medium and high fertilizer,respectively,in late winter wheat fertility compared to the no fertilizer treatment,which was higher than the corresponding reductions of 3.9%,7.6%and 11.6%under flat planting.Under the medium fertilizer application,RI regulated the spatial and temporal distribution of soil water.RI increased the soil water content in the 0–100 cm soil layer（5.2%on average）and when irrigation was applied once,twice and without irrigation,RI on average 7.4%,9.9%and 3.1%lower than the corresponding BI,respectively.（2）Ridge-furrow mulching system promoted root growth and dry matter accumulation of winter wheatRidge-furrow mulching system significant promoted the root growth of winter wheat.The root dry matter,root length density and root surface area density at 0–100 cm increased by 31.7%,25.5%and 36.1%compared to flat planting,respectively.Meanwhile,the above-ground dry matter accumulation of winter wheat under ridge-furrow mulching system increased significantly by 17.7%.Increasing the fertilizer application in a certain range can effectively promote the growth of winter wheat,and the optimum rate was medium.Under the medium fertilizer application,the root dry matter,root length density and root surface area density at 0–100 cm increased by 54.0%,32.6%,and 30.8%on average under RI compared with BI.The aboveground dry matter accumulation of winter wheat at regreening-heading stage was increased by 12.4%under RI compared with BI.（3）Ridge-furrow mulching system increased soil nitrate nitrogen residue and accumulationAfter 4 years in-situ experiment,it was found that ridge-furrow mulching system significantly increased the nitrate-N content in the 0–300 cm soil layer（8.4%lower under no fertilizer）,with an average increase of 12.5%,3.6%and 1.4%at low,medium,and high fertilization,respectively.Nitrate-N accumulation was mainly concentrated in the 120–260cm soil layer under ridge-furrow mulching system,compared with flat planting（120–240cm）,it was moved down 20 cm,and the cumulative amount increased exponentially with the increase of nitrogen application rate.When N application rate≥180 kg ha^–1（medium fertilizer）significantly increased the risk of nitrate leaching into deep soil,and the soil residual nitrate nitrogen content under medium fertilizer was 2.9 and 3.2 times higher than that under low fertilizer under ridge-furrow mulching system and flat planting,respectively.Under the medium fertilization,RI significantly increased the residual nitrate-N content of soil compared with BI.In the 0–200 cm soil layer,the nitrate-N content with irrigation once,twice and no irrigation under RI were significant increased by 28.9%,37.0%and 25.8%on average compared with the corresponding BI,respectively.（4）Ridge-furrow mulching system decreased N₂O cumulative emission during winter wheat growing stageCompared with flat planting,ridge-furrow mulching system significantly reduced cumulative N₂O emission during winter wheat growing stage,and decreased 128.8%,101.1%,109.0%and 107.7%under no fertilization,low,medium and high fertilization,respectively.Fertilizer application drove N₂O emissions,and both under ridge-furrow mulching system and flat planting showed a significant increase in N₂O emission fluxes with increasing fertilizer application.Under the medium fertilizer application,RI significantly reduced the cumulative the cumulative N₂O emissions during winter wheat growing season compared with BI.The cumulative N₂O emissions with irrigation once,twice and no irrigation under RI were decreased by 37.6%,28.1%and 37.1%,respectively.The cumulative N₂O emissions increased significantly with the increase of irrigation under the same irrigation mode.（5）Ridge-furrow mulching system regulated the community structure of soil denitrifying bacteriaThe abundance of nir S-type denitrifying bacteria was significant reduced by 6.9%under ridge-furrow mulching system compared with flat planting,while the abundance of nir K-type denitrifying bacteria and OTUs number were significantly increased by 3.5%and10.8%,respectively.The dominant bacterial groups of nir S-type and nir K-type denitrifying bacteria were Proteobacteria.The community structure of nir S-type and nir K-type denitrifying bacteria was similar under low fertilizer and no fertilizer.The changes of nir S-type and nir K-type denitrifying bacterial community structure were related to soil physicochemical properties closely,and the main influencing factors include nitrate nitrogen content,soil water content,urease activity and soil total nitrogen.（6）Ridge-furrow mulching system improve winter wheat yield,water use efficiency,nitrogen uptake and nitrogen production efficiencyThe grain yield of no,low,medium and high fertilizer application under ridge-furrow mulching system were 13.5%,17.1%,7.6%,and 7.7%higher,water use efficiency were17.0%,19.3%,12.4%,and 15.7%higher than that under flat planting,respectively.The nitrogen uptake of winter wheat with no,low,medium and high fertilizer application under ridge-furrow mulching system was improved 22.3%,25.6%,18.6%and 21.3%.Moreover,Nitrogen uptake efficiency of low,medium and high fertilizer application under ridge-furrow mulching system were higher 25.6%,18.4%and 21.5%than that in flat planting,respectively.Nitrogen production efficiency was increased by 22.3%and 11.0%in low and medium fertilizer treatments,respectively.With the increasing of fertilizer application,grain yield and water use efficiency increased first and then decreased,reaching a maximum at medium fertilizer application.Under medium fertilizer application conditions,compared with BI,RI used 50%less irrigation water when irrigation once,twice but the yield was 93.3%–104.6%of that under border irrigation（P>0.05）,the“water-saving and yield-maintaining effect”was significant.The yield of RI treatment under no-irrigation conditions was 12.1%higher than that of the corresponding BI.The water use efficiency,nitrogen uptake,and nitrogen uptake efficiency were significant increased by 7.4%–14.6%,1.1%–9.2%and 6.4%–42.3%,11.4%,14.2%and 26.7%,11.8%,14.2%and 21.7%,respectively when irrigation once,twice and no irrigation.In conclusion,ridge-furrow mulching system enhanced the matching of soil water supply and winter wheat water demand,effectively promoted the root growth and nitrogen uptake and utilization of winter wheat,regulated the community structure of soil denitrifying bacteria,reduced the N₂O emission and significantly improved the yield and water use efficiency,but caused the increase of nitrate nitrogen residue in soil and the risk of deep leaching,and tended to be intensified with the increase of fertilizer application rate.N 90–180 kg ha^–1+P₂O₅ 60–120 kg ha^–1 was recommended as high-yield and high-efficiency management scheme of wheat in semiarid region of Loess Plateau.Based on the potential of high-efficiency utilization of water and nitrogen in this mode,the technology of ridge-furrow mulching system and supplementary irrigation was further developed by coupling it with the theory of minimum-no-irrigation,which could significantly reduce irrigation water consumption and provide technical reference for establishing water-saving,stable yield,high-efficiency nitrogen and green wheat production system in semiarid region.