| Arid and semi-arid areas account for about 60% of the total land area of the Loess Plateau,and the development of dryland agriculture is of vital importance to the country.However,the scarcity of soil water and nitrogen in this region has made fertiliser application and mulching the main means of increasing food production in the region.The long-term application of large amounts of chemical fertilisers in the mulching system has led to poor nitrogen utilisation and the nitrate nitrogen accumulation in the soil,posing a potential environmental risk.Therefore,it is important to identify nitrogen loss pathways and losses in mulch systems,analyse the factors affecting nitrogen losses and improve nitrogen fertilizer management measures for the sustainable development of mulch systems.In this study,three fertilizer treatments(conventional urea,slow-release compound fertilizer and urea +nitrification inhibitor)were sampled,and the characteristics and fluxes of nitrate leaching and nitrogenous gas emissions in the soil profile were investigated using structural equation modelling to analyse the factors of nitrogen loss in dryland soils.To provide a theoretical and practical basis for the management of nitrogen fertilization in dryland mulched maize systems in the Loess Plateau region.The main results are as follows.(1)The two-year trial found that ridge-furrow mulching was able to increase soil NO3--N(N)accumulation in the surface layer and soil N accumulation in the deeper layer in the flat crop without mulching.Ridge-furrow mulching increased N residues in the 0-180 cm soil profile by 2.55 times(conventional urea in 2019),1.40-2.03 times(slow-release fertiliser)and 2.23-3.37 times(urea + DCD)than the corresponding flat crop without mulching treatment.Compared to conventional urea application,the slow-release and urea + DCD application treatments in the ridge-furrow mulch increased the accumulation of nitrate N in the soil profile(mainly concentrated in the 0-10 cm top soil layer)while reducing the accumulation in the 100-180 cm soil layer.(2)Compared to the flat crop without mulch,the ridge-furrow mulch increased cumulative N2 O emissions by 24.51-59.09% but reduced cumulative NH3 volatilization by41.25-53.86%.Both slow-release and urea + DCD fertilization had the potential to reduce N2 O emissions,with slow-release and urea + DCD fertilization reducing cumulative N2 O emissions by 17.86-29.03% and 54.84-66.67%,respectively,compared to conventional urea,while increasing cumulative NH3 volatilization by 6.24-41.21% and 7.58-45.40%.(3)Slow-release fertilizer and urea + DCD fertilization significantly increased N losses in the flat crop without mulch,with gas N losses being the main loss pathway,followed by N N leaching losses,with total losses of 89.76 and 88.08 kg ha-1,respectively.The total losses were 73.30 and 74.43 kg ha-1 for the slow-release and urea + DCD applications,respectively,which significantly reduced N2 O emissions and nitrate leaching losses,but increased NH3 volatilisation losses.(4)There was a positive correlation between N accumulation in the root layer and deep leaching in the conventional urea treatment in the ridge-furrow,which was the main factor contributing to the increase in deep leaching in the soil.Therefore,slow release fertiliser and urea + DCD were in reducing N leaching.Soil water content and N content were positively correlated with N2 O emissions,with higher water content and N content in mulch soils being the cause of higher N2 O emissions;higher crop uptake and low soil N content(0-50 d)were the main reasons for the reduction of N2 O from slow-release fertiliser and urea + DCD applications.There was a positive correlation between soil ammonium-N content and ammonia volatilisation,with higher soil ammonium-N content in the slow-release fertiliser and urea + DCD application treatments being the main cause of increased NH3 volatilisation.(5)The total carbon footprint per unit area(CFa)was 65.20-68.82%% higher for the ridge-furrow mulch treatment compared to the flat crop without mulch,with 67.05-73.10%contributed by plastic mulch input.Slow-release fertiliser and urea + DCD reduced the carbon footprint of N losses from the ridge-furrow mulch.Although the ridge-furrow mulching increased maize yield,it failed to offset the large increase in total CFa and resulted in a 22.73-35.00% increase in yield per unit of maize seed(CFy)respectively.Generally,slow-release fertiliser and urea + DCD applications reduced soil N losses from the ridge-furrow mulch,mainly by reducing nitrate N leaching,but slow-release fertiliser and urea + DCD were not conducive to long-term planting without mulch in flat crops.At the same time,ridge-furrow mulching increased the total carbon footprint per unit area.Therefore,there is a need to find alternatives to plastic film for mulching,such as biodegradable mulch,which could potentially reduce the carbon footprint per unit area from the production process while ensuring crop yield,but this needs to be verified. |
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