| The Loess Plateau is the largest rain-fed agricultural area in China,and is greatly affected by the continental monsoon climate,with scarce and uneven precipitation and severe seasonal drought that greatly limits agricultural production.In addition,long-term intensive cultivation management has led to poor soil nutrient content and structure,and optimizing field management practices is considered a key way to improve this issue.To achieve efficient collection and utilization of precipitation on crop growth in the early stages,ridge-furrow plastic-film mulching planting is widely used in rainfed agriculture,and its high production capacity has been fully recognized.Rational fertilization is an effective way to bring the benefit of mulch film into play.The combination of ridge-furrow plastic-film mulching planting and fertilization is considered to be a stable measure to increase yield of rain-fed maize.However,there are few studies on the response of soil fertility and aggregates to ridge-furrow plastic-film mulching planting under different nitrogen application levels.Therefore,this study used a two-factor randomized block experiment design,with planting method（traditional flat planting（P1）and ridge-furrow plastic-film mulching planting（P2））and nitrogen application level(180 kg N ha-1（N1）and 300 kg N ha-1（N2）)as two factors to clarify their effects on soil nutrient and enzyme activity,aggregate particle size distribution,stability,carbon-nitrogen components,and crop productivity in rainfed spring maize fields.The main research results are as follows:（1）Soil nutrient content was affected by planting pattern and nitrogen application rate.In the two growing seasons,compared with flat planting,ridge and furrow mulching increased the content of soil water,soil organic carbon,easily oxidized organic carbon,dissolved organic carbon,dissolved organic nitrogen,microbial biomass carbon,microbial biomass nitrogen,peroxidase,urease,and sucrase by 7.74%-8.78%,4.25%-6.46%,16.01%-17.55%,2.07%-2.92%,5.72%-6.69%,1.07%-1.39%,11.43%-13.42%,0.9%-2.32%,3.82%-6.36%,1.08%-1.95%,respectively,but soil total nitrogen and available phosphorus and available potassium showed the opposite trend,decreasing by 9.52%-11.9%,7.27%-9.47%,1.44%-1.82%,respectively.Under the same planting method,compared with N1,N2nitrogen application level increased soil organic carbon,total nitrogen,dissolved organic carbon,dissolved organic nitrogen,microbial biomass carbon,microbial biomass nitrogen,peroxidase,urease,and sucrase content by 9.63%-11.52%,15.4%-18%,2.56%-4.64%,4.14%-6.35%,4.15%-6.75%,6.99%-9.66%,9.86%-13.35%,13.65%-20.14%,3.13%-6.1%,respectively,while decreasing soil water and available phosphorus and available potassium content by 1.01%-3.58%,18.91%-20.85%,1.36%-3.17%,respectively.Overall,the best soil fertility effect was observed under ridge and furrow mulching combined with N2nitrogen application level.（2）The composition and stability of soil aggregates were significantly affected by planting pattern and nitrogen application rate.Compared to flat planting,ridge and film mulching significantly increased the composition of mechanical and water-stable aggregates with a particle size of>2 mm by 13.32%-21.77%and 38.88%-59.32%,respectively,but decreased those with a particle size of<0.25 mm by 16.34%-26.41%and 11.92%-18.63%.Under the same planting method,compared to N1 nitrogen application rate,N2 nitrogen application rate increased the composition of mechanical and water-stable aggregates with a particle size of>2 mm by 14.01%-19.27%and 19.12%-72.44%,respectively,but decreased those with a particle size of<0.25 mm by 29.05%-38.79%and 9.16%-12.42%.For the stability of soil aggregates,ridge and film mulching significantly increased the mean weight diameter（MWD）and geometric mean diameter（GMD）of mechanical aggregates and the content of aggregates with a particle size of>0.25 mm(R0.25)by 9.08%-15.39%,11.74%-22.17%,and 1.94%-3.13%,respectively,compared to flat planting,as well as the MWD,GMD,and R0.25 of water-stable aggregates by 24.01%-37.34%,15.79%-26.24%,and 27.78%-43.13%.Under the same planting method,compared to N1 nitrogen application rate,N2 nitrogen application rate significantly increased the MWD,GMD,and R0.25 of mechanical aggregates by 10.57%-16.17%,17.32%-24.88%,and 4.12%-4.68%,respectively,as well as the MWD,GMD,and R0.25 of water-stable aggregates by 15.15%-32.58%,15.46%-20.88%,and 17.43%-24.51%.Overall,the optimal soil aggregate structure and stability were observed in the N2 application rate under ridge and film mulching planting.（3）The variations in carbon and nitrogen components of mature mechanical aggregates at different particle sizes were basically consistent with the response of the whole soil to planting pattern and nitrogen application rates,with the highest content found in the particle size of<0.25 mm.Under two nitrogen application rates,ridge and film mulching planting significantly increased the organic carbon content in aggregates with a particle size of>2 mm compared to flat planting,with an increase of 5.49%-9.88%on the ridge and 11.11%-17.97%in the furrow,showing a decreasing trend in the magnitude of increase with decreasing particle size.The organic carbon content was increased by 7.9%-13.64%,4.37%-9.19%,and 2.92%-5.61%in particle sizes of 1-2 mm,0.25-1 mm,and<0.25 mm,respectively.Compared to the N1 nitrogen application rate,the N2 nitrogen application rate significantly increased the organic carbon content in aggregates with particle sizes of>2 mm,1-2 mm,0.25-1 mm,and<0.25 mm by 11.56%,12.21%,9.22%,and 10.68%,respectively.（4）The planting pattern and nitrogen application rate significantly affected the plant height,stem diameter,and dry matter of spring maize,with a consistent trend among treatments:N2P2>N1P2>N2P1>N1P1.Compared to flat planting,ridge-furrow mulching significantly increased the number of ears per plant,hundred-grain weight,and the number of ears per unit area by 13.53%,7.51%,and 8.21%,respectively.Compared to N1,N2 nitrogen application rate significantly increased the number of ears per plant and the number of ears per unit area by 6.09%and 5.51%,respectively,but decreased the hundred-grain weight by 1.35%.Ridge-furrow plastic-film mulching planting significantly increased the number of ears per plant,number of grains per ear,ear length,and ear diameter of spring maize by 5.24%,6.5%,3.34%and 4.19%,respectively,and decreased the length of bare tip by 30.9%.Based on the positive response of yield components,ridge-furrow plastic-film mulching planting significantly increased grain yield by 21.49%and 20.66%,respectively,compared to flat planting,under N1 and N2 nitrogen application levels.In this study,the effects of planting methods and nitrogen application amount on soil aggregates,nutrients and the productivity of rain-fed maize were clarified.It was proved that ridge-furrow plastic-film mulching planting had significant positive effects on soil enzyme activities,aggregate composition,carbon and nitrogen components,corn yield and other aspects,and showed significant differences under different nitrogen application levels.Therefore,furrow mulching combined with nitrogen fertilizer management is recommended as an effective way for the sustainable production of rain-fed maize in the Loess Plateau. |
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