Abstract:

The partial replacement of chemical nitrogen fertilizers with green manure can improve crop yields and soil physical properties. A two-factor split-plot field experiment with maize and hairy vetch was conducted from 2020 to 2022. The main treatment was the cultivation mode before maize planting ［winter fallow field （FF） and total return of hairy vetch planted in the winter fallow field （HV）］ and the sub-treatment was the nitrogen application level ［0 kg·ha^-1 （0%N）， 135.0 kg·ha^-1 （50%N）， 270.0 kg·ha^-1 （100%N）］ to maize as the following crop. The soil physical properties were determined by measuring soil aggregate composition and distribution， mean weight diameter （MWD） and geometric mean diameter （GMD） of aggregates， percentage of aggregate destruction （PAD）， soil erodibility factor （K）， soil bulk density （BD）， total porosity （TP）， capillary porosity （CP）， non-capillary porosity （NCP）， maximum water holding capacity （MWHC）， capillary water holding capacity （CWHC）， non-capillary water holding capacity （NCWHC）， soil organic carbon （SOC） content， and aggregate-associated organic carbon （AOC） content in the 0-10 cm and 10-20 cm soil horizons. Maize yield was also determined. The results showed that， compared with FF， HV significantly increased the proportion of macroaggregates （R_0.25） in the 0-10 cm and 10-20 cm soil horizons by 8.95% and 13.13%， MWD by 40.84% and 62.87%， GMD by 30.57% and 51.68%， TP by 5.89% and 5.02%， CP by 1.47% and 0.76%， NCP by 4.42% and 4.25%， MWHC by 15.01% and 13.11%， CWHC by 6.41% and 3.32%， NCWHC by 27.08% and 27.86%， and SOC content by 7.29% and 7.10%， respectively； and significantly reduced PAD by 8.83% and 12.14%， K by 20.79% and 30.73%， and BD by 5.99% and 7.31%， respectively. The AOC content of each particle size fraction in each soil layer and maize yield were significantly higher in HV than in FF. The nitrogen application level had significant or extremely significant impacts on the AOC content of each particle size fraction in each soil layer， R_0.25， and other soil physical indexes and maize yield. The following indexes were not significantly different between the FF100%N and HV50%N treatments： SOC content， AOC contents of the >5 mm fraction of the 0-10 cm and 10-20 cm soil horizons， AOC content of the 0.50-1.00 mm fraction of the 0-10 cm soil horizon， the BD， TP， CP， NCP， MWD， CWHC， NCWHC of the 10-20 cm soil horizon， and maize yield. However， the following indexes were higher in the HV50%N treatment than in the FF100%N treatment： AOC contents of the 2.00-5.00 mm， 1.00-2.00 mm， 0.25-0.50 mm， and <0.25 mm fractions of the 0-10 cm and 10-20 cm soil horizon， AOC content of the 0.50-1.00 mm fraction of the 10-20 cm soil horizon， the R_0.25， MWD， and GMD of the 0-10 cm and 10-20 cm soil horizons， and the TP， NCP， MWHC， and NCWHC of the 0-10 cm horizon. The PAD and K of the 0-10 cm and 10-20 cm soil horizons and the BD of the 0-10 cm soil horizon were significantly lower in HV50%N than in FF100%N. There were significant or extremely significant correlations between the AOC content of each particle size fraction and SOC content； the content of each particle size fraction and the AOC content； soil physical property indexes and the content of each particle size fraction； and maize yield and soil physical property indexes. The increased SOC content after returning green manure laid the foundation for improved aggregate structure， enhancing soil erosion resistance and WHC. The addition of nitrogen and organic carbon derived from green manure improved the soil’s physical properties. The use of green manure achieved the aims of reducing chemical nitrogen inputs and increasing yield.

Key words: hairy vetch, nitrogen application level, soil organic carbon content, soil physical properties, yield of maize