Returning Winter Cover Crop Residue Influences Soil Aggregation and Humic Substances under Double-cropped Rice Fields

ABSTRACT Residue management in cropping systems may improve soil quality. However, there are few studies on the effects of residue management on soil aggregation and carbon content in the humin (C-HUM), humic acid (C-HAF) and fulvic acid (C-FAF) fractions in South China. Therefore, the effects on soil aggregation and on the C-HUM, C-HAF, C-FAF from incorporating winter cover crop residues in a double-cropped rice (Oryza sativa L.) system in South China fields were studied. The experiment has been conducted since winter 2004. Five winter cropping systems were used: rice-rice-ryegrass (Ry-R-R), rice-rice-Chinese milk vetch (Mv-R-R), rice-rice-potato (Po-R-R), rice-rice-rape (Ra-R-R) and rice-rice with winter fallow (Fa-R-R). The results indicated that the organic C content in the paddy soil under the Ry-R-R, Mv-R-R, Po-R-R, and Ra-R-R systems was significantly higher than the content in the Fa-R-R system at the early rice and late rice maturity stages. The different sizes of aggregates under the five treatments showed similar trends. The Po-R-R systems had the highest percentage of soil aggregates in each size class and the Fa-R-R systems had the lowest percentage of soil aggregates in each size class in the 0.00-0.05, 0.05-0.10, and 0.10-0.20 m soil depth at the early rice and late rice maturity stages. The C-HUM, C-HAF, and C-FAF increased through long-term application of winter cover crop residues. Statistical analysis showed that the C-HAF under the Ra-R-R systems was significantly higher than that in the Fa-R-R systems at the early rice and late rice maturity stages. The C-FAF and C-HUM under the Mv-R-R systems was significantly higher than the C-FAF and C-HUM in the Fa-R-R systems at the early rice and late rice maturity stages. As a result, the soil organic C content, the soil aggregates in each size class, and the C-HUM, C-HAF, and C-FAF increased from application of winter cover crop residues in double-cropped rice systems.

摘要 作物种植体系中的残体管理（residue management）可改善土壤质量。然而，当前针对华南地区残体管理对土壤团聚体（soil aggregation）以及胡敏素（humin）、胡敏酸（humic acid）、富里酸（fulvic acid）组分中碳含量（即C-HUM、C-HAF、C-FAF）影响的研究较为匮乏。为此，本研究以华南双季稻（double-cropped rice，Oryza sativa L.）种植田为对象，探究还田冬季覆盖作物残体（winter cover crop residues）对土壤团聚体以及C-HUM、C-HAF、C-FAF的影响。本实验于2004年冬季开始实施，共设置5种冬季种植模式：稻-稻-黑麦草（Ry-R-R）、稻-稻-紫云英（Mv-R-R）、稻-稻-马铃薯（Po-R-R）、稻-稻-油菜（Ra-R-R）以及稻-稻-冬季休耕（Fa-R-R）。结果显示，在早稻与晚稻成熟期，稻-稻-黑麦草、稻-稻-紫云英、稻-稻-马铃薯及稻-稻-油菜体系下的稻田土壤有机碳含量均显著高于稻-稻-冬季休耕体系。5种处理下各粒径土壤团聚体的变化趋势一致，在早稻、晚稻成熟期的0.00-0.05 m、0.05-0.10 m及0.10-0.20 m土层中，稻-稻-马铃薯体系各粒径团聚体占比最高，稻-稻-冬季休耕体系各粒径团聚体占比最低。长期还田冬季覆盖作物残体可提升土壤C-HUM、C-HAF与C-FAF含量，统计分析表明，早稻与晚稻成熟期，稻-稻-油菜体系的C-HAF含量显著高于稻-稻-冬季休耕体系；稻-稻-紫云英体系的C-FAF与C-HUM含量均显著高于稻-稻-冬季休耕体系。综上，双季稻种植体系中还田冬季覆盖作物残体可提升土壤有机碳含量、各粒径团聚体占比以及C-HUM、C-HAF与C-FAF含量。