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

Abstract

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.

Soil organic carbon stock is improved by cover crops in a tropical sandy soil

“…Low biomass production limited the humin content in the soil surface layer (fallow and G+L), consistent with a previous report (Tang et al, 2017), but decreased fulvic acid content in the 0.30-to-0.40-m layer. Effects of the treatments on fulvic acid content at greater depths were expected because fulvic acid has a lower molecular weight and greater mobility in the soil than humic acid and humin (Tang et al, 2017). Humin represented more than 50% of the chemical fraction of organic matter, which is advantageous because this fraction has greater stability in soil (Rossi et al, 2011;Tang et al, 2017).…”

“…Effects of the treatments on fulvic acid content at greater depths were expected because fulvic acid has a lower molecular weight and greater mobility in the soil than humic acid and humin (Tang et al., 2017). Humin represented more than 50% of the chemical fraction of organic matter, which is advantageous because this fraction has greater stability in soil (Rossi et al., 2011; Tang et al., 2017). Higher soil levels of humin than fulvic acid and humic acid have been previously reported in tropical climates, mainly at a depth of 0.10–0.30 m (Guimarães et al., 2013; Rossi et al., 2011).…”

Regulation of Soil Microbial Community Structure and Biomass to Mitigate Soil Greenhouse Gas Emission

“…Mixed CCs are an important management method used extensively to increase SOM and subsequently increase cash crop productivity ( Sainju and Singh, 2008 ). Growing CCs can provide physical protection to the soil by reducing the impact of rainfall and also improve soil structure and aggregation ( Tang et al, 2017 ), and similarly improve soil microorganisms ( Araujo et al, 2019 ). Morales Salmeron et al (2019) found that soil structure and fertility are improved by the presence of legumes and legume-grain mixtures in row crop systems.…”

“…It has been used extensively to boost SOM and consequently increase cash crop productivity ( Sainju and Singh, 2008 ). CCs cultivation not only provides physical protection to the soil by reducing the impact of rainfall but can also improve soil structure aggregation and microorganisms ( Tang et al, 2017 ; Araujo et al, 2019 ). Soil organic carbon (SOC) is the critical component of SOM, soil functions, and agricultural ecosystems sustainability ( Muhammad et al, 2018 ; Chalise et al, 2019 ).…”