Abstract
Tillage systems can influence C sequestration by changing aggregate formation and C distribution within the aggregate. This study was undertaken to explore the impact of no-tillage without straw (NT-S) and with straw (NT+S), and moldboard plow without straw (MP-S) and with straw (MP+S), on soil aggregation and aggregate-associated C after six years of double rice planting in a Hydragric Anthrosol in Guangxi, southwest of China. Soil samples of 0.00-0.05, 0.05-0.20 and 0.20-0.30 m layers were wet-sieved and divided into four aggregate-size classes, >2 mm, 2.00-0.25 mm, 0.25-0.053 and 2 mm aggregate fraction and reduced the proportion of 0.25 mm macroaggregate fraction also significantly increased in the 0.00-0.5 m layer in NT system. However, those within the 2.00-0.25 mm aggregate fraction were significantly reduced in the 0.05-0.200 m layer under NT system. Straw incorporation increased not only the SOC stock in bulk soil, but also the proportion of macroaggregate, aggregate associated with SOC and humic and fulvic acids concentration within the aggregate. The effect of straw on C sequestration might be dependent on the location of straw incorporation. In conclusion, the NT system increased the total SOC accumulation and humic and fulvic acids within macroaggregates, thus contributing to C sequestration in the 0.00-0.05 m layer.
Highlights
In agroecosystems, soil aggregation formation is considered an important process in soil organic carbon (SOC) stabilization by hindering decomposition of SOC and its interactions with mineral particles (Urbanek et al, 2011;Gunina and Kuzyakov, 2014)
As soil humic and fulvic acids are linked to SOC dynamics, it is hypothesized that the conversion from moldboard plow (MP) without straw incorporation to NT with or without straw incorporation may increase the C storage by increasing the stabilization of aggregate, physically protected C within the aggregate size fraction under the double rice system
We found that the NT system had a greater SOC concentration in the macroaggregate fraction than the MP system in the 0.00-0.05 m layer
Summary
Soil aggregation formation is considered an important process in soil organic carbon (SOC) stabilization by hindering decomposition of SOC and its interactions with mineral particles (Urbanek et al, 2011;Gunina and Kuzyakov, 2014). As soil humic and fulvic acids are linked to SOC dynamics, it is hypothesized that the conversion from MP without straw incorporation to NT with or without straw incorporation may increase the C storage by increasing the stabilization of aggregate, physically protected C within the aggregate size fraction under the double rice system. All aggregate fractions were separately kept in plastic containers and oven-dried at 40 °C for 48 h and weighed, and further sieved through a 0.149 mm sieve for determination of aggregate-associate SOC and humic and fulvic acids concentration. Assuming that the sand contents were the same within aggregate-size classes, the water stable aggregates index, aggregate-associate SOC and humic and fulvic acids concentration were calculated without correcting sand content in all aggregate fractions by dispersion with sodium hexametaphosphate. All statistical analyses were performed using the DPS 7.05 statistical package
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