Changes in soil micro- and macro-aggregate associated carbon storage following straw incorporation

Inadequate soil management strategies weaken soil quality. Soil aggregates and aggregate-associated soil organic carbon (SOC) are important attributes of the soil and can serve as indicators of changes in soil quality. The objective of this study was to optimize an improved soil management that slowed turnover of aggregates and increased SOC storage in Northern China. Four tillage methods were examined: (i) RT (rotary tillage without straw return), (ii) RS (rotary tillage with straw return), (iii) DS (deep tillage with straw return), and (iv) TS (RS applied annually and with DS applied at a two-year interval). The results indicated that straw return treatments increased macroaggregate formation and sequestrated greater SOC. The C inputs among RS, DS, and TS were similar in magnitude, ranging from 8.86 to 8.99 t ha(-1) year(-1). Compared to RS, DS enhanced the turnover of macroaggregates in the 0-20 cm layers, and led to more SOC loss in occluded microaggregates than in macroaggregates in the 0-30 cm layers, indicating a reduced protection of aggregates to SOC. Similar to DS, the mass of macroaggregates under TS was greater than RS in the 10-30 cm layers. However, TS increased the SOC storage in macroaggregates by 0.66 and 0.90 t ha(-1) in the 0-30 cm layers, respectively, compared to RS and DS. Moreover, the SOC storage in occluded microaggregates under TS was 0.52 and 1.06 t ha(-1) greater than RS and DS, respectively, in the 0-30 cm layers. SOC variations among treatments in this study were dominated by tillage methods; thus, appropriate soil disturbance in deep layers (TS) has great potential in activating more C sequestration in macroaggregates and occluded microaggregates. These findings are of great importance for formulating soil management strategy and probably beneficial for crop production.