Soil Aggregate Stability and Aggregate-Associated Carbon Under Different Tillage Systems in the North China Plain
The influences of tillage systems on soil carbon (C) stocks have been studied extensively, but the distribution of soil C within aggregate fractions is not well understood. The objective of this study was to determine the influences of various tillage systems on soil aggregation and aggregate-associated C under wheat (Triticum aestivum L.) and corn (Zea mays L.) double cropping systems in the North China Plain. The experiment was established in 2001, including four treatments: moldboard plow (MP) with residue (MP+R) and without residue (MP-R), rotary tillage with residue (RT), and no-till with residue (NT). In 2007 soil samples were collected from the 0-5, 5-10, and 10-20 cm depths, and were separated into four aggregate-size classes (>2 000, 250-2 000, 53-250, and <53 μm) by wet-sieving method. Aggregate-associated C was determined, and the relationships between total soil C concentration and aggregation-size fractions were examined. The results showed that NT and RT treatments significantly increased the proportion of macroaggregate fractions (>2 000 and 250-2 000 μm) compared with the MP-R and MP+R treatments. Averaged across all depths, mean weight diameters of aggregates (MWD) in NT and RT were 47 and 20% higher than that in MP+R. The concentration of bulk soil organic C was positively correlated with MWD (r=0.98; P=0.024) and macroaggregate fraction (r=0.96; P=0.036) in the 0-5 cm depth. In the 0-20 cm depth, comparing with MP+R, total C occluded in the >2 000 μm fraction was increased by 9 and 6% under NT and RT, respectively. We conclude that adoption of conservation tillage system, especially no-till, can increase soil macro-aggregation and total C accumulation in macroaggregates, which may improve soil C sequestration in the intensive agricultural region of the North China Plain.