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<53μm) 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 000μm) 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 000μm 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.