Soil Aggregation and Associated Organic Carbon Fractions as Affected by Tillage in a Rice–Wheat Rotation in North India

Soil samples were obtained from a long-term trial conducted on a silty loam at Sardar Vallabhbhai Patel University of Agriculture & Technology, Modipuram (Meerut), in 2007–2008 to study the effects of various combinations of conventional and zero-tillage (ZT) and raised-bed systems on soil aggregation and associated organic C fractions in the 0- to 5-cm and 5- to 10-cm depth in a rice–wheat (Orysa sativa L.–Triticum aestivum L.) rotation. Macroaggregates increased under a ZT rice (direct-seeded or transplanted) and wheat rotation with the 2- to 4-mm fraction greater than that of the 0.25- to 2-mm fraction. Bulk and aggregate associated C increased in ZT systems with greater accumulation in macroaggregates. The fine (0.053–0.25 mm) intra-aggregate particulate organic C (iPOM-C), in 0.25- to 2-mm aggregates, was also higher in ZT than conventional tillage. A higher amount of macroaggregates along with greater accumulation of particulate organic C indicates the potential of ZT for improving soil C over the long-term in rice-wheat rotation.