Effect of conservation agriculture on soil organic and inorganic carbon sequestration and lability: A study from a rice-wheat cropping system on a calcareous soil of the eastern Indo-Gangetic Plains

Increasing soil carbon (C) in arable soils is an important strategy to achieve sustainable yields and mitigate climate change. We investigated changes in soil organic and inorganic carbon (SOCandSIC) under conservation agriculture (CA) in a calcareous soil of the eastern Indo-Gangetic Plains of India. The treatments were as follows: conventional-till rice and wheat (CT-CT),CTrice and zero-till wheat (CT-ZT),ZTdirect seeded rice (DSR) andCTwheat (ZT-CT),ZTDSRandZTwheat without crop residue retention (ZT-ZT),ZT-ZTwith residue (ZT-ZT+R), andDSRand wheat both on permanent beds with residue (PB-PB+R). TheZT-ZT+R had the highest totalSOCin both 0-15 and 15-30 cm soil layers (20% and 40% higher (p < .05) thanCT-CT, respectively), whereas totalSICdecreased by 11% and 15% in the respective layers underZT-ZT+R compared withCT-CT. Non-labileSOCwas the largest pool, followed by very labile, labile and less labileSOC. The benefits ofZTand residue retention were greatest for very labileSOC, which showed a significant (p < .05) increase (~50%) underZT-ZT+R compared withCT-CT. TheZT-ZT+R sequestered ~2 Mg ha(-1)totalSOCin the 0-15 cm soil layer in 6 years, whereCTregistered significant losses. Thus, the adoption ofCAshould be recommended in calcareous soils, for C sequestration, and also as a reclamation technique.