Diversification of maize-wheat cropping system with legumes and integrated nutrient management increases soil aggregation and carbon sequestration

Abstract

Retention of carbon in arable soils has been recommended as an important mechanism to mitigate the climate change and sustainability of the agro-ecosystems. We reasoned that legume-inclusive crop rotations and integrated nutrient management would promote higher soil aggregation and carbon sequestration compared with continuous cereal-cereal [maize (Zea mays L.) – wheat (Triticum aestivum L.)] rotation and chemical fertilization. To test the hypothesis, we used a long-term field experiment (13 years) in Typic Ustochrept soil of Kanpur, India. The field experiment was undertaken in split-plot design comprised of four crop rotations: maize–wheat (MW), maize–wheat–mungbean (Vigna radiata L.) (MWMb), maize–wheat–maize–chickpea (Cicer arietinum L.) (MWMC) (2 years rotation), pigeonpea (Cajanus cajan L.)-wheat (PW) in main plot, and three nutrient management treatments: without fertilization (CT), recommended dose of inorganic fertilizers in the region (NPKSZnB), and integrated nutrient management (INM) in sub-plot. Water stable macroaggregates (>0.25 mm), aggregate ratio, mean weight diameter, and geometric mean diameter followed the order of PW > MWMb > MWMC > MW (p < 0.05) for crop rotations, and INM > NPKSZnB > CT (p < 0.05) for nutrient management practices. The PW rotation and INM practice retained higher coarse macroaggregated- and ‘silt + clay’-carbon compared with MW and NPKSZnB treatments. The PW and MWMb rotations allocated 69.7 and 65.7% carbon in macroaggregates, respectively. While, MW rotation allocated higher carbon in microaggregates (55%). The PW and MWMb rotations significantly enhanced the active (very labile + labile) and passive (less labile + non labile) carbon pools compared with that of MW rotation. The PW stabilized 15% higher carbon in less labile fraction (Cfrac3) over the MW (p < 0.05). It indicated that higher passive carbon pool and its stabilization in PW and MWMb rotations could promote the carbon sequestration. Therefore, MWMb and PW systems had 14.7 and 3.9% higher carbon management index than that of MW rotation (p < 0.05). Among nutrient management treatments, INM resulted in higher active (26%) and passive (8%) carbon pools compared with that of NPKSZnB. Further, INM increased carbon management index by 29 and 16% (p < 0.05) compared with those of CT and NPKSZnB, respectively. Principal component analysis indicated that PW(INM) and MWMb(INM) distinctly situated from MW(CT) and MW(NPKSZnB) in coordinates. Thus, PW and MWMb rotations with INM practice can enhance the soil aggregation and carbon sequestration in long-run. The research findings can be extrapolated in the South Asian and other countries, where continuous cereal-cereal induced soil health issues are a pervasive problem.