TILLAGE AND CROP ROTATIONS IMPACT ON SOIL CARBON SEQUESTRATION

Abstract

There is a global concern about progressive increases in greenhouse gases especially CO 2 in the atmosphere by human-induced activities. An increasing awareness about environmental pollution by CO 2 emissions has led to recognition of the need to enhance soil C sequestration for minimizing greenhouse effects, by sequestering C through sustainable agricultural management practices. Conventional tillage has many benefits including reducing soil compaction, preparing favorable seedbed, and controlling weeds, contrarily; it accelerates erosion, off-site movement of nutrients, and enhances loss of soil organic matter. Conservation management systems like no-till (NT) and crop rotation have been reported to increase soil organic C content by creating less disturbed environment. Variations in the soil C substances due to tillage operations or crop rotations have been recognized, however, the information on C sequestration is limited. The present study was planned to improve our understanding that how no-till and crop rotation can enhance C sequestration and soil quality. The study was conducted on Vanmeter farm of the Ohio State University South Centers at Piketon Ohio, USA from 2002 to 2007. Tillage treatments included conventional (CT) and no-till (NT) were factored into continuous corn (CC), corn-soybean (CS) and corn–soybean-wheat- cowpea (CSW) rotations by following randomized complete block design with 6 replications. The findings of present long-term study revealed that no-till had significantly improved biological, chemical, physical and humified carbon fractions compared to conventional tillage. In case of biological parameters total microbial biomass (C mic ), basal (BR), and specific respiration rates (qCO 2 ), potentially mineralizable carbon (C min ), increased because of no-till compared to conventional tillage. Microbial biomass and associated biological properties decreased significantly with increase in soil depth irrespective of tillage; however, the decrease was higher in case of no-till than conventional till. Among crop rotations corn soybean wheat showed significantly improved impact on microbial biomass and associated biological properties. However, crop rotation had variable effect on biological properties along the soil depth.Soil physical parameters like aggregate stability, macroaggregate, particulate organic matter and particulate organic carbon and nitrogen were significantly improved with no–till as compared with conventional tillage. When measured along the soil depth they decreased significantly with increase in soil depth. Corn soybean wheat rotation had significantly improved the various physical parameters as compared with continuous corn and corn soybean. Likewise, No-till showed significant increase in total, active, passive salt extractable and microwave extractable carbon and nitrogen fractions compared to conventional tillage. Among crop rotation corn-soybean-wheat had higher values of physical parameters as compared with other crop rotation treatments. Tillage and crop rotation had non-significant interaction influence on biological, chemical and physical parameters; however, with time as factor the interaction significantly influenced the biological, chemical and physical properties. Total humified carbon, sugar free humified carbon concentration and stocks did not vary significantly, however, the humic, fulvic acid, humic and fulvic acid glucose and humin contents were significantly increased under no-till and decreased under conventional tillage over time. Similar effects on humified carbon fractions by crop rotation were observed. Tillage and crop rotation had a non- significant interaction on humified carbon fraction, the inclusion of time as a factor with tillage and crop rotation interaction significantly influenced the carbon fraction. No-till with all crop rotation acted as net biological, chemical, physical and humified carbon sink while conventional till with different crop rotation acted as a carbon source. The estimated soil quality index was significantly higher in soil under no-till than conventional tillage. Similarly the corn soya bean wheat had shown significant difference in soil quality index as compared with other crop rotations. Sensitivity index revealed that soil microbial biomass can be utilized as sensitive indicator of soil quality.