Effect of contrasting tillage and cropping systems on soil aggregation, carbon pools and aggregate-associated carbon in rainfed Vertisols

Worldwide, conservation agriculture practices involving minimal soil disturbances and retention of crop residue (>30%) have been practised increasingly and recognized to enhance soil health by optimizing key soil attributes. However, little information is available on the short-term effects of conservation agriculture practices on soil properties under rainfed Vertisols of Central India. Thus, our aim was to study the short-term effects of contrasting tillage treatments and cropping systems on soil aggregation, aggregate-associated carbon (C), carbon pools and crop productivity. This study comprised three tillage systems (TS), reduced tillage (RT), no tillage (NT) with retention of crop residue and conventional tillage (CT), together with four cropping systems (CS), namely soya bean (Glycine max L.)+pigeon pea (Cajanus cajan L.) (2:1), soya bean-wheat (Titricum durum L.), maize (Zea mays L.)+pigeon pea (1:1), and maize-chickpea Cicer arietinum L.). The experiment was laid out in a split-plot design with three replicates. Soil samples were collected at four depths: 0-5, 5-15, 15-30 and 30-45cm from the experimental field after completion of four crop cycles. Results indicated that at depths 0-5 and 5-15cm, tillage and cropping system had a significant effect on aggregate mean weight diameter (MWD). The MWDs of 0.97 and 0.94mm were larger for NT than CT (0.77 and 0.83mm) at 0-5- and 5-15-cm depths, respectively. Water-stable aggregates (WSAs) were also larger for NT (70.74%) and RT (70.09%) than CT (59.50%) at 0-5cm. Tillage practice, cropping system and their interaction had a greater effect (P<0.05) on the content of aggregate-associated C for large macroaggregates (LM). There was more aggregate-associated C for NT and RT at 0-5-cm depth than for CT. Cropping system also had a significant effect (P<0.05) on aggregate-associated C at 0-5-cm depth. Soil organic C (%) fractions were in the order of non-labile >very labile >less labile >labile for 0-5- and 5-15-cm depths after four crop cycles. Less labile and non-labile C fractions contributed >50% of TOC, indicating a more recalcitrant form of carbon present in the soil. Tillage had no significant effect (P>0.05) on crop yields after four crop cycles. Conservation agriculture can have a positive effect on aggregate stability, aggregate-associated C and different carbon pools in a Vertisol. Highlights Does conservation agriculture affect soil aggregation, aggregate stability and carbon pools more than conventional tillage? The SOC concentration increases with aggregate size and provides physical protection and stabilization of carbon ( C). Aggregate- associated C content was significantly affected by tillage practices and cropping system. Less labile and non- labile C fractions contribute > 50% TOC in the rainfed Vertisols of central India.