Retentionof carbon(C)inarable soilshas beenconsidered as apotentialmechanismtomitigate soil degradation
and to sustain crop productivity. Hence, we appraised the 3-year effect of different conservation
agriculture (CA) practices on grain yield, biomass productivity and soil organic C (SOC) accumulation rates
under a tropical rice (Oryza sativa L.)-wheat (Triticum aestivum L.) and rice–wheat–green gram (mungbean
in Hindi; Vigna radiata) cropping systems. Results indicate mean (of three years) rice grain yield
under mungbean residue + direct seeded rice (DSR) followed by zero tilled wheat (ZTW) with rice residue
(RR) retention and zero tilled relay summer mungbean (MBR + DSR-ZTW+ RR-ZTMB) plots was similar to
farmers’ practice [transplanted rice (TPR)- conventionally tilled wheat(CTW)], despite TPR-CTWplotshad
∼18% higher rice yield than MBR + DSR-ZTW+ RR-ZTMB plots in the first year. The MBR + DSR-ZTW+ RRZTMB
treated plots had about 15 and 10% higher mean wheat grain yield and mean system productivity
(sum of grain yields of all crops) than TPR-CTW plots, respectively. The plots under DSR + brown manuring
(BM)-ZTW+ RR plots had comparable mean rice and wheat yields to MBR + DSR- ZTW+ RR-ZTMB
plots. Harvestable aboveground biomass productivity of MBR + DSR-ZTW+ RR-ZTMB treated plots was
∼2.89 Mg ha−1 yr−1 higher than TPR-CTW. Total estimated C input (∼12.1 Mg C ha−1 in three years) under
MBR + DSR-ZTW+ RR-ZTMB treated plots was ∼117 and 127% higher than DSR-ZTW and TPR-CTW treatments,
respectively. All CA plots had significantly higher gain (over initial value) in total SOC than that
in TPR-CTW and TPR-ZTW treatments in the 0–15 cm layer and the gain in total SOC in the plots under
MBR + DSR- ZTW+ RR-ZTMB was significantly higher than all CA plots, despite having similar total SOC
stocks.Again, plotsunderMBR + DSR-ZTW+ RR-ZTMBhad∼24%larger labileCpools thanthat of TPR-CTW
(3.1 g kg−1)treated plots in the topsoil. Soil bulk density under MBR + DSR- ZTW+ RR-ZTMB and DSR + BMZTW+
RR treated plots significantly decreased in the 5–15 cm layer compared to TPR-CTW plots. Thus,
the MBR + DSR-ZTW+ RR-ZTMB treatment (a novel CA practice), has considerable potential to retain C
in surface soil, decrease soil compaction and increase system (rice–wheat–green gram) productivity and
hence its adoption is recommended.