Soil quality indices in a conservation agriculture based rice-mustard cropping system in North-western Indo-Gangetic Plains

The systematic research on the effect of medium-term conservation agriculture (CA) on soil quality, especially under the rice (Oryza sativa L.)-based cropping systems is limited. Hence, the specific objective of the study was to develop soil quality indices with key soil physical, chemical and biological indicators under the conservation and conventional tillage practices in a rice-mustard [Brassica juncea (L.) Czern.] cropping system. Eight treatment combinations including tillage and crop establishment, crop residue and cropping system intensification with inclusion of short duration summer mungbean [Vigna radiata (L.) Wilczek] were adopted in rice mustard cropping system in hot semi-arid, sub-tropical north-western Indo-Gangetic Plains agro-ecoregion of India. Soil samples collected from topsoil (0-5 cm) and 5-15 cm soil layer were analyzed for 15 physical, chemical and biological properties to develop unified soil quality index (SQI) through principal component analysis (PCA). The highest SQI was obtained in the zero till direct seeded rice (ZTDSR) - zero till mustard (ZTM) -ZT summer mungbean (ZTSMB (+R) (mungbean residue in ZTDSR rice residue in ZTMmustard residue in ZTSMB) treatment followed by the ZTDSR + BM (brown manuring) - ZTM (+R) (mustard residue in ZTDSR with BM - rice residue in ZTM). The lowest SQI was obtained in transplanted puddled rice (TPR) conventional till mustard (CTM) for both soil layers. The identified key indicators for SQI in this Inceptisol were saturated hydraulic conductivity (Ks), pH, total N, available P, and available K. Besides, the plots under ZTDSR - ZTM - ZTSMB (+R) resulted in 14 % higher total organic C in topsoil and 28 % higher aggregate stability than the TPR CTM plots. This ZTDSR - ZTM-ZTSMB (+R) treatment had 65 % higher surface soil microbial biomass C than the TPR - CTM treatment. The ZTDSR - ZTM-ZTSMB (+R) treatment also led to higher Ks, which was in the order of triple ZT > double ZT > ZT > conventional tillage. Thus, the medium-term CA with triple or double zero tillage with crop residue retention could lead to maintain agricultural sustainability under rice-mustard system. Hence, it may be recommended to the farmers for adoption.