Conservation Agriculture in rice-mustard cropping system for five years: Impacts on crop productivity, profitability, water-use efficiency, and soil properties

Developing suitable crop rotations and crop establishment practices is an important mechanism that can enhance factor productivity and sustainability of an agro-ecosystem. However, the impact of Conservation Agriculture (CA) on alternate crop rotation of the most-dominant but tillage- and input-intensive rice (Oryza sativa L.)-wheat (Triticum aestivum (L.) emend Fiori & Paol) rotation of the Indo-Gangetic Plains (IGP) of India is not elaborately studied. Hence, we evaluated the effect of CA on crop and water productivity, profitability, and soil carbon status in rice-mustard (Brassica juncea L.) rotation in the North-western IGP of India for five consecutive years. Eight treatments comprising of tillage, crop residue, brown manuring (BM) using Sesbania bispinosa, and summer mungbean [Vigna radiata (L.) Wilczek] (SMB) were adopted in rice - mustard cropping system. The conventional transplanted puddled rice (TPR) - conventional fill mustard (CTM) (similar to TPR-CTM) rotation resulted in significantly higher rice grain yield than zero fill direct-seeded rice (ZTDSR) - ZT mustard (ZTM) system with or without crop residue in all five years. However, in this regard, the CA-based ZT rice - mustard - SMB with residue [ZTDSR-ZTM-ZTSMB (+ RA was comparable with it during first three years, but was inferior to it in 4th and 5th years. The ZTDSR-ZTM-ZTSMB ( +R) had overall 10.9 % lower five-year mean rice yield than that in the TPRCTM system. This CA-based system gave significantly higher mustard grain yield in all the years (except first year), and the five-year mean mustard yield was 30.3 % higher than in the TPR-CTM. Another CA-based double cropping system having ZTDSR + BM - ZTM (+ R) was comparable with TPR-CTM in all the years and resulted in 27.6 % higher five-year mean mustard yield than the TPR-CTM practice. The ZTDSR-ZTM-ZTSMB (+ R) practice gave 44 % (including SMB) and 8.1 % (excluding SMB) higher system productivity and significantly higher sustainable yield index of the rice-mustard system compared with the TPR-CTM practice. The ZTDSR-ZTM-ZTSMB (+ R) practice encountered significantly lower weed density in mustard in all five years than TPR-CTM system. The cost-benefit analysis revealed that this CA practice fetched higher net returns by INR 53,000 and 21,400 ha(-1) from the rice-mustard system with and without SMB, respectively over the TPR-CTM system. Again, this ZTDSR-ZTM-ZTSMB (+ R) system led to an increase in irrigation water productivity by 27.8 % in rice and 35.1 % in mustard, and the total water (irrigation + rainfall) productivity by 35.7 % in mustard crop compared with the TPR-CTM system (P <= 0.05). This CA-based rice-mustard system resulted in significantly higher very labile (similar to 50.6 %) and labile (similar to 47.7 %) carbon concentration at 0-5 cm depth of soil compared to the conventional TPR-CTM system. The CA system being productive, profitable, and resource-efficient can be recommended for North-western IGP of India and in similar agro-ecologies of the tropics and sub-tropics. It can be adopted with suitable site-specific refinement in South-Asian countries, where decline in crop productivity and soil health is a consistent pervasive problem due to continuous cereal-cereal rotation.