Water balance in direct-seeded rice under conservation agriculture in North-western Indo-Gangetic Plains of India

Direct-seeded rice (Oryza sativa L.) (DSR) supported by conservation agriculture (CA)-based crop management practices is perceived to address the challenge of producing more rice grain with less water. DSR is endowed with multiple benefits/advantages over transplanted puddled rice (TPR) through savings in labour (40–45%), water (30–40%), fuel/energy (60–70%), and reductions in greenhouse gas emissions. It can be an economic alternative to TPR, but the performance of CA-based no-till and residue retained DSR has been hardly studied. Therefore, this field experiment consisting of eight treatments was designed in the sixth year of a continuing experiment under CA-based rice–mustard cropping system to estimate and analyse water budgeting in rice. Results revealed that, in the 0–15 cm soil layer, both DSR and TPR plots showed similar soil moisture content (SMC) values at initial, developmental, mid-season, and late-season periods. However, the overall SMC in a triple zero-till system that constituted mungbean residue (MBR) + zero-till DSR (ZT DSR) − rice residue (RR) + zero-till mustard (ZTM) − mustard residue (MR) + summer mungbean (SMB) treatment was 9.7 and 10% in soil surface, and in 15–30 cm soil layer, 32 and 12.6% higher than that in TPR − ZTM and TPR − CTM (conventional till mustard) treatments, respectively. Irrigation water requirment, including effective rainfall, was the highest during the mid-season (380.2 mm), followed by the initial stage (312.9 mm). The total amount of irrigation water applied to DSR plots was 924.3 mm against 1441.4 mm in TPR plots, indicating a 517 mm water saving. The amount of water used for puddling and ponding in TPR was 135 and 96 mm, respectively. The best treatment (MBR + ZTDSR − RR + ZTM-MR + SMB) showed a deep percolation of 5.8 mm day−1 that was 26% lower than the highest deep percolation (7.8 mm day−1) observed in TPR–CTM. Thus, a DSR crop under the triple zero-till system with retention of crop residues for three seasons can be recommended for attaining higher crop and water productivity. An extrapolation of these results revealed that, by adoption of this technology, 60060 Mm3 of water can be saved which can irrigate 6.72 Mha additional rice areas in the entire IGP (Indo-Gangetic Plains; total area under rice–wheat cropping system is 10.5 Mha). This may also lead to the mitigation of climate change effects. This practice can be adopted in the irrigated rice-growing belts of the North-western IGP of India and in similar agro-ecologies of the tropics and sub-tropics.