Quantification of water stress impacts on canopy traits, yield, quality and water productivity of onion (Allium cepa L.) cultivars in a shallow basaltic soil of water scarce zone

Understanding and mitigating the adverse impacts of water stress on agriculture production have become global concern in water scarce environments. Particularly, Deccan plateau, the largest semi-arid zone of peninsular India, is confronted with severe water resources conflicts and extensive pressure for food production under climate change scenario. For sustainable agriculture, it is critical to quantify the impact of water stress on major crops like winter onion (Allium cepa L.) which is grown under diverse water management practices on shallow basaltic soils of this region. We conducted a field experiment during two growing seasons (2017–18 and 2018–19) for evaluating responses of different cultivars of red (B. Raj, B. Kiran, B. Super, B. Red and Local-Fursangi) and white (B. Shubra, B. Sweta and B. Safed) onion to variable water stress created using a line source sprinkler (LSS) system. There was a 1.1, 1.6, 3.9, 9.2 fold decline in total bulb yields (TBY) with increasing water deficit i.e. when depth of irrigation water (IW) applied equalled 0.60, 0.40, 0.20 and 0.00 times the cumulative open pan evaporation (CPE) as compared with the recommended practice (IW:CPE 0.80). The TBY increased between 86.2 and 106.6 Mg ha−1 in red cultivars when irrigation was scheduled at excess to optimum water regimes (IW: CPE 0.80–1.00), while it was improved by 5.0–20.4% for white cultivars under medium (0.40–0.59) to severe (0.0–0.39) water deficit stress. Further, highest (4.3–16.2%) improvement in TBY of Local cultivar was reported irrespective to different water stress levels. Local and white cultivars could have better tolerance to water stress by keeping cooler canopy temperatures, higher leaf relative water content and modulating the stomatal opening. Lower yield losses due to rotting (0.30–1.81%) and splitting (4.4–6.5%) of bulbs were observed in red and white cultivars. This study further endorses the appropriate selection of onion cultivars reduces water requirements by 37.5–61% to attain similar water productivity (16.0 kg m−3) as with recommended irrigation level. Increased in water stress levels though reduced quality of physical traits of harvested bulbs viz., mean weight, average dia., shape index (SI), harvest index (HI) and firmness, these improved the storage quality. Water deficit also increased accumulation of soluble solids, total phenolics, protein, dry matter and elevated the pH and rehydration quality besides potentially affecting the enzymatic activity (SOD and POD) of onion cultivars. It was concluded that white onion cultivars like B. Shubra with higher WP under medium and severe water deficit stress and ‘Local’ red cultivar should be preferred for efficient utilisation of water resources both in terms of the productivity and post-harvest quality of onion under drought prone and shallow basaltic regions of Deccan plateau.