Assessment of yield and water productivity of subsurface drip irrigated onion under varying lateral spacing and irrigation water quality, and in comparison with surface drip irrigation method

Freshwater scarcity in arid and semi-arid regions has increased reliance on poor-quality irrigation water. Conjunctive use of saline water with freshwater is an effective long-term strategy to deal with water scarcity in such regions while maximizing irrigation water use efficiency (IWUE) and yield. Management of canal fresh water and saline water under subsurface drip irrigation (SSD) was studied to maximise onion yield and IWUE by selecting the optimal irrigation treatment (IT) and lateral spacing (LS) in the semi-arid region of northern India. Treatments comprised of 4 water qualities (canal fresh water – C; conjunctive use of canal fresh water and saline water in 1:1 ratio – C1S1; in 1:2 ratio – C1S2; and saline water – S) and 2 LS (45 and 60 cm) under SSD methods. The effects on soil water–salt dynamics, growth parameters, IWUE and yield of onion grown using SSD were evaluated under different treatments in the years 2018 and 2019. Additionally, yield and IWUE under surface drip (SD) and SSD were compared. In general, soil moisture decreased vertically downward and radially outward, whereas soil salinity increased and decreased with increase in radial distance and soil depth, respectively. Significant effects of irrigation treatments were observed on plant growth parameters, yield and IWUE under both LS. The highest yield (36.69 tꞏha−1) and IWUE (16.17 kgꞏm−3) were recorded at 45 cm LS under Treatment C; the lowest yield (27.01 tꞏha−1) and IWUE (10.96 kgꞏha−1ꞏm−3) were observed under Treatment S. Differences in results between Treatment C and C1S1 were non-significant, suggesting that C1S1 can be adopted for onion cultivation in sandy loam soils without compromising yield and IWUE. No significant differences were observed between SD and SSD for yield or yield-related parameters during the experimental period. The results highlight the importance of IT and LS for maximum onion production under SSD.