Forgoing the fallow in Bangladesh's stress-prone coastal deltaic environments: Effect of sowing date, nitrogen, and genotype on wheat yield in farmers’ fields

•Farmer-managed trials show wheat is a viable alternative to fallows in Bangladesh.•Yield is reduced by 57kgha−1 for each day sowing is delayed beyond November 20.•Existing stress-tolerant genotypes show little advantage over traditional ones.•Profitable N rates for early and late sowing are at most 100 and 67kgha−1.•Variable effects of environment necessitate site- and time-specific management. Rising wheat demand in South Asia necessitates crop intensification to meet food security needs. Increased grain output can be achieved by bridging yield gaps on currently farmed land or by expanding cultivation to new land, though the latter entails environmental trade-offs and offers limited potential as most of South Asia's arable land is already cropped. Alternatively, opportunities for boosting production may exist where farmers can transition from single to double cropping and forgo dry season fallows – which are estimated at between 240,000 and 800,000ha in southern Bangladesh – and establish a crop such as wheat following monsoon season rice. Southern Bangladesh's fallows result from prolonged post-monsoon soil saturation, soil salinity, and farmers’ low risk-bearing and investment capacity. In response, we assessed the potential to sow wheat on land that is seasonally fallow with approaches that optimize yields while reducing risk and rationalizing costs. Working with 64 farmers in eight production environments, we examined yield response to three genotypes, BG25 and BG27 (with salinity- and heat-tolerant traits) and BG21 (local check), across a gradient of sowing dates, grouped as ‘early’ (sown before 15 December) and ‘late’ (after 15 December), under 0, 100 and 133 and 0, 67 and 100kgNha−1 for early- and late-sowing groups, respectively. Across environments and genotypes, yield ranged from 2.11 to 4.77tha−1 (mean: 3.9tha−1) under early-sowing, and from 0.83 to 4.27tha−1 (mean: 2.74tha−1) under late-sowing. Wheat performance varied with environment (1.68–4.77tha−1 at 100kgNha−1 across sowing groups); the lowest yields found where early sowing was delayed and soil salinity levels were elevated. Small but significant (P