Variation in the yield of sunflower (Helianthus annuus L.) due to differing tillage systems is associated with variation in solute potential of the soil solution in a salt-affected coastal region of the Ganges Delta

Intensification of crop production in the coastal zones of the mega-deltas of Asia by dry season cropping requires timely crop establishment to mitigate the adverse effects of waterlogging, drought, salinity and poor soil structure. In the salt-affected coastal zone of the Ganges Delta, the best method of mechanized cultivation for the timely establishment of non-rice dry season crops on poorly structured, wet clay soils is unknown. Two field experiments were conducted to evaluate the effects of tillage systems with different levels of soil disturbance on the establishment, growth and yield of sunflower, and on soil physical and chemical properties. In 2016-17, five tillage treatments were tested: zero tillage (ZT), narrow strip tillage (NST), bed planting (BP), single pass shallow tillage (SPST) and double pass shallow tillage (DP); in 2017-18, four tillage types were tested: NST, wide strip tillage (WST), BP and SPST. Intensive soil disturbance (BP, DP and SPST) maintained higher soil water content in the surface soil (0–15 cm depth) than less disturbance (ZT, NST and WST) in both years. Tillage treatments had no effect on soil salinity (EC_1:5) in 2016-17, but in 2017-18 BP significantly reduced the soil salinity relative to NST throughout the season. Highest yields (19 % and 10 % improvements in 2016-17 and 2017-18 respectively) were associated with tillage treatments with greatest soil disturbance, the BP and DP treatments in 2016-17, and the SPST treatment in 2017-18. These effects were mostly due to increases in soil water content and solute potential in surface soil layers. We conclude that for a wet-clay soil, heavy soil disturbance, such as with BP has the potential to increase the yield of sunflower by increasing soil water supply, decreasing soil salinity and maintaining a higher solute potential in the upper soil layers.