Puddling of clay soils for rice transplanting causes a loss of soil structure and vertical shrinkage cracks that are hypothesized to hamper sunflower root growth in the following dry season. To alleviate soil constraints for sunflower root growth and yield, we examined the effects of three levels of mulch and two irrigation regimes in the dry season on a clay-textured soil in the coastal zone of Bangladesh. These treatments were no-mulch, rice straw mulch at 5 t ha⁻¹ and 10 t ha⁻¹, irrigation applied to the field capacity (I1) and a water supply double that of the I1 treatment (I2). The rice straw mulch significantly increased soil water content by 3–9% and decreased soil penetration resistance by 28–77% and crack volume by 84–91% at A 0–30 cm soil depth relative to the no-mulch treatment. The better root development with the rice straw mulch increased sunflower yield by 23%. No benefit or further reduction in soil penetration resistance or yield improvement was obtained from increasing the level of mulch from 5 to 10 t ha⁻¹ or the volume of irrigation water. It is concluded that ameliorating soil constraints by mulch application led to better root growth in the upper root zone and the increased yield in the clay soil.

Sunflower (Helianthus annuus L.), which is widely grown globally for its high-quality edible oil, is reasonably salt and drought tolerant but it is susceptible to waterlogging. In the saline coastal zone of the Ganges delta, sunflower is often exposed to sudden heavy rainfall during early growth but plant tolerance to such events is not known. Hence, we evaluated the effect of short-term soil inundation (referred to as waterlogging) for 0, 24, 48 and 72 h on sunflower at emergence, 2-leaf, and 4-leaf stages in early- and late-sown crops under field conditions (saline, clay-textured soil, and shallow groundwater). Waterlogging for 24 h did not affect sunflower at any stage but waterlogging for 48 and 72 h suppressed emergence and growth at the 2 and 4-leaf stages. Waterlogging for 72 h completely prevented the emergence for early sowing, whereas emergence was less affected for later sowing. Shoot and root dry weight were most affected at the emergence and 2-leaf stage, not at the 4-leaf stage. In conclusion, waterlogging caused by more than 24 h soil inundation at up to the 4-leaf stage severely depressed emergence and growth, indicating the need for effective drainage at sowing of sunflower in the low-lying coastal saline zone of Bangladesh.

Three constraints affect the growth of crops in the Rabi (dry) season in southern Bangladesh: these are the clay nature of the soils which decreases the infiltration of water, the conserving of soil moisture with the increasingly dry conditions and the accumulation of salts on the soil surface through capillary from saline groundwater. Field experiments were conducted in the salt-affected areas of southern Bangladesh. The objectives of the study were to: (i) evaluate the effect of straw and irrigation frequency on crop growth and yield in maize and sunflower, and (ii) determine the combined effect of straw and irrigation frequency on the salinity, osmotic potential and moisture of soils. The experiment was carried out in farmers’ fields with eight treatments and was replicated three times during the dry (rabi) season of 2018–2019. There were two rice straw treatments (with or without straw), and 4 irrigation frequencies (at intervals of 5–7,10–12,15–17 or 20–25 days). Maize and sunflower seeds were sown by dibbling in no-tilled systems. The results showed that rice straw significantly affected the crop growth and yield, increasing the yield of maize and sunflower by 22% and 4.3% compared to treatments of without residue. The irrigation treatments also significantly affected crop yields. There was no interaction between straw levels and irrigation. The causes of these effects appeared to be improved water relations: rice straw and more frequent irrigations both reduced the salinity and osmotic potential of soils compared with treatments without straw while the soil moisture was greater in rice straw treatments and increased with the increased soil layers. We conclude that straw mulching and irrigation management practice could be used in coastal saline of heavy soils to reduce soil salinity, osmotic potentials thereby increasing crop yields in no-tilled systems.

Silicon (Si), a beneficial metalloid, alleviates various abiotic stresses including salinity. Studies on Si-mediated alleviation of salinity stress of plants were mostly done in solution culture, very rare in soil culture including sunflower. Due to scarce literature on whether soil-supplied Si alleviates salinity stress in sunflower and there is no soil application rate of Si available for sunflower, the current pot study investigated for an optimum Si rate that can ameliorate the salinity effect. The 2-year (2022 and 2023) pot study consisted of two factors: (i) irrigation of crop ~0 or 8 dS m-1 (ii) Si levels, 0, 0.1, 0.2, 0.3 g Si kg-1 soil with three replications. The results showed that salinity reduced the yield, yield attributes and dry matter significantly while application of Si gradually increased those yield parameters and seed yield. In case of sodium (Na), potassium (K) and Si uptake, salinity increased Na uptake and reduced K and Si uptake while application of Si decreased the Na uptake but increased the K and Si uptake. Silicon also increased the leaf number per plant and plant height. Among Si levels, 0.2 and 0.3 g kg-1 soil showed almost similar ameliorative effect of salinity. The results of the study suggest that soil application of Si can ameliorate salinity stress on sunflower and 0.2 to 0.3 g Si kg-1 soil should be suffice to ameliorate the negative effects of salinity. Studies on Si-mediated amelioration of salinity on sunflower and other suitable winter crops should be done in the farmers’ field of coastal region of Bangladesh where fresh water is scarce. J Bangladesh Agril Univ 23(1): 25–32, 2025