Mitigating toxicity of arsenic in sunflower (Helianthus annuus L.) with phosphate rock and farmyard manure using contrasting soil textures

Arsenic (As) immobilization in soil using inorganic/organic amendments may improve the productivity of As-contaminated soils. However, the degree of immobilization may vary depending on soil texture, phosphorus and organic matter content. A pot study was designed to investigate the effect of phosphate rock (PR) and farmyard manure (FYM) on As solubility in three soil types (sand, loam and clay), its transfer to plant parts and the resultant impact on physiology and achene yield of Helianthus annuus L. under alkaline calcareous condition. Plants were treated with As (60 and 120 mg kg−1 soil), PR (5 and 20 g kg−1 soil) and FYM (5 and 20% w/w) with a control. After sixteen weeks of growth period, results showed that As solubility decreased by 22.07–44.85% and 21.33–36.35% in sand, 17.55-45.80% and 30.83-45.98% in loam, while 22.81-36.89% and 20.92-42.41% in clay soils at As-60 and As-120, respectively with varied PR+FYM combinations compared to control. Integrated PR+FYM application restricted As movement from soil to plant, reducing achene As concentration by 22.22–41.26%, 26.08–43.47%, and 25.80-45.16% in sand, loam and clay soils, respectively, at As-120 compared to without PR+FYM. Thus, integrated PR+FYM application could be recommended to enhance the productivity of As-contaminated marginal lands by sunflower cultivation. Numerous studies investigate the ameliorating effect of phosphorus (P) and organic amendments to mitigate As stress. However, research on the use of PR as a P source to mitigate As stress is limited. Moreover, a majority of researchers use a single type of soil texture to study As dynamics but in our study, three varied soil textural types (sand, loam and clay) are used. In this way, our study could be the first to evaluate dynamics of As solubility, adsorption/desorption processes and bioavailability in sand, loam and clay textured soils under alkaline calcareous conditions. It also elucidates the integrated effect of PR and FYM to immobilize As in three different soil textures and describe the different mechanisms of As immobilization in alkaline calcareous condition, uptake by different sunflower parts and its subsequent impacts on growth, physiology and antioxidant enzymes activity under As stress. Arsenic solubility in soil significantly affected by soil texture, with clay soil exhibiting the least As availability followed by loam and sand texture.Integrated PR and FYM effectively immobilize As in all soil types by reducing water-soluble As with more pronounced reduction in loam texture compared to untreated control.PR and FYM restrict As translocation by suppling adequate P to sunflower, leading to improved photosynthetic rate and reduced antioxidant enzyme activities. Arsenic solubility in soil significantly affected by soil texture, with clay soil exhibiting the least As availability followed by loam and sand texture. Integrated PR and FYM effectively immobilize As in all soil types by reducing water-soluble As with more pronounced reduction in loam texture compared to untreated control. PR and FYM restrict As translocation by suppling adequate P to sunflower, leading to improved photosynthetic rate and reduced antioxidant enzyme activities.