Arsenic behavior in different textured soils amended with phosphate rock and farm yard manure

Abstract

Restricted arsenic (As) mobility in soil by the use of inorganic and/or organic substances might facilitate the detoxification of metalloid and improve the productivity of As-contaminated soils. However, potential of these substances to immobilize As may vary with the nature and properties of soil. The present study is planned to investigate As fate in different textured soils and the role of phosphate rock (PR) and farm yard manure (FYM) on As fractionation in soil and accumulation by sunflower (Helianthus annuus L.) under alkaline calcareous conditions. For this purpose, four sets of experiments were conducted. First study was based on the hypothesis that As mobility and bioavailability may vary with soil textural type. The treatment plan was comprised of three soil textural types (sandy, loamy and clayey) and five As levels (0, 50, 100, 150 and 200 mg kg-1 soil) with a control and replicated thrice. Six As fractions i.e. labile As (L-As), aluminum bound As (Al As), iron bound As (Fe-As), calcium bound As (Ca-As), organic matter bound As (OM-As) and residual As (R-As) were determined. On an average, L-As (the most phytoavailable among the extracted fractions) was 48.9, 19.8 and 6.6% of the total As while the bioaccumulation factor for root ranged between 1.9-9.5, 1.8-4.4 and 0.8-2.1 for sandy, loamy and clayey textured soils, respectively. Second study was based on the hypothesis that As adsorption/desorption capacity of soil may differ depending upon phosphorus (P) supply. Experimental plan was comprised of three soil textural types (sandy, loamy and clayey), two As levels (60 and 120 mg kg-1 ) and four PR levels (0, 5, 10 and 20 g kg-1 soil) with a control and three replications. L-As increased by 16.9-48.0% at As60 while 36.0- 68.1% at As120 in sandy, 19.1-64.0% at As60 while 11.5-52.3% at As120 in loamy, and 21.8-58.2% at As60 while 22.3-70.0% at As120 in clayey soil by the application of different levels of PR as compared to respective As treatments without PR. Third study was planned to investigate the effect of FYM on As adsorption/desorption in different textured soils. The treatment plan was comprised of three soil textural types (sandy, loamy and clayey), two As levels (60 and 120 mg kg-1 soil) and four FYM levels (0, 5, 10 and 20%) with a control and three replications. FYM increased As immobilization in all the three textured soils. Highest level of FYM (20%) reduced L-As by 31.03, 46.87 and 55.17% at As60 while 32.57, 55.50 and 64.86% at As120 in sandy, loamy and clayey soils, respectively as compared to respective As treatments without FYM. Fourth study was comprised of three soil textural types (sandy, loamy and clayey), two As levels (60 and 120 mg kg-1 soil), two PR levels (5 and 20 g kg-1 soil) and two FYM levels (5 and 20%) with a control and three replications. Arsenic solubility decreased by 22.07-44.85% at As60 while 21.33-36.35% at As120 in sandy soil, 17.55-45.80% at As60 while 30.83-45.98% at As120 in loamy soil, and 22.81-36.89% at As60 while 20.92-42.41% at As120 in clayey soil with different combinations of PR + FYM as compared to respective As treatments without amendments. Integrated use of PR and FYM reduced As accumulation in sunflower roots, shoots, leaves and achenes with the consequent improvement in photosynthetic pigment, photosynthesis rate, transpiration rate, stomatal conductance as well as yield and yield attributes. In conclusion, soil texture greatly influenced As mobility. Highest As solubility and toxicity to sunflower growth, physiological and yield characteristics was found in the order of sandy > loamy > clayey. Arsenic accumulation in plants ordered as roots > leaves > shoots > achenes. Although, individual application of P could increase As solubility but reduced its accumulation by plants and improved plant survival to As stressed environment. Farm yard manure either alone or in combination with PR reduced As solubility in soil, its transfer to plants and improved physiological characteristics, leading to enhanced sunflower adaptability to As-contaminated soils.