Selenium adsorption in soils as influenced by different anions

Abstract

Studies on selenium adsorption were conducted on seleniferous and non‐seleniferous soils of north‐west India. Soils were equilibrated with graded levels of Se ranging from 1 to 100 μg ml—1 tagged with 75Se in the presence of sulphate, nitrate and phosphate ions, generally being applied to soils as inorganic fertilizers. The adsorption of Se on different soils, both in the presence and absence of competing anions, increased with increase in the level of Se added. Adsorption of Se conformed to Langmuir equation. In the absence of any competing anions, adsorption maxima of Se for different soils ranged from 270 to 461 μg g—1. The corresponding values decreased appreciably in the presence of competing anions; per cent decrease ranged from 3 to 21 at 10 μg SO4‐S ml—1, from 8 to 40 at 60 μg NO3‐N ml—1 and 32 to 56 at 15 μg H2PO4‐P ml—1. The bonding energy of Se in different soils decreased by 33 to 66 per cent in the presence of only phosphate ions. The changes in bonding energy were inconsistent in the case of nitrate and sulphate ions. At equal concentration of added P and Se, the amount of P adsorbed was 2 to 3 times the amount of Se adsorbed. With increasing concentration of Se, greater amounts of S were released in the equilibrium solution. The distribution coefficients (Kd) decreased significantly in the presence of different anions; the effect was conspicuous in the case of phosphate ions.

Impact of sulphur fertilisation on crop response to selenium fertilisation

“…Increased Se availability was observed in the incubation experiment where an addition of sulphate significantly increased the extractability of selenate added to the soils. A similar result was found by Dhillon and Dhillon (2000), where the addition of sulphate as gypsum decreased the retention of Se in soils. This enhanced selenate extractability could explain the increased Se uptake from Se fertiliser by S addition in Experiment 1, where the soil effect may dominate over the plant physiological effect because the crop was not deficient in S. The enhanced selenate extractability may occur as a result of decreased selenate adsorption by the soil minerals in the presence of sulphate.…”

“…Indeed, selenite has been found to be the dominant Se species in UK arable field soils (Stroud et al 2009), and in wheat field trials before and after selenate fertilisation . Sulphate added to soil may decrease selenate adsorption (Dhillon and Dhillon 2000) or suppress microbial uptake and assimilation of selenate (Lindblow-Kull et al 1985;Zehr and Oremland 1987). These effects could result in enhanced availability of selenate fertiliser for plant uptake.…”

Effect of phosphorus status of the soil on selenium availability

“…While not as much studied as the interaction of sulfate and selenate, some studies confirm an antagonistic effect of phosphate on selenite uptake in plants (Hopper and Parker, 1999;Broyer et al, 1972), whereas others found little effect (Mora et al, 2008;Nakamaru and Sekine, 2008;Yläranta, 1990b). However, phosphate may reduce selenite adsorption on soil solid surfaces due to competition for binding sites, since it is more strongly adsorbed than selenite, and thus make Se more plant-available (Barrow et al, 2005;Dhillon and Dhillon, 2000;Yläranta, 1983). Still, an addition of phosphate did not significantly increase leaching of selenite from clay, sandy loam, or Carex peat in a study by Yläranta (1991) which could be expected if selenite was adsorbed to a lesser extent.…”

Liming and selenium application impact on plant available selenium in selected soils of Malawi

“…Bioavailability of Se in soils is a function of sorption and desorption of Se. Both sorption and desorption of Se are, in turn, determined mainly by the soil pH, redox potential, microbial activity, mineralogy, soil organic matter, and other anions such as phosphate, sulphate, oxalate, and molybdate for adsorption sites (Dhillon and Dhillon, 2000;Goh and Lim, 2004). Selenite is sorbed more strongly than selenate onto clays, but not as strongly as phosphate or fluoride (Barrow and Whelan, 1989).…”