Selenium fractions in selenate-fertilized field soils of Finland

Abstract

Depending on the soil environment, selenium (Se) can exist as several species differing greatly in bioavailability. Characterization of soil Se reserves is thus necessary in assessing the nutritional supply of this essential element. In low-Se areas, Se fertilization is an option for securing adequate Se nutrition. Fertilization is, however, challenged by the unknown fate of the residual Se. In this study, we aimed to clarify the Se status of selenate-fertilized field soils by fractionating soil Se into five pools: salt-soluble (KCl), adsorbed (KH 2 PO 4 /K 2 HPO 4 ), organically associated (NaOH), elemental (Na 2 SO 3 ) and recalcitrant Se (NaOCl). Changes induced in these fractions by repeated application of low selenate doses were examined by comparing samples collected from the same locations in 1992 and 2004. The distribution of Se among the five fractions was relatively similar in all soils. On average, 1% of the amount of Se acquired was salt-soluble, 17% adsorbed, 39% organically associated, 14% elemental and 29% recalcitrant organic Se or metal selenides. The added Se was distributed among several fractions, leading to a relatively small change in each fraction. However, in mineral soils (n = 5), a significant increase in soil Se concentration was found between 1992 and 2004 in adsorbed, organically associated and recalcitrant Se, as well as in the total amount of Se acquired as a sum of the fractions. Our findings provide the first field-scale experimental support for the theoretical assumption of accumulation of residual selenate in acidic mineral soil in insoluble form.

Plant species and growing season weather influence the efficiency of selenium biofortification

“…Approximately half of the Se fertilizer that has been absorbed by the crop plants is returned with the organic residues into the soil after harvest. The small increase in organic Se pool in our study is in line with earlier results by Yläranta (1985) and Keskinen et al (2011).…”

“…In their 25-year followup study with selenate, Eurola et al (2008) found no change in hot-water extractable soil Se concentration). In contrast, long-term (1992 to 2004) selenate application to mineral soil is reported to have elevated the Se concentration in adsorbed, organically associated and recalcitrant (organic Se or metal selenides extracted by NaOCl) fractions by 5, 15 and 9 lg kg -1 , respectively (Keskinen et al 2011). This outcome supports Yläranta's (1985) assumption that residual Se accumulates in soil in an insoluble form.…”

Determining the fate of selenium in wheat biofortification: an isotopically labelled field trial study

“…Whilst the uptake of Se by crops in biofortification studies has been studied extensively, the retention of residual Se in the soil has received limited attention (Keskinen et al 2011). This issue needs to be addressed if Se biofortification is to be implemented on a large scale and over long time periods.…”

The behaviour of irrigation induced Se in the groundwater-soil-plant system in Punjab, India

“…Due to the relatively low annual Se addition (10-20 g ha À1 ) the time frame since the rst application of selenate in biofortication measures (20-30 years) has been too short to allow reliable conclusions about the environmental fate of the remaining 80-95% of the added Se. 72,92,93 In our study, the interval between rst selenate input and detectable changes is considerably shortened due to the large quantity of irrigation induced Se (2.6 to 5.2 kg ha À1 ) and can thus be taken as helpful case study to resolve questions about the biofortication inuenced Se cycling.…”