No abstract

Considering that there are only few studies involving selenite sorption in tropical soils, mainly in Brazil, this study aimed to evaluate the influence of soil management, ionic strength (IS), and soil properties on selenite (SeIV) adsorption in tropical soils from the Brazilian Cerrado. A total of 16 soil samples were collected, being eight from cultivated fields and eight from the respective native area (uncultivated soils). Adsorption tests of Se(IV) were carried out in all soil samples, where solutions containing Se(IV) at concentrations of 100, 500, and 5000 μg L −1 were added in two IS, 15 and 150 mM. Results showed that all soils present high adsorption of Se(IV), mainly the clayey soils. For the sandy soils, higher Se(IV) adsorbed amounts were found for the uncultivated soils. Selenite retention was not affected by the tested IS, which indicate that the main adsorption mechanism of Se(IV) in these oxidic soils is by inner-sphere complex, which explains the low Se(IV) desorbed amounts found in the present study. Data from principal component analysis (PCA) showed that clay, S, Fe 2 O 3 , and Al 2 O 3 positively correlated with the adsorption of Se(IV), while (P-rem) available P, Fe OX , Al OX , PZSE, and pH have shown to affect negatively the Se(IV) adsorption. It can be concluded that Se(IV) is strongly adsorbed on Brazilian tropical soils, being this process unaffected by IS (which was not observed for selenate in a previous study) and affected by soil management and soil properties.

Selenium (Se) is essential for animals and humans, and studies assessing the influence of sulfur (S) and phosphorus (P) on Se availability and biofortification in tropical soils are required. This study evaluated the adsorption of selenate (SeVI) and selenite (SeIV) in two oxidic soils with contrasting soil texture and assessed effects of phosphate and sulfate as competitive anions on Se desorption. The study also examined Se biofortification of Panicum maximum cv. Mombaça grown in Se-treated clayey soil under increasing rates of P fertilisation. In the laboratory, different Se concentrations were added to soils for adsorption studies (0, 1, 2, 4 mg L–1 for SeVI and 0, 4, 8, 16 mg L–1 for SeIV), with Se desorption performed by adding different concentrations of P (0, 2.18, 4.36, 10.90, 21.90 mg L–1) or S (0, 3.75, 7.5, 15, 30 mg L–1). Mombaça grass was grown in pots for 43 days in the clayey soil fertilised with SeVI and increasing P rates. Selenium adsorption varied depending on Se speciation, Se rate and soil texture, with SeIV showing greater adsorption than SeVI. In general, amounts of SeVI desorbed increased with increasing addition of P and (mainly) S. However, only P had a positive effect for releasing SeIV from soils. At all SeVI rates added in the clayey soil, Se contents in the shoot dry matter of Mombaça grass increased with increasing P fertilisation rate, agreeing with the desorption results. Further studies combining desorption with biofortification data are recommended for assessing the influence of P in sandy clay loam tropical soils.

Context Agronomic biofortification is recognised as being an important strategy to increase selenium (Se) contents in food crops. The effectiveness of agronomic biofortification may differ depending on the methods of how Se is applied in agricultural systems. Aims This study aimed to evaluate different Se application methods (involving Se addition in the soil via Se-enriched fertilisers and foliar Se application) and rates for biofortification of common bean and to assess residual effects of soil Se additions for biofortification of Mombaça grass grown after the common bean. Methods Both experiments were carried out in a greenhouse. In the first cultivation (common bean), Se (as sodium selenate) was added at 0.0, 0.2, 0.4, 0.6, and 0.8 mg/dm3 using six different methods, as follows: Se-enriched monoammonium phosphate, Se-enriched urea, Se-foliar application, Se-enriched monoammonium phosphate + Se-enriched urea, Se-enriched monoammonium phosphate + Se-foliar application, and Se-enriched urea + Se-foliar application. To evaluate the residual effects of soil Se additions, Mombaça grass plants were grown after the common bean (second cultivation) without additional Se supply. Key results Agronomic biofortification effectiveness varied among methods, with higher Se contents in common bean grains being found when Se-enriched urea, Se-foliar application, and the combination of both methods were applied. Conclusions Selenium addition methods via soil using fertilisers as carriers to add Se, including Se-enriched monoammonium phosphate, showed a potential of residual effects on succeeding crops since these methods were efficient for increasing Se contents in Mombaça grass shoots.