Multiple soil and landscape properties are associated with the spatial variation of selenium concentration in maize grain in Malawi

Dietary selenium (Se) deficiency is widespread in Malawi, due to the limited supply of Se in the predominantly maize based-food system characterised by low Se concentration. In this study, the aim was to examine the spatial variation of Se in maize grains in Malawi, in relation to soil properties and landscape features. Co-located soil and maize grain samples were collected in a spatially representative survey. Selenium concentration in maize, soil properties, and environmental covariates were determined. Soil and environmental variables were tested as potential predictors of Se concentration in maize. A false discovery rate (FDR) control was used within a linear mixed model (LMM) framework. Selenium concentrations in maize ranged from below detection limits (7.69 µ g kg ^−1 ) to 1852 µ g kg ^−1 with mean and median values of 39.1 and 16.8 µ g kg ^−1 respectively. The ranges of concentrations of Se fractions in soil were (i) soluble Se 0.181–18.8 µ g kg ^−1 with mean and median values of 3.94 and 3.29 mg µ g kg ^−1 respectively; (ii) adsorbed Se 0.019–119 µ g kg ^−1 with mean and median values of 3.72 and 3.02 µ g kg ^−1 respectively; (iii) organically bound Se 9.43–1334 µ g kg ^−1 with mean and median values of 123 and 92.3 µ g kg ^−1 respectively. A LMM for maize Se concentration was used for which the independent log transformed variables of soil soluble Se, adsorbed Se, oxalate extracted oxides, soluble and exchangeable sulphur had predictive value ( p $\lt$ 0.01 in all cases, with FDR controlled at $\lt$ 0.05). Downscaled mean annual temperature also explained some of the spatial variation in grain Se concentration. Spatial variation of Se in maize showed relationships with soil and environmental variables, which can be used to identify areas most at risk of Se deficiency and thus inform policy responses. However, only a small proportion of the variation was explained indicating more analysis of Se geochemistry in soil may provide more explanatory insights.