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Aims Selenium (Se) as selenate shares similarities with sulfate in transport and assimilation by plants. Uptake and assimilation of Se might be affected by S and vice-versa, which could affect Se and S concentration in plant tissues, and metabolic pathways such as biosynthesis of sugars, amino acids, and storage proteins. This study aimed to evaluate Se and S combination on cowpea plants under field conditions. Methods The experimental design was a 4 × 4 interaction between four rates of Se (0, 10, 25, and 50 g ha− 1) and four rates of S (0, 15, 30, and 60 kg ha− 1) in two consecutive years of cowpea cultivation. Concentrations of Se, S, total sugars, sucrose, total free amino acids, and storage proteins in plant tissue were measured. Results The Se x S interaction did not affect cowpea yield or growth. Antagonistic effects of S on Se concentrations in leaves and seeds were observed mainly for the second crop season. Selenium did not decrease S concentrations in leaves and seeds of cowpea plants. The combination of 25 g Se ha− 1 and 30 kg S ha− 1 provided the greater concentrations of total sugars. Interaction between Se and S was associated with greater sucrose, amino acids, and storage proteins concentrations in cowpea seeds. Conclusions The Se and S interaction did not impair plant growth but application of S decreased Se content in cowpea. Further studies are needed to better understand the physiological roles of Se and S combination in producing primary metabolic compounds.

The dataset comprises primary data for the concentration of 29 mineral micronutrients in cereal grains and up to 84 soil chemistry properties from GeoNutrition project surveys in Ethiopia and Malawi. The work provided insights on geospatial variation in the micronutrient concentration in staple crops, and the potential influencing soil factors. In Ethiopia, sampling was conducted in Amhara, Oromia, and Tigray regions, during the late-2017 and late-2018 harvest seasons. In Malawi, national-scale sampling was conducted during the April–June 2018 harvest season. The concentrations of micronutrients in grain were measured using inductively coupled plasma mass spectrometry (ICP-MS). Soil chemistry properties reported include soil pH; total soil nitrogen; total soil carbon (C); soil organic C; effective cation exchange capacity and exchangeable cations; a three-step sequential extraction scheme for the fractionation of sulfur and selenium; available phosphate; diethylenetriaminepentaacetic acid (DTPA)-extractable trace elements; extractable trace elements using 0.01 M Ca(NO3)2 and 0.01 M CaCl2; and isotopically exchangeable Zn. These data are reported here according to FAIR data principles to enable users to further explore agriculture-nutrition linkages.

Dietary zinc (Zn) deficiency is widespread globally, and in particular among people in sub-Saharan Africa (SSA). In Malawi, dietary sources of Zn are dominated by maize and spatially dependent variation in grain Zn concentration, which will affect dietary Zn intake, has been reported at distances of up to ~ 100 km. The aim of this study was to identify potential soil properties and environmental covariates which might explain this longer-range spatial variation in maize grain Zn concentration. Data for maize grain Zn concentrations, soil properties, and environmental covariates were obtained from a spatially representative survey in Malawi (n = 1600 locations). Labile and non-labile soil Zn forms were determined using isotopic dilution methods, alongside conventional agronomic soil analyses. Soil properties and environmental covariates as potential predictors of the concentration of Zn in maize grain were tested using a priori expert rankings and false discovery rate (FDR) controls within the linear mixed model (LMM) framework that informed the original survey design. Mean and median grain Zn concentrations were 21.8 and 21.5 mg kg−1, respectively (standard deviation 4.5; range 10.0–48.1). A LMM for grain Zn concentration was constructed for which the independent variables: soil pH(water), isotopically exchangeable Zn (ZnE), and diethylenetriaminepentaacetic acid (DTPA) extractable Zn (ZnDTPA) had predictive value (p

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