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Micronutrient deficiencies (MNDs) remain widespread among people in sub-Saharan Africa 1 – 5 , where access to sufficient food from plant and animal sources that is rich in micronutrients (vitamins and minerals) is limited due to socioeconomic and geographical reasons 4 – 6 . Here we report the micronutrient composition (calcium, iron, selenium and zinc) of staple cereal grains for most of the cereal production areas in Ethiopia and Malawi. We show that there is geospatial variation in the composition of micronutrients that is nutritionally important at subnational scales. Soil and environmental covariates of grain micronutrient concentrations included soil pH, soil organic matter, temperature, rainfall and topography, which were specific to micronutrient and crop type. For rural households consuming locally sourced food—including many smallholder farming communities—the location of residence can be the largest influencing factor in determining the dietary intake of micronutrients from cereals. Positive relationships between the concentration of selenium in grain and biomarkers of selenium dietary status occur in both countries. Surveillance of MNDs on the basis of biomarkers of status and dietary intakes from national- and regional-scale food-composition data 1 – 7 could be improved using subnational data on the composition of grain micronutrients. Beyond dietary diversification, interventions to alleviate MNDs, such as food fortification 8 , 9 and biofortification to increase the micronutrient concentrations in crops 10 , 11 , should account for geographical effects that can be larger in magnitude than intervention outcomes. Geospatial variation in the micronutrient composition (calcium, iron, selenium and zinc) of staple cereal grains is nutritionally important at subnational scales in Ethiopia and Malawi; these data could be used to improve surveillance of micronutrient deficiencies in the region.

Background Mineral nutrient uptake and utilisation by plants are controlled by many traits relating to root morphology, ion transport, sequestration and translocation. The aims of this study were to determine the phenotypic diversity in root morphology and leaf and seed mineral composition of a polyploid crop species, Brassica napus L., and how these traits relate to crop habit. Traits were quantified in a diversity panel of up to 387 genotypes: 163 winter, 127 spring, and seven semiwinter oilseed rape (OSR) habits, 35 swede, 15 winter fodder, and 40 exotic/unspecified habits. Root traits of 14 d old seedlings were measured in a ‘pouch and wick’ system ( n  = ~24 replicates per genotype). The mineral composition of 3–6 rosette-stage leaves, and mature seeds, was determined on compost-grown plants from a designed experiment ( n  = 5) by inductively coupled plasma-mass spectrometry (ICP-MS). Results Seed size explained a large proportion of the variation in root length. Winter OSR and fodder habits had longer primary and lateral roots than spring OSR habits, with generally lower mineral concentrations. A comparison of the ratios of elements in leaf and seed parts revealed differences in translocation processes between crop habits, including those likely to be associated with crop-selection for OSR seeds with lower sulphur-containing glucosinolates. Combining root, leaf and seed traits in a discriminant analysis provided the most accurate characterisation of crop habit, illustrating the interdependence of plant tissues. Conclusions High-throughput morphological and composition phenotyping reveals complex interrelationships between mineral acquisition and accumulation linked to genetic control within and between crop types (habits) in B. napus . Despite its recent genetic ancestry (<10 ky), root morphology, and leaf and seed composition traits could potentially be used in crop improvement, if suitable markers can be identified and if these correspond with suitable agronomy and quality traits.

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 (Zn E ), and diethylenetriaminepentaacetic acid (DTPA) extractable Zn (Zn DTPA ) had predictive value ( p  < 0.01 in all cases, with FDR controlled at < 0.05). Downscaled mean annual temperature also explained a proportion of the spatial variation in grain Zn concentration. Evidence for spatially dependent variation in maize grain Zn concentrations in Malawi is robust within the LMM framework used in this study, at distances of up to ~ 100 km. Spatial predictions from this LMM provide a basis for further investigation of variations in the contribution of staple foods to Zn nutrition, and where interventions to increase dietary Zn intake (e.g. biofortification) might be most effective. Other soil and landscape factors influencing spatially dependent variation in maize grain Zn concentration, along with factors operating over shorter distances such as choice of crop variety and agronomic practices, require further exploration beyond the scope of the design of this survey.

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.Measurement(s)Trace Element • soil chemical propertiesTechnology Type(s)Inductively-Coupled Plasma Mass SpectrometryFactor Type(s)Geography • Staple cereal cropSample Characteristic - OrganismStaple cereal food cropsSample Characteristic - EnvironmentSmallholder farmingSample Characteristic - LocationEthiopia • Malawi

Aims The principal aim of this research was to quantify retention of a single, realistic Se biofortification application (10 g ha−1) in contrasting soils over two growing seasons utilizing an enriched stable Se isotope (77Se) to discriminate between applied Se and native soil Se. Methods Isotopically enriched 77Se (Na2SeO4) was applied (10 g ha−1) to four replicate plots (2 m × 2 m) of winter wheat, on three contrasting soils on the University of Nottingham farm (UK), at early stem extension in May 2012. Labelled 77Se was assayed in soil and crop fractions by ICP-MS. Results Topsoil retained a proportion of applied Se at harvest (c. 15 – 31%) with only minor retention in subsoil (2-4%), although losses were 37 – 43%. Further analysis of topsoil 77Se, the following spring, and at second harvest, suggested that labelled Se retained in soil was fixed and uptake by a following crop was negligible. Conclusions Prolonged biofortification leads to accumulation of Se in soil but the retained Se has very low bioavailability and mobility. The time required to double the soil Se content would be about 500 years. However, reincorporation of cereal straw could provide a residual source of Se for a following crop, depending on timing and management.

Uptake kinetics and translocation characteristics of cadmium and zinc are presented for two contrasting ecotypes of the Cd/Zn hyperaccumulator Thlaspi caerulescens, Ganges (southern France) and Prayon (Belgium). Experiments using radioactive isotopes were designed to investigate the physiology of Cd and Zn uptake, and a pressure-chamber system was employed to collect xylem sap. In contrast to similar Zn uptake and translocation, measurements of concentration-dependent influx of Cd revealed marked differences between ecotypes. Ganges alone showed a clear saturable component in the low Cd concentration range; maximum influx Vmax for Cd was fivefold higher in Ganges; and there was a five-fold difference in the Cd concentration in xylem sap. Addition of Zn to the uptake solution at equimolar concentration to Cd did not decrease Cd uptake by Ganges, but caused a 35% decrease in Prayon. There is strong physiological evidence for a high-affinity, highly expressed Cd transporter in the root cell plasma membranes of the Ganges ecotype of T. caerulescens. This raises evolutionary questions about specific transporters for non-essential metals. The results also show the considerable scope for selecting hyperaccumulator ecotypes to achieve higher phytoextraction efficiencies.

The success of risk assessment of metal contaminated soils depends on how precisely one can predict the bio-availability of metals in soil and transfer to the human food chain. In the present investigation, we tested several formulations of the 'free-ion activity model (FIAM)' to predict uptake of Cd, Zn and Cu by perpetual spinach (Beta vulgaris, Cicla) grown on a range of soils amended with sewage sludge. The model was parameterised using data measured on samples of pore water extracted by centrifugation and with porous Rhizon samplers installed within the rhizosphere of the growing plants. Free ion activities (M super(2+)) were estimated following speciation of solution data using version 6 of the 'Windermere Humic Aqueous Model (WHAM-VI). For all three metals, the best formulation of the FIAM appeared to require only one hypothetical root sorption site without competition from protons. Values of (M super(2+)) could also be predicted satisfactorily from a pH-dependent Freundlich relation. Thus, from a combined FIAM-Freundlich relation and population dietary information, it was possible to estimate risk (hazard quotients) to consumers from very simple soil measurements: extractable metal content (0.05 M EDTA (Zn and Cu) or 1 M CaCl sub(2) (Cd)), soil humus content and pH. The role of increased soil organic matter content and soil pH, in reducing risk to consumers, is illustrated for Cd in a hypothetical soil at the current UK statutory Cd limit for sludge application to agricultural land.

Selenium (Se) is an essential element for human health. However, our knowledge of the prevalence of Se deficiency is less than for other micronutrients of public health concern such as iodine, iron and zinc, especially in sub-Saharan Africa (SSA). Studies of food systems in SSA, in particular in Malawi, have revealed that human Se deficiency risks are widespread and influenced strongly by geography. Direct evidence of Se deficiency risks includes nationally representative data of Se concentrations in blood plasma and urine as population biomarkers of Se status. Long-range geospatial variation in Se deficiency risks has been linked to soil characteristics and their effects on the Se concentration of food crops. Selenium deficiency risks are also linked to socio-economic status including access to animal source foods. This review highlights the need for geospatially-resolved data on the movement of Se and other micronutrients in food systems which span agriculture–nutrition–health disciplinary domains (defined as a GeoNutrition approach). Given that similar drivers of deficiency risks for Se, and other micronutrients, are likely to occur in other countries in SSA and elsewhere, micronutrient surveillance programmes should be designed accordingly.

Short rotation coppice (SRC) such as Salix spp. can be grown as an energy crop and offers some potential for economic and practical phytoextraction of marginally contaminated arable soil. This study tested various soil amendments intended to increase soil metal availability to Salix, investigated the distribution of metal between different tree fractions and assessed the viability of phytoextraction using SRC on arable soils. Several Salix genotypes were grown in field trials over 4 years. Cd and Zn concentrations were generally ranked in the order leaves > bark > wood. Metal concentrations in wood increased towards the top of the willow stems, whereas concentrations in leaves showed the opposite trend. None of the amendments significantly increased uptake of Zn by willow. However, in response to a range of soil HCl treatments, mean Cd concentrations in stems and leaves were 112% and 130% of control values. Data from the current experiment, and previous studies, were combined to develop a predictive model of Cd and Zn stem uptake by Salix. The minimum biological concentration factor (BCF) required to achieve a prescribed soil metal target was also calculated based on typical proportions of bioavailable Cd in sludge-amended soils for a 25-year Salix rotation. The best Salix genotypes investigated achieved less than 20% of the uptake rate required to remove one third of the soil Cd content (equivalent to the average isotopically exchangeable Cd fraction in soils at the study site).

We investigated several formulations of the 'free ion activity model' (FIAM) as a means of describing plant uptake of soil Cd and Zn from contaminated soils. Lolium perenne was grown on a range of urban and metal-spiked agricultural soils selected to provide a wide range of Cd and Zn concentrations, pH values and other physicochemical properties. Plants were grown under controlled conditions and above-ground biomass was harvested at regular intervals. Concentrations of Cd and Zn in the grass were compared with estimates of metal 'capacity' (total or radio-labile metal content in the soil) and 'intensity' (metal concentration in the soil solution or free divalent ion activity). The results suggested that 'capacity' terms alone were poor predictors of plant metal uptake (r2 values between 0.001 and 0.43), while metal ion 'intensity' provided quite reasonable predictions of the variation observed for several harvests of the grass (r2 = 0.60–0.87). Soil solution-to-plant transfer factors were highly pH-dependent which may suggest significant competition between trace metals and protons for sorption sites on roots. However, resolution of this question was confounded because of the strong co-variance between pH and p(M2+) in the soil pore water. Thus the influence of pH could not be separated from the effect of changing metal ion activity on uptake rate. Other possible effects on metal uptake such as dilution from increased biomass during growth and competition for uptake between different metal ions (Zn vs. Cd), or with Ca2+, appeared to play very minor roles in determining bioavailability. Several formulations of the FIAM failed to provide a consistently superior prediction of metal uptake when compared to purely empirical regression with pH and p(M2+) within the range of the data used to parameterise the models.