Geospatial modelling of soil geochemistry at national-scale for improved human nutrition

Mineral micronutrient deficiencies (MND), prevalent in Ethiopia and Malawi among most countries in sub-Saharan Africa, are linked to soil type. Dietary mineral intake is influenced by mineral content of edible portions of crops, and there is strong evidence that cereals grown in these regions have low uptake of micronutrients. The low nutrient uptake is attributed to soil conditions. Spatial information on soil and crop properties is therefore required to improve local estimates of MND risk in order to implement targeted and efficient interventions. Obtaining spatial information on soil micronutrients status and other relevant properties that affect their uptake requires substantial effort, and there are uncertainties in the resulting information, which depend, in part on the methods used for prediction and the sampling design. Therefore, it is necessary to use robust and efficient methods for spatial prediction which characterise the uncertainty of the predictions reliably. Furthermore, it is necessary that these uncertainties can be communicated effectively to stakeholder groups so that they can account for them at all stages from commissioning the survey through to making decisions based on the information. In this study, it was important first to understand how uncertain spatial information can be communicated to stakeholders (e.g., those in public health or nutrition and agronomy or soil science) through a systematic evaluation in the forms of maps. Evaluation of the test methods were done through a structured elicitation of the opinions of members of a stakeholder group about the usefulness of the methods. Stakeholders found that general measures of uncertainty, such as prediction error variances (e.g., kriging variance) were less clear than measures which integrated the uncertainty explicitly with the decision—e.g., the probability that the true value of a variable at a site if interest falls below a critical threshold. There was no evidence that they found verbal phrases these (e.g., “very uncertain”) clearer than numerical values (i.e., a probability in the interval [0,1]). Following on this finding, it was necessary to examine how stakeholders interpret such probability information in more detail. Specifically, is it possible to estimate a probability threshold which a stakeholder group would choose to intervene, reflecting their assessment of the costs attached to errors of commission and omission? Further does this probability depend on framing of the problem (e.g., probability that a threshold is exceeded or that it is not exceeded) and does it depend on professional background of the stakeholder? In a designed experiment, stakeholders were presented with uncertain information on micronutrient supply from a crop, with the uncertainty expressed as a probability with positive framing (probability of adequate supply) or negative framing (probability of insufficient supply). The results showed that probabilities presented in a negative framing led to more conservative decisions, i.e., deciding to intervene at a much smaller probability of deficiency than if the equivalent probability of sufficiency were presented. The elicited probability threshold is prone to framing effects (i.e., how the question is posed), and that this effect interacts with professional group. The two components of this thesis described above showed how uncertain information can be effectively communicated to stakeholders to support decisions. The next task was to develop a framework for the planning, execution, and evaluation of surveys to address specific requirements of these stakeholders. This was based on a decision-theory approach to analyse the particular task, to identify the key uncertainties and their implications and so to enable stakeholders to ensure that an approach to survey would meet their needs. A particular task, based on research practices within the GeoNutrition project (Bill & Melinda Gates funded) was identified —the selection of the study sites to evaluate agronomic biofortification strategies for MND at selected sites based on soil soluble Se. The information required were analysed, and then the outputs of spatial prediction at national-scale of soil soluble Se by ordinary kriging, indicator kriging, linear mixed models and random forest were evaluated. There were substantial uncertainties by all three methods, and challenges with dealing with a complex statistical distribution. This work showed the importance of validation—internal and independent for understanding the suitability of spatial prediction to support decision making. Uncertainty should be considered when planning sampling for a geostatistical survey. It is important to consider how stakeholders can assess the implications of uncertainty in spatial predictions to determine appropriate sampling grid space for a geostatistical survey. Four approaches (offset correlation, prediction intervals, conditional probabilities and implicit loss functions), that can be used to assess the implications of uncertainty in spatial predictions using prior information on variability of the target properties, were presented to a diverse group of stakeholders in order to determine an appropriate grid spacing. There were variations in the selection made by each method. Some were not well understood. The one which stakeholder favoured, offset correlation, is not directly linked to decision making. More work is needed to develop sound but accessible ways to engage stakeholders with uncertainty consistent across planning and interpretation. Findings from this research will help in better understanding of uncertainties in the data obtained in the GeoNutrition projects thereby facilitating improved use and uptake of that information by decision makers in Ethiopia and Malawi. Better decisions will be made on sampling for such surveys in other countries which decide to undertake those using better methodologies for national-scale surveys of soil properties or similar environmental variables

Geospatial modelling of soil geochemistry at national-scale for improved human nutrition

Mineral micronutrient deficiencies (MND), prevalent in Ethiopia and Malawi among most countries in sub-Saharan Africa, are linked to soil type. Dietary mineral intake is influenced by mineral content of edible portions of crops, and there is strong evidence that cereals grown in these regions have low uptake of micronutrients. The low nutrient uptake is attributed to soil conditions. Spatial information on soil and crop properties is therefore required to improve local estimates of MND risk in order to implement targeted and efficient interventions. Obtaining spatial information on soil micronutrients status and other relevant properties that affect their uptake requires substantial effort, and there are uncertainties in the resulting information, which depend, in part on the methods used for prediction and the sampling design. Therefore, it is necessary to use robust and efficient methods for spatial prediction which characterise the uncertainty of the predictions reliably. Furthermore, it is necessary that these uncertainties can be communicated effectively to stakeholder groups so that they can account for them at all stages from commissioning the survey through to making decisions based on the information. In this study, it was important first to understand how uncertain spatial information can be communicated to stakeholders (e.g., those in public health or nutrition and agronomy or soil science) through a systematic evaluation in the forms of maps. Evaluation of the test methods were done through a structured elicitation of the opinions of members of a stakeholder group about the usefulness of the methods. Stakeholders found that general measures of uncertainty, such as prediction error variances (e.g., kriging variance) were less clear than measures which integrated the uncertainty explicitly with the decision—e.g., the probability that the true value of a variable at a site if interest falls below a critical threshold. There was no evidence that they found verbal phrases these (e.g., “very uncertain”) clearer than numerical values (i.e., a probability in the interval [0,1]). Following on this finding, it was necessary to examine how stakeholders interpret such probability information in more detail. Specifically, is it possible to estimate a probability threshold which a stakeholder group would choose to intervene, reflecting their assessment of the costs attached to errors of commission and omission? Further does this probability depend on framing of the problem (e.g., probability that a threshold is exceeded or that it is not exceeded) and does it depend on professional background of the stakeholder? In a designed experiment, stakeholders were presented with uncertain information on micronutrient supply from a crop, with the uncertainty expressed as a probability with positive framing (probability of adequate supply) or negative framing (probability of insufficient supply). The results showed that probabilities presented in a negative framing led to more conservative decisions, i.e., deciding to intervene at a much smaller probability of deficiency than if the equivalent probability of sufficiency were presented. The elicited probability threshold is prone to framing effects (i.e., how the question is posed), and that this effect interacts with professional group. The two components of this thesis described above showed how uncertain information can be effectively communicated to stakeholders to support decisions. The next task was to develop a framework for the planning, execution, and evaluation of surveys to address specific requirements of these stakeholders. This was based on a decision-theory approach to analyse the particular task, to identify the key uncertainties and their implications and so to enable stakeholders to ensure that an approach to survey would meet their needs. A particular task, based on research practices within the GeoNutrition project (Bill & Melinda Gates funded) was identified —the selection of the study sites to evaluate agronomic biofortification strategies for MND at selected sites based on soil soluble Se. The information required were analysed, and then the outputs of spatial prediction at national-scale of soil soluble Se by ordinary kriging, indicator kriging, linear mixed models and random forest were evaluated. There were substantial uncertainties by all three methods, and challenges with dealing with a complex statistical distribution. This work showed the importance of validation—internal and independent for understanding the suitability of spatial prediction to support decision making. Uncertainty should be considered when planning sampling for a geostatistical survey. It is important to consider how stakeholders can assess the implications of uncertainty in spatial predictions to determine appropriate sampling grid space for a geostatistical survey. Four approaches (offset correlation, prediction intervals, conditional probabilities and implicit loss functions), that can be used to assess the implications of uncertainty in spatial predictions using prior information on variability of the target properties, were presented to a diverse group of stakeholders in order to determine an appropriate grid spacing. There were variations in the selection made by each method. Some were not well understood. The one which stakeholder favoured, offset correlation, is not directly linked to decision making. More work is needed to develop sound but accessible ways to engage stakeholders with uncertainty consistent across planning and interpretation. Findings from this research will help in better understanding of uncertainties in the data obtained in the GeoNutrition projects thereby facilitating improved use and uptake of that information by decision makers in Ethiopia and Malawi. Better decisions will be made on sampling for such surveys in other countries which decide to undertake those using better methodologies for national-scale surveys of soil properties or similar environmental variables

Selenium deficiency is widespread and spatially dependent in Ethiopia

Selenium (Se) is an essential element for human health and livestock productivity. Globally, human Se status is highly variable, mainly due to the influence of soil types on the Se content of crops, suggesting the need to identify areas of deficiency to design targeted interventions. In sub-Saharan Africa, including Ethiopia, data on population Se status are largely unavailable, although previous studies indicated the potential for widespread Se deficiency. Serum Se concentration of a nationally representative sample of the Ethiopian population was determined, and these observed values were combined with a spatial statistical model to predict and map the Se status of populations across the country. The study used archived serum samples (n = 3269) from the 2015 Ethiopian National Micronutrient Survey (ENMS). The ENMS was a cross-sectional survey of young and school-age children, women and men. Serum Se concentration was measured using inductively coupled plasma mass spectrometry (ICPMS). The national median (Q1, Q3) serum Se concentration was 87.7 (56.7, 123.0) μg L−1. Serum Se concentration differed between regions, ranging from a median (Q1, Q3) of 54.6 (43.1, 66.3) µg L−1 in the Benishangul-Gumuz Region to 122.0 (105, 141) µg L−1 in the Southern Nations, Nationalities, and Peoples’ Region and the Afar Region. Overall, 35.5% of the population were Se deficient, defined as serum Se < 70 µg L−1. A geostatistical analysis showed that there was marked spatial dependence in Se status, with serum concentrations greatest among those living in North-East and Eastern Ethiopia and along the Rift Valley, while serum Se concentrations were lower among those living in North-West and Western Ethiopia. Selenium deficiency in Ethiopia is widespread, but the risk of Se deficiency is highly spatially dependent. Policies to enhance Se nutrition should target populations in North-West and Western Ethiopi

Communicating uncertainties in spatial predictions of grain micronutrient concentration

The concentration of micronutrients in staple crops varies spatially. Quantitative information about this can help in designing efficient interventions to address micronutrient deficiency. Concentration of a micronutrient in a staple crop can be mapped from limited samples, but the resulting statistical predictions are uncertain. Decision makers must understand this uncertainty to make robust use of spatial information, but this is a challenge due to the difficulties in communicating quantitative concepts to a general audience. We proposed strategies to communicate uncertain information and present a systematic evaluation and comparison in the form of maps. We proposed testing five methods to communicate the uncertainty about the conditional mean grain concentration of an essential micronutrient, selenium (Se). Evaluation of the communication methods was done through a questionnaire by eliciting stakeholder opinions about the usefulness of the methods of communicating uncertainty. We found significant differences in how participants responded to the different methods. In particular, there was a preference for methods based on the probability that concentrations are below or above a nutritionally significant threshold compared with general measures of uncertainty such as the prediction interval. There was no evidence that methods which used pictographs or calibrated verbal phrases to support the interpretation of probabilities made a different impression than probability alone, as judged from the responses to interpretative questions, although these approaches were ranked most highly when participants were asked to put the methods in order of preference

Mineral micronutrient status and spatial distribution among the Ethiopian population.

Multiple micronutrient deficiencies are widespread in Ethiopia. However, the distribution of Se and Zn deficiency risks has previously shown evidence of spatially dependent variability, warranting the need to explore this aspect for wider micronutrients. Here, blood serum concentrations for Ca, Mg, Co, Cu and Mo were measured (n 3102) on samples from the Ethiopian National Micronutrient Survey. Geostatistical modelling was used to test spatial variation of these micronutrients for women of reproductive age, who represent the largest demographic group surveyed (n 1290). Median serum concentrations were 8·6 mg dl-1 for Ca, 1·9 mg dl-1 for Mg, 0·4 µg l-1 for Co, 98·8 µg dl-1 for Cu and 0·2 µg dl-1 for Mo. The prevalence of Ca, Mg and Co deficiency was 41·6 %, 29·2 % and 15·9 %, respectively; Cu and Mo deficiency prevalence was 7·6 % and 0·3 %, respectively. A higher prevalence of Ca, Cu and Mo deficiency was observed in north western, Co deficiency in central and Mg deficiency in north eastern parts of Ethiopia. Serum Ca, Mg and Mo concentrations show spatial dependencies up to 140-500 km; however, there was no evidence of spatial correlations for serum Co and Cu concentrations. These new data indicate the scale of multiple mineral micronutrient deficiency in Ethiopia and the geographical differences in the prevalence of deficiencies suggesting the need to consider targeted responses during the planning of nutrition intervention programmes

Zinc deficiency is highly prevalent and spatially dependent over short distances in Ethiopia

Zinc (Zn) is an essential nutrient for human health. In Ethiopia, a high prevalence of Zn deficiency has been reported. To explore demographic variation and spatial dependencies in the Zn status of the Ethiopian population, we analyzed archived serum samples (n = 3373) from the 2015 Ethiopian National Micronutrient Survey (ENMS), a cross-sectional survey of young children, school-age children, women of reproductive age (WRA) and men conducted in all 9 regions and two city administration of Ethiopia. Serum Zn concentrations, measured using inductively coupled plasma-mass spectrometry (ICPMS), were compared to thresholds based on age, sex, fasting status, and time of blood collection, after adjusting for inflammation status. Median serum Zn concentration of the population was 57.5 μg dL−1. Overall, it is estimated that 72% of the population was Zn deficient, with high prevalence in all demographic groups. Spatial statistical analysis showed that there was spatial dependence in Zn status of WRA at distances of up to 45 km. Zinc deficiency is spatially dependent over short distances. Although WRA in most areas are likely to be Zn deficient, prevalence of deficiency varies at regional scale and between rural and urban inhabitants, suggesting there is scope to explore drivers of this variation, prioritize nutritional interventions, and to design more representative surveillance programs

A pilot survey of selenium status and its geospatial variation among children and women in three rural districts of Zimbabwe

IntroductionSelenium (Se) deficiency is increasingly recognized as a public health problem in sub-Saharan Africa.MethodsThe current cross-sectional study assessed the prevalence and geospatial patterns of Se deficiency among children aged 6–59 months (n = 741) and women of 15–49 years old (n = 831) selected by simple random sampling in rural Zimbabwe (Murewa, Shamva, and Mutasa districts). Venous blood samples were collected and stored according to World Health Organization guidelines. Plasma Se concentration was determined by inductively coupled plasma-mass spectrometry.ResultsMedian, Q1, and Q3 plasma Se concentrations were 61.2, 48.7, and 73.3 μg/L for women and 40.5, 31.3, and 49.5 μg/L for children, respectively. Low plasma Se concentrations (9.41 μg/L in children and 10.20 μg/L in women) indicative of severe Se deficiency risk was observed. Overall, 94.6% of children and 69.8% of women had sub-optimal Se status defined by plasma Se concentrations of &lt;64.8 μg/L and &lt;70 μg/L, respectively.DiscussionHigh and widespread Se deficiency among women and children in the three districts is of public health concern and might be prevalent in other rural districts in Zimbabwe. Geostatistical analysis by conditional kriging showed a high risk of Se deficiency and that the Se status in women and children in Murewa, Shamva, and Mutasa districts was driven by short-range variations of up to ⁓12 km. Selenium status was homogenous within each district. However, there was substantial inter-district variation, indicative of marked spatial patterns if the sampling area is scaled up. A nationwide survey that explores the extent and spatial distribution of Se deficiency is warranted

Perceived local evidence of climate change and variability impacts on natural resources in smallholder communities of eastern Zimbabwe

Declining crop and livestock production due to a degrading land resource base and changing climate among other biophysical and socio-economic constraints, are increasingly forcing rural households in Zimbabwe and other parts of southern Africa to rely on common natural resource pools (CNRPs) to supplement their household food and income. This study investigated the nature and dynamics of CNRPs that are utilised by smallholder-farming communities of Dendenyore and Ushe wards (local development unit) in Hwedza district in eastern Zimbabwe, as influenced by climate change and variability. Special attention was paid to quantifying how community responses to climate change and variability have influenced natural resource use patterns and gender roles among households differing in resource endowments in Dendenyore and Ushe wards. A combination of farmer participatory research approaches, Geographic Information Systems (GIS) and remote sensing were employed between 2011 and 2013 to characterise the contribution of CNRPs to household food and income of these smallholder communities. Across study sites, wetlands and woodlands were ranked as the most important CNRPs. These were given highest priority because of their provisioning services by providing fruits (Mazhanje (Uapaca kirkiana) and Hacha (Parinari curatellifolia)), raw materials for crafts (Tsanga (Phragmites mauritianus) and Mutsvairo (Miscanthidium sorghum)), and firewood for energy. The extraction and use patterns of products obtained from the wetlands and woodlands varied significantly by household resource endowment, with the resource-constrained (RG3) depending more on natural resources. For example, RG3 households extracted greatest quantities of fruits such as Mazhanje approximately 35 kg per capita-1 year-1 between 2011 and 2012 compared to RG1 and RG2 households who only extracted 11 and 25 kg per capita-1 year-1, respectively. Despite their importance CNRPs, wetlands and woodlands, decreased by > 30% between 1972 and 2011. This reduction in prioritised CNRPs was attributed to a number of factors which were ranked in the order: land use changes (33% of the respondents) < less rainfall (31%) < and increasing temperatures (27%). The communities also perceived that the severe droughts of 1983/1984, 1991/1992, 2002/2003 and 2007/2008 seasons increased the rate of extraction of natural resources and this resulted in depletion of the natural resource base. For example during a drought, participation of men in extraction of water and indigenous fruits increased at least 40%, from a good (favourable season) to a bad (drought season) year. Provisional services of CNRPs are likely to be affected directly and indirectly by factors such as projected increase in rainfall variability and population increase amongst other factors. Despite their apparent decline communities in Dendenyore and Ushe are continually relying on a degraded natural resource base, suggesting limited livelihood options to adapt to climate change and variability, and other existing socio-economic and biophysical challenges. This suggests limited options for rural communities to adapt to the changing food production systems in the wake of climate change and variability and other challenges such as declining soil fertility. There is therefore a need to design adaptive farm management options that enhance both crop and livestock production in a changing climate as well as identifying other livelihood alternatives outside agriculture to reduce pressure on CNRPs. There need for active participation of communities and government agencies in proper land use planning and management of natural resources. In addition, promotion of alternative resources options to firewood (e.g. solar, woodlots) and indigenous fruit trees (e.g. orchards) among rural communities could reduce extraction of natural resources from wetlands and woodlands.,EU-funded FAO-SOFECSA-UZ Climate Risk Project, Deutscher Akademischer Austausch Dienst (DAAD) In-country scholarship award (A/11/95775), Global SysTem for Analysis, Research and Training (START

Mulching and Fertilization Effects on Weed Dynamics under Conservation Agriculture-Based Maize Cropping in Zimbabwe

A two-year study was conducted to assess how mulch influences weed dynamics following imposition of different fertilization treatments under three crop establishment options: (i) conventional; (ii) ripping; and (iii) basin, in a two-year maize-legume rotation. Eight treatments were imposed within each crop establishment option and received maize stover mulch applied at 0% or 30% cover before planting  maize (Zea mays) or cowpea (Vigna unguiculata) as test crops. Maize received nitrogen (N) at 35, 90, or 120 kg·ha−1 and phosphorus (P) at 14 or 26 kg·ha−1 applied alone or in combination with 4 or 7 t cattle manure·ha−1, while cowpea received 8 or 17 N·kg·ha−1 and similar P rates to maize. Results indicated that both weed biomass and diversity were influenced more by fertilization than method of crop establishment. On treatments under high fertilizer application rates, or previously planted to cowpea weed biomass ranged between 220 and 400 g·m−2 under mulch and 370–510 g·m−2 (no mulch). Here species richness ranged between 7–16 and was dominated by dicotyledons. This was in contrast to biomass ranges of 75–200 g·m−2 in the low fertilized and control plots, where only one or two grass types dominated. Overall, weed densities were 6% to 51% higher under conventional tillage compared to the two conservation agriculture (CA) options, although the data indicated that mulch significantly (p &lt; 0.05) depressed weed density by up to 70%. We concluded that mulching could be a potential mechanism for reducing weeding labor costs for smallholders and the general environmental and health concerns associated with the use of herbicides in CA systems

Stakeholder interpretation of probabilistic representations of uncertainty in spatial information: an example on the nutritional quality of staple crops

Spatial information, inferred from samples, is needed for decision-making, but is uncertain. One way to convey uncertain information is with probabilities (e.g. that a value falls below a critical threshold). We examined how different professional groups (agricultural scientists or health and nutrition experts) interpret information, presented this way, when making a decision about interventions to address human selenium (Se) deficiency. The information provided was a map, either of the probability that Se concentration in local staple grain falls below a nutritionally-significant threshold (negative framing) or of the probability that grain Se concentration is above the threshold (positive framing). There was evidence for an effect of professional group and of framing on the decision process. Negative framing led to more conservative decisions; intervention was recommended at a smaller probability that the grain Se is inadequate than if the question were framed positively, and the decisions were more comparable between professional groups under negative framing. Our results show the importance of framing in probabilistic presentations of uncertainty, and of the background of the interpreter. Our experimental approach could be used to elicit threshold probabilities which represent the preferences of stakeholder communities to support them in the interpretation of uncertain information