Regionalization and Partitioning of Soil Health Indicators for Nigeria Using Spatially Contiguous Clustering for Economic and Social-Cultural Developments

Boluwade Boluwade

doi:10.3390/ijgi8100458

Abstract

Understanding the spatial variability of soil health and identifying areas that share similar soil properties can help nations transition to sustainable agricultural practices. This information is particularly applicable to management decisions such as tillage, nutrient application, and soil and water conservation. This study evaluated the spatial variability and derived the optimal number of spatially contiguous regions of Nigeria’s 774 Local Government Areas (LGAs) using three soil health indicators, organic carbon (OC), bulk density (BD) and total nitrogen (TN) extracted from the Africa Soil Information Service database. Missing data were imputed using the random forest imputation method with topography and normalized difference vegetation index (NDVI) as auxiliary variables. Using an exponential covariance function, the spatial ranges for BD, SN, and OC were calculated as 18, 42, and 60 km, respectively. These were the maximum distances at which there was no correlation between the sample data points. This finding suggests that OC has high variability across Nigeria as compared with other tested indicators. The ordinary kriging (OK) technique revealed spatial dependency (positive correlation) among TN and OC on interpolated surfaces, with high values in the southern part of the county and low values in the north. The BD values were also high in the northern regions where the soils are sandy; correspondingly, TN and OC had low values. The “regionalization with dynamically constrained agglomerative clustering and partitioning” (REDCAP) technique was used to divide LGAs into a possible number of regions while optimizing a sum of squares deviation (SSD). Optimal division was not observed in the resulting number of regional partitions. Conducting the Markov Chain Monte Carlo (MCMC) method on within-zone heterogeneity (WZH) revealed three partitions (two, five, and 15 regions) as optimal, in other words, there would be no significant change in WZH after three partitions. Ensuring a proper understanding of soil spatial variability and heterogeneities (or homogeneities) could facilitate agricultural planning that combines or merges state and local governments that share the same soil health properties, rather than basing decisions on geopolitical, racial, or ethnoreligious factors. The findings of this study could be applied to understand the importance of soil heterogeneities in hydrologic modeling applications. In addition, the findings may aid decision-making bodies such as the United Nations’ Food and Agricultural Organization, the International Fund for Agricultural Development, or the World Bank in their efforts to alleviate poverty, meet future food needs, mitigate the impacts of climate change, and provide financial funding through sustainable agriculture and intervention in developing countries such as Nigeria.

Highlights

A lack of adequate information regarding soil health status, few government incentives for access to post-harvesting facilities, and inadequate planning are among the primary threats to food security in developing countries
Bouma and McBratney [5] described the importance of soil health in providing ecosystem services and defined global sustainability as establishing food, energy, and water security; reducing the impacts of climate change; protecting biodiversity; and supporting human health [6]
This paper aims to quantify the spatial variability of Nigeria’s soil health indicators (SHIs) using variogram modeling and to partition the total area into a set of spatially contiguous regions using the following soil properties: bulk density (BD), soil nitrate (SN), and organic carbon (OC)

Summary

Introduction

A lack of adequate information regarding soil health status, few government incentives for access to post-harvesting facilities, and inadequate planning are among the primary threats to food security in developing countries. According to [2], soil health can be defined as “the capacity of a living soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health”. According to the Centre for Agriculture and Bioscience International [4], soil health plays a major role in ensuring food security. Soil health is important for food and agricultural production, especially in light of the growing global population [4]. Bouma and McBratney [5] described the importance of soil health in providing ecosystem services and defined global sustainability as establishing food, energy, and water security; reducing the impacts of climate change; protecting biodiversity; and supporting human health [6]. From the perspective of ensuring sustainability and food security, this connection between soil health and food security should be sustained

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