Can local nutrient-circularity and erosion control increase yields of resource-constraint smallholder farmers? A case study in Kenya and Uganda

Arabel Amann,Mathew Herrnegger,Jeninah Karungi,Allan John Komakech,Hope Mwanake,Lea Schneider,Christoph Schürz,Gabriel Stecher,Alice Turinawe,Matthias Zessner,Jakob Lederer

doi:10.1016/j.jclepro.2021.128510

Abstract

As many regions in sub-Saharan Africa, the border region of Kenya (KE) and Uganda (UG) has faced a declining soil fertility for decades, resulting from soil erosion, intensely managed agricultural soils due to population pressure and small inputs of mineral and organic fertilizers. With limited financial means, farmers need measures and/or technologies that effectively reduce nutrient losses or increase inputs at a low cost. In this study, four such measures are in focus, namely erosion reduction practices, vermicomposting of animal manure, collection of human urine in jerry cans and, collection of human excreta in urine-diverting dry toilets. Current soil nutrient balances in five districts in the Sio-Malaba-Malakisi River Basin and the potential of these measures to reduce the soil nutrient deficit are studied using the method of material flow analysis and the software STAN. Furthermore, crop-nutrient-response functions are used to determine their potential impact on maize harvests. Overall, results reveal that there exists a non-negligible and exploitable potential of local resources to reduce the soil nutrient deficit, improve harvests and in turn food security of the smallholder farmers in the region. Soil nutrient deficits could be reduced by 20–30%, 23–42% and 9–15% for nitrogen (N), phosphorus (P) and potassium (K), respectively. Subsequently, maize harvests could be increased by 8–40%, depending on the applied technology and area. This research provides useful insights for agricultural extension workers, politicians and researchers alike, highlighting that simple and easily available technologies can harness similar amounts of nutrients as more complex and expensive ones if all specific technology-constraints are adequately incorporated in the analyses.

Highlights

Countries in sub-Saharan Africa (SSA) face one of the lowest foodself-sufficiency rates in the world
As can be seen from the following results, these differences are mainly attributed to high erosion rates, as some of the analysed units show a much higher risk than the units studied in the mentioned literature
The nutrient balances performed in this study by the use of material flow analysis (MFA) showed highly varying soil nutrient deficits for district and counties of close vicinity in the border region of Kenya and Uganda

Summary

Introduction

Countries in sub-Saharan Africa (SSA) face one of the lowest foodself-sufficiency rates in the world (van Ittersum et al, 2016; Wichern et al, 2017). In. Declining soil-fertility has been and still is the single-most researched factor related to food-insecurity in SSA (Vanlauwe et al, 2017). Declining soil-fertility has been and still is the single-most researched factor related to food-insecurity in SSA (Vanlauwe et al, 2017) Underlying issues for this decline are manifold, e.g. high erosion rates (Schürz et al, 2020), limited input of external and inadequate management of on-farm nutrient sources and organic matter (Andersson, 2015; Castellanos-Navarrete et al, 2015), reduced time of land laying fallow due to population pressure (Tittonell et al, 2008) and a high dependency on rainfall (Barasa, 2014; Epule et al, 2017). Potential technologies and management practices of all forms, sizes and costs have been studied to cope with these issues, from simple reduction of erosion by reduced tillage (Kaizzi et al, 2007) to complex and cost-intensive biogas technology with the use of digestate as a fertilizer (Walekhwa et al, 2009; Clemens et al, 2018)

Methods

Results

Discussion

Conclusion