Potential for soil organic carbon sequestration in grasslands in East African countries: A review

Bezaye Tessema,Kristin Piikki,Mats Söderström,Sylvia Nyawira,Lulseged Tamene,An Notenbaert,Rolf Sommer,Birthe Paul,Sara Namirembe

doi:10.1111/grs.12267

Abstract

AbstractGrasslands occupy almost half of the world's land area. Soil organic carbon (SOC) is a key indicator of soil fertility and grassland productivity. Increasing SOC stocks (so‐called SOC sequestration) improves soil fertility and contributes to climate change mitigation by binding atmospheric carbon dioxide (CO2). Grasslands constitute about 70% of all agricultural land, but their potential for SOC sequestration is largely unknown. This review paper quantitatively summarizes observation‐based studies on the SOC sequestration potential of grasslands in six East African countries (Burundi, Ethiopia, Kenya, Rwanda, Tanzania and Uganda) and seeks to identify knowledge gaps related to SOC sequestration potential in the region. In the studies reviewed, SOC stocks in grasslands range from 3 to 93 Mg C/ha in the upper 0.3 m of the soil profile, while SOC sequestration rate ranges from 0.1 to 3.1 Mg C ha‐1 year‐1 under different management strategies. Grazing management is reported to have a considerable impact on SOC sequestration rates, and grassland regeneration and protection are recommended as options to stimulate SOC sequestration. However, a very limited number of relevant studies are available (n = 23) and there is a need for fundamental information on SOC sequestration potential in the region. The effectiveness of potential incentive mechanisms, such as payments for environmental services, to foster uptake of SOC‐enhancing practices should also be assessed.

Highlights

Grasslands are areas where the vegetation is dominated by grasses (Poaceae family)
Soil organic carbon (SOC) content is a key indicator of soil fertility and grassland productivity, and SOC sequestration is considered a means to mitigate climate change through
The higher SOC stocks in grasslands are due to their perennial nature which results in constant carbon inputs from aboveground vegetation and the large quantities of carbon to the subsoil via root exudates and decomposing deep roots (Zimmermann, Dauber, & Jones, 2012)

Summary

| INTRODUCTION

Grasslands are areas where the vegetation is dominated by grasses (Poaceae family). They are an intrinsic part of both rangelands and pasturelands and constitute about half of the global land area. Soil organic carbon (SOC) content is a key indicator of soil fertility and grassland productivity, and SOC sequestration is considered a means to mitigate climate change through. Understanding the capacity of grassland soils to store organic carbon is vital in developing climate change mitigation strategies and in addressing soil health issues (Gray, Bishop, & Wilson, 2015). Grassland management practices have substantial effects on the turnover rates of soil organic matter, carbon inputs and soil nutrients (Blair, Lefroy, & Lisle, 1995), leading to varying effects on SOC. The aim of this study was review observation-based studies on grassland systems in East African countries (Burundi, Ethiopia, Kenya, Rwanda, Tanzania and Uganda (Figure 1)) in order to: (a) assess the SOC sequestration potential of existing management practices; (b) assess the key drivers affecting SOC sequestration in grasslands in the region; and (c) identify the knowledge gaps regarding SOC sequestration potential in East African grasslands and provide recommendations for further studies

| MATERIALS AND METHODS

| Literature search and selection

| DISCUSSION

| Data availability

Findings

| CONCLUSIONS