Crop and soil organic matter simulation models – A brief review of their basic features and application in sub-Saharan Africa

Over the past decades, numerous crop-soil models have been developed to represent dynamic processes in cropland systems, including soil organic carbon (SOC) dynamics (Campbell and Paustian, 2015). These models use mathematical equations that determine carbon allocation in the vegetation and biomass and soils to represent biogeochemical processes, such as photosynthesis, respiration and decomposition. Furthermore, a range of crop management practices are represented in most of the models, enabling an assessment of their impacts on SOC in agricultural systems. Although models were initially developed for research purposes, they are increasingly becoming important in many aspects of environmental policies (Manlay et al., 2007). Extensively tested models provide effective tools that can be used in identifying sustainable land management practices across different agroecological conditions. Compared to field experiments, which are time and resource consuming, models are more effective for making predictions and understanding crop and SOC dynamics on large scales and different time scales. However, the choice of the model depends on the ability of the model to simulate key processes in the region of interest. We conducted a survey to identify the features of the commonly used crop-soil models in order to inform the choices for application in sub-Saharan Africa. The survey was administered online to the model developers. In addition, we also conducted a literature search to assess the usage of the different models in different parts of sub-Saharan. In this brief, we provide a basic summary of the information from the survey and literature review

East Africa Soil Carbon Workshop: Science to inform policy

Introduction and rationale: Global soils contain about 2344 billion tons of organic carbon. This is the largest terrestrial pool of organic carbon. Small changes in soil organic carbon (SOC) stocks could result in significant impacts on the global carbon balance. Trapping carbon in the soil contributes to reducing greenhouse gas (GHG) emissions from agriculture. Managing our soils better can also help us to adapt to a changing climate by improving soil health, soil productivity (and crop yields) and agro-ecosystem resilience. However, not all soils are the same. Geography, climate, and land use play a crucial role in how much carbon soils can potentially absorb, or how much they lose. While expectations are high – especially for degraded soils of sub-Saharan Africa – that soils can play crucial role in mitigating climate change, details on the where, how, and potential costs are missing. The East Africa Soil Carbon Workshop – Science to Inform Policy brought together 28 participants from 11 countries: Ethiopia, Kenya, Uganda, Rwanda, Tanzania, South Africa, Madagascar, Germany, France, Netherlands, and Sweden (10 women and 18 men). Participants included decision makers, practitioners and implementers, and researchers in the fields of biophysical and social science. The aim was to exchange state-of-the art knowledge; review and discuss latest methods, metrics and tools for assessing SOC and mapping & monitoring SOC dynamic hotspots; and to discuss entry points for shaping gender-sensitive policies towards a green economy where carbon sequestration in soils is a recognized component. During group work sessions, the participants discussed and developed key messages that are relevant for policymaking on SOC sequestration in East Africa and beyond. This report summarizes contributions from participants, lessons learnt and action points

Soil health and ecosystem services: Lessons from sub-Sahara Africa (SSA)

Management practices to improve soil health influence several ecosystem services including regulation of water flows, changes in soil biodiversity and greenhouse gases that are important at local, regional and global levels. Unfortunately, the primary focus in soil health management over the years has been increasing crop productivity and to some extent the associated economics and use efficiencies of inputs. There are now efforts to study the inter-relationship of associated ecosystem effects of soil health management considering that sustainable intensification cannot occur without conscious recognition of these associated non-provisioning ecosystem services. This review documents the current knowledge of ecosystem services for key management practices based on experiences from agricultural lands in sub-Sahara Africa (SSA). Here, practicing conservation agriculture (CA) and Integrated Soil fertility management (ISFM) have overall positive benefits on increasing infiltration (> 44), reducing runoff (> 30%) and soil erosion (> 33%) and increases soil biodiversity. While ISFM and Agroforestry increase provisioning of fuelwood, fodder and food, the effect of CA on the provisioning of food is unclear. Also, considering long-term perspectives, none of the studied soil health promoting practices are increasing soil organic carbon (SOC). Annual contributions to greenhouse gases are generally low (< 3 kg N2O ha−1) with few exceptions. Nitrogen leaching vary widely, from 0.2 to over 200 kg N ha−1 and are sometimes inconsistent with N inputs. This summary of key considerations for evaluating practices from multiple perspectives including provisioning, regulating, supporting and cultural ecosystem services is important to inform future soil health policy and research initiatives in SSA

Unlocking the potential of soil organic carbon in agricultural landscapes in Kenya and Ethiopia

Soils are a very important component of the global carbon cycle as they contain the largest sink of carbon in the terrestrial biosphere. At the same time, soil organic carbon (SOC) is the basis for soil fertility and the production of food to feed the growing global population. Healthy soils are not only important from an agricultural production point of view, but they also provide a multitude of other benefits that are critical to human well-being

Soil carbon policies in Ethiopia and Kenya: evolution, challenges, and opportunities

The policy brief provides a general statues of the soil carbon policies in Kenya and Ethiopi

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

Grasslands 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

Rangeland Degradation: Causes, Consequences, Monitoring Techniques and Remedies

Rangelands occupy 25% of the total land surface globally. In Africa, rangelands are estimated to cover 66% of the land surface, although there are variations from country to country. In Eastern Africa, for example, land surface coverage of rangeland areas varies from 44% in Uganda and 65% in Ethiopia to 74% in Tanzania and over 80% in Kenya. Rangelands have environmental, social and economic benefits, including support to national economies through tourism and employment. In Kenya, tourism, much of which is attributed to rangelands, accounts for 13% of the gross domestic product. In Tanzania, tourism contributed 9.0% of the total GDP, supporting 26% of total exports, 8.2% of the total employment, and 8.7% of total investment in the year 2017. Despite their benefits, rangelands are under threat of continued degradation driven by anthropogenic and natural causes. Natural causes of rangeland degradation include climate change and variabilities, aridity and desertification, drought, as well as alien species invasion. Anthropogenic rangeland degradation can manifest through agricultural activities and associated developmental practices, overstocking and overgrazing, as well as breakdown of social structures and government policies/by-laws. Continuous overgrazing and overstocking not only affect soil physical (compaction, breakdown of aggregates) but also chemical (soil pH and salinization, nutrient leaching, diminishing organic matter content), and biological properties. These decrease rangeland production potentials. However, numerous strategies to arrest and remedy rangeland degradation, such as rangeland re-vegetation, water harvesting, soil surface scarification, and livestock grazing management are available. This report addresses rangeland degradation and potential control measures with a strong focus on soil aspects