Rolf Sommer

• PhD
• Managing Director at WWF Germany

This study was designed to accompany the Upper Tana Nairobi Water Fund, a large public–private partnership fund that promotes sustainable land management (SLM) practices among smallholder farmers to protect supply and quality of water to one of Kenya's most economically important regions. Co‐benefits or trade‐offs of the promoted practices might in...

Increasing yields in farmer fields is a priority to address increasing food demands. The study was conducted within four wheat-growing areas in Ethiopia: Debre Birhan, Hosaina, Sinana and Maychew. The objectives were to identify (1) best-bet soil fertility management options based on agronomic performance and economic evaluation and (2) key yield-r...

This report provides a summary/synthesis of key research outputs and messages gathered from the four year BMZ-funded project on "Scaling up soil carbon enhancement interventions for food security and climate across complex landscapes in Kenya and Ethiopia." More info: https://hdl.handle.net/10568/111805

Improved management practices should be implemented in croplands in sub-Saharan Africa to enhance soil organic carbon (SOC) storage and/or reduce losses associated with land-use change, thereby addressing the challenge of ongoing soil degradation. DayCent, a process-based biogeochemical model, provides a useful tool for evaluating which management...

The sustainable land management program (SLMP) of Ethiopia aims to improve livelihoods and create resilient communities and landscape to climate change. Soil organic carbon (SOC) sequestration is one of the key co-benefits of the SLMP. The objective of this study was to estimate the spatial dynamics of SOC in 2010 and 2018 (before and after SLMP) a...

Phosphorus is a critical nutrient for plant growth. Several agronomic practices have been promoted to improve soil fertility and crop productivity in Western Kenya. Yet, despite their benefits, a dearth of knowledge exists on their long-term effects on soil microbial biomass and phosphorus solubilizing microbial species (PSMs) abundance especially...

During the conference ‘Rediscovering the soil with Alexander von Humboldt. Soil and Biodiversity - Everything is connected with everything’ in Berlin on December 5, 2019, a political statement was prepared as a major result of the discussion. Many important German organisations for nature conservation and soil protection (Tab. 1) signed this politi...

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 e...

Cropland soils are considered to have the potential to sequester atmospheric CO2 through agronomic best management practices (BMPs). To estimate this potential in East Africa, the authors reviewed 69 published studies from Ethiopia, Kenya, Rwanda, Tanzania, Uganda, and Burundi assessing the effect of land use conversion from native vegetation to cr...

Livestock productivity in East Africa, and especially in Tanzania, remains persistently low, while greenhouse gas (GHG) emission intensities are among the highest worldwide. This mixed methods study aims to explore sustainable livestock intensification options that reduce agro-environmental trade-offs across different smallholder farming systems in...

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 al...

Farming practices in sub-Saharan Africa have resulted in declining soil fertility. Hence, Green Manure Cover Crops (GMCC) are promoted for soil improvement and protection. Adoption of GMCCs by farmers, including integration in their cropping systems, requires a good understanding of the multi-dimensional impacts of these crops. We, therefore, devel...

In Sub-Saharan Africa (SSA), many smallholder communities continuously grapple with soil-based poverty as the coarse-textured (sandy) soils, on which they eke out a living, have low water and nutrient retention capacities. The new sub-surface water retention technology (SWRT), which is based on the subsurface installation of impermeable water-retai...

Farming practices in sub-Saharan Africa have resulted in declining soil fertility. Hence, Green Manure Cover Crops (GMCC) are promoted for soil improvement and protection. Adoption of GMCCs by farmers, including integration in their cropping systems, requires a good understanding of the multi-dimensional impacts of these crops. We, therefore, devel...

Land restoration is considered to be the remedy for 21st century global challenges of land degradation. As a result, various land restoration and conservation efforts are underway at different scales. Ethiopia is one of the countries with huge investments in land restoration. Tremendous land management practices have been implemented across the cou...

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. Rangel...

Soil organic carbon (SOC) sequestration is important in the global carbon cycle and an integral part of many initiatives and policies to mitigate climate change. For efficient targeting of measures leading to SOC sequestration, it is necessary to know the actual SOC content (%) and a realistic target SOC content (in contrast to the saturation conte...

This poster is licensed for use under the Creative Commons Attribution 4.0 International license (CC BY 4.0) 2018-09. Design: JL Urrea (CIAT) This work was undertaken as part of the CGIAR Research Program on Livestock. We thank all donors that globally support our work through their contributions to the CGIAR system.

Core Ideas We investigated liming in soil mesocosms from 11‐yr managements: no input, mineral N+P, and manure. There were minor or no changes in labile inorganic P, labile organic P, and microbial biomass P. Changes in the activity of different phosphatases following liming depended on management. Liming decreased acid phosphomonoesterase/phosphodi...

The role of soil organic carbon in global carbon cycles is receiving increasing attention both as a potentially large and uncertain source of CO2 emissions in response to predicted global temperature rises, and as a natural sink for carbon able to reduce atmospheric CO2. There is general agreement that the technical potential for sequestration of c...

Phosphate rock (PR) is an alternative fertilizer to increase the P content of P-deficient weathered soils. We evaluated the effects of fertilizer form on indicators of biological cycling of P using an on-farm trial on a Rhodic Kandiudox in western Kenya. Treatment plots were sampled after 13 cropping seasons of P applications as Minjingu phosphate...

Background & aim A potential benefit of conservation agriculture (CA) is soil organic carbon (SOC) accrual, yet recent studies indicate limited or no impact of CA on total SOC in tropical agroecosystems. We evaluated biochemical indicators of soil C cycling after 9 years (18 seasons) of contrasting tillage with and without maize residue retention i...

Agriculture is a global contributor to greenhouse gas emissions, causing climate change. Soil organic carbon (SOC) sequestration is seen as a pathway to climate change mitigation. But, long-term data on the actual contribution of tropical soils to SOC sequestration are largely absent. To contribute to filling this knowledge gap, we measured SOC in...

Water stress is a major crop production constraint for common bean (Phaseolus vulgaris L). The response of bush and climbing bean to excessive and minimal soil moisture at various plant growth stages was investigated under greenhouse for two growing periods; September–February 2016 and March–July 2016. The control consisted in watering with recomme...

Secondary and micronutrients are important in enhancing crop productivity; yet, they are hardly studied in sub-Sahara Africa. In this region, the main focus has been on macronutrients but there is emerging though scattered evidence of crop productivity limitations by the secondary and micronutrients. Elsewhere, widespread deficiencies of these nutr...

We evaluated forages for increased output and quality • Our farmer participatory forage evaluation included Brachiaria, Napier grass, Desmodium and the benefits of proper agronomic measures • We involved livestock researchers and extension workers in Tanzania to make the work sustainable Maziwa

Agricultural insurance products have been piloted in Sub-Saharan Africa (SSA) to address climate related risks faced by farmers. However, these products in general face low rates of adoption in SSA. Factors and challenges that may explain the low uptake of index-based insurance products in SSA are reviewed in this paper with the objective of assess...

The widespread promotion of conservation agriculture (CA) in regions with weathered soils prone to phosphorus (P) deficiency merits explicit consideration of its effect on P availability. A long-term CA field trial located on an acid, weathered soil in western Kenya was evaluated for effects of reduced tillage and residue retention on P availabilit...

SUMMARY The yield gap has arisen again as a focus for agricultural research to ensure food security and economic growth for farmers around the world. To examine this renewed interest, we carried out a review of key literature in the field of yield gap analysis to identify important gaps in research and analysis. In so doing, both the complexities i...

More than 100 countries pledged to reduce agricultural greenhouse gas (GHG) emissions (Richards et al., 2015a) in the 2015 Paris Agreement of the United Nations Framework Convention on Climate Change. Yet technical information about how much mitigation is needed in the sector versus how much is feasible remains poor. We identify a preliminary globa...

More than 100 countries pledged to reduce agricultural greenhouse gas (GHG) emissions (Richards et al., 2015a) in the 2015 Paris Agreement of the United Nations Framework Convention on Climate Change. Yet technical information about how much mitigation is needed in the sector versus how much is feasible remains poor. We identify a preliminary globa...

This study argues that heterogeneous farms operating under a delivery target may yield significant economic benefits if they coordinate their production portfolio. To analyze the gains from cooperation, we simulate various cooperative game solutions over seven cotton producing farms in a bio-economic model of a water users association. The study re...

Restoring soil fertility in smallholder farming systems is essential to sustain crop production. An experiment was conducted in 2011 and 2012 to study the effect of compost and inorganic fertilizer application on soil chemical properties and wheat yield in northwest Ethiopia. Full factorial combinations of four levels of compost (0, 4, 6, 8 t ha-1)...

Integrated soil fertility management (ISFM) is a concept that includes the management of organic matter in smallholder farming systems for sustainable intensification. To determine whether ISFM is also eco-efficient, we measured and simulated nitrogen (N)-dynamics and nitrous oxide (N2O) emissions in an ISFM long-term maize trial in Western Kenya....

Restoring soil fertility in smallholder farming systems is essential to sustain crop production. An experiment was conducted in 2011 and 2012 to study the effect of compost and inorganic fertilizer application on soil chemical properties and wheat yield in northwest Ethiopia. Full factorial combinations of four levels of compost (0, 4, 6, 8 t ha-1)...

Motivated by global and regional challenges in food production and a broader consideration of ecosystem services, there has been a substantial increase in the demand for integrated agricultural systems models and spatially-distributed applications that can be used for regional and global assessments and as decision support tools. This demand marks...

When assessing soil organic carbon (SOC) sequestration and its climate change (CC) mitigation potential at global scale, the dynamic nature of soil carbon storage and interventions to foster it should be taken into account. Firstly, adoption of SOC-sequestration measures will take time, and reasonably such schemes could only be implemented graduall...

Participants at the international conference on policies for water and food security in the dry areas, held in June 2013, agreed that, given the fast pace of depletion of groundwater, the issue of water valuation in the dry areas is no longer one of whether or not, but rather of how. Policies that have been or are perceived to have adverse effects...

The majority of soils in sub-Saharan Africa (SSA) are highly weathered with limited intrinsic soil fertility. Smallholder farmers face crop production challenges and consequently food insecurity as a result of soil phosphorus (P) deficits. Investing in the P capital of these regions by increasing P inputs is a recognized strategy for lifting P limi...

Restoring soil fertility in smallholder farming systems is essential to sustain crop production. An experiment was conducted in 2011 and 2012 to study the effect of compost and inorganic fertilizer application on soil chemical properties and wheat yield in northwest Ethiopia. Full factorial combinations of four levels of compost (0, 4, 6, 8 t ha-1)...

Land use and crop production in the Khorezm region in western Uzbekistan, exemplarily for the irrigated lowlands of Central Asia, are challenged by the excessive, non-sustainable use of irrigation water and repeated water shortages on one hand, and soil degradation by secondary salinization on the other hand. One of the research objectives of the G...

Zero-tillage (ZT) and crop residue retention on the soil surface—two components of Conservation Agriculture (CA)—have been identified as promising management practices for sustainable agri- cultural intensification for some time. However, CA technology uptake by farmers in the dry areas of West Asia and North Africa (WANA) has yet to happen large-s...

Abstract: Restoring soil fertility in smallholder farming systems is essential to sustain crop production. An experiment was conducted in 2011 and 2012 to study the effect of compost and inorganic fertilizer application on soil chemical properties and wheat yield in northwest Ethiopia. Full factorial combinations of four levels of compost (0, 4, 6,...

In addition to nine major nutrients, eight micronutrients [i.e., boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn)] are also essential for healthy growth and reproduction of higher plants. Globally, crop production is largely dependent on chemical fertilizer use, especially in developed co...

The economic and environmental benefits of conservation agriculture (CA) are widely documented in many different parts of the world. However, in the Central and West Asia and North Africa adoption of zero-tillage (ZT), crop residue retention and diversified rotations have been slow. Three long term field experiments have been running at Tel Hadya,...

Improving the adaptive capacity of rural producers to climate and weather risks may become an urgent issue in the early stages of political stabilization in Syria. Therefore, this study analyses the agro-ecological, economic and social benefits of – and the institutional challenges to – establishing index-based insurance markets to catalyse rural d...

Although most of the research on phosphorus (P) in developed countries focuses on the environmental implications of excess P fertilizer use, the opposite occurs in developing countries. The northern Africa–western Asia region has low-input agriculture with limited P fertilizer use, and cropping is constrained by low rainfall. The evolution of P res...

Climate change (CC) may pose a challenge to agriculture and rural livelihoods in Central Asia, but in-depth studies are lacking. To address the issue, crop growth and yield of 14 wheat varieties grown on 18 sites in key agro-ecological zones of Kazakhstan, Kyrgyzstan, Uzbekistan and Tajikistan in response to CC were assessed. Three future periods a...

Various agricultural policies have been implemented in post-Soviet countries as they move from centrally planned to market economies. In the agriculture sector of Uzbekistan, Central Asia, several reforms have been implemented to increase the operational autonomy of agricultural producers. However, land and water use in agriculture remains directly...

The active participation of the stakeholder community is viewed as a crucial consideration in the regional assessment of climate change in the Mediterranean. Each of the CIRCE integrating case studies has bene fi tted from the real-life experience and expertise of local and regional stakeholders. The level of involvement has included stakeholder di...

The active participation of the stakeholder community is viewed as a crucial consideration in the regional assessment of climate change in the Mediterranean. Each of the CIRCE integrating case studies has benefitted from the real-life experience and expertise of local and regional stakeholders. The level of involvement has included stakeholder dial...

The final stage of the CIRCE case-studies integrated assessment involved identification and evaluation of the effectiveness of local and regional adaptation options in collaboration with stakeholders, and in the context of wider national adaptation policies and strategies. This stage provides a synthesis of both the case-study work and the wider CI...

Fertilizers have been largely responsible for the massive increases in world food production in the past half century that permitted accelerated global population growth to current unprecedented levels. Fertilizer use not only impacts crop yields but also affects animal production. While nitrogen (N) has been the main driver of such changes, phosph...

The Mediterranean climate allows for rainfed cropping in the relatively moist cool period from autumn to late spring/early summer. Drought has a constant influence. Soil fertility was partly maintained by fallowing, nitrogen-fixing plants, and animal manures. Considerable changes have occurred due to land use pressure, i.e. decreasing fallow and in...

The current status of the agricultural soils in Khorezm is closely linked to their development influenced by past river flows and more recent human-managed irrigation and drainage practices. The initial relief of the Amudarya river delta was formed by ancient channels that carried large amounts of sediments. When irrigation was introduced, sediment...

In the irrigated areas of Uzbekistan the nitrogen (N) fertilizer efficiency in crop production is low, as N is partially leached to the groundwater. The N-fertilizer use is still based on recommendations from Soviet times when fertilizer supply was subsidized to maximize production at all costs. Also irrigation water is applied sub-optimally, and g...

Many studies have shown that zero tillage (ZT) in combination with a surface crop residue layer – two components of conservation agriculture (CA) practice – can improve the agronomic water balance by increasing the amount of water that is readily plant available. However, no account has yet been published in which this effect had been fully quantif...

A Farm-Level Economic Ecological Optimization Model (FLEOM) was developed in the ZEF/UNESCO Khorezm project as a land-use planning and decision-support tool at the level of farms and Water Users Associations (WUAs) to couple ecological and economic optimization of land allocation. The agronomic database for cotton, winter wheat and maize that under...

Chemical fertilizer use has contributed significantly to increased global food output in the past half century, especially in climatically favourable regions of the world. However, in drier agro-ecological zones, such as in West Asia and North Africa (WANA) with a Mediterranean-type climate, fertilizer use has been low but has increased rapidly in...

Sustainability of dryland cropping is a major issue in the typical Mediterranean climatic environment of West Asia and North Africa. Management of crop residues and soil organic matter (SOM) and its interrelationship with tillage and crop rotation is of central importance for maintaining soil quality and sustaining crop yields. We examined the medi...

Expectations have been raised that carbon sequestration in soils could provide a short-term bridge to reduce the impacts of increasing carbon emissions until low-carbon technologies are available. To assess the role of Central Asia in this regard, the organic carbon in soils of Central Asia and losses in response to land use were quantified in a sp...

The paper compares the risk coping potential of insurances that are based on indices derived from weather (rainfall and temperature) data as well as from crop model and remote sensing analyses. Corresponding indices were computed for the case of wheat production in the Aleppo region of northern Syria, representative for agricultural production syst...

Tillage is an important procedure for modifying the soil environment to enhance crop growth and conserve soil and water resources. Process-based models of crop production are widely used in decision support, but few explicitly simulate tillage. The Cropping Systems Model (CSM) was modified to simulate tillage and related field operations for single...

Two methods are presented that allow converting the van Genuchten (VG) soil-water-retention (SWR) model parameters to equivalent parameters of the Campbell (C) model. The first method builds on an available solution to convert the VG model to an equivalent Brooks-Corey (BC) model, but accounts for the fact that the effective water content of the BC...

Fertilizer-applied Nitrogen (N) may be lost from the soil by various mechanisms, i.e., runoff, leaching, denitrification, and volatilization. The latter process is of primary concern in calcareous soils of arid and semi-arid regions, especially when urea is used. In this field study from northern Syria, urea alone, urea with either an incorporated...