1. Sustainable Intensification for Adaptation and Mitigation of Climate Change and Advancement of Food Security in Africa

Africa is endowed with diverse eco-regions, climates, soils, landscapes and water resources. There were three regions of crop domestication in Africa. In addition to the Fertile Crescent in Mesopotamia, crop domestication also occurred in West Africa for yam and cassava, and in the Horn of Africa for teff, coffee, and the cucumber tree. With a land area of 30.2 million km² and population approaching one billion, Africa has a vast potential for agricultural and economic development. Africa’s population has been increasing rapidly since the beginning of the twentieth century. The population (million) was 120 in 1900, 221 in 1950, 796 in 2000, 867 in 2010, and is projected to be 1,081 in 2020, 1,804 in 2050 and 2,255 in 2100. Thus, food security has been a major concern since 1970s, and the Green Revolution by-passed the resource-poor and small landholders of the continent. There were 240 million food-insecure people in Africa (approximately 1 in 4) in 2012, 223 million in Sub-Sarahan Africa (SSA) in 2013, and the number is projected to increase by an additional 17 million (+6 %) by 2020. The problem is likely to be exacerbated by the changing and uncertain climate, because SSA is a vulnerable region, subject to the vagaries of projected climate change. Some project that as much as 65 % of the global total increase in climate-related hunger would occur in SSA. Climate change vulnerability in SSA is exacerbated by severe soil degradation, depletion of soil organic matter (SOM) and the negative soil nutrient balance of N, P, K at 40–50 kg/ha/year on continental scale. Soil degradation is the result of many factors, including wide spread use of extractive farming practices, poor structural stability and high erosion potential associated with harsh climates. Soils are highly prone to accelerated erosion by water and wind, crusting and hard setting, acidification and salinization. The rate of fertilizer input is low (~8 kg/ha) and less than 5 % of the potentially irrigable land is equipped for irrigation. Thus drought is a perpetual problem in SSA. A large yield gap exists between attainable and national average yield of most crops grown in the region. Recommended management practices (RMPs) for soils include conservation tillage, mulch farming, cover cropping, using integrated nutrient management and manuring, growing nitrogen fixing legumes and trees, and applying bio-solids to enhance SOM reserves. Important among water management techniques are water harvesting and recycling, micro irrigation, recycling city water and grey water. The strategy is to create positive C and nutrient budgets and improve soil quality and its rhizospheric processes. A wide spread adoption of RMPs can improve soil quality, enhance input use efficiency, increase climate change resilience, narrow the yield gap and sustain agronomic production. Sequestration of C in soils and vegetation (trees) can also mitigate climate change by reducing net anthropogenic emissions. Payments to land managers for provision of ecosystem services, such as C sequestration, water quality improvement, and bio diversity enhancement, can create additional income streams and promote the adoption of RMPs. Sequestration of C in agro-ecosystems is a win-win situation. It will enhance agronomic production and sustain the use of soil and water resources while improving the capacity of smallholder agriculture to adapt to climate change and off set anthropogenic emissions.