Adaptation by Smallholders in Eastern Africa to Climate Change through Conservation Agriculture

© 2015 by Taylor & Francis Group, LLC. Management of agricultural lands in East Africa has remained a matter of concern since the German colonial times. Soil and water conservation in this area has progressed very slowly owing to farmers’ poor response to interventions on conservation. Inappropriate land husbandry in the area is a result of pressure on the land resources, which has led to the development of various forms of land degradation. Several studies have been initiated in the region aimed at sustainable land husbandry and appropriate management of agricultural lands. This chapter focuses on land degradation processes, plant nutrient depletion, and adaptation measures based on the principles of conservation agriculture (CA) in the context of climate change. It provides broad experiences and an in-depth knowledge of smallholder farming adaptation to climate change using the principles of CA in East Africa. The highlights from this chapter show that interrill and rill erosion, tillage erosion, and landslides are dominant land degradation processes in the region of East Africa. Very high soil losses are reported particularly from interrill and rill erosion ranging from 91 to 258 Mg/ha/year in mountainous areas. Studies have also demonstrated significant rates of soil flux due to tillage erosion increasing with slope gradient, from 16 kg/m/tillage pass at a slope gradient of 31% to 60 kg/m/tillage pass at a slope gradient of 0.1%, and available phosphorus <5 mg/kg. Inappropriate land uses also have contributed significantly to soil and nutrient losses. In the Lake Victoria Basin settlements, compounds and footpaths produced soil losses of up to 199 Mg/ha/year, while agricultural lands cropped with cotton and cassava produced soil loss of up to 27 Mg/ha/year. CA is among the adaptation strategies that have been practiced in East Africa by the smallholder farming community to reduce land degradation. It comprises three principles that have been applied simultaneously: minimum soil disturbance, permanent soil cover, and complex rotations/crop associations with some land management options, including application of farm yard manure, green manure, composting, mineral fertilizer, weed control, and in situ rainwater harvesting. Recent studies have indicated a positive trend in practicing CA in many areas of East Africa owing to the integration of both indigenous and scientific knowledge. In Ethiopia, for example, two local tillage systems, terwah+ and derdero+, using the traditional mahresha ard plough on Vertisol under crop rotation (wheat, grass, pea, wheat) significantly increased soil organic matter to 2.0% when compared with conventional tillage (1.4%) for 0-15 and 15-30 cm soil depths. In this study, the mean yield of wheat for 3 years increased from 2.8 Mg/ha for conventional tillage to 3.7 Mg/ha for terwah+ and derdero+ tillage systems. CA has been also demonstrated to increase the yield of vegetables in the Uluguru Mountains, Tanzania, from 0.88 to 44.68 Mg/ha. The combination of miraba (an indigenous soil erosion control practice), farmyard manure (FYM), and mulching reduced annual soil and nutrient loss from 132 to 0.5 Mg/ha/year, total nitrogen from 342 to 9 kg/ha/year, and available phosphorus from 0.4 to