ABSTRACT
Chapter 2 RESEARCH BACKGROUND AND HYPOTHESES In Chapter 1, problems related to conventional tillage systems with the traditional tillage implement, the Maresha Plow, were presented. In this chapter, we will look at the more general problems of conventional tillage systems and review of research on conservation tillage in Ethiopia, in Africa and in the world. 2.1 Definitions of Conservation Tillage Conservation tillage is defined by the Conservation Tillage Information Center (CTIC) as any tillage and planting system that covers 30 percent or more of the soil surface with crop residue, after planting, to reduce soil erosion by water. According to the European Conservation Agriculture Federation (ECAF), conservation agriculture refers to several practices which permit the management of soil for agrarian uses, altering its composition, structure and natural biodiversity as little as possible and protecting it from erosion and degradation (ECAF, 1999). Synonymous to conservation tillage are conservation farming and conservation agriculture. The Food and Agriculture Organization (FAO) uses the name Conservation Agriculture (CA) and defines CA as the simultaneous application of minimum soil disturbance, soil cover and crop rotation (Benites and Ashburner, 2001). The main justification for the change in the name to conservation agriculture is the inclusion of other issues such as crop rotation and soil cover while no tillage is advocated. A recent definition of CA by Dumanski et al (2006) states that the principles of CA include maintaining permanent soil cover, promoting a healthy, living soil, promoting balanced application and precision placement of fertilizers, pesticides, and other crop inputs, promoting legume fallows, composting, and organic soil amendments, and promoting agroforestry to enhance on-farm biodiversity and alternate sources of income. In Africa, the term conservation tillage has been used in a more flexible way to refer to any tillage system which conserves or reduces soil, water and nutrient loss or which reduces draft power requirements for crop production (Steiner, 1998). According to Rockström et al (2001), conservation tillage is any tillage system that conserves water and soil while saving labour and traction needs. The attempts made to adapt the definitions of conservation tillage to an African context have been influenced mainly by lack of soil cover as a result of competition for crop residue by livestock and the inherently low bio-mass production due to shortage of rainfall. In this thesis, emphasis has been given to conservation tillage systems that address the issue of water productivity by positively altering rainfall partitioning in the semi arid areas of Ethiopia.
