INTRODUCTION

Chapter 1 INTRODUCTION 1.1 Overview Land productivity in many parts of sub-Saharan Africa is declining (Middleton and Thomas, 1997). Crop yields from staple food crops such as maize, millet and sorghum remain in the order of 1 t grain ha-1 in smallholder rain fed farms (Rockström and Jonsson, 1999). There is an urgent need for the introduction of sustainable soil management practices in order to reverse the food crises in subSaharan Africa. In the semi-arid regions of Africa, short intense storms coupled with prolonged dry spells make crop production difficult. Intensive rainfall causes a high proportion of surface runoff that also carries away the top fertile soil. Due to high temperatures, soil evaporation can reach 30-50% of the total rainfall leaving only 10-30% for crop transpiration (Figure 1.1). Poor rainfall partitioning leads to low water productivity. Considering the limitations to a wider application of irrigation schemes among the resource poor farmers, it is critical that the

Figure.1.1 General overview of rainfall partitioning in farmers' fields in semi-arid savannah agro ecosystems in sub-Saharan Africa. P = seasonal rainfall, ES = soil evaporation and interception, S = soil moisture, T = plant transpiration, QS = surface runoff and R = deep percolation. (Adapted from: Rockström et al., 2001)

available rainwater is managed properly by increasing infiltration and water holding capacity of the soil and by minimizing evaporation losses especially during the dry periods. Ethiopia is located in the Horn of Africa between 30 and 180 North latitude and 330 and 480 East longitude (Figure 1.2). Its population is currently estimated to be more than 70 million. Agriculture is the mainstay of the country’s economy with 60% of GDP coming from the sector. It is a means of livelihood for about 85% of the total population. The main power sources in agriculture have been human and animals. According to surveys conducted earlier (Pathak, 1987), over 90% of the total agricultural produce comes from 5.5 million farmers employing 5 million oxen and cultivating 95% of the land under plow. Figure 1.2. The location of Ethiopia in Africa. The semi-arid areas in Ethiopia (Figure 1.3) cover 301,500 km2, which is 27 % of the country. The semi-arid areas represent the crop production zone suffering from a serious moisture stress (Engida, 2000). It is in these areas that food insecurity and famine has always been reported (IGAD and FAO, 1995). Shortage of rainfall is normally reported as the cause of famine in Ethiopia. However, the total rainfall in the semi-arid areas can be as high as 700 mm-yr-1 (Figure 3.1). One could ask why so much annual rainfall wouldn’t be sufficient to grow crops. The underlying reason for the inability of farmers to feed themselves in these areas is the high proportion of losses mainly as a result of surface runoff and soil evaporation as demonstrated in Figure 1.1. In addition to the environmental factors, the causes of poor rainfall partitioning are believed to

be poor soil management with traditional tillage systems (Rockström et al., 2001).