Soil erosion, soil nutrient depletion, and soil moisture stress are the major land degradation problems facing the region. Though soil erosion is prevalent throughout Ethiopia, this problem is particularly severe in Tigray. The early settlement and expansion of agriculture, together with the steep terrain and the erratic and intense nature of the rainfall has caused erosion to be a major problem. Quantitative soil loss estimates are rare in Tigray (Berhanu, 1998). Nonetheless, the persistent deterioration of the quality of the cultivated land, the ever expanding gullies, and the poor yields, partially explained by the poor water holding capacity of the soil, suggest that soil erosion is a critical problem. The available estimates give us a general picture of the magnitude of the problem.
The soil of the region is highly degraded. Hurni (1988) estimated that more than half of the area of the highlands of Tigray was severely degraded, with soils less than 35 cm deep (Ibid.). According to Hurni and Perich (1992), Tigray's soils are believed to have lost 30–50 per cent of their productive capacities compared to their original state some 500 years ago. REST's recent studies in seven woredas of the central zone of Tigray indicate that about 46 per cent of the currently cultivable land is exposed to severe soil erosion. Though two decades ago, about 30 per cent of the cultivated land is said to have required soil and water conservation measures (Hunting, 1975); now almost all the cultivable land needs treatment. At the present rate of conservation work, 20–25 years would be necessary to cover all of Tigray (Tekeste and Smith, 1989).
Estimates of soil erosion rates vary substantially, but are high in many areas. According to the Hunting Report (1975) the average rate of erosion in the central highlands of Tigray, the most densely populated area, was measured to be above 17 metric tones per hectare per year. Other studies in the 1980's reported estimates of erosion rates of more than 80 tonnes per hectare per year (REST, 1989a; 1989b; Tekeste and Smith, 1989).9 A recent study of erosion in part of central Tigray near Adwa estimated that 18% of the area studied was eroding at rates exceeding 10 tons/ha/year, based upon the Universal Soil Loss Equation (USLE) (Eweg, et al. 1997). According to the Ethiopian Highlands Reclamation Study (EHRS), about 80 per cent of the erosion in the Ethiopian highlands was estimated to occur on croplands, and the remainder on overgrazed grasslands, wastelands and newly deforested areas (EHRS, 1985). The annual loss from cultivated land in the Ethiopian highlands was estimated to be 130 tons/ha, and this was expected to result in a loss of 7.6 million ha of cropland to productive use in Ethiopia by the year 2010 (Ibid.). Hurni subsequently estimated much lower erosion rates from cultivated land (42 tons/ha/year), though still much higher than the rate of soil regeneration (3–7 tons/ha/year) (Hurni, 1988). Based on Hurni's erosion estimates, Sutcliffe (1993) estimated that 0.5 million ha of cropland and 5.7 million ha of pastures would be lost by 2010.10
9. One needs to be cautious about the reliability of the information. Few thorough assessments have been made under various conditions.
10. The EHRS did not estimate the area of pastures expected to be lost to erosion.
There is also considerable variation in estimates of the production and economic impacts of soil erosion in the Ethiopian highlands. The Highlands Reclamation Study estimated that erosion would result in a reduction of crop production of 2.6 million tons by 2010, while Sutcliffe's (1993) estimates are only 13% of this. Estimates of the annual costs of erosion in the Ethiopian highlands range from EB 10 million to EB 135 million per annum (0.05% to 0.7% of agricultural GDP); while the estimated gross discounted present value of cumulative losses caused by erosion ranges from EB 3 billion to EB 7 billion (Bojo and Cassells, 1995). Despite the debate over these magnitudes, it is clear that soil erosion is causing substantial costs to agriculture in the Ethiopian highlands. The relative impacts are probably greater in Tigray, where soil erosion is more severe than in much of the highlands.
Soil nutrient depletion poses a related and likely at least as critical a problem for agricultural production in Tigray. No estimates are available on the extent of the problem in Tigray specifically. For Ethiopia as a whole, estimated nutrient losses were more than 80 kg of nutrients per hectare in 1983 (including 41 kg of N, 13 kg of P2O5 , and 31 kg of K2O), among the highest rates of depletion in sub-Saharan Africa, and are predicted to be even higher by the year 2000 (Stoorvogel and Smaling, 1990). The main cause of nutrient outflow in Stoorvogel's and Smaling's estimates is soil erosion (about 60 kg/ha), followed by removal of harvested products and crop residues; while inflows from manure and chemical fertiliser are very low (averaging less than 10 kg/ha). In Tigray, the use of chemical fertiliser is even lower than for most of Ethiopia, averaging less than 3 kg/ha (BOPED, 1995).
A major cause of the high removal of nutrients in crop residues and low addition of manure is burning of dung and crop residues to satisfy household energy needs. Sutcliffe (1993) estimated the impact of nutrient depletion due to burning of dung and crop residue in the Ethiopian highlands to be 465,000 tons of grain and 1 million tropical livestock units (TLU) of livestock production in 1990, valued at EB 580 million. Bojo and Cassells (1995) estimate the gross discounted cumulative loss due to this to be about EB 8 billion (compared to their estimate of EB 3 billion for cumulative losses due to erosion). Thus the costs of nutrient depletion due to burning of dung and crop residues may be larger than (though of the same order of magnitude as) the costs of soil erosion. Although these estimates are clearly subject to substantial uncertainties, and most are not specific to Tigray, they suggest that both soil nutrient depletion and soil erosion are major problems in Tigray.
Soil erosion and nutrient depletion are exacerbated by, and also exacerbate, the problem of moisture stress inherent in the semi-arid environment of Tigray. The amount of rainfall, even in a normal year, is not sufficient to sustain normal crop growth in most parts of Tigray, unless water harvesting mechanisms or supplementary irrigation is introduced. Under average conditions and presuming the moisture deficit is uniformly distributed over the growing season, yields will be 45% below potential (SAERT, 1994a). The problem is of course much worse in poor rainfall years, and where soils are thin and degraded. The very thin layer of topsoil and low organic matter content of the soil in many places as a result of erosion and limited recycling of organic matter limit the moisture holding capacity of the soil. Low soil moisture in turn reduces the ability of plants to utilise the nutrients that are available, leading to increased nutrient losses through leaching and volatilisation. It also reduces the return and increases the risk of applying fertiliser, thus reducing inflows of nutrients as well. Poor soil moisture and nutrient conditions lead to poor plant growth and low vegetative cover during erosive rainfall periods, leading to higher rates of erosion, and reduced availability of crop residues to recycle into the soil. The result is a viscous cycle of erosion, low organic matter content, low soil moisture, and poor soil and plant nutrition, contributing to worsening land degradation, low productivity and poverty.
Other major and related natural resource problems in the region include the degree of deforestation, causing a severe shortage of fuelwood and construction material, and overgrazing, causing a severe shortage of feed resources. These problems are also of course related to soil erosion and soil nutrient depletion. Both contribute directly to soil erosion and to the general shortage of biomass in Tigray, which limits the ability of farmers to recycle nutrients from dung and crop residues into the soil.
The implications of all these processes are lower and less reliable crop yields, reduced grazing and browsing for livestock, decrease in availability of fuelwood, decrease in soil water holding capacity, declining dry season water flow and thereby low irrigation possibility. These all mean a decrease in the potential for sustained crop production. Crop production in most areas of Tigray does not reach the subsistence level, even in times of adequate rainfall. For example, according to the survey done by REST and NORAGIC (1995) in the central zone of Tigray, the number of households that can feed themselves for about 4–6 months of the year amount to 42 per cent against 17 per cent that are food self-sufficient.11 The situation is worse in the eastern zone as the zone is more severely affected by drought and moisture stress.
11. About 82 per cent of the households are classified as food insecure.
The consequence has been a series of both localised and regional disasters, characterised by drought, famine, and associated population displacements. Among the recent regional calamities are the famines of 1971–75 and 1984–85. Famine as a natural and social phenomenon induces loss of animal and human life, disposition of meagre household assets, and more pressure on natural resources to compensate for lost incomes (e.g. sale of firewood). These in turn affect farmers' ability and willingness to invest in conserving their land. Studies in very similar conditions elsewhere in Ethiopia have indicated that poor farmers living under stress with severe material or cash needs have very short time horizons and are thus less able to plan or invest for the future (Holden et al., 1998). The cumulative effect has been profound socioeconomic and resource stress. Although there has been some improvement in socioeconomic conditions in recent years, alleviating land degradation and its impacts on food insecurity and poverty remains an issue of highest priority in the region.
