Land productive farm lands at lower slope areas

Land degradation is a
worldwide problem that has revived the issue of resources sustainability which
is mainly caused by improper land use (Hurni, 1997). Due to its various
negative impacts on environmental degradation, agricultural productivity and its
effects on food security, land degradation has been a major global issue since
the last century (Eswaran et al., 2001). The agricultural land is most vulnerable
and affected by degradation. De Graaff et al., (2009) indicated that out
of the total agricultural land in the world 40 percent is degraded severely. One
basic process that threatens the land resource is soil erosion by water
(erosive rainfall). Among the sever degradation of the world’s agricultural
land 80 % of it is caused by soil erosion (De Graaff et al., 2009).

Soil erosion by water is the critical problems and processes of land degradation
(Woldeamlak and Sterk, 2002; Wagayehu, 2003). Soil erosion has onsite and offsite
effects. The onsite effects of soil erosion is washing out of important soil
nutrients,  reduction of soil depth, decreasing
water holding capacity of the soil and finally leads to lower agricultural
productivity (Aklilu, 2006; Gebreegziabher et al., 2006). On the other
hand, soil erosion causes off site effects like siltation in dams and reservoirs, degradation of wetlands and loss of
productive farm lands at lower slope areas (Gete et al., 2005).

The problem of soil
erosion existed all over the world nevertheless the severity level is high in developing
countries, as their economy mainly dependent on agriculture. In Sub-Saharan
Africa countries, soil erosion problem is worst in which the rate of soil
erosion on averages is nearly 10 times greater than the rate of soil
regeneration (Holden et al., 2005). Loss
of top fertile soil by water erosion creates severe limitations to sustainable
agricultural land use, which leads to reduction in productivity of the soil and
food insecurity (Tadesse, 2001 and Bewket, 2007).

In Ethiopia, since more
than 80% of the livelihood of the country’s population is dependent on agricultural
activities (Aklilu, 2006) land is a crucial resource.
Population pressure increases the food requirement and intensive
subsistence cultivation exacerbated the cultivation of grazing and forest land
(Taddese, 2001; Lu et al., 2007). As a
result, 26% of the total area of the country is degraded and 20.6 million
population are affected by the cost of sever and continuous land degradation
(Bai et al., 2008). Thus population pressure, past political crisis, policies
and there implementations contributes a lot for land resource degradation in
Ethiopia (Holden et al, 2005).

Population pressure and
its related effect and interaction with poverty is the major factor for sever land
degradation in the highland parts of Ethiopia (Sonneveld and Keyzer, 2003). Consequently
the land holding size decreased and resulted continuous intensive cultivation
without possible land management measures. Such conditions aggravate the land
resource degradation and lowering agricultural productivity (Shiferaw and
Holden, 2001). IMF (2005) reported that the amount of crop yield increased by
0.4% and cultivated land increased by 5.7% from 1991 to 2003 per year on
average. FAO
estimated that 25% of the highlands of Ethiopia have been seriously affected by
soil erosion (FAO, 2004).

Most of the
Ethiopian highlands experience high amount of annual rainfall and it has high
spatial and temporal variability with long dry months of the year (Bewket and
Sterk, 2005). The heavy rainfall during the rainy season causes overland runoff
and erosion on the already disturbed agricultural and other degraded lands. Rain
fall based soil erosion is severe (Bewket and Sterk, 2003) and soil losses reach
up to 7 ton/ha annually (Garzanti et al, 2006).  The report by Environment for Development also
indicated that, in 1995 the net amount of soil loss in Ethiopia was 130 million
metric tons and shifted to 182 million metric tons in 2005 (EfD, 2010).  USAID (2000) also estimated that the average
annual soil loss rate in Ethiopia ranges from 12 tons ha-1 yr-1 to greater than
300 tons ha-1 yr-1 in which the area is steep slopes and limited vegetation
cover. There is also greater local spatial variability of soil erosion rates which
ranges from less than 1 – greater than 400 t/ha/year (Mitiku et al., 2006; Tebebu
et al., 2010). It is true that soil erosion rate in Ethiopia is far greater (on
average 10 times) than soil formation rate (Holden et al., 2005).  As a result of this extensive soil erosion, the
productivity of the soil has been decreased and agricultural production has not
been able to feed the growing population.

Therefore, to reduce
such problems soil and water conservation was initiated in Ethiopia during
1960s (Kcclcy and Scoones, 2000). Extensive and remarkable works have been observed
since 1970s and 1980s in most highland areas of the country (Nyssen et al.,
2008; Tefera and Sterk, 2010). With respect to this, different researches have
been done to see the impacts of soil and water conservation. However, there
exists contradicting results in studies on its impacts. Some of the researchers
found that soil and water conservation contributes for reduction in runoff and
sediment loss (Zenebe,
2009; Kirubel and Gebreyesus, 2011),
soil moisture conservation
(Haregeweyn et al., 2012, 2015; Nyssen et al., 2010) and
increases seedling survival (Gebreyesus,
2011; Mekuria et
al., 2007).
Some other findings also identified
that soil and water conservation practices increased agricultural production
significantly where drought, erosion prone and moisture stressed arid and semi
arid areas (Gebrekidan, 2003).
et al., (2012) also found that soil and water conservation efforts are not
resulted in decreasing sediment concentrations.

Though, the understanding
of conservation measures and its implementation increased in the past few
decades, the problem of soil erosion remains prevalent and the adoption of  conservation measures are limited (Yeraswork,
2000; Berhanu and Swinton, 2003; Mitku et al., 2006). Hence, in large parts of Ethiopia soil erosion
problem remains significant and it could get worse for the future due to the
predicted population increase and extreme rainfall events in the 21st
century (Niang et al., 2014), which also threatens agricultural sustainability (Anley
et al., 200).

Therefore, investigating the dynamics of soil erosion in different
slope conditions and crop covers in an agricultural land would be important for
identification of the vulnerability of the land and suggest some conservation
measures. Moreover, the evaluation of the effectiveness of soil and water
conservation measures done since 1995 would be significant to learn lessons and
further improvement.