Increased human influences on soils frequently result in widespread land and soil degradation. The processes of soil and water degradation are closely linked, as unfavourable changes in the hydrological processes affect soil water regimes. In the last 15-20 years there has been increased interest in human-induced climate change, associated with increased atmospheric concentrations of greenhouse gases. Most of the present and future problems of land and soil degradation, water supply and natural disasters are mainly attributed to these climate changes. At the same time, and probably related to it, there has been a change in the focus of research on soil and water conservation. From the late 1960s there was an increasing interest in stimulating studies related to soil and water conservation. This was a great change from the previous emphasis on more static studies of the characteristics of the soil resource, mainly for soil classification and mapping, and for land evaluation related to agricultural and other uses. This situation was due to the increasing evidence of the global problems of land, soil and water degradation, and their effects on food production and the environment. Particular attention was paid to the processes of soil and water degradation in relation to their use and management for agricultural purposes. These efforts led to the development of models and evaluation systems mainly using empirical approaches. Later studies demonstrated the limitations of the generalized universal use of these empirical approaches. Concurrently there was an increase in related organizations, conventions, congresses and conferences associated with the renewed interest on soil and water conservation. A global assessment of human-induced soil degradation (GLASOD) demonstrated the paucity, difficult accessibility and poor quality of basic information. This information, however, is essential for adequate planning and effective application of practices to prevent soil and water degradation. The most recent conventions and programs at international and regional levels are generally based on re-interpretations, and a different processing method or representation of old information using “new” terminology. In other cases, new information has been mostly generated through indirect or remote sensing deductions, usually without adequate ground-truthing. The decreasing public or private support for more integrated interdisciplinary studies and the compulsion to quickly publish papers has resulted in a very specialized and isolated consideration of different aspects related to the degradation of soil functions. This frequently results in over-simplifications, failures and even contradictions in the proposed strategies to control soil degradation. Currently we have reached quasi-stagnation in soil conservation research and a new series of soil conservation terms (soil quality, desertification, tillage erosion) and clichés (“C sequestration”, “no-tillage”) have been introduced. These are derived from different interests, but generally they are very empirical approaches without a strong scientific basis. However, they attract increased attention from organizations setting policies and providing funds for research in soil and water conservation, and as a consequence many research activities in the last 20 years have been concentrated in such topics. Regretfully, these approaches have very limited accuracy and are insufficient for developing adequate policies for land use and management. Climate, soil and socio-economic conditions differ greatly from one location to another and are changing continuously. There cannot therefore be simple universal prescriptions regarding practices of sustainable soil management for crop production and environmental protection or for mitigation of the greenhouse effect by “C sequestration” in soils. The adequate selection of those sustainable practices must be based on research with a broader vision of soil conservation, where all the system components and their interactions are considered and understood with a far-sighted approach, to ensure that short term gains in one aspect or location do not induce long-term losses in other aspects or elsewhere. Research needs to be directed to better the understanding of the processes and reactions in soils related to chemical recycling and water balance over a range of spatial and temporal scales, with the common objective of improving crop production and environmental protection. Lasting solutions will only be found if adequately trained researchers in soil science and hydrology, who recognize the complexity of the problems, develop appropriate strategies.
Impacts of Soil and Water Conservation Practices on Crop Yield, Run-off, Soil Loss and Nutrient Loss in Ethiopia: Review and Synthesis
