Soil Burning in Ethiopia.

A review is made of soil burning or "guie" in the context of Ethiopian condition. Based on the work done in the laboratory,greenhouse and field conditions, the effect that soil burning has on the physical, chemical and mineralogical properties of soils is elucidated. Soil burning fuses clay into sand sized particles., results in the destruction of organic matter, loss in cation exchange capacity, dehydration and collapse of the crystalline lattice and hence a change in mineralogy. On the otherhand, through the decomposition of organic matter, N. and micronutrients are made available. There is a rise in pH towards neutrality and the aggregation of clay into sand sized particles induces better drainage. While soil burning per se can be considered destructive, its long lasting effect is confounded due to the small volume of soil affected in relation to the total unaffected mass, and the incorporation of unaffected soil through subsequent ploughing following a long fallow period that might stretch upto fifteen years. It is concluded, however, that the tedious backbreaking and wasteful practice of "guie" can be replaced with the introduction of cultural practices, such as the application of fertilizers and the provision of better drainage either by deeper ploughing with a moldboard plough or the construction of cambered beds. The other alternative of substituting crop production under "guie"with grazing is entertained but its prospects are thought to bedim. Most of tropical subsistence agriculture is based on shirting cultivation where farmers use fire for land clearing. To improve crop yields, burning combustible matter on land has also been practiced for centuries by the Chinese Indians Romans, etc. (7). However, in the central highlands of Ethiopia a unique traditional system of soil management for crop improvement is being practiced in that the soil itself rather than plant materials is "burnt"*. Such a system of soil heating or "burning" is locally known as "guie" and is practiced by small scale farmers whenever they bring into cultivation fallow land with heavy clay and hydromorphic horizon. It has been long realized that burning brush, grass, etc. brings about an increase in available soil nutrients and in some cases, an improvement in the physical properties of the soil (12). However, the application of heat to the soil per se brings about quantifiable changes in the physical and chemical properties of the soil whose magnitude depends on the intensity of heating and on soil properties. The changes so induced could either be beneficial or detrimental to the soil and hence to crop production; and in a country where the system is being practice such information is vital. Yet, literature on soil burning or "guie" is limited. Nevertheless, the studies done so far, in small measured, have helped in the understanding of the traditional system of soil burning in agronomic terms. The purpose of this paper, therefore, is to review the present state of knowledge on "guie" as a first step in understanding the "guie" system and the effect it has on soil fertility and land productivity.