Impact of Early Fires on Soil Physicochemical Properties in Sudan Savanna in Chad

Fire is a seasonal phenomenon prevalent in savannah ecosystems [1]. In Chad, as throughout the African savannah areas, bush fires are caused by various causes, including the preparation of new agricultural plots, regeneration of pastures, protection of dwellings and ceremonial rituals. There are also accidental fires due to smoking of hives or carbonization. The importance given to bush fires in Africa is also justified by the fact that fires are used by managers of the environment for management reasons. Fires can also occur through negligence due to favorable climatic conditions [2]. Early fires are lit at the end of the rainy season to improve pasture production and maintain the composition and specific richness of herbaceous plants [3]. These fires, often intentional, burn a still active vegetation with a relatively high water content. This type of fire is considered to be the least harmful because it consumes less plant material. In general, the fire progresses slowly and many saved organisms will allow an active recovery during the first rainfall or simply during a rise in the hygrometry [4]. In Sudan savannahs and particularly in Chad, early fires are officially approved and are generally observed between October and November. Fire, by its action, induces changes in the physical and chemical properties of the soil. The physical impact of fire on the soil includes the destruction of the structure and the reduction of the soil water holding capacity [5]. Some important physical characteristics in the soil are affected by the heating of the soil due to fires [6]. These features include soil color, texture and pH. The color of the soil is deeply altered after a fire with a high concentration of fuel [7]. The ash from the combustion is gray or black in the case of a moderate fire. The color of soils subjected to fires with a temperature of at least 600 o C with 45 minutes of exposure turns red [8]. Soil texture components (sand, silt and clay) generally react at very high temperatures on the soil surface [6]. The clay remains the sensitive fraction, already at 400° C, the hydration and the lattice structures of the clay begin to collapse and then between 700 and 800° C., the complete destruction of Abstract: This paper deals with the study of early fire on soil properties in the savanna. The approach chosen is based on the study of experimental plots in relation to early fires. The study was conducted in the Guirkouh forest in the Sudanian zone in Chad. The main objective of this study is to contribute to the knowledge of the effects of early fires on the physicochemical properties of the soil in the savanna. The research work was carried out in an experimental system covering 0.25 ha. Three fuel treatments were considered in addition to the control in the early fire regime. The results showed no significant difference in the rate of progression and in the intensity of the fire. And no significant differences were observed between the profiles either before or after the passage of fire. Similarly, no interaction effect of these factors on the particle size distribution was observed. However, a greater nutrient enrichment of the surface layers was observed. Depending on soil sampling depth, a 1%, 2% and 5% decrease in total phosphorus (Pt) was also observed for 0-5 cm horizons, respectively; 5-10 cm and 10-15 cm. Overall, the study shows that pH, total Carbon (Ct), the ratio C/N and total Nitrogen (Nt) not significantly varied (P > 0.05) during the three years of application of early fire.