Control of gully erosion in Upper Atbara River (Elshowak, Sudan)

The study is about the gully erosion phenomenon in upper Atbara River in the eastern Sudan. The objectives of the study were to understand this problem, which faces the farmers at this site. To assess the extent, causes and consequences to propose simple, cheap and easily adaptable technique to reduce the rate of gully erosion advancement into the agricultural land. The final goal is to have an agroforestry system to be adopted to reduce soil deterioration by gully erosion. Erodibility of the soil of this site was found to be the main cause of this problem in addition to the torrential rainfall of the Showak area. Erodibility includes both vegetation cover, which was found to be less than 3% in addition to slope and farming practices of mono-cropping without rotation. Clearance of vegetation for mechanized cultivation, over grazing and cutting of trees for firewood and charcoal are the main causes of soil degradation. The existing tree cover is low (2.3%) mainly shared by three species Acacia nubica, Acacia mellifera and Balanites aegyptiaca. Average crown cover for the species trial area was found to be about one square m /tree for the three species. Runoff experiments at the incipient gulling revealed that 98% of the eroded soil was silt and clay. Nitrogen, sodium, potassium and phosphorus are the main elements, which are lost by the erosion of topeoil, in addition to other elements. The cut off drain technwue proved to reduce the weight (t/h) of soil eroded by more than 45% compared with control. The average weight of soil eroded using this technique was found to be 0.9337 (t/h) of soil, while in the case of control was 1,6078 (t/h) at (0.005) significance level and standard error of 0.0267 (t/h). Bioassay trial results at laboratory and nursery revealed that plants grown in intact soil were better than in gullied soil for any period of time (7 days, 15 days, 30 days and 60 days). This was reflected in plant helight green and dry weight differences. Moisture content and infiltration rate trials also proved that gully erosion increased both parameters. Survival rates of the species tried were found to be 30% for Acacia tortilis and 21.4% for Acacia mellifera and 19.7% for Acacia seyal grown for eight month. These trees proved to be the promising species for control of gully erosion as well as for conservation of land, especially when planted in micro-catchments to enhance growth during the dry period of the year. The interview survey among farmers showed that most of them felt that gukky erosion is a real peoblem. They expressed their willingness to partiicipate in its control. It is important that their awareness should be raised. Technical and logistic support should be provided. There are many factors confronting the farmers to participate in protective measures due to their low income, which is due to low productivity accompanied with decline in prices. Raising awareness among the people related to agriculture is also important. Other problems such as weeding harvesting and finance masked the erosion problem. Farmers are willing to participate through manual work and looking after trees planted if availed by the government or other non governmental Organization (N.G.Os) authorities