Characteristics and extent of soil loss by water erosion at the cropland level in the Kivu dorsal, South Kivu, DR.Congo
(2018) SoWaSe 2018 (Soil and Water Security): Challenges for the next 30 years! — Location: Imola, Italy (6.June.2018)
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- In cultivated areas of the African highlands, soil erosion is a widespread phenomenon threatening the sustainability of agricultural production. However, quantitative estimates are scarce, particularly for the Kivu dorsal in D.R. Congo where little research on water erosion has been carried out since colonial times. To address this deficiency, the extent of linear erosion and associated explanatory factors were studied in two representative watersheds of the Kivu dorsal across a wide range of crops and cropping systems, soil characteristics and land management practices. Rill and gully erosion volumes were measured every 2 weeks in 45 fields per watershed by the transect methods during four successive long(SA) and short (SB) rainy seasons (2015-2017). In addition, field characteristics (crop types and cover, slope, management practices, soil physico-chemical properties) and volume of rainfall were determined. Statistical analyses consisted in descriptive, correlation and linear mixed model regression analysis. The average maximum soil loss by linear erosion was significantly different between seasons (5.5 and 1.8 mm in SA/2015, 2.6 and 2.6 mm in SB/2016, 2.4 and 3.2 mm in SA/2016 and 3.5 and 3.7 mm in SB/2017 for rill and gully erosions, respectively) but did not differ between the two watersheds. As a result of the difference both in natural factors (e.g., precipitation and steep slopes) and management conditions(cropping systems and vegetation cover) across farmers’ fields, there was a large variability in cumulated soil erosion rates over the 4 seasons from 0.01 to 32.75 mm and 0.13 to 16.27 mm for rills and gullies, respectively. These erosion rates are far above the highest tolerable soil loss rates (10 t ha-1 year-1 or 0.7-0.8 mm depending on the soil bulk density). Given that rill erosion was both higher and more variable than gully erosion, the regression analysis focused on this process. Rill erosion rates tended to decrease with increasing P content, sum of bases and effective CEC content and decreasing slope length and slope gradient, while combined intercrop-monocrop systems tended to increase rill erosion, while high total rainfall increased the gully erosion rates. Overall, the two studied watersheds showed very high rates of land degradation by rill erosion, suggesting the need for rapid implementation of erosion control methods. The results could be used to prioritize sites at risk of water erosion in order to install mitigation measures at the scale of small watersheds.
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Heri Kazi Bisimwa, A., & Bielders, C. (2018). Characteristics and extent of soil loss by water erosion at the cropland level in the Kivu dorsal, South Kivu, DR.Congo. Proceedings. Published. SoWaSe 2018 (Soil and Water Security): Challenges for the next 30 years!, Imola, Italy. https://hdl.handle.net/2078.5/251455 (Original work published 2018)