Abstract
BackgroundGrazing by livestock and cultivation have been considered as two important causes of soil erosion and nutrient export. However, there has been limited evidence that grazing or cultivation matters to soil erosion and nutrient export in Ethiopia. Hence, this study was conducted in the Galesa watershed in Ethiopia to examine the effects of grazing and cultivation on runoff, soil loss, and nutrient export. Daily values of runoff, soil erosion, and nutrient outflow were measured for three consecutive years following standard procedures. Independent t test was performed to check if the means of runoff, soil loss, and nutrient loss from grazing and cultivated lands were significantly different. Moreover, repeated analysis of variance (ANOVA) was used to test if mean values of runoff, soil loss, and nutrient export varied significantly over the study years.ResultsAlthough the average annual runoff depth was 7.8% higher in grazing land (GL), soil erosion was significantly lower (39%) in GL as compared to cultivated land (CL). Similarly, sediment and runoff-associated annual losses of total nitrogen (N), available phosphorus (P), exchangeable potassium (K), and organic carbon (OC) were low in the GL treatments. Lowest losses of total N (9.30 kg ha−1 year−1), available P (0.83 kg ha−1 year−1), and exchangeable K (1.84 kg ha−1 year−1) were recorded in GL treatment. Likewise, lowest losses of sediment-associated total N (32.8 kg ha−1 year−1), available P (0.39 kg ha−1 year−1), exchangeable K (0.23 kg ha−1 year−1), and soil organic carbon (630 kg ha−1 year−1) were recorded from GL over the 3 years of experimentation.ConclusionOur results indicate that cultivation increased soil erosion as compared to grazing. Although there were significant reductions in soil erosion and nutrient export from grazing lands compared with cultivated lands, the absolute losses were still high. This implies the need for grazing land management using appropriate physical and biological erosion control measures to increase productivity and reduce soil erosion as well as nutrient export.
Highlights
More than 80% of the total population of Ethiopia is engaged in agricultural activities (CSA 2012)
Over the 3 years, an average of 281 mm and 259 mm runoff depth was generated from grazing land (GL) and cultivated land (CL), respectively
Higher runoff from GL might be due to low infiltration rate that can be explained in two ways
Summary
More than 80% of the total population of Ethiopia is engaged in agricultural activities (CSA 2012). Some evidence shows that soil erosion is costing the Ethiopian economy about 4.3 billion USD per year (Gebreselassie et al 2016). This means that there is an urgent need to tackle the problem of soil erosion and restore degraded areas to enhance overall system productivity. This study was conducted in the Galesa watershed in Ethiopia to examine the effects of grazing and cultivation on runoff, soil loss, and nutrient export. Independent t test was performed to check if the means of runoff, soil loss, and nutrient loss from grazing and cultivated lands were significantly different. Repeated analysis of variance (ANOVA) was used to test if mean values of runoff, soil loss, and nutrient export varied significantly over the study years
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