Runoff and sediment-associated nutrient losses under different land uses in Tigray, Northern Ethiopia

Nutrient transport in surface runoff associated with sediment constitutes an important nutrient loss in Tigray, Northern Ethiopia, but little information is available on this aspect. This paper analyses runoff coefficient, runoff volume, sediment yield and sediment-associated nutrient losses under different land uses (cultivated, grazing, eucalyptus plantation, and exclosure lands) in the Tigray highlands. Two years data on rainfall, runoff volume, sediment yield and sediment-associated nutrient losses were collected from 31 runoff plots of 20 m2. Results show that runoff coefficient, runoff volume and sediment yield are significantly higher in cultivated land than in the other land uses. On average, runoff volume from cultivated land is two times higher than in open grazing land at Gum Selassa, but at Maileba it is 5, 6, 16 times higher than in plantation, open grazing, and exclosures, respectively when extreme rainfall events were excluded. The respective values for sediment yield from cultivated land at Maileba are 4, 5 and 27 times higher. Variation in total rainfall amount that produced runoff explained 69% of the annual runoff volume variability, and this in turn explained 76% of the annual sediment yield variability. Among the plot variables, vegetation ground cover was significantly and negatively correlated with runoff coefficient; and runoff generation tends to be negligible when the ground cover exceeds 72%.