Soil Erosion and Nutrient Losses from a Volcanic Ash Soil in Kilimanjaro Region, Tanzania

摘要

Effect of soil erosion on productivity is not known for many soils of the tropics. This study was conducted to determine effect of erosion on nutrient losses from a Mollic Andosol in Kilimanjaro Region, Tanzania. The extent of previous erosion at thestudy site was determined by a survey of thickness of the Ah horizon as follows: 12-16 cm (severely eroded), 18 cm to 23 cm (moderately eroded), and 25 cm to 32 cm (slightly eroded). Three runoff plots of 4 m X 10 m were established on each erosion phasein order to quantify effect of past erosion on present runoff and erosion. Samples of sediments and runoff-water were analyzed to quantify losses of N, P and C. Maize (Zea mays var. Kilima) was planted in the plots at the onset of the rainy season in 1995 and 1996. Total amount of runoff measured from the plots was 44.6 mm in 1995 and 142 mm in 1996, while soil loss was 12 and 32 tha~(-1) in 1995 and 1996, respectively. Depth of Ah horizon had no significant effect on soil loss, but runoff increased with increasing topsoil depth (TSD) for both years. The total losses of N, P and C through runoff and soil loss in 1996 were 109, 13 and 969 kgha~(-1), respectively. These results indicated that nutrient loss due to erosion is a major contributor to soil fertility decline for this soil.