Comparing Runoff, Soil and Nutrient Losses from Three Small Watersheds in Indonesia

B. Hermiyanto, M. A Zoebisch, G. Singh, S. L Ranamukhaarachchi, R. Clemente, F. Agus

Abstract


The effects of land cover at the watershed scale on soil and nutrient losses are important
criteria for improved soil conservation management. The objective of this study was to
assess runoff, soil and nutrient losses from 3 neighboring small agricultural watersheds in
Java, Indonesia, in relation to the prevailing land use. In the area, Inceptisols and Alfisols
are dominant. The three watersheds are characterized by distinctly different land uses, i.e.,
annual cropping (in the Tegalan watershed), perennial cropping (in Rambutan) and mixed
cropping (in Kalisidi). Field measurements were carried out over a two-year period (2000
and 2001). The mean annual rainfall in the area was about 3180 mm. The annual sediment
yields (soil losses) from the watersheds were 9.6 t ha-1 (in 2000) and 15.4 t ha-1 (in 2001)
for Tegalan; 1.0 t ha-1 (in 2000) and 0.2 t ha-1 (in 2001) for Rambutan; and 0.5 t ha-1 (in
2000) and 0.8 t ha-1 (in 2001) for Kalisidi. The annual runoff from the watersheds in 2000
and 2001 were 1,980 m3ha-1 and 1,190 m3ha-1 (Tegalan), 230 m3ha-1 and 80 m3ha-1
(Rambutan), and 6,090 m3ha-1 and 6,200 m3ha-1 (Kalisidi). Enrichment ratios for P ranged
between 1.2 and 2.3, for Mg between 1.1 and 2.4, and for K between 1.2 and 1.3. No
significant overall correlation was observed between enrichment ratio (ER) and soil loss,
but the differences between the watersheds were significant. Soil losses did not
systematically increase with runoff. Overall, land cover has shown to be the most likely
determinant of soil loss, and hence, nutrient losses in the study area. Nutrient losses due to
erosion appear to be a major cause of soil fertility depletion in the area. Soil management
practices to improve the levels of P, K and organic matter would be required to compensate
losses of plant nutrient and to improve soil-quality in general.

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