16. Soil erosion, water runoff and their control on steep slopes in Sumatra.
Trop. Agric. (Trinidad), 68, No. 4, 1991, pp. 321-324
In this paper soil erosion research and water runoff rates under conventional cultivation (i.e., without soil conservation practices) and when several soil conservation measures were used on steep, intensively-cultivated slopes in Sumatra, Indonesia are examined.
Erosion-inducted effects on selected soil physical and chemical properties and on crop yields were also examined. Based on these results, recommendations were developed for the introduction of appropriate soil conservation measures.
This study was conducted in the highland valley of Kerinci, Sumatra, Indonesia. Irrigated rice cultivation is the dominant land use in the valley; annual and perennial cash crops are cultivated on the hills above the valley floor. Most farmers in Kerinci cultivate both a rice field and one or more hillside farms.
Soils in Kerinci are complex red-yellow podzolics.
Soil erosion and water runoff losses associated with conventional and conservation farming practices were measured on enclosed runoff plots, using a randomized complete block design with three replications.
Five practices (treatments) were selected for study:
- control by conventional cultivation (corn planted two seeds per hole at 75 cm intervals) with no soil conservation measures employed;
A variety of soil conservation practices are used on small farms throughout the tropics. Some of the more common practices include: contour ploughing, conservation tillage, the use of cover crops and mulches, grass and leguminous shrub plantings along the contour, grassed runoff channels, contour bunds, ditches and bench terraces.
Agronomic soil conservation techniques are generally preferred to engineering methods (e.g., bench terraces) by low-income or subsistence farmers because of lower capital and labour requirements. The construction of bench terraces can result in reducing crop yields where shallow topsoils overlie undesirable subsoils.
In this study, the use of bench terraces, grass bunds and grass plus Gliricidia sepium bunds with mulch resulted in significant (P<0.05) reductions in soil loss and water runoff in comparison with conventional cultivation methods on steep hillside farms in Sumatra. No significant differences in soil erosion rates were observed between conservation treatments.
No significant differences in mean groundnut yields and total above ground biomass production were observed between the conservation or control treatments (on a per plant basis).
This research suggests that agronomic soil conservation practices known to be effective on gentle (less than 15%) slopes may also be suited to some steep tropical slopes. Simple agronomic conservation farming measures warrant careful consideration and empirical field-testing in soil conservation and watershed management projects throughout the tropics.
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