Kajian tingkat erosi, sekuestrasi karbon dan daya simpan air pada berbagai tipe penggunaan lahan di sub DAS Jenneberang Hulu

Abstract

The objective of this research were to assess the level of run off and erosion, carbon sequestration, and water holding capacity in various types of land use in the Upper Jenneberang Sub Watershed. Transformation of natural ecosystems into agricultural ecosystems generally increase soil erosion. Soil carbon or organic matter is an important component of soil constitute as a function of soil quality. Soil carbon can enhance and improve the quality of the soil physical properties; it can increase infiltration rate, aggregate stability, soil structure, water-holding capacity, and in turn decrease run off and erosion. This study was carried out from December 2006 through March 2007 at the Upper Jenneberang watershed, Saluttoa Village, Tinggimoncong Sub District, Gowa District, South Sulawesi Province. Based on the preliminary study there were found four types of land used and were treated as observation units: 1) Natural forest, 2) Agroforestry dominated by gamal tree (Gliricidia sepium) (AF1), 3) Agroforestry dominated by coffee tree (AF2), 4) Maize monoculture. To meet the purpose of this research all experiment at units were arranged in Randomized Block Design. Data collected in this experiment includes soil physical characteristics (bulk density, permeability, aggregate stability, water holding capacity), as well as the rate of infiltration, run off and erosion, the amount of rain fall, total biomass, C-biomass content and watershed water holding capacity. Results of this study indicated that the rate of infiltration and the permiability were significantly higher on natural forest compared with other land utilizations due to its higher porosity and organic matter content. When convertion of the natural forest takes place, the agroforestry systems and maize monoculture significantly increased the run off and consequently soil erosion. The magnitude of run off were increased three times when the land use were converted into agroforesty dominated by coffee tree and increased seven times when it was converted into maize monoculture. The magnitude of erosion were increased seven times when the land use were converted into agroforesty dominated by coffee tree and increased eleven times when it was converted into maize monoculture. The biomass and C-biomass in natural forest were significantly higher than that in the agroforestry systems (AF1 and AF2). The total biomass and C-biomass of each type of land utilization were in line with the the total C-organic in the soil. The concentration of C-organic on maize plot was significantly lower. The activity of soil microorganism in the natural forest was significantly higher than that in agroforestry systems and maize monoculture. The magnitude of water-holding capacity of soil were decreased 21% when the land use were converted into agroforesty dominated by coffee tree and decreased 39% when it was converted into maize monoculture. Simulation analysis showed that the total water-holding capacity of the Upper Jenneberang Sub Watershed was as much as 795.4 mm or equal to 39% of total precipitation.