a case study of Indonesia Andriyani, Idah creator Jourdain, Damien Chairperson Shivakoti, Ganesh P. Examination Committee Soni, Peeyush Examination Committee Kuwornu, John K. M. Examination Committee Directorate General of Higher Education (DIKTI) / Ministry of Research, Technology and Higher Education, Indonesia Scholarship Donor text series technical report th Pathum Thani, Thailand Asian Institute of Technology 2017 continuing eng 136 leaves : ill.+1 online resource Land use in the upper parts of South-east Asian watersheds often affects downstream populations in terms water resources availability and of erosion loads. Both are impacting negatively the irrigated systems located in the lower part of these catchments. This is particularly the case in Indonesia. Our study area is located on the foothills of the Merapi Volcano in Central Java, Indonesia. In the upstream part, intensive farming systems based on high value but erosive crops such as tobacco, maize, and vegetables have led to high erosion that affected the irrigated systems based on lower parts of the catchment. The main impacts were the degradation of the water storage infrastructures such as high sedimentation load in the river and irrigation channel therefore reducing the efficiency of irrigation. This research focused on the feasibility of reducing erosion created by the farming systems found in these upper parts of these catchments. This reduction in erosion can be obtained by a change in the land use, a change in the type of crops grown or a change in the farming practices. Results suggest that farmers in the upstream part did not use soil and water conservation techniques because of water, labor, or cash constraints. Rapid assessment of the erosion yields using a RUSLE based model showed that farmers in the steep slope zone (SSZ) produced the highest erosion yields followed by those in the medium slope zone (MSZ) and the low slope zone (LSZ) who had the lowest erosion yields. However, erosion yields produced by all farming systems in the study area were still higher than the maximum allowable limit erosion yields in Indonesia. Farming systems of upstream areas produced high erosion yields and caused land degradation, threatening the sustainability of farming systems both upstream and downstream. A farm typology using cluster analyses allowed us to identify different farm types based on the farm and household characteristics, the impact of farming systems on erosion, and their constraints. Results suggested the presence of five homogenous groups of farmers. Among them, we selected three farm types that generated medium to high levels of erosion yield, and analyzed how policies could induce some changes in their selection of activities or agricultural practices. We developed and calibrated a farm model using mathematical programming and simulated various policies that could modify their farming systems and ultimately reduce their erosion yields. We tested a tax imposed to erosive crops, a subsidy for anti-erosive crops and a combination of tax and subsidy. To analyze the impacts of various scenarios on erosion change, land use/cropping system change was applied using a RUSLE based model. Imposing taxes on high value but erosive crops were effective in changing land use and cropping systems, but created large revenue losses especially on small farms. More specifically, the level of tax to be imposed would be large (ranging from 14% to 28% of sale price of crops products) to obtain a reduction of erosion yields by 32%. This suggests such a change would be opposed by many farmers. On the other hand, a subsidy would also be effective in changing the cropping system. Contrary to taxes, it also provided farmers with an opportunity to acquire sustainable income sources. Finally, when applying a combination of tax-subsidy scenarios, results showed that the imposition of tax had a significant influence on the change in land use compared to the subsidy scenario. The provision of a subsidy forsome new cropping systems reduced the tax levels to 8% to obtain the same level of erosion yield. Overall, we also noted that the tax-subsidy scheme would lower the overall cost of reducing the erosion yield. However, it would require that some of the conservation costs being shared between the government and the farmers. The polluter-payer principle would not be strictly applied in this case. Finally, we simulated erosion reduced at catchment area level and analyzed the policies impacts on farmer revenue, government budget and cost to society. These simulations and analyses were useful to identify effective and acceptable scenarios to reduce erosion at the catchment level (regional level) as well as to target farm types with significant influences on the implementation of the policies. To conclude, in the steep sloping zone, farmers with less constraints -especially less constrains on capital- have highest contribution on erosion reduced in the study area. All policies were effective to reduce erosion in that zone. In contrast, at MSZ, erosion reduced by LCS-MEC and DivAg-MEC were very small compared to erosion reduced by UpAg HEC. Smaller size of cropping area managed by farmer in LCS-MEC and DivAg-MEC constrained farmers to adopt the policies because small size of cropping area changed leads to small revenue changed for the farmer. Therefore, small revenue changed was less powerful to drive cropping system. Second, in some policies which were able to change cropping system in the LCS-MEC and DivAg-MEC erosion reduced was too small in total erosion reduced at catchment level. it leads to high cost to change (reduce erosion). In another hand, a highest number erosion reduced by UpAg-HEC leads cheapest cost to change for farmer of UpAg-HEC. Third, implementation policies to reduce erosion at steep slope zone area reduced erosion at significant amount as well as cheaper costs indicates that the projects will be effective to be implemented at steep zone area in conditions farmers have less capital constraints (cash balance and large cultivated area). The possibility to reduce farmer{u2019}s capital constraint may increase willingness of the farmer in the medium slope area to participate in the projects. A Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Agricultural Systems and Engineering Thesis (Ph.D.) - Asian Institute of Technology, 2017 Soil Erosion Indonesia Agriculture and state Indonesia Sustainable agriculture Indonesia Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B21610 http://203.159.5.9/ait-thesis/detail.php?q=B21610 190813 20260817161946.0