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In this article we investigate if qualitative soil fertility datasets derived during participatory processes can be combined with a corresponding land use change model (i) to improve the understanding of the social-ecological complexity of land use change and (ii) to allow testing of alternative scenarios even in data-poor environments. To test this hypothesis, a participatory assessment approach was combined with the spatially explicit, soil fertility driven FALLOW (Forest, Agroforest, Low-value Landscape Or Wasteland?) model. For a case study village in Northwest Vietnam, participatory evaluations with two age groups of farmers were employed in an iterative way to derive qualitative and quantitative model input data to test scenarios of current and improved management on upland soil fertility evolution with FALLOW. The indigenous colour-based soil quality classification was successfully integrated into the Trenbath FALLOW soil module. The model baseline scenario was validated by calculating the goodness-of-fit of model outputs with land cover maps (Fₜ 0.78) from remote sensing. Model scenario analysis suggested a masking effect of ongoing soil fertility decline by use of fertilizers and hybrid crop varieties, indicating a resource overuse that becomes increasingly irreversible without external interventions. Simulations further suggest that success of introduction of improved cropping management methods becomes less effective with increasing soil degradation and cannot fully restore initial soil fertility. We conclude that the coupled semi-quantitative approach is useful at the village level as it generated meaningful insights into local land use change dynamics without the need for long-term and data-intensive studies.
