要旨
Agricultural intensification continues to be a major threat to sustainable development in mountain regions of the world since it is largely associated with lower soil fertility, increased soil erosion, pollution and eutrophication of water bodies, reduced biodiversity, and livelihood challenges. Agroforestry, the purposeful cultivation of trees and crops in interacting combinations, has the potential to provide environmental benefits and to contribute to livelihood security, and is receiving increasing attention as a sustainable land management option. Whereas many studies highlight general positive environmental and socio-economic effects of agroforestry systems, effects of the transition to agroforestry practices have rarely been quantified and studied in detail, in particular in Nepal. This paper analyses alterations of soil properties after the adoption of agroforestry practices in a typical mid-hill region of Nepal. Three agrosystems were compared with a special focus on soil fertility: (i) a mature, fully developed agroforestry system (AF); (ii) the predominant conventional system (CS) characterized by mono-cropping; and (iii) a system that has been in transition to AF for two years (TS). The results show significant differences in soil pH, aluminium content, base saturation, electric conductivity, organic matter and nitrogen content, and cation exchange capacity between AF and CS soils, indicating a higher soil quality and more fertile soil conditions in the AF soils. The contrasting soil quality has to be largely attributed to the differing land management practices. After two years of transition, the TS soil data already show a convergence towards the AF values in several parameters. This study gives quantitative evidence that agroforestry systems have the potential to significantly enhance soil quality and long-term soil productivity, with positive effects appearing shortly after the conversion from conventional monocropping systems.
