Background and aims: Agroforestry systems combining trees with crops or pastures have been widely used to reduce water, soil, and nutrient losses and associated water pollution from agricultural lands in both temperate and tropical regions. However, reviews on improvement/efficiency and the scope of such reductions by soil, management, climate, and hydrological processes are limited.
Methods: This paper synthesized the available evidence on the reduction in surface runoff, soil erosion, nutrient, and pollutant losses (e.g., herbicides, pesticides, and antibiotics) to quantify the effectiveness of agroforestry systems on water quality improvement based on published studies.
Results: On average, agroforestry systems reduced surface runoff, soil, organic carbon, and related nutrient losses by 1~100%, 0~97%, –175~92%, and –265~100%, respectively, with average values of 58%, 65%, 9%, and 50%, respectively; these systems also reduced herbicide, pesticide, and other pollutant losses by –55~100% (49% on average).
Conclusions: Reduction efficiencies of agroforestry systems are site-dependent and vary widely depending on different biophysical factors. A comprehensive science-based review is needed to generalize agroforestry design and site adaptability for water and soil conservation where climatic, geographical, ecological, and socio-economic conditions are relatively similar in the world. 
