农业投入补贴改革与水质：来自赞比亚的证据

摘要

I study the environmental impacts of agricultural input subsidy reform by evaluating Zambia’s staggered transition from a traditional physical fertilizer distribution program to a flexible electronic voucher system. Using a 5 km 5 km spatial panel of satellite-derived water quality measures and a staggered difference-in-differences design, I estimate the downstream environmental effects of the reform from 2010 to 2023. I find that the introduction of the e-voucher significantly improves downstream water quality, reducing chlorophyll-a concentration by 13.0%, phycocyanin concentration by 11.0%, and total suspended matter by 7.5%. The estimated effects are larger in districts with higher densities of private agro-dealers and are concentrated in areas with highly leachable soils and historically intensive maize monocropping. At the household level, I find that greater input flexibility reduces synthetic nitrogen use and increases crop diversification toward nitrogen-fixing legumes. These changes are consistent with a reduction in nutrient losses and improvements in soil stability. Overall, the findings suggest that replacing fixed agricultural subsidies with flexible systems can improve downstream water quality while encouraging more sustainable agricultural practices.