Effectiveness Overview of Agricultural Conservation Practices for Water Quality Improvement Part II.

Although significant governmental investment has been provided to implement agricultural conservation practices (ACPs) for water quality improvement, eutrophication and hypoxia persist in coastal and fresh waters. A better understanding of the comparative effectiveness of ACPs is needed to improve environmental outcomes with the funding available. The objectives of this overview article are to (1) compare the performance and cost effectiveness among all the ACPs reviewed in both the first and second editions of the Special Collection and (2) present critical perspectives for researchers, policymakers, and funding entities seeking to improve water quality. The ten ACPs reviewed encompassed a range of goals, strategies, and landscape placement and varied widely in performance for their reduction of sediment, nitrogen (N), and phosphorus (P) and their cost-effectiveness. Three ACPs included performance measures for all three constituents: sediment, N, and P, whereas others focused only on N (nine ACPs) and/or P (six ACPs). The four ACPs that are considered "water management" practices: drainage water management, denitrifying bioreactor, saturated buffer, and constructed wetland were all effective in mitigating the effects of nutrients in subsurface drainage water and showed average nitrate-N load reductions of 40%-46%. In contrast, few practices were found effective in reducing dissolved P (DP) loss from agricultural fields. Four ACPs (residue and tillage management, conservation crop rotation, drainage water management, and nutrient management) demonstrated possible net economic benefits, while perspectives were provided for prioritizing financial assistance for other ACPs. Monitoring recommendations developed during the literature reviews highlighted the need for more long-term field-scale monitoring to better reflect multi-year climatic variability.