An Overview of the Effectiveness of Agricultural Conservation Practices for Water Quality Improvement.

This article introduces a Special Collection of literature reviews documenting the performance and cost-effectiveness of six agricultural conservation practices (ACPs): conservation crop rotation, cover crop, filter strip, nutrient management, denitrifying bioreactor, and constructed wetland. The overall objectives of the Special Collection are to: (1) review published studies on ACP effectiveness in reducing nutrient and sediment losses from agricultural fields; (2) compare, integrate, and synthesize the results from those studies to obtain a systematic understanding of the mitigation efficacy of each ACP in a consistent format across the selected ACPs; and (3) assemble cost analyses and obtain general insights on performance-based costs of the ACPs. The specific objectives of this introductory article are to summarize key information from each of the six review articles and develop a comparative understanding of the performance and cost-effectiveness of the six ACPs. Among the selected ACPs, denitrifying bioreactor, constructed wetland, cover crop, crop rotation, and nutrient management were all effective in reducing nitrate-N loads in subsurface drainage, with performance effectiveness in load reduction ranging from 23% to 40%. A corn-soybean rotation (relative to continuous corn) was the most cost-effective among the selected ACPs and can reduce nitrate-N load at a net benefit of about USD $5 per kg nitrate-N compared to continuous corn. Filter strip was most effective in reducing sediment, total nitrogen (N), and total phosphorus (P) loads from surface runoff and can be effective in reducing nitrate-N and dissolved P. Cover crop was also effective in reducing sediment and total P loads. Studies of the selected ACPs for their performance effectiveness for dissolved P are limited, and results varied among the ACPs included; thus, more research is needed relative to ACP effectiveness in reducing dissolved P loss, particularly in subsurface flow. Finally, although each review article included cost-analysis information, more data and analyses are needed to better understand the cost-effectiveness of ACPs and their ecological benefits.