Ecosystem Services Provided by Agroecosystems: Applying Scientific Outcomes to Develop Nitrogen Management Policy.

Nitrogen (N) management in agroecosystems impacts multiple ecosystem services including potable water supply, aquatic habitat, and greenhouse gas regulation, in addition to crop production. Agroecosystems that are managed as N-saturated systems have little capacity to store N application which exceeds crop uptake. Instead, these systems emit NO3- to aquatic ecosystems or N trace gases to the atmosphere. We have studied N dynamics under contrasting land management scenarios using techniques ranging from literature review, farm-scale budgets, simulation modeling, and empirical modeling. Through comparison of multiple quantitative techniques, we demonstrate that ecological agroecosystem management using cover crops can reduce nitrate leaching by up to 70 % relative to conventional management with winter bare fallows. Given the convergence of multiple quantitative results demonstrating reduced nitrate leaching under cover crop management, scientific data can support the enhancement of water supply and habitat ecosystem services by policies promoting cover crops. Scientific tools to quantify greenhouse gas emissions are more limited than water quality tools. N gas flux measurements are labor-intensive and expensive techniques, and therefore few sites have N gas flux observations. As a result, N gas flux modeling studies rely on limited data for model validation. Our research suggests a wide range of mean cumulative N2O flux depending on management practice and soil type. Extreme N2O flux events are observed both in field data as well as in model simulations. However, the significance of these extreme emission events to policy development and compliance assessment is difficult to quantify from current limited observations. Current scientific results provide tools to quantify ecosystem services across the agricultural landscape. However, demonstrating compliance with policy objectives is difficult to accomplish with available data and models. Developing adequate compliance metrics remains a challenge for integrated ecological and socioeconomic research.