Nitrogen Management on the Far Side of Complexity: Using the N Balance Approach to Reduce NO3 Leaching.

Nitrogen (N) is the Achilles heel of agriculture – without N we cannot produce enough food for a growing global population, yet nitrogen losses from agriculture are a major contributor to water and air pollution and to climate change. Farmers have made great progress in improving nutrient management, but face growing public demand to take more action to reduce N pollution. Without a robust and easy-to-understand N indicator that is directly tied to farm management it is difficult to demonstrate the progress that is being made, and agriculture remains vulnerable to regulation and litigation. The complexity of the N cycle – influenced by water, temperature, organic matter, and management – can be overwhelming to policy makers and sustainability program designers, as well as to the farmers, crop consultants, and researchers on the ground. We are exploring the potential role of a simple input/output model of N balance to serve as both a tool for guiding improvement in nitrogen management and as an indicator for demonstrating progress in reducing nitrate (NO₃) losses. We use a hierarchical (multi-level) model meta-analysis of field research data in corn-based systems of North America to look at the relationship between N balance and N losses as NO₃. We explore how more information on management, soil, and weather characteristics can increase certainty, and try to determine when more data may be irrelevant (or uneconomical). What factors have the greatest modifying effect on the relationship between N balance and NO₃ losses? How much detail is needed to guide management decisions or accurately predict losses? The goal is a tool that can help reduce N losses, without requiring everyone to be a soil biogeochemist.