Review of nutrient modeling tools available to assess the impact of small grains on nitrogen and phosphorus

This document is a summary of research and interviews conducted to identify a model that could assess the potential for on-farm production of small grains to reduce nutrients (nitrogen and phosphorus) leaving farms and entering the Great Lakes Basin watershed.  Our investigation led to two conclusions: 1) models do indeed make sense for predicting causal relationships in a case such as small grains and nutrient loading, where the research literature is insufficient to depend principally upon it as guidance; but 2) unfortunately, that dearth of literature also means that currently no model is sufficiently parameterized for small grains to accomplish this goal. 

This conclusion informed our decision to not run any of the currently available models, reinforced by recommendations from the diverse experts with whom we consulted, because the resulting data could misrepresent findings based on incomplete or incorrect input data and assumptions. Essentially, these models are not meant to answer the questions we are asking. We did, however, identify opportunities for investment that would bolster existing models to address these inquiries, supporting efforts underway to expand certain models over the coming years in ways that could support these investigations. Those findings are outlined in this summary, along with commentary from experts that assisted in drawing these conclusions. 

The primary limitation of most existing models is their lack of small grain inclusion as a cash crop rotation. Furthermore, declining small grain acreage in the region has reduced investment into understanding the role small grains could play as a nutrient reduction strategy, and thus the models are often not calibrated to express this potential. The existing models focus instead on corn and soybean crops and other more commonly deployed conservation practices such as cover cropping. This highlights the need to support research exploring small grain and nutrient interactions within the region’s cropping systems, as identified in the accompanying literature review.