Conservation Practices to Reduce Nutrient Loss: How Do They “Stack” Up?

Conservation practices recommended to reduce nutrient loss from fields are generally classified as in-field practices, edge-of-field practices, and land use change practices. Each practice has a different effectiveness for reducing nutrient loss as well as different associated costs and cost efficiencies. Beyond these important differences, there are several additional details about each practice — level of change required, stackability, and trackability — that are important to consider when weighing options to improve water quality. The adoption or implementation of any conservation practice will necessarily require a change from a given status quo. Some recommended practices, such as converting corn or soybean acres to perennial energy crops or pasture, will be relatively major shifts from conventional agricultural management. Other practices, like shifting nitrogen fertilizer applications from the fall to the spring, will be relatively smaller changes.Another consideration is that some practices can be layered with other practices so that the practices are essentially “stacked” together. The “stack-ability” of a practice refers to the fact that some practices pair naturally together, while others may actually be mutually exclusive. For example, in-field and edge-of-field practices are often highly compatible, but a denitrifying woodchip bioreactor and a constructed wetland would generally not treat the same drainage outflow, at least at the field scale (that is, they might be mutually exclusive).“Track-ability” is a third important concept. It will take time for water quality improvement occurring at the field and farm scale to accumulate to significant levels at the watershed scale and then eventually migrate to the Gulf of Mexico to ultimately reduce the size of the annual hypoxic zone. This, after all, is the goal of reducing nutrient loss from fields in the Mississippi River basin. Tracking the adoption of recommended practices is important for states and federal agencies to quantify progress toward Gulf of Mexico hypoxia goals given the lag time to physically observe improved water quality at such a large scale. However, the implementation of some types of conservation practices is harder to track than others. For example, conservation practices that are adopted without federal incentive payments present a significant challenge for tracking and reporting purposes.