Dairy farms depend on alfalfa for high-quality forage and on manure recycling to maintain soil fertility, yet the interactions between these two foundational components of dairy nutrient management are not fully reflected in current nitrogen management guidelines. As a result, farmers often face uncertainty when determining nitrogen needs for corn silage, the primary crop following alfalfa in dairy rotations. Inaccurate assumptions about alfalfa-derived and manure-derived nitrogen can lead to fertilizer overapplication driven by concerns about under-fertilizing corn, variable alfalfa stand vigor, and poorly understood nitrogen interactions. These challenges increase input costs and environmental risks while limiting opportunities to improve nitrogen use efficiency. Given the central role of alfalfa and manure in Wisconsin dairy systems, addressing these knowledge gaps is essential for improving whole-farm nutrient management, reducing operational costs, and ensuring a reliable feed supply.

Dairy Innovation Hub funding supports the establishment of a field trial and complementary laboratory mineralization study to better understand manure-alfalfa interactions. Leveraging an existing alfalfa stand at the Arlington Agricultural Research Station, the project will evaluate how alfalfa termination timing (fall versus spring) interacts with manure applications to influence soil nitrogen mineralization, plant nitrogen uptake, and the effective nitrogen credit available to first-year corn. The project will also generate improved alfalfa- and manure-specific nitrogen credit recommendations that can replace static guideline tables currently used by producers.

In parallel, a laboratory study will examine the mineralization of organic nitrogen from alfalfa-manure mixtures under simulated field temperature conditions. By clarifying how biologically fixed nitrogen from alfalfa and organic nitrogen from manure interact under dairy management systems, the project will provide producers with more precise nutrient-planning tools, reduce unnecessary fertilizer expenditures, lower environmental nitrogen losses, and strengthen the agronomic, economic, and environmental sustainability of Wisconsin’s dairy sector.