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 reflected in current nitrogen guidelines. As a result, farmers face substantial 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 often leads to fertilizer over‑application due to concerns about under‑fertilizing corn, variable alfalfa stand vigor, and unknown nitrogen interactions, increasing input costs and environmental risks. These challenges are compounded by a lack of data on how termination timing, together with manure application influence soil nitrogen release, microbial processes, and manure nitrogen retention. Given the central role of alfalfa and manure in Wisconsin dairy systems, addressing these gaps is essential for improving whole‑farm nitrogen use efficiency, reducing operational costs, and ensuring a reliable feed supply.

These funds will support the establishment and data collection of a field trial and a corresponding laboratory mineralization study. Leveraging an existing alfalfa stand at the Arlington Agricultural Research Station to evaluate manure–alfalfa interactions the project will (1) determine how termination timing (fall vs. spring) interacts with manure to influence soil nitrogen mineralization, plant nitrogen uptake, and the effective nitrogen credit to first‑year corn, and (2) develop improved, alfalfa and manure‑specific nitrogen credit recommendations to replace static guideline tables. In addition, the laboratory study will evaluate mineralization of organic nitrogen from an alfalfa- manure mixture under simulated field temperatures. By clarifying how biologically fixed nitrogen from alfalfa and organic nitrogen from manure interact under dairy management conditions, this work 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.