Estimating Cover Crop Nitrogen Contributions and Management Costs with a New Online Calculator.

Many farmers use cover crops to build soil organic matter and improve soil fertility. However, few can predict plant available nitrogen (PAN) contributions from cover crops, estimate the cost of managing cover crops, or compare the value of cover crops and fertilizers with confidence. In field trials we compared cover crop sampling methods to identify a recommended method for farms in Oregon. In later field and laboratory trials we tested the ability of a published mineralization model to predict the release of plant-available nitrogen from incorporated cover crop residues. We found a strong correlation between the model and our data, and incorporated the model into a new online Excel-based Cover Crop Calculator. The Calculator and research background is online at http://smallfarms.oregonstate.edu/calculator. Growers and advisors can now use the Calculator to better understand the cost and benefits of cover crops compared to fertilizers. By using the Calculator they can account for cover crop nitrogen contributions and reduce nitrogen fertilizer rates. The Calculator also helps growers select the most cost effective supplemental fertilizers and develop fertilizer programs that match crop nutrient requirements.