Applying nitrogen fertilizer is a balancing act for farmers. Too little can limit crop yields. Too much wastes money, increases pest risk, and harms water quality. For organic and sustainable farmers, managing nitrogen is especially complex.
Organic farmers work with higher soil organic matter and legume cover crops—two key sources of nitrogen that are hard to measure. At the same time, organic nitrogen fertilizers are often five times more expensive than synthetic ones. Reducing unnecessary inputs not only saves money, but also energy, since synthetic nitrogen production is energy intensive.
Using the OSU Organic Fertilizer and Cover Crop Calculator protects water quality, reduces greenhouse gas emissions and promotes soil health — benefits that extend beyond individual farms to entire communities.
To address these challenges, Oregon State University Extension faculty developed decision-support tools tailored to organic vegetable production. The OSU Organic Fertilizer Calculator, first released as a downloadable spreadsheet in 2008, helps farmers estimate nitrogen release from organic fertilizers, calculate nutrient application rates, and compare costs per pound of nutrient.
In 2010, the tool was expanded into the OSU Organic Fertilizer and Cover Crop Calculator, which estimates nitrogen release from cover crops and the cost of managing them. This version introduced per-acre calculations and incorporated findings from on-farm trials and laboratory research. A simplified version was later released for gardeners and small-scale farmers.
Since 2020, new features have improved accuracy. Updates to the nitrogen models account for short-term nitrogen tie-up from low-nitrogen cover crops like cereals. Seed calibration worksheets were also added to support better cover crop establishment.
These calculators serve as planning tools and are best used in combination with nitrate monitoring. Monitoring tracks nitrogen contributions from fertilizers, cover crops and soil organic matter, helping farmers refine practices over time. Many organic growers appreciate this approach because they understand the high cost of inputs and want to protect water quality and avoid pest issues.
In 2022, OSU Extension launched a new online education series: Organic nutrient management for vegetable production. The five-module course helps farmers and agricultural professionals understand best practices in nutrient management for organic systems.
Since its launch, the Organic Fertilizer and Cover Crop Calculator has had broad local, national and international impact. From 2008 to 2017, more than 2,400 users from 47 countries and all 50 U.S. states registered to use the calculator — managing over 160,000 acres in total. Of those users, 36% identified as farmers and 39% as other agricultural professionals. If just 25% of users saved $50 per acre annually, the estimated economic benefit would exceed $2 million.
OSU Extension publications supporting the project have been accessed thousands of times across more than 40 countries, with nearly half of U.S. readers located in Oregon. The tools and resources have also been widely cited by other institutions and shared in national publications, reinforcing their continued value to producers, educators and researchers alike.
By helping organic and sustainable farmers optimize nitrogen use, OSU Extension's tools protect water quality, reduce greenhouse gas emissions and promote soil health — benefits that extend beyond individual farms to entire communities. These resources also strengthen local food systems by improving farm profitability and resilience, while supporting informed decision-making among agricultural professionals.
