Spring Nitrogen Management for Grass Hay and Pasture

By Justin Brackenrich    

Cool-season forage grass demand for nitrogen is high in the spring, making application and supply important. Nitrogen not only affects the tonnage of dry matter production but also increases the protein content of the hay. In many hay and pasture fields, we rely on legumes like clover or alfalfa to supply grasses with their nitrogen need, but what if clover isn't present to fix the needed nitrogen for grass production? Let's consider some recommendations and guidelines to ensure applications meet production goals and livestock needs. 

Rate

Varying rates for spring nitrogen applications depend on the university publication, region, and soil where the application will be made. Too little nitrogen, the forage lacks a macronutrient, and growth may be limited. Too much nitrogen and a surplus of nitrogen may lead to economic waste and the potential for lodging. Minnesota and Kansas recommend 30 pounds, Iowa State recommends different rates by species (cool-season and warm-season) basis, but for Pennsylvania, 50 pounds is the recommendation. What do they all have in common? Pounds N/ton of forage produced. All recommendations for nitrogen applications are based on the forage produced in the subsequent harvest. For example, if you wish to produce two tons of hay per acre in the second cut, that grass needs 100 lbs. of nitrogen per acre after the first harvest.

Something to consider with the rate is how much is enough. First-cutting hay production in Pennsylvania is often challenging due to the volume and unfavorable weather conditions. If you struggle to get first-cut hay harvested on time and at the proper maturity, applying additional nitrogen can worsen this problem. Consider applying only 30-50 lbs. per acre in spring rather than 50-100 lbs.

Timing

In agriculture, we typically use a visual term of 'green-up' to identify the proper time for these applications. This is the point that the plant is breaking dormancy and no longer relies on root reserves and storage but begins producing its food and growing. This is the time to begin making spring nitrogen applications. This time can occur anywhere between mid-March and mid-April. Industries like turfgrass and grass seed use growing degree days (gdd) to narrow these application windows. For cool-season grasses, nitrogen application can begin at around 200 gdd (base 32). Research from Kansas State University shows that the earlier applications of nitrogen will increase forage tonnage and protein. However, applications in the late vegetative stage do not increase yield but can still significantly improve forage protein content.

When making nitrogen applications to pasture, it is important to stagger applications. If all fields receive applications at the same time, forage will all be ready for grazing at the same time. Nitrogen should be applied to pasture fields in seven-to-ten-day increments based on a grazing management system.

Applications

Since nitrogen is mobile in the soil and environment, management of this nutrient is more intensive than others. Using a controlled-release product or split applications is essential to ensuring proper nitrogen management in hay and pasture.

Controlled-release nitrogen products have a polymer coating for a slower release. These products vary but have a release time of 50 to 80 days and work well when in-season application is difficult. These products should be applied with a blend of urea or AMS to have an available source to pair with the controlled-release product. A blend of these products allows for a single application in spring that will apply nitrogen throughout the growing season.

Using granular or liquid urea or ammonium sulfate products requires split applications. This requires applications before each cutting to supply the nitrogen needed. Applications in spring around 200 gdd (base 32) and after the first and second cuttings are advised for increased production. For a complete look at nitrogen management and split application, review Soil Fertility Management for Forage Crops: Maintenance.

Additional Thoughts

• Nitrogen management will improve tonnage and forage quality, but proper harvest timing and management are most important to producing a quality product.
• Nitrogen is only one piece of the puzzle when producing quality forages. Ensure that soil fertility is tested every three years and adequate levels of phosphorus and potassium are available to the plant. Iowa State University's article describes nitrogen, phosphorus, and potassium management. This information can be found at Spring Forage Fertilization Considerations.
• If the summer appears very droughty and unfavorable for growth, wait for the in-season application until the weather is forecasted to have more rain.
• Read Understanding Growing Degree Days by Penn State Extension for more information on growing degree days.
• Last year, nitrogen trials were held in western PA, looking at rates and sources of nitrogen. This trial and its results are found in the Western Pennsylvania Nitrogen Trial on Grass Hay, Western PA Nitrogen Trial- First Harvest, and Western PA Nitrogen Trial- What We Learned from Second Harvest. This trial will continue this year.