Nitrogen fertilization may be furthest thing from a one-size-fits-all situation. The nutrient required for plant growth and protein synthesis is a critical factor of forage production, but its mobile status and leaching potential require a thoughtful approach to application.
In a recent article from Penn State University Extension, Justin Brackenrich encourages producers to ponder nitrogen application rate and timing before fertilizing pastures and hayfields this spring. The extension agronomy educator points out that applying nitrogen can not only have an effect on forage growth, but also on farm expenses and the environment.
Right rate
While legumes can provide nitrogen to grass in mixed stands, pure grass pastures and hayfields will likely benefit from fertilization. With that said, there can be a fine line between too little and too much.
“Too little nitrogen, and 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,” Brackenrich writes. He adds that applying too much nitrogen can also exacerbate the spring flush, which is something he’s witnessed on farms in his own state.
“First-cutting hay in Pennsylvania is often challenging due to the volume [of forage] and unfavorable weather conditions,” he writes. “If you struggle to get first-cut hay harvested on time at the proper maturity, applying additional nitrogen can worsen this problem.”
Brackenrich notes that many university extension services offer application rate recommendations online; however, these rates vary by state and/or region, grass species, and soil texture. Even so, most nitrogen recommendations are based on the expected tons of forage produced per acre during the following harvest.
Right time
Aim to apply nitrogen when hayfields break dormancy and begin showing signs of green up. At this point, forage will start to transition from using root reserves for energy to photosynthesizing.
“This can occur anywhere between mid-March and mid-April,” Brackenrich writes. He notes growing degree days (GDD) are used as a tool in the turfgrass and grass seed industries to time nitrogen applications, which can be useful for forages as well.
For cool-season grasses, Brackenrich recommends applying fertilizer around 200 GDD. Research shows fertilizing earlier than this does not benefit forage yield. Applying nitrogen in later vegetative stages has not been shown to have a significant effect on yield either but may boost forage protein content.
Grass pastures may warrant a more staggered approach to nitrogen fertilization than hayfields. “If all [pastures] receive applications at the same time, all forage will be ready for grazing at the same time,” Brackenrich states. “Nitrogen should be applied to pastures in seven- to 10-day increments based on the grazing management system.”
Application options
Controlled-release products or split nitrogen applications can be essential to manage forage nitrogen, especially considering that nitrogen is a mobile soil nutrient that is subject to leaching. Brackenrich explains that controlled-release fertilizers have a polymer coating that prolongs the release time over 50 to 80 days, depending on the product. These fertilizers can be advantageous if split applications are challenged by weather or adverse field conditions.
“These products should be applied with a blend of urea or ammonium sulfate to have an available source to pair with the controlled-release product,” Brackenrich says. “A blend of these products allows for a single application in the spring that will apply nitrogen throughout the growing season.”
Split applications, on the other hand, can occur before each hay cutting. Granular or liquid urea and ammonium sulfate products require split applications, and Brackenrich recommends targeting the first application around 200 GDD and then splitting subsequent applications after first and second cuttings.
Overall, soil fertility must be in balance to unlock nutrient availability. Brackenrich recommends testing soil and adjusting fertility levels to ensure phosphorus and potassium — as well as other micronutrients — are adequate. And even though calculated nitrogen applications can enhance grass yield and protein content, he suggests harvest timing and grazing management will be more important factors for capturing quality forage.
