Understanding the nitrogen benefits of manure in farming

By Scout Nelson

“Manure is the gift that keeps on giving,” especially when it comes to nitrogen. Manure provides nitrogen in two forms: organic and inorganic. Inorganic nitrogen, primarily ammonium, is immediately available to plants once applied, while organic nitrogen is slow-release, requiring soil microbes to convert it into a plant-available form.

The nitrogen content in manure varies based on animal species and storage methods. For instance, hog manure and poultry litter typically have higher inorganic nitrogen than cattle manure due to differences in digestion and feed. Liquid hog manure has about 75-80% inorganic nitrogen, making most of it plant-available in the first year.

Storage and handling also influence nitrogen availability. Liquid manures generally have higher inorganic nitrogen than solid manures, which often contain bedding materials. Liquid dairy and beef manures have just over 50% inorganic nitrogen, while solid versions contain only about 10-15%, releasing nutrients more slowly.

The method of manure application plays a crucial role in nitrogen retention. If manure is left on the surface, nitrogen can volatilize as ammonia gas, especially in warm or windy conditions. Incorporating or injecting manure into the soil reduces these losses, maintaining more nitrogen for crops.

Weather significantly impacts nitrogen availability, as soil microbes, which aid in nitrogen release, require optimal conditions to work effectively. Wet, dry, hot, or cold conditions can slow down or speed up the process, affecting crop nutrient uptake.

Research also examines how cropping systems influence manure nitrogen availability. For example, applying manure to a living cover crop may reduce volatilization due to the crop canopy. Additionally, manure appears to behave differently in continuous corn versus corn-soybean rotations, with ongoing studies exploring the reasons behind this variability.