There are situations where applying a heavy dose of manure before planting alfalfa may not be a good idea. When applying a heavy dose of manure, site selection is critical. These heavy doses contain a lot of nitrogen and phosphate along with many other nutrients. That’s fine, even good, for the alfalfa but it can create an environmental risk.
One of the risks is nitrogen leaching into the ground water or being transferred to creeks or rivers via drainage tile. Another risk is soil erosion carrying phosphorus and pathogens.
Alfalfa seedlings initially grow slowly. It often takes a couple months or more before a new stand of alfalfa is capable of stabilizing soil so it won’t blow or runoff during storms. And if erosion does occur, the phosphorus, nitrogen, and other nutrients in the manure will move along with the soil, often ending up in rivers, lakes, or ditches where they might do significant damage.
Take steps to minimize leaching and erosion risk. Incorporate slurry manures while maintaining as much crop residue as possible to reduce erosion from soil surfaces. Plant a fast growing companion crop like oats along with the alfalfa to stabilize the site more quickly. Avoid applying manure to frozen ground or very long before planting alfalfa. Best of all, only apply heavy doses of manure to sites with minimal leaching and erosion risk, such as flat, heavy soils.
If these steps can’t be followed, avoid heavy doses. Test the nutrient concentration of the manure and then limit the amount of manure applied to an amount that will supply just a couple hundred pounds of phosphorus per acre.
Your good stewardship will pay off in the long run.