Forage Fertilization

Alfalfa requires continuous fertilizer management for maximum economic production. Potassium fertilization is a major component of effective alfalfa management. A section is provided in Table 3 for topdressing.

Fertilizers for establishment are usually higher in phosphorus and lower in potassium than for topdressing. This reduces the likelihood of fertilizer injury to the seedlings and provides higher phosphorus for establishment.

Nitrogen is not required for the establishment of legumes, but it is needed for the establishment of grasses. Nitrogen fertilizer favors the establishment and growth of the grass at the expense of the legume in a legume-grass mixture. Therefore, nitrogen is not recommended for the establishment of either a legume or a legume-grass mixture.

Nitrogen is recommended when the legume content of a legume-grass stand is less than 50 percent. When the legume content is between 25 and 50 percent, 20 to 40 pounds per acre of nitrogen is recommended as a topdressing in early spring. The response to nitrogen may not be economical, however, especially considering the loss of legume from the stand. The nitrogen rate suggested for topdressing a legume-grass stand containing 25 percent or less legume is 30 to 50 pounds per acre. It is not economical to topdress nitrogen on stands containing 25 percent or more legumes on low-yield potential sites such as droughty, wet, or acidic soils or where the soil fertility is low.

Improved pastures and grasses respond to nitrogen, phosphorus, and potash. The fertilizer, especially most of the nitrogen, should be applied in early spring to get maximum growth of the grass. Unimproved grass pastures do not respond as well as improved pastures with timothy, orchardgrass, and bromegrass because unimproved pastures have a lower yield capacity.

Alfalfa requires a soil pH of 6.5 to 7.0, and birdsfoot trefoil stands do well at pH 6.2 to 7.0, but birdsfoot trefoil stands should be limed to pH 6.5 at establishment. Improved grass pastures should be maintained at or above pH 6.0. Unimproved pastures with a low soil pH should be limed to pH 6.0 before receiving fertilizers. See "Lime Guidelines" for lime rates.

If soil test results are not available and previous crops have been properly fertilized, use the fertilizer rates for medium soil test results. If previous crops have not been properly fertilized, use the fertilizer rates given for the low soil test results.