Why apply manure on alfalfa and other perennial forage crops? There are several benefits, but also some concerns or challenges to be considered.
Alfalfa and other forages have a large nutrient need – potassium, phosphorus, sulfur,micronutrients, and for grass forages, nitrogen. Manure is a good source of these nutrients and can produce yield increases if nutrients are deficient. Application of manure to forage crops increases the acreage base, which may be important to meet nutrient management plan requirements and avoid over application of P. And applying manure after harvest during the growing season opens up windows of time for manure application not available with most annual crops. While alfalfa and other legumes don’t benefit from nitrogen in manure, applied N reduces the amount of symbiotic N fixation, helping to buffer N availability and reducing the risk of nitrate leaching due to N application from manure. And the deep rooting pattern of alfalfa can capture nitrate that leached beneath the root zone other crops from excessive manure or fertilizer N application. (See Russelle and Jokela, 2013, for more detail.)
There are also some challenges or limitations associated with manure application on forages – smothering and leaf coating, soil compaction and crown damage from wheel traffic, pathogens and feed contamination, surface runoff of nutrients, and odor and ammonia emission. Most of these concerns are associated with broadcast application after harvest and will be discussed in a later section.
There are three general manure application strategies or times of application: preplant (before forage seeding), following last harvest at termination of the stand, and after harvest during the season.