At this time of year, established alfalfa fields that have just been cut may be the only option you have for emptying a full manure storage structure. Ideally, manure should not be applied to alfalfa because it is a legume and it can get all the nitrogen it needs through fixation. Due to this fact, the DEP Manure Management Manual does not give you any acceptable rates for manure application to alfalfa. This is important to note because as of October 2011, every farm that is land applying manure and is not classified as a Concentrated Animal Operation (CAO) or Confined Animal Feeding Operation (CAFO) must follow the guidelines in the Manure Management Manual.
If you absolutely have to apply manure to an established alfalfa field, you should (at a bare minimum) complete a Nutrient Balance Sheet (available on Pennsylvania’s Nutrient Management Website at panutrientmgmt.cas.psu.edu/) to determine your acceptable application rate in order to stay in compliance with DEP manure management regulations.
Manure applications to alfalfa do have the potential to cause damage. So, if you have no other choice but to apply manure to harvested alfalfa, there are some important guidelines you should follow. Here are some of the guidelines according to Cornell University’s Agronomy Fact Sheet 16:
- Do not apply manure at a rate that exceeds 75-85% of the nitrogen during harvest. According to the Penn State Agronomy Guide, alfalfa removes 50 pounds of nitrogen per ton.
- Apply the manure as soon as you can after harvest (before new leaves emerge) to minimize the potential for burn and salt injury due to ammonium and salts in the manure.
- Regardless of nutrient removal, do not apply more than 4,000 gallons/acre of liquid manure. The Alfalfa Management Guide (www.agronomy.org/files/publications/alfalfa-management-guide.pdf) tells you not to apply more than 3,000 gallons/acre of liquid manure.
- Although not recommended, semi-solid manure should be applied at a rate of no more than 10 tons/acre. The Alfalfa Management Guide tells you to adjust your spreader to make sure that it is breaking up the large chunks of manure during application so that it does not smother the new growth.
Source:extension.psu.edu