There are both benefits and liabilities for manure applications to alfalfa. Manure can be an excellent source of phosphorus and potassium for alfalfa. Alfalfa requires high phosphorus and potassium soil fertility and has a high demand for these nutrients. Alfalfa stands have high infiltration capacity and low potential for erosion so manure applications to these fields have a low potential for nutrient losses in runoff.
Manure applications on alfalfa also create some challenges. Poorly timed applications can damage alfalfa stands. If the stand has a significant grass component, the N in the manure can stimulate the grass and further crowd out the alfalfa thus shortening the productive life of the stand. Alfalfa is a legume so it has no nitrogen fertilizer need because it fixes nitrogen from the air. This means nitrogen in the manure has no real value when it is applied to alfalfa.
Ultimately the correct answer to this question requires you to weigh the positives and liabilities to determine if manure applications on alfalfa are a good idea for your alfalfa field at its current age and condition. If manure is to be applied to alfalfa, preference should be given to older stands that will soon be rotated to another crop. This practice will be less likely to affect the life of the stand and may increase overall productivity in the final year of the stand if the alfalfa is thin and grass has filled in.
Visit the E-Extension web page Manure Applications on Alfalfa for more detailed information on this topic.
John A. Lory
Associate Professor of Extension
University of Missouri
