Manure use and Alfalfa

As the dairy industry continues to try to find ways to cut costs many are scrutinizing field amendments to attempt to decrease input costs. Obviously we cannot limit nutrients to crops but sometimes simply changing where those nutrients come from may be of economic benefit. A perfect example of this is the use of manures for potassium in alfalfa.

On dairy farms we often have an excess of manure and our manures are typically pretty high in potassium. We also often have lots of acres of alfalfa that need potassium fertilizer. On alfalfa fields we typically use commercial fertilizers to add only the nutrients needed to the sward. One of the main issues with manure on any of our crops is the fact that it is a complete package fertilizer so we get even the nutrients we don't need, in this case nitrogen. If all of the manure could be used on corn, it would be better to save the manure for the corn ground where you will get more of the full value of the nutrients, especially N. In this case you need to push the pencil to see if it is more economical to buy N for the corn or K for the alfalfa.

Excess nitrogen can lead to increased competition in alfalfa stands of grasses as well as other weeds. Because of this the typical recommendation is to not use alfalfa on newly established stands. Older stands will likely be rotated in a few years and may also have a competitive advantage to the young stands when it comes to keeping weeds at bay.

Another important note on using manures in alfalfa is to stay away from manures that may clump or get picked up with future harvests such as dairy pack manure. Dry poultry manure may be used on alfalfa stands but typically our liquid manures are the best option.

Manure application to alfalfa should occur immediately after a cutting is taken. Make sure you have a current soil test as well as manure test and apply to potassium levels to get a lower rate of application. This lower rate will allow less traffic across the field and can limit the negative impact on the alfalfa stand that may be seen from the heavy loads.

So yes, application of manures to alfalfa can be an economic way to get a cheap source of potassium; however some negatives may be realized. Remember the best practices are

• Apply to oldest stands or declining stands
• Use only liquid manures or poultry litter
• Apply directly after cutting
• Minimize traffic on fields