Using Manure on Alfalfa

Warren C. Thompson
National Forage Specialist: America’s Alfalfa

For most farmers, especially dairy farmers, animal manure can be a blessing or a tragedy in the making. Manure, as a source of both fertility (nutrients especially nitrogen, phosphorus and potassium) and organic matter is a fantastic resource. Some of the methods of using manure to its best advantage is the area that I will deal with in this abbreviated form. So let me assure you that I will not cover all of the bases. Should you want more information, contact your county agent or your soils or forage specialist at your university.

How and where are the best places to use manure in alfalfa production?

1. In the crop rotation, especially with grain crops mainly corn is by far the best place to use manure for the best returns. If the manure is stored so that there is little weather related nutrient losses, you can expect a 1300-1400 pound cow to produce about 200 pounds of actual nitrogen of which about 40% will be available nitrogen. Phosphorus production is about 48 pounds per cow of which 60% or 30 pounds are available. Potassium production in manure is in the ballpark of 180 pounds per cow total of which 70% is available to crops. Another way to look at it is that the amount of nutrients in 10 tons of solid waste or 3000 gallons of liquid manure. Of course, these vary somewhat, but this is a listing of numbers that seem to be average. Ten tons of manure from the dairy herd contains about 40 pounds of commercial nitrogen equivalent, 12 pounds of phosphate, and 56 pounds of potash. Check with you fertilizer dealer to see the price he charges for chemical sources of these nutrients and you can put a price tag on your manure piles. No question about it, manure is one heck of a source of nutrients that when accumulated and used wisely, can greatly reduce any commercial fertilizer bill plus the bonus of organic matter for maintaining and building soil structure.

2. Top-dress pasture fields that are basically grass. Especially those grass fields that will eventually go back into the crop rotation system. Even in these fields, applications exceeding 10 tons of solid waste or 3000 gallons of liquid manure are not recommended otherwise expect some plant burn or even plant suffocation.

3. About using manure on alfalfa. Over a decade ago, a very detailed longtime on-farm study was conducted in Pennsylvania to find the ‘pieces to the puzzle’ that were essential in producing consistent high yielding alfalfa. In this study they found that manure usually complicated production and very often reduced the life span and crop yields when it was used as a top dressing. Yet, when manure was applied before seeding, it became a very essential element in elevating yields and persistence.

4. When there is no recourse but to spread some of the manure back in alfalfa fields I always advise that you top dress fields that are likely to be going out of production soon and back into grain rotation. Fields that thinning and are over-run with grass or weeds is a good place to start. If you have no other place to use the manure and you find that you have to apply it on splendid fields, first be aware of the environmental rules and follow them to the ‘letter’. Then if you have done this, apply the manure immediately after harvest when possible. Application in a two to five day window is essential and always when the soil is firm to help reduce stand and yield losses. When spreading solid waste, be sure to adjust the beaters to break large manure chunks that are sure to smother plants and result in a poor distribution plan.

Don’t let this happen to you!

5. As stated before, spread manure when the soil is firm. Otherwise, you can expect some long lasting soil and plant damage. Americas Alfalfa has already released a patented manure tolerant variety (AmeriStand 403T) that will stand up under more punishment than any other varieties yet tested. But don’t expect these features to overcome severe conditions and become your ‘license’ to abuse soil and plants under terribly wet soggy, rut making conditions.

Yes, manure is a fantastic ‘home grown’ fertilizer and organic matter resource. But when it comes to using it in the alfalfa production system, apply it where it will become a great asset, not a problem, in your farming program.