Mixing manure and alfalfa

Follow application guidelines to get the most benefit and avoid problems.

One of Russell Robaidek's customers always wants him to apply manure when the alfalfa is 6 or 7 in. tall. He has just one rule: “Don't keep driving in the same places.”

This older Wisconsin farmer always makes good yields, Robaidek says. But his timing flies in the face of conventional wisdom. Most experts, including Robaidek, a custom manure hauler and applicator, say to apply manure to alfalfa as soon as possible after cutting.

In the northern half of the country, the practice of applying manure slurry to alfalfa is still limited primarily to the few farmers who are partial to it, and to those who just need someplace to apply — anyplace.

On the other hand, Southern farmers sometimes view alfalfa fields as a great place to put effluent from their lagoons. Alfalfa takes up a lot of phosphorus while tending to use the manure-applied nitrogen instead of fixing its own.

Nonetheless, a combination of research and practice seems to be expanding the limits some people have placed on the manure-alfalfa interaction.

Robaidek, for example, uses a form of injection on established alfalfa fields. He applies manure slurry through a manifold of hoses onto the ground directly in front of the blades of an AerWay aerator. The aerator punches holes in the ground, making way for infiltration.

Although Robaidek owns and uses semi-trailer trucks and field-application tankers, he and most of his customers prefer his dragline hose system. The only equipment needed is a tractor and either a coulter-knife injector or an aerator.

A pump at the farmer's pit can push the slurry up to 3 miles through the hose to a field. The tractor simply attaches to the hose and drags it along behind.

Some companies actually suggest alfalfa growers use a true injection machine on their established fields. Because of the potential for crown damage to the plants, many agronomists shudder when they hear this. Still, it's being done.

The amount of manure farmers apply to established stands seems to be rising as well. Some of the literature still calls 3,000 gals./acre a high rate. Researchers in Minnesota and Massachusetts recently used 5,000 gals./acre quite safely. One was swine, the other dairy.

Three application times

There are three main times to apply manure to alfalfa fields, says Mike Rankin, crops and soils agent for Fond du Lac County, WI:

• Fall of the final year. This might work, but isn't the best practice, Rankin says. The combination of nitrogen fixed by the alfalfa and added in the manure might increase the chance for leaching and nitrogen escape.

  Rankin suggests 40 units, or about 4,000 gals./acre, of liquid manure as a maximum for this practice.

• Fall or spring before establishment. Manure application ahead of an alfalfa crop comes highly recommended. In fact, several research projects have shown high rates of manure ahead of a new alfalfa seeding can boost early years of production significantly.

Rankin says a 12,000-14,000 gal./acre preplant application has been proven to outproduce stands using annual applications of commercial fertilizer. It also helps eliminate the need for topdressing.

However, heavy manure applications are an environmental concern, warns Mike Schmitt, Minnesota extension soil scientist. As manure's nitrogen converts to nitrate and becomes available to plants, it also becomes susceptible to denitrification on fine-textured soils and to leaching on medium- and coarse-textured soils. Avoid fall applications on coarser-textured soils where leaching can be a threat, Schmitt advises.

Spring-applied manure provides less time for nitrogen loss, but the rapid breakdown surge in spring is more likely to temporarily tie up some of the otherwise-available nitrogen, creating short-term imbalances.

Some farmers apply manure in winter, where legal, but Schmitt doesn't encourage it in cold environments. Incorporation is not possible, so most of the inorganic nitrogen will be lost. With manure lying on the soil surface, it's more likely to run off into waterways.

If manure must be spread in winter, select level sites and apply conservative rates.

• Between cuttings. This seems to be getting more popular, especially in situations where incorporation isn't required. It's often seen as a rescue for having too much manure and not enough corn ground. Regardless of the motivation, here are some guidelines:

1. Be quick. Put manure on established stands as soon as possible after cutting to reduce the risk of nitrogen burn and salt damage.

2. Choose fields with the most grass, usually the oldest stands, since they'll benefit most from nitrogen in manure.

3. Remember that high levels of manure are more likely to cause salt burn and damage or suffocate plants. If high levels of fertility are needed, consider commercial fertilizer as a supplement to manure.

4. If you're applying dry manure, adjust the spreader to break up large chunks that might smother regrowth.

5. Spread manure when soils are firm to limit soil compaction and avoid crown damage.

6. Spread evenly. Concentrating too much manure in one spot can smother plants, in addition to increasing the concentration of nutrients and salts. Keep equipment moving with liquid systems and spread dry manures evenly and finely.

7. Hot, dry weather makes the plants more susceptible to damage from salt and ammonia in manure. Avoid if possible. Applying in cool weather also may reduce odor problems. This is particularly important for fields with close neighbors.

8. Consider planting a manure-tolerant variety in new stands. USDA research in Minnesota shows one variety, Ameristand 403T, averaged 14% more yield and 18% better stand persistence under midseason manure applications than some other popular varieties.