Dairy manure can supply the potassium (K) needed by a 5 ton/acre alfalfa crop, says Douglas Beetle, Penn State University soil fertility specialist.

Due to high fertilizer prices, many farmers haven’t been applying recommended rates of K fertilizer, and deficiencies have become common, says Beetle. Alfalfa removes 50 lbs of K2O per ton of dry hay equivalent, or about 250 lbs for a 5-ton yield, and silage corn removes a similar amount. That need can be met with 10,000 gallons of typical liquid dairy manure or 30 tons of solid manure.

Manure is also a good source of nitrogen (N) and phosphorus (P). But in an alfalfa-corn rotation, cornfields are still the best place to spread manure because alfalfa can’t use the N.

“The first priority economically is to apply the manure to the cornfields to get the value from all of the nutrients,” he says. “Then, if there is more left over, this can then be applied to the alfalfa fields to supply P and K.”

If you have the choice of which alfalfa fields to spread manure on, go to older fields and use fertilizer on newer seedings. Beetle lists several words of caution about spreading manure on alfalfa:

  • Do not spread a large amount at one time to avoid smothering the alfalfa.
  • During the growing season, spread as soon after harvest as possible to avoid burning the new growth or injuring the new growth by manure spreader traffic.
  • Avoid spreading when the soil is wet to avoid compaction.
  • Realize that spreading manure on alfalfa has the potential to introduce or encourage weed growth. So good weed control is essential.

The best nutrient utilization comes from applying the manure as close to the time of crop uptake as possible; therefore winter is not a good time. But if you must spread manure in winter, alfalfa fields may be the best place because the crop begins growing and taking up nutrients in early spring. Otherwise, choose fields with cover crops or at least good residue.
Here are some of Beetle’s guidelines for winter manure application:

  • Stay as far away from water as is practical.
  • Select the most level fields available and especially avoid significant slopes.
  • Avoid areas in fields were concentrated water-flow is likely.
  • Avoid poorly drained fields.
  • Don’t spread on snow unless it’s unavoidable.
  • Try to avoid spreading when rain or melting conditions are expected.
  • Stay away from roads and don’t spread in road ditches.
  • Keep application rates as low as practical – less than 5,000 gallons/acre of liquid manure, 20 tons/acre of solid manure or 5 tons/acre of poultry manure.