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Topdressing hay crops with manure

Published on 20 June 2011

Very wet spring conditions have made it almost impossible to spread manure in April and much of May, and some of what was spread would have been better remaining in storage – that is unless, like many, storage was about to overflow.

Last month some dairy manure was irrigated onto very wet and rolling open fields in the Champlain Valley, followed almost immediately by an inch or more of rain. We don’t like to think about the fate of that manure, even as we consider which is worse: Point or nonpoint pollution.

One result of seemingly endless early spring rains is very full manure storage, and questions are being asked about where and how much manure can be applied to hay fields after first cut. Some suggestions and observations:

• The best candidates for manure topdress are grass fields and older alfalfa-grass stands that have at least 50 percent grass. Manure will really give these fields a boost, and in most cases should eliminate the need for topdressed fertilizer – a real money-saver.

• Don’t spread manure on spring seedings; allow the plants to become well established before rolling over them with manure spreaders. Manure applications during the corn rotation often build soil fertility, so the seeding may not need the added nutrients. Of course, check soil test results to be sure.

• There’s nothing wrong with applying manure to established alfalfa stands. The N in the manure won’t do much to help the alfalfa, but neither will it hurt it.

• Forget anything you may have heard about the N in manure “putting alfalfa’s nitrogen-fixing bacteria to sleep.” In fact, nitrogen will slightly increase alfalfa yield but not enough that we recommend using N fertilizer on established alfalfa (although that’s what they used to do in Hungary back in the 1980s when urea there was dirt cheap).

Rate
This depends on the solids content of the manure, but with typical 5 to 8 percent solids content, 4,000 gallons per acre is fine and 6,000 gallons probably won’t hurt the stand. The tractor and manure spreader tires will do more damage to alfalfa plants than the manure will, with most of this occurring in the following cutting. That’s because the tires squash the crown buds that will become the next crop.

Timing
The sooner after harvest the better. That’s why Miner Institute bought a truck equipped with a tank spreader, so both forage harvest and manure application could be occurring at the same time.

Research there found no difference in second-cut alfalfa-grass yield or quality when manure was applied zero vs. three days post-harvest, but there was a trend to lower yield when manure application was delayed by seven days.

The difference wasn’t huge, though, nor was it statistically significant, so if you’re desperate to get manure applied don’t sweat the small stuff.

Manure pathogens
This may be of concern if the manure is applied long after regrowth has started and the crop is harvested as dry hay.

However, two years of research at Miner Institute on this topic found that a very high percentage of manure pathogens were killed when alfalfa-grass was manured several days after first cut, then second-cut harvested and preserved as silage.

Two Japanese studies found that M. paratuberculosis, the super-tough bacterium causing Johne’s disease, was killed by proper ensiling of alfalfa.  FG

—Excerpts from Miner Insitute Farm Report, June 2011

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