Too much of a good thing can be too much of a good thing, especially when it comes to spreading manure on alfalfa. And newly harvested alfalfa fields are prime sites for summer-time manure spreading. In fact, they may be the only fields accessible at this time of year, says Quirine Ketterings, Cornell University agronomist.
Ketterings and a team of forage, dairy and animal science colleagues at Cornell have put together a Web site list of do's and don'ts for spreading on established fields. You'll find the full list at www.nnyagdev.org, under "Project Fact Sheets". But here are some key points:
Established alfalfa-grass stands of more than 60% respond to extra N because of the grass in the stand. They're better alternatives for manure application than newly established clear seedings of alfalfa.
Adding N (via manure) suppresses, but doesn't eliminate, N fixation. Manure application rates should not exceed 75 to 85% of N removed in harvest to minimize annual manure N losses.
Surface applications leads to N losses through volatilization. Deep cracks in the soil, root channels and earthworm burrows can speed flow of manure to tile drains; so tile outflow should be watched.
Delaying manure application after harvest increases burn risk and salt injury as new leaves are most sensitive to manure ammonium and salts. To reduce risk of burn, smothering and/or salt injury, liquid manure application rates shouldn't exceed 4,000 gallons per acre per application.
Soil test phosphorus levels should be monitored over time as manure application rates in excess of 4,000 gallons per acre per year will likely result in a P application exceeding P crop removal.
Check manured fields for forage potash content if the forage is being fed to non-lactating cows. It's recommended to only feed forage with less than 2.5% K (dry matter basis) to non-lactating cows.
Application of manure from animals infected with pathogens, particularly Johne's disease, can potentially spread these infections. In the case of Johne's disease, animals less than one year old should not have access to contaminated pastures or to feed from such fields.