Manure Application Method Effect on Alfalfa Yield, and Nitrous Oxide and Ammonia Emissions.

The use of manure on alfalfa (Medicago Sativa L.) has increased on dairy farms in recent years; it provides essential nutrients that can increase yields on nutrient-deficient soils, and it is one of the few crops grown that is harvested multiple times a year, providing in-season options for manure spreading. The dominant method of application is surface broadcast, which may contaminate forage and, especially at excessive rates, cause leaf burn and smothering. It also has the potential for large losses of ammonia (NH₃), as well as the transport of phosphorus (P) to surface waters in runoff. Band-application of liquid manure, with or without injection or aeration, may minimize these problems. We compared a no-manure control, and broadcast, banded, aerator banded, and shallow injection application methods, and found little or no yield effects of manure application or application method. Ammonia loss was reduced 95% by injection, 52% by aerator banding, and 30% by banding compared to surface broadcast. However, N₂O emissions were greatest in aerator band and injection treatments, almost 6 kg ha^-1 y^-1 and 4.5 kg ha^-1 y^-1, respectively, compared to 3.2 kg ha^-1 y^-1 for banding and 3.6 kg ha^-1 y^-1 for broadcast. Our results showed that these alternative application methods can substantially reduce NH₃ emission, while maintaining alfalfa yields, in these somewhat poorly drained soils in the upper Midwest. However, there are environmental tradeoffs because the methods most effective at reducing NH₃ loss also tended to be have the greatest N₂O emission.