Assessment of Ammonia Volatility From Fall Surface- Applied Liquid Dairy Manure.

Ammonia emissions from dairy and livestock operations are of environmental and human health concern in the United States. Conservation of ammonia from fall surface-applied manure benefits farmers by retaining nitrogen for use by crops in the spring growing season. We hypothesized that application of manure in cooler fall temperatures will slow the rate of ammonia volatilization.  This objective was achieved by studying the effect of temperature on ammonia volatility from liquid dairy manure applied to a field in Massachusetts once every month from September-December, 2008.  Manure was surface-applied to a field cover cropped with winter rye (Secale cereale L.) on September 15^th.  Emissions were measured using a chamber method.  In September, a total 5131 mg NH₃/m² (46 lb/ac) was lost over 146 hours and the average chamber temperature was 34°C while in December, a total 1028 mg NH₃/m² (9 lb/ac) was lost over 147 hours and the average chamber temperature was 7°C.  Colder temperatures significantly reduced rates of ammonia volatility and resulted in greater amounts of nitrate found in spring soil. Total nitrogen accumulation in the cover crop fluctuated and was not significantly different from month to month.  The greatest nitrogen retention and lowest rates of ammonia volatility came from manure applied to frozen ground in December.  Surface application of liquid dairy manure should be conducted as late as possible in the fall before snow fall for the least amount of nitrogen lost to ammonia volatilization.  Planting a cover crop at the time of fall harvest in conjunction with a late fall (November or December) manure application is a nutrient management strategy which deserves further investigation.