Livestock manure has the potential to provide significant benefits for soil health and crop nutrient supply; but it also can contribute to a range of environmental problems, including ammonia emission. In particular, maximizing crop utilization of manure N requires careful management to control N losses.
Manure N can be lost by several different processes—nitrate leaching, gaseous denitrification, and surface runoff of N. But the process that commonly has the potential for the greatest N loss from manure – and the one most readily controlled by management – is ammonia volatilization (Fig. 1). Besides the obvious economic loss requiring replacement with purchased fertilizer N, there are potential environmental concerns as well. Ammonia emission can contribute to eutrophication of surface waters (esp. marine and estuarine) via atmospheric deposition. The decreased amount of available N in manure reduces the N:P ratio and leads to a more rapid build-up of P in the soil for a given amount available N. And ammonia in the atmosphere can form fine particulates that lower air quality.