On-farm Comparison of Manure Application Methods in Terms of Ammonia and Odor Emissions and Costs

Ammonia and odor emissions from land application of dairy manure, and costs associated with manure land application methods are serious concerns for dairy owners, regulators, and the general public. Odor and ammonia samples from agricultural fields receiving liquid dairy manure applied by surface broadcast and subsurface injection were collected and analyzed. Costs associated with both of the manure application methods were estimated. The test results showed a 68% reduction in ammonia emissions with subsurface injection vs. surface broadcast over a two-day period across two fields. Olfactometry results showed subsurface injection reduced odor emission by 33% compared with surface broadcast; therefore, applying liquid dairy manure by subsurface injection could be recommended as one of the best management practices to control ammonia and odor emissions. The estimated costs associated with surface broadcast were lower than subsurface injection. Further studies evaluating both the manure application costs and agronomic benefits of retained manure N fertilizer in soil are warranted to conclude which manure application method is more economically viable. INTRODUCTION Dairy production stands as the single largest agricultural pursuit in the state of Idaho. Currently, Idaho has roughly 550 dairy operations with 580,000 milk cows. Over 70% of milk cows are located in the Magic Valley in southern Idaho. A number of dairies in the Magic Valley use flushing systems resulting in huge amount of lagoon water which is applied to crop lands near the lagoons via irrigation systems. The volatilization of ammonia (NH3) from the irrigated lands is not only a loss of valuable nitrogen (N), but also causes air quality concerns (Hristov et al., 2011). The land spreading of animal manure accounts for approximately one-third of the total NH3 emissions from agriculture (Misselbrook et al., 2000) so there has been much interest in the adaptation of dairy manure land application techniques as industry best management practices (BMP) to abate NH3 emissions. Another impact of land application of dairy manure is odor. Manure spreading has been identified as producing more annoying odor to nearby residents than does the livestock facility itself (Jacobson et al., 2001). Injection incorporates manure directly beneath the soil surface and thus minimizes odor and NH3 emissions during application. A range of manure injection technologies have been in use for some time, and they typically lead to reductions in NH3 emissions of 40 to over 90% compared to broadcast application (Wulf et al., 2002). However, it is still new to Idaho and there has been no quantification of these reductions under Idaho conditions. The objectives of this research were to 1) evaluate the manure injection method under Idaho conditions in terms of mitigating odor and NH3 emissions, and 2) estimate costs associated with the manure injection method.