Gaseous emissions and nutrient fate modeling in dairy operations
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Rise of the Earth's average air temperatures observed since the mid 20th century has been attributed to increase concentrations of green house gases (GHG) -- carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) -- in the atmosphere. Although not considered a GHG, ammonia (NH3) contributes to fine particular matter (PM) when combines with acid pollutant present in the atmosphere. Agriculture can be a sink of carbon (farmland) but it is also an important source of emissions. Agricultural soils are the main source of N2O while animals and manure storage are a great source on CH4 and CO2. Intensive dairy operations produce big volumes of manure loaded with nutrients such as (C), nitrogen (N) and phosphorus (P) that require careful management to minimize not only gaseous emissions but also leakage. Identifying the contribution of each source throughout the entire dairy operation as well as characterizing the manure nutrient content at different stages during management and treatment is the first step to implement mitigation strategies. Direct measurements can be expensive, time consuming and impractical while emission factors (EF) do not account for the effect of specific managements and local weather conditions. A model was developed to estimate GHG and NH3 emissions and to track nutrients (C, N, P) in a dairy operation. The model includes the following components: animals, barn, lagoon, and anaerobic digester. Solid separation (SS) and nutrient recovery system (NR) were included due to the huge effect this processes have on manure characteristics and nutrient content. Model simulations of lagoon NH3 emissions as well as NH3 and CH4 emissions from the barn were compared to data found in the literature and direct measurements from dairy lagoons in Pullman, WA and Moscow, ID with good results. CO2 emissions from lagoon were compared to flux measurements taken with an infrared gas analyzer (IRGA) located in the dairy in Pullman, WA. The model was used to simulate a dairy farm to study the effect of manure management (SS, NR and AD) on total GHG emissions and nutrient fate. Lowest emissions were obtained for complete (anaerobic digestion, solid separation, nutrient recovery and lagoon) manure treatment.