A mass balance model based on total ammoniacal nitrogen for estimating ammonia volatilization from beef cattle manure management in Alberta Canada

Abstract

<abstract> <bold>Abstract.</bold> Animal feeding operations have been identified as the primary contributor of anthropogenic ammonia (NH₃) emissions in North America. Quantifying NH₃ volatilization from each stage of livestock manure management is important for developing corresponding technologies and methods to reduce emissions and nutrient losses. A regionally specific mass balance model based on total ammoniacal nitrogen (TAN) was developed for estimating NH₃ emissions from beef manure management operations in western Canada. Different beef cattle sub-categories were differentiated, and for each sub-category the animal diet and nutrient utilizing activities (e.g., N metabolism) were combined to estimate N excretion and the separation into urinary N and feces N. Diverse reactions and processes in manure, such as mineralization of organic compounds, immobilization of TAN, nitrification and denitrification of N compounds, were incorporated in the model to analyze the transformation of TAN. Ammonia emission factors were specified for different manure management approaches, and designed to react dynamically to the variation of environmental factors (e.g., temperature). To demonstrate the applicability of the developed model, we calculated the NH₃ emissions from beef cattle (including cows, calves (<1 year), bulls, steers, heifers for slaughter and replacement) housing, grazing, manure storage and land application in Alberta, the dominant beef farming province in Canada. Estimated NH₃ emissions were about 1.11×10⁵ Mg in Alberta in 2006, with the mean of 18.5 kg·animal^-1·yr^-1. In anima subcategories, steers and heifers (slaughter) were the two biggest contributors, which contributing 31.5 and 32.7% of total emissions, respectively. For stages of manure managements, the housing contributed 54.6% of total NH₃ emissions, 99.6% of which occurred from feedlots. Initial model development efforts targeted beef cattle operations in Canada, and will be extended in future to encompass also other major livestock operations, such as dairy, swine, and poultry. This TAN mass balance model will be incorporated into the HOLOS model - a farm-level greenhouse gas calculator, which is used to estimate pollutant emission budgets and to conduct life cycle assessments for individual farms.