California Air Resources Board

Principal Investigator/Authors: Ermias Kebreab,

Contractor: University of California, Davis

Contract Number: 19RD028

Project Status: Completed

Relevant CARB Programs: AB 32 Climate Change Scoping Plan, California Greenhouse Gas Emissions Inventory Program, Dairy and Livestock Greenhouse Gas Emissions Working Group

Topic Areas: Climate Change, Greenhouse Gas Inventory, Short-Lived Climate Pollutant Inventory, State Implementation Plans (SIPs), Agriculture, Modeling

Research Summary:

The overall objective of this project is to develop, demonstrate, and transfer to the California Air Resources Board (CARB) a comprehensive process-based model, the California dairy emissions model (CADEM), which can be applied to refine estimations of emissions of greenhouse gases (GHG) and nitrogen (N) gases from California dairy farms. Models for enteric fermentation from lactating dairy cattle and heifers were challenged with California-based data, and the best performing models were selected. Additionally, manure-related outputs such as fecal and urine amount and composition, and water excretion models were developed. Multivariate models of GHG emissions, manure excretion, and water intake (Waterin), along with milk production, were developed for lactating cows, nonlactating cows, and heifers. Most equations predicted the response variables with reasonable accuracy, except Waterin, total urine (Ut), and urine carbon (Uc). No obvious differences were found between multivariate and univariate models because the correlation of random effects between traits was not strong; therefore, the univariate models were selected for CADEM. The emission and excretion models were then integrated with a modified Manure-DNDC. CADEM also simulated the impacts of feed additives on methane (CH4) emissions from dairy cows. The modifications to Manure-DNDC included incorporation of processes to simulate transfers and interactions of water, carbon (C), N, and phosphorus (P) among multiple slurry storage areas and between slurry storage areas and other components (i.e., housing, digesters, crop fields) within a dairy farm, distinguishing solid and liquid manure during manure transfer. New model interfaces have been developed to improve the usability of CADEM. In addition, the project team has trained CARB staff to gain proficiency in CADEM and provided materials and guides on applying CADEM.

Keywords: dairy, methane, greenhouse gases, GHG, emission sources, CADEM, modeling