RESEARCHERS: Nick Clark, UC ANR, and Dr. Deanne Meyer, UC Davis, UC ANR, 2020


• Manure samples from 20 Central Valley dairies using various methods of manure handling and treatment technologies were analyzed for mineral content, total solids, volatile solids, and particle size.

• Results showed seasonal differences and production management differences in total solids and mineral concentration of manure streams. 

• Differences are indicative of manure type and can be used to inform next-generation manure management options.


California dairies currently use several methods of manure handling and treatment technologies that can impact manure characteristics. The goal of this project was to explore the chemical and physical properties of manure across these different methods. Results will help support dairy operators and forage farmers using manure as fertilizer or value-added feedstock in upcycled manure products. 

Study researchers sampled manure across all four seasons in the year from various manure management practices/systems used in California. This included six anaerobic digesters, four vacuum systems, two compost-bedded pack barns, and six other types of manure handling systems (one aerobic algae treatment, two chemical flocculation treatments, one scrape-screw press treatment, one inclined screen separator, and one drained lagoon sludge excavation). Several of these practices are likely to become more commonplace as environmental and economic pressures and incentives drive dairy operators towards carbon, nitrogen, and salt management efficiency innovations. 

The researchers characterized the physical and chemical composition of the dairy manure samples, including mineral content, total solids, volatile solids, and particle size. Among the digester effluent samples, differences in solids and nutrient concentrations were observed between seasons, with higher concentrations in winter months. In the vacuumed samples, higher concentrations of minerals and solids were also noted from samples collected during winter months compared with summer months. There was some variability in physical and chemical properties of compost bedded pack barn manure between seasons, but it was not as clear as the differences between the two facilities sampled. To better capture the sources and magnitude of variability, the researchers recommend more frequent collection and more detailed analysis of specific handling and treatment methods.

The variability discovered by this research project will help inform industry stake-holders as to the potential seasonal and facility-level differences of various California dairy manure streams.