Applied and Environmental Chemistry of Animal Manure: A Review

Animal manure consists of predominantly urine and feces, but also may contain bedding materials, dropped feed, scurf, and other farming wastes. Manure is typically applied to soils as fertilizer for agricultural production. The estimated amount of manure produced in 12 major livestock-producing countries is 9 × 109 Mg of manure annually. Manure is rich in plant nutrients. However, manure is also considered as an environmental pollutant when it is over-applied to cropland or following runoff into surface water. Manure can also influence global climate change via emissions of methane (CH4) and nitrous oxide (N2O). Thus, increased and updated knowledge of applied and environmental chemistry of animal manure is needed to shed light on the research and development of animal manure utilization and minimization of its adverse environmental concerns. The advances in basic and applied studies of manure major components, organic matter, phosphorus, and nitrogen, primarily related to US livestock production are summarized in this review. Detailed focus was placed on three notable challenges for future manure research: 1) soil application of animal manure, 2) manure phytate phosphorus, and 3) manure nitrogen availability. This review may contribute to the global effort in sustainable and environmentally sound agriculture by stimulating new ideas and directions in animal manure research, and promoting application of knowledge and insight derived from manure research into improved manure management strategies.