Nutrient data from US manure systems from 2012 to 2022: Spatial and temporal trends

Most published manure nutrient concentration approximations (book values) used today were derived from manure data prior to 2003 and do not reflect potential differences across US regions. Using ManureDB data, the University of Minnesota database with manure total nitrogen (N), ammonium-N (NH₄-N), phosphorus (P₂O₅), and potassium (K₂O) data spanning from 1998 to 2023 from 15 laboratories across the United States, we analyzed nutrient data from 2012 to 2022. Eight common US poultry and livestock manure types were used in this analysis, which showed that 91% of the slurry/liquid and 66% of the semisolid/solid manure nutrient categories had significant regional differences. Liquid swine and liquid dairy manure in the Southeast (SE) region had significantly lower nutrient data than the Northeast (NE) and US Midwest (MW) regions every year for swine and 10 out of 11 years for dairy. Nutrient concentrations in the solid chicken manures were the most temporally volatile across the decade with 38% of the region-analyte combinations having significant trends. This was followed by liquid dairy (33%), solid dairy (25%), solid turkey (25%), solid beef (8%), liquid swine (8.3%), and liquid beef (no trends). The frequency of significant manure nutrient trends in the NE and SE regions was triple that of the MW region. Decreasing manure nutrient concentrations were four times more prevalent than increasing nutrient concentrations across 2012-2022, perhaps displaying the impact of precision animal nutrition on manure nutrient content. Updated US manure nutrient characteristics provide a revised baseline for farmers, consultants, and researchers, while simultaneously highlighting manure nutrient variability.