Relationship of total nitrogen and total phosphorus concentration to solids content in animal waste slurrries

Quantifying the nutrient content of liquid swine and dairy manure immediately preceding field application has the potential to reduce environmental impact from over-applying nutrients and better match slurry application rates with the fertility needs of subsequent crops or crop removal rates. This study determined if manure solid content, storage facility, animal growth stage, and season could be used as predictors of the nutrient content of animal manures. Samples were collected from earthen storage basins and deep pits, on one farm, during liquid manure loading into a manure application wagon in 1999, 2000, and 2001. The correlation of nitrogen and phosphorus content with solids content gave good linear fits (R² = 0.65 to 0.86) for the earthen storage basins. Data for an earthen storage basin exhibited consistent decrease in solids content by sequential load for a given day. Regression of nitrogen content versus solids content data for manure from deep-pit swine finishing facilities provided an undesirable fit (R² = 0.19). Regression results support the conclusion that animal growth stage/storage facility affects the base TN concentration (Y-intercept) in the absence of solids. The gestation and finishing TN data suggests TN for an individual manure wagonload could be predicted if the base TN concentration, in the absence of solids, was determined. Total P was found to be highly correlated to TS, but was also affected by animal growth stage/storage facility. Deep pits showed consistent nutrient content across pumping seasons and growth stage with the exception that nitrogen content decreased slightly during fall application.