Swine anaerobic lagoon nutrient concentration variation with season, lagoon level, and rainfall.

Twenty swine anaerobic lagoons (8 finish, 6 nursery, and 6 sow) were monitored for lagoon liquid nutrient concentrations and liquid level above or below the stop-pump level. Weekly rainfall was also recorded. Significant differences in total nitrogen (N) concentrations existed between lagoons and also between types of farms. The N concentration varied within the same lagoon by a factor of two or more during the 4-yr study period and typically displayed a seasonal trend of decreasing during the summer and increasing during the winter. Years of operation (8 to 29 yr) were not a significant factor for mean N concentration over the 4-yr period. The lagoon liquid level was not a significant factor for N or total phosphorus (P) concentration. The finish farms displayed a decreasing trend of average annual nitrogen concentration with increase in annual rainfall.