Influence of Dissolved Carbon and Nitrogen on Mineralization of Dilute Liquid Dairy Manure

In confinement-style milk cow (Bos taurus) dairies, which are common in California, often >50% of the manure is collected by flushing animal housing areas with water. The resulting dilute (<2% solids) wastewater is stored in anaerobic lagoons and, after removal of coarse solids, is applied to crop fields through the irrigation system. There is little published data on the C and N mineralization characteristics of these dilute dairy lagoon waters, which tend to have a proportionally high dissolved C and N content relative to the solid fraction. As a result, there is the potential for the dissolved fraction to have a large influence on the manure's mineralization behavior. To address these issues, we conducted soil incubations with both lagoon water (LW) and concentrated LW-solids from which >82% of dissolved C and N was removed by centrifugation. For the LW, apparent net N mineralization after 63 d was 17% (range 5–26%, n = 7), and CO2–C evolution was 59% (range 38–70%, n = 7) of manure total C. For the LW-solids, apparent net N mineralization after 63 d was 45% (range 41–51%, n = 6), and CO2–C evolution was 40% (range 33–48%, n = 6) of added manure total C. A 15N tracer experiment indicated that 23% (range 6–33% n = 7) of NH4–N in the LW was denitrified during the first 21 d of the incubation. Denitrification losses were not measured for the LW-solids. When denitrification losses were taken into account, actual N mineralization from the LW was calculated to be 48% (range 29–73%, n = 7). These results demonstrate that the dissolved C and N fraction can have a large influence on N mineralization for dilute liquid dairy manures.