Separation of pig slurry and plant utilization and loss of nitrogen-15-labeled slurry nitrogen

Separation of slurry by centrifugation concentrates nutrients and facilitates the transport of surplus nutrients away from livestock farms. Nitrogen-15 labeled pig slurries containing urine N-15 or fecal N-15 were produced to compare the utilization and fate of N in separated and unseparated pig slurry. There was good agreement between the mineral fertilizer equivalence (MFE) of manure fractions estimated from N-15 uptake and by a traditional non-isotopic method, but the IN method was more precise. The weighted utilization of N in separated slurry was similar to the N utilization in unseparated slurry. The MFE of slurry total N was 75 to 79% after incorporation before sowing spring barley (Hordeum vulgare L.) and 59 to 64% after surface application in winter wheat (Tritium aestivum L.). Both the origin of the slurry N and the fractionation influenced the N availability. The uptake of urinary N-15 in the first barley crop was 35 to 53% and the uptake of fecal N-15 21 to 44% with the lowest availability of N-15 in the dry-matter-rich fraction (DMR). The uptake of IN in the following cover crop and barley crop was low (1-4.5%). The residual N effect of the manures in the year after application (MFE) was equivalent to 1% for the liquid fraction, 3% for the slurry, and 5% for the DMR. The amount of N-15 remaining in soil 15 mo after application was 30 to 53% for urinary N and 44 to 61% for fecal N. It is concluded that the overall utilization of N is unaffected by slurry separation, but the separation facilitates a better distribution of nutrients.