Nitrogen fertilizer value of slurry from fattening pigs fed rations with elevated contents of bacterially fermentable substrates (BFS) 1(st) Report: Effect of increasing levels of BFS

Feces and urine quantitatively collected from fattening pigs were used to o btain slurries defined by feeding for subsequent determination of the nitri fication in slurry/soil mixtures (200 mg N/kg soil) incubated for upto 16 w eeks at 20 degrees C and of N fertilizer value for Lolium multiflorum. Four feed rations with gradually increasing levels of bacterially fermentable s ubstrates (BFS) were fed to six pigs each. Increasing BFS decreased NH4-N p roportions of total slurry N. In the incubation and the plant experiment, a part from the four different slurries, non-fertilized controls were used, a nd in the latter NH,NO, was supplied as a further control. In the plant exp eriment the mineral fertilizer and the different types,of slurry were added at levels of either 2 x 200 mg or 2 x 400 mg N/kg soil directly after the 1(st) and the 2(nd) cut. The type of slurry had no clear effect on NO3-N co ntents of the slurry/soil mixture and nitrification of slurry NH4-N was com pleted after 2 weeks of incubation. Plant dry matter production and N expor tation were clearly reduced by the slurry obtained from the ration with the highest BFS content at the 2(nd) cut when compared with the slurry from th e low-BES ration. Intermediate values were found with slurries from the oth er rations. A great part of these differences, particularly at the low leve l of fertilization, were compensated in later cuts. Overall, the difference s to mineral fertilizer were much greater. Slurry gained from feeds with in creasing BFS contents initially also resulted in a reduction of N content o f the plants. Total N uptake of the plants was not affected by the type of slurry at the low fertilizer N level but was lower with slurry from pigs fe d higher BFS amounts at the high fertilizer N level. Corresponding slurry e ffects were obtained in N use efficiency but not in N mineral use efficienc y. Soil N balance and the percentage of N input non-recovered in plants and soil at the end of the experiment were not clearly influenced by slurry ob tained from pigs fed different BFS amounts. It was concluded that feeding p igs with higher amounts of BFS to a limited-degree reduces the fertilizer v alue of slurry N but assists to reduce overall N emissions.