Abstract
Organic nitrogen compounds in the animal waste once applied to soil is followed by chemical modification. Microbial transformation of nitrogen in cattle slurry applied to an Andisol grassland with no-cattle grazing over 20 years in northeastern Japan was analyzed with a focus ontemporal changes in chemical composition (ammonium- and nitrate-nitrogen) and the natural abundance of nitrogen isotopes, 515N. Most urea and related metabolites, which were major organic constituents of nitrogen in cattle excreta, were hydrolyzed into ammonium-nitrogen during storage in an underground closed tank. Nitrification of the ammonium-nitrogen was largely delayed under lower soil temperature conditions with average air temperature (4-14°C), whereas rapid nitrification occurred under higher air temperature conditions (17-27°C). A coupled process of denitrification followed by nitrification was evidenced by a rapid decrease in the nitrate content with a simultaneous increase in the 515N values of the residual. Such a process was facilitated by a combination of the high water retention property of the Andisol with an ample supply of organic matter.
