Losses of Nitrogen During Decomposition of Plant Material in the Presence of Inorganic Nitrogen1

Oat straw and alfalfa hay were decomposed in the presence of added inorganic nitrogen under differing conditions of incubation. Changes in organic, ammonium, and oxidized forms of nitrogen were determined. With plant material in shallow (3 mm) layers and at two-thirds moisture saturation, there was loss of nitrogen in decomposition of alfalfa, but not in decomposition of oat straw. Some influences of pH, moisture content, pore size, added energy-rich materials, kind of inorganic nitrogen, and of addition of germicidal materials on the occurrence and extent of denitrification are reported. Vigorous bacterial activity and an alkaline reaction were necessary for any extensive denitrification from added nitrate. An active fungus flora was commonly encountered in decompositions in which there were no appreciable losses of nitrogen. Nitrite toxicity appeared to be an important ecological factor in preventing bacterial growth and biological denitrification in acid substrates.