DENITRIFICATION LOSS FROM 2 PENNSYLVANIA FLOODPLAIN SOILS

Denitrification losses and dissolved nitrous oxide concentration withi n a well- and poorly-drained soil under ryegrass (Lolium perenne L.) w ere measured for approximate to 12 mo. The soils received up to 252 kg N/ha as potassium nitrate in two equal amounts. Denitrification incre ased in March as the soil warmed to 5 to 7 degrees C with the highest rates occurring soon after N was applied. Approximately 30% of annual loss occurred within 2 wk of fertilization. Dissolved nitrous oxide co ncentration peaks corresponded to periods with elevated denitrificatio n. On average, the poorly-drained soil denitrified the equivalent of 4 0% of applied N (up to 110 kg N/ha). Less than 2.5 kg/ha was denitrifi ed from the mil-drained soil. The degree of anoxia in the measurement apparatus substantially effected measured denitrification rates. Conse quently, it is important to know the relationship between redox in-sit u and in the measurement apparatus.