Carbon and nitrate utilization in soils: the effect of long-term fertilization on potential denitrification

Soil samples were taken from plots at 3 different experimental sites that had received different fertilizer applications for more than 20 years. Denitrification capacity (DC) and denitrification potential (DP), defined as the amount of N2O released from the soils amended with KNO3 and KNO3 + glucose, respectively, and incubated anaerobically in the presence of 10 kPa acetylene were measured at 25 degrees C for up to 48 h. Also, CO2 evolution and microbial biomass were determined. Both DC and DP were significantly influenced by the treatments. Application of manure (40 t ha(-1) every 4 yr) and lime (5 t CaCO3 ha(-1) every 4 or 5 yr) alone as well as in combination with moderate amounts of inorganic fertilizers (80 kg N + PK ha(-)1 yr(-1)) increased DC and DP. In highly fertilized soils (manuring, liming and 160 kg N + PK ha(-1) yr(-1)), however, DC was further enhanced in one soil only, while DP was significantly decreased in all soils. When no lime was applied but large amounts of fertilizers were (manure and 160 kg N + PK ha(-1) yr(-1)), DC and DP were further significantly decreased, in some cases even below the rates in unfertilized soils. Overall carbon dioxide production from soils followed similar pattern as DC and DP. Fertilization did not significantly affect microbial biomass in limed soils, but decreased it in unlimed soils. Possible indirect influences of long-term fertilization, related to changes in soil chemistry in general and in soil pH in particular, are discussed. (C) 1998 Elsevier Science B.V.