Microbial control of nitrate concentrations in an agricultural soil treated with dairy waste compost or ammonium fertilizer

We conducted a 112-day laboratory incubation of an agricultural soil treate d with dairy-waste compost or ammonium sulfate ((NH4)(2)SO4) to examine the role of microbial production and consumption of NO3- in controlling soil N O3- concentrations. Inorganic N, net N process rates, nitrification potenti als and gross N process rates were measured at various time periods in the treated soils. Microbial consumption of NO3- was not an important process i n controlling soil NO3- concentrations in these soil systems. Transient gro wth in the nitrifier population was observed with ammonium sulfate but not compost addition. Nitrification rates were significantly correlated with an d comprised about 50% of the gross N mineralization rates, suggesting that nitrifying bacteria were not weaker competitors for soil NH4+ than heterotr ophs in these systems. (C) 2000 Elsevier Science Ltd. All rights reserved.