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 treated with dairy-waste compost or ammonium sulfate ((NH4)2SO4) to examine the role of microbial production and consumption of NO−3 in controlling soil NO−3 concentrations. Inorganic N, net N process rates, nitrification potentials and gross N process rates were measured at various time periods in the treated soils. Microbial consumption of NO−3 was not an important process in controlling soil NO−3 concentrations in these soil systems. Transient growth in the nitrifier population was observed with ammonium sulfate but not compost addition. Nitrification rates were significantly correlated with and comprised about 50% of the gross N mineralization rates, suggesting that nitrifying bacteria were not weaker competitors for soil NH+4 than heterotrophs in these systems.