Influence of pH on the release of NO and N2O from fertilized and unfertilized soil

Abstract

NO and N2O release rates were measured in an acidic forest soil (pH 4.0) and a slightly alkaline agricultural soil (pH 7.8) after the pH was adjusted to values ranging from pH 4.0 to 7.8. The total release of NO and N2O during 20 h of incubation was determined together with the net changes in the concentrations of NH4+, NO2−and NO3−in the soil. The release of NO and N2O increased after fertilization with NH4+and/or NO3−; it strongly decreased with increasing pH in the acidic forest soil; and it increased when the pH of the alkaline agricultural soil was decreased to pH 6.5. However, there was no simple correlation between NO and N2O release or between these compounds and activities such as the NO2−accumulation, NO3−reduction, or NH4+oxidation. We suggest that soil pH exerts complex controls, e.g., on microbial populations or enzyme activities involved in nitrification and denitrification.