EFFECT OF NITROGEN FERTILIZERS AND OTHER FACTORS ON POTENTIAL NITROGEN-FIXATION AND DENITRIFICATION ACTIVITY OF GRAY FOREST SOIL

A plot experiment in which com was grown on Gray Forest soil was used to investigate the effect of the concentration of mineral nitrogen app lied in fertilizer on the potential nitrogen-fixation and denitrificat ion activity of the soil in the presence of various concentrations of organic carbon. All levels of application of nitrogen fertilizer produ ced a significant inhibition of the potential nitrogen-fixation activi ty. Application of cellulose in the absence of nitrogen fertilizer sti mulated nitrogen-fixation activity in the absence of corn plants to a greater extent than when they were present. The presence of free nitra te in the soil is the key factor governing denitrification activity. T he denitrification activity was significantly lower in the soil on whi ch corn plants were grown. The application of cellulose did not affect the denitrification activity.