EFFECT OF A NITRIFICATION INHIBITOR ON IMMOBILIZATION AND MINERALIZATION OF SOIL AND FERTILIZER NITROGEN

The effect of nitrapyrin (N-Serve 24E) on N transformations in an actively nitrifying soil was studied in the laboratory in unlabelled soil and soil labelled with (15NH4)2SO4. Samples were incubated for 12 days with sampling every 3 days. Nitrapyrin (12.8 μg g-1 soil) inhibited nitrification by 90% at day 12, but had no effect on net N mineralization. However, gross rates of N immobilization and N mineralization, estimated by isotope-dilution, were slightly inhibited by nitrapyrin. The addition of (15NH4)2SO4 did not affect net N mineralization, but the quantity of unlabelled (NH+4 + NO-3)-N extracted in inhibitor-treated and untreated samples increased. The increased quantity of unlabelled inorganic-N was similar to the amount of labelled N immobilized, suggesting an apparent added N interaction due to pool substitution. The inhibitor had no effect on the added N interaction. © 1990.