Relationships between stability of Cu complexes and nitrification inhibition effects of corresponding ligands in soils

In order to investigate the relationships between the stability of Cu complexes and the nitrification inhibition effects of corresponding ligands, the effects of 22 kinds of Cu (II) ligands and eight kinds of Cu (I) ligands were evaluated in three types of soil on nitrification potentials (NPs) under short-term incubation (5 h) and nitrification inhibitory rates (NIRs) under long-term incubation (14 d). The results showed that the inhibitory effect of Cu (II) or Cu (I) ligands on nitrification exhibited significant linear relationships (P < 0.01) with the logarithms of the first stability constants (lgK ₁) and the total stability constants (lgK f) of corresponding complexes. Furthermore, lgK f of Cu (II) complexes exhibited a greater linear correlation than the corresponding lgK ₁ with the nitrification inhibition effects of the corresponding ligands; lgK f of Cu (I) complexes exhibited a steeper linear relationship than that of Cu (II) complexes with NPs or NIRs, and hence, nitrification inhibition effects of Cu (I) ligands almost doubled that of Cu (II) ligands when the lgK f values of Cu (I) and Cu (II) complexes have the same changes.