EFFECTS OF AMMONIUM AND NITRATE ON MINERALIZATION OF NITROGEN FROM LEGUMINOUS RESIDUES

A laboratory incubation experiment was conducted to compare the effect s of NH4+ and NO3- on mineralization of N from N-15-labelled vetch (Vi cia villosa Rotn) in an Illinois Mollisol, and to determine the effect of a nitrification inhibitor (nitrapyrin) on mineralization of vetch N when used with NH4+. The addition of either NH4+ or NO3- (100 and 20 0 mg N kg(-1) soil) significantly increased mineralization of vetch N during incubation for 40 days. The effect was greater with NH4+ than w ith NO3-, and a further increase occurred in the presence of nitrapyri n (10 mg kg(-1) soil). The addition of NO; retarded the nitrification of NH4+-N derived from vetch.