Abstract: It is the object of the present invention to develop agent combinations having an improved synergistic effect with regard to the inhibition or control of ammonium nitrogen nitrification.It was unexpectedly found that agent combinations which consist of at least one compound of the general formula ##STR1## with M with n=1 and greater than 1--in case of coordination compounds--standing for several mono- and multivalent metal ions, but being negated with n=0 in case of metal salts of substituted pyrazoles,A being the counterion in case of anion complexes and pyrazolates, preferably ammonium, alkali and alkaline earth, the 3-methyl pyrazolium cation in case of anion complexes and additionally Fe and Al in case of metal salts; b being in the range of 0 to 4,X being the same or different and embodying several mono- and multivalent inorganic or organic anions with q=0 to 6,R.sub.1 being hydrogen, methyl or halogen andZ representing hydrogen, CONH.sub.2, CNHNH.sub.2 or CSNH.sub.