Abstract: The use of an N-heterocyclic compound of the general formula (a) or (b) with the following definitions: X1 being S or X2 being S or O and at least one of X1 and X2 being S R2 H or C1-4-alkyl, R3 H or C1-4-alkyl R6 and R7 are hydrogen or together form a covalent carbon-carbon bond in general formula (a) R1 being H, C1-12-alkyl or —CH2—NR4R5 with R4 hydrogen or C1-4-alkyl, R5 C1-12-hydrocarbon residue which can contain one to three halogen atoms and/or one to four heteroatoms, selected from the group consisting of nitro-gen, oxygen and sulfur, it also being possible for R4 and R5, together with the nitrogen atom joining them, to form a 5- or 6-membered saturated or unsaturated heterocyclic radical, which optionally may also contain one or two further heteroatoms selected from the group consisting of nitrogen, oxygen and sulfur, in general formula (b) R1 being H or C1-17-hydrocarbon, preferably H, or —CH2—R5 with R5 being H or C1-16-hydrocarbon residue, which hydrocarbon can contain one to three halogen atoms an

Abstract: The use of a pyrazolo[3,4-b]pyridine-4-carboxamide of the general formula (I) with the following definitions: R1 hydrogen or C1-4-alkyl, R2 C1-12-hydrocarbon residue which can contain one or two heteroatoms, selected from the group consisting of nitrogen, oxygen and sulfur, it also being possible for R1 and R2, together with the nitrogen atom joining them, to form a 5- or 6-membered saturated or unsaturated heterocyclic radical, which optionally may also contain one or two further heteroatoms selected from the group consisting of nitrogen, oxygen and sulfur, R3 C1-12-hydrocarbon residue which can contain one heteroatom, selected from the group consisting of nitrogen, oxygen and sulfur, R4 C1-8-hydrocarbon residue, R5 hydrogen or C1-4-alkyl, as nitrification inhibitor.