Abstract: Azulmic acids, stabilized by condensation with carbonyl compounds, said modified azulmic acids containing from 0.5 to 55 percent by weight of ionic groups of the formula ##STR1## in which R represents hydrogen, ammonium, one equivalent of a protonated or quaternized organic nitrogen base or of a sulphonium cation or one equivalent of a metal cation, and containing from 0.5 to 15 percent by weight of groups formed by decarboxylation reaction of the formula ##STR2## and acid addition salts and complex compounds of these stabilized azulmic acids, and also mixed products of these stabilized azulmic acids with additives can be used as agrochemicals. The products are particularly useful as fertilizers and as soil improving agents.