Humic acids are complex organic molecules formed by the breakdown of organic matter in the soil. They are not considered to be fertilizers, but soil enhancers and improvers.
the substance mentioned serves as a catalyst
a catalyst is anything that aids activity, and humic acids do that in soil
( z1 serve :ARG0 ( z2 substance :ARG1-of ( z3 mention ) ) :ARG1 ( z4 catalyze ) )