Humic acids are reported to increase the permeability of plant membranes, so promoting the uptake of nutrients . They attributed this effect to the presence of iron in the humic acids or to their colloidal nature or they regarded humic substances as organic catalysts. They are capable of degrading a wide range of substances including celluloses, hemicelluloses, proteins and lignin. Some members of this family, such as Streptomyces may excrete a range of vitamins, growth substances and antibiotics. The breakdown or cycling of cellulose in the soil may be the reason why organic matter readings may be increased after the application of a New Mexico humate to soils high in undecomposed organic matter.
Humic substances work for many reasons, depending on soil and environmental conditions .
The consensus is that they work well in low organic matter soils. In low amounts they do not perform in soils of high organic content, and at high rates they seem to tie-up soil nutrients. This may be the reason why humate sometimes produces no results when used on an acid soil in humid areas. Acid soils may have large amounts of soluble aluminum and iron present, therefore these soils should be limed to optimum levels to produce the best results, with or without added humates. Western soils with high free lime levels have very low iron and aluminum levels as calcium tends to precipitate soluble aluminum, iron and manganese.