ABSTRACT
It is well known that soil organic matter has a favorable effect on the physical, chemical, and biological characteristics of soils. By changing the various soil properties, soil organic matter in general, and especially its humic fractions, are known to have indirect and direct effects on plant growth and crop production. Increasing soil aggregation, water-holding capacity, and improving aeration and soil permeability are some of the beneficial indirect effects in soil physics. Chemically, humic acids (HAs) increase the cation exchange capacity (CEC), providing to soils a stronger buffer capacity to resist sudden drastic chemical changes, which are important indirect effects of enhancing soil fertility and environmental quality. Toxic materials introduced into the soil by agricultural, industrial, and domestic operations will be intercepted from polluting soils and reaching the groundwater by the presence of humic acids with their huge cation exchange capacities. The effect on respiration, enzyme activity, and enhancing the growth of a viable microbial population, necessary in decomposition and mineralization not only for agronomic practices but also for several of the organic cycles-carbon and nitrogen cycling-are just a few among the indirect effects from the science of soil biological properties.
