Humic Product Effects on Corn Root Growth and Plant Biochemistry in Field Conditions.

Corn (Zea mays L.) root growth and tissue biochemistry responses to two humic products were evaluated separately in three-year field studies. In each humic product treatment, a defined soil volume (50 cm L x 30 cm W x 30 cm D) was excavated at about the V8, V14, and R2 growth stages to measure the root systems of three adjacent corn plants.  Soil was removed by careful washing and roots were cut for scanning.  At the R2 growth stage, the recommended rate of product application provided for about 20% increase in root length compared to the control in nearly all growing seasons.  Most of this increase occurred between the V14 and R2 growth stages and was due to faster emergence of nodal roots from the corn stalk and subsequent differentiation into lateral roots.  All ten size classes based on root diameter showed comparable proportional increases in root length. In cases, root biomass increased further yet with product application than did root length, suggesting denser roots.  The timing of the root response lagged behind those of leaf area and ear development, suggesting root growth was not solely responsible for improved plant growth with humic product application. Analysis of roots and stover at physiological maturity for one product (Enersol) showed season-specific responses of plant biochemistry.  In two growing seasons having drought stress, Enersol promoted plant lignification, with increases by up to 10-25% for all 11 phenols measured by CuO oxidation.  In the single year with negligible stress, Enersol promoted carbohydrate accumulation but lacked a phenol response. These season-specific responses suggest humic products might interact with environmental stimuli in affecting plant growth. Increased root production and enhanced root lignification would together cause larger input of recalcitrant carbon forms into the soil, potentially benefiting stable soil C stocks and soil health.