Submitted to: International Humic Substances Society Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/21/2002
Publication Date: 7/21/2002
Citation: Clapp, C.E., Chen, Y., Hayes, M., Cline, V., Palazzo, A., Molina, J., White, D., Baker, J.M. 2002. Humic substances for enhancing plant growth. International Humic Substances Society Conference. p. 328-329. Interpretive Summary: Natural humic substances, as components of soil organic matter, have played a vital role in soil fertility and environmental quality. The multiple roles played by these materials can greatly benefit plant growth. Examples are their contributions in plant growth enhancement, increasing fertilizer efficiency, or reducing soil compaction. Our work indicates that plant stimulation provided by increased micro-elements iron and zinc availability, in the presence of humic substances, is the most important factor. The results of these experiments have been shared with turfgrass scientists, horticultural specialists, and agricultural extension agents. The impact will be to provide a simpler and less costly method for supplying required trace metals like iron and zinc to agricultural and horticultural crops, while decreasing risk of possible pollution by over-application of nutrients.
Technical Abstract: Studies on the effects of humic substances (HS) on plants, under conditions of adequate mineral nutrition, consistently show stimulation of plant growth. Enhancement of root growth was usually more apparent than stimulation of shoot growth. Both increase in root length and development of secondary roots have been observed for HS in nutrient solutions. Typical response curves showed enhanced growth with increasing HS concentration, followed by a decrease in growth at high concentrations. Shoots generally showed similar trends in growth response to HS. Agricultural and horticultural plants have continued to show stimulation effects from HS applied in the pouch experiments. Corn and soybean cultivars particularly have responded to humic acid (HA) and fulvic acid (FA) additions to nutrient solutions. Root growth and chlorophyll enhancement were especially noticed. Favorable effects of HS have been widely reported. Plant parameters affected are: root and shoot weight, root initiation, seedling emergence and growth, rhizosphere microbial population, nutrient uptake and flowering. These effects were found for both HAs and FAs as well as for compost-derived HS. In most experiments the activity of HAs was found to be similar to that of FAs, although some of our results gave higher activity for low molecular weight products. It is concluded that growth enhancement of plants in nutrient solutions and soil by HS should mostly be attributed to the maintenance of Fe and Zn in solution at sufficient levels. This effect is pH dependent and decreases with pH.