Submitted to: Humic Substances and Organic Matter in Soil and Water Environments; Charact
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/1998
Publication Date: N/A
Technical Abstract: Studies on the effects of humic substances (HS) on plant growth, under conditions of adequate mineral nutrition, consistently show stimulative effects on plant biomass. 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. Some researchers attributed the stimulative effects of HS to higher uptake of nutrients. Others, however, suggested that hormone activity of HS promotes plant growth. These components are considered to increase cell membrane permeability and to exhibit hormone-like activity. The hypothesis that HS originating from various sources contain plant growth hormones was tested recently. The results will be discussed, in light of supporting literatur data, that plant growth enhancement results from increased nutrient availability, due to their chelation by HS. Present research focuses on the activity of laboratory-grade and commercially prepared HS on root and shoot growth of creeping bentgrass and ryegrass, in growth chamber microsystem experiments. A novel screening system for HS effects on plants grown in nutrient solution will also be described. Our results indicate that the system is responsive to nutrient and HS dynamics. Larger scale greenhouse experiments in simulated golf green mixes of sand or sand/peat showed some HS products to be effective turfgrass growth promoters. The feasibility and impact of HS utilization in horticulture will be discussed.