Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/1998
Publication Date: N/A
Interpretive Summary: For centuries it has been recognized that soils with high levels of decaying plant material are generally more fertile than sandy soils. Scientists have recently been trying to find the specific components of the decaying plant material that contribute to increased plant growth. Humic acid has been identified as one of these compounds. This material has been tested with many crops and found to increase plant growth and root development. It is currently being promoted for use on turfgrass but there is very little data supporting its use. In this work we used a variety of sources of humic acid and applied them both to the leaves and roots of plants growing in sand-culture and solution-culture. A granular form of humic acid increased root growth when mixed into the sand used to grow a common turfgrass. Humic acid increased phosphorus uptake of the grass when grown in sand-culture. It appears that humic acid has very little effect when plants have adequat nutrients (solution-culture) but may be more important when plant nutrition is limited (sand-culture).
Technical Abstract: Positive effects of humic substances on plant growth have been well documented for many crops, but not for turfgrasses. Two greenhouse experiments were conducted to determine if application of humic substances to creeping bentgrass (Agrostis stolonifera L.) turf would improve root mass, root length, or nutrient uptake. A commercially mined granular humate, a commercial liquid humic acid (HA), and liquid HA's extracted from other sources were applied to creeping bentgrass growing in either sand or solution culture. Foliar applications included monthly (sand-culture) or biweekly (solution-culture) applications of HA's at 0, 100, 200, or 400 mg HA/l. Granular mined humate was incorporated into the top 10 cm of selected pots for evaluation in the sand-culture experiment only. In sand-culture, incorporated humate stimulated greater rooting at the 0-10 and 10-20 cm depth and significantly increased maximum rooting depth compared to all HA treatments and non-treated turf. Foliar applications of HA in sand-culture and solution-culture was did not affect root growth. Phosphorus uptake of plants in sand-culture was significantly increased by incorporated humate and foliar application of peat or Leonardite-derived HA. In solution-culture no increase in P uptake resulted from HA application. These results support the hypothesis that humic acids have limited effects when plants are adequately supplied with nutrients.