In a research study, originally published in Frontiers in Plant Science, May 2021, Vol. 12:660224, the biostimulant properties of humic acid (HA) were tested on Micro Tom tomato plants under increasing nutritional stress. The results confirmed the positive role humic acids play in enhancing nutrient efficiency uptake in plants.
A team of scientists from the Bio Huma Netics, Inc. (Hiarhi Monda, Ryan Fountain, and Rich Lamar) collaborated with Amy M. McKenna of the National High Magnetic Field Laboratory, Ion Cyclotron Resonance Facility, to conduct this research. The researchers believe that the increasing demands for biostimulants in the agricultural market requires the industry to provide research-based data on the efficiency and safety of this particular product category. This was the motivation that led them to initiate this extensive research.
To conduct the experiment, a sedimentary lignite ore (Idaho), ground to pass a 1,000 µm sieve, was used as the humic acid source and was systematically added at the pre-plant stage. Tomato seeds (Solanum lycopersicum L., Micro Tom) were surface sterilized and individually sown into pots containing a mixture of coconut coir and sand (2:1). Plants were grown for 4 months in a climate-controlled growth chamber. On day 15, seedlings were provided with a standard NPK fertilizer solution at either 25%, 50%, or 100% of the recommended amount and watered at 70% of water-holding capacity. Nutritional dose and HA concentration were selected based on a previous experiment so that a nutritional stress condition was triggered at low nutrient levels.
A total of 6 treatments with 8 replicates per treatment were arranged in a randomized complete block design. During the experiment, plant height was tracked and chlorophyll content was measured. At the end of the experiment, roots and shoots were separated and fresh and dry weights were determined. Tomato yield was evaluated by measuring the number of fruits and the fresh weights. Quality (acidity and Brix) and antioxidant parameters were also assessed.
The results concluded that the humic acid application proved effective in alleviating the nutrient stress of tomatoes, with better results than control plants that did not receive humic acids. Increased yield (up to 19%) and fruit quality (in the range of + 10%–24%), higher ascorbic acid content, and better root growth were the primary parameters impacted by HA application, mostly when the plants were under high nutrient stress conditions (25% recommended nutrition). Analysis of the chemical composition of HA revealed the presence of antioxidants such as flavonoids and pro-oxidants such as quinones. The researchers suggested that the combined action of these elements could help plant defense systems to rapidly cope with stress situations by reprogramming plant development status.
The researchers also emphasized that the use of humic acids as a biostimulant represents a cost-effective and environmentally friendly tool to improve nutrient uptake by promoting sustainable agricultural practices.