Low Concentrations of Humic Substances Enhanced the Growth of Lactuca sativa L.

Abstract

Aim: The experiments were completed to evaluate the efficacy of humic substances at low concentrations on the growth of lettuce (Lactuca sativa L.). Methodology: Lettuce (Lactuca sativa L.) of Grand Rapids variety seedlings were grown in seven deep water culture growing units. Each unit represented one treatment, in which twelve plants were grown in solution containing limited amount of nutrients and different rates of a liquid (extracted) humic product at 0, 70, 500, 4,000, 6,000, 14,000 and 42,000 mgL-1, corresponding to 0, 1, 7, 55, 83, 193 and 580 mgL-1 humic substances, respectively. All plants were harvested and evaluated in a two month period. Results: Only one plant perished from a total of 84, indicating that the growing units were effective. Plant length measurements were analyzed for means, standard deviations, ANOVA (P=.05) and Fisher’s least significant difference (α=.05). Leaf counts and plant weight measurements were recorded. Significant plant growth was observed at low product ratesbetween70 and 500 mgL-1, corresponding to 1 and 7 mgL-1 humic substances. At increased rates, the growth was reduced. At much higher rates, plant growth was again observed, that was likely caused by the presence of nutrients in the product. Conclusion: These experiments demonstrated the efficacy of humic substances at low concentrations on the growth of lettuce (Lactuca sativa L.), a critical finding in the context of sustainable horticulture, in which maximum yields from minimum input would be desired.