Abstract
Humic substances are ubiquitous in the environment, complex mixtures, and known to be beneficial to plant growth. To better understand and identify components responsible for plant growth stimulation, a terrestrial aquatic DOM sample was fractionated according to pH and polarity, obtaining acid-soluble and acid-insoluble portions, as well as acid-soluble hydrophobic and hydrophilic fractions using C18. The various fractions were characterized then evaluated for their biological effects on plant growth using bioassays with corn at two carbon rates. Approximately 43% and 57% of the carbon, and 31% and 69% of the iron, was found in the acid-insoluble and acid-soluble fractions, respectively. Upon separating the acid-soluble portion using C18 extraction, about 64% and 36% of the carbon (and 96% and 4% of the iron) was present in the hydrophilic and hydrophobic fractions, respectively. The acid-insoluble portion was more aromatic and less oxygenated than the acid-soluble fraction. The hydrophilic filtrate was oxygen-rich and contained mostly tannin-like molecules, while the hydrophobic retentate was more aromatic and lignin-like. During bioassay testing, it was found that more hydrophilic samples (those that are more oxygenated) yielded the highest response for shoot measurements. For root measurements, the lower DOC rate (0.01 mg/L C) gave better results than the higher DOC rate (0.1 mg/L C). Also, the hydrophobic, less oxygenated acid-insoluble sample performed better than the more hydrophilic acid-soluble portion. The polarity fractions at the lower carbon application showed that larger root systems occurred when there was more hydrophobic C18 retentate material present. The opposite was true for the root system at the higher carbon application, where larger roots existed when more hydrophilic C18 filtrate material was present. Compositional differences were found when comparing the acid-soluble versus acid-insoluble portions and the hydrophobic versus hydrophilic C18 fractions, and activity with respect to plant stimulation was discerned. While a carbon rate affect was observed during foliar application to corn plants (with the lower carbon rate generally yielding the best biological stimulation), the various observed trends indicate that plant response is due to not only the amount of carbon present but also the type of carbon.
Highlights
Humic substances are ubiquitous in the environment, complex mixtures, and known to be beneficial to plant growth
The “acid-soluble” portion was fractionated further using C18 solid phase extraction (SPE, [30]), to obtain the hydrophobic retentate portion and the hydrophilic filtrate portion
The acid-soluble portion was fractionated further, and the C18 hydrophilic filtrate accounted for 64% of the carbon in the acid-soluble portion, and the C18 hydrophobic retentate contained 36%
Summary
Humic substances are ubiquitous in the environment, complex mixtures, and known to be beneficial to plant growth. Humic substances, which are ubiquitous in the environment, are present in varying amounts in all natural waters, soils, and sediments [1,2,3]. They are complex mixtures, containing thousands of individual molecules, all varying in their individual structure, function, reactivity, and polarity. Humic substances have long been regarded as beneficial to soil fertility and plant growth, and there are multiple excellent reviews on the subject that encompass decades of studies [4,5,6]. It is likely that the optimal method and quantity for treatment varies depending on the crop, soil properties, and environmental conditions, as the mechanism for enhanced plant growth is uncertain
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Chemical and Biological Technologies in Agriculture
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
