Dana L. Dinnes

On-Farm Evaluation of a Humic Product in Iowa (US) Maize Production

The benefit to corn (Zea mays L.) production of a humic product derived from lignite was evaluated for 3 years under otherwise conventional crop management in Iowa farmers’ fields. A liquid extract, it was applied at a rate of 3.57 L ha−1, generally as a foliar spray mixed into routine pesticide applications during early stages of crop growth. In each of 3 years, hand-sampled corn plants collected at physiological maturity in 30–35 farmers’ fields across Iowa showed a significant increase in grain weight with product application in 70–80% of the cases, covering a range of soil types and grain yield levels. Mean increases were 630–940 kg ha−1, and these were inflated, as expected, compared to a limited number of yield increases estimated by mechanical combine, typically 310–630 kg ha−1, or about 5% of normal yield levels. Grain weight increases were associated with longer, thicker, and heavier cobs and slightly larger stover biomass. Plant nutrient concentrations were not affected at harvest. In-season measurements in a few intensively monitored farmers’ fields associated product application with slightly taller plants, increased leaf area, earlier onset of pollination, extended grain filling, and delayed senescence, i.e., extended duration of photosynthesis and decayed rotting of stems. Limited visual observations indicated great proliferation of roots, especially lateral roots. Ongoing data assessment will identify any environmental factors of product efficacy, an issue that to date remains unexplored in the humic product literature. Initial studies of alfalfa (Medicago sativa L.) found biomass increases with product application of 7–29%. A newly begun corn trial on nitrogen fertilizer response will estimate the amount of N fertilizer input that can be replaced by humic product application to save input costs and mitigate environmental degradation. The humic product increased economic yield in a large majority of cases by amounts that were agronomically modest but economically significant. Future work will expand to soybean (Glycine max (L.) Merr.) production.

Humic products in agriculture: potential benefits and research challenges—a review

Humic products have been used in cropland agriculture for several decades, but lack of widespread credibility has restricted their use to small proportions of farmers. To improve the credibility of humic products, we identify four knowledge gaps and propose pathways of future action to close these gaps. First, while the capacity of humic products to improve plant growth has been proven in greenhouse and growth chambers, more such work is needed in field conditions, especially to determine the modifying effects on humic product efficacy of environmental and management factors, including crop type, annual weather patterns, soil type, and fertility management. Many of the published field studies fail to address any of these factors. Second, full acceptance of humic products by the research community may first require a mechanistic explanation for plant responses to humic products. Some research groups are exploring plant-based mechanisms, but almost entirely in controlled conditions, not in field conditions. Industry often attributes yield responses to enhancement of soil nutrient availability without citing adequate evidence. Microbial-based explanations are also possible. Third, consumer trust in available humic products would be strengthened through industry-wide measures for quality control of humic product production and sale, including standard procedures for measuring their humic and fulvic acid contents and rapid bio-assays for distinguishing effective products from inert frauds. Finally, humic products are widely presumed to promote root growth, which offers the potential to increase soil C inputs and thereby improve soil health. Yet virtually, no such evidence has been presented, in part due to the absence of long-term field trials. Humic product companies in North America have organized a trade association to promote a more knowledge-based industry. To acquire a database that will support these objectives, we propose establishment of a global network of field sites that would measure crop responses to humic products across ranges of humic products, crop types, soil types, and climates. Plant and soil samples would be analyzed by cooperating specialists in advanced laboratories to identify mechanistic processes and benefits to both plant production and soil health. We believe the industry will indeed become more knowledge-based and the credibility of humic products will improve as (i) we learn more about their field efficacy across ranges of field conditions for improving crop yield and soil health, (ii) we gain further insights into possible mechanistic explanations, and (iii) the consumer gains the ability to discern genuine products from fraudulent materials.

Chemical Properties of Humic and Fulvic Acid Products and Their Ores of Origin

Commercial products consisting of humic and fulvic acids are thought to boost plant growth and economic yield in cropland agriculture. The specific mechanism for their benefit is unknown, in part because little information is available on the chemical nature of these products. We examined the chemical nature of eight humic acid products, three fulvic acids and seven of their source materials, lignite and leonardite ores, and humic shales. All samples were from the United States and Canada. Analysis by 13C cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy found that the humic acid products and the ores were dominated by large signals at aliphatic C (ca. 30 ppm) and aromatic C (ca. 130 ppm). These products were distinguished from one another by their relative proportions of aromatics and aliphatics and relative percentages of smaller signals for carboxyl C (approximately 175 ppm) and ketones/aldehydes C (ca. 200 ppm). These samples were also extracted for their concentrations of seven carbohydrates through anion exchange chromatography and pulsed amperometric detection. All ores and humic acid products had low concentrations of carbohydrates. The ores and products made without alkali extraction had slightly greater concentrations of carbohydrates than did extracted products, suggesting that alkali extraction for production of the humic acid products discriminated against carbohydrates. Results will also be discussed for sample concentrations of amino acids, two amino sugars, and lignin-derived phenols. Although these products share the same dominant chemical traits, they cannot be considered as chemically similar until the chemical mechanism for their effect on plant growth is identified and the corresponding compound(s) or functional group(s) is/are measured in these products and ores. Until then, field efficacy established for one product cannot be transferred to other products.