Humic products in agriculture: Potential benefits and research challenges-a review

Authors: Olk, Daniel - Dan; Dinnes, Dana; SCORESBY, RENE - Minerals Technologies (MTI); CALLAWAY, CHAD - Ag Logic Distributers, Llc; DARLINGTON, JERALD - Minerals Technologies (MTI)

Submitted to: Journal of Soils and Sediments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2018
Publication Date: 1/24/2018
Citation: Olk, D.C., Dinnes, D.L., Scoresby, R., Callaway, C.R., Darlington, J.W. 2018. Humic products in agriculture: Potential benefits and research challenges-a review. Journal of Soils and Sediments. 18:2881-2891. https://doi.org/10.1007/s11368-018-1916-4.
DOI: https://doi.org/10.1007/s11368-018-1916-4

Interpretive Summary: Humic products are made from young coal deposits, and their application to plants is claimed to increase plant growth. However, they are used by only small proportions of farmers to improve crop growth and grain yield. Here we discuss four limitations to their market growth. The limitations include inadequate information on how environmental and management factors alter crop responses to humic products, the lack of field-tested explanations for how humic products improve plant growth, the absence of widely accepted laboratory methods for measuring their properties and effectiveness, and the lack of attention given to their potential benefits to soil properties. We suggest specific actions for solving these limitations. By identifying key knowledge gaps, our proposed actions could bring researchers and vendors together to make the industry more knowledge-based and give the consumer more confidence when using humic products. These results are useful to the humic product industry, to potential users of the products, and to researchers who study humic products.

Technical Abstract: 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 greenhouses and growth chambers, more 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 to support this claim. 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. 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 in a variety 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.