Variable humic product effects on maize structural biochemistry across annual weather patterns and soil types in two Iowa (U.S.A.) production fields

Authors: Olk, Daniel - Dan; Dinnes, Dana; Hatfield, Ronald; SCORESBY, JOSEPH - Minerals Technologies (MTI); DARLINGTON, JERALD - Minerals Technologies (MTI)

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2022
Publication Date: 1/12/2023
Citation: Olk, D.C., Dinnes, D.L., Hatfield, R.D., Scoresby, J.R., Darlington, J.W. 2023. Variable humic product effects on maize structural biochemistry across annual weather patterns and soil types in two Iowa (U.S.A.) production fields. Frontiers in Plant Science. 13. https://doi.org/10.3389/fpls.2022.1058141.
DOI: https://doi.org/10.3389/fpls.2022.1058141

Interpretive Summary: Humic products are created from young coals. Their addition to crop fields is claimed to improve plant growth. Visual observations indicated their ability to strengthen corn against wind damage. To explain these observations, we analyzed the biochemical contents of corn stems and roots from field experiments having humic product application. During a dry year we found the humic product caused greater woodiness of the roots. Fewer changes were observed in the stems. Greater woodiness is a natural corn response for adjusting to dry conditions, and the humic product increased this response. These results provide one possible explanation for how humic products might help maintain corn growth during dry years. These results also demonstrate complex interactions between the corn plant, the humic product and the environment. The results will be valuable to corn producers in drier regions and to researchers who are interested in developing greater corn resistance to drought or understanding how humic products can help crop growth.

Technical Abstract: Humic product effects on plant structural biochemistry under field conditions have received little attention, despite the potential for mitigating environmental stresses. Maize (Zea mays L.) concentrations of 11 phenols and five carbohydrates were measured by cupric oxide (CuO) oxidation and acid hydrolysis, respectively, for whole plant stover (four growing seasons) and roots (two growing seasons) at physiological maturity. These samples were collected from either of two production fields in Central Iowa. Stover and root tissues tended toward greater phenol concentrations in an eroded hilltop transect but greater carbohydrate concentrations in a toe slope transect, possibly as a response to greater drought stress in the hilltop transect. Two humic product treatments (application at the fourth leaf growth stage or a split application) further affected plant phenols and carbohydrates in hilltop roots. Compared to an unamended control, the phenolic content of hilltop roots increased significantly with humic product application in the drier season of root sampling (2013). Phenol increases above the control averaged 20% for each monomer, reaching as high as 30% for vanillin. Carbohydrates in the hilltop roots did not respond to humic product application. In the second year of root sampling (2014), which by contrast had abundant rainfall, hilltop root phenols did not respond to the humic product, but five root carbohydrates increased on average by 11 or 20% for each humic product treatment compared to the control, reaching significance (P< 0.10) in 7 of 10 cases. Phenol responses to the humic product were less clear in the hilltop stover, and trends were not apparent for hilltop stover carbohydrates or in the toe slope for phenols or carbohydrates in either roots or stover. The phenols that were more responsive to the humic product or to drier conditions included p-coumaric acid and syringaldehyde, which are heavily involved in late-season lignification of maize. Some but not all of these phenol trends gained by CuO oxidation were confirmed by alternative methods for phenol contents for the internode above the ear leaf at the milk reproductive growth stage in 2013. In summary, for maize roots the humic product further promoted root lignification as a natural response to drought stress. Yet under non-droughty conditions it promoted root carbohydrate production. Together with independent observations, these results suggest that carbohydrate production might be the intrinsic plant response to humic product application under favorable growing conditions. These results indicate complex interactions in field conditions between plant biochemical pathways, environmental signals, and the humic product.