Location: Soil, Water & Air Resources Research
2022 Annual Report
Objectives
Objective 1: Develop improved crop practices based on carbon management that can be used to enhance soil physical properties in agricultural production systems, including better soil drainage and degradation of a subsoil fragipan.
Subobjective 1.A: Investigate decadal impacts of artificial drainage on soil health.
Subobjective 1.B: Evaluate annual ryegrass cover crops for improving seasonal soil water dynamics in fragipan soils.
Subobjective 1.C: Determine the chemical composition of fragipans at varying stages of degradation by ryegrass or humic product application.
Subobjective 1.D: Determine the effects of a humic product on the chemical speciation and quantities of root exudates released by ryegrass in a hydroponic system.
Objective 2: Establish the benefits of plant biostimulants, including humic products, to enhance plant growth and improve soil properties, and identify their mechanistic effects on plant physiological processes to develop more resilient agroecosystems.
Subobjective 2.A: Identify plant physiological processes that respond to humic product application for multiple plant types in diverse field settings and determine environmental influences on the plant responses.
Subobjective 2.B: Evaluate humic product impacts on soil physical properties.
Objective 3: Determine the responses of soil organic matter biochemistry to crop management practices in order to establish mechanistic interrelationships among soil carbon cycling, physical properties, and nutrient availability, and therefore develop improved management practices to optimize cropping system sustainability.
Approach
At multiple Corn Belt sites, historical changes in soil carbon (C) stocks and associated soil properties will be measured under current soil drainage practices, including proposed future practices, to help drainage management adapt to changing precipitation patterns in the Midwest. In the southern Corn Belt, existing studies of annual ryegrass and humic products as management options for degrading a hardened subsoil fragipan will be expanded. Their benefits will be measured for improving seasonal water relations and extending rooting depth through fragipan degradation at multiple sites. Existing field investigations of humic products as a crop amendment will be expanded by identifying their seasonal effects on plant carbohydrate production and plant hormone fluxes, as potential mechanistic explanations for the improved grain yield that was demonstrated previously in corn-soybean rotations. The commonality of these plant process responses to humic products will be established by expanding the scope of field sites to include natural grasslands, wheat, and potentially additional crops in other U.S. regions. To distinguish the relative contributions of plant vs. microbial materials to soil C sequestration, the concentrations of plant and microbial bio-marker compounds will be measured in labile fractions of soil organic matter for field treatments in two wheat-based and corn-based agroecosystems where soil C has been sequestered. Project results will provide critical information needed to guide the use of C amendments and other crop management practices for promoting soil C accumulation, enhancing other soil properties, and increasing crop performance, primarily for corn-based Midwestern cropping systems.
Progress Report
Objective 1. Due to loss of scientific and technical personnel, progress on Objective 1 was limited. Soil moisture sensors were installed in two production fields in southern Illinois where ryegrass has been planted as a long-term management option for degrading the hardened subsoil fragipan layer. Sensors were temporarily removed for spring field operations. A different model of soil moisture sensor was initially used in each of the two fields. Superior performance by one model led to its re-introduction in both fields once spring field operations were complete. Soil moisture data acquired by the sensors were transmitted remotely to Ames.
Objective 2. A serious flaw in an analysis for soluble leaf carbohydrates was identified and corrected. This method was used at three sampling times in one humic product field and once in two other field experiments. A portable photosynthesis system became available, and its operation learned. Additional methods for analyzing plant enzymes related to carbohydrate production and transformations were reviewed, and their installation was begun.
Accomplishments
1. The biostimulatory nature of a humic product is indicated by its complex interactions with nitrogen fertilizer on corn grain yield. Humic products are liquid or solid materials that are made from young coal deposits. Vendors claim humic product application can increase crop growth and fertilizer use efficiency. To test these claims, ARS scientists in Ames, Iowa, are studying corn growth responses to a humic product at five nitrogen (N) fertilizer rates. At the higher N rates, the humic product led to significant increases in grain yield. These results suggest that humic product use can replace some N fertilizer input while still meeting grain yield targets. However, at the second lowest N rate (70 kg ha-1), substantial decreases in grain yield occurred with humic product application. Similarly, corn grain yield with zero N input had slight numeric reductions with humic product use. Early- to mid-season growth of corn stems and leaves increased with the humic product at each non-zero N rate. Hence the grain yield loss at the 70 kg N ha-1 rate suggests a late-season growth inhibition. It contradicts claims that humic products promote soil nutrient availability and instead suggests that humic products are biostimulants, promoting plant growth through means that do not involve nutrient availability. These findings are useful to researchers who study humic product benefits on crop growth and land managers who seek to avoid excessive N fertilizer applications.
Review Publications
Olk, D.C., Dinnes, D.L., Callaway, C.R. 2022. Maize growth responses to a humic product in Iowa production fields: An extensive approach. Frontiers in Plant Science. 12. Article e778603. https://doi.org/10.3389/fpls.2021.778603.
Yuzhi, X., Liu, K., Yao, S., Zhang, Y., Zhang, X., He, H., Feng, W., Ndzana, G.M., Chenu, C., Olk, D.C., Mao, J., Bin, Z. 2022. Formation efficiency of soil organic matter from plant litter is governed by clay mineral type more than plant litter quality. Geoderma. 412. Article e115727. https://doi.org/10.1016/j.geoderma.2022.115727.
