Location: Soil, Water & Air Resources Research
2021 Annual Report
Objectives
Objective 1: Assess humic products and cover crops as management options for promoting soil carbon pools, nutrient cycling for crop growth, and increased yield.
Objective 2: Assess the effectiveness of grass buffers, blind inlets, and carbon-based reactive barriers in the form of filter socks for phosphorus management.
Objective 3: Quantitatively characterize soil health and crop productivity responses to carbon input from crop sequences and carbon losses from tillage, crop residue management and harvest.
Approach
To enhance management of soil carbon, laboratory analyses for specific carbohydrates, amino compounds, phenols, and fatty acids will be used to distinguish between labile and recalcitrant fractions of soil organic matter (SOM). Effects of applying humic products and cover crops on short- (e.g., nutrient cycling and soil structure) and long-term (e.g., carbon sequestration) soil changes will be determined. Humic product application will be evaluated as a mitigation strategy for SOM loss due to excessive crop residue removal for bioenergy production. Filter socks filled with wood chips and bark will be evaluated as a means to efficiently catch dissolved and sediment-bound phosphorus moving with runoff water into surface inlets, subsurface drainage systems, and ultimately natural water bodies. Process-level knowledge from laboratory and plot-scale research will enhance development of site-specific subfield management strategies for increasing producer profitability and providing sustainable feedstock supplies at field and landscape scales. Several different crop rotations utilizing corn, soybean, alfalfa, wheat, rye, field pea, and tillage radish will be evaluated with various levels of stover harvest. No-tillage, strip-tillage, and chisel-plow management as well as effects of biochar will be determined. Effects on nutrient cycling, soil carbon stocks, and soil health (using the Soil Management Assessment Framework) will be quantified. Project results will provide critical information needed to elucidate the effects of crop residue management and carbon-based amendments on soil physical and biochemical properties, economic returns, and long-term sustainability of corn-based Midwestern cropping systems.
Progress Report
Objective 1. A field experiment having nitrogen fertilizer treatments and humic product subplots was continued for a second year. Measurements were expanded to include in-season plant carbohydrate production and assays for key enzymes involved in plant carbohydrate and phenol production. Biochemical and microbiological analyses of soil organic matter fractions and whole soils from the cover crop field experiment were completed but at a slowed pace due to the pandemic. Large datasets from humic product field experiments were finalized, statistically analyzed, and incorporated into several manuscripts that were submitted for peer review. To expand a new activity, an unmanned aerial vehicle (UAV) equipped with sensors was flown over the corn field having nitrogen fertilizer treatments and also two of our long-term field experiments of humic product application that were planted to either corn or soybean this year. Crop light absorption at ten wavelengths were measured. The data were used to determine UAV capabilities for both rapid assessment of crop nitrogen deficiencies and also humic product benefits to crop growth. Additional measurements planned for a second field experiment on nitrogen fertilizer treatments and humic product subplots, including UAV and also root exudate measurements, were aborted because a destructive wind storm in the previous season (August 2020) destroyed that year’s corn crop, scattering corn kernels across the field and creating the likelihood of unwanted volunteer corn plants in the 2021 season.
Objective 2. No work was planned toward this objective, as the scientist who developed this objective retired two years ago. This position was filled by a new scientist in September 2020 toward a new research direction, namely interactions between soil physical properties and carbon.
Objective 3. Impacts of tillage and crop residue management on yields and soil health indicators after ten years of treatments were analyzed. As a new activity, the plots were converted to a uniformity trial after 13 years of treatments and planted to an oat-clover rotation to test impacts of past management on oat yields. Soil health measurements were collected from a subset of treatments, including detailed measurements of penetration resistance with a hydraulic cone penetrometer. Cone index values were statistically analyzed and a manuscript assessing impacts of tillage on subsurface compaction was prepared for peer-review. As an additional new activity, a large U.S. dataset of tillage effects on soil health indicators was reanalyzed to determine whether changes in bulk density influence interpretation of carbon stock changes. Soil carbon stocks were re-analyzed using an equivalent soil mass procedure and compared to a fixed-depth approach.
Accomplishments
1. Responsiveness of corn root biochemistry to humic product application. Humic products are liquid or solid materials that are made from young coal deposits, and they are sold for the purpose of increasing plant growth. They are receiving increasing attention as on-farm amendments for crop production, but their effects on plant growth in field conditions are poorly understood. Statistical analyses by ARS scientists in Ames, Iowa, on four years of field results identified the much greater effects of humic product application on corn root biochemistry than on aboveground biomass biochemistry. In a droughty year, humic product application enhanced root woodiness compared to plants not receiving the humic product. Increased woodiness is a normal corn response to drought, perhaps to promote water uptake, hence the humic product effect might help improve drought tolerance. In a non-droughty year, by contrast, root woodiness did not increase with humic product application while root carbohydrate concentrations increased significantly compared to plants not receiving the humic product. In both years, carbohydrates and phenols concentrations of the aboveground biomass did not change significantly with humic product application. Recent statistical analysis of previously measured concentrations of some plant hormones also found stronger responses to the humic product in the roots than in aboveground biomass. These results demonstrate in greater detail the effects of humic products on plant composition in field conditions than have previously been shown. They provide one possible explanation for the field observation that corn grain yield responds to humic product application more significantly in droughty conditions than in non-droughty conditions. They also identify roots as a key plant part for measurement in future studies that will further seek to explain crop responses to humic product application. Successful studies would better identify the roles that humic products can play in benefiting crop production during droughty conditions.
Review Publications
Li, D., Zhao, B., Olk, D.C., Zhang, J. 2020. Soil texture and straw type modulate the chemical structure of residues during four-year decomposition by regulating bacterial and fungal communities. Applied Soil Ecology. 155. Article 103664. https://doi.org/10.1016/j.apsoil.2020.103664.
Gent, D.H., Claassen, B.J., Massie, S.T., Phillips, C.L., Shellhammer, T.H., Trippe, K.M., Twomey, M.C. 2021. Delayed early season irrigation: impacts on hop yield and quality. Journal of the American Society of Brewing Chemists. 80:62-65. https://doi.org/10.1080/03610470.2021.1915053.
Phillips, C.L., Meyer, K.M., Hanson, C.V., Biraud, S., Trippe, K.M. 2020. Manipulating rangeland soil microclimate with juniper biochar for improved native seedling establishment. Soil Science Society of America Journal. 85(3):847-861. https://doi.org/10.1002/saj2.20207.
Olk, D.C., Dinnes, D.L., Scoresby, R.J., Darlington, G.W., Hurburgh, C.R., Rippke, G.R. 2021. Maize growth and grain yield responses to a micronized humic product across soil types and annual weather patterns in Central Iowa, United States. Frontiers in Plant Science. 12. Article 672078. https://doi.org/10.3389/fpls.2021.672078.
Russell, A.E., Marek, R.F., Olk, D.C. 2021. Tree species of wet tropical forests differ in their tissue biochemistry and effects on soil carbon dynamics. Frontiers in Forests and Global Change. 4. Article 674213. https://doi.org/10.3389/ffgc.2021.674213.
