Research Project: Managing Carbon and Nutrients in Midwestern U.S. Agroecosystems for Enhanced Soil Health and Environmental Quality

Location: Soil, Water & Air Resources Research

2020 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. Two field experiments having nitrogen fertilizer treatments and humic product subplots were set up and conducted instead of the scheduled single experiment. Each evaluates a humic product from a different vendor and is at a different location in central Iowa. Biochemical analyses of soil organic matter fractions and whole soils from the cover crop field experiment were slowed by laboratory renovation, which required transfer of all laboratory equipment and supplies to and from a temporary room. Progress was further slowed by sharing the principal analytical instrument with another research group performing an unrelated carbohydrate analysis. Large datasets from humic product field experiments were finalized, statistically analyzed, and incorporated into several manuscripts for peer review. As a new activity, an unmanned aerial vehicle (UAV) equipped with light sensors was flown over one of the two fields having nitrogen fertilizer treatments. Data were collected at multiple wavelengths to determine UAV capabilities for rapid assessment of crop nitrogen deficiencies and humic product benefits to crop growth. Objective 2. The scientist retired in FY 2018, and this position remained vacant nearly all of FY 2020. Objective 3. The scientist was retired through FY 2019, and this position was abolished.

Accomplishments
1. Phenol accumulation in California rice soils correlated with late-season inhibition of crop nitrogen uptake. A key factor of rice grain yield is late-season crop uptake of soil nitrogen, which promotes grain filling. Collaborators at the University of California, Davis found that on-farm rice fields in the Sacramento Valley, California, vary widely in their amount of late-season crop uptake of nitrogen, for unknown reasons. Selected rice fields were categorized by their degree of late-season nitrogen uptake, crop residue management, and soil flooding durations. Soil samples from these fields were analyzed collaboratively with ARS researchers in Ames, Iowa, for their phenol contents, which previous ARS research had correlated with an inhibition of late-season nitrogen uptake in rice field trials at a University of Arkansas research station. The phenol concentrations of the California on-farm soils were moderately correlated with the late-season inhibition of rice nitrogen uptake, providing first-time on-farm evidence to strengthen the ARS findings from Arkansas. These results are consistent with in-season aeration of rice soils as a means for decomposing soil phenols and maintaining late-season nitrogen supply to the rice crop while reducing greenhouse gas emissions and other forms of environmental degradation. The basis for increased soil aeration arose partially from the ARS rice research in Arkansas, which is now being studied in additional rice-producing states in the United States. The practice of increased soil aeration has also been incorporated into the Sustainable Rice Platform (http://www.sustainablerice.org/), which is a global organization composed of more than 100 institutional members. It is striving to improve rice management practices of one million small farmers worldwide.

2. Validating alkaline extraction as a means to study natural organic matter and its roles in soil and water processes. Alkaline extraction is the classical approach for removing soil organic matter fractions from soil for detailed laboratory analyses of organic matter composition. But it has been increasingly criticized in recent publications because it allegedly creates new molecules that are not found in nature. In response, ARS researchers in Ames, Iowa, were invited by the Journal of Environmental Quality (JEQ) to publish an article that refuted major conceptual criticisms of alkaline extractions and described several case studies in which alkaline extraction was used to resolve agricultural and environmental problems involving natural organic matter in soil and aquatic settings. Published as part of a debate, this article was downloaded 2,000 times from the JEQ website in its first 8 months after publication, five times the average number of lifetime downloads for JEQ articles. This debate inspired JEQ to call for volunteered manuscripts to further evaluate the validity of alkaline extractions. ARS researchers in Ames, Iowa, contributed to the organization of manuscript submissions, including one senior authorship and one junior authorship. The resulting set of publications, together with the previously published debate, prompted the three impartial editors of this special publication set to declare in a summary article that alkaline extraction is a valid approach and it has contributed significantly to our understanding of natural organic matter in soils and natural waters. Both senior author papers by ARS scientists are posted on the website of the International Humic Substances Society. This favorable outcome can be used to justify continued use of alkaline extractions and to refute further attempts to ban publication of alkaline extraction studies.

Review Publications
Nunes, M.R., Karlen, D.L., Denardin, J.E., Cambardella, C.A. 2019. Corn root and soil health indicator response to no-till production practices. Agriculture, Ecosystems and Environment. 285. https://doi.org/10.1016/j.agee.2019.106607.
Chen, X., Ye, X., Chu, W., Olk, D.C., Cao, X., Schmidt-Rohr, K., Zhang, L., Thompson, M.L., Mao, J., Gao, H. 2020. Formation of char-like, fused-ring aromatic structures from a nonpyrogenic pathway during decomposition of wheat straw. Journal of Agricultural and Food Chemistry. 68(9):2607-2614. https://doi.org/10.1021/acs.jafc.9b06037.
Karlen, D.L., Veum, K.S., Sudduth, K.A., Obrycki, J.F., Nunes, M.R. 2019. Soil health assessment: Past accomplishments, current activities, and future opportunities. Soil & Tillage Research. 195(104356). https://doi.org/10.1016/j.still.2019.104365.
Poffenbarger, H.J., Olk, D.C., Cambardella, C.A., Kersey, J., Liebmann, M., Mallarino, A., Six, J., Castellano, M.J. 2020. Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs. Agriculture, Ecosystems and Environment. 291. https://doi.org/10.1016/j.agee.2019.106810.
He, Z., Olk, D.C., Tewolde, H., Zhang, H., Shankle, M. 2019. Carbohydrate and amino acid profiles of cotton plant biomass products. Agriculture. 10(1):2. https://doi.org/10.3390/agriculture10010002.
Chen, X., Jin, M., Xu, Y., Chu, W., Olk, D.C., Hu, J., Jiang, Y., Mao, J., Gao, H., Thompson, M.L. 2019. Potential alterations in the chemical composition of soil organic matter during NaOH extraction. Journal of Environmental Quality. 48(6):1578-1586. https://doi.org/10.2134/jeq2019.02.0077.
Olk, D.C., Bloom, P.R., De Nobili, M., Chen, Y., McKnight, D.M., Wells, M.J.M., Weber, J. 2019. Using humic fractions to understand natural organic matter processes in soil and water: Selected studies and applications. Journal of Environmental Quality. 48(6):1633-1643. https://doi.org/10.2134/jeq2019.03.0100.
Xu, J., Zhao, B., Li, Z., Chu, W., Mao, J., Olk, D.C., Zhang, J., Xin, X., Wei, W. 2019. Demonstration of chemical distinction among soil humic fractions using quantitative solid-state 13C NMR. Journal of Agricultural and Food Chemistry. 67(29):8107-8118. https://doi.org/10.1021/acs.jafc.9b02269.
Abdelrahman, H.M., Cocozza, C.C., Olk, D.C., Ventrella, D., Montemurro, F., Miano, T. 2020. Changes in labile fractions of soil organic matter during the conversion to organic farming. Journal of Soil Science and Plant Nutrition. https://doi.org/10.1007/s42729-020-00189-y.
Lenssen, A.W., Olk, D.C., Dinnes, D.L. 2019. Application of a formulated humic product can increase soybean yield. Crop, Forage & Turfgrass Management. 5(1):1-6. https://doi.org/10.2134/cftm2018.07.0053.