Research Project: Developing Aspirational Practices Through Improved Process Understanding to Protect Soil and Air Resources and Increase Agricultural Productivity in the Upper Midwest U.S.

Location: Soil and Water Management Research

2023 Annual Report

Objectives
Objective 1. Evaluate and develop innovative cropping systems and management practices to increase the resiliency and decrease the environmental impacts of agricultural systems. a. Develop management practices that address the key impediments to adoption of kura clover living mulch systems for corn production. b. Quantify the agronomic and environmental performance of corn grown with and without the use of novel soil amendments in integrated management systems. Objective 2. Improve fundamental understanding and predictability of nitrogen and carbon transformation processes to improve crop nutrient use efficiency and reduce nutrient losses, especially through engineered solutions. a. Reveal chemical mechanisms of N and C transformations occurring with biochar amendments and develop guidance for agronomic use. b. Quantify fundamental N process rates following urea addition to soil with and without soil amendments and incorporate missing processes into a dynamic model.

Approach
This project will address key challenges facing corn producers in the upper Midwest U.S., which include the need for strategies that extend vegetative cover for longer periods and reduce reactive nitrogen losses to aquatic systems and greenhouse gas emissions. These challenges will be addressed through a combination of field, lab, and modeling-based studies structured around two main objectives and four integrated sub-objectives. Objective 1 will utilize field and laboratory studies to evaluate and develop innovative cropping systems and management practices to increase the resiliency and decrease the environmental impacts of agricultural systems. Sub-objective 1A will evaluate the feasibility of overseeding kura clover into an existing alfalfa stand to maintain forage productivity during the kura clover establishment period and determine if reduced intensity tillage can produce early corn growth similar to rotary zone tillage if combined with injected anhydrous ammonia as a nitrogen source. Sub-objective 1B will quantify the agronomic and environmental performance of corn grown with and without the use of novel soil amendments in integrated management systems. The overall aim of Objective 2 is to improve fundamental understanding and predictability of nitrogen and carbon transformation processes to improve crop nutrient use efficiency and reduce nutrient losses. Sub-objective 2A will use laboratory studies to reveal the chemical mechanisms of nitrogen and carbon transformations occurring with biochar amendments which will be used to develop guidance for the agronomic use of biochar. Sub-objective 2B will quantify fundamental nitrogen process rates following urea addition to soil with and without soil amendments and incorporate missing processes into a dynamic nitrogen cycling model. This research will increase our understanding of fundamental soil processes to allow improved prediction of agronomic and environmental outcomes and generate recommended practices for corn producers and policy makers that utilize innovative cover crops, row establishment systems and soil amendments to maintain productivity, increase climate resilience and soil carbon storage, and decrease environmental risks.

Progress Report
In support of Sub-objective 1A, four manuscripts were initiated and/or completed relating to the kura clover living mulch (KCLM) system for corn production. One manuscript was revised and accepted for publication in Soil and Tillage Research. This work was aimed at comparing clover and corn grain performance using a previously deployed tillage method, rotary zone tillage (RZT), to a lower-intensity tillage method, shank strip tillage (ST). The ST system achieved adequate suppression of the clover early in the season to allow the corn to achieve acceptable grain yields while the RZT treatment reduced clover root biomass relative to ST. Fertilizer N source did not affect clover biomass pools or corn grain yields. We conclude that ST can be used with any form of banded N fertilizer to successfully manage corn in KCLM while maintaining a greater level of clover root biomass than RZT. One manuscript was revised and accepted for publication in Agrosystems, Geosciences & Environment. This work investigated the effect of row-establishment technique and fertilizer nitrogen (N) rate on corn grain yield and N uptake in KCLM systems in Arlington, Wisconsin, and Rosemount, Minnesota. Row establishment treatments included RZT, ST, and banded herbicides (BH), each evaluated at six N rates from 0 to 225 kg N per hectare. Extended periods of drought were experienced during the study period which were more pronounced at the Minnesota location. Row establishment method affected grain yield differently at each site. Under the more severe drought conditions at Rosemount, BH maximized yield, whereas under moderate drought, the higher intensity tillage (RZT) maximized yield. This work indicates that decisions about row establishment methods in KCLM systems should consider spring environmental conditions and expected weather outlook. A third manuscript that was prepared and submitted to Plant and Soil which reported on the temporal and spatial distribution of clover biomass and its decomposition in the soil profile. The observations were used as inputs to a model that was used to estimate the in-season N contributions from KCLM to corn. The results showed that a substantial amount of N, ranging from 59 to 84 kg N per hectare was contributed by the clover from mid-June to mid-October, and that the corn took up 88% of these N inputs. A fourth manuscript reporting observations of elevated soil nitrous oxide (N2O) emissions and corresponding soil N concentrations under KCLM management is currently being prepared with an expected submission date prior to October 1, 2023. In further support of Sub-objective 1A, unit scientists recognized that the kura clover perennial crop used in the above experiments and in our aspirational LTAR system has characteristics that may provide a ground cover in solar farms that could maintain agricultural production (hay and honey) while providing enhanced infiltration and erosion protection. A cooperative agreement was established with Flint Hills Resources to test kura clover under 40 acres of a solar installation being developed near their oil refinery in Rosemount, Minnesota. Unit scientists plan to install sensors to measure distribution of solar radiation, soil moisture, temperature, and biomass production. In support of Objective 1, Goal 1A, new field experiments were established to investigate the impacts of: (1) row establishment method, (2) timing of planting, and (3) fertilizer application rates on corn grown in KCLM systems. One year of experiments at Rosemount, Minnesota, are complete and data analysis is ongoing. Year two of the experiment is underway. Complementary experiments are being established on new plots in Lamberton, Minnesota, to evaluate KCLM on more poorly drained soils. Kura clover biomass data from ongoing experiments are being combined with phenology data collected from primary literature and are being used to develop crop management schedules compatible with the Soil and Water Assessment Tool (SWAT) watershed scale model. A SWAT model was parameterized for three agricultural watersheds in Minnesota (Le Sueur River Basin, Cottonwood River Basin, High Island Creek) and one in Iowa (Little Cedar River). Model calibration and integration of KCLM management schedules into the SWAT modeling framework are ongoing. In support of Objective 1, Goal 1B, lab microcosm experiments examining the effectiveness of procyanidin compounds for decreasing N2O production in fertilized soils were continued. New experiments compared procyanidin mixtures obtained from two different commercial sources and quantified the stability of the chemicals under different storage conditions. The experiments showed that one source was more effective than the other and that storage had minimal impacts on its effectiveness. Additional experiments examined the effectiveness of individual compounds within the mixture and found that some compounds had effects that detracted from the effectiveness of the mixture as a whole, suggesting that purification of the mixture could enhance its efficacy. These results were combined with previous results to prepare a manuscript that was submitted for publication to Applied Soil Ecology. The lab incubation system developed last year was improved by adding a humidification loop to avoid artifacts due to soil drying. Several rounds of testing were conducted with the new system to optimize the program timing so that near-continuous and simultaneous measurements could be made of N2O, nitric oxide (NO), nitrogen dioxide (NO2), ammonia, carbon dioxide, methane, and water vapor. In support of Objective 1, Hypothesis 1B, the field experiment initiated last year in St. Paul, Minnesota, was replicated for a second growing season. This experiment is quantifying the effects of row-spacing (8-in versus 30-in) and fertilizer addition (with or without N fertilizer) on soil N2O emissions and nitrate availability during soybean production. Nitrogen fertilizer was provided to one treatment using a product containing a dual microbial inhibitor designed to improve crop N uptake and reduce N losses. Due to the extreme drought conditions experienced last year, it was expected that this year would provide a contrast to assess the impact of weather conditions. However, dry conditions have continued this following planting in May persisted until late June which inhibited plant emergence and required supplemental irrigation. Manual flux chambers were installed in 16 plots to measure N2O and CO2 fluxes to capture spatial variation on a twice-weekly frequency. Automated flux chambers connected to a field instrument trailer were used to measure gas fluxes in six locations four times per day to better capture temporal variability. Weekly to bi-monthly sampling for soil nitrate availability is being conducted as well as quantification of rhizobia nodulation approximately monthly. In support of Objective 2, Goal 2A, research continued with measurements of NO and NO2 production rates (collectively referred to as NOx) in different biochar samples. Production of NOx following addition of nitrite solutions was observed to vary as a function of biochar feedstock type, pyrolysis temperature, and nitrite concentration, and treatment of the biochars with hydrogen peroxide was found to increase NOx production. A publication is in preparation detailing these observations. Further progress was impacted by a critical instrument (isotope ratio mass spectrometer) becoming inoperable. This component of the research is delayed but will be completed once the instrument is functional or access to an alternative instrument can be obtained. In support of Objective 2, Hypothesis 2B, the N process model was further developed by formulating a new component that accounts for diffusion of gases through the soil and across the soil-atmosphere interface. A previously published diffusion model that accounts for gas diffusion in two-dimensions was reformulated to account for 3-dimensional (3D) transport equation using a more precise numerical technique that solves the transport equation with 3-spatial coordinates (depth, width, and length) as well as time. The next goal is to integrate the diffusion and biogeochemical components which will allow for better testing of hypotheses regarding effects of spatial variability on N losses to the atmosphere. The model was also modified so that input parameters can be provided in a simple spreadsheet file which will make the model more accessible to a wider audience. Testing of the diffusion component was initiated. We constructed soil probes for collecting gas samples from below the surface to examine how N2O and CO2 gas concentrations change over time to compare the model simulations. Probes were installed as part of the field experiment (Hypothesis 1B). Samples analysis is underway. As described above for Goal 2A, the fixation experiments using N isotopes have been delayed due to the unavailability of the required analytical instrument. Additional progress related to the project objective of measuring soil N2O emissions was made under a cooperative agreement with Rowbot Systems LLC, the aim of which is to develop a mobile robot for measuring greenhouse gases (GHG) from agricultural fields. Unit scientists worked with Rowbot Systems to help design a prototype robot equipped with a remotely operated GHG flux chamber and to compare the gas concentrations in robot-collected samples with samples collected manually using conventional chambers. Analysis of these comparisons is underway.

Accomplishments
1. Soil additives used to reduce N2O emissions have unintended water quality impacts. Soil emissions of the potent greenhouse gas (GHG) nitrous oxide (N2O) account for more than 50% of the total GHG budget of the U.S. agricultural sector. Many approaches are being investigated for reducing N2O emissions, including products that contain nitrogen-fixing microbes (NFM) or chemicals that target specific microbial processes such as urease inhibitors (UI) and nitrification inhibitors (NI). In a two-year field study conducted in both irrigated and rainfed corn production systems, ARS scientists in St. Paul, Minnesota, found that the beneficial effects of these additive for reducing N2O emissions were counteracted by increased leaching of nitrate below the root zone, which can negatively affect local and regional water quality. This effect occurred most consistently when UI or NFM were applied either as single additives or when they were applied together with NI, where nitrate leaching increased by a factor of 2 to 7 compared to treatments without additives. In some cases, the increased nitrate leaching completely offset the decreased N2O emissions after accounting for the potential conversion of nitrate to N2O in receiving waters. These results indicate that the use of these soil additives requires caution and further study and will be of interest to researchers, policy makers, and regulators charged with identifying effective practices for reducing the carbon footprint of U.S. agriculture.

Review Publications
Menefee, D.S., Scott, R.L., Abraha, M., Alfieri, J.G., Baker, J.M., Browning, D.M., Chen, J., Gonet, J.M., Johnson, J.M., Miller, G.R., Nifong, R.L., Robertson, P., Russel, E.R., Saliendra, N.Z., Schreiner-Mcgraw, A.P., Suyker, A., Wagle, P., Wente, C.D., White Jr, P.M., Smith, D.R. 2022. Unraveling the effects of management and climate on carbon fluxes of U.S. croplands using the USDA Long-Term Agroecosystem (LTAR) network. Agricultural and Forest Meteorology. 326. Article 109154. https://doi.org/10.1016/j.agrformet.2022.109154.
Kleinman, P.J., Spiegal, S.A., Silviera, M., Baker, J.M., Dell, C.J., Bittman, S., Cibin, R., Vadas, P.A., Buser, M.D., Tsegaye, T.D. 2022. Envisioning the manureshed: Towards comprehensive integration of modern crop and animal production. Journal of Environmental Quality. 51(4):481-493. https://doi.org/10.1002/jeq2.20382.
La Scala, N., Martinez, A.S., Spokas, K.A. 2023. CO2 emission and its interface with soil organic matter: A multidisciplinary vision. In:Bettiol, W., Silva, C.A., Martin-Neto, C.E.P., de Andrade, C.A., editors. Soil Organic Matter.Embrapa, Brazillia, Brazil. p. 297-316.
Gamiz, B., Velarde, P., Spokas, K.A., Cox, L. 2022. The role of nanoengineered biochar activated with Fe for sulfanilamide removal from soils and water. Molecules. 27(21). Article 7418. https://doi.org/10.3390/molecules27217418.
Alexander, J., Baker, J.M., Venterea, R.T. 2023. Maize performance in a kura clover living mulch under drought conditions. Agrosystems, Geosciences & Environment. 6(1). Article e20329. https://doi.org/10.1002/agg2.20329.
Alexander, J.R., Baker, J.M., Gamble, J.D., Venterea, R.T., Spokas, K.A. 2023. Spatiotemporal distribution of roots in a maize-kura clover living mulch system: Impact of tillage and fertilizer N source. Soil & Tillage Research. 227(3). Article 105590. https://doi.org/10.1016/j.still.2022.105590.
Dalzell, B.J., Fissore, C., Nater, E. 2022. Topography and land use impact erosion and soil organic carbon burial over decadal timescales. Catena. 218. Article 106578. https://doi.org/10.1016/j.catena.2022.106578.
Law, J.Y., Slade, A., Hoover, N., Feyereisen, G., Soupir, M. 2022. Amending woodchip bioreactors with corncobs reduces nitrogen removal cost. Journal of Environmental Management. 330(15). Article 117135. https://doi.org/10.1016/j.jenvman.2022.117135.
Christianson, L.E., Wickramarathne, N., Johnson, G.M., Feyereisen, G.W. 2022. No/low-cost chipped woody debris nutrient composition benefits and tradeoffs for denitrifying bioreactors. Bioresource Technology Reports. 20. Article 101237. https://doi.org/10.1016/j.biteb.2022.101237.
Toczydlowski, A., Slesak, R., Venterea, R.T., Spokas, K.A. 2023. Pyrolysis temperature has greater effects on carbon and nitrogen biogeochemistry than biochar feedstock when applied to a red pine forest soil. Forest Ecology and Management. 534. Article 120881. https://doi.org/10.1016/j.foreco.2023.120881.
Schaedel, M., Ishii, S., Wang, H., Venterea, R.T., Paul, B., Mutimura, M., Grossman, J. 2023. Temporal assessment of N-cycle microbial functions in a tropical agricultural soil using gene co-occurrence networks. ISME Communications. 18(2). Article e0281442. https://doi.org/10.1371/journal.pone.0281442.
Wei, H., Song, X., Liu, Y., Wang, R., Zheng, X., Buterbach-Bahl, K., Venterea, R.T., Wu, D., Ju, X. 2023. In situ 15N-N2O site preference and O2 concentration dynamics disclose the complexity of N2O production processes in agricultural soil. Global Change Biology. 29(17):4910-4923. https://doi.org/10.1111/gcb.16753.
Souza, E., Rosen, C., Venterea, R.T., Muhammad, T. 2023. Intended and unintended impacts of nitrogen-fixing microorganisms and microbial inhibitors on nitrogen losses in contrasting maize cropping systems. Journal of Environmental Quality. Article 20500. https://doi.org/10.1002/jeq2.20500.