Location: Soil, Water & Air Resources Research
2024 Annual Report
Objectives
Objective 1: Develop new methods and improve the characterization of carbon, nitrogen and water cycles and agrochemical dynamics to improve management opportunities for better productivity and reduced environmental impact.
Subobjective 1.1: Evaluate and compare management system influences on ET, CO2 exchange, surface energy balance partitioning and N2O emissions as a function of conventional and cover crop tillage practices.
Subobjective 1.2: Evaluate effect of drainage depth and spacing on N2O emissions.
Subobjective 1.3: Develop an improved measurement technique to quantify volatilization and atmospheric transport of agrochemicals necessary to develop and evaluate agrochemical management and remediation strategies.
Objective 2: Improve understanding of nutrient partitioning and flows from animal production to field application of manure to reduce gaps in emission inventories and improve mitigation techniques.
Subobjective 2.1: Determine NH3 and H2S emissions from swine finishing barn and manure storage based on feed inputs.
Subobjective 2.2: Assess manure injection/incorporation methods for impact on residue/surface cover, soil disturbance, and NH3 emissions.
Subobjective 2.3: Develop improved techniques for quantifying ammonia deposition near livestock production sites.
Objective 3: Identify drivers of soil and plant associated microbial community structure and function to improve soil health, nutrient use efficiency, and system resilience.
Subobjective 3.1: Test cropping system influence on soil and plant associated microbial communities.
Approach
This project will focus on knowledge gaps that remain in nutrient cycling, water use efficiency, and fate of resource inputs for cropping-livestock systems including cropping systems with highly structured canopies. Three approaches will be pursued for addressing knowledge gaps: 1) Long-term agriculture research (LTAR) networks to evaluate tillage, cover-crop, and fertilizer management influence on surface energy partitioning, water use efficiency, soil health and greenhouse gas emissions; 2) Turbulent transport mechanisms will be determined, including deposition and management practices that reduce the loss of agrochemicals from cropping systems; and 3) The partitioning of nutrients in livestock systems will be determined to evaluate management practices that reduce nutrient emissions and deposition. Field studies at LTAR network sites using eddy covariance towers will quantify evapotranspiration, carbon dioxide exchange and surface energy partitioning from reduced tillage practices with chamber studies at LTAR sites being used to quantify nitrous oxide (N2O) emissions from a range of soil and nitrogen management strategies. In other field studies, eddy covariance towers will be used to quantify water use efficiency through variable irrigation scheduling in vineyards and chamber studies used to quantify N2O emissions through intensified drainage practices. The transport parameters controlling volatile losses of agrochemicals from cropping systems based on tillage practices will be quantified using eddy covariance micrometeorology techniques to determine turbulent flux from whole fields. The relaxed eddy accumulation technique will be used to provide accurate eddy diffusivities for agrochemical vapor transport to improve agrochemical volatilization flux estimates. Riparian buffer zones will be used to quantify the fraction of agrochemicals captured by vegetative buffers to the fraction of agrochemicals volatilized. Open path ammonia (NH3) lasers will be used to quantify NH3 emissions using both barn ventilation and micrometeorology inverse dispersion modeling techniques. The partitioning of nutrients between animal, manure, and gas emissions will be quantified based on nutrient inputs (feed, animals, and residue manure) and nutrient outputs (live and dead animals, manure, and gas emissions of nitrogen (N) and sulfur (S) compounds from barns). Open path methane (CH4) and NH3 lasers and an array of NH3 passive samplers along a transect from an animal feeding operation will quantify NH3 dry deposition using both a tracer gas technique and a bidirectional NH3 flux modeling technique. The quantification of soil extracellular polymeric substances and soil aggregate stability coupled with microbial genome sequencing analysis will be used to evaluate tillage and cover-crop impact on soil health. Knowledge gained through this research will provide producers and regulatory agencies scientific data to improve the sustainability of agricultural production facilities in U.S. farming systems.
Progress Report
In support of Objective 1, the field monitoring of eddy covariance (EC) water vapor and carbon dioxide (CO2) and surface energy flux measurements are continuing at the Long-Term Agroecosystem Research (LTAR) and AmeriFlux sites in both Williams and Brooks, Iowa. Long-term continuous measurement programs are quantifying water vapor and CO2 exchanges over a production field under reduced tillage operations (Williams) and conventional tillage (Brooks) for understanding the impact of water and carbon dioxide exchanges (hydrological water balance and CO2 cycling) between the atmosphere and vegetative layer of the Upper Mississippi Basin.
Long-term evapotranspiration and CO2 flux data stream is being prepared for intensive analysis to quantify multi-year water and carbon dioxide energy balances for the LTAR and AmeriFlux sites. At the Williams site (North field), an 8-chamber system designed to measure soil emissions of nitrous oxide (N2O) and methane (CH4) gases from this year’s soybean production field was tested for the 2024 production season during the freeze-thaw period beginning in late February 2024 through the end of March 2024. Timing synchronization of the N2O and CH4 laser analyzer system was improved but not to the level needed to conduct appropriate trace gas flux measurements.
ARS Scientists continued to work with Los Gatos Research (LGR) technicians until the synchronization issue was finally resolved and evaluated (March 2024) to the level needed to begin making reliable trace gas flux measurements. Eddy covariance trace gas flux (N2O, CH4) began in April 2024 at the North Williams site.
Chamber measurements in support of the EC N2O and CH4 emissions were measured throughout the year to characterize temporal variability emissions concerning rainfall and diurnal soil temperature.
In the reduced tillage and fertilizer management study at the Upper Midwest River Basin (UMRB) LTAR site in Ames, Iowa, field measurements continued with experimental treatments to quantify management impacts on N2O emissions. This is the 9th year in a long-term study. All treatments were in a corn-soybean rotation and included: 1) fall chisel plow, spring disk with spring-applied anhydrous ammonia (Basic Practice (BP)); 2) no-tillage with no cover crop with sidedress application of point injected urea ammonium nitrate (NT); 3) no-till with winter rye cover crop and sidedress point injected UAN (Rye cover, RC); 4) spring tillage with cover crop and an over-wintering winter camelina relay crop between corn and soybean (Winter camelina, WC); and 5) a fertilized and harvested rye cover crop in a no-till system (Fertilized rye, FR). The FR treatment was initiated in the fall of 2022, to evaluate the environmental performance of a rye bioenergy or forage crop that could provide grower revenue. In addition to regular gas sampling, automatic chambers were deployed to collect high temporal resolution data in select plots in the 2023 and 2024 growing seasons.
Field measurements continued to quantify the effects of subsurface drainage depth and intensity on N2O emissions. Drainage treatments were monitored weekly during the growing season and every other week during the fall and winter. In the 3rd year of the study, 2023, plots with subsurface drainage had 50% reduced N2O emissions compared to an undrained treatment. While N2O emissions were higher in the undrained plots, treatments that varied drainage depth or intensity (spacing) did not influence cumulative N2O emissions. 2024 is this study's fourth year, and field measurements are ongoing to determine whether these trends hold across years of varying weather patterns.
To further investigate the hydrological controls of drainage manipulation on trace gas production and emission from soil, a controlled environment experiment was conducted using intact soil columns (25 x 60 cm). Water-tight columns allowed ARS researchers to independently manipulate water table depth. Columns were instrumented with gas ports to quantify pore space gas concentrations, microlysimeters to measure pore water nitrate (NO3) concentrations, soil moisture and temperature probes, and soil tensiometers. Automatic chambers were interfaced to a nitrous oxide analyzer to provide high-resolution measurements of N2O emissions. The soil columns were collected from three soil series that vary in drainage status and were subjected to either a brief or prolonged four-day saturating event to test the interaction of legacy soil properties and immediate hydrological properties on gas emissions. Data analysis is ongoing.
Work in California on the GRAPEX (Grape Remote sensing Atmospheric Profile & Evapotranspiration eXperiment) project was expanded to include more vineyards as well as an almond and olive orchard in response to California’s diverse agricultural systems, all of which are operating under the threat of a shrinking water supply. A new design of synchronized high-frequency EC measurements for below/within vine canopies was developed and tested. This system is being deployed in a production vineyard near Madera, California, and a production almond orchard near Vacaville, California. Synchronized high-frequency evapotranspiration (ET) measurements will be conducted to validate ET remote sensing estimates in July 2024 for 3 weeks for a greater understanding of the vertical turbulence characteristics and transport in structured agricultural canopies and to improve remote sensing modeling of (ET for vineyards, almond and olive orchards. Improved irrigation strategies are being developed to reduce over-irrigation issues while still maintaining sustainable yield production during drought cycles in California.
In support of Objective 2, deployment of ammonia (NH3) and methane (CH4) open-path lasers was delayed in the barn until July 2024 as pressure sensors were calibrated for measuring room static pressures. Room static pressures are used in calculating ventilation rates. A hydrogen sulfide probe will be tested in July 2024 for monitoring gas concentrations in the liquid manure. Data collected the previous year were screened and are being formatted for the database.
A spring manure application (April 2024) was monitored from a swine finishing barn in Central Iowa. Soil samples were collected before and after manure application. Surface and soil cores were collected to approximately 40 cm depth and manure samples were collected from barns during the mixing phase before field application. Surface soil NH4, NO3, pH, moisture, and organic matter increased after field manure application. Gas concentrations for NH3 and CH4 were monitored onsite using open-path lasers one day before manure application for background concentrations. Gas concentrations of NH3 and CH4 were monitored before and one week after manure was applied to the field. High winds during monitoring made laser use challenging as wind gusts misaligned lasers and mirrors. Future work includes data screening of gas concentration and chemical analyses of manure and soil.
The N deposition research continues to be developed and instruments and methods validated. Fifteen three-meter sampling posts with inverted plastic shelters and passive samplers were deployed at a cooperator’s site in central Iowa. A weather station with probes and 3D sonic anemometers was tested and validated before deployment in April 2024. Additional sensors/probes included leaf, soil moisture, soil temperature, and canopy cover. Laboratory protocols were developed and validated for: 1) extraction of passive samplers for NH3 quantification; and 2) extraction of both vegetive and soil samples for NH3. Passive sampler concentrations from a two-week deployment were compared to a co-located cavity ring-down spectrometer that measured NH3 continuously. Preliminary analysis shows good agreement between the two methods for NH3 concentration. Langmuir adsorption isotherms are being developed to describe the equilibrium between NH3 and soils housing passive samplers. Vegetation and soil collected around passive samplers were extracted in early spring and summer for NH3 content.
In support of Objective 3, a study was conducted at the UMRB LTAR site in Ames, Iowa, to assess the impacts of tillage and winter cover crops on root associated microbial communities and their relationships to soil health.
Soybean root, rhizosphere soil, and bulk soil samples were collected monthly from management systems that vary in the extent of disturbance (tillage), winter carbon inputs (cover crops), and arbuscular mycorrhizal fungi (AMF) host status (rye vs brassica winter cover). Samples will be analyzed to test the hypotheses that: 1) Reduced tillage and winter cover crops alter seasonal patterns of succession in soil and plant-associated microbial communities; and 2) Soil extracellular polymeric substances and AMF (two critical soil binding factors) and soil aggregate stability will be more abundant and less variable over time in treatments with reduced disturbance and continuous plant cover. DNA was extracted from soil, plant root and rhizosphere samples, and amplicon libraries of 16S rRNA and ITS2 genes were prepared and sequenced to assess microbial community composition.
Additional assessments were root colonization by AMF, soil aggregate stability, and ester-linked fatty acid methyl-esters. Initial results indicate that AMF colonization is similar among the treatments, but AMF biomass in soil is maintained at higher levels throughout the growing season following a winter host cover crop. Moreover, AMF biomarkers are correlated with higher aggregate stability early in the growing season. These results indicate that management can favor beneficial plant microbiomes, with cascading effects on soil health. Analysis of shifts in community composition with time and between the treatments is ongoing.
Accomplishments
1. Long-term conservation practices reduce nitrate leaching while maintaining yields in tile-drained Midwestern soils. Nitrate leaching from drained Midwestern corn-soybean soils into the Mississippi River is a leading contributor to hypoxia or the “dead zone” in the Gulf of Mexico. Conservation practices such as cover crops and woodchip bioreactors can reduce these nitrate losses and improve water quality. However, the long- term performance of these practices has not been sufficiently quantified. ARS researchers in Ames, Iowa, analyzed 19 years of data that revealed higher annual precipitation resulted in increased effectiveness of in- situ woodchip bioreactor, while the effectiveness of rye cover crop increased in dry years. Overall, both the rye crop and in-situ bioreactors reduced N leaching by nearly 60% compared with the prevailing business as usual corn-soybean system. Notably, the effectiveness of in-situ woodchip bioreactors did not diminish over the study period highlighting its long-term viability. Minimal or no yield penalty was observed following adoption of these conservation practices, which is important for their wider acceptance by the agriculture community. This research will help producers in their efforts to design and implement effective management systems to reduce N loads to the Mississippi River Basin and Gulf of Mexico while maintaining crop production, benefiting local and downstream communities.
2. Improved water use efficiency in California almond orchards. Water scarcity threatens agriculture in California. During the last two decades, severe droughts have led to severe water shortages. California produces 80% of the world’s almonds, which require consistent water supplies for irrigation. ARS scientists in Ames, Iowa, collaborated with scientists from the University of California-Davis and the Almond Board of California in developing the Tree-Crop Remote Sensing of Evapotranspiration Experiment (T-REX), which identifies the water needs of orchards to develop new management practices to maximize water use efficiency and carbon sequestration in almonds and other woody perennial tree crops. The project combines satellite, unmanned aerial vehicles, and proximal sensing technologies to retrieve key variables to increase model predictions of ET flux for almond orchards. Positive results will benefit almond producers through improved water use efficiency.
3. Predicting odor formation in swine manure. Odor emissions from swine production are a leading air quality issue in rural communities. ARS researchers in Ames, Iowa, and Florence, South Carolina, in collaboration with scientists from South Korea and Iowa State University, compared odorants in manure with manure properties, and the manure microbiome composition to predict odor formation. While microorganisms are critical in producing odorants from undigested feed material in manure, no specific microbial population or groups of organisms were linked to odor formation. The research showed that measures of manure solids and pH have a higher predictive ability for odor formation compared to the utility of the microbial community. This study provides growers and engineers with specific targets to monitor and manage in order to effectively control odors from swine finishing operations.
4. Holding carcasses to mitigate leachate contamination of the environment. Outbreaks of infectious diseases involving depopulation of animals require on-farm practices to stage/hold carcasses when final disposal methods are unavailable. ARS researchers in Ames, Iowa, in collaboration with scientists from Digital Agronomy, LLC and Iowa State University, compared how holding techniques affect leachate from decaying animals. Leachate volume was more significant for carcasses held in a pile, covered with a tarp or soil than those held on corn stover bedding or wrapped in a tarp. Soil-covered carcasses decayed faster than carcasses held in a pile or on corn stover. Corn stover promoted carcass decomposition and reduced leachate material by 95%. Lime applied to carcasses delayed the decomposition of carcasses. Wrapping carcasses in tarps reduced decomposition and eliminated leachate loss. The study provides growers and engineers with tools for reducing leaching from decaying carcasses during temporary holding periods when depopulation is necessary to control an infectious disease outbreak.
Review Publications
Hwang, O., Emmett, B.D., Andersen, D., Howe, A., Ro, K.S., Trabue, S.L. 2024. Effects of swine manure dilution with lagoon effluent on microbial communities and odor formation in pit recharge systems. Journal of Environmental Management. 358 Article 120884. https://doi.org/10.1016/j.jenvman.2024.120884.
Rogovska, N.P., O'Brien, P.L., Malone, R.W., Emmett, B.D., Kovar, J.L., Jaynes, D., Kaspar, T., Moorman, T., Kyveryga, P. 2023. Long-term conservation practices reduce nitrate leaching while maintaining yields in tile-drained Midwestern soils. Agricultural Water Management. 288. Article e108481. https://doi.org/10.1016/j.agwat.2023.108481.
Malone, R.W., Radke, A.G., Herbstritt, S., Wu, H., Qi, Z., Emmett, B.D., Helmers, M., Schulte, L., Feyereisen, G.W., O'Brien, P.L., Kovar, J.L., Rogovska, N.P., Kladivko, E.J., Thorp, K.R., Kaspar, T., Jaynes, D.B., Karlen, D., Richard, T. 2023. Harvested winter rye energy cover crop: multiple benefits for North Central US. Environmental Research Letters. 18(7). https://doi.org/10.1088/1748-9326/acd708.
Bambach, N., Knipper, K.R., McElrone, A.J., Nocco, M., Torres-Rua, A., Kustas, W.P., Anderson, M.C., Castro, S., Edwards, E., Duran-Gomez, M., Gal, A., Tolentino, P., Wright, I., Roby, M.C., Gao, F.N., Alfieri, J.G., Prueger, J.H., Hipps, L., Saa, S. 2023. The Tree-Crop Remote Sensing of Evapotranspiration Experiment (T-REX): A science-based path for sustainable water management and climate resilience. Bulletin of the American Meteorological Society. 105(1):E257-E284. https://doi.org/10.1175/BAMS-D-22-0118.1.
Liang, K., Qi, J., Zhang, X., Emmett, B.D., Johnson, J.M., Malone, R.W., Moglen, G.E., Venterea, R.T. 2023. Nitrous oxide emissions from multiple agroecosystems in the U.S. Corn Belt simulated using the modified SWAT-C model . Environmental Pollution. 337(2023). Article e122537. https://doi.org/10.1016/j.envpol.2023.122537.