Project : USDA ARS

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Research Project: Improved Management of Nutrients, Water, Agrochemicals, and Energy to Enhance Agriculture System Sustainability

Location: Soil, Water & Air Resources Research

2025 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, continuous field measurements of the meteorological condition including the surface fluxes of heat, moisture and carbon dioxide were collected via Eddy Covariance (EC) at the Long-Term Agroecosystem Research (LTAR) and AmeriFlux sites near Williams and Brooks, Iowa. These long-term measurements are being used to quantify water vapor and carbon dioxide exchanges over cropped fields under reduced tillage at the Williams site and conventional tillage at the Brooks site to understand the effect of tillage practice on the water cycle in the Upper Mississippi Basin. In support of Objective 1.1.2, researchers measured gaseous nitrogen loss under contrasting tillage and fertilizer treatments as a part of a 9-year study at the Upper Midwest River Basin LTAR site near Ames, Iowa. Sub-weekly gas samples were collected across the experimental plots to identify how “4R” nitrogen management (right time, right amount, right formulation and right placement) impacts system nitrogen losses and nitrogen use efficiency when compared with prevailing practices. To capture hot moments of enhanced nitrogen loss, researchers utilized an automatic chamber system coupled with a trace gas analyzer to compare two treatments with contrasting fertilizer and tillage regimes (chisel plow with spring applied anhydrous ammonia and no-till with 4R nitrogen management). High-temporal resolution data will better enable dentification of environmental and management drivers of nitrogen transformations and better support modeling efforts to evaluate management scenarios. Data analysis is ongoing. Data collection, including surface flux measurements, continued at multiple field sites in California as a part of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) along with a U.S.-Israel Binational Agricultural Research and Development (BARD)-funded site in Israel. Also, as a part of ongoing collaborations with ARS scientists in Beltsville, Maryland, a new vineyard site near Geneva, New York, was identified and instrumented to represent the cooler, wetter conditions often found in vineyards in the Eastern U.S. These data are being used to understand the physical processes controlling evaporative water loss, i.e. evapotranspiration (ET), in structured agricultural canopies, refine remote sensing-based models for monitoring ET, and develop improved irrigation management strategies. An intensive field campaign focusing on enhanced water loss due to advection, i.e. the transport of hot dry air across a cool moist surface, was carried out at the GRAPEX vineyard site near Fresno, California, during July 2024. Field activities included the collection of: a) surface flux measurements of heat, moisture, and carbon dioxide along an extended transect of eddy covariance towers; b) visible and near-infrared imagery of the site via fixed-wing unmanned aircraft (UAV); c) atmospheric profiles wind speed, temperature, and humidity at multiple locations via drones; and d) measurements of leaf area index and leaf-level gas exchange. Analyses of this data have already provided insights into the effects of advection on ET. For example, it shows that advection enhancement of ET accounts for as much as 40% of the water loss from the vineyards and this process begins much earlier in the day than expected. These results, along with development of novel wavelet-based method for characterizing intermittency, are the basis for a manuscript currently in preparation. In support of Objective 2, ammonia (NH3) and methane (CH4) open-path lasers and mirrors were deployed prior to the arrival of the animals at a finishing barn with no pit fans to monitor the continuous release of NH3 gas over an entire growth cycle from wean to finish. Room static pressure sensors are being installed at the facility to calculate ventilation rates. Efforts are being developed to determine what fraction of the NH3 gas is associated with manure in the deep-pit and what fraction is associated with gases from the barn floor surface. The nitrogen deposition research continues to be carried out at a swine facility in central Iowa. An air quality model is being used to determine NH3 deposition. Data collected include: 1) NH3 air concentration; 2) NH3 soil sorption; and 3) NH3 sorption onto surround vegetation. Preliminary data shows a decreasing soil nitrogen content for samples collected farther away from swine barns. Soil samples collected from surrounding locations just outside the barns exhibited more than two-fold higher values than samples taken further away from the barns. In support of Objective 3, a study was conducted to analyze the effects of tillage and winter cover crops on root-associated microbial communities, nutrient cycling capacity, and soil health. The researchers hypothesized that reduced tillage and winter cover crops alter the composition and succession of microbial communities and enhance soil aggregate stability through increased abundance of arbuscular mycorrhizal fungi (AMF), fungi that have a symbiotic relationship with the roots of plants. Initial findings indicate that the dominant AMF taxa were common among the cropping systems, and AMF colonization of the soybean root system remained consistent across treatments. The AMF community exhibited dynamism throughout the season and was influenced by management practices, with fungi within the Glomeraceae, Entrophosporaceae, and Ambiosporaceae families being enriched in non-tillage systems. The largest impact of the management system was evident in AMF biomass in the soil which was higher following a winter host cover crop and associated with higher aggregate stability, a key measure of soil health affecting infiltration and water retention in soil. Data analysis is ongoing.

Accomplishments
1. Microbial indicators of soil health in Midwestern agriculture. Microbial communities are a crucial component of soil health and drive productivity and sustainability of agricultural systems. Regional environmental factors and agricultural management practices shape soil microbial communities and their functions related to nutrient cycling, soil organic matter stabilization and aggregation, water conservation, and disease control. To understand the microbial response to agricultural management within a national context, 22 ARS scientists from 15 ARS locations across the U.S. collaborated in designing a study to identify the effects of environment, soil properties, and conservation practices on the structure (diversity and composition) and function (i.e., nutrient cycling capacity) of soil microbial communities and their relation to soil health. This study demonstrates the strong relationship of soil microbial communities to soil organic carbon which is particularly relevant to the high organic matter soils of the upper Midwest. Within this context, fungi emerge as particularly responsive to agricultural management and may be a key indicator for growers interested in improving soil health.

2. Improved nitrogen retention in corn-soybean cropping systems. Nitrous oxide loses from agricultural systems are an environmental concern and the focus for reducing these loses has mainly been on improving nitrogen fertilizer management. Legumes such as soybean are often neglected in these management schemes because they do not receive nitrogen fertilizer and are assumed to contribute little to nitrous oxide production and therefore offer little opportunity to reduce nitrogen losses. University researchers and ARS collaborators have shown that this assumption to be incorrect. Approximately 40% of nitrous oxide loss from corn-soybean rotations are attributable to the soybean phase of the system. These researchers developed a systems approach that combines cover crops and earlier planting of soybean varieties with a longer growing season to reduce nitrous oxide losses from soybean production by 30%. These practices complement nitrogen fertilizer management in corn and are widely accessible to farmers. Therefore, the proposed management changes represent an immediate and unique opportunity to reduce the environmental impact of soybean production while increasing soybean yields, which is important to producers, scientists, crop advisers, and policy makers.

3. Minimizing carcass decomposition and gas emissions. Outbreaks of infectious diseases involving depopulation of animals require on-farm practices to stage carcasses when final disposal methods are unavailable. Techniques need to slow decomposition and limit scavenger activity to reduce spread of diseases. ARS researchers in Ames, Iowa, in collaboration with scientists from Digital Agronomy, LLC and Iowa State University, compared how stagging techniques affect decomposition and gas losses from decaying animals. Covering or containing carcasses in tarp material reduced air exchange and decomposition rates by 40 and 90%, respectively; corn stover material desiccated and reduced decomposition rates by 50%, while covering carcasses with soil or lime did not affect decomposition. No treatment effectively reduced gas fluxes of dimethyl disulfide a major chemical attractant for scavengers. These findings highlight the need for integrated management strategies that reduce carcass decomposition and increase biosecurity around carcasses. Information from this research will be of value to researchers, growers, and veterinarians working with livestock during an animal health emergency.

4. Management practices have contrasting impacts on leaching of essential nutrients. Nutrient losses from agricultural systems represent economic costs to growers and negatively impact downstream communities. As part of the Long-Term Agroecosystem Research Network (LTAR) team, ARS scientists in Ames, Iowa, demonstrated drivers of soil nutrient loss in tile drainage from a corn-soybean rotations varied with conservation practices and the nutrient of interest. Importantly, nitrate loss in tile drainage did not decrease in plots that received no nitrogen application in over 10 years when compared with plots fertilized at recommended rates, despite greatly reduced crop yields. In contrast, winter cover crops and wood chip bioreactors reduced nitrogen leaching by nearly 60%. These results suggest that soil organic matter mineralization during the fall and early spring, when cash crops are not growing in the field, is the major source of nitrogen loss in highly productive midwestern Mollisols. As a result, reducing nitrogen fertilization beyond economically optimum fertilizer rates may not contribute to reductions in nitrate leaching in these soils. These findings support the revised Iowa Nutrient Reduction Strategy, which no longer recommends reducing nitrogen fertilizer rates as a best management practice to decrease nitrogen leaching losses, thus providing growers with better science-based recommendations for nutrient management.

5. Monitoring agroecosystem response using phenocam imagery. Agroecosystems, such as croplands and grazing lands, are subject to constantly changing management practices, vegetation composition, and weather conditions. Understanding how agroecosystems respond to these changes is critical to developing methods that ensure sustainability while increasing the productivity and profitability of American agriculture. To address this need, ARS scientists at multiple Long-Term Agroecosystem Research Network (LTAR) locations, along with university collaborators, determined a simple and inexpensive approach using phenocam imagery, i.e. continuously collected digital images of the vegetation, to monitor water and carbon dynamics using the Green Chromatic Coordinate (GCC) vegetation index. While it was most effective for estimating gross primary productivity (GPP) in croplands, GCC was shown to be useful for estimating evaporative water loss and GPP across a range of agroecosystems. Therefore, GCC is a useful tool for developing and evaluating modeling systems and management techniques that will benefit producers, ranchers, crop advisers, scientists, and policy makers by simplifying irrigation, grazing, and other management decisions.

6. Identifying major chemical odorants associated with pumping of swine manure deep-pits. Odors released during the field application of swine manure are a leading air quality issue in rural communities. Currently, there are no standard practices to reduce odor generated during field manure application. ARS researchers in Ames, Iowa, in collaboration with scientists at Iowa State University, compared gas fluxes from manure before, during, and after agitation. Agitating manure increases the gas losses of all compounds, including odorous compounds. Volatile sulfur compounds (VSC) were 100 times higher during agitation, whereas ammonia and other volatile organic compounds (VOCs) increased only fourfold. Before agitation, 80% of the odor was associated with VOCs, but after agitation odor from VOCs dropped to less than 5%. Odor from VSC during agitation increased to over 90% of the total odor. Manure additives that oxidize, adjust pH, or use electrochemical techniques that react with VSC could be tools used to minimize odor during pumping of swine manure. The study gives growers and engineers targets to control and manage odor during manure application to fields.

U.S. DEPARTMENT OF AGRICULTURE

Soil, Water & Air Resources Research: Ames, IA