Project : USDA ARS

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Research Project: Reducing the Environmental Footprint from Agricultural Systems through Managing Resources and Nutrient Inputs

Location: Soil, Water & Air Resources Research

2019 Annual Report

Objectives
Objective 1: Characterize and improve accounting of N emissions as N2O and NH3 losses from cropping systems. Subobjective 1.1: Quantify the soil and environmental factors contributing to N2O production by nitrifying and denitrifying bacteria. Subobjective 1.2: Assess the effect of cover crops on N2O production in the field. Subobjective 1.3: Assess manure injection/incorporation methods for impact on residue/surface cover, soil disturbance, and N emissions. Objective 2: Enhance process-level characterization of agrochemical emissions, fate and transport across spatial scales from micro-environments to regions. Subobjective 2.1: Determine the effect tillage practices have on agrochemical volatilization losses from agricultural fields. Subobjective 2.2: Improve measurement and modeling approaches to describe agrochemical emissions and transport from agricultural operations. Subobjective 2.3: Determine the emission flux of NH3 and other gases from cattle feedlot surfaces using flux-gradient technique. Subobjective 2.4: Compare particulate plume data measured with LiDaR to conventional model (ex. AERMOD) predictions to assess model accuracy for both near facility and downwind transport. Subobjective 2.5: Develop an improved physics-based model on the dispersion of herbicide droplets from mechanical sprayers by incorporating ambient turbulence conditions, the turbulent kinetic energy generated by the motion of the sprayer, and atmospheric stability. Objective 3: Develop strategies to manage the effects of manure properties and air flow on NH3 emissions. Subobjective 3.1: Manipulate swine diet formulations to improve N utilization, and reduce N excretion and NH3 emission along with other gaseous emission into the environment. Subobjective 3.2: Evaluate and develop ventilation practices for reducing NH3 and other air quality emissions.

Approach
This project will focus on knowledge gaps that exist in the loss of N and agrochemicals from cropping and animal systems. Three approaches will be pursued for addressing knowledge gaps: 1) quantify soil and environmental factors contributing to N2O and NH3 emissions in animal production and field cropping systems; 2) determine soil properties that drive volatile loss and transport of agrochemicals and N compounds, and 3) determine effectiveness of N control strategies for reducing NH3 emissions. In cropping systems, there are large gaps in our understanding of the N budget in soil including both mechanisms and magnitude of losses through emissions. Laboratory studies on N2O emissions will use stable isotopes to quantify both the effect of temperature and kinetics of denitrification under varying NH3 concentrations. Field studies using chambers will be used to quantify N2O emission for a range of soil and nitrogen management strategies. Assessing the effect residue/surface cover and soil disturbance have on N loss from manure application in cropping systems will be conducted during late fall and early spring. Whole field emissions loss of N will be quantified using both an open path laser system coupled with inverse dispersion modeling for NH3 and eddy covariance with a quantum cascade laser system for N2O emissions. Quantifying the transport parameters controlling volatile losses of pesticides from cropping systems based on tillage practices will use eddy covariance micrometeorology techniques to determine turbulent flux from whole fields. The relaxed eddy accumulation technique will be used to provide more accurate eddy diffusivities for pesticide vapor transport to improve agrochemical volatilization flux estimates. In addition, LiDaR will be used to develop dispersion models for droplets from mechanical sprayers for physics-based models on the loss of agrochemicals from fields due to spray drift. Quantifying the transport parameters controlling volatile losses of N compounds and particulates from animal production systems will involve LiDaR- to measure plume dynamics and produce a remote-sensing approach to quantify emissions and compare these results to conventional modeling approaches. In animal production systems, NH3 is the dominant form of N emissions, but gaps exist in effective N control/mitigation strategies that reduce N emissions. Reducing NH3 emissions from animal production will focus on improving N utilization in animal diets by use of feed additives and improving grind size of feed particles. Ventilation practices will be evaluating and optimized for reducing NH3 emissions. Knowledge gained through this research will provide producers and regulatory agencies scientific data to improve sustainability of agricultural production facilities in U.S. farming systems.

Progress Report
Objective 1: Field monitoring study on experiments were conducted to quantify nitrous oxide production in response to temperature and soil water conditions. Nitrous oxide emissions were measured throughout the year and the temporal variability analyzed with respect to rainfall and diurnal soil temperature. It was found that nitrous oxide variability was largely explained by soil water content, but a significant portion of the variability in N2O emissions was driven by diurnal soil temperature patterns. Development of field protocol for measuring N loss through emissions from land applied manure was not completed due to a lack of available field sites. Only one field manure application was monitored. The wet/cold weather patterns in late fall and early spring made it challenging for coordination with manure haulers. Based on the limited data most of the NH3 was loss was within the first two days. Major limitation in nitrous oxide emissions is the ability to supply continuous AC power to the instrument. Objective 2: Relaxed Eddy Accumulation (REA) Pesticide volatilization (vapor transport) is a dominant vapor loss pathway for many pesticides. This pathway is variable and specific to pesticide type, chemical formulation, surface target characteristics (vegetation/soil) and local meteorological conditions. Turbulence is the primary transport mechanism for pesticide vapor from a surface to the atmosphere. A new and simplified pesticide volatilization measurement system (REA) has been developed and tested in a laboratory setting. This system will enable the simultaneous measurements of pesticide vapor with vertical wind motion common with turbulence. The system was ready for field deployment in June 2019 at the Optimizing Production Inputs for Economic and Environmental Enhancement (OPE3) site located in Beltsville, Maryland. A spray drift field experiment was delayed from the previous year to identify an anomaly of the laser system that was biasing plume quantification of spray droplets. This issue was resolved by researchers at the University of Iowa and we are on track to conduct a field experiment in July 2019 to measure spray drift from a standard spray applicator. A pilot test conducted previously showed drift plumes exceeding 15 -20 m above the soil surface and drift distance exceeding 50 -100 m. Characterization of particulate emissions from animal production facilities are inherently complicated due to the diversity of landscape features and facility structures that ultimately impact transport processes across spatial scales from micro-environments to regional. Previous campaigns have produced a large number of two-dimensional particulate plume images across different animal production facilities using a Light Detection and Ranging (LiDar) approach. Local meteorological data were also acquired at the same time to capture meteorologically driven transport processes that carry the particulates downwind and offsite. A review of past field campaign results conducted in 2019 suggest that transport processes often show a bimodal distribution involving Gaussian and non-Gaussian processes that are strongly influenced by local meteorological conditions. Discussions between ARS scientists and University of Iowa researchers were conducted to outline new analysis techniques to differentiate when Gaussian and non-Gaussian processes prevail. This will aid greatly in developing a more coherent understanding of emission transport from animal production facilities as a function of facility structures, local meteorology and turbulence transport. Objective 3: A monitoring study was started to compare indoor air quality at tunnel ventilated buildings compared to naturally ventilated buildings. In general, naturally ventilated barns had lower concentrations of particulate matter (PM), ammonia (NH3), and hydrogen sulfide (H2S) than tunnel ventilated barns. A PM, NH3 and carbon dioxide (CO2) concentration gradient along a transect in tunnel ventilated barns was observed with the highest concentrations at the exit. For tunnel ventilated barns, concentrations of NH3 and CO2 concentrations were inversely related to ventilation rate, which in turn was directly associated with outside temperatures. In future research, the impact of indoor air quality on animal performance is being added. A swine feeding trial was completed investigating the effect of diet particle size formulation on manure and gas emissions. Six diets were tested, three diets used different source material that included a standard corn soybean mill (CSBM) diet, and others with CSBM supplemented with 35% DDGS and CSBM supplemented with soyhull material. Each of these diets were fed as originally milled course ground (635 mm average particle size) or finely ground to reduced particle size (374 mm average particle size). Animals fed finely ground diets gained more with higher feed efficiencies. Animals fed different diet source material had significantly different manure pH, solids, N, C, and S with finer ground diets reducing nutrient excretion of solids, N, and C. Sulfur in manure was not impacted by diet grind size. Odorants in manure were significantly different between diets and finer ground diets generally had lower concentrations of odorants than coarsely ground diets. Gas emissions for the different diets were significantly different for NH3, VFAs, and phenol compounds. Courser ground diets tended to have greater crusting over manure storage surfaces thereby reducing gas emissions. Additional work will be conducted on swine diets to investigate the potential emissions during agitation and pumping of storage facilities.

Accomplishments
1. Soil water and temperature interdependence on temporal variability of N2O emissions. Water content and temperature exert strong controls on soil N2O emissions. Understanding these relationships will aid in development of more accurate predictive relationships for N2O emissions. ARS researchers in Ames, Iowa, monitored nitrous oxide emission from field applied fertilizer over a one-year period. It was determined that 2/3 of temporal N2O emission variability was driven by soil water content. However, daily diurnal patterns of N2O emissions were correlated to diurnal soil temperature patterns and accounted for 1/3 of N2O emission variability. It was also observed that temperature variability decreased with time. Information from this research will provide better guidance in developing predictive models for N2O emissions from agriculture.

2. Nitrate removal via denitrification in pore water through saturated riparian buffers (SRB). Nitrate in tile drain waters from agriculture degrade the quality of the water in watersheds in which they are located. ARS researchers in Ames, Iowa, in collaboration with an Iowa State University scientist monitored an edge-of-field nitrate removal practice using SRBs to maximize soil denitrification with the addition of carbon in carbon-limited environments. Temperature affected the SRB’s maximum denitrification potential which varied between buffers to varying degrees. The oldest SRB had the highest in situ denitrification rates, while the youngest SRB had the lowest rate indicating a potential riparian buffer age effect on denitrification beyond elevated carbon additions. It is thought that increased soil aggregation positively increases denitrifying microbial communities. Information from this research will enable farmers to better understand the proper design of SRBs.

3. Quantifying and mitigating particulate emissions from poultry building using a vegetative buffer. Quantifying particulate emissions from animal production facilities remains a challenging issue. The challenge is due to the complex and diverse array of production buildings that alter the mean wind flow and thus the transport of particulates. ARS scientists from Beltsville, Maryland, Florence, South Carolina and Ames, Iowa, in collaboration with a University of Delaware and a University of Iowa scientist conducted a field trial using Light Detection and Ranging (LiDaR) to determine the effectiveness of vegetative buffers. Particle emission was simulated using clay material that were released in front of an exhaust fan inside the tree barrier. Estimates of the efficiency of capture of particles were between 30-84%. Information from this study shows the effectiveness of vegetative buffers in mitigating particulate emissions.

4. Dietary sulfur (S) concentrations in swine diets effect on manure and odor emissions. Sulfur is a key nutrient in swine diets, and its levels are increasing as growers turn to cheaper feed ingredients. Excess S is potentially associated with both odor emissions and animal health. ARS researchers in Ames, Iowa, conducted a swine feeding trial to test the effect of dietary S on manure composition and gas emissions from finishing pigs. Increased S in the swine diet lowered manure pH but increased manure solids, nitrogen and S contents by 10% for each doubling of S content in the swine diet. Concentrations of sulfide in manure increase with increasing dietary S levels. Hydrogen sulfide emissions increased by 8% for each doubling of S content in the swine diet, while odor increased by only 2% with increased S levels in the swine diet. Information from this research will be useful for growers and engineers as they consider alternative feed ingredients and odor control.

5. Impact of dietary sulfur (S) source on gas and odor emissions. Swine growers are increasingly turning to alternative feed ingredients to lower production costs, but many of these cheaper sources have increased concentrations of S in both organic and inorganic forms. ARS researchers in Ames, Iowa, conducted a swine feeding trial to determine how the source of S in the diet affects manure properties and gas emissions. Diets tested include the following: standard corn soybean meal diet; standard diet enriched with inorganic S; diet with both inorganic and organic S; and a diet enriched with organic S. Diets with increased levels of organic S had significantly higher levels of ammonia, volatile fatty acids, and phenols in manure compared to animals fed standard diets. Hydrogen sulfide emissions were highest for swine diets with inorganic S additions, but emissions of volatile organic compounds and volatile sulfur compounds were highest in animals fed organic S diets. Manures of animals fed diets with increased organic S were determined to be the most odorous by human panels. Information from this research will be useful for growers and engineers as they consider alternative feed source impact on emissions.

6. Source tracking odor from swine finishing operation. ARS researchers in Ames, Iowa, conducted a study at a commercial swine deep-pit finishing operation to monitor odorous material emitted and transported offsite. Major odorous chemical classes included volatile sulfur compounds (VSC), volatile fatty acids (VFA), phenol and indole compounds. Manure storage was the main source of odorous compounds that were detected 1.5km downwind from the swine facility. Odorous compounds generated during agitation and pumping of the deep pits was the single most odorous event at the facility and was the dominant odorous compound. Odorants were mainly transported in the gas phase with less than 0.1% being associated with particulates/dust. This information will be of value to growers, engineers, and scientists developing odor mitigation practices and technologies as it assists in targeting the types of compounds responsible for odor and the main sources of those odorous compounds.

U.S. DEPARTMENT OF AGRICULTURE

Soil, Water & Air Resources Research: Ames, IA