Figure1. Gas sampling equipment used during the study.
Little information is currently available concerning odor emissions following land application of beef cattle manure. This study was conducted to measure the effects of diet, tillage, and time following land application of beef cattle manure on the emission of volatile organic compounds (VOC).
Each of the experimental treatments which included tillage (broadcast or disked) and diet (0, 10, or 30% wet distillers grain (WDGS)) were replicated twice. A 5-m tandem finishing disc was used to incorporate the manure to a depth of approximately 8 cm. Small plots (0.75 m x 2.0 m) were constructed using 20 cm-wide sheet metal frames. A flux chamber was used to obtain air samples within the small plots at 0, 1, 2, 6, and 23 hours following manure application. The flux of fifteen VOC including fatty acids, aromatic compounds, and sulfur containing compounds were measured. Based on odor threshold, isolavleric acid, butyric acid, and 4-methylphenol provided 28.9%, 18.0%, and 17.7%, respectively, of the total measured odor activity. Heptanic acid, acetic acid, skatole, 4-methyphenol, and phenol each contributed less than 1% of the total odor activity. Dimethy disulfide (DMDS) and dimethyl trisulfide were the only measured constituents that were significantly influenced by diet.
DMDS values were significantly greater for the manure derived from the 30% WDGS diet than the other manure sources. No significant differences in DMDS values were found for manure derived from diets containing 0% and 10% WDGS. Tillage did not significantly affect any of the measured VOC compounds. Each of the VOC was significantly influenced by the length of time that had expired following land application. In general, the smallest VOC measurements were obtained at the 23 hour sampling interval. Diet, tillage, and time following application should each be considered when estimating VOC emissions following land application of beef cattle manure.
Why Study Factors Affecting Manure Application Odors?
Measure the effects of diet, tillage and soil moisture on odor emissions follow land applied beef manure.
Figure 2. Relative contribution of odorant to the total odor activity.
What Did We Do?
Twelve plots were established across a hill slope. Treatments were tillage (broadcast or disked) and diet (0%, 10%, or 30% WDGS). Beef manure was applied at 151 kg N ha-1 yr-1. Gas samples were collected using small wind tunnels and analyzed using a TD-GC-MS. (Fig. 1). VOC samples were collected at 0, 1, 2, 6, and 23 hours following manure application. A single application of water was applied and the gas measurement procedure was repeated. The effects of tillage, diet, test interval, and the sample collection time on VOC measurements were determined using ANOVA (SAS Institute, 2011).
What Have We Learned?
Isovaleric acid, butyric acid, and 4-methylphenol accounted for 28.9%, 18.0%, and 17.7%, respectively of the total odor activity (Fig. 2). Dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) emissions were significantly increased by the 30 % WDGS diet. The flux increase for DMDS was over 4 times greater for the 30% WDGS diets. Tillage did not significantly affect any of the measured VOC compounds. The largest propionic, isobutric, butyric, isovaleric, and valeric acid measurements occurred with no-tillage under dry condition (Fig. 3A-E). Generally, measured values for these constituents were significantly greater at the 0, 1, 2, and 6 hour sampling intervals than at the 23 hour interval (Fig. 3A-E). The larger emissions for no-till, dry conditions may be due to the drying effect resulting when the manure was broadcast on the surface. As the manure begins to dry, the water soluble VOCs are released from solution. The tilled and wet conditions would reduce its release of VOC due to the increased moisture conditions.
Figure 3. Flux values for propionic, isobutyric, butyric, isovaleric , valeric acid and indole as affected by tillage, soil moisture, and time.
Additional studies are planned to quantify the moisture and temperature effect on odorous emissions.
Bryan L. Woodbury, Research Agricultural Engineer, USDA-ARS, firstname.lastname@example.org
John E. Gilley, Research Agricultural Engineer, USDA-ARS;
David B. Parker, Professor and Director, Commercial Core Laboratory, West Texas A&M University;
David B. Marx, Professor Statistics, University of Nebraska-Lincoln;
Roger A. Eigenberg, Research Agricultural Engineer, USDA-ARS
We would like to thank Todd Boman, Sue Wise, Charlie Hinds and Zach Wacker for their invaluable help on making this project a success.
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