Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2006
Publication Date: 4/15/2006
Citation: Yates, S.R. 2006. Measuring herbicide volatilization from bare soil. Environmental Science and Technology. 40(10):3223-3228 Interpretive Summary: Several monitoring studies have shown that agricultural use of pesticides can contaminate air and water resources. Past research has shown that pesticide movement in soils is affected by many interrelated factors such as the pesticide application methods, soil and environmental conditions, and water management practices. A field experiment was conducted to measure the volatilization rate of triallate after application to a bare soil. The purpose of this experiment was to obtain information needed to provide a better understanding of the soil and environmental conditions that affect and control the surface volatilization rate in semi-arid agricultural regions. To achieve this, the volatilization rate, the soil triallate distribution and other environmental conditions were obtained. Even though triallate has a low vapor pressure, the total volatilization losses were approximately 20-25% of the applied mass.
Technical Abstract: A field experiment was conducted to measure surface dissipation and volatilization of the herbicide triallate after application to bare soil. The volatilization rate was measured using several methods including micrometeorological, chamber and soil-loss methods. Environmental conditions were measured to relate the physical conditions in the field to pesticide behavior. The volatilization rate was measured continuously for 6.5 days and daily peak values for the integrated horizontal flux method were from 32.4 (day 5) and 235.2 g ha-1 d-1 (day 1), for the theoretical profile shape method were from 31.5 and 213.0 g ha-1 d-1, and for the flux chamber were from 15.7 to 47.8 g ha-1 d-1. The target application rate was 11.5 kg/ha (i.e., 3.35kg/0.292ha). Soil samples were taken within 30 min after application and the measured mass of triallate was 8.75 kg ha-1, somewhat less than the target application rate. This was probably caused by inaccuracies in the reported target application rate, chemical drift during application, material applied outside the circular plot area, volatilization and any material remaining in the spray equipment. The measured triallate soil concentration was used as the initial condition, since this measurement coincided with the start of the volatilization measurements. The measured triallate mass in the soil at the end of the experiment was 6.81 kg ha-1 based on soil cores taken to 12 cm depth. The triallate dissipation rate, obtained by soil sampling, was approximately 400 g ha-1 d-1 and the average rate of volatilization was 361 g ha-1 d-1. Soil sampling at the end of the experiment showed that approximately 22% (0.565kg/2.56kg) of the triallate mass was lost from the soil. Significant volatilization of triallate is possible when applied directly to the soil surface without incorporation.