Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/11/2002
Publication Date: 11/11/2002
Citation: WANG, D., SPOKAS, K., KOSKINEN, W.C. IMPROVED DETERMINATION OF SOIL PORTIONING OF AGRICULTURAL FUMIGANTS. ASA/CSSA/SSSA. 2003. CD-ROM. ABSTRACT NO. S11-WANG085109-POSTER. Interpretive Summary:
Technical Abstract: The sorption of agricultural fumigants onto soils is commonly accounted for through the use of a distribution coefficient (Kd). This factor relates the chemical adsorbed to the soil minerals per unit mass to the amount of chemical remaining in the solution in contact with the soil at equilibrium. The Kd values have been used extensively in the modeling of environmental transport of chemicals. There have been numerous laboratory procedures developed to measure the distribution coefficient; however, a majority of these methods rely on saturated (or solution conditions) that would not be realistic for vadose zone investigations. In addition, the microbial degradation of the compound can significantly impact the result, biasing the Kd factor higher. This is particularly important for soil fumigation studies. Incorrect distribution coefficients can lead to erroneous results for predictive transport modeling. Static and multiple extraction headspace methods have been modified to aid in the determination of the Kd factor for chloropicrin and methyl isothiocyanate at multiple levels of water saturation, while accounting for the effects of microbial degradation. The result of the preliminary investigations into this methodology have correlated with traditional batch studies for the determination of the Kd for the range of soils tested to date (r2 = 0.61). One of the major difficulties is to separate the microbial degradation from soil sorption mechanisms for mathematical modeling. The method presented here illustrates one potential mechanism by accounting for the degradation and soil sorption separately. Separation of these factors will improve the modeling of the fate and transport of agricultural fumigants.