2007 Annual Report
Development of near-infrared tools for analyzing the spatial distribution of soil properties at a field scale is continuing. Laboratory analyses of samples collected from 11 fields in central Iowa are complete. Preliminary statistical analysis of spectral data and the soil laboratory data has been completed.
Studies were designed and conducted to quantify the interaction between cation exchange selectivity and adsorption of an organic compound (dinitrobenzene) by clay minerals. Preliminary results suggest that organic molecules on clay surfaces influence the affinity of the clay for various cations and conversely the type of cation on the clay surfaces influences the affinity of the clay for organic molecules through a complex feed-back system. This research was conducted under subordinate project 3625-11120-003-06R.
Analytical tools for the analysis of amino acids, amino sugars, phenolic acids, and carbohydrates in soils are essential for meeting Objectives 1A and 1D. To strengthen their laboratory development, an exhaustive literature review was conducted to identify strengths and weaknesses of various proposed methods for analyses of these compounds. The literature review is being developed into a peer-reviewed publication. Potential improvements to the analytical methods for aminos and phenols were identified and are being evaluated in ongoing laboratory work. Collaborations were established with scientists who perform alternative analyses for amino acids and phenols, and soil samples will be jointly analyzed. One comparison of phenols analyses has been completed for a set of humic samples. The phenols analysis was installed at a Vietnamese university, where collaborating researchers are conducting field and greenhouse studies that conform to Subobjective 1D.
Work is continuing on development of electrical and thermal probes that can be used to analyze soil structure. Undisturbed soil samples were collected from a prairie and nearby soybean field. Soil electrical properties were analyzed using a refined twelve-wire insertion probe, and thermal properties were analyzed with a dual heat pulse probe. Soil structural properties related more to thermal properties than to electrical properties. Further soil sampling from other states is in progress, to expand to a broader range of soils.
Title: Interactions between nitroaromatic compounds and soil clay minerals. Problem addressed: Recent research has shown that nitroaromatic compounds are adsorbed on soil clays at much higher levels than anticipated, which suggests a lack of understanding of the mechanisms by which these compounds interact with clays. Accomplishment: Through a series of studies we have shown that 4, 6- dinitro-o-cresol (DNOC) is adsorbed on smectite clays as a complex with potassium ions and that this adsorption can occur at acidities (pHs) well above the dissociation constant (pKa) of DNOC, and primarily occurs on the outside surfaces of clay particles in aqueous suspensions. Due to the dynamic nature of clay particles, DNOC may become trapped inside of clay particles as a clay suspension dries. Impact: This research will help scientists to better understand how nirtoaromatic compounds are adsorbed on soil clays and thus to better predict fate of these compounds in soil environments. National Program 202: The research contributes to NP202 Problem Area 7, "Managing Pesticides in Soils."
ARS scientists coordinates the U.S. Chapter of the International Humic Substances Society. Members include university and government researchers, students, and private sector employees, mostly vendors of humic products.
Charles, S., Teppen, B.J., Hui, L., Laird, D.A., Boyd, S.A. 2006. Exchangeable Cation Hydration Properties Strongly Influence Soil Sorption of Nitroaromatic Compounds. Soil Science Society of America Journal. 70(5):1470-1479.
Li, H., Pereira, T., Teppen, B., Laird, D.A., Johnston, C.T., Boyd, S. 2007. Ionic Strength-Induced Formation of Smectite Quasicrystals Enhances Nitroaromatic Compound Sorption. Journal of Environmental Science and Technology. 41(4):1251-1256.
Laird, D.A. 2006. Influence of layer charge on swelling of smectites. Journal of Applied Clay Science. 34:74-87.
Pils, J., Laird, D.A., Evangelou, V.P. 2006. Role of cation demixing and quasicrystal formation and breakup on the stability of smectitic colloids. Journal of Applied Clay Science. 35:201-211.
Pils, J., Laird, D.A. 2007. Sorption of tetracycline and chlortetracycliine on K- and CA- saturated soil clays, humic substances, and clay-humic complexes. Environmental Science and Technology. 41(6):1928-1933.
Li, H., Teppen, B., Laird, D.A., Johnston, C., Boyd, S. 2006. Effects of Increasing Potassium Chloride and Calcium Chloride Ionic Strength on Pesticide Sorption by Potassium- and Calcium-smectite. Soil Science Society of America Journal. 70(6):1889-1895.
Logsdon, S.D. 2006. Uncertainty effects on electrical conductivity and permittivity spectra. Soil Science. 171:737-746.