Effects of crop residue derived char on the bioavailability of sorbed atrazine.
Vijay.A. Loganathan1, Yucheng Feng1, Guangyao Sheng2, and T.Prabhakar Clement1. (1) Auburn University, Auburn, AL 36849, (2) University of Arkansas, Fayettville, AR 72704
The bioavailability of pesticides in soils is influenced by the addition of crop residue derived char since it alters the sorption and desorption characteristics of the soils. Desorption and bioavailability assays were performed using two soils (Hartsells and Grady), wheat (Triticum aestivum L.) char, and soils amended with 1% of wheat char. Pseudomonas sp. strain ADP, capable of utilizing atrazine as its sole nitrogen source, was used in the bioavailability assay. The extents of atrazine mineralization in char-amended soils and char were 11% and 20% lower than in soils, respectively. A sequential desorption biodegradation and mineralization (DBM) model was used to assess the bioavailability of sorbed atrazine in the soil systems. The model results show sorbed phase bioavailability in soils and in soil-amended char systems, but not in char system. In char system, the desorption rate constant was found to be higher than the mineralization rate constant and hence mineralization of atrazine was not limited by desorption. The multi-step desorption kinetics and desorption equilibrium experiments showed that the site fractions were concentration dependent. Hence, a dynamic DBM model which accounted for the variation in site fractions as a function of atrazine concentration was developed. The results of the dynamic DBM model supports that sorbed phase atrazine was not utilized in char alone slurries. Furthermore, the results indicate that degraded atrazine occurred at equilibrium and non-equilibrium sites, but not at the non-desorption sites. The study clearly shows that the presence of char in soil affects both sorption and desorption processes, and hence influence the bioavailability of atrazine.