Crop-residue-derived char influences sorption, desorption and bioavailability of atrazine in soils

The bioavailability of pesticides in soils is affected by the addition of crop-residue-derived char, which alters the sorption and desorption characteristics of the soils. Sorption, desorption, and biodegradation experiments were performed using atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-l,3,5-triazine-2,4-diamine] as the target compound in two soils (Hartsells and Grady) with and without a wheat (Triticum aestivum L.) char, and the char alone. The sorption isotherms for both soils were highly linear, whereas the isotherms for 1% char-amended soils showed an increased sorption capacity and isotherm nonlinearity. The amount of atrazine sorbed by the char alone was 800 to 3800 times greater than sorbed by the soils. Successive desorption experiments showed that char-amended soils contained higher nondesorbable fractions of atrazine than soils without char amendment. Pseudomonas sp. strain ADP capable of rapidly mineralizing atrazine was used to evaluate atrazine bioavailability. The presence of char reduced [sup.14]C[O.sub.2] production by 11 and 20% in the char-amended soils and char, respectively. The two-step successive desorption experiments appeared to be able to predict the bioavailabilty of atrazine in char-amended soils. This study shows that the presence of char in soils significantly influences the sorption and desorption processes and, ultimately, the bioavailability of atrazine. Abbreviations: LSC, liquid scintillation counting; SOM, soil organic matter.