Bioavailability of Atrazine in Char-Amended Soils.

Crop residue-derived char, a form of black carbon, influences the bioavailability of pesticides in the soil. Sorption, desorption and biodegradation experiments were performed using atrazine in two soils in the presence and absence of a wheat char with reference to the char itself. The sorption isotherms for the two soils were highly linear, suggesting that partitioning into organic matter was the primary sorptive mechanism. The isotherms for 1% char-amended soils showed an increased sorption capacity and nonlinearity. The 1% char amendment to both soils produced similar isotherms, indicating that the presence of a small amount of char may dominate the overall sorption. The amount of atrazine sorbed by char alone was 800 – 3800 times greater than those sorbed by the soil alone systems. Hysteresis effects were observed in soils and char-amended soils, but not in char. Multistep desorption experiments showed that the non-desorbable fractions varied with atrazine concentrations in soils and char-amended soils but not in char. Pseudomonas sp. strain ADP, capable of utilizing atrazine as its sole nitrogen source, was used in the biodegradation experiment. The presence of char reduced ¹⁴CO₂ production by 11% and 20% in the char amended soils and char, respectively. This study shows that the presence of char in soils affected the sorption and desorption processes and, ultimately, the bioavailability of atrazine.