As soils represent a major sink for most pesticides, factors influencing pesticide degradation are essential in identifying their potential environmental risk. Desorption of C-14-azoxystrobin was investigated over time in two soils under sterile and non-sterile conditions using exhaustive (solvent) and non-exhaustive (aqueous) methods. Desorption data were fitted to a two-compartment model, differentiating between fast and slow desorbing fractions. With increased ageing, rapid desorption (F-rap) (bioaccessibility) decreased with corresponding increases in slowly desorbing fractions (F-slow). The rapid desorption rate constant (k(fast)) was not affected by ageing, sterility or extraction solvent. The non-exhaustive extractions had similar desorption profiles; whereas exhaustive extractions in aged soils had the highest Frap. In non-sterile soil, F-rap was lower resulting in higher F-slow, while desorption rates remained unaffected. Organic matter (OM) reduces Frap; but not desorption rates. Microorganisms and OM enhanced ageing effects, reducing the fraction of fast desorbing chemicals and potentially the bioaccessibility of pesticides in soil. (C) 2014 Elsevier B.V. All rights reserved.