Journal of Hazardous Materials 231–232 (2012) 70–78 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials j our na l ho me p age: www.elsevier.com/locate/jhazmat Marked changes in herbicide sorption–desorption upon ageing of biochars in soil Sheridan M. Martin a , Rai S. Kookana a,c,∗ , Lukas Van Zwieten b , Evelyn Krull a a Sustainable Agriculture Flagship, CSIRO Land and Water, PMB 2, Glen Osmond 5064, Australia b NSW Department of Primary Industries, Wollongbar 2477, Australia c University of Adelaide, PMB 1, Glen Osmond 5064, Australia h i g h l i g h t s ◮ Fresh biochars undergo rapid ageing process with contact time in soil. ◮ Fresh biochars in soils exhibited high sorption and non-singular sorption–desorption isotherms. ◮ Aged biochars in soil showed sin- gular sorption–desorption isotherms for atrazine. ◮ At 10 t ha -1 , biochars in a Ferrosol lost their high sorption capacity in three years. ◮ Herbicide application rates may need to be frequently adjusted after biochar addition to soils. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 6 February 2012 Received in revised form 15 June 2012 Accepted 19 June 2012 Available online 26 June 2012 Keywords: Herbicide efficacy Aged biochar Sorption Desorption a b s t r a c t We studied the sorption–desorption behaviour of two herbicides (diuron and artrazine) in a soil rich in Fe and Al oxides (Ferrosol), either amended freshly with two different types of biochars or that contained biochars aged under field conditions. Standard batch sorption–desorption experiments were conducted on soil samples freshly amended with two biochars, (namely, poultry litter – PL and paper mill – PM sludge) as well on those collected from field 32 months after biochar application. Soils that were freshly amended with biochars @ 10 t ha -1 showed a two (PM) to five (PL) fold increase in sorption of herbicides as compared with that in the unamended soil. For example, the fresh amendments with PL biochar at 10 t ha -1 led to a highly significant (P < 0.001) increase in the Freundlich sorption coefficient (K f ) of atrazine; i.e. 20.71 (n = 0.40) as compared with 4.02 (n = 0.70) for the control soil. Sorption was reversible in the unamended soil but sorption–desorption hysteresis was prominent in the soil amended with fresh biochars. In contrast, the soil containing aged biochars (at 10 t ha -1 ) exhibited sorption–desorption properties that were statistically similar to that of the control soil, especially for atrazine. Ageing of biochars in the soil over a 32 months period reduced the sorption capacity by 47% (PM) to 68% (PL) for diuron. These findings may have implications for herbicide efficacy in biochar amended soils. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction The amendment of biochar to soil, especially farmland, is advo- cated both as an important means of sequestering carbon, and also to improve soil fertility [1,2]. In many instances, biochar has ∗ Corresponding author. Tel.: +61 8 8303 8450; fax: +61 8 8303 8565. E-mail address: Rai.Kookana@csiro.au (R.S. Kookana). been found to possess a high affinity for organic pollutants. For example, Yang and Sheng [3] reported that the level of diuron adsorbed by wheat char/ash (produced by burning in an open field) was 400–2500 times greater than that of a silty loam soil (2.1% organic carbon – OC). Biochar has been shown to be an effective sorbent for several herbicides including acetochlor, atrazine, ame- tryn, benzonitrile, diuron and simazine [4–6]. The highly sorptive nature of biochar can be either beneficial or problematic depend- ing on how the material is utilized. In the case of its agronomic 0304-3894/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2012.06.040