Abstract
ABSTRACT The application of sewage sludge (SS) in agriculture is a practice used worldwide, and it is commonly applied in sugarcane to supply nutrients, with beneficial effects on crop productivity and soil; but SS can increase sorption and decrease desorption of herbicides. However, in tropical soils such as in Brazil, there are no studies regarding the behavior of pre-emergent herbicides, mainly aminocyclopyrachlor and mesotrione, in SS-amended soil. The aim of the present study was to determine the effect of municipal SS applied in agriculture on the sorption–desorption of aminocyclopyrachlor and mesotrione in clay soil. Aminocyclopyrachlor (pyrimidine-2-14C-aminocyclopyrachlor) and mesotrione (cyclohexane-2-14C-mesotrione) sorption–desorption was evaluated using a batch equilibrium method. Soil was amended at 0% (control – unamended), 0.1%, 1%, and 10% (w∙w–1) of air-dried SS corresponding to 1.2, 12, and 120 t∙ha–1. The Freundlich Kf sorption values of aminocyclopyrachlor and mesotrione were similar for all treatments, ranging from 1.07 to 1.45 and 3.48 to 4.25 µmol (1–1/n) L1/n∙kg–1, respectively. Overall, the lowest Kd sorption value of these herbicides was reported for SS-amended soil (1%), while in the SS-amended soil (10%) it was higher than unamended soil. The H value for aminocyclopyrachlor was ~1 (no hysteresis) and for mesotrione was on average 0.4 (hysteresis occurring). In conclusion, the present study indicates that SS applied in any crop to supply nutrients can slightly affect the sorption–desorption of aminocyclopyrachlor and mesotrione, but this small difference does not affect the bioavailability of these herbicides for weed control.
Highlights
The application of municipal sewage sludge (SS) in agriculture is a practice used worldwide, with beneficial effects on crop productivity, such as in sugarcane in Brazil (Franco et al 2010)
In order to ensure that the SS does not pose any danger to the environment, the Conselho Nacional do Meio Ambiente – CONAMA (2006) legislation regulated by resolution N.375/06 was created in Brazil, together with Companhia de Tecnologia de Saneamento Ambiental – CETESB (1999) regulated by rule P4.230 in São Paulo State, to regulate the agricultural use of SS on soil
In all cases the isotherms are linear with a slope value (1/n) of ~1 for aminocyclopyrachlor, according to Francisco et al (2017) and Oliveira Jr. et al (2011), and ranging from 0.92 to 0.94 for mesotrione, according to Mendes et al (2016), resembling the C-type curve described by Giles et al (1960)
Summary
The application of municipal sewage sludge (SS) in agriculture is a practice used worldwide, with beneficial effects on crop productivity, such as in sugarcane in Brazil (Franco et al 2010). In order to ensure that the SS does not pose any danger to the environment, the Conselho Nacional do Meio Ambiente – CONAMA (2006) legislation regulated by resolution N.375/06 was created in Brazil, together with Companhia de Tecnologia de Saneamento Ambiental – CETESB (1999) regulated by rule P4.230 in São Paulo State, to regulate the agricultural use of SS on soil. The application of SS to soil can increase sorption and decrease desorption of herbicides, depending on both the organic amendments and herbicide properties (Pinna et al 2009). Sorption and desorption are important processes as they regulate the leaching of an herbicide in soil. Chemical and biological processes, sorption to organic matters is one of the dominant processes determining the fate of herbicides in the environment (Cheng 1990)
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