Pre-emergence herbicides are frequently reported to be responsible of watercourses pollution because of their runoff on the treated fields. Terbuthylazine is a pre- emergence herbicide largely applied to control most annual broad-leaved weeds in maize. The study was aimed to assess the effect of an untreated strip located on the downhill field border on the mitigation of the runoff of the herbicide after its application. The study was carried out in 2007 on a sandy soil of the Po valley (Northern Italy), characterized by a slope of 0.5% in the direction of the field length, to favor removal of the waters in excess and runoff of those used for irrigation. Two adjoining plots of 2100 m2 (14 m x 150 m) each, both cultivated with maize were considered. One plot (Control), had no buffer strip, while the other was characterized by the presence of a 6 m wide strip located on the downhill field border. The plot with the buffer strip was divided in two sub-plots; one with the untreated buffer strip planted with maize (Maize Buffer) and the other with the untreated buffer strip planted with Italian ryegrass (Ryegrass Buffer). Terbuthy- lazine was applied at 750 g a.i./ha in pre-emergence with conventional farm equipment on the entire plot area, with the only exception of the buffer strips. Over the growing season both plots were subjected to a total of 380 mm of water out of which 220 provided by rainfall and the balance by 3 sprinkling irrigations. Concentrations of terbuthylazine and its main metabolite desethyl-terbuthy- lazine were assessed in runoff water, collected at the downstream head of the field border, and in soil samples (2 cm depth), collected both in the treated area and across transects 1m-spaced in the untreated strips. Determination of both chemicals in water and soil samples was performed by HPLC, adopting a methodology with a detection limit of 0.05 µg/L and 0.6 µg/kg, respectively. Highest concentrations of terbuthylazine and desethyl- terbuthylazine (136.18 and 43.55 µg/L, respectively) in runoff water were recorded in Control 23 days after treatment (DAT), immediately after a heavy rain. At that time the concentrations of terbuthylazine and desethyl- terbuthylazine assessed in runoff water collected from Maize Buffer were 0.94 and 1.13 µg/L, respectively and from Ryegrass Buffer 0.06 and 1.10 µg/L, respectively. Runoff samples collected 120 DAT from Control showed a content of 0.74 µg/L of terbuthylazine and 1.12 µg/L of its metabolite. Terbuthylazine concentrations in the soil of the untreated strips varied remarkably over the time from the herbicide application and through the strips.
Buffer strip effect on terbuthylazine runoff in light level soil
MILAN, MARCO;VIDOTTO, Francesco;TESIO, FRANCO;NEGRE, Michèle;PIANO, Serenella;FERRERO, Aldo
2008-01-01
Abstract
Pre-emergence herbicides are frequently reported to be responsible of watercourses pollution because of their runoff on the treated fields. Terbuthylazine is a pre- emergence herbicide largely applied to control most annual broad-leaved weeds in maize. The study was aimed to assess the effect of an untreated strip located on the downhill field border on the mitigation of the runoff of the herbicide after its application. The study was carried out in 2007 on a sandy soil of the Po valley (Northern Italy), characterized by a slope of 0.5% in the direction of the field length, to favor removal of the waters in excess and runoff of those used for irrigation. Two adjoining plots of 2100 m2 (14 m x 150 m) each, both cultivated with maize were considered. One plot (Control), had no buffer strip, while the other was characterized by the presence of a 6 m wide strip located on the downhill field border. The plot with the buffer strip was divided in two sub-plots; one with the untreated buffer strip planted with maize (Maize Buffer) and the other with the untreated buffer strip planted with Italian ryegrass (Ryegrass Buffer). Terbuthy- lazine was applied at 750 g a.i./ha in pre-emergence with conventional farm equipment on the entire plot area, with the only exception of the buffer strips. Over the growing season both plots were subjected to a total of 380 mm of water out of which 220 provided by rainfall and the balance by 3 sprinkling irrigations. Concentrations of terbuthylazine and its main metabolite desethyl-terbuthy- lazine were assessed in runoff water, collected at the downstream head of the field border, and in soil samples (2 cm depth), collected both in the treated area and across transects 1m-spaced in the untreated strips. Determination of both chemicals in water and soil samples was performed by HPLC, adopting a methodology with a detection limit of 0.05 µg/L and 0.6 µg/kg, respectively. Highest concentrations of terbuthylazine and desethyl- terbuthylazine (136.18 and 43.55 µg/L, respectively) in runoff water were recorded in Control 23 days after treatment (DAT), immediately after a heavy rain. At that time the concentrations of terbuthylazine and desethyl- terbuthylazine assessed in runoff water collected from Maize Buffer were 0.94 and 1.13 µg/L, respectively and from Ryegrass Buffer 0.06 and 1.10 µg/L, respectively. Runoff samples collected 120 DAT from Control showed a content of 0.74 µg/L of terbuthylazine and 1.12 µg/L of its metabolite. Terbuthylazine concentrations in the soil of the untreated strips varied remarkably over the time from the herbicide application and through the strips.
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