Abstract
This study focuses on the assessment of herbicide adsorption and degradation in three soils (Haplic Chernozem, Haplic Fluvisol, and Arenic Regozem) from different agricultural regions of the Czech Republic where sunflower is cultivated. Soil samples were used in laboratory batch adsorption and degradation experiments for six herbicides commonly used on sunflower crops. The findings are used to examine the effect of soil and herbicide properties on adsorption and degradation, as well as to determine the possible relationship between the two processes. The (Kf) sorption coefficient ranged from 1.07 to 135.37 cm3/nμg1−1/ng−1, and sorption increased in the following order: dimethenamid-p < pethoxamid < S-metolachlor < flurochloridone < aclonifen < pendimethalin. Adsorption of all six herbicides was positively correlated with soil organic matter content (p < 0.001), and cation exchange capacity (p < 0.001). pH was negatively correlated with the adsorption of all six compounds (p < 0.001). Degradation rates of herbicides ranged from 0. 012 to 0. 048 day−1, which corresponding to the half-lives (DT50) between 14 and 57 days, respectively. The highest half-life values were found in Haplic Fluvisol (a loam with higher organic matter content and lower pH). Results showed that both adsorption and degradation of herbicides are mainly controlled by soil organic matter. A negative relationship was found between the sorption coefficient and the rate of degradation. It can be concluded that the Freundlich sorption coefficient (Kf) can be a good predictor for the degradation of the studied herbicides.
Highlights
Soil adsorption and pesticide degradation are the main processes that assess the environmental quality effects of pesticide use (Quintero et al 2005)
The Kf values ranged from 1.07 to 135.37cm3/n μg1 − 1/n g− 1 and sorption of herbicides increased in the order dimethenamid-p < pethoxamid < s-metolachlor < flurochloridone < aclonifen < pendimethalin
The average pendimethalin half-life value was within the same range (24.4–34.4 days) as those calculated by Kočárek et al (2016) in a Haplic Chernozem soil under greenhouse conditions. These findings indicate that pendimethalin was rapidly degraded in the studied soils; the rate of dissipation was not related to the hydrophobicity and the degree of adsorption, even though the pendimethalin was strongly adsorbed by all three soils (Table 3)
Summary
Soil adsorption and pesticide degradation are the main processes that assess the environmental quality effects of pesticide use (Quintero et al 2005). Degradation is accompanied by complex processes involving a variety of interactions between soil and pesticide components (Rao et al 1983; Ainsworth et al 1993). Several factors, including pesticide physicochemical properties and soil properties (e.g. pH, OM, clay content, and soil texture) are responsible for controlling soil degradation processes (Walker et al 2001). Climate conditions such as soil water content and temperature, are another factor that influences the rate of degradation. The effect of temperature and soil moisture content on the degradation of herbicides has been extensively investigated (Vischetti et al 2002; Alletto et al 2006)
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