Abstract
Volatilization may represent a major dissipation pathway for pesticides applied to soils or crops, and these losses may be modified by soil surface conditions or in the presence of plant residues. This paper investigates the effect of surface conditions on volatilization through experimental results. The two experiments consisted of volatilization flux measurements for 3days after an application of S-metolachlor together with benoxacor: one with two wind tunnels to compare the effect of the presence of crop residues on the soil on volatilization losses and another one at the field scale from bare soil without crop residues. Volatilization fluxes were large immediately after application (between 77 and 223ngm-2s-1 for S-metolachlor depending on experimental conditions), decreasing down to a few nanograms per square meter per second on the last day. Volatilization fluxes followed a diurnal cycle driven by environmental conditions. The losses found for both compounds were in accordance with their physicochemical properties. The crop residue on the soil surface modified soil surface conditions-primarily the soil water content essentially, the degradation of S-metolachlor, and the dynamics of volatilization loss.
Highlights
Reducing tillage intensity leads to significant and complex changes in the soil
Gravimetric soil water content measured on MM1 and MM3 was 0.15 and 0.21 g g−1 in the 0–0.05 m at the beginning of the experiment and decreased down to 0.06 and 0.17 g g−1 in the 0–0.02 m in T-MM1 and T-MM3, respectively, at the end of the experiment (Fig. 1b)
At 0.1 m depth, soil water content measured with time-domain reflectometer (TDR) sensors gave 0.131 and 0.233 g g−1 under TMM1 and T-MM3, respectively
Summary
Reducing tillage intensity leads to significant and complex changes in the soil. Physicochemical properties and biological activities are interrelated with each other and can affect the fate of applied pesticides (Alletto et al 2010). Wienhold and Gish (1994) observed a larger volatilization of alachlor and atrazine under conservation tillage but only until the first rainfall occurred (5 days after application) Following this rainfall, volatilization in conservation tillage was significantly reduced which could be explained by the transport of the pesticides from the plant residues to the soil. After 35 days, the cumulative volatilization loss accounted for 9 and 14 % of applied alachlor and 4 and 9 % of applied atrazine under conservation tillage and conventional tillage, respectively (Wienhold and Gish 1994) This later study showed a significant effect of pesticide formulation on volatilization. Starch-encapsulated alachlor was less volatile under conservation tillage than the commercial formulation, and a similar effect was measured for atrazine under both conservation tillage and conventional tillage systems
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