Spatial variability of atrazine dissipation in an allophanic soil

Abstract

The small-scale variability (0.5 m) of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) concentrations and soil water contents in a volcanic silt loam soil (Haplic Andosol, FAO system) was studied in an area of 0.1 ha. Descriptive and spatial statistics were used to analyse the data. On average we recovered 102% of the applied atrazine 2 h after the herbicide application (CV = 35%). An increase in the CV of the concentrations with depth could be ascribed to a combination of extrinsic and intrinsic factors. Both variables, atrazine concentrations and soil water content, showed a high horizontal variability. The semivariograms of the atrazine concentrations exhibited the pure nugget effect, no pattern could be determined along the 15.5-m long transects on any of the seven sampling days over a 55-day period. Soil water content had a weak spatial autocorrelation with a range of 6-10 m. The dissipation of atrazine analysed using a high vertical sampling resolution of 0.02 m to 0.2 m showed that 70% of the applied atrazine persisted in the upper 0.02-m layer of the soil for 12 days. After 55 days and 410 mm of rainfall the centre of the pesticide mass was still at a soil depth of 0.021 m. The special characteristics of the soil (high organic carbon content, allophanic clay) had a strong influence on atrazine sorption and mobility. The mass recovery after 55 days was low. The laboratory degradation rate for atrazine, determined in a complementary incubation study and corrected for the actual field temperature using the Arrhenius equation, only accounted for about 35% of the losses that occurred in the field. Results suggest field degradation rates to be more changeable in time and much faster than under controlled conditions. Preferential flow is discussed as a component of the field transport process.

Modeling the effect of rainfall intermittency on the variability of solute persistence at the soil surface

“…This can be seen by the decline in the coefficient of variation at smaller values ofC x (see Figure 2). Therefore, in some cases where multirate dissipation is observed the random fluctuations of dissipation due to rainfall variability [Müller et al, 2003b] might not have had sufficient time under experimental conditions to reflect the mean dissipation behavior. The implication of this is that estimates of DT 50 and DT 90 from a single experiment may significantly overestimate or underestimate the climate mean dissipation rate.…”

“…[8] Dissipation under field conditions tends to be faster than what is observed in the laboratory because of the combined impact of all loss processes [Sparks, 1989;Lennartz et al, 1997;Boesten, 2000;Racke, 2003;Müller et al, 2003b;Renaud et al, 2004]. As a first approximation, pesticides are assumed to undergo first-order degradation; that is, they decrease in concentration exponentially with time.…”

“…Modeling studies have demonstrated that a variable boundary condition has a significant impact on solute leaching close to the soil surface [Jury and Gruber, 1989;Foussereau et al, 2001]. However, only a few experimental studies have measured the variability of dissipation [Müller et al, 2003b]. One reason may be that chemical dissipation is often measured over decimeters, the plough layer for example.…”

Effects of physicochemical soil properties of five agricultural soils on herbicide soil adsorption and leaching

“…Thus, the incorporation of organic soil amendments increase the adsorption of some pesticides, decreasing leaching and increasing persistence. Nevertheless, as pluviometry is varied through simulated rain, persistence is modified, but not leaching, which indicates that adsorption itself could be a better signal of the deep movement of a pesticide compared with other processes, such as degradation (FouqueBrouard and Fournier, 1996;Muller et al, 2003;Alister et al, 2005;Kogan et al, 2007).…”

Predictivity Strength of the Spatial Variability of Phenanthrene Sorption Across Two Sandy Loam Fields

“…It is commonly agreed that their concentration tends to show a large horizontal variability (Muller et al 2003) along with soil physical and chemical properties (Nielsen et al 1973). However, there is still insufficient knowledge about PAH retention rates with horizontal spatial heterogeneity.…”