Transport of Anions and Herbicides in a Loamy and a Sandy Field Soil

Abstract

A field experiment was conducted to investigate preferential transport of herbicides and to explore processes that cause rapid movement. Bromide, chloride, and three herbicides (triasulfuron, atrazine, and terbuthylazine) with different mobility characteristics were applied to six 1.4 x 1.4 m field plots on a loamy and a sandy soil. At both sites, three of the plots were covered with a plastic roof 1 month before the beginning of the experiment to achieve different initial water contents between the plots. Two days before the beginning of the tracer experiment, crops were removed, and the soil surface was homogenized with a spade to a depth of 15-20 cm. One day after application of the chemicals the plots were irrigated with a sprinkling apparatus. The cumulative amounts of infiltration until the time of sampling were 30, 60, and 90 mm within 1, 2, and 3 days, respectively. A trench was excavated, and soil cores were taken horizontally from a 1 x 1 m profile in a regular 0.1 x 0.1 m grid. The loamy and the sandy soil showed completely different transport patterns. In the loamy soil the bulk mass of herbicides remained in the top layer; however, considerable amounts of herbicides were transported below the root zone. A few percent for triasulfuron and atrazine and <1% for terbuthylazine were detected below 0.5 m depth after 90-mm cumulative infiltration. Traces of all herbicides were found down to 0.9 m. The depth distributions for anions and all herbicides were similar. These results show that the herbicides were only partly adsorbed by the soil matrix. A fraction of these chemicals was transported with or without minor adsorption along cracks or fissures. In the sandy soil, chemical movement was confined to the top 0.4 m, and the penetration depth of the herbicides was consistent with their mobility characteristics: triasulfuron showed greatest mobility, atrazine was moderately mobile, and terbuthylazine was the least mobile of all three.

Threshold behaviour in hydrological systems as (human) geo-ecosystems: manifestations, controls, implications

“…These allow for, locally, up to 100-1000 times faster water fluxes than compared to matrix flow (Beven and Germann, 1982) because capillarity may be neglected in those structures and flow resistances in the direction of the driving potential gradient are much smaller. Flury et al (1994Flury et al ( , 1995 were among the first to develop effective methods to visualize infiltration and flow patterns in heterogeneous field soils by using dye tracer techniques. Today we know of numerous studies that have provided further evidence, demonstrating that that preferential flow in structured soils is indeed the rule rather than the exception (Fig.…”

Single and dual-permeability models of chlorotoluron transport in the soil profile

“…Kamra et al (2001) studied pesticides transport in small soil columns applying non-equilibrium two-region/mobile-immobile model. Flury et al (1995) investigated preferential flow in the field. In this study herbicide was only partly sorbed by the soil matrix.…”

Site S-7 VOC Transport modeling for the Vadose Zone Monitoring System (VZMS), McClellan AFB - 1999 Semi-Annual Report

“…First, the simpler single-continuum model seems inadequate to model the observed VOC concentration data, and second, the last decade of research has shown that, with a few exceptions (e.g., Wierenga, 1991;Hills et al, 1991), preferential flow is pervasive in the vadose zone (Kung, 1990a,b;Ghodrati and Jury, 1990;1992;Li and Ghodrati, 1994;Flury et al, 1994Flury et al, , 1995McCord et al, 1997).…”