Preferential Flow Pathways and Their Capacity to Transport Isoproturon in a Structured Clay Soil

Abstract

A field experiment was established to monitor preferential flow pathways and their capacity to transport isoproturon in a heavy clay soil. A hydrologically defined plot of 600 m2 at a field site on the Oxford University Farm at Wytham was created with integral flow monitoring and sampling devices. Data are presented from two flow events which occurred in April and May 1994. The highest concentrations of isoproturon (130 pg litre-') were observed in the drainage system. The vast majority of the 0.7% of applied pesticide that left the plot was via the drainage system (75-90%) with lateral subsurface flow accounting for a smaller proportion (max 23%). Whilst high pesticide concentrations could be found in overland-flow water, the volumes of water moved by this route were small (max 3%). Less water was estimated to have left the field in response to rainfall than in the previous year. This was attributed to decay of the mole drain system. Consequently the amount of applied pesticide lost in runoff (0.7%) was less than that estimated for the first year (1.5%). The work has shown that, even when a farmer follows best practice in the application of a herbicide to a winter cereal in a drained clay field, high concentrations of the herbicide (relative to the EC drinking water limit) will contaminate surrounding watercourses.

A field study to assess the degradation and transport of diuron and its metabolites in a calcareous soil

“…Several previous studies have observed preferential flow mechanisms operating in soils (Harris et al, 1994;Johnson et al, 1996) and this is appears to be occurring at this site. Rainfall data (Figure 4) shows heavy precipitation in the days just before the major pulse of diuron and its metabolites migrate more rapidly through the soil after 36 days.…”

Predicting rapid herbicide leaching to surface waters from an artificially drained headwater catchment using a one dimensional two-domain model coupled with a simple groundwater model

“…most clay soils in the UK) frequently experience problems because pesticides can be transported via preferential flow pathways to field drains (e.g. Gärdenäs et al, 2006;Haria et al, 1994;Harris and Catt, 1999;Harris et al, 1994;Jarvis, 2007;Johnson et al, 1996;Köhne et al, 2009;Larsson and Jarvis, 1999). One example is provided by the Upper Cherwell catchment (1°14′W, 52°12′ N; area 176 km 2 : May et al, 2001) which is a tributary of the River Thames (Fig.…”

“…Other investigations have been concerned with individual small plots which contain one or two tile drains; monitoring usually includes the quantity and quality of outflows from tile drains due to pesticide leaching. In one field study (Johnson et al, 1996), isoproturon was applied to a tile-drained field of winter wheat, the first drain flow following pesticide application reached a maximum discharge within 3 h and the maximum pesticide concentration occurred 30 min later. Further examples of detailed field investigations are presented by Richard and Steerhuis (1988), Haria et al (1994), McVoy et al (1995), Harris and Catt (1999), Villholth et al (2000), Gerke and Köhne (2004), Gärdenäs et al (2006) and Stone and Wilson (2006); apart from the investigation of Gärdenäs et al (2006), the studies relate to areas of less than 1 ha with ground slopes less than 3%.…”

Micro‐Trench Experiments on Interflow and Lateral Pesticide Transport in a Sloped Soil in Northern Thailand

“…We know little about the mechanisms of lateral pesticide transport. Johnson et al (1996) studied the relative importance of surface‐, lateral subsurface‐, and drainage transport of isoproturon [3‐(4‐isopropylphenyl)‐1,1‐dimethyluree] in a moderately sloped clay soil in Oxford, UK, during two major rain events. They stated that 23% of a total recovery of 0.7% of mass was transported with lateral subsurface flow.…”