Particle‐facilitated Pesticide Leaching from Differently Structured Soil Monoliths

Abstract

The leaching of soil particles and surface applied 14C-labeled glyphosate and pendimethalin from intact soil columns (height: 50 cm; diameter: 30 cm) were investigated, and the relative significance of particle-facilitated pesticide transport was quantified. Investigations were performed with a recently plowed (four columns) and an untilled (five columns) sandy loam soil. Leaching was driven by three irrigation events (15 mm h(-1); 2 h each). Samples of the leachate were filtered immediately (within 1.5 minutes) using 20 nm filters, and the 14C-pesticide content was determined for filtered and unfiltered samples. Pesticide leaching was driven by preferential water flow in macropores. For the plowed structure, 68+/-10% of the leached glyphosate (average of 6 events+/-std.) was bound to particles whereas significantly less glyphosate was bound to particles in leachate from minimally disturbed columns (17+/-12%). Thus, the results suggest that soil structure affected the mode of transport of glyphosate. It is likely that glyphosate sorbed strongly when applied on recently plowed soil (Kd=503 L kg(-1) for the soil), and that it could be mobilized and transported independently of soil particles more easily when applied on the minimally disturbed soil covered in part with crop residues (Kd<1 L kg(-1) for straw). Significantly less amounts of soil particles were leached from minimally disturbed (119-247 mg) than from recently plowed (441-731 mg) columns. The significance of particle-facilitated pendimethalin leaching could not be accurately quantified due to disagreement between control measurements based on both 14C-activity and chemical analyses.

Adsorption and mobility of glyphosate in different soils under no-till and conventional tillage

“…Leaching in field conditions have been reported before (Kjaer et al, 2011;Gjettermann et al, 2009). After glyphosate application in the field, the presence of the herbicide is limited to the surface layer of the soil, favoring the association between soil particles.…”

“…Gjettermann et al (2009) had a maximum recovery in the leached samples of 0.32% from the initially applied glyphosate. They found that 68% of the leached glyphosate was bound to the soil particles (N20 nm), suggesting that particle-facilitated transport is an important process involved in glyphosate transport.…”

“…Soil structure is an important factor influencing glyphosate transport (Aronsson et al, 2011;Gjettermann et al, 2009). Several laboratory and lysimeter studies have indicated that glyphosate may be transported by preferential flow in structured soils (Vereecken, 2005).…”

“…Vertical transport has also been studied in laboratory conditions using undisturbed or repacked soil columns (e.g. de Jonge et al, 2000;Dousset et al, 2004;Strange-Hansen et al, 2004;Barrett and McBride, 2006;Gjettermann et al, 2009Gjettermann et al, , 2011. The results from the studies are variable and depend on the selected experimental conditions, such as input flow, herbicide concentration, time duration and the type of soil studied.…”

Effects of Soil Compaction and Organic Carbon Content on Preferential Flow in Loamy Field Soils

“…6 and Table 2 lead to the conclusion that preferential flow was more pronounced at the Silstrup site, leading to higher susceptibility to leaching of agrochemicals and colloids (Norgaard et al, 2012). As demonstrated in numerous studies (e.g., Petersen et al, 1997;Gjettermann et al, 2009;Ersahin et al, 2002), pore geometry and macropore features are highly affected by soil management. Presumably, the period without tillage (almost 2 years) at Silstrup ) and significant fracturing, which is common for soils composed of glacial deposits overlying clayey till.…”