Temporal Dynamics of Preferential Flow to a Subsurface Drain

Abstract

We conducted a sequential tracer leaching study on a 24.4 by 42.7 m field plot to investigate the temporal behavior of chemical movement to a 1.2-m deep field drain during irrigation and subsequent rainfall events over a 14-d period. The herbicides atrazine [6-chloroN-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] along with the conservative tracer Br were applied to a 1-m wide strip, offset 1.5 m laterally from a subsurface drain pipe, immediately before an 11.3-h long, 4.2-mm h −1 irrigation. Three additional conservative tracers, pentafluorobenzoate (PF), o-trifluoromethylbenzoate (TF), and difluorobenzoate (DF) were applied to the strip during the irrigation at 2-h intervals. Breakthrough of Br and the two herbicides occurred within the first 2-h of irrigation, indicating that a fraction of the solute transport was along preferential flow paths. Retardation and attenuation of the herbicides indicated that there was interaction between the chemicals and the soil lining the preferential pathways. The conservative tracers applied during the later stages of irrigation arrived at the subsurface drain much faster than tracers applied earlier. The final tracer, applied 6 h after the start of irrigation (DF), took only 15 min and 1 mm of irrigation water to travel to the subsurface drain. Model simulations using a twodimensional, convective, and dispersive numerical model without an explicit preferential flow component failed to reproduce Br tracer concentrations in the drain effluent, confirming the importance of preferential flow. This study showed that preferential flow in this soil is not a uniform process during a leaching event. ABSTRACTalso found Cl concentrations in tile water to peak within 1 h of the onset of irrigation, which they attributed toWe conducted a sequential tracer leaching study on a 24.4 by

Tillage management effects on pesticide fate in soils. A review

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Measurement and Modeling of Unsaturated Hydraulic Conductivity

“…The extremely simplified type of analysis presented here assumes that flow through the unsaturated zone proceeds as described by the Richards' equation. Many studies show that there are processes, such as preferential flow, that are not adequately described by Richards' equation (Perkins et al, 2011;Tyner et al, 2006;Köhne and Gerke, 2005;Jaynes et al, 2001;Yoder, 2001;Iragavarapu et al, 1998, Flury et al, 1994. There are recent studies suggesting that hydraulic conductivity and water retention may be important for modeling diffuse matrix flow; however, they may not capture some of the dominant field-scale processes such as preferential flow.…”

Determinación De La Concentración De Glifosato en Agua Mediante La Técnica De Inmunoabsorción Ligada a Enzimas (Elisa)

“…Estudios de lixiviación y escurrimiento indican que el glifosato puede ser transportado hacia las capas profundas del suelo debido al flujo preferencial por macroporos o hacia cursos de agua superficiales cuando su aplicación se realiza en momentos anteriores a lluvias intensas (Flury 1996, Villholth et al 2000, Jaynes et al 2001, Elliot et al 2002, Petersen et al 2002. En Argentina, la Subsecretaría de Recursos Hídricos de la Nación publicó en el año 2003, los niveles guía nacionales de calidad de agua ambiente correspondientes a glifosato.…”