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Alachlor Transport during Transient Water Flow in Unsaturated Soils
Author(s) -
Selim H. M.,
Zhou L.,
Xue S. K.
Publication year - 2002
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2002.1773
Subject(s) - alachlor , soil water , infiltration (hvac) , tillage , water content , soil science , environmental science , chemistry , hydrology (agriculture) , materials science , geology , agronomy , geotechnical engineering , atrazine , pesticide , composite material , biology
In most herbicide mobility investigations, laboratory experiments are often restricted to the traditional miscible displacement methods where water saturated conditions and constant flux are maintained. In this study, we examine the mobility of alachlor herbicide under soil‐water unsaturated and transient conditions. Gigger (a Typic Fragiudalf) surface soil samples were collected from long‐term soybean management system under no‐till with wheat (NTW, Triticum aestivum L.), conventional tillage with wheat (CTW), and conventional tillage with hairy vetch (CTV, Vicia villosa Roth). Air‐dried soil was packed in columns which were horizontally maintained. The inflow end was connected to a water supply which was maintained at zero head. The input pulse was made up of tritium and 14 C‐alachlor solution. During horizontal infiltration, the advance of the wetting front and volume infiltrated into the soil was monitored over time. When the wetting front reached 25 cm, the column was dismantled and the soil moisture and alachlor concentrations in each 1‐cm section quantified. All alachlor distribution profiles appeared retarded and did not show sharp solute fronts. Rather the concentration distributions were of moderately shaped fronts reaching some 10 cm from the source and followed by a gradual decrease up to 20 cm. Alachlor movement was modeled based on transient flow in unsaturated soils. Such results were compared with equilibrium type models of the linear and nonlinear type under steady and transient flow conditions. Parameters needed were soil water‐diffusivity, solute‐dispersion coefficients and retention parameters for alachlor for individual soils. Independently derived parameters provided a good description of the BTC under unsaturated conditions.