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Leaching of Herbicides Through Undisturbed Cores of a Structured Clay Soil
Author(s) -
White R. E.,
Dyson J. S.,
Gerstl Z.,
Yaron B.
Publication year - 1986
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/sssaj1986.03615995005000020004x
Subject(s) - leaching (pedology) , tracer , leaching model , soil science , chemistry , chloride , environmental chemistry , soil water , environmental science , lessivage , water flow , hydrology (agriculture) , geology , geotechnical engineering , soil salinity , physics , organic chemistry , nuclear physics
The leaching of the herbicides bromacil and napropamide through large undisturbed cores of a structured Evesham clay (Aquic Eutrochrept) was studied under continuous and discontinuous watering regimes and at different initial moisture contents. A greater proportion of both herbicides was leached from initially dry cores (θ = 0.24) than from prewet cores (θ = 0.35). This was consistent with differences in the amount of herbicide retained in the soil, most of which was retained in the top 0.05 m. Continuous leaching resulted in greater herbicide breakthrough than did the discontinuous treatment, presumably because some herbicide diffused from the conducting channels into the soil aggregates during the quiescent period, where it was less susceptible to subsequent leaching. At a continuous input rate of 12 mm h −1 to initially dry soil, 85% of the applied napropamide ( K d = 17.7 L kg −1 ) and almost 100% of bromacil ( K d = 1.73 L kg −1 ) were leached out of the soil by one pore volume of water. Chloride was used as a tracer for water flow through the soil. Chloride breakthrough curves were analyzed using a transfer function equation, which yielded the median travel time of a solute molecule in the soil. It is suggested that preferential flow of water down cracks and channels between soil aggregates led to short travel times and apparently low volumes of soil water participating in solute transport (θ st ). The θ st values were inversely correlated with the percentages of the applied herbicides that were leached.