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Effects of Initial Water Content on Macropore/Matrix Flow and Transport of Surface‐Applied Chemicals
Author(s) -
Shipitalo M. J.,
Edwards W. M.
Publication year - 1996
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1996.00472425002500040005x
Subject(s) - macropore , water content , lysimeter , alachlor , soil water , chemistry , atrazine , surface water , soil science , environmental chemistry , environmental science , hydrology (agriculture) , pesticide , agronomy , environmental engineering , geology , mesoporous material , biochemistry , geotechnical engineering , biology , catalysis
Pesticides and fertilizers are often broadcast on no‐till fields in the spring when soil water content can be quite variable. Soil water content may influence the contribution of macropores and matrix porosity to water movement and chemical transport in subsequent rainfalls. Therefore, we surface‐applied SrBr 2 6H 2 O, atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐ s ‐triazine), and alachlor [2‐chloro‐2′,6′‐diethyl‐ N ‐(methoxymethyl) acetanilide] on nine, 30 by 30 by 30 cm, undisturbed soil blocks obtained from a no‐till corn ( Zea mays L.) field and maintained at three initial moisture levels 1 h before a 30‐mm, 0.5‐h simulated rain. To distinguish applied water from resident water and assess interaction of the rainwater with the soil matrix, RbCl was added to the simulated rain as a tracer. Sequential percolate samples were collected from the base of the blocks in ≈ 10‐mL increments using a 64‐cell grid lysimeter. Flow‐weighted concentrations of Cl − and Rb + , respectively, were 75 and 836% higher in percolate from dry (θ = 0.11 kg kg −1 ) than from wet blocks (θ = 0.21 kg kg −1 ), indicating that displacement of resident water and interaction of rainwater with the matrix increased with initial soil water content. As a result, percolate concentrations of the reactive, surface‐applied, constituents (Sr 2+ , atrazine, alachlor) decreased with increasing soil water content. High block to block variability precluded detection of significant differences in percolate volume and total chemical transport among moisture levels. The relative contribution of macropores to chemical transport and water movement appears to be greatest when the soil is dry and decreases as the soil becomes wetter.