Fxm. Casey et al., MEASUREMENT OF FIELD SOIL HYDRAULIC AND SOLUTE TRANSPORT PARAMETERS, Soil Science Society of America journal, 62(5), 1998, pp. 1172-1178
Agricultural chemical presence in groundwater has drawn attention towa
rd transport processes occurring in soil. Hydraulic conductivity (K) a
nd water-holding capacity of a soil have great influence on water now
and solute transport. However, much of the chemical transport to groun
dwater ran occur through preferential flow pathways. The simplified, p
referential now, mobile-immobile model partitions the water content (t
heta) into mobile (theta(m)) and immobile (theta(im)) domains, with so
lute exchange between the domains characterized by the mass-exchange c
oefficient (alpha). In this study a sequential tracer application tech
nique was used and K, theta, theta(im), and alpha were estimated for a
series of pressure heads (H = 10, -30, -60, and -150 mm). This method
uses a tension infiltrometer to measure both hydraulic and solute tra
nsport parameters in situ. The study took place in a no-till corn (Zea
mays L.) held mapped as a Harps series soil (fine-loamy, mixed, mesic
Typic Calciaquoll). Unsaturated values of theta and K were distinct f
rom the saturated values. Similarly, though less clear cut, distinctio
ns between saturated and unsaturated values of theta(im), immobile wat
er fraction (theta(im)/theta), and alpha were observed. The medians of
theta for the sequence of decreasing H values were 0.40, 0.31, 0.34,
and 0.33 m(3) m(-3) The median K values for the same sequence of H wer
e 108, 1.69, 1.51, and 0.72 mu m s(-1). The median theta(im)/theta val
ues for the H sequence were 0.40, 0.28, 0.25, and 0.39. The median val
ues of alpha for the H sequence were 0.59, 0.015, 0.0028, and 0.0029 h
(-1). A strong correlation between alpha and H suggests a velocity dep
endence of alpha.