Geoscience Reference
In-Depth Information
for varying rates of compost, manure, and commercial fertilizer with the use of cover crops. Addi-
tionally, sequential EMI surveys were examined as a tool in monitoring N cycle dynamics in a corn
silage research field.
19.2
MethodS
19.2.1 s
i t e
d
e s c R i P t i o n
A center-pivot irrigated field (244 m × 244 m) of silage corn (
Zea mays
L.), located at the U.S. Meat
Animal Research Center (USMARC), served as a comparison site for various manure and compost
application rates for replacement of commercial fertilizer, with the same treatment assigned to field
plots for 10 consecutive years. The soil series at this site is a Crete silt loam (fine, montmorillonitic,
mesic Pachic Argiustolls), 0 to 1 percent slope.
19.2.2
f
i e l d
o
P e R a t i o n s
o n
t h e
R
e s e a R c h
c
o R n f i e l d
The study site was laid out as a split-plot design (Figure 19.1), with four replications of the main plot
of cover crop (+CC) versus no cover (−CC) (the cover crop was a winter wheat [
Secale cereale
L.]
no-till drilled following silage harvest). Subplot application to treatment strips (6.1 m, eight corn
rows wide) was made with two manure sources: beef feedlot manure and composted beef feed-
lot manure. Applications were made each spring according to two strategies: (1) to approximately
supply the total crop demand for N (Ferguson et al., 2003), denoted MN and CN for manure and
compost, respectively, and (2) to supply the approximate crop demand of P (Ferguson et al., 2003),
denoted MP and CP for manure and compost, respectively. Treatments MP and CP each had suf-
ficient carryover phosphorus after 1998 so that no manure or compost was applied to these treatment
strips for the 2000 to 2003 study.
19.2.3 e
q u i P M e n t
Two different magnetic dipole soil conductivity meters were used in this study: (1) an EM-38, manu-
factured by Geonics Ltd., Mississauga, Ontario, Canada
(2000 and 2001 seasons) and (2) a Dualem-2
manufactured by Dualem Inc., Milton, Ontario, Canada (2002 and 2003 seasons). The EM-38 was
operated horizontally and had a response that varied with depth in the soil, yielding EC
a
t hat wa s cen-
tered at a depth of about 0.75 m. The Dualem-2 operates in the horizontal and vertical dipole modes
simultaneously, with EC
a
centered at 1.5 and 3.0 m, respectively. Only the horizontal response of
each instrument is reported in this study and is designated EC
a
. The EMI instruments were mounted
on a plastic sled and transported through the field, pulled by an all-terrain vehicle (ATV), or by hand
when the corn became too tall for the ATV. Surveys were planned on weekly intervals throughout
the corn growing season for all 4 years. A Trimble PRO-XR GPS (global positioning satellite) unit
was used to obtain positional data.
Soil conductivity responds to soil temperature (McKenzie et al., 1989). An array of thermo-
couple temperature probes was buried at the cornfield site prior to the 2002 growing season. Probes
were installed at incremental depths to 315 cm. The thermal profile was used with known Dualem-2
response (Dualem, www.dualem.com) curves to provide an effective soil temperature correction for
each survey date (McKenzie et al., 1989). The soil temperatures demonstrated predictable tempera-
ture patterns that allowed temperature corrections to be estimated for the Geonics instrument for
the 2000 and 2001 season. Precipitation events were recorded at the cornfield site using a tipping
bucket rain gauge and a portable event recorder.
Soil cores were taken on survey dates throughout the growing season with a hand probe to
a depth of 0 to 30 cm. The cores were analyzed by a local commercial soil testing laboratory to
