Geoscience Reference
In-Depth Information
Farm
Hundreds of ha
Multiple ha
Field
Hundreds of m
2
EC
a
Productivity Zone
Sub meter
Sampling Site
Microbe
Micron
fIGURe 18.1
The EC
a
-based productivity zone functions as a pivotal point through which measurements
spanning the hierarchy of experimental scale can be related.
questions of operational scale and advance research relevance (Drinkwater, 2002; Rzewnicki,
1991). Field-scale research permits study of intact agroecosystems wherein the interrelationships
between soil edaphic properties, biological processes, and management can be studied for yield,
farm economic, pest, and on- and off-site environmental impacts. However, two critical issues must
be resolved if field-scale investigations are to gain widespread acceptance. Innovative methods are
needed to obtain reasonable estimates of experimental error in lieu of replication to and relate data
collected at small (microbial), medium (soil physical/chemical), and large scales (crop yields and
farm economics).
Cost-effective technologies capable of producing maps that define within-field areas of similar
production potential, termed “productivity zones” (Kitchen et al., 2005), may benefit both produc-
tion agriculture and agronomic research. Productivity zones could function as intermediate units of
reference to permit shifts in operational scale (Figure 18.1)—that is, smaller for farmers and larger
for researchers—to better address sustainability issues. Apparent soil electrical conductivity (EC
a
)
may be one option for mapping productivity zones.
In individual fields, the magnitude and spatial patterns of mapped EC
a
are largely driven by
one or two soil characteristics including salinity, clay type/percentage, bulk density, water content,
or temperature (Rhoades et al., 1989). Crop yields are not always correlated with EC
a
because cor-
relation requires that the same soil factors control both EC
a
and yield. For this reason, the EC
a
-yield
relationship varies among reports (Corwin et al., 2003a; Jaynes et al., 1993; Johnson et al., 2001;
Kitchen et al., 1999).
Research in a dryland system in semiarid northeastern Colorado was designed to evaluate the
effectiveness of EC
a
-based productivity zones as a framework for addressing key sustainability
issues in production agriculture and research. Specifically, EC
a
zones were considered as a basis
for (1) zone soil sampling and monitoring the impact of management on soil ecological trends;
(2) site-specific application of inputs (i.e., fertilizer, herbicide, and seed); (3) linking small- (micro-
bial-scale), medium- (sampling site), and large-scale (field and farm) economic and ecological
measurements; and (4) designing and statistically evaluating field-scale experiments to circumvent
traditional replication.
18.2 MAteRIAlS And MethodS
All experiments were conducted at the farmer-owned and -managed Farm-Scale Intensive Cropping
Study (FICS) near Sterling, Colorado (Johnson et al., 2001) (Figure 18.2). This dryland experi-
ment encompasses a contiguous section of farmland (≈250 ha) managed for nearly seventy years
in a traditional winter wheat (
Triticum aestivum
L.)—fallow rotation using conventional tillage.
