Geoscience Reference
In-Depth Information
18
Productivity Zones Based
on Bulk Soil Electrical
Conductivity
Applications for Dryland
Agriculture and Research
Cinthia K. Johnson, Rhae A. Drijber, Brian J. Wienhold,
and John W. Doran
ContentS
18.1 Introduction ......................................................................................................................... 263
18.2 Materials and Methods........................................................................................................264
18.3 Results and Discussion........................................................................................................ 267
18.3.1 Phase I: The EC
a
Map ........................................................................................... 267
18.3.2 Phase II: EC
a
versus Soil Edaphic Properties ....................................................... 267
18.3.3 Phase III: EC
a
versus Crop Yields ........................................................................ 268
18.3.4 Phase IV: EC
a
versus Microbial-Scale Measurements.......................................... 269
18.3.5 Phase V: EC
a
for Experimental Design and Analysis........................................... 269
18.4 Conclusions ......................................................................................................................... 270
References ...................................................................................................................................... 271
18.1 IntRodUCtIon
Soil is inherently variable in the physical, chemical, and biological properties that determine yield
potential, a fact that complicates the identification and implementation of sustainable management
practices. Historically, a lack of means to delineate and address within-field heterogeneity has forced
farmers to operate at the large scale, using the field as a primary management unit. Soils are sampled
and inputs applied to target average requirements across fields, resulting in underperforming yields
in some areas and wasted inputs in others. Increasingly, farmers seek to manage land at a smaller
level of resolution (site-specific management) to improve economic and ecological outcomes.
Paradoxically, soil heterogeneity has the opposite impact on agronomic research. Scientists
have traditionally relied upon small or plot-scale experiments as a means to control spatial variabil-
ity and reduce experimental error. Yet, the importance of research conducted at a level of scale so
divergent from that of production agriculture is sometimes questioned. Conclusions based upon data
extrapolated beyond the spatial context of sampling assume the scale independence of patterns and
processes (Wiens, 1989), an erroneous assumption (Cambardella et al., 1994). For this reason, grow-
ing numbers of scientists and farmers promote large-resolution (field-scale) experiments to address
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