Geoscience Reference
In-Depth Information
a semiarid landscape where carbonates were present, and therefore, there was a larger range of pH
values. Soil pH was best described by a spherical model (r
2
= 0.91, RSS = 1.7E
−8
).
Use of statistical methods to direct soil sampling and estimate the spatial pattern exhibited by
soil properties will provide additional information that can be used to understand crop production
and improve management. Previous research has shown that the relationship between EC
a
and crop
yield is inconsistent and appears to be dependent on crop, growing season precipitation, and inci-
dence of fallow (Johnson et al., 2003; Kitchen et al., 1999). Maps showing the relationship between
EC
a
and inherent soil properties will be useful for explaining the interaction between weather, crop,
and soils. At this study site, the areas having high clay content tend to be low yielding in years of
below-normal precipitation. In years of above average precipitation these areas often exhibit higher
yields than depositional areas where drainage is insufficient to prevent short-term waterlogging and
conditions favoring denitrification.
Maps delineating the spatial distribution of soil chemical properties have potential for improv-
ing the management of inputs such as fertilizer and lime. In this study, parts of the field having high
EC
a
also had low NO
3
-N concentrations. Even though these areas of the field are lower yielding than
the field average, they still require fertilizer N. Areas having low EC
a
values were areas of the field
having high NO
3
-N concentrations. Applying additional N to these areas will probably have little
effect on yield and will increase the potential for emission of nitrous oxides or leaching of NO
3
-N.
Because there are so many processes affecting N availability, much work needs to be done to realize
the potential for varying fertilizer N inputs.
Lime is another major input for many agricultural systems. In this study, soil pH was below
the optimum for crop production. Even though pH was poorly correlated with EC
a
there was spatial
structure in the map of predicted pH. When lime requirement was determined for the sample sites
and a variable rate lime application was compared to a constant application rate, the variable rate
was 85 percent that of the constant rate. The variable rate application required 6 Mg less lime and
represents a substantial reduction in input costs for this field.
11.4 ConClUSIonS
This study utilized a statistical approach for directing soil sampling that can be used to characterize
the spatial structure in soil properties affecting crop production. An understanding of the spatial
structure of soil properties combined with yield maps has been shown to be useful for explaining
year-to-year differences in yield patterns (Schepers et al., 2004). The approach presented in this
study has potential for reducing the sampling intensity required for characterizing spatial patterns
present in a field. Characterizing the spatial variability will be useful in studying dynamic processes
affecting water and nutrients. Improved understanding of these processes will allow development of
management practices that better match inputs with crop needs.
11.5 AUthoRS' note
Trade or manufacturer's names mentioned do not constitute endorsement, recommendation, or
exclusion by the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS).
USDA-ARS, Northern Plains Area, is an equal opportunity/affirmative action employer and all
agency services are available without discrimination.
RefeRenCeS
Eigenberg, R.A. et al. Electrical conductivity monitoring of soil condition and available N with animal manure
and a cover crop.
Agric. Ecosyst. Environ.
88, 183-193, 2002.
Johnson, C.K. et al. Field-scale electrical conductivity mapping for delineating soil condition.
Soil Sci. Soc.
Am. J
. 65, 1829-1837, 2001.
