Geoscience Reference
In-Depth Information
tAble 4.2
outline of Steps for an eC
a
-directed Soil Sampling Survey
1. Site description and EC
a
survey design
(a) Record site metadata
(b) Establish site boundaries
(c) Select Global Positioning System (GPS) coordinate system
(d) Establish EC
a
measurement intensity
2. EC
a
data collection with mobile GPS-based equipment
(a) Geo-reference site boundaries and significant physical geographic features with GPS
(b) Measure geo-referenced EC
a
data at the predetermined spatial intensity and record associated metadata
3. Soil sample design based on geo-referenced EC
a
data
(a) Statistically analyze EC
a
data using an appropriate statistical sampling design to establish the soil sample site
locations
(b) Establish site locations, depth of sampling, sample depth increments, and number of cores per site
4. Soil core sampling at specified sites designated by the sample design
(a) Obtain measurements of soil temperature through the profile at selected sites
(b) At randomly selected locations obtain duplicate soil cores within a 1 m distance of one another to establish
local-scale variation of soil properties
(c) Record soil core observations (e.g., mottling, horizonation, textural discontinuities, etc.)
5. Laboratory analysis of appropriate soil physical and chemical properties defined by project objectives
6. If needed, stochastic or deterministic calibration of EC
a
to EC
e
or to other soil properties (e.g., water content and
texture)
7. Spatial statistical analysis to determine the soil properties influencing EC
a
and crop yield
(a) Soil quality assessment:
(1) Perform a basic statistical analysis of physical and chemical data by depth increment and by composite depth
over the depth of measurement of EC
a
(2) Determine the correlation between EC
a
and physical and chemical soil properties by composite depth over the
depth of measurement of EC
a
(b) Site-specific crop management (if EC
a
correlates with crop yield, then)
(1) Perform a basic statistical analysis of physical and chemical data by depth increment and by composite depths
(2) Determine the correlation between EC
a
and physical and chemical soil properties by depth increment and by
composite depths
(3) Determine the correlation between crop yield and physical and chemical soil properties by depth and by
composite depths to determine depth of concern (i.e., depth with consistently highest correlation, whether
positive or negative, of soil properties to yield) and the significant soil properties influencing crop yield (or
crop quality)
(4) Conduct an exploratory graphical analysis to determine the relationship between the significant physical and
chemical properties and crop yield (or crop quality)
(5) Formulate a spatial linear regression (SLR) model that relates soil properties (independent variables) to crop
yield or crop quality (dependent variable)
(6) Adjust this model for spatial autocorrelation, if necessary, using Restricted Maximum Likelihood or some other
technique
(7) Conduct a sensitivity analysis to establish dominant soil property influencing yield or quality
8. Geographic information system (GIS) database development and graphic display of spatial distribution of soil
properties
Source:
Corwin, D.L., and Lesch, S.M.,
Comp. Electron. Agric.
, 46, 103-133, 2005. With permission.
to correlate strongly with some parameter of interest (e.g., crop stress, soil type, soil salinity, etc.),
but the exact parameter estimates (associated with the calibration model) may still need to be deter-
mined via some type of site-specific sampling design. This approach explicitly optimizes this site
selection process.
