Agriculture Reference
In-Depth Information
Napa Valley, California, embracing the Napa Valley Viticultural Area (section
9.5.1), soil types separated on the basis of land slope are aggregated into soil se-
ries (based mainly on texture and stoniness) that are recognized in Soil Taxonomy.
8.2.2
Soil Survey
8.2.2.1
The Process
Collecting soil and landscape data for soil classification and mapping is called
soil
survey
. In the case of viticulture, the first step in conducting a soil survey is to
gather information on
climate
and
geology
. Depending on the vigneron's objec-
tives, such data will identify broad areas potentially suited to the grape varieties,
and the style of wine, to be produced. The next step may be gathering remotely
sensed data (box 8.2) to delineate differences in vegetation, landforms, and pos-
sibly hydrology that could be the outward expression of soil differences. At this
stage, the notional soil classes identified will be fairly broad, and further infor-
mation on specific soil properties, such as salinity, for example, may be sought us-
ing an EM survey (see box 7.2). This is called
proximal sensing
. These data can be
collected at a high density and mapped on a very large scale.
Once boundaries separating notional soil classes have been marked on aerial
photographs, satellite images, or digital maps, soil surveyors must go into the field
to check their significance, relocating the boundaries if necessary. This process is
called
ground-truthing
.
8.2.2.2
The Field Survey
Once an area has been identified as potentially suited to vines, a detailed soil sur-
vey is carried out, often by digging pits on a grid pattern, usually at a 75-m
75-m spacing (about 2.5 pits per ha). This implies that the soil should be mapped
Box 8.2
Remote Sensing for Soil and Land Surveys
Devices used for remote sensing in soil and land surveys detect
electromagnetic radiation (EMR). The sensing may be active or passive.
Active
sensing occurs when the sensing device directs EMR at an object and detects the
amount of energy reflected back. Examples are radio wave emissions, radar
(wavelength
m), and laser-imaging radar, and near-infrared, visible, and
UV radiation (wavelengths from 10
10
3
m to 10
3
m).
Passive
sensing takes place
when the sensing device detects EMR originating from another source, such as
(gamma) rays emitted from the soil or reflected radiation from the sun (e.g., aerial
photos).
Remote sensing relies on detecting differences in the reflected or emitted
radiation from different areas of the land over a range of wave lengths. Data are
gathered mainly from air- or spacecraft and are recorded photographically or
digitally. One example of digital data is a Landsat image from a satellite.
Conventional aerial photos must be digitized before undergoing
image analysis
and
data processing by computer. In digital format, remotely sensed data provide a
natural input to a GIS where they can be put into layers along with other spatial
data (e.g., roads, buildings, and streams) and linked to
attribute
data that describe
the properties, such as soil properties, of any spatial feature in the GIS.
