Agriculture Reference
In-Depth Information
Location
of soil pits
×
Inferred soil
boundary based
on soil pit observations
×
Line of
free
survey
×
×
Additional sampling
sites to check on
inferred soil boundaries
×
×
Soil class boundaries identified from grid sampling, supported by free survey.
Figure 8.2
at a scale of 1:7,500, because at that scale 1 cm on the map would represent 75
m in the field (see box 8.1). If the pattern of soil distribution is particularly com-
plex, a 50-m
50-m grid may be necessary (about 6 pits per ha), justifying a map
scale of 1:5,000. With the aid of a soil auger, additional sites can be sampled by
conducting a
free survey
, which might be guided by remotely sensed information
(e.g., differences in topography or vegetation) or by observable soil features (e.g.,
a change in soil color, possibly related to drainage, or a stony surface that might
indicate a shallow soil profile). The pits or auger holes should be dug to a depth
of 1.8-2 m, depending on the depth to a rock barrier. Boundaries between soil
types are interpolated from the grid and free survey data (fig. 8.2).
An intensive soil survey, involving remote and proximal sensing supported by
detailed ground-truthing, is expensive. Provided that the observation points are
accurately located by GPS, all soil and other attribute data can be entered into a
GIS, thus facilitating the subsequent application of precision viticulture (section
5.3.5). Grid surveys with a large number of sampling points (
100 pairs) also
permit an analysis of any spatially dependent variation in soil properties. Where
this is identified, techniques of
geostatistics
can be used to obtain the best estimates
of soil properties within localized areas. Specialist texts, such as Webster and Oliver
(2000), give full details on geostatistical analysis.
The more detailed the knowledge of soil variation, the better equipped the
vigneron is to choose the location of specific cultivars, the design of an irrigation
system, appropriate soil amelioration (deep ripping, fertilizers, amendments), vine
spacing, and trellising (section 8.4.2).
Describing the Soil Profile
The basic features of a soil profile—the A, B, and C horizons—and of the main
soil-forming processes are outlined in chapter 1. However, to select a vineyard
8.2.2.3
