Agriculture Reference
In-Depth Information
between irrigation sessions is important to reduce filling time, as is regular flush-
ing and checks on operating pressure.
One of the functions of deep ripping is to improve soil drainage. However,
if poor drainage is due to an impermeable subsoil or a groundwater table that
rises within 2 m of the soil surface, an artificial drainage system may need to be
installed. Soil conditions predisposing to poor drainage and the means of alleviat-
ingthisproblemarediscussedin“WhatCausesPoorDrainage?”inchapter4.
Summary Points
1. Site potential expresses the suitability of a site for particular grape
varieties and the expectation of vine vigor expressed through vegetative
growth. Climate, topography, geology, and soil type all influence site
potential and hence site selection for a vineyard.
2. Traditionally, most attention has focused on the regional climate in site
selection, and a number of climatic indices have been developed. Locally,
climate interacts with topography through land height, slope, and aspect
(the mesoclimate), while the nearness to large bodies of water moderates
daily and seasonal temperature variations.
3. A more complete approach to site selection involves taking account of
other determining factors, notably soil, to develop a local site index (LSI).
4. Because soil is important in determining site potential, detailed
knowledge of soil properties, spatially mapped through a soil survey, is an
essential prerequisite for the establishment and subsequent management
of a vineyard.
5. Soil survey is greatly aided by remote and proximal sensing techniques,
such as the EM38, which responds to changes in electrical conductivity
(
EC
) down to a depth of at least 50 cm. When the sensed positions
arelocatedwithaglobalpositioningsystem(GPS)andtheoutputis
streamed to a geographic information system, an accurate map of soil
variation can be produced. With such a map, points covering the full
range of soil variation can be efficiently located on the ground and
examined in soil pits. Samples from the pits can be used to calibrate maps
for particular soil properties such as depth, clay content, and salinity.
6. A range of tests is recommended for soil chemical fertility (see chapter 3),
physical properties (see chapter 4), and biological condition, including
the presence of pest and disease organisms (see chapter 5). From these
tests, a winegrower may decide on preplanting treatments such as deep
ripping (to break up compacted layers), fumigation (for disease control),
terracing (for erosion control), or sowing a cover crop. Soil amendments,
