Agriculture Reference
In-Depth Information
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Sodicity often develops in soils that are, or have been, saline. This condition leads
to soil structural problems. A
sodic soil
is one with an
exchangeable Na percentage
(
ESP
)
6 (Australia) or 15 (United States). The soil's
ESP
can be predicted from
the
SAR
of irrigation water, which is defined as
[Na
]
Ca
2
Mg
2
1/2
2
■
The application of gypsum (CaSO
4
.2H
2
O) is recommended to ameliorate so-
dicity.
■
Waterlogging
is a problem associated with a high water table or an impermeable
subsoil. Waterlogging is alleviated in clay soils by installing pipe drains and deep
ripping to improve water flow to the drains. In sandy soils, the groundwater can
be pumped to the surface.
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A biologically healthy soil has a rapid turnover of organic residues, with a diverse
population of organisms and a water-stable structure. The diverse population of
organisms facilitates the breakdown of pesticide and herbicide residues, which min-
imizes their tendency to move off-site and cause damage to nontarget organisms.
■
Ideally, the root louse
phylloxera
should be absent from a healthy vineyard soil,
and the
nematode
population should be low. Where this is not the case, resistant
rootstocks, bred from the American
Vitis
species such as
V. riparia
,
V. rupestris
,
and
V. berlandieri
(for phylloxera), and
V
.
champini
and
Muscadinia rotundifolia
hybrids (for nematodes), should be used.
■
Cover crops
of annual or perennial species are sown in many vineyards. These im-
prove soil structure and trafficability, especially under wet conditions.
Mulches
of
cover crop mowings, straw, or compost are used in the vine rows to encourage bi-
ological activity and reduce soil summer temperatures and evaporation.
■
Cultivation is used to control weeds, but it tends to destroy soil structure. Culti-
vation is usually practiced in conjunction with flood or furrow irrigation. On
slopes, a bare surface is likely to be eroded by water. Wind erosion is rarely a prob-
lem in vineyards.
■
Erosion
removes the more fertile topsoil and induces undesirable off-site effects.
The extent of erosion is determined by the interaction between
rainfall erosivity
and
soil erodibility
. Erosion can be lessened by an improved soil structure, by a
change in the length and steepness of slope by terracing or contouring, and by
management practices such as planting a cover crop.
■
Dissolved P ions and sorbed P carried on eroded soil particles create the poten-
tial for
eutrophication
of receiving surface waters, and consequential algal blooms.
Excess NO
3
in the soil after the grape harvest may be leached during winter,
raising the NO
3
concentration of groundwater above the acceptable limit of 10
(United States and Australia) or 11.3 mg N/L (Europe).
