Agriculture Reference
In-Depth Information
Related Factors in Site Selection
8.3
Biological Factors
Soil physical and chemical tests should be complemented by tests for disease and
pests, such as nematodes. Knowledge of the previous cropping history is impor-
tant. Land that has been used for vegetable and potato growing, for example, of-
ten has a high nematode population. Samples of moist soil can be assessed for the
number and type of nematodes present, and to determine whether fumigation is
necessary (section 7.3.3.2). Land with old oak trees may be infected with the oak
root fungus,
Armillaria mellea
. Replanted vineyards on land previously under vines
may have a phylloxera problem. The GFL virus is soil-borne and transmitted by
the dagger nematode.
One important decision facing the vigneron is whether to grow own-rooted
vines or grafted vines. Cuttings of the former are cheaper, but rootstocks give pro-
tection where there is a danger of phylloxera and/or nematode attack, as discussed
in sections 7.3.3.1 and 7.3.3.2, respectively. Certain rootstocks are also more salt-
tolerant (section 7.2.2.3) than own-rooted vines. However, most of the rootstocks
derived from American species of
Vitis
are more susceptible to Fe-chlorosis on cal-
careous soils than
V. vinifera
(section 5.5.2).
8.3.1
Quantity and Quality of Water
A reliable supply of high-quality water is vital for vineyards that need irrigation.
Different countries have different laws governing the rights to underground and
surface waters—the amount extracted in any one season and the degree of secu-
rity of the water entitlement. The total quantity of water required is set by that
needed in a dry year, as shown in box 8.3. The rate of water supply should be
8.3.2
Box 8.3
Estimating Water Needs for an Irrigated Vineyard
In the Central Valley of California, which has hot, dry summers, nearly all the
vineyards are irrigated. Peak demand occurs in July, when the average daily water
need is about 0.33 acre-in. (Verdegaal 1999). The following calculations, in metric
units, illustrate the quantity of water required. Conversion from metric to U.S.
units is explained in appendix 15.
Thus, 0.33 acre-in. of water per day is equivalent to 34 m
3
, which, if spread
over 1 ha of soil, amounts to 3.4 mm of irrigation water per day. If irrigation were
scheduled every 7 days, the quantity of water required per week would be 0.238
ML per ha.
This figure could be adjusted down or up, depending on whether some form
of
RDI
or
PRD
was practiced or cover crops were grown in the inter-rows.
The inland vineyard areas in Australia also have high water requirements for
irrigation. For example, in the Griffith irrigation area, the average application for
drip-irrigated vines in midsummer is about 18 L per dripper per day. If there are
2,500 drippers per ha, this amounts to 4.5 L/m
2
(4.5 mm) or 0.045 ML/ha/day of
water. The quantity required per week in the Griffith irrigation area, 0.315 ML, is
higher than that in the Central Valley, California.
