The Nutrition of Grapevines - Understanding Vineyard Soils - page 88

Box 3.5 Stages in Grapevine Growth and Fruit Ripening
Bud burst (bud break in Europe)—bud dormancy is broken and young leaves begin
to emerge and expand in spring (early October or April in cool-climate regions
of the southern and northern hemispheres, respectively). Flowering (bloom in
North America)—may extend over several weeks in cool climates but usually 10 to
14 days. The midpoint occurs when 50% of fruit clusters (bunches) are in flower;
cell division begins in the fertilized flowers. Fruit set —may extend over a few
weeks, but the midpoint occurs when 50% of bunches have berries 3 to 5 mm in
diameter; all unfertilized berries should have been shed; from fruit set to veraison,
berry growth is by cell division and expansion. Veraison —berries begin to soften
and change color (white varieties begin to turn yellow and red varieties turn red) as
ripeningbeginsandsugarsstarttoaccumulate.Midveraisonoccurswhen50%of
bunches are coloring (for red grapes); after veraison (postveraison), berry growth
is mainly by cell expansion. Maturity —full ripeness attained; red grapes fully
colored, stems turn woody, bunches are harvested. Postharvest —vines continue
to grow, especially through root growth, provided temperature and soil water are
adequate;leavesturnyellowanddie.
SelectingtheSampleMaterial
The traditional method is to take a composite sample from a block of vines of
the same variety on each soil type. Seventy-five to 100 petioles are collected from
randomly chosen vines in the block. Separate composite samples should be taken
from areas that are performing badly or well.
Even on one soil type, measurements at a very high density may show consid-
erable variation in the nutrient concentrations over short distances. Figure 3.10
shows the variation in petiole P concentration in a Cabernet Sauvignon vineyard
in the Coonawarra region, South Australia. Such variation probably reflects the
influence of soil physical properties on growth, in addition to an effect of the
soil's P supply. Thus a strong case can be made for targeted sampling based on the
known pattern of soil variability, which goes further than the recommendation
that separate samples be taken from “good” and “bad” areas. However, the cost of
the extra analyses must be balanced against the potential value added by the more
precise information, so methods of analyzing many samples rapidly and cheaply
needtobeconsidered,asdiscussedinthischapterin“PrecisionViticulturefor
BetterSoilManagement.”
Interpreting Plant Analyses
Analyses for micronutrients are reported in milligrams per kilogram dry matter
and as percentage dry matter for the macronutrients (details are given in box 3.1).
The result always has some uncertainty because of natural variability in the soil