Agriculture Reference
In-Depth Information
Tip
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2
4
6
3
8
5
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Select petiole opposite either
Collect petioles taken
of the basal clusters during full bloom.
from the most recently developed, full-sized leaf.
(
a
)
(
b
)
(a) Position of leaf petioles to be sampled for tissue analysis at flowering (bloom) (b) from
mature leaves at veraison (Christensen et al. 1978). Reproduced with permission of
Division of Agriculture and Natural Resources, University of California.
Figure 5.3
as shown in figure 5.3. For later sampling, select the most recently matured leaf
on a shoot after the flowering period—usually the fifth to seventh leaf behind the
tip. Petioles are preferred over blades, for ease of handling, so the petiole is sepa-
rated from the blade and placed in a paper bag, to be sent for analysis. If toxicity
is suspected, blades may also be sent for analysis because elements such as B ac-
cumulate more in the blade than in the petiole. The samples should be rinsed in
distilled water or rainwater to remove dust and possible spray contaminants, and
blotted dry.
A Representative Sample
. Take one leaf per vine from the same variety on each
soil type. Usually 75-100 petioles from basal leaves or 100-150 petioles from the
youngest mature leaves are adequate for analysis. For comparative purposes, it is
wise to take separate samples from areas that are either performing well or poorly.
Test Results.
The results are reported in mg element (e.g., K) per kg dry mat-
ter, or as a percentage of dry matter (e.g., %N), as described in box 4.1. Remember
that biological material is naturally variable, so each mean or average value will
have an associated random error. With careful sampling and analysis, this error
can be kept to around
10%. Regular testing over several seasons should show
the general trend in nutrient concentrations, even though there may be some ran-
dom noise in the data. This is the basis of
crop logging
.
Keeping Records
. The condition of the vines and soil (especially soil moisture)
should be recorded at sampling, as well as the history of fertilizer or manure ap-
plications and any cultural operations (e.g., spraying with fungicides). These
records, together with the tissue tests and any soil tests, provide a valuable crop
log when compiled over several seasons.
