Agriculture Reference
In-Depth Information
Optimum
range
“Luxury
consumption”
“Hidden humger,”
symptoms may
not be obvious
Severe
deficiency,
marked visual
symptoms
Critical
value
Tissue N concentration (%)
Figure 3.8 Stages from severe nutrient deficiency to luxury
consumption according to tissue concentrations. (White, 2003)
Sampling Protocol for Plant Analysis
Which Part?
Because nutrients can be remobilized in response to a change in the site of great-
est demand as a vine grows, the part to be sampled for analysis must be specified.
It is generally recommended that leaf petioles be sampled because they are more
responsive to a vine's nutrient status than leaf blades. Whether blades or petioles
are sampled, washing and damp-drying are advisable to avoid the effect of dust on
the analysis.
The leaf sampled should be a basal leaf opposite a bunch—usually the fourth
or fifth leaf from the base of a shoot, as shown in figure 3.9A. The petiole is sepa-
rated from the blade and placed in a paper bag, to be sent to a laboratory for
analysis as soon as possible. If toxicity is suspected, leaf blades may also be sent
for analysis because elements such as B accumulate more in the blade than the
petiole. If blades are sampled, the most recently matured leaf on a shoot is recom-
mended—usually the fifth to seventh leaf behind the tip (figure 3.9B).
Time of Sampling
The concentration of nutrients such as N, P, and K is greatest in young leaves and
declines as the leaf ages. Table 3.5 gives an example of how the concentrations of
mobile elements can change with the stage of growth. Traditionally, petioles are
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