Agriculture Reference
In-Depth Information
Examples of Element Deficiencies and Their Visual Symptoms in Grapevines
Table 5.1
Deficient Element
Description of Symptoms
N
Fe, Mg, Mn
K
Overall reduction in growth; leaf yellowing
Interveinal chlorosis; chlorophyll retained along the leaf veins only
Starts as a yellowing of older leaf margins. As deficiency worsens,
margins die (necrosis) and curl, and the chlorotic areas become a
bronze color.
Stunted lateral shoots with small leaves; fruit set is affected
Dark green, small leaves; short internodes, stunted growth
Stunting of the shoot and death of the shoot tip; leaves near the tip
develop interveinal chlorosis and die
Zn
Cu
B
chlorosis, stunted growth of shoots, necrosis of leaf margins, irregular fruit set,
and small berries. Chlorosis is a generic term for leaf yellowing due to loss of
chlorophyll. N deficiency typically causes an overall chlorosis of the leaves, but in
other cases chlorosis occurs between the leaf veins (interveinal chlorosis). Some
examples of visual symptoms are given in table 5.1 and figure 5.1.
The location of visual symptoms depends on the mobility of the element in
the plant tissues, as indicated in table 5.2. Elements are mobile because they are
primarily in ionic form in the tissue (e.g., K
, Na
, and Cl
) or because they are
in high demand for growth, and so are translocated from older, mature organs to
young growing tissues (e.g., N and P). Further details of visual symptoms of de-
ficiency or toxicity are given in specialist topics such as Christensen et al. (1978)
and Goldspink (1996).
Diagnosing deficiencies and toxicities can be confusing because of the simi-
larity between symptoms caused by different elements (e.g., Fe, Mg, and Mn).
The confusion is compounded if more than one element is deficient. Also, visual
symptoms appear only after the plant has suffered a check to growth due to a
“hidden hunger” for the element. This is illustrated by the well-established rela-
tionship between yield and the concentration of an essential element in a plant's
tissues (fig. 5.2). The relationship shows that plant yield responds to an increase
in the supply of a nutrient, such as N, up to a maximum value. The N concen-
tration in the tissue also increases, and the approximately linear range between
“severe deficiency” and “optimum” is used to assess the degree of deficiency. This
is the basis for the diagnosis of nutrient status by plant analysis, or
tissue testing
.
The
critical value
is the element concentration in the plant below which an
increase in supply leads to increased yield (fig. 5.2). Note that in the “luxury con-
sumption” range, yield may decline due to nutrient imbalances or outright tox-
icity. A good example in grapevines is toxicity that results from excess concentra-
tions of Na
and Cl
in the leaves, which shows up as severe marginal leaf burn.
Perennial crops such as grapevines are more suited to tissue testing than annual
crops, for which soil analysis or
soil testing
is more common. However, soil test-
ing is the only tool available to a grower at the establishment stage of a vineyard.
Soil testing is also most useful for determining whether lime is needed (section
5.5.3) and for assessing soil salinity (section 7.2.2). It can also be used as a backup
for tissue testing. Soil testing is discussed in section 5.3.
