Agriculture Reference
In-Depth Information
compounds to form complexes that can be used as micronutrient fertilizers (see
“MicronutrientFertilizers”).
Molybdenumoccursasthemolybdateanion(MoO
4
2−
), which behaves like
H
2
PO
4
−
. It is strongly adsorbed to Fe and Al oxides at low pH and becomes more
available as the pH increases. Boron occurs as neutral boric acid (H
3
BO
3
) up to
pH 8, when it begins to dissociate and release the borate anion B(OH)
4
−
, which is
weakly adsorbed by oxides.
Testing for Deficiencies and Toxicities in Grapevines
What You Can See
The first sign of a nutritional problem may be a “visual symptom”—an abnormal-
ity in growth, leaf color, flowering, or fruit set—that suggests one or more of the
essential elements is in short supply, or perhaps there is a toxicity, as might occur
with too much Na or Cl. Where the symptoms appear depends on an element's
mobility. An element is mobile if it exists as an ion in the tissue (e.g., K
+
, Na
+
,
and Cl
−
) or because it is in high demand and is translocated from older, mature
parts to young growing tissues (e.g., N and P). Some of the more obvious visual
symptoms are
• Chlorosis,referringtoleafyellowingresultingfromalackofchlorophyll.
Nitrogendeiciencytypicallycausesoverallchlorosis,whereasFe,Mg,
and Zn deficiencies cause yellowing between the leaf veins (interveinal
chlorosis)
• Necrosis,referringtothedeathofleaftissue.Asadeiciencybecomes
more severe, leaves may discolor and begin to die. Necrosis can also start as
a scorching of leaf margins, as in the case of Cl toxicity
• “Henandchickens”appearance,whichreferstobuncheshavingafew
normal berries and many small, seedless berries. This can occur with Zn
and B deficiencies.
Table 3.4 summarizes nutrient deficiency symptoms, and figure 3.7 shows
examples of deficiencies. Goldspink and Howes (2001) give further details of defi-
ciency and toxicity symptoms in grapevines.
Plant Analysis
Diagnosis of deficiencies and toxicities can be confusing when symptoms
causedbydiferentelementsaresimilar(e.g.,Fe,Mg,andZn).Also,visual
symptoms appear only after the plant has suffered a check to growth as a result
