Agriculture Reference
In-Depth Information
which should be cultivated into the soil to accelerate their effect in raising soil
pH. The amount of lime needed to raise the soil pH to the desired value is called
the
lime requirement
. The desired pH is in the range 5.5-6.5, high enough to
eliminate any inhibitory effect of Al
3
ions on root growth and to optimize mi-
cronutrient availability.
■
S is supplied in SSP, gypsum, or K
2
SO
4
, and also as elemental S in wettable dusts
for powdery mildew control. N and S can also come from the atmosphere in rain
or as dry deposition. P has a long residual effect in soil as a result of
P fixation
,
and does not leach. S leaches as SO
4
2
, and does not have a long residual effect
(unless it remains in the elemental form).
■
K is supplied as K
2
SO
4
, KNO
3
, and KCl, though extra input of Cl should be
avoided in soils with some salinity. High concentrations of tissue K (
2% DM)
must be avoided because of adverse effects on berry pH and wine quality.
■
The availability of micronutrients is influenced by soil pH. The cations Fe
3
,
2
Mn
2
, Cu
2
, and Zn
2
are more available at low pH, whereas the anion MoO
4
is more available at high pH. B exists as H
3
BO
3
, and as B(OH)
4
at high pH.
Micronutrient deficiencies are most commonly corrected with foliar sprays. Lime-
induced Fe chlorosis on calcareous soils depends on the fraction of “active” (finely
divided) CaCO
3
.
■
Waterlogging should be avoided, not only because of its direct impact on vine
growth but also because of undesirable redox reactions, such as denitrification, re-
duction of Mn and its increased solubility (to potentially toxic levels), and re-
duction of SO
4
2
.
■
Organic viticulture involves growing grapes without the use of manufactured
chemicals as fertilizers or for weed, pest, and disease control. Certified organic
vineyards must be registered and inspected by recognized organizations. But many
vignerons are voluntarily reducing their reliance on pesticides and fungicides
through
integrated pest management
.
■
Organic manures (mainly poultry manure), composted plant material, and cover
crops can potentially be used in organic viticulture. RPRs, elemental S, and Bor-
deaux Mixture (a traditional Cu spray) are also acceptable.
