Agriculture Reference
In-Depth Information
Table 3.12
Common Magnesium and Potassium Fertilizers for Vineyards
Element
content (%)
Compound
Chemical formula
Comments
Magnesium
a
Epsom salts
MgSO
4
.7H
2
O
10
Water-solubleformofMgfertilizer;
used as a foliar spray at rates up
to 10 g/L
Potassium
Sulfate of potash
K
2
SO
4
41
Supplies K and S; preferred on saline
soils
Potassium nitrate
KNO
3
38
Verysoluble,suppliesKandN;not
to be used if vine N status is high;
used as a foliar spray at rates up
to 10 g/L
Muriateofpotash
KCl
50
Verysolubleinwater;granularand
easier to handle than K
2
SO
4
; not
suitable as a foliar spray because of
Cl content
a
Magnesiumisalsosuppliedinsomelimingmaterials(seetableB3.6.1).
industrialized regions. Spray sulfur is supplied as a wettable powder with more
than 80% of particle sizes less than 125 μm and is easily mixed with water.
Rain washes the fine S particles from leaves into the soil where they must be
oxidized to SO
4
2−
before being absorbed by vine roots. The oxidation of S is slow
and produces some sulfuric acid (H
2
SO
4
) that contributes to soil acidification.
WiththeseSinputs,speciicapplicationsofSfertilizersarerarelyrequiredin
vineyards.
Micronutrient Fertilizers
Micronutrientsarecommonlyappliedasfoliarsprays,forthereasonthatelements
suchasFe,Cu,Zn,andMnarestronglyboundbyclaysandorganicmatterand
also form insoluble precipitates at neutral to alkaline pHs. For example, grape-
vines are susceptible to Fe deficiency in chalk and limestone soils, a condition
called lime-induced chlorosis (see figure 3.7A). Susceptibility to lime-induced
chlorosis of vines on own roots or rootstocks is discussed in “Other Rootstock
Attributes,” chapter 5.
Copper,Zn,andMnarepresentinmanyfungicidalsprays,which,ifused,
remove the need for dedicated foliar applications. The effectiveness of a spray
depends on how easily the nutrient penetrates a leaf and its mobility within the
tissue. A surfactant included in the spray improves leaf wetting and nutrient
penetration.
