Agriculture Reference
In-Depth Information
Applying Potassium
Potassium is relatively immobile on heavy-textured soils and, in such cases,
is best broadcast throughout the orchard before planting your trees. On
sandy soils, potassium can be highly mobile and is best broadcast shortly be-
fore or at the time of planting. On loams and heavier soils, apply the potassi-
um 1 or 2 years before planting fruit trees. Base your potassium applications
on “available potash” or K O. As with phosphorus, many materials contain
2
high concentrations of potassium, but not necessarily in forms that are avail-
able to plants.
Be cautious not to add too much potassium, as it can interfere with cal-
cium uptake and metabolism in fruit trees. The problem is especially serious
with apples, where excessive amounts of potassium may increase bitter pit
problems in stored fruit.
Sulfur
Sulfur is seldom deficient in soils to the extent that it is necessary to apply
sulfur amendments before planting. Deficiencies are most likely to occur on
sandy soils that are low in organic matter, which allows the sulfur to leach
from the root zone. If your soil test shows less than 10 ppm sulfur and your
soil pH is 6.5 or below, add about 175 pounds of gypsum per acre any time
before planting. Repeat annually, as necessary, until soil tests show 10 ppm
or more sulfur. If your soil pH is above 7.0, add elemental sulfur a year be-
fore planting your trees. Table 4.4 shows the amount of elemental sulfur
needed, depending on soil pH and soil type.
Calcium
Calcium is seldom deficient in soils, particularly in arid regions. It is most
likely to be deficient in sandy, acidic soils. The amount of calcium available
to crops, however, depends not only on the amount of calcium present in the
soil, but also on the cation exchange capacity of the soil (CEC), which is re-
ported in milliequivalents/100 grams of soil. CEC refers to the ability of neg-
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