Nutrient Management - Growing Organic Orchard Fruits - page 404

Greensand. This is a source of potassium (see page 104 ➔ ).
Gypsum. Also known as calcium sulfate, gypsum adds both calcium and sul-
fur to the soil without changing the soil pH (see page 105 ➔ for more inform-
ation). When calcium is needed and the soil is already at pH 6.5 or greater,
gypsum is an excellent source of calcium. Likewise, when sulfur is needed
and the soil is pH 6.5 or lower, gypsum is the material of choice.
Gypsum is often touted as a “soil conditioner.” That claim is true, but only
in very specific cases. Gypsum is used to reclaim saline-sodic soils that are
found most often in the arid regions of western North America. These soils
have both high pH values and high sodium contents. They are very com-
pacted and drain poorly, often forming what appear to be oily patches, earn-
ing them the common name of “slick soils.” High concentrations of sodium
in such soils displace calcium and other nutrients, destroying soil aggregates
and creating dense, virtually lifeless soils. When gypsum is combined with
tillage and water to flush the sodium soils out of the root zone, the calcium in
gypsum occupies the negatively charged sites on soil particles, flocculating
(fluffing up) the soil and forcing the sodium out. Aside from its effective-
ness on saline-sodic soils, however, gypsum's “soil conditioner” properties are
highly questionable. Although it is a valuable tool for orchardists, be careful
not to give gypsum more credit than it deserves.
In conventional cropping systems, borated gypsum is often used to supply
boron. This material typically contains about 1 percent boron and is applied
at a rate of about 175 pounds per acre, broadcast across the entire field.
There are naturally occurring sources of boron-containing gypsum, but not
many. If you choose to apply borated gypsum, ensure that it is approved for
organic use and ensure that the boron concentration is not high enough to
damage your crops. Limit boron applications to no more than 1 to 2 pounds
of actual boron per acre and only when soil or tissue analyses document a
boron deficiency. Never band boron-containing fertilizers into crop rows.