Agriculture Reference
In-Depth Information
ity levels greater than 4,000 ยต mho/cm that cannot be reclaimed by leaching
with large amounts of low-saline water, the production of horticulture crops
is limited to a few vegetable crops, including beets, broccoli, squash, toma-
toes, and asparagus.
Particularly troublesome are saline-sodic soils found in the American
west. The abundant sodium and other ions in these soils interfere with the
formation of soil aggregates that are necessary for water drainage. Such
soils form slick, sometimes oil-colored, deposits that do not support plant life.
Saline soils can be reclaimed, in some cases, by leaching with large amounts
of water. Saline-sodic soils can be reclaimed using gypsum and leaching. A
much better practice, however, is to avoid planting fruit trees on saline or
saline-sodic soils.
Soil Organic Matter
The management of organic matter in soil is very important but sometimes
misunderstood. Organic matter, as measured in soil tests, refers to chemically
stable, invisible compounds, such as humic acids, that bind soil particles to-
gether. It does not refer to visible pieces of plant matter or manures.
As organic materials fall onto or are incorporated into the soil, they begin
a complex process during which they break down and are changed physic-
ally and chemically. During this process, the organic matter provides food for
micro- and macroorganisms in the soil, adds nutrients to the soil, and alters
soil water-holding capacity and drainage. Chemicals are eventually formed
from the organic residues and serve as glues that bind soil particles into lar-
ger clumps or aggregates. As the aggregates develop, open pore spaces also
form in the soil. These pore spaces allow for the exchange of gases, facilitate
root growth, and provide surfaces where roots can take up water and nutri-
ents.
Sandy soils are inherently low in organic matter and respond slowly to
programs designed to increase organic matter. In commercial Washington
State orchards located on sandy soils, for example, soil organic matter may
require 5 to 10 years to increase significantly after transition to organic
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