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2. Soil Fundamentals
Excessive salts in soils can also make it harder
for roots to take up salty water in the soil and
can result in drought-like symptoms in plants,
even following a recent rain or irrigation event
Excessive amounts of sodium can deteriorate
soil structure due to aggregate breakdown.
As described above in the sections on pore
space and compaction, loss of aggregates can
cause poor water infiltration. These changes
make plant growth difficult and may drastically
affect crop yield.
In New Mexico and Colorado, considerable
areas experience salinity and sodicity
concerns for soils. These concerns can be
addressed through management of irrigation,
drainage, and plant selection, but remediation
can take considerable time, especially under
prolonged drought conditions.
Salts—including chlorides, nitrates,
carbonates, sulfates, and sodium, potassium,
calcium, and magnesium—most often come
from the bedrock. When there is insufficient
weathering from water to flush them from the
upper soil horizons, they remain in the soil.
Salts can also be transported to soil through
irrigation water or some composted manures.
As water flows through irrigation ditches,
especially unlined dirt canals, it can pick up
salts from soils and deposit them on the field
where it is used for irrigation. Overtime, these
salts accumulate in the soil when evaporation
occurs faster than precipitation. Evaporation
increases with the replacement of native,
deep-rooted, perennial plant communities
with annual crop species, as well as with soil
surface exposure.
Salinity and Sodicity
Glossary
Salinity
the measure of salts in soil. Salinity can be
measured in soil and irrigation water using a
test called electrical conductivity.
Glossary
Sodicity
the accumulation of sodium salt relative
to other types of salts, especially calcium.
Sodicity is measured with the sodium
absorption ratio (SAR), based on the relative
amounts of sodium compared to calcium
and magnesium. SAR can be determined for
soil and also for irrigation water. In sodic soils
the SAR will be greater than 13. In saline soils
it will be below 13, and the concentration of
salts will be sufficient to impair productivity.