Our Indispensable Soil - Soil: Reflections on the Basis of our Existence - page 12

How Salt Affects Soil
Increasing salinity is another major problem in world food production. It is caused
when mineral salts released from the bedrock rise with water to the earth's surface
in areas of low rainfall. Salt crystals form at the surface, especially if crops are irri-
gated with saline groundwater, which can lead to the land becoming infertile. Cato
the Elder, who is said to have concluded his speeches to the Roman Senate with the
words “I declare that Carthage must be destroyed”, sought to achieve this objective
by spreading salt on the fields to make them unfit for cultivation. The Romans did
indeed take Carthage in the end, but sought to harness rather than destroy the town's
resources. They invested in infrastructure, building Roman baths, and when I visited
the site, north of Tunis, I found the land to be lush and green. Cato either refrained
from implementing his project or else rain washed the salt away.
Annual rainfall is considerably lower in southern Tunisia than in Carthage, and
large areas of land here are impacted by salinity. Salt has a number of negative effects
on the soil and the plants that grow on it. Sodium, found in common household salt,
damages soil aggregates and earth containing high levels of sodium and low levels of
calcium tends to become compacted and almost impervious to plant life. Adding cal-
cium, preferably in the form of gypsum, improves the soil structure and adds porosity.
The ways of salt. Some plants manage to grow in saline soils by forming substances that can retain
water in their roots even when the groundwater is salty. Some of them secrete excess salt through
special glands in their leaves, which has the added benefit of protecting them from being grazed by
sheep and goats. The photo shows the salt crystallized into a white powder on the soil surface