Page 155 - Soil Degradation, Conservation and Remediation

144 5 Chemical Soil Degradation

Fig. 5.1 Underground pipe drainage system removes leaching water (Photo courtesy of USDA-NRCS)

requirement models have been proposed by Corwin et al. (2007). Leaching is most
often accomplished by ponding fresh water on the soil surface and allowing it to
infiltrate. Effective leaching occurs when the salty drainage water is discharged
through subsurface drains that carry the leached salts out of the area under reclama-
tion. Leaching may reduce salinity levels when there is sufficient natural drainage,
that is, the ponded water drains without raising the water table. Leaching should
preferably be done when the soil moisture content is low and the groundwater table
is deep. The ability to leach water through the soil profile is dependent upon good
internal drainage. In fact, the overall effectiveness of a reclamation system is depen-
dent upon leaching. Leaching carries the salts down through the soil profile and out
of the rooting zone. Without it, salts will accumulate regardless of any applied soil
amendments. If natural drainage is poor, then a tile or pipe drain (Fig. 5.1) should
be installed under expert supervision of professionals. When properly installed, they
are highly effective at carrying away the leached salts. Tile can only drain water if
it is placed below the zone of saturation. Several methods of irrigation and drainage
may be employed for salt and water management in saline soils. Drip and sprinkler
irrigation methods are suitable in slightly saline soils.

5.5 Salt-Tolerant Crops

Some crops are tolerant to a level of soil salinity. It means that the yield of the crop is
not reduced more than 25 % in the ECe level. Some crops are slightly tolerant; others
are highly tolerant. Farmers should choose crops or crop sequences on the salinity
values of their soils. Salinity tolerance of some field crops is given in Table 5.8.