Management of Salt-Affected Soils in the Nile Delta

Abstract

Salt-affected soils in the Nile Delta are formed as a result of climate and inappropriate soil management (secondary is important here because there is initial or primary salinity referring to the effect of parent material, but the Egyptian parent material is the mud which comes by the Nile stream and leached through 1,800 km, the distance between Egypt and Ethiopia). Irrigation water, water logging, and saline water intrusion of the Mediterranean are the three sources of different types of salt-affected soils in the Nile Delta. Saline, saline-sodic, and sodic soils have strong presence in the delta land and represent an average of 37% of the total cultivated soils. The south delta is threatened by sodicity according to the low-salinity soils and highly carbonated irrigation water, while the north delta contains the highest area of saline and saline-sodic soils reaching 46%. Poor drainage in addition to reuse of more than 10 billion cubic meters of saline drainage water supports the buildup of salinity and sodicity. Gypsum amendment (CaSO₄·2H₂O) associated with intermittent leaching is the common method used in reclaiming salt-affected soils in Egypt. Furrow irrigation and rice cultivation under ponding are another two methods to adapt and mitigate salinity and sodicity buildup in the delta lands. The dominant salts in the delta are saline and sodic soils are sodium sulfate (NaSO₄) and sodium carbonate and bicarbonate (Na₂CO₃ and NaHCO₃). The solubility of these salts decreases sharply with temperature decreases; accordingly the reclamation and leaching processes should be applied during the summer warm season only. Improving drainage and preventing industrial and sanitary wastes in agricultural drain is a must.

Glossary

Exchangeable sodium percentage (ESP)

Percentage of the cation exchange capacity that is filled by sodium. To convert SAR to ESP, use the following equation:

ESP = 1.475 × SAR/1 + (0.0147 × SAR)

Productive soil

A soil in which the chemical, physical, and biological conditions are favorable for the production of crops suited to a particular area.

Reclamation rehabilitation/restoration

The process of reconverting disturbed land to its former or other productive uses.

All practicable and reasonable methods of designing and conducting an activity to ensure:

1.  Stable, non-hazardous, non-erodible, favorably drained soil conditions, and equivalent land capability.

2.  The removal of equipment or buildings or other structures and appurtenances. The decontamination of buildings or other structures or other appurtenances, or land or water. The stabilization, contouring, maintenance, conditioning, or reconstruction of the surface of land. Any other procedure, operation, or requirement specified in the regulations (regulatory definition).

Rehabilitation reclamation/restoration

Implies that the land will be returned to a form and productivity in conformity with a prior land use plan, including a stable ecological state that does not contribute substantially to environmental deterioration and is consistent with surrounding aesthetic values.

Remediation decontamination

The removal, reduction, or neutralization of substances, wastes, or hazardous material from a site so as to prevent or minimize any adverse effects on the environment now or in the future.

Saline-alkali soil (saline-sodic soil)

A soil containing enough exchangeable sodium to interfere with the growth of most crop plants and containing appreciable quantities of soluble salts. The exchangeable sodium percentage is greater than 15, the conductivity of the saturation extract is greater than 4 dS/m at 25 °C, and the pH is usually 8.5 or less in the saturated soil; or a saline-alkali soil has a combination of harmful quantities of salts and either a high alkalinity or high content of exchangeable sodium, or both, so distributed in the profile that the growth of most crop plants is reduced.

A non-alkali soil containing soluble salts in such quantities that they interfere with the growth of most crop plants. The conductivity of the saturation extract is greater than 4 dS/m, the exchangeable sodium percentage is less than 15, and the pH is usually less than 8.5.

Saline soils

State in soil caused by the presence of soluble salt (ions such as Na, Ca, K, Mg, Cl, SO4) yielding an electrical conductivity of at least 2 dS/m.

Salinization

The process of accumulation of salts in soils.

Sodicity

A measure of the amount of sodium on the exchange complex (often expressed as sodium adsorption ratio—SAR).

Sodic soil

A soil containing sufficient exchangeable sodium to interfere with the growth of most crop plants. SAR of the saturation paste extract is greater than 15.

Soil degradation

Any change or disturbance to the soil perceived to be deleterious or undesirable.

The decline in soil productivity through its use and/or misuse by humans.

The result of one or more processes which lessen the current and/or potential capability of soil to produce (qualitatively and/or quantitatively) goods and/or services.

Soil improvement

Increasing a soil’s capability to sustain plant growth by drainage and irrigation or through the addition of various soil amendments such as fertilizers.

Soil management

The sum total of all tillage operations, cropping practices, fertilizer, lime, and other treatments conducted on or applied to a soil for the production of plants.