Soil salinity

ENVIRONMENTAL POLLUTION B 324, BT 327

DR. AHMAD MEKAWY

Soil salinity

 Soil salinization arises from natural causes and anthropogenic activity, such as irrigation in arid and semi-arid regions.

Soil salinity

 Saline soils contain a variety of salts, including Na₂SO₄, MgSO₄, CaSO₄, NaCl,MgCl₂, KCl and Na₂CO₃, but are normally dominated by NaCl, which causes most of the salt problems for higher plants in nature (Flowers et al., 1977).

 More than 800 million hectares of land throughout the world are salt affected (FAO.

2008). This amount accounts for more than 6% of the world’s total land area.

Salinity stress

Ionic stress Osmotic stress

Na⁺ toxicity

Excess Na⁺ influx K⁺ deficiency

• Leaf scenecense

• Inhibition of:

Protein synthesis Enzyme activity Dehydration

Inhibition of:

Cell elongation Leaf development

Inhibits Water uptake

Cell death

Ion homeostasis Na⁺ exclusion

Na⁺ compartmentation Na⁺ recirculation

Ion transporters:

HKT, NHX, SOS1 Osmotic adjustment

Accumulation of:

Ions, Solutes,

Organic compounds e.g. Proline

Salinity stress: Effects and tolerance mechanisms in plants

Adaptation

Enzymatic anti- oxidant defense

Anti-oxidant Enzymes:

APX, CAT, SOD, GR

Non-enzymatic anti- oxidant defense

Ascorbate, Glutathione, Polyamines,

Metallothioneins

Tolerance

Adaptation

Cell death

Adaptation

Excessive generation of reactive oxygen species

(ROS)

H₂O₂, OH^•, O₂ ⁻

Degradation:

Lipids, Proteins,

Photosynthetic pigments, Nucleic acids

ROS scavenging

Introduction

Salinity

Oxidative

stress

Epidermis

Cortex

Endodermis

X.Parenchyma

Xylem

Phloem Cs

?

CNGC1

PMP3

HKT2;1

Na⁺ Na⁺

H⁺

H⁺

H⁺

H⁺

Root Sheath

Leaf

HAK7

K⁺

Established function of Na⁺ transporters

Epidermis Cortex

Endodermis

X.Parenchyma Xylem

Cs

Na⁺ Na⁺

H⁺

H⁺

Root Sheath

Leaf

K+

(Sensitive variety)

Salinity stress conditions

Epidermis Cortex X.Parenchyma Xylem

Cs

Na⁺ Na⁺

H⁺

H⁺

Root Sheath

Leaf

K+

Salinity stress conditions

(Tolerant variety)

Endodermis

Soil salinization and management of salt-affected soils in the Nile Delta of Egypt

Case study

• Egypt is located in the northeastern part of Africa

Climate

• Daily evaporation ranges from ca. 2.0 to 10.0 mm (MPWRDU, 1981). Thus, crop production requires intensive irrigation.

• The climate is categorized as arid in the north (Alexandria) to extremely arid in the south (Aswan).

• The mean effective rainfall over the entire country is near zero since precipitation is nil.

• Almost 35% of the agricultural lands (1 Mha) in Egypt suffer from salinity, wherein the electrical conductivity (EC) is higher than 4 dS/m (GARE, 1992).

Soil salinization

Indeed, the current situation is serious and threatens the agricultural sustainability.

• The majority of the salt affected lands exist in the Lower Delta.

The Nile Valley

• Croplands in Egypt are 100% irrigated since precipitation is very scarce and evaporation is very high.

• Before the construction of Aswan dam, floods from the Nile brought high water and

natural nutrients and minerals that annually enriched the fertile soil along the floodplain and delta; this made the Nile valley ideal for farming.

• The intensive irrigation of cropland under an arid climate is the main reason for secondary soil salinization in Egypt.

Nile Valley Nile Delta

When the traditional flood basin irrigation was substituted by perennial method without establishing an adequate drainage system, farmers started to experience soil salinization problems :

Causes of soil salinization in the Nile Valley

• High water table, resulting from either over-irrigation or insufficient drainage system,

• Irrigation with salty drainage and groundwater,

• Accumulation of surface runoffs in low-lying areas, lateral movement of subsurface water from up slope to down-slope irrigated lands,

• Overuse of salt-generating agrochemicals.

Nile Valley Nile Delta

In the Mediterranean coastal plains and lower Delta, excessive rates of groundwater withdrawal has resulted in a large drop in the water table and, as a consequence, seawater intruded into the aquifers (GARE, 1992).

Causes of soil salinization in the Nile Delta

The main reasons for soil salinity in these areas include:

• Seawater intrusion,

• Irrigation with low quality (saline) water as they are located at the downstream regions of the system,

• Inadequate field drainage.

Management of soil

salinization problem

• The severity of the salinization problem has forced both government and private sectors to work jointly to alleviate production losses from drainage-impacted lands. The Egyptian Public Authority for Drainage Projects (EPADP) has installed a network of

subsurface drainage

ca. 50% of the total cultivated areas in Egypt.

Drainage system installation

Crop yields have markedly increased after completion of the first phase of tile drainage projects in 250 000 ha of the Nile Valley and Delta.

• The Government has, moreover, initiated an ambitious land improvement program. Carrying out sub-soiling to improve the sub-soil drainage conditions, land leveling by laser beam,

mechanical cleaning of water courses, and application of gypsum (CaSO₄) amendment to control alkalization.

The increase in yield has sharply dropped after three years. Therefore, it may be necessary to renew the soil improvement program every three years.

Land improvement

Marginal Productive

• In 1997, 89 newly bred rice lines were tested under saline conditions with some commercial varieties.

Some promising entries exhibited higher yield than the respective check varieties.

Breeding for salinity tolerance

• Salinity-tolerant varieties are badly needed for presently cultivated saline soils and newly reclaimed lands in Egypt.

• Breeding for salinity tolerance is in progress and a further program of hybridization between salinity- tolerant varieties and different required characters has been taken up.