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    3. SALINE SOILS AND THEIR MANAGEMENT

    3. SALINE SOILS AND THEIR MANAGEMENT

    3.1 Characteristics

    3.2 Reclamation and management

    3.3 Crops in saline soils

    3.1 Characteristics

    3.1.1 Measuring salinity status

    3.1.2 Salinity and plant growth

    The distinguishing characteristic of saline soils from the agricultural standpoint, is that they contain sufficient neutral soluble salts to adversely affect the growth of most crop plants. For purposes of definition, saline soils are those which have an electrical conductivity of the saturation soil extract of more than 4 dS/m at 25°C (Richards 1954). This value is generally used the world over although the terminology committee of the Soil Science Society of America has lowered the boundary between saline and non-saline soils to 2 dS/m in the saturation extract. Soluble salts most commonly present are the chlorides and sulphates of sodium, calcium and magnesium. Nitrates may be present in appreciable quantities only rarely. Sodium and chloride are by far the most dominant ions, particularly in highly saline soils, although calcium and magnesium are usually present in sufficient quantities to meet the nutritional needs of crops. Many saline soils contain appreciable quantities of gypsum (CaSO4, 2H2O) in the profile. Soluble carbonates are always absent. The pH value of the saturated soil paste is always less than 8.2 and more often near neutrality (Abrol et al., 1980). Physico-chemical characteristics in respect of a few typical saline soil profiles are presented in Tables 5-8.

    Excess salts keep the clay in saline soils in a flocculated state so that these soils generally have good physical properties. Structure is generally good and tillage characteristics and permeability to water are even better than those of non-saline soils. However, when leached with a low salt water, some saline soils tend to disperse resulting in low permeability to water and air, particularly when the soils are heavy clays. Leaching may also result in a slight increase in soil pH due to lowering of salt concentration but saline soils, as will be shown later, rarely become strongly sodic upon leaching if there is an adequate drainage system.

    In field conditions, saline soils can be recognized by the spotty growth of crops and often by the presence of white salt crusts on the surface. When the salt problem is only mild, growing plants often have a blue-green tinge. Barren spots and stunted plants may appear in cereal or forage crops growing on saline areas. The extent and frequency of bare spots is often an indication of the concentration of salts in the soil. If the salinity level is not sufficiently high to cause barren spots, the crop appearance may be irregular in vegetative vigour.

    Moderate salinity, however, particularly if it tends to be uniform throughout the field, can often go undetected because it causes no apparent injuries other than restricted growth. Leaves of plants growing in salt infested areas may be smaller and darker blue-green in colour than the normal leaves. Increased succulence often results from salinity, particularly if the concentration of chloride ions in the soil solution is high. Plants in salt-affected soils often have the same appearance as plants growing under moisture stress (drought) conditions although the wilting of plants is far less prevalent because the osmotic potential of the soil solution usually changes gradually and plants adjust their internal salt content sufficiently to maintain turgor and avoid wilting.

    Symptoms of specific element toxicities, such as marginal or tip burn of leaves, occur as a rule only in woody plants. Chloride and sodium ions and boron are the elements most usually associated with toxic symptoms. Non-woody species may often accumulate as much or more of these elements in their leaves without showing apparent damage as do the woody species.

    Table 5 CHARACTERISTICS OF TYPICAL SALINE SOILS

    * pHS - pH measured on soil saturated paste.

    Table 6 TYPICAL SALINE SOIL REPRESENTING ADDALA SERIES, IRAQ (Sehgal, 1980)Depth cmMechanical Composition %pHsECe dS/mComposition of the Saturation Extract me/lSAROrganic Matter %Clay <2 Silt (2-50 )Sand (50 m- 2 mm)Na+Ca++Mg++Cl-SO4 -

    0 - 15 1.1 39 46 15 7.4 12 20 78 30 111 16 2.7 15 - 37 0.9 40 46 14 7.6 13 48 70 30 123 20 6.7 37 - 66 0.6 43 51 6 7.9 10 66 30 28 87 42 12.0 66 - 127 0.6 37 52 11 7.9 14 106 40 26 93 68 18.0 127 - 136 0.5 37 55 8 7.9 15 123 32 38 105 96 22.0

    Table 7 TYPICAL SALINE SOIL REPRESENTING ABU-HALANA SERIES, IRAQ (Sehgal 1980)Depth cmMechanical Composition %pHsECe dS/mComposition of the Saturation Extract me/lSAROrganic Matter %Clay <2 Silt (2-50 )Sand (50 m- 2 mm)Na+Ca++Mg++Cl-SO4 -

    0 - 17 1.1 49 49 2 7.0 49 320 164 178 618 26 24 17 - 57

    स्रोत : www.fao.org

    Introduction to Soil Salinity, Sodicity and Diagnostics Techniques

    It is widely recognized that soil salinity has increased over time. It is also triggered with the impact of climate change. For sustainable management of soil salinity, it is essential to diagnose it properly prior to take proper intervention measures. In this...

    Introduction to Soil Salinity, Sodicity and Diagnostics Techniques

    Shabbir A. Shahid, Mohammad Zaman & Lee Heng

    Chapter Open Access

    First Online: 29 November 2018

    45k Accesses 27 Citations 21 Altmetric

    Abstract

    It is widely recognized that soil salinity has increased over time. It is also triggered with the impact of climate change. For sustainable management of soil salinity, it is essential to diagnose it properly prior to take proper intervention measures. In this chapter soil salinity (dryland and secondary) and sodicity concepts have been introduced to make it easier for readers. A hypothetical soil salinity development cycle has been presented. Causes of soil salinization and its damages, socio-economic and environmental impacts, and visual indicators of soil salinization and sodicity have been reported. A new relationship between ECe (mS/cm) and total soluble salts (meq/l) established on UAE soils has been reported which is different to that established by US Salinity Laboratory Staff in the year 1954, suggesting the latter is specific to US soils, therefore, other countries should establish similar relationships based on their local conditions. Procedures for field assessment of soil salinity and sodicity are described and factors to convert EC of different soil:water (1:1, 1:2.5 & 1:5) suspensions to ECe from different regions are tabulated and hence providing useful information to those adopting such procedures. Diversified salinity assessment, mapping and monitoring methods, such as conventional (field and laboratory) and modern (electromagnetic-EM38, optical-thin section and electron microscopy, geostatistics-kriging, remote sensing and GIS, automatic dynamics salinity logging system) have been used and results are reported providing comprehensive information for selection of suitable methods by potential users. Globally accepted soil salinity classification systems such as US Salinity Lab Staff and FAO-UNESCO have been included.

    Keywords

    Salinity Sodicity Diagnostics Electromagnetic Geostatistics GIS Kriging Electron microscopy

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    1 Introduction

    Soil is a non-renewable resource; once lost, can’t be recovered in a human lifespan. Soil salinity, the second major cause of land degradation after soil erosion, has been a cause of decline in agricultural societies for 10,000 years. Globally about 2000 ha of arable land is lost to production every day due to salinization. Salinization can cause yield decreases of 10–25% for many crops and may prevent cropping altogether when it is severe and lead to desertification. Addressing soil salinization through improved soil, water and crop management practices is important for achieving food security and to avoid desertification.

    1.1 What Is Soil Salinity?

    Soil salinity is a measure of the concentration of all the soluble salts in soil water, and is usually expressed as electrical conductivity (EC). The major soluble mineral salts are the cations: sodium (Na+), calcium (Ca2+), magnesium (Mg2+), potassium (K+) and the anions: chloride (Cl−), sulfate (SO4 2−), bicarbonate (HCO3 −), carbonate (CO3 2−), and nitrate (NO3 −). Hyper-saline soil water may also contain boron (B), selenium (Se), strontium (Sr), lithium (Li), silica (Si), rubidium (Rb), fluorine (F), molybdenum (Mo), manganese (Mn), barium (Ba), and aluminum (Al), some of which can be toxic to plants and animals (Tanji 1990).

    From the point of view of defining saline soils, when the electrical conductivity of a soil extract from a saturated paste (ECe) equals, or exceeds 4 deci Siemens per meter (dS m−1) at 25 °C, the soil is said to be saline (USSL Staff 1954), and this definition remains in the latest glossary of soil science in the USA.

    1.1.1 Units of Soil Salinity

    Salinity is generally expressed as total dissolved solutes (TDS) in milli gram per liter (mg l−1) or parts per million (ppm). It can also be expressed as total soluble salts (TSS) in milli equivalents per liter (meq l−1).

    The salinity (EC) was originally measured as milli mhos per cm (mmho cm−1), an old unit which is now obsolete. Soil Science has now adopted the Systeme International d’Unites (known as SI units) in which mho has been replaced by Siemens (S). Currently used SI units for EC are:

    milli Siemens per centimeter (mS cm−1) or

    deci Siemens per meter (dS m−1)

    The units can be presented as:

    1 mmho cm−1 = 1 dS m−1 = 1 mS cm−1 = 1000 micro Siemens per cm (1000 μS cm−1)

    EC readings are usually taken and reported at a standard temperature of 25 °C.

    For accurate results, EC meter should be checked with 0.01 N solution of KCl, which should give a reading of 1.413 dS m−1 at 25 °C.

    No fixed relationship exists between TDS and EC, although a factor of 640 is commonly used to convert EC (dS m−1) to approximate TDS. For highly concentrated solutions, a factor of 800 is used to account for the suppressed ionization effect on EC.

    Similarly, no one relationship exists between ECe and total soluble salts (TSS), although a factor of 10 is used to convert ECe (dS m−1) to TSS (expressed in meq l−1) in the EC range of 0.1–5 dS m−1 (USSL Staff 1954). One relationship between ECe and TSS is presented in the Agriculture Handbook 60 (USSL Staff 1954). This relationship was developed using USA soils and has been widely used (worldwide) for over six decades. No efforts have been made to validate this relationship in other soils, though recently Shahid et al. (2013) have published a similar relationship for sandy desert soils ranging from low salinity (desert sand) to hyper-saline soils (coastal lands) in the Abu Dhabi Emirate. This latter work established a relationship between ECe and TSS which differs significantly from that of USSL Staff (1954), thus, opening the way for other countries to develop country-specific relationships which will allow better prediction and management of their saline and saline-sodic soils.

    स्रोत : link.springer.com

    Classification of Salt

    Download Citation | Classification of Salt-Affected Soils | Irrigated agriculture in arid and semiarid regions of the world has resulted in salinity and waterlogging problems that are threatening the... | Find, read and cite all the research you need on ResearchGate

    Article

    Classification of Salt-Affected Soils

    December 2004Arid Land Research and Management 19(1):61-79

    DOI:10.1080/15324980590887344

    Authors: R. CHHABRA Download citation Request full-text Download citation

    To read the full-text of this research, you can request a copy directly from the author.

    Abstract

    Irrigated agriculture in arid and semiarid regions of the world has resulted in salinity and waterlogging problems that are threatening the sustainability of our lands. Based on pH of the saturated paste, electrolytic conductivity of the saturated paste extract (ECe), and exchangeable sodium percentage (ESP), these soils have been classified as saline, alkali, and saline-alkali per the criteria of the U. S. Salinity Laboratory. Apart from textural B horizon, the Soil Taxonomy considers only ESP for defining a natric and ECe for defining a salic horizon. It does not consider pH and the nature of soluble salts as criteria for classifying these soils. All soils with high pH values (>8.5) as well as high ESP (>15) and high ECe (>4 dS m) developed in situ, soils with high pH values (>8.5) as well as high sodium adsorption ratio (SAR > 13) and high ECe (>4 dS m) formed due to use of irrigation waters containing high residual sodium carbonate (RSC > 2.5 mol m), and those with moderate pH values (7 to 8.5) but high SAR (>13) and high ECe (>4 dS m) formed due to shallow saline water table, are classified as saline-alkali soils. These are classified as Salidic Natrustalfs under Alfisols, since such soils contain both salic and natric horizons. Reclamation of such soils requires both leaching to remove soluble salts and application of amendments to lower ESP. This creates confusion in the mind of soil survey officials, planners, and development authorities. An examination of the composition of saturated paste extracts of these soils shows that these are either to be treated as saline or alkali for the purpose of adopting reclamation techniques. Soils that have the ratio of either and/or , expressed in mol m, should be treated as natric and require chemical amendments for reclamation. When soils have both these ratios

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