Faculty of Agriculture
Department of Soil Sscience
A thesis Submitted for the Degree of Master of Science
In Soil Science
Assessment of Soil Genesis in a Salt-Affected Plain for Soil Reclamation and Improvement Strategies in Miandoab Region
Dr. S. Rezapour
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In order to monitoring nature and genetic properties of salt-affected soils under influence of Urmia Lake in Miandoab region, western-Azerbaijan province, seven soil profiles were described, sampled, and analyzed. The significant differences between the soluble values of Cl-1, Na+1, K+1, Mg+2, and Ca+2 at each profiles date indicated clearly a temporal distribution, which can be attributed to other soils properties (e.g., particle-size distribution) and the high soluble salt content of groundwater in the study area. Based on the values of organic carbon (OC), the majority of soil samples were categorized as extremely poor (< 0.6% of OC) and poor (0.6-1.2% of OC) probably due to poor plant growth and low input rates of organic matters. In accordance with the soil texture and the low organic matter content, the cation exchange capacity (CEC) of the soils were rated in low to medium category, ranging 6 to 27 cmol kg-1. The soils indicated some differences in the value of iron oxides and their vertical distribution within the profiles that might related to pedogenic processes, seasonal fluctuations in water table, and repeated cycles of sediment accumulation. The XRD patterns of the clay fraction from all of the soil profiles exhibited a similar composition of phyllosilicate minerals, including illite, smectite, chlorite, vermiculite, and kaolinite. Indeed, the minerals were similar in type but some different were observed in the intensity, position, and peak figure of them (except kaolinite) mainly due to the change in drainage condition and ground water table depth. Suggested management practices to improve of these soils are the combination of physical management, leaching and drainage, the application of elemental S, organic matter, farm manure, mulching, and planting of salt-tolerant crops.
Keywords: salt-affected soils, Soil profile, Drainage condition, Iron oxides, Clay minerals.
Salt-affected soils are found on more than half of the earth arable lands. They dominate most arid and semi-arid environments of the world. However they can also be occur in other areas where the climate and mobility of salts cause saline waters and soils for short period of time (Brady and Weil, 1999). Worldwide about one third of the irrigated lands have salt problems.
Salt-affected soils deteriorate as a result of changes in soil reaction (pH) and in the proportions of certain cations and anions present in the soil solution and on the exchangeable sites. These changes lead to osmotic and ion-specific effects as well as to imbalances in plant nutrition, which may range from deficiencies in several nutrients to high levels of sodium (Na+). Such changes have a direct impact on the activities of plant roots and soil microbes, and ultimately on crop growth and yield (Naidu and Rengasamy, 1993; Mengel and Kirkby, 2001).
Salt-affected soils are classified as saline, sodic, and saline-sodic soils. Briefly, saline soils are detoured by high levels of soluble salts, sodic soils have high levels of exchangeable sodium, and saline-sodic soils have high contents of both soluble salts and exchangeable sodium. The parameters determined to describe salt-affected soils depend primarily on the concentrations of soluble salts in the saturation extract (ECe), the soil pH, the sodium adsorption ratio (SAR), and the percentage of exchangeable Na+ of the soil (ESP). Accordingly, saline soils have traditionally been classified as those in which the ECe > 4 dS m-1, pH < 8.5, SAR < 13, and ESP < 15; sodic soils have an ECe < 4 dS m-1, pH > 8.5, SAR > 13, and an ESP > 15%; and saline-sodic soil have an ECe > 4 dS m-1, pH < 8.5, SAR > 13 and an ESP > 15% (Sparks, 2003).
In general, soil salts are mainly chlorides and sulphates of sodium, calcium, magnesium and potassium. Saline soils contain a concentration of these salts sufficient to interfere with the growth of many plants. Salts are commonly brought to the soil surface by evaporating water, creating a white crust, which accounts for the name white alkali that is sometimes used to designate these soils (Mengel and Kirkby, 2001).
Sodic soils are an important category of salt-affected soils that exhibit unique structural problems as a result of certain physical processes (slaking, swelling, and dispersion of clay) and specific conditions (surface crusting and hardsetting) (Qadir and Schubert, 2002). These problems can affect water and air movement, plant available water holding capacity, root penetration, seedling emergence, runoff and erosion, as well as tillage and sowing operations.
As the use of sodic soils for crop production is expected to increase in the near future, the sustainable use of such soils for food and feed production will become a serious issue. However, if mismanaged, the use of sodic soils could aggravate salinity and sodicity problems. Sodic soils are ameliorated by providing a readily available source of calcium (Ca2+), to replace excess Na+ on the cation exchange complex. The displaced Na+ is leached from the root zone through the application of excess irrigation water. This requires adequate amounts of water and an unimpeded flow through the soil profile. Over the past 100 years, several different site-specific approaches—involving the use of chemical amendments, tillage, crop diversification, water, and electrical currents—have been used to ameliorate sodic soils. Of these, chemical amendments have been used most extensively (Oster et al., 1999).
Saline-sodic soils have characteristics intermediate between those of saline and sodic soils. Like saline soils, they contain appreciable levels of natural soluble salts, as shown by ECe levels of more than 4 dS m-1. But they have higher ESP levels (greater than 15) and higher SAR values (at least 13). Crop growth can be adversely affected by both excess salts and excess sodium levels. The physic-chemical conditions of saline-sodic soils are similar to those of saline soils.
The problems of salt-affected soils have serious implications in the semi-arid region where both soil and land were prone to different levels of salinity. Salinity-induced land degradation is a major issue in Iran. In addition, sodicity-induced land degradation and microelement salinity such as boron salinity have been developed in some of its areas. The salinization of land resources in Iran has been the consequence of both naturally occurring phenomena (causing primary or fossil salinity and/or sodicity) and anthropogenic activities (causing secondary salinity and/or sodicity) (FAO, 2000).
In Iran more than 25 million ha (over 15%) from total land have associated with saline and sodic characteristics (Mahler, 1979; Barzgar 2002) and most of the land are found in the Central Plateau, the Khuzestan Plain and the northwest regions of the country.
In western-Azerbaijan province, about 24,500 hectares of the studied land have the quality of salt-affected soils (Samadi, 1963) and the most of these areas are located at the margins of Urmia Lake. In the past, most of these lands were used as natural pasture but in recent years due to the development of cultivation, the use of such land has expanded rapidly for cropping.
In view of the fact that salt-affected soils are very sensitive to degradative aspects, it is essential to first determine the basic characteristics of the soils before improvement any management strategies. To examine this hypothesis, the combination of environmental, morphological, physicochemical, and mineralogical properties was investigated in a salt-affected plain from Miandoab region (with area of 16,503 ha) in western-Azerbaijan province (36° 59’ to 37° 16’ N and 45° 40’ to 46° 0’ E).
The main aims of the research are as following:
- To evaluate the basic characteristics of the examined region using a combination of morphological and physiochemical attributes.
- To determinate the clay mineral types and iron oxides forms as well as their genetics in soils of the region.
- To investigate the potential and limitations soils of the region and provide some data that focus on employing more sustainable management systems for soil reclamation and improvement strategies.
2.1 Overview of Salt-Affected Soils
While salinity is often thought of as a soil issue characterized by the accumulation of high total soluble salt concentrations, it encompasses plant responses as well as effects of topically applied saline irrigation water (USDA-ARS, 2008). Thus, “salinity” is not a single stress or problem, but there are four major salinity issues that are the primary problems that require intensive site-specific attention on an individual basis in response to each stress (Qadir and Oster, 2004; Carrow and Duncan, 2010). These four primary salinity stresses are as follows:
- Excessive levels of total soluble salts, that is, total salinity causing salt-induced drought stress.
- Na+ permeability hazard: excessive levels of Na on the soil cation exchange sites (cation exchange capacity or CEC) and precipitated as Na carbonates causing soil structure degradation.
- Ions that are toxic to roots or shoots or may cause other problem ion issues as they accumulate.
- Actual nutrition concentrations, interactions, and imbalances caused by nutrients and other ions in the water or soil.
تعداد صفحه : 97
قیمت : 14700 تومان