Morphological and Physico-Chemical Characterization of Salt-Affected Soils of Muktsar

Morphological and Physico-chemical characterization of salt-affected soils of Muktsar district of Punjab

O. P. Sandhu, H. S. Jassal, S. S. Dhaliwal and Narender

Department of Soil Science, Punjab Agricultural University, Ludhiana- 141004

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Nine representative salt-affected soils from different parts of the Muktsar district of Punjab were studied for their morphological and physico-chemical characteristics. Nine profiles (P1 to P9) were exposed based on field observation from different parts of the Muktsar district. Three profiles P1, P2 and P3 belong to saline soils, other three profiles P4, P5 and P6 belong to sodic soils, and three profiles (P7, P8 and P9) represent the saline-sodic soils on the basis of differences in physical and chemical properties. The structural development of the these soils generally indicated weak to moderate, fine to medium subangular blocky structure. The massive structureless condition was observed in C horizon of the soils. The most of the soil profiles had friable to firm consistent. The friable consistence in the surface horizons in most of the soils suggests good workability of the soils. All the soil profiles have varying degree of calcium carbonate concretions. The amounts of calcium carbonate concretion in saline-sodic soils were comparable to saline soils but higher than sodic soils. The soils gave strong to violent effervescence with dilute HCl exhibiting relatively high calcium carbonate or calcareous nature of the parent material.The texture of these soils varied from silty clay loam, silt, silt loam through loam to sandy loam whereas soil pH ranged from 8.3 to 10.2, 8.6 to 10.0 and 8.2 to 9.4 in the saline, sodic and saline-sodic soils, respectively. Electrical conductivity in surface horizon varied from 4.96 to 19.1 dS m-1 in saline soils, 0.44 to 2.25 dS m-1 in sodic soils and 2.30 to 11.8 dS m-1 in saline sodic soils.The higher EC at or near the surface was probably due to upward movement of soluble salts through capillary rise due to aridity of this region. Organic carbon content varied very widely and ranged from 0.02 to 0.87 per cent in saline soils, 0.01 to 0.29 per cent in sodic soils and 0.01 to 0.68 per cent in saline-sodic soils. Generally organic carbon content of the surface horizon was higher than that of the sub-surface horizon. The definite trend of variation of organic carbon was observed with depth. Calcium and magnesium cations were dominated on the exchange complex and their content varied from 3.2 to 6.4 cmol(+)kg-1 and that of Na+ and K+ varied from 0.09 to 2.87 and 0.06 to 2.33 cmol(+)kg-1, respectively.The soils of the study area are highly alkaline and calcareous in nature. Suggested management practices to improve upon the productivity of these soils are ridges/mounds, application of gypsum, organic manures and residues, planting of salt-tolerant crops, agroforestry, leaching and drainage.

Keywords:Salt affected soils, Morphological and physico-chemical Chracterization., Punjab soils

Introduction

Increasing world population, more particularly in South Asia will lead to higher demand offood, animal feed, fiber and fuel. In recent years, with increasing competition fornatural resources like land and water for human inhabitation and survival, meeting the globalfood demand for 9 billion strong populations will be a daunting task by the year 2050. The net cultivated area has remained constant since the last four decades at 140 ± 2 m ha and there is very little possibility of bringing additional area under cultivation. In fact, the per capita availability of cultivated land which was 0.48 ha in 1951 had decreased to 0.14 ha in 2010. Mismanagement of natural resources, particularly soil and water, has further created problems like waterlogging and soil salinity, and degraded the natural resource base (Singh et al 2009). The problems of salt-affected soils have become a global issue because of poor land and water management. The salinity and sodicity are the serious problems in arid and semi-arid regions of the world particularly for agricultural production. Salt-affected soils exist in India since the ‘vedic’ times as obvious from their grouping as ‘lavaniya’ (saline) and 'kshariya’ (alkali) categories since that time. These soils pose serious problems for plant growth due to their adverse characteristics.

Salt affected soils are found throughout the world especially in arid and semi arid regions where potential evapo-transpiration greatly exceeds precipitation (Sehgal 2005). These soils pose serious problems for plant growth due to their adverse characteristics and hence hinder agricultural production. The total area of salt affected soils in the world is about 95.5 million hectare. Salt-affected soils have occupied about 7 million ha in India out of which 50% occured in Indo-Gangetic plains. The soils of Punjab also have the problem of salinity and sodicity, however its area has reduced substantially with adoption of reclamation technology in the past. The salt-affected soils in Punjab have reduced from 0.7 m ha in 1972 to 0.152 m ha in 1996 (Sharma et al 1996). Now, out of the total geographical area 5.03 m ha, about 0.06 m ha of land is still affected with salinity or sodicity in Punjab (Sharma et al 2009). According to Central Soil Salinity Research Institute, Karnal this figure is about 0.15 m ha (Sharma et al 2007).

Brouckert and Rouiller (1982) observed that in salt-affected soils HCO3- and CO3-2 anions react with H3O+ to fix a proton disturbing the ionic dissociation of water and therefore OH ion increases with a consequent rise in pH.

HCO3- + H3O+ ⇌ H2CO3 + H2O

CO3-2 + 2 H3O+⇌ H2CO3 + 2 H2O

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 exchange 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, Fortmeier and Schubert 1995, Grattan and Grieve 1994, Mengel and Kirkby 2001). It has been suggested that some salt-affected soils are formed due to natural processes including release of electrolytes by weathering, their transportation by water and subsequent accumulation in situ or elsewhere primarily caused by impeded drainage. Other soils are developed due to the faulty management of irrigation water, resulting in secondary salinization (Yadav 1993). Some of the salt problems in South -West part of Punjab was related to rise in water table and waterlogging. The water table, which was about 42 M deep in 1895 was shown gradual rise at an alarming rate of 0.5 to 1.5 meter annually and thus reached close to surface with one to two meters depth in 1985 (Anonymous 1985).

Hence, keeping in mind the seriousness of the salt affected soils, the present study was carried out to study the morphological and physic-chemical properties of salt-affected soils of Muktsar district of Punjab.

Materials and Methods

The study area falls in Muktsar district of Punjab which is a part of the Sutlej sub-basin of Indo-Gangetic alluvial plain formed during Pleistocene to Recent periods (Wadia, 1976). The flat alluvial plain covering the major part of the district is often traversed by sand dune complexes constituting nearly 14 per cent of the district (Sharma et al., 2004). The annual rainfall of the area is 380 mm where eight to nine months in any year receive less than 30mm and the other 3-4 months more than 60 mm of monthly rainfall. The maximum summer temperatures are very high with May to June temperature ranging from 45-48 °C. The major parts of the area have an aridic (torric) moisture regime whereas the soil temperature regime is hyperthermic (Soil Survey Staff, 1998). The climate type of the area is semi-arid (semi dry) less hot (Sehgal et al., 1987). The water balance diagram of Muktsar is presented in Fig2.

A total of nine salt-affected profiles (P1 to P9) were exposed from barren and farmer fields, three each from the saline soils (P1, P2 & P3), the sodic soils (P4, P5 & P6), and the saline-sodic soils (P7, P8 & P9). The locations were noted by taking reading from the GPS used during the field work (Fig 3).

The sampling was carried out from all the nine profiles. The soil samples were collected from each of the morphologically differentiated horizon.The soil samples were collected from each of the morphologically differentiated horizon up to a depth of 150 to 200 cm.Six samples were collected horizon-wise from each profile. The soil samples were placed in shade air drying. The dried samples were crushed gently in wooden pestle and mortar, and then passed through 2mm sieve for separating coarse fragments, if any. The fine soil fraction passing through 2mm sieve used to carri

ed out analysis for various phyico-chemical

Determination of physico-chemical properties

(i) Particle size distribution (Texture)

Particle size distribution was determined by the International Pipette method (Page et al 1982). The soil was dispersed by stirring the sample, treated with 1 per cent sodium hexa-metaphosphate. The sand was separated by wet sieving through 300 mesh sieve. Silt and clay were collected in one litre capacity sedimentation cylinder. Volume of silt plus clay suspension in the cylinder was made to one litre and these contents were thoroughly mixed using a plunger. Twenty five ml of suspension was pipette-out from a depth of 10 cm in the cylinder after a requisite settling time for greater than 2µ particles. Percentage of clay was calculated from the sample so obtained. Percentage of silt was computed by subtracting sand plus clay percentage from 100. The USDA textural triangle was used for determining textural classes.

ii) Soil reaction (pH)

A soil suspension was prepared with distilled water keeping 1:2 soil to water ratio and the concentration of hydrogen ions in soil (pH) of suspension was measured by potentiometric method (Jackson 1973). The pH of the solution being proportional to the potential developed on the glass membrane was measured in conjunction with saturated calomel electrode as reference electrode.

(iii) Electrical conductivity (EC)

The soil suspension used for pH determination was also used to measure soluble salts after keeping them overnight to obtain a clear supernatant solution. The soluble salts in the soil were measured with a conductivity meter, also known as salt bridge. The conductivity of electric current through soil suspension is proportional to the concentration of soluble salts in it (Richard 1954). The EC was expressed as deci siemens per meter (dS m-1).

(iv) Organic carbon (OC)

Rapid titration method (wet digestion method) was used for organic carbon determination (Walkley and Black 1934). In this determination 2 gm of dried soil was treated with 10 ml of 1N K2Cr2O7 solution in a 250 ml conical flask. A 20 ml of concentrated H2SO4 was slowly added to the flask. After 30 minutes, about 0.5 gm of NaF, 100 ml of distilled water and 10 drops of diphenylamine indicator were added to the flask. These contents were titrated against 0.5N ferrous ammonium sulphate solution. The change from violent to bright green through blue colour was the end point. The value of ferrous ammonium sulphate used for titration was adopted for calculating organic carbon and was expressed as percentage. In another flask, 10 ml of 1N K2Cr2O7 solution was titrated without soil against 0.5N ferrous ammonium sulphate solution to determine blank reading.

(v) Calcium carbonate (CaCO3)

Rapid titration method of Puri (1930) was employed to determine calcium carbonate equivalent of soil.

(vi) Exchangeable cations and exchange capacity (CEC)

The rapid method for simultaneous determination of exchange capacity and exchangeable cations was applied for the soil samples collected from the profiles (Belyayeva 1967). Five gram of soil was washed with 100 ml of 80-90 percent methanol to free the soluble salts in three different washings. The exchangeable cations then were extracted with freshly prepared ammonium chloride solution (methanol + HCL + NH4OH). The extract was analyzed for Na and K using Elico CL22D flame photometer, and Ca and Mg by versenate titration method (Barrows and Simpson 1962). The sum of exchangeable cations is reported as exchange capacity.

Results and Discussion

Morphological properties of salt-affected soils

The soils under study were characterized for their morphological properties in the field and their characteristics are given in Tables 1 to 3 Morphological characteristics of the soils are discussed in the following sections.

Saline soils

The saline soils are represented by profiles P1, P2 and P3. Soil colour of the different horizons of the saline soils had hue value 10YR and 2.5Y (Table 1). The profile P1 had 10YR hues throughout the profile. However lower horizon of profiles P2 and P3 had 2.5Y hue. The value varied from 3 to 6 and the chroma was in the range of 2 to 6. The yellower hue (2.5 Y) and lower chroma (=2) in the lower horizons of the P2 and P3 soils suggested occurrence of reducing condition due to water logging during some period of the year. Except in profile P2 value follow no definite pattern with depth. The soils showed varied textural composition in different horizons in these soils. The texture of the different horizons of these soils varied from silty clay loam through silt loam, loam to sandy loam. All the soils showed relatively coarser texture in upper horizons and finer texture in underlying horizons. The textural composition of these soils is because of the kind of material that deposited and built up in such geomorphic units.

The soil structures were generally weak to moderate, fine to medium subangular blocky but in some surface horizon granular. The lower most horizons (C horizons), however showed structure-less massive condition. The soils had moist friable to firm consistent due to lower clay, plasticity and stickiness. The friable consistence in the surface horizons in P1, P2 and P3 suggests good workability of the soils. Textural composition appears to have greater influence on the consistence of the soils. The invariably contain calcium carbonate concretions in most of the horizons. The soils had occasional to frequent and very fine to coarse calcium carbonate concretions. The P2 soils had more developed concretions than other two saline soils (P1 and P3). All the soils gave strong to violent effervescence with dilute HCl indicating high calcium carbonate or calcareous nature of the parent material. The different soil horizons show presence of roots but density of roots decrease with depth. The soils successive horizons showed clear or gradual smooth boundaries.

4.1.2 Sodic soils

The profiles P4, P5 and P6 represent the sodic soils of the study area. The different horizons of sodic soils had 10YR and 2.5Y hues (Table 2). The P6 had 10YR hues throughout the profile. However lower horizon of profile P4 and P5 had 2.5Y hue. The hue of 2.5Y in these soils suggests their poor drainage condition particularly in lower horizons. The value and chroma both varied from 3 to 6 in the different horizons. The value increases with suggesting lighter shades in lower horizons. The profile P6 invariably have chroma 4, whereas in other soils (P4 and P6) have this value in lower horizons. The soils showed varied textural composition in different horizons in these soils. The texture of the different horizons of these soils varied from silt, silty clay loam, silt loam, loam and sandy loam. The sodic soils (P5 and P6) were relatively finer texture (silty clay loam to loam) compared to saline soils (P1 and P2). The subsurface argillic horizon was observed in P6 profile. The presence of argillic horizon evidenced with a significantly higher percentage of silicate clay in subsurface horizon than the overlying soil material. It shows evidence of clay illuviation. The textural data of the soil P3 showed frequent change in textural class with depth suggesting stratified nature of the parent material.

The soils had weak to moderate, fine to medium, granular to subangular blocky structure in different horizons. The structure-less massive condition was observed in the lowermost horizon. The soils had moist friable to firm consistent due to loamy nature. The friable consistence in the surface horizons in P4 suggests good workability of the soils. Textural composition has greater influence on the consistence of the soils. The calcium carbonate concretions are little less in sodic soils compared to other soils. The calcium carbonate concretions are missing from many horizons of these soils.The soils gave strong to violent effervescence with dilute HCl indicating presence of free high calcium carbonate in the soils. The soils are, therefore calcareous nature. The accumulation of calcium carbonate in 70-106 cm depth is so high that it developed into calcic horizon. The different soil horizons show presence of roots but density of roots decrease with depth.

Saline-sodic soils

The saline-sodic soils are represented by P7, P8 and P9 profiles. The most of the horizons of saline-sodic soils had 10YR hue but some also showed 7.5YR and 2.5Y hues (Table 3). The soil P7 has relatively redder colour as its lower horizons showed 7.5YR. The redder colour of P7 suggests its better arable and drainage conditions. The yellower hue (2.5 Y) and low chroma (=2) in the lowermost horizon of P9 soil, however suggest occurrence of reducing condition at certain intervals. The value varied from 3 to 5 and the chroma was in the range of 2 to 6. The values and chroma follow no definite pattern with depth. The colour variables generally indicated relatively better drainage condition compared to saline soils and sodic soils. The textural composition was relatively uniform in different horizons of these soils. The texture of the different horizons of these soils varied from silt through silt loam to loam. The saline- sodic soils (P7) were relatively finer texture (silt loam and loam) than P8 and P9 soils (silt and silt loam). No textural variation in composition was observed in these soils with depth suggesting uniform nature of parent material. The textural variation among soils is because of the kind of material deposited during development of geomorphic units.