studies on chemical characteristics and classification...

Vol. 5 | No.1 | 74-85 | January - March | 2012

ISSN: 0974-1496 | CODEN: RJCABP

http://www.rasayanjournal.com

STUDIES OF SOILS FROM SANGAMNER AREA K. K. Deshmukh

STUDIES ON CHEMICAL CHARACTERISTICS AND

CLASSIFICATION OF SOILS FROM SANGAMNER AREA,

AHMEDNAGAR DISTRICT, MAHARASHTRA, INDIA

K. K. Deshmukh Sangamner Nagarpalika Arts, D.J. Malpani Commerce & B.N. Sarda Science College,

Sangamner – 422605, Dist. Ahmednagar, (M.S.), India.

E-mail: [email protected]

ABSTRACT

Studies were conducted to know the chemical characteristics of the soils and their classification from Sangamner

area, Ahmednagar district, Maharashtra. For this purpose, 62 surface soil samples were analyzed for pH, EC, Ca2+

,

Mg2+

, Na+, K

+, Cl

-, HCO3

-, SO4

2- from saturation extract. The exchangeable cations like Na

+, K

+, Ca

2+ and Mg

2+ by

neutral ammonium acetate extract and CEC were estimated by standard procedures. pH ranged from 8 to 9.7

reflecting alkaline nature of soils. Higher EC in the downstream part reflecting low flushing rate and sluggish

groundwater movement in the area. EC study showed 35.48% soils are normal and 64% soils are problematic which

requires reclamation. Estimation of CaCO3 content showed 79% of the soils are strongly calcareous and remaining

are having moderate CaCO3 content. The concentration of soluble cations are in the order Na+>Ca

2+>Mg

2+>K

+

whereas Cl- is predominant followed by SO4

2- and HCO3

- in the soluble anions. 24.19% soils have SAR greater than

13 indicating shallow water table conditions and congestion of drainage. Out of the total exchangeable cations, Ca2+

is dominating over rest of the cations. The CEC values ranged from 32.14 to 82.47 C mol (P+) per kg indicating the

soils in the area texturally classified as clay loam to clay. High CEC indicated presence of smectite in clay fraction.

35.48% soils showed ESP>15 which are located in the backwater zone of Ojhar weir. The soils from the study area

are easily waterlogged during the rainy season. The problem is further aggravated due to decrease in depth of water

table by injudicious irrigation and canal seepage. Therefore, there is an urgent need to focus the attention on the

protection of soils particularly in the irrigation sector. Frequent awareness and training programs for farmers can be

arranged to know the chemical composition and quality of soil to avoid further degradation.

Keywords: Calcareousness, Soluble cations and anions, Exchangeable cations, Sodium Absorption Ratio (SAR),

Cation Exchange Capacity (CEC) and Exchangeable Sodium Percentage (ESP). © 2012 RASĀYAN. All rights reserved.

INTRODUCTION Soil is one of the most precious natural resource, which provides a medium for plant growth to meet our

food and fiber need. Soil filters water, decomposes waste, stores heat and exchanges gases and hence

have great bearing on environmental balance. Formation of 1 cm top soil layer requires 100-400 years1.

Past decades witnessed a considerable shrinkage in the soil due to unscrupulous increase in the

urbanization and industrialization. Agricultural technologies that led to Green revolution resulted in the

degradation of this precious natural resource owing to over exploitation under intensive irrigation and

cultivation with mis - management. Due to this, soil has reached a stage of fatigue resulting in the decline

in the productivity. In order to meet the ever increasing food requirement for growing population, it is

essential that soil and water resources should be used judiciously. At present, the majority of our land

resources are degraded. It is estimated that 8.087 million hectares of land in India are affected by

problems of salinity and sodicity2. In Maharashtra, about 0.54 million hectares of soils are reported to be

salt affected and waterlogging3. Therefore, it is important to maintain soil health for sustainable

productivity, food security and increasing agricultural production for multiple demands against fast

mounting pressure on limited soil resource base.

A lack of consciousness in the society towards soil quality has been to the extent that soil is used as a

disposal site of hazardous waste as well as pathways of many contaminants and other applied hazardous


STUDIES OF SOILS FROM SANGAMNER AREA K. K. Deshmukh 75

chemicals which pose serious risk to human health. Soil quality indicators that directly monitor the soil

are grouped into physical, chemical and biological indicators. Some soil chemical properties such as pH,

EC, plant nutrient availability, ESP, SAR, CEC etc are the indicators of soil quality1. These chemical

properties of soils play an important role in determining the retention and availability of nutrients in soils.

The nutrient supply in soil depends on the level of organic matter, CaCO3 content, degree of microbial

activity, change in pH, types and amount of clay and status of soil moisture4. Extensive research work has

been done on the chemical characteristics and their classification of soils5-11

. The study area falls under

dry zone receiving scanty rainfall. Therefore, lithology, topography and climate have controlled the

development of soils in Sangamner area. The soils of study area are derived from Deccan Trap basalt.

Although the parent material of the soils is the same, there are wide variations in soil types. Earlier

researchers have thrown some light on the nature of soils from study area6,11

. Establishment of industrial

estate by the Government of Maharashtra at Sangamner and growth of sugarcane and allied industries has

started deteriorating the soil quality in some parts of study area. Hence, attempts have been made to study

the chemical characteristics and their classification of these soils properly.

Fig.-1: Location map showing soil sampling stations in the Study area

The Study Area

The Sangamner area is located in the Ahmednagar district of Maharashtra. Sangamner is a Taluka

headquarter which is located at a distance of 150 km from Pune on Pune-Nashik National Highway No.

50 (Fig.1). The area is drained by the Pravara River which is a tributory of Godavari. Pravara River

originates in the mountainous region of Western Ghats and flows into low-lying fertile alluvial plain in

the downstream part. Several dams and weirs have been constructed across Pravara River. Of these,

Bhandardara dam is located in the source region and the Ozar dam is in the downstream direction of

Sangamner town. These dams have been augmenting the irrigational water needs of the area. Over 90% of



the study area is practising intensive agriculture. It should be noted that subsequent to the establishment

of co-operative sugar-mill at Sangamner in 1967, the agriculture in the area has witnessed rapid changes

in the cropping pattern. The industrial units developed in the area generate large volumes of waste water

which mixes with surface and groundwater resources thereby contaminating them. At places, the lagoons

used for storage of waste waters have caused degradation of soils as well as water due to infiltration of

effluents. Thus, the soil resources are facing severe threat from both irrigation practices as well as from

agro-based industry. In view of the above, the studies on the chemical characteristics of the soils and their

classification from Sangamner area were undertaken.

EXPERIMENTAL Selected 62 surface soil samples (0-20cm) were collected in cloth bags as per the standard procedure

recommended by United States Department of Agricultural Sciences12

. Quartering technique was used for

preparation of soil samples. The samples were dried in air and passed through 2 mm sieve. The processed

soil samples were analyzed for their chemical characteristics as per the standard procedures. The soil

pH,EC,Ca2+

,Mg2+

,Na+,K

+,CO3

2-, HCO3

-,Cl

- and SO4

2- were determined from the saturation extract (l:5 soil

water ratio) of soils13

. The exchangeable cations viz Ca2+

, Mg

2+, Na

+ and K

+ are determined from neutral

ammonium acetate extract of the soils as per the standard procedures13,14

. The CaCO3 content was

estimated by rapid titration method15

. In addition, the SAR and ESP were also calculated13

. The CEC was

determined by using sodium as an index 13,14,16

.

RESULTS AND DISCUSSION Chemical properties of soils

The chemical properties of soils are determined by the colloidal portion of soils i.e. clays and humus. The

chemical environment of soil not only influences the crop growth but also it decisively determines the

physical environment of soil. Therefore, in order to characterize the soils from the area, the chemical

properties like pH, EC, soluble cations and anions, exchangeable cations, calcium carbonate, CEC and

ESP of soil extract were estimated and presented in Table 1 and 2.

Soil pH pH is an important parameter as it helps in ensuring availability of plant nutrients e.g. Fe, Mn, Zn and Cu

are more available in acidic than alkaline soils. It also helps in maintaining the soil fertility and to

quantify the amendments used for amelioration17

. A pH range of 6.5 to 7.5 of the saturation extract is

considered as the pH range in which most of the soil nutrients are available to plants. Table-1: Saturation extracts analysis of the soils from Sangamner area

EC Saturation extract analysis (1:5 soil water ratio) meq/l S. No. pH

dS/m Ca Mg Na K CO3 HCO3 Cl SO4

SAR

S1 8.6 2.84 1.52 0.44 11.59 0.1 1.6 2.4 24.12 5.22 11.71

S2 8.6 25.4 26.78 3.75 235.9 1.29 1.2 1.8 125.3 11.44 60.38

S3 8.5 36 43.56 36.07 280 0.78 0 4 553.5 11.6 44.37

S4 8.3 19.8 22.67 13.04 76.16 0.26 0 1.6 65.34 10.94 18.02

S5 8.5 8.1 4.46 4.91 28.14 0.1 0.8 2.8 10.8 9.79 13

S6 8.9 22.1 26.78 4.02 145 0.75 0 2 58.14 11.54 36.91

S7 8.5 26.1 33.03 8.93 225.9 0.52 0 2.2 182.7 10.79 49.32

S8 8.6 17.3 17.85 6.7 71.19 0.26 0 2.8 36 10.8 20.32

S9 8.4 8.3 11.16 4.01 37.25 0.18 0.4 0.4 22.5 10.62 13.53

S10 8.8 11.8 13.39 1.78 134 0.26 0 2.2 50.4 10.62 48.84

S11 8 7.9 5.89 4.1 28.14 0.18 0 3.2 25.02 9.33 12.59

S12 9.5 8 0.54 3.04 58.77 0.06 1.6 4.8 27.18 10.55 43.98

S13 8 6.4 2.32 2.14 24 0.1 1.2 2.8 8.64 9.09 16.06

S14 8.6 11.6 24.64 7.5 48.82 0.26 0 2.4 35.1 12.08 12.18

S15 8.5 6 3.57 3.93 31.44 0.1 0 2.6 8.64 10 16.24



S16 8.5 46.8 35.35 48.75 323 0.62 1.2 3.8 245.7 12 49.78

S17 8.4 4.1 3.57 1.79 20.69 0.11 1.2 4.8 8.1 9.78 12.64

S18 8.4 2.9 1.43 1.79 12.39 0.07 1.2 3 3.37 10.16 9.77

S19 9.1 1.6 1.96 0.89 8.278 0.07 1.2 3.6 4.86 3.87 6.93

S20 8.7 5.6 2.86 2.5 24.84 0.1 4 2.8 12.42 8.83 15.18

S21 9.7 6.3 0.89 1.52 18.21 0.1 1.2 4.4 28.8 4.86 16.59

S22 9.1 2.16 1.61 0.18 8.29 0.06 0.8 4 4.32 4.69 8.77

S23 8.5 0.1 1.96 1.37 10.34 0.05 0 2.4 6.3 1.58 8.01

S24 8.6 1.1 1.16 1.52 5.38 0.1 0 3.6 3.06 0.91 4.65

S25 8.4 0.1 3.48 2.23 8.62 0.08 0 2.8 8.1 4.69 5.1

S26 8.7 4.7 1.25 0.89 11.58 0.06 0.4 2.8 4.14 3.49 11.19

S27 7.8 3.9 24.19 20.44 20.28 0.98 0 3.2 65.52 8.77 4.29

S28 8.6 5.5 1.16 2.23 4.97 0.08 0 2.4 4.5 1.74 3.82

S29 8.4 0.2 1.79 0.54 2.9 0.06 0.4 3 3.6 1.68 2.69

S30 8.9 1.42 0.8 0.8 4.14 0.03 1.2 2.4 2.7 1.79 4.62

S31 8.3 1.75 2.68 1.7 5.38 0.08 0.4 2.8 6.88 1.89 3.64

S32 8.4 0.82 2.23 1.79 2.48 0.05 - 2.8 4.8 1.48 1.75

S33 8.6 1.11 1.34 1.25 6.62 0.03 0.4 2.8 4 2.04 5.82

S34 8.2 0.44 1.16 1.16 2.07 0.02 0.8 2.2 1.6 0.35 1.92

S35 8.3 0.52 1.16 0.45 2.9 0.04 0.4 3.4 1.6 0.33 3.23

S36 8.2 3 3.12 3.12 6.62 0.08 0.8 2.6 8 3.91 3.75

S37 8.1 2.07 3.3 2.14 4.97 0.16 0.4 3 6.4 1.84 3.01

S38 8 4.17 4.46 3.93 7.04 0.15 0.4 2.4 16.16 1.75 3.43

S39 8.4 1.54 2.05 0.62 6.62 0.06 0.8 2.8 6.56 0.61 5.72

S40 8.2 1.88 2.86 2.05 1.24 0.23 0.4 3 4.48 1.21 0.79

S41 8.2 0.77 1.34 0.98 1.66 0.05 0.8 2.2 2.72 0.56 1.54

S42 8.2 0.79 1.52 1.52 1.24 0.05 0.4 3.4 1.6 0.05 1.01

S43 8.4 0.39 0.89 0.81 1.24 0.05 0.4 2.8 1.28 0.09 1.35

S44 8.8 0.66 0.89 0.36 7.04 0.04 0.4 2.6 1.6 0.2 8.9

S45 8.4 0.44 1.7 0.27 1.86 0.02 1.6 2.4 3.52 1.86 1.88

S46 8.3 0.71 1.34 0.8 1.66 0.05 0.4 2.4 1.76 0.12 1.6

S47 8.4 0.503 0.89 0.72 2.07 0.01 0.4 3.2 1.12 0.01 2.3

S48 8.5 0.383 0.98 0.8 1.66 0.01 0.4 3.6 1.6 0.06 1.75

S49 8.4 0.836 0.98 0.8 2.42 0.06 0.4 2.8 1.6 0.79 2.56

S50 8.4 0.57 1.52 0.62 1.45 0.03 0.4 2 1.28 0.8 1.4

S51 8.5 1.74 0.62 1.61 8.69 0.04 0.4 2.8 5.6 1.76 8.23

S52 8.6 0.45 1.16 0.45 2.28 0.08 0.4 1.8 7.52 0.45 2.54

S53 8.5 4.61 0.98 2.01 15.31 0.06 0 2 11.36 2.57 12.51

S54 8.9 1.7 0.62 0.89 6.83 0.05 0.4 3 2.88 1.28 7.84

S55 8.8 1.12 0.71 0.63 4.97 0.04 0.4 2 5.28 0.22 6.07

S56 8.6 1.84 0.8 1.25 9.93 0.04 0.8 2.2 4.64 0.76 9.81

S57 8.4 1.3 1.79 0.27 6.21 0.04 0 2.8 3.6 1.22 6.13

S58 8.8 0.94 0.98 1.07 7.24 0.02 0.4 2.6 4 1.36 7.15

S59 8.4 0.44 0.98 1.07 1.86 0.06 0.4 3.4 0.96 0.06 1.84

S60 8.7 0.41 0.89 1.25 1.45 0.22 0 2.2 1.6 0.37 1.4

S61 8.4 0.57 1.61 0.18 2.48 0.05 0 3 1.76 0.77 2.63

S62 8.6 1.04 0.98 0.71 4.35 0.05 0.4 2.8 4.8 1.63 4.72

In the present study, pH ranges from 8.0 to 9.7 reflecting alkaline nature of soils. It is interesting to

observe a narrow range of variation in pH in the area. This can be attributed to high buffering capacity of

the soils and absence of carbonate in the saturation extract 18

. The higher values of pH are recorded

(S.No. S6, S10, S12, S19, S21, S30, S44, S54, S55 and S58) in the central and downstream part of the

area. These high values are possibly due to presence of soluble and exchangeable sodium along with



HCO3- ions, which precipitates calcium and magnesium carbonates during evaporation. High pH values

are thus indicative of development of salinity / sodicity in the area. These results were in confirmatory

with the results reported by several workers 3,6,19,20

.

Table-2: Chemical properties of soils from Sangamner area

Exchangeable cations CEC CaCO3

meq/100g

ESP

% meq/100g %

S. No.

Na+ K

+ Ca

++ Mg

++

S1 9.71 0.38 31.75 18.28 17.47 55.64 11.87

S2 25.2 0.31 27.5 23.54 59.15 42.6 11.66

S3 16.59 1.2 35 8.014 51.57 32.17 11.08

S4 10 0.37 44.75 17.03 21.3 46.95 5.41

S5 7.5 0.52 36 21.78 15.13 49.56 11.08

S6 11 1.08 31.5 8.01 30.12 36.52 12.91

S7 12 0.88 36 7.01 36.32 33.04 12.7

S8 9 0.56 30.5 14.27 26.54 33.91 15.2

S9 7.2 0.58 38.25 17.28 15.06 47.82 15.83

S10 10.35 0.56 32.5 4.5 22.46 46.08 13.33

S11 4.5 0.71 37.5 25.05 8.77 51.3 12.7

S12 9.2 0.3 18.5 1.25 25.19 36.52 12.49

S13 4.5 0.36 23.75 15.52 8.77 51.3 14.16

S14 5.09 0.48 33.25 12.77 11.71 43.47 13.33

S15 4.5 0.25 23 22.79 10.56 42.6 10.31

S16 12.89 0.41 46.5 26.54 38.01 33.91 10.62

S17 4.47 0.43 30.75 25.54 11.18 40 11.87

S18 3.5 0.22 27 21.53 8.39 41.73 10.41

S19 5.5 0.24 23.75 20.78 17.1 32.17 8.33

S20 7.4 0.31 28.5 23.54 15.47 47.82 14.58

S21 8.5 0.38 12.5 3 20.37 41.73 14.58

S22 5.5 0.42 21.5 18.53 15.43 35.65 10.41

S23 5.68 0.19 28.25 19.53 14.2 40 13.95

S24 6.46 0.51 24 22.29 19.55 33.04 10.83

S25 7.5 0.31 25 31.3 15.4 48.69 11.45

S26 8.27 0.35 23 28.3 15.85 52.17 12.91

S27 6.2 0.91 27.75 25.05 15.5 40 12.08

S28 3.87 0.37 23 22.29 8.56 45.21 20.2

S29 2.58 0.19 31.75 17.03 6.18 41.73 16.16

S30 4.34 0.28 27.5 19.78 9.24 46.95 14.58

S31 3.72 0.3 24.25 28.3 6.9 53.91 17.49

S32 2.27 0.16 29.5 31.8 3.96 57.39 12.7

S33 3.72 0.21 27.75 26.54 6.58 56.52 9.79

S34 3.72 0.17 37.5 27.54 6.79 54.78 6.87

S35 3.1 0.33 37.75 18.53 5.57 55.65 15.2

S36 2.79 0.19 28.75 32.8 5.01 55.65 10.2

S37 3.2 0.52 46.5 22.54 7.01 45.65 12.08



S38 2.37 0.3 32.5 14.77 7.27 32.6 12.08

S39 3.51 0.19 28 22.03 9.79 35.86 11.66

S40 2.067 0.63 34.25 25.29 5.66 36.52 14.37

S41 1.96 0.25 45.75 19.28 4.29 45.65 5.83

S42 1.34 0.22 43.75 16.78 3.42 39.13 16.24

S43 1.44 0.3 36.5 20.78 3.56 40.43 10.2

S44 6.4 0.28 22.22 28.05 15.1 42.39 10.83

S45 2.48 0.19 55.5 4.5 3.26 76.17 5.2

S46 1.65 0.24 39.5 47.33 2.21 74.65 11.24

S47 2.17 0.14 38.75 22.29 2.68 81 12.28

S48 1.86 0.43 38.25 23.79 2.26 82.47 13.74

S49 2.37 0.3 37.5 26.29 3.08 76.91 8.95

S50 1.44 0.16 39.5 20.53 1.95 73.71 11.24

S51 3.3 0.12 21.25 19.03 4.07 81 13.74

S52 1.55 0.35 25.25 18.53 2.18 71 8.12

S53 8 0.16 24.5 22.29 15.33 52.17 18.95

S54 5.37 0.34 27.5 17.78 9.5 56.52 15.83

S55 4.34 0.28 31.5 21.53 8.18 53.04 16.45

S56 4.75 0.18 22.5 22.54 8.28 57.39 14.99

S57 5.16 0.23 46.5 34.06 8.36 61.73 8.12

S58 6.61 0.18 30.75 44.58 10.86 60.86 7.91

S59 2.48 0.36 43.25 29.05 3.8 65.21 8.74

S60 1.86 1.36 25 12.52 3.32 56.08 9.58

S61 3.72 0.25 36.75 26.8 5.49 67.82 6.66

S62 2.07 0.19 52 20.53 2.89 71.73 12.49

Classification of Soils on the basis of pH

The characteristics of the soils show wide variations from one place to another depending upon the

rainfall, topography, climate, geology and land use pattern of the area. Therefore, in order to know the

exact situation at a particular location classification of soil is necessary. Different criteria based on

different parameters such as pH, EC, CaCO3 content, degree of alkalinity (ESP), degree of salinity (EC)

and pH of soil extract have been widely used to classify the soils12

.

The classification of soils from study area on the basis of pH is summarized in Table 3

Table-3: Classification of soils on the basis of pH from study area

12.

pH range Type No. of Soil Samples and locations

Less than 6 Acidic

soil

Nil

6.0 to 8.5 Normal S3, S4, S5, S7, S9, S11, S13, S15, S16, S17, S18, S23, S25, S27, S29, S31,

S32, S34, S35, S36, S37, S38, S39, S40, S41, S42, S43, S45, S46, S47, S48,

S49, S50, S51, S53, S57, S59, S61 = 38(61.29%)

Greater than 8.5 Alkali

soil

S1, S2, S6, S8, S10, S12, S14, S19, S20, S21, S22, S24, S26, S28, S30, S33,

S44, S52, S54, S55, S56, S58, S60, S62 = 24 (38.70%)

It is observed from the table that out of 62 soil samples 38 (61.29%) samples shows normal soils which

are located on the upstream and topographically higher areas while 24 (38.70%) samples shows pH



greater than 8.5 leads to alkali soils. These alkali soils are observed in the central and downstream part of

the area.

Electrical Conductivity The electrical conductivity (EC) in the saturation extract is used as an index for grading the soil type

along with ESP and pH of the soils 12

. It is characterized by cations like sodium, potassium, calcium and

magnesium and anion like chlorides, sulphates, bicarbonates, phosphates and nitrates.

The EC values range from 0.1 to 46.8 dS/m in the study area. The higher values of EC have been

obtained from downstream part (S.No. S2, S3, S4, S5, S7 and S16) reflecting low flushing rate and

sluggish groundwater movement. The salt accumulation in the area is associated with the areas of high

(shallow) water table. In this area, particularly at Jorve, Rahimpur and Kolhewadi transpiration of salts

with surface runoff is negligible. Instead evaporation of surface and groundwater at shallow depth leave

behind the salts which appear as encrustation on soils. On the other hand, lower values of EC are recorded

for upstream and topographically higher areas can be attributed to the rolling topography, relatively

higher gradient, seasonal irrigation and alternating cropping pattern (S.No. S23, S25, S29, S32, S34, S35,

S45, S48, S49, S50, S52, S59 and S60). Similar findings were reported20-22

in the further downstream area

which is in close proximity of the study area.

Classification of soils on the basis of EC The soils from the study area are also classified on the basis of EC which are summarized in Table 4.

Table-4: Classification of soils on the basis of EC from study area

23.

EC (dS/cm) Soil Type No. of Soil Samples and locations

Less than 1 Normal soil S23, S24, S25, S29, S32, S41, S42, S43, S44, S45, S46, S47, S48,

S49, S50, S52, S58, S59, S60, S61 = 22 ( 35.48%)

1-2 Critical for

germination

S19, S30, S31, S33, S39, S40, S51,S54, S56, S57, S62 = 12 (19.35%)

2-3 Critical for growth

of salt sensitive

crops

S1, S18, S22, S36, S37

= 5 (8.06%)

Greater than 3 Severely injurious

to crops

S2, S3, S4, S5, S6, S7, S8,S9, S10, S11, S12, S13, S14, S15, S16,

S17, S20, S21, S26, S27, S28, S38, S53 = 23 (37.09%)

It is evident from the table that 22 (35.48%) samples shows normal soils while the remaining are

problematic i.e. 12 (19.35%) soil samples are critical for germination, 5 (8.06%) critical for growth of

salt sensitive crops and 23 (37.09%) severely injurious to crops. These soils are located in the downstream

part of Pravara River.

Calcium Carbonate (Calcareousness) Impure calcium carbonate locally known as kankar usually occurs in natural state in irrigation soils. The

presence of calcium carbonate in the soil is due to climatic factors. It is known that the soils in the areas

characterized by semi – arid and arid climates usually show precipitation of calcium carbonate24

. The

calcareousness influences the pH of soil as well as the availability of micro and macronutrients required

for plant growth. The physical conditions of the soils are also greatly influenced by the quantity and size

of concretions. However, the effect of carbonate on soil fertility is not uniform. A moderate amount of

CaCO3 damages the physical properties of soils and cements the soil mass 25

. The data of CaCO3 content

of the soils from study area is presented in Table 2. Critical examination of data from Table 2 reveals that

CaCO3 content in the soil varies from 5.2 to 20.2 %. Overall, higher concentrations of CaCO3 are

observed in majority of the samples. This is attributed to alkaline pH of soil indicative of a tendency of

precipitation of CaCO3 during irrigation. This is because the soils from the area are formed from basaltic

and alluvium lithology under semi – arid climatic condition, characterized by low precipitation and high

rate of evaporation favoring more accumulation and precipitation of CaCO3.



Classification of soils on the basis of CaCO3 content The rating for calcareousness of soils depending upon calcium carbonate percentage in the area are

categorized 26

(Table 5).

Table-5 : Classification of soils on basis of CaCO3 content from study area

26

% CaCO3 Soil Class No. of samples

Less than 4 Non – calcareous Nil

4-10 Moderately calcareous 13 (20.9%)

Greater than 10 Strongly calcareous 49 (79%)

It is evident from the table that majority of the soils (79%) are strongly calcareous followed by

moderately calcareous class (20.96%). The unusually high values of CaCO3 were recorded at base of

Ghat sections and hill slope area of transect (S.No. S31, S40, S42, S55 and S 54). This is the colluviums

rich deposit over which the soils have been developed. High proportion of CaCO3 is indicative of

insufficient leaching of salts from host rock basalt. Similar findings were also reported6,26

.

Soluble Cations

The concentration of soluble cations are in the order Na+>Ca

2+>Mg

2+ >K

+ in the soils from study area

(Table 1). The sodium concentration ranges from 0.36 to 280 meq/l. The higher concentrations of Na+ in

saturation extract were found in river bank areas (S.No

S2,S3,S4,S5,S6,S7,S8,S9,S10,S12,S16,S20,S21,S26andS53). This is possibly due to precipitation of

calcium–magnesium carbonates owing to high pH conditions. The concentration of Na+ is more than Ca

2+

and Mg2+

indicating the alkalization process in the shrink – swell type of soils that are predominating.

Soluble Anions

Among the anions, chloride is predominant anion followed by sulphate and bicarbonate in the soils. The

chloride content ranged from 0.96 to 55.36 meq/l. The sulphate and bicarbonate content ranged between

0.01 and 12.07 meq/l and 0.4 – 4.8 meq/l respectively. The higher concentrations of chloride and

sulphate were found in the samples showing higher Na+ (S.No. S2, S3, S4, S5, S6, S7, S8, S9, S10, S12,

S14, S16S, S21, S27 and S53). The accumulation of salts on the surface of soil can be seen in areas with

high water table (<2m). Higher content of HCO3- in some soil samples in the downstream part (S.No. S1,

S19, S22, S24, S25, S27 and S44) could be related to strong alkaline reaction and local changes in

hydromorphic set up. The carbonate ions are almost negligible or lesser in amount in majority of soil

samples. This is due to precipitation of calcium and magnesium as carbonates. It is also observed that

chloride ion concentration increases markedly with EC values of soils (Table 1). Similar observation were

also reported 27,28

.

Sodium Absorption Ratio (SAR) The sodium absorption ratio (SAR) is used to estimate exchangeable sodium percentage (ESP) of soil.

The SAR is used in the soil studies because of its good co-relation with ESP besides its easy estimation

and calculation than ESP. However, it is also found that estimation of ESP from SAR values may be more

accurate than ESP analysis29

. SAR indicates the equilibrium relation between soluble and exchangeable

cations.

The SAR values below 13 categorize into normal soils whereas above 13 are indicating salt affected soils.

This is to say that SAR above 13 implies that exchangeable sodium has greatest effect on plant growth by

dispersing the soil29

.

The SAR of soil extracts from study area was calculated from the values of sodium, calcium and

magnesium presented in Table 1. It is observed that SAR values ranges from 0.79 to 60.38 in the soil

extracts. Further, out of 62 samples, 15 samples (24.19%) have SAR values greater than 13. These

samples are collected from the backwater zone of Ojhar weir on Pravara River (S.No.

S2,S3,S4,S5,S6,S7,S8,S9,S10,S12,S13,S15,S16,S20 and S21). Impoundment of water in the weir causes

shallow water table conditions and congestion of drainage, which has lead to evaporative concentration of

salts in the area. As a result, high values of SAR have been obtained due to precipitation of Ca and Mg



under strongly alkaline condition. The remaining 47 samples (75.80%) have SAR less than 13 suggesting

non-saline characteristics of the soils.

Exchangeable Cations The phenomenon of ion exchange is of great importance in soil chemistry. The soil properties are greatly

affected by exchangeable cations30

. The nutrient uptake by plants is governed by ion exchange

phenomenon.

The exchangeable cations present in agricultural soils are Ca2+

, Mg2+

, Na+, K

+ and NH4

+. Their relative

absorption affinities on soil are in the order Ca2+

> Mg2+

> Na+> K

+ = NH4

+ >Na

+

24. That is to say that

among all cations, Ca2+

has maximum replacing capacity while Na+ has minimum. This is because Ca

2+

has greater valancy and a smaller hydrated radius than that of Na+. As a result of this, the proportion of

these ions on colloidal surfaces constantly changes depending upon the ions added from the dissolving

minerals, fertilizers, gypsum etc. Losses by plant absorption or by leaching also change cation

proportions29

. During this processes the cations of the clay / colloidal matter are exchanged in equivalent

quantities with the cations of salt solution. This process of exchange of cation of soil and salt solution is

known as cation exchange17

.

In the present study, the concentrations of four cations (viz., Ca2+

, Mg2+

, Na+, and K

+) from the soil

extracts have been determined. The results are expressed in terms of meq/100 g and are presented in

Table 2.

Out of the total exchangeable cations in the soils, Ca2+

is dominant over rest of the cations. This can be

attributed to greater adsorption strength of calcium on soil compared to other cations. In semi – arid

weathering environments, Ca2+

is expected to occupy major position on the exchange complex 29

.

From the Table 2, it is observed that the exchangeable calcium ranges from 12.5 to 55.5 meq/100g and

that of magnesium between 1.25 to 47.23 meq/100g. The predominance of Ca2+

in majority of the soil

samples in indicative of Ca - clay. This is particularly observed in the non – irrigated area. (S. No. S16,

S37, S41, S57 and S62). Such soils with exchangeable Ca2+

possesses an excellent physical condition,

develop a good crumb structure and allow the free movement of water and air.

The exchangeable K+ on exchange complex is very low (0.12 to 1.2 meq/100 g) in comparison with the

other cations. The exchangeable Na+ were found to be higher (1.34-25.2 meq/100 g) in the downstream

part of study area (S.No. S1,S2, S3, S4, S5, S6, S7, S8, S9, S10, S12, S13, S14, S16, S19,

S20,S21,S23,S24,S25,S26,S27,S44,S53 and S54). This is possibly due to impeded drainage and base

rich-pedo environment, which is responsible for higher exchangeable Na+. If exchangeable Na

+ consists

more than 10 to 15 percent of the total exchangeable cations in the soil, then it leads to alkaline condition 17

. In the present study, 29 soil samples (46.77%) showed their exchangeable Na+% more than 10,

reflecting alkaline soils (Table 2). The higher pH value (pH>8.5) corresponding to these soils supports

this inference. In such soils, colloidal Ca-clay turns into Na-clay, which further greatly disturbs the

physical conditions of the soils. Such situation restricts the free movement of air and water changing

them into sticky soils when wet.

Exchangeable cations are higher in black soils than the other soil types (S.No. S11, S16 and S45) in the

area. Similar observations were also recorded 21,31

in other parts of Pravara basin of study area.

Cation Exchange Capacity (CEC) The cation exchange capacity (CEC) denotes the ability of a soil to hold nutrient cations in readily

available forms. It is the quantity of nutrient cations present in exchangeable form. CEC influences the

pH of soil solution and its salt composition. It is the direct source of mineral nutrition to plants. It affects

the physical properties of soils. It is an index used in the diagnosis and classification of soils. It also helps

to predict leaching requirement and irrigation of soils with saline water 25

.

The CEC values of soils in study area range from 32.14 to 82.47 C mol (P+) per kg (Table 2).

Considering these values, the soils in the area can be texturally classified as clay loam to clay 29

. The

higher values of CEC were noted in topographically higher part of study area, which is non – irrigated

(S.No. S48, S46, S45, S62, S49, S50, S51 and S52). These soils are in general clayey in nature occurring

in small depressions. However, they are well drained. In the downstream part of the area, CEC is found

to be relatively on lower side, inspite of the fact that they are texturally more clayey. This is attributed to



the waterlogging conditions created by impeded drainage, which does not allow free circulation of air and

water in the area.

Higher CEC indicates presence of smectite (montmorillonite) clay. On the contrary, low CEC reflects

kaolinite as the predominant clay minerals in soils17

.

In general, the CEC values of soils are low as compared to total exchangeable cations (Table 2). This is

due to variation in clay and organic matter content of the soils 25.

Exchangeable Sodium Percentage (ESP)

ESP is a very important chemical property that defines the physical character of salt affected soils. ESP is

the percentage of exchangeable sodium to the total exchangeable cations in the soil sample 12

. It is

calculated from the formula.

Exchangeable Sodium (meq/100g)

ESP = X 100

Cation Exchange capacity (meq/100g)

Excess exchangeable Na is harmful to plants principally because it induces undesirable physical and

chemical change in the soils 24

. The ESP value is generally 15 to 30% larger than SAR. In case of fine

textured soils with montmorillonite clay, an ESP of 15 is a good approximation. Therefore, ESP greater

than 15 is indicative of the presence of alkali soils and those below this value reflects non – alkali soils 5.

In the present study, the ESP values in the area ranged from 1.95 to 59.15 (Table 2). The ESP > 15 was

observed for 22 samples (35.48%) from the study area. Such soils are located in the vicinity of the

backwaters zone of Ojhar weir (S.No. S2, S3, S7, S8, S10 and S12). Here strong alkaline soil

environment has favored the precipitation of Ca-Mg carbonates. Such reaction is enhanced under semi

arid climatic condition with low partial pressure of CO2 and low content of organic matter in soil.

However, the soils located at higher elevation in the area show low ESP i.e. < 15 (S.No. S42, S45, S46,

S47, S49, S50, S52, S59, S60, S61 and S62). In such soils it was observed that the water uptake capacity

was improved which favors the crop growth. It was noticed that the high ESP soils after irrigation

retained more water on the surface, which is then lost through evaporation. This, in turn, considerably

reduces the water uptake capacity of soils. Hence, it is inferred that the high ESP of soil changes the soil

water relation 32

. In the intensively irrigated area, the accumulation of excessive clay and high degree of

sodium saturation in soil tends to produce adverse physical condition resulting into poor permeability and

drainage. On the contrary, the better permeability was noticed in non-irrigated area.

Classification of soils based on ESP, EC and pH of soils The most accepted classification of soil is based on degree of alkalinity (ESP), degree of salinity (EC) and

pH of soil extract12

. The classification based on these criteria from study area is summarized in Table 6

Table-6: Classification of soils based on ESP, EC and pH of soils from study area

12

Soil Type pH EC (dS/m) ESP (%) No. of soil samples

Normal Less than 8.5 Less than 4 Less than 15 33 (53.22%)

Saline Less than 8.5 Greater than 4 Less than 15 7 (11.29%)

Sodic Less than 8.5 Less than 4 Greater than 15 7 (11.29%)

Saline – sodic Variable Greater than 4 Greater than 15 15 (24.19%)

It is noticed that the salt affected soils viz. Saline, sodic and saline-sodic have been confined to

the low – lying parts and in the catchment area of Ojhar weir. The saline – sodic soils (S.No. S2,

S3, S4, S5, S6, S7, S8, S9, S10, S12, S16, S20, S21, S26 and S53) form the patches of wasteland

at Jorve, Kolhewadi and Rahimpur villages. The area occupied by saline sodic soils (S.No. S11,

S13, S14, S15, S17, S28 and S38) is enveloped by sodic followed by saline and normal soils.

Possible sources that have lead to the formation of such soils in the area are excess and

unscientific irrigation practices, congestion of drainage due to flat topography, heavy



applications of chemical fertilizers, monoculture type of cropping patterns and low rainfall and

semi – arid climatic condition.

However in the upstream area with normal soils were having undulating topography and also the

non – irrigated type of land use. This suggests that low rainfall and climatic condition alone are

not the cause of degradation of soils in the area.

CONCLUSION In order to understand the chemical characteristics of the soils from the Sangamner area, the chemical

properties like pH, EC, soluble cations and anions, exchangeable cations, CaCO3 content, CEC and ESP

of soil were estimated by analyzing 62 soil samples. pH of the soils ranges from 8 to 9.7 reflecting

alkaline nature. The higher values of pH are observed in the central and downstream part of the area

which is indicative of development of salinity / sodicity in the area. The EC values ranges from 0.1 to

46.8 ds/m. The higher of EC have been observed from downstream part indicating low flushing rate and

sluggish groundwater movement. The lower values of EC are recorded for upstream and topographically

higher areas. EC study shows 35.48% of the soils from the area are normal whereas remaining are

problematic soils requires reclamation. The CaCO3 content in the soils varies from 5.2 to 20.2 %. Higher

concentration of CaCO3 i.e. strongly calcareous are observed in 79% of the soils followed by moderately

calcareous class (20.96%). This is because the soils from the study area are formed from basaltic and

alluvium lithology under semi – arid climatic conditions, characterized by more accumulation and

precipitation of CaCO3.

Among the soluble cations, higher concentration of Na+ in river bank areas followed by Ca

2+ and Mg

2+

indicating the alkalization process in the shrink – swell types of soils. As far as anions are considered

chloride is predominant followed by sulphate and bicarbonate in the soils. The higher concentration of

chloride and sulphate were found in the soils having higher Na. Higher content of HCO3 in some soils in

the downstream part due to strong alkaline reaction. The SAR values ranges from 0.79 to 60.38 in the

soils. 24.19 % samples have SAR greater than 13 in the backwater zone of Ojhar weir. This is due to

precipitation of Ca and Mg under strongly alkaline condition. 75.80% soils have SAR less than 13

suggesting non-saline characteristics of the soils.

Out of the total exchangeable cation, Ca2+

is dominated over the other cations due to greater absorption

strength of Ca2+

in non – irrigated area. The exchangeable Na+ is found to be higher in the downstream

part due to impeded drainage and base rich pedo environment. The CEC values of soils ranges from 32.14

to 82.47 C mol (P+) per kg. Higher CEC were observed in topographically higher part of study area

which is non – irrigated. CEC is found relatively low in downstream part due to clayey nature of soils

attributed to water logging. Out of 62 soil samples, 22 (35.48%) soil samples have ESP>15 located in the

backwater zone of Ojhar weir and remaining soils have ESP<15 indicating better permeability which

favors crop growth in the non-irrigated area.

ACKNOWLEDGEMENT The author is thankful to Dr. N. J. Pawar, Vice-Chancellor, Shivaji University, Kolhapur for his valuable

guidance and constant encouragement. The author is also thankful to Head, Department of Environmental

Science, University of Pune and Post-Graduate Research Centre in Chemistry, Sangamner College,

Sangamner for providing necessary research facilities.

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