Chapter 4: Soil Quality and Soil Organic Carbon …shodhganga.inflibnet.ac.in/bitstream/10603/82190/13/13...Climate Change Impacts: Vegetation And Plant Responses In Gujarat 119 Chapter

Climate Change Impacts: Vegetation And Plant Responses In Gujarat

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Chapter 4: Soil Quality and Soil Organic Carbon under Different Agro-Climatic Zones of Gujarat.

Forest of Ratanmahal, Dahod Forest of Rampara, Rajkot

Gir forest, Gir Various coloured soil of Gujarat Figure-26: General topography of various areas in Gujarat


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Introduction

Soil Soil is a repository for decaying plant matter and the largest terrestrial storehouse of

carbon. Soil management is of central importance. Soils currently are estimated to

contain about 82% of all terrestrial carbon. Carbon is sequestered in the part of soil

called humus, which provides more stable storage of carbon than biomass. Humus is

made up of a collection of organic matter that results from decomposition of animal

and vegetative litter. It composes a relatively stable carbon pool (Jeff and Hill,

2009).

Understanding the role of the soil-vegetation system in the carbon cycle is important.

Movement of carbon inside the soil across different physical and chemical pools is

crucial to maintain the soil as a sink or turn it into a source. Understanding these

processes at the tropics becomes more imperative because of the heterogeneity of the

carbon pool and also of the diverse vegetal cover (Dinakaran and Krishnayya, 2008).

Soil may be an important sink for the carbon storage in the form of soil organic

carbon. Plants are the main source of the soil organic carbon, either from the

decomposition of aerial plant parts or underground plant parts, e.g. roots in the form

of root death, root exudates and root respiration (Kumar et al., 2006).

Soil as Carbon Sink

Soil is the largest pool of terrestrial organic carbon (Kumar et al., 2006; Dinakaran

and Krishnayya, 2008). Soil contains about 1.5-3 times more organic carbon than

vegetation and about twice as much carbon than is present in the atmosphere (Kumar

et al., 2006; Dinakaran and Krishnayya, 2008; Scherr and Sthapit, 2009). Soils

contain much more C (1500 Pg of C to 1 m depth and 2500 Pg of C to 2 m; 1 Pg =

1´1015 g) than is contained in vegetation (650 Pg of C) and twice as much C as the

atmosphere (750 Pg of C) (Batjes, 1996; Batjes, 1998; Sombroek et al., 1993;

Schlesinger 1997; Batjes & Sombroek, 1997; FAO, 2001; Resh et al., 2002; Farage

et al., 2003; Kumar et al., 2006; Ramachandran et al., 2007; Luske & Kamp, 2009).


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Soil organic carbon (SOC) is dynamic on decadal timescales and is sensitive to

climate and human disturbance (Dinakaran and Krishnayya, 2008).

About half of the 6.5 billion tonnes of carbon emitted globally by burning of fossil

fuels is taken up by vegetation and stored as organic matter (OM) (Dinakaran and

Krishnayya, 2008). Soil OM which constitutes 1 to 8% of the weight of most soils

(Kumar et al., 2006) is a heterogeneous mixture consisting of plants, animals and

microbial materials in all stages of decay, combined with a variety of decomposition

products of different ages and levels of complexity (Dinakaran and Krishnayya,

2008). Carbon in the form of organic matter is a key element to healthy soil. It is

estimated that each tonne of soil organic matter releases 3.667 tonnes of CO2, which

is lost into the atmosphere. Similarly, the build-up of each tonne of soil organic

matter removes 3.667 tonnes of CO2 from the atmosphere (Kumar et al., 2006).

Soil-Vegetation systems play an important role in the global carbon cycle (Dinakaran

and Krishnayya, 2008). Through photosynthesis, plants convert CO2 into organic

forms of carbon, viz. sugars, starch and cellulose, also known as carbohydrates. In

natural habitats, carbon from plants is deposited in the soil through roots and plant

residues, such as fallen leaves (Kumar et al., 2006). The annual global rate of

photosynthesis is generally balanced by decomposition and represents one-tenth of

the carbon in the atmosphere or one-twentieth of the carbon in soils. Carbon,

nitrogen, oxygen and hydrogen are the building blocks of life on earth. They also are

the most important constituents of soil organic matter. The earth’s carbon cycles

have the ability to restore and even increase the soil organic matter content, improve

fertility, increase the water-holding capacity, and improve tilth if properly

established scientific principles are applied to good soil management and sustainable

agriculture (Kumar et al., 2006). The process of carbon sequestration or flux of

carbon, into soils forms part of the global carbon cycle. Movement of carbon

between the soil and the above ground environment is bidirectional and consequently

carbon storage in soils reflects the balance between the opposing processes of

accumulation and loss (Farage et al., 2003). The cycle of transfer of C from

inorganic to organic by plant and from organic to inorganic in soil provides a better

environment for C sequestration and maintaining soil quality. Balance between OM


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inputs and decomposition is the primary determinant of OM accumulation or

depletion in soil (Shrawat et al., 2005).

Carbon sequestration refers to taking carbon dioxide from the atmosphere through

plants and storing the carbon in soil in the form of soil organic matter (Kumar et al.,

2006). All the organic carbon found in the soil is primarily plant derived. The two

main sources of carbon in the soil are: (1) accumulation of soil organic matter due to

the humification after plant death and (2) root exudates and other root-borne organic

substances released into the rhizosphere during plant growth as well as sloughing of

root hairs and fine roots by root elongation. Carbon is added in the soil system by

plant roots through root death, root exudates and root respiration (Kumar et al.,

2006). Soil organic carbon is composed of a wide range of compounds that

decompose at different rates depending on their chemistry, soil temperature and

moisture, organisms present, association with soil minerals and the extent of

aggregation. Excess exploitation results in loss of soil fertility and can be attributed

to the misuse of the soil and its organic matter (Kumar et al., 2006).

Soil holds about 20–24% of the total forest carbon (Sulistyawati et al., 2007). In the

forest system although carbon is sequestered in the upper 5 cm of the mineral soil, it

is offset by carbon release from the lower soil layers (5-15 and 15-25 cm) (Baral and

Guha, 2004). Because there is more carbon stored in the soil than in the atmosphere,

forests and all vegetation combined (Jeff and Hill, 2009) sequestration of carbon in

soils used for agriculture, forestry and land reclamation has been recognized as a

potential option to mitigate global change (Kumar et al., 2006).

Factors influencing soil organic carbon

The ability of lands to store or sequester carbon depends on several factors, including

climate, soil type, type of crop or vegetation cover and management practices. The

amount of carbon stored in soil organic matter is influenced by the addition of

carbon from dead plant material and carbon losses from respiration, the

decomposition process and both natural and human disturbance of the soil (Jeff and

Hill, 2009). SOC also depends on C content, bulk density and depth of soil

(Chandran et al., 2009). The carbon content of a soil is a function of parent material,


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climate/environment, vegetation, topography, soil management and time (Luske &

Kamp, 2009).

Land’s ability to store or sequester carbon depends on many factors including:

1). Climate – In cooler climates, decomposition happens more slowly, so the plant

residue has a greater chance of becoming humus, which is a stable part of soil with

high organic carbon content (Dinakaran and Krishnayya, 2008; Misra et al., 2008;

Jeff and Holly Hill, 2009; Luske & Kamp, 2009).

2). Soil type – Poorly-drained soil types have the capacity to store carbon more

readily than others (Farage et al., 2003; Dinakaran and Krishnayya, 2008; Jeff and

Hill, 2009).

3). Type of crop or vegetation cover – Plant residues in agricultural soils do not

represent a large storage pool. However, their management influences water

penetration, wind and water erosion and the extent of formation of soil organic

matter, thus affecting long-term soil fertility and carbon storage (Kumar et al., 2006).

Making certain plant choices (which produce more amount of residue, more organic

carbon and carbon) can help capture more carbon from the atmosphere and make it

available to processes that may lead to longer-term storage (Sampson, 2000; Kumar

et al., 2006; Dinakaran and Krishnayya, 2008; Jeff and Hill, 2009). The carbon

sequestration potential in soils is strongly affected by root production. Soils with

seasonal herbaceous cover in the tropics can be considered as one of the potential

sinks (though small) for carbon, as in their case, the proportion of carbon going

down is significantly larger compared to the inputs. SOC content in soils with natural

vegetal cover (trees) is sufficiently large, indicating their sink capacity. Difference in

vegetal cover not only influenced SOC content of the top layer, but also of the

deeper layers. The type of vegetal cover has been found to have a significant impact

on SOC up to a depth of 1.5 m. SOC decomposition is significantly different across

different vegetal covers due to substrate availability (Dinakaran and Krishnayya,

2008).

4). Microbial activity: Decomposition of SOC is dependent on the type of fraction

and microbial activity at that depth (Dinakaran and Krishnayya, 2008). Changing

temperature alters the microbial activity in the soil that causes the breakdown of


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organic matter at faster rates and results in greater release of CO2 (Misra et al.,

2008).

5). C content: A soils’ potential to function as a carbon sink is therefore highly

dependent on the initial carbon stock of the soil, as well as land use practices.

Compared to other soils, arid desert soils have a relatively high potential to act as a

carbon sink, as their initial carbon stock is usually minimal (Chandran et al., 2009;

Luske & Kamp, 2009)

6). Depth and Bulk density: Understanding variations in SOC content across

different depths of soils with different vegetal covers is important. In all the sites,

SOC decreased as the depth of the soil increased. The distribution of SOC with depth

and total SOC density (kg/m2) are affected by vegetation, soil texture, landscape

position, soil truncation, and the effect of run-on and run-off or wind

erosion/deposition (Dinakaran and Krishnayya, 2008; Chandran et al., 2009)

7). Land use/Management practices: Large scale disruption or changes on land

drastically alter the harmonious movement of carbon (Sampson, 2000; Resh et al.,

2002; Ramachandran et al., 2007; Jeff and Hill, 2009; Luske & Kamp, 2009; Scherr

and Sthapit, 2009). Changes in land-use pattern severely reduced sink capacity of

soils. Land- use alteration can convert a soil system from a sink to a source of carbon

(C). Many uncertainties persist in the estimation of net flux of CO2 from the soils of

tropical forests largely due to inconsistency in land-use and land-cover pattern.

Evaluating the influence of changes in land-use pattern on carbon sequestration in

tropical systems is necessary as tropical systems have a greater role in regulating the

carbon cycle (Dinakaran and Krishnayya, 2008).

Deforestation may contribute to the loss of soil C by changing the balance between

biomass production and decomposition. Tropical deforestation may be a net source

of 0.2×10-15 g C/y, with up to 25% coming from soils (Houghton 2007). Intensive

cultivation can also decrease soil C, contributing to terrestrial net fluxes of C to the

atmosphere and decreased net primary productivity (Resh et al., 2002). Land use and

soil management practices can significantly influence SOC dynamics and C flux

from the soil (Ramachandran et al., 2007).


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8). Physical soil properties such as soil structure, particle size and composition:

Physical SOC fractionation gives a better understanding of SOC movement in the

soil. Physical soil properties such as soil structure, particle size and composition

have an impact on soil C. Soil particle size has an influence on the rate of

decomposition of SOC. OM found on the exterior of soil aggregates is physically far

more accessible to degradation than C compounds physically protected in the interior

of these aggregates. Soil aggregation is an important process of carbon sequestration

and perhaps a useful strategy to mitigate the increase in concentration of atmospheric

CO2. SOC concentration was shown to increase with decreasing particle size

(Dinakaran and Krishnayya, 2008).

9). Temperature: Higher rates of removal of leaf litter and deadwood from forest

floor with increase in population pressure coupled with higher soil respiration under

warmer regimes will reduce downward movement of organic carbon more so in open

environments (Sampson, 2000; Farage et al., 2003; Maikhuri et al., 2003; Smith et

al., 2003; Misra et al., 2008). Global warming just by 2°C is predicted to increase

additional C release from soil by more than 10 PgC (pentagram or 1015 gm of C) per

year, resulting into more GHE (Pandey, 2002). Under such circumstances

characterizing the temperature response for forest soils is particularly important,

because these soils contain more than 70% of the world’s pool of C in the soil (Smith

et al., 2003).

The size of soil organic matter pools in natural ecosystems decreases exponentially

with temperature (Lal, 2008). Drier soil per se is less likely to lose carbon (Glenn et

al, 1993) and consequently the residence time of carbon in dryland soils is much

longer than forest soils (Gifford et al, 1992). Soil OM can also increase or decrease

depending on numerous factors, including climate, vegetation type, nutrient

availability, disturbance, land use and management practices (Dinakaran and

Krishnayya, 2008). The carbon sequestration potential of a soil depends on its

capacity to store resistant plant components together with protecting, and

accumulating, humic substances. The quantity of soil carbon present is controlled by

a complex interaction of processes determined by carbon inputs and decomposition

rates. Factors controlling the quantity of organic matter in soil include temperature,


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moisture, oxygen, pH, nutrient supply, clay content and mineralogy. Accumulation

of carbon will be favoured by conditions that do not promote decomposition, i.e. low

temperature, acid parent materials and anaerobic conditions (Farage et al., 2003).

The loss in the soil carbon pool is due to three factors: the reduction of plant roots

and residue return as grass and trees give way to crops, the increase of biological

decomposition as soil aeration is increased by cultivation and soil temperatures rise

due to loss of shade and any increase in soil erosion that carries carbon-rich soil

materials from the site (Sampson, 2000). Decomposition further decreases the SOC

content with increased exposure to bare soil. Thus SOC decline is rapid within 5-25

years of forest clearing, with loses ranging from 25-75% in the surface soil horizons

(Chandran et al., 2009). Depending on the changes happening to soil OM and SOC,

soils can act as a sink or a source for carbon in the atmosphere (Dinakaran and

Krishnayya, 2008)

Importance of Soil Organic Carbon

Soil carbon is an important determinant of site fertility due to its role in maintaining

soil physical and chemical properties (eg. aggregate stability, carbon exchange

capacity) (Ramachandran et al., 2007). Plant increase the soil organic matter, which

will store more atmospheric carbon and result in greater soil fertility, better soil tilth,

greater water-holding capacity, and reduced erosion. It also will make plants more

stress-resistant and thus be able to better withstand the predicted climatic

fluctuations. Control of water levels during periods of non-plant growth could result

in C sequestration, improved water quality, flood control and better wildlife habitat.

Carbon deposits in soil result in the building of soil organic matter, which will

reduce soil erosion, nutrient loss, and environmental pollution and improve nutrient

mobilization, water-retention capacity and microflora. Carbon components reduce

pH, nutrient mobilization and microbial growth. The exact amount of sequestration

depends on land-management practices, edaphic factors, climate, and the amount and

quality of plant and microbial inputs. Carbon sequestration will certainly contribute

in reducing atmospheric CO2 concentration and will mitigate drought, salinity stress

and desertification. Thus, sequestered soil carbon may be used for agriculture,


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forestry, and will be a potential option to mitigate global change (Kumar et al.,

2006).


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Literature Review

Carbon sequestration involves the capture of carbon dioxide from the atmosphere

and storage in the plant tissue in the form of carbohydrates by the process of

photosynthesis (Phani Kumar et al., 2009).

Soil-vegetation systems play an important part in the global carbon cycle (Dinakaran

and Krishnayya, 2008). Soil is the largest pool of terrestrial organic carbon (Jobbagy

et al., 2000; Lal, 2004; Romanovskaya, 2006). Soil organic carbon is sensitive to the

climate and human disturbances and degrades fast (Amundson, 2001). Soil has three

times more carbon than vegetation (Wang et al, 2004) and twice as much as the

atmosphere (Lal, 2004).

MacDicken (1997) analysed and constructed a guide for monitoring carbon storage

in forestry and agroforestry, USA.

Jenny and Raychaudhari (1960) studied the effect of climate and cultivation on the N

and OC reserves in the Indian soils. They collected soil samples across the country

from cultivated fields and forested soils in relation to a climatic grid in which mean

annual temperature and mean annual precipitation appeared as independent

variables. Based on the analysis of 500 soil samples for OC and total N across India

these authors showed that the climatic effects on SOM and N status are pronounced.

Soil N and C increased with increasing mean annual precipitation and decreased with

increasing mean annual temperature. Soils in the drier region had low reserves of

OM and N compared to those in the humid and sub-humid zones of the country.

Velayutham and Bhattacharyya et al., (2000) carried out studies on carbon stocks in

Indian soils. Analysis of thousands of soil samples in the course of the study helped

prioritize research on C sequestration potential in soils of SAT (semi-arid tropics)

region in India.

Ramachandran et al., (2007) estimated the carbon stock of wood biomass and soil in

natural forest using geospacial technology in the Eastern Ghats of Tamil Nadu, India.

Dinakaran and Krishnayya, (2008) studied the influence of different vegetal covers,

changes in land-use pattern and heterogeneity of physical fractions of the soil

organic carbon (SOC) pool on soil carbon. They found that SOC was much higher in


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soils with natural tree cover and concluded that the type of vegetal cover had a

significant impact on SOC up to a depth of 1.5 m. SOC content in soils with natural

vegetal cover (trees) is sufficiently large, indicating their sink capacity. Seasonal

herbaceous cover in tropical systems can be taken as a potential sink as more

proportion of carbon moves downwards compared to the inputs. Phani Kumar et al.,

(2009) analysed the soil organic carbon in soil samples in the Nubra valley, Ladakh,

India. Luske & Kamp (2009) investigated the carbon storage potential of reclaimed

desert soil in Egypt under organic management. The results show that in 30 years of

organic agriculture, the soil carbon stock increased from 3.9 to 28.8-31.8 tons C/ha, a

raise of ca 24.9-27.9 t C/ha. On average, the soil stored 0.9 t C/ha/y in these 30 years.

Thus, an atmospheric CO2 reduction of 3.2 tons CO2-equivalents/ha/year had taken

place. Chandran et al., (2009) concluded from his study that the SOC value of the

forest area is more followed by horticultural and least in the agricultural land. So, the

land management practices do influence the SOC content of the soil.

Significance of the study

Spatially distributed estimate of SOC pools and flux are important requirement for

understanding the role of soils in the global C cycle and for assessing potential

biospheric responses to climatic change or variation. SOC is concentrated in the

upper 12 inches (30 cm) of the soil. Thus it is readily depleted by anthropogenic

disturbances such as land use changes and cultivation (Smith et al., 2007;

Ramachandran et al., 2007).

There are various factors influencing the SOC of the soil and therefore, we analyzed

the differences in the soil quality and SOC of the soils collected from different agro-

climatic zones of Gujarat.


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Material and Method

Study area

Figure-27: Map showing Agro-climatic zones of Gujarat (Source: GEC)

Gujarat is situated at latitude of 20°01' 24.07"N and longitude of 68°04' 74.04"E

with a total area of 196,077 km2. It is surrounded by Pakistan on the North-west,

Arabian Sea on the South-west, Rajasthan on the North-east, Madhya Pradesh on the

East and Maharashtra towards the South. Gujarat state has mild pleasant and dry

winters with average temperatures ranging from 12-29°C, while summers are

extremely hot and dry with average temperatures ranging from 29-41°C. The North-

west region of Gujarat is desert, while the southern area of Gujarat is wet and moist

due to heavy monsoon in the area. Gujarat has a tropical climate with the

temperature in the range from 1-46°C. The annual rainfall is quite variable ranging

from 250 mm in the North West to more than 1500 mm in South Gujarat.


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On the basis of rainfall received Gujarat has been divided into 7 agro-climatic zones

by Gujarat Ecological Commission (Fig-27). My study area encompasses 6 agro-

climatic zones of Gujarat excluding the fifth zone (The North West Arid) including

Kutchh district. The seven agro-climatic zones of Gujarat are as follows;

1). Southern Hills: It is the heavy rainfall zone of the south Gujarat comprising

Valsad, Navsari and The Dangs districts, with annual rainfall of 1500 mm. The soil

samples were collected from Waghai Botanical Garden, Dangs (0.24 km2; 20°45'

26.34"N and 73°29' 58.35"E; 181.66 m a.s.l.) and Purna Wild Life Sanctuary, Dangs

(160.84 km2; 20°56' 12.99"N and 73°40' 21.64"E; 390.45 m a.s.l.). The forest is of

Tropical moist deciduous type with forest type of soil, which is neutral and sandy

with high organic matter and lime composition. The dominant tree species are of

Teak, Haldu, Sisam, Khair, Katas, Manvel etc.

2). Southern Gujarat: It includes the moderate to heavy rainfall zone of south

Gujarat comprising Surat, Bharuch and Narmada districts, with rainfall varying from

1000-1500 mm. Average maximum and minimum temperatures in summer and

winter are 40°C and 23°C respectively. The soil samples were collected from Surat

(21°11' 42.86"N and 72°50' 06.76"E; 10.97 m a.s.l.) and Shoolpaneshwer Sanctuary,

Narmada (607.07 km2; 21°45' 44.34"N and 73°45' 47.60"E; 479.75 m a.s.l.). The

forest is of Tropical moist deciduous type with deep black soil which is found at a

depth of 60 cms, it is composed of 40-70% clay and is dark brown to very dark

grayish brown in colour. Teak, Haldu, Sisam, Khair, Katas, Manvel etc. are the main

species of these forests.

3). Middle Gujarat: It includes Vadodara, Anand, Kheda, Panchmahal and Dahod

districts with moderate rainfall received varying from 800-1000 mm. The soil

samples were collected from Ratanmahal Sanctuary, Dahod (55.65 km2; 22°29'

37.51"N and 74°04' 55.75"E; 239.88 m a.s.l.) and Jambughoda Sanctuary,

Panchmahal (130.38 km2; 22°21' 14.71"N and 73°40' 32.63"E; 184.4 m a.s.l.). The

forest is of Tropical dry deciduous type with teak as dominant tree species and with

medium black soil found at a depth of 30-60 cms.


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4). North Gujarat: It includes the dry zones of Ahmedabad, Gandhinagar, Mehsana,

Patan, Banaskantha and Sabarkantha districts, with rainfall in the range of 625-875

mm. The climate is of semi-arid type. The soil samples were collected from Gujarat

University Botanical Garden, Ahmedabad (1.1 km2; 23°02' 10.28"N and 72°32'

48.11"E; 55.78 m a.s.l.); Jessore Sloth Bear Sanctuary, Banaskantha (180.66 km2;

24°23' 37.69"N and 72°31' 40.06"E; 219.76 m a.s.l.) and Balaram Ambaji Sanctuary,

Sabarkantha (542.08 km2; 24°18' 23.77"N and 72°46' 49.98"E; 428.24 m a.s.l.). The

forest is of Tropical dry deciduous with Teak, Anogessius, Timru, Butea and

Boswellia as dominant tree species and Northern tropical thorn forest with prominent

thorn bushes and species of Acacia and Prosopis. Sabarkantha area has two types of

soils; medium black soil and the residual sandy soil which is shallow and reddish

brown in colour. Banskantha has both the residual sandy and alluvial type of the soil.

5). North West Arid: It comprises the arid desert area of Kutchh and rainfall falls in

the range of 250-500 mm. The forest is of Northern tropical thorn forest type with

prominent thorn bushes and species of Acacia.

6). North Saurashtra: It comprises the arid cum dry zones of Surendranagar,

Rajkot, Jamnagar, Porbandar, Amreli and Bhavnagar districts, with annual rainfall of

400-700 mm. The climate here is of semi-arid type. The soil samples were collected

from Porbandar (21°38' 30.42"N and 69°37' 45.21"E; 9.14 m a.s.l.), Hingolgadh

Sanctuary, Rajkot (6.54 km2; 22°08' 56.31"N and 69°37' 45.21"E; 9.14 m a.s.l.) and

Rampara Sanctuary, Rajkot (15.01 km2) and Pania Wild Life Sanctuary, Amreli

(39.63 km2; 21°13' 58.76"N and 70°51' 48.42"E; 341.98 m a.s.l.). The forest is of

Northern tropical thorn forest type with prominent thorn bushes and species of

Acacia, Zizyphus sps. The soil is shallow black soil which has a depth of 0-30 cm

and is grey in colour, hill soils are also found which have a poor profile and fertility

and are composed of undecomposed rock fragments.


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7). South Saurashtra: It includes Junagadh district which receives annual rainfall in

range of 700-1000 mm. The climate here is of semi-arid type, but the weather here is

influenced by its close proximity to the sea. The soil samples were collected from the

Gir Wild Life Sanctuary, Junagadh (1153.42 km2; 21°06' 57.88"N and 70°47'

32.39"E; 289.56 m a.s.l.). The forest is of Tropical dry deciduous with Teak, Timru,

Aegle and Butea as dominant trees and Northern tropical thorn forest type with

prominent thorn bushes and species of Acacia. The soil of Junagadh is of two types;

the shallow black soil which has a depth of 0-30 cm and is grey in colour and the

forest soil which is neutral and sandy with high organic matter and lime composition.

Calculating soil organic carbon

• Soil samples were collected from different sites by random sampling method.

• Three soil samples were taken sequentially up to a depth of 20cm (surface

sample, sample at a depth of 10cm and sample at a depth of 20 cm) (Fig-28).

• It was dried (Fig-26) and sieved through 2mm sieve. The undisturbed soil

clumps were used to determine the bulk density.

• The soil was further ground with pestle and mortar and sieved through the

0.5mm sieve.

• The soil organic carbon was determined by wet oxidation method (Walkey

and Black, 1934) for each soil sample and was statistically analysed for

computation of standard deviation and standard error across different depths

of soil and different agro-climatic zones of Gujarat.

• The soil was also analyzed for the pH (pH meter), EC (Conductivity meter),

nitrogen, phosphorous and potassium (Fig-29). (Jaiswal, 1999 and Kalra,

2000)

• The soil quality and SOC were then compared for all the agro-climatic zones

of Gujarat for factors influencing its composition


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a) b)

Figure-28: Soil being sampled at selected sites. a) Soil collection; b) Depth of soil collection

a) b)

c) d)

e) f) Figure-29: Instruments for soil quality analysis a) pH meter; b) Conductivity meter; c) Colorimeter; d) Soil samples; e) Spectrophotometer; f) Flame photometer


135

Result and Discussion

Soil samples were collected at all places from 30 different sites from surface, and at

depth of 10 cm and 20 cm (Table-4).

General comparison of result obtained from the soil analysis of various agro-

climatic zones of Gujarat

1. Soil type: The soil in the Southern hills and South Gujarat arid zone of Gujarat is

black in colour, rich in organic matter and clayey. The soil in the Central Gujarat

zone is reddish brown in Jambughoda and yellowish in Ratanmahal area. The soil in

Northern Gujarat was sandy and brownish in colour. The soil in the Northern

Saurashtra region was black in colour and in the Southern Saurashtra (Gir) it was

dark brown in colour and rich in organic matter (Fig-26).

2. Soil pH: The soil pH was measured for surface soil and soil at depth of 10 cm and

20 cm (Table-4; Fig-30). The soil pH in the Southern hills, South Gujarat and in

Central Gujarat was found to be neutral ranging from 6-7. While, in North Gujarat,

North Saurashtra and South Saurashtra it is slightly alkaline.

3. Soil EC: According to the measurements EC (Table-4; Fig-30) has been found to

be more in the surface soil than in the lower layers of the soil. The mean EC was

normal in all areas of Gujarat as it was less than 1. The EC was less in the South

Gujarat, Central Gujarat and South Saurashtra with least found in Purna (0.14) and

was found to be more in the areas of North Gujarat and North Saurashtra with

maximum in Jessore (3.6).

4. Bulk Density: The bulk density (gm/cm³) (Table-4; Fig-30) at all places in

Gujarat had the same pattern of increasing as the depth increases. Bulk density was

least of the surface soil and maximum of the lowest layer. Maximum bulk density

was measured at Balaram (1.45 gm/cm³) and least bulk density was found in

Porbander (1.03 gm/cm³).

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at where the

is was the r

ices. The S

South Saura

was found

e nitrogen c

maximum co

he depth inc

t where the

Impacts: V

eristics: a) in various

OC): The S

he surface so

he depth inc

e SOC con

result of dep

SOC conten

ashtra, Nort

in the soil

content (%)

ntent in the

creased the

nitrogen co

Vegetation A

Soil pH; bagro-clima

SOC at all p

oil and less

creased the

ntent at surf

pletion of th

nt was highe

th Saurashtr

l of Wagha

) (Table-4;

e surface soi

nitrogen co

ontent at su

And Plant R

) EC; and catic zones o

places follo

in the midd

SOC decre

face was lo

he SOC of

est in South

ra and least

ai (2.08) an

Fig-31) at

il and less in

ontent decre

urface was l

Responses

c) Bulk denof Gujarat

owed a typi

dle and low

eased. One

ower than a

the surface

h Gujarat f

in North G

nd least in

all places

n the middl

eased. One

ower than a

In Gujarat

136

nsity at

cal trend of

west layer of

exceptional

at the lower

e soil due to

followed by

Gujarat. The

the soil of

followed a

e and lower

exceptional

at the lower

t

6

f

f

l

r

o

y

e

f

a

r

l

r

layers

to agri

by cen

The ma

of Bala

Fig

7. Pho

being h

Gujara

conten

soil. T

and mi

8. Pota

in the s

Climat

of soil. Thi

cultural pra

ntral Gujara

aximum nit

aram (10.08

gure-31: a)

osphorous:

high in the

at, Central G

nt was highe

The maximu

inimum in t

assium: Th

surface and

te Change I

is was the r

actices. The

at, South Sa

trogenwas f

8%).

SOC; b) Nvariou

The phosp

e surface an

Gujarat and

est in the m

um content

the soil of W

e potassium

d less in the

Impacts: V

esult of dep

nitrogen co

aurashtra, N

found in the

Nitrogen; c)us agro-clim

phorous co

nd less in t

d Saurashtra

middle layer

of phospho

Waghai (8.7

m content (T

middle and

Vegetation A

pletion of th

ontent was h

North Saura

soil of Wag

) Phosphormatic zones

ontent (Tab

the middle

a. But in th

r and less i

orous was

0 kg/hec).

Table-4; Fig

d lower laye

And Plant R

he nitrogen

highest in S

ashtra and l

ghai (29.15

rous; d) Potof Gujarat

le-4; Fig-3

and lower

he North Gu

n the surfa

found in B

g-31) showe

er of soil in

Responses

of the surfa

South Gujar

least in Nor

%) and leas

tassium cont

1) showed

layer of so

ujarat the p

ce and low

Balaram (97

ed a trend of

South Guja

In Gujarat

137

ace soil due

rat followed

rth Gujarat

st in the soil

ntent in

a trend of

oil in South

phosphorous

west layer of

.01 kg/hec)

f being high

arat, Central

t

7

e

d

.

l

f

h

s

f

)

h

l


138

Gujarat, North Gujarat and North Saurashtra. But in South Saurashtra (Gir) and

Jambughoda the potassium content was highest in the lowest layer followed by

surface and middle layer of soil. The maximum content of potassium was found in

Jessore (1296.1 kg/hec) and minimum in the soil of Surat (255.36 kg/hec).

Table-4: Soil quality and SOC analysis of various agro - climatic zones of

Gujarat

Sr. No.

Soil sample level pH EC SOC P

(kg/hec)

K (kg/ hec)

N (%) Bulk

density (gm/cm³)

1 Purna 0 cm

6.42 ±0.29

0.15± 0.03

1.77± 0.83

93.27 ± 114.95

817.15± 458.18

25.45± 11.95

1.15 ± 0.04

10 cm 6.76± 0.65

0.14± 0.01

1.36± 0.67

46.99 ± 39.51

682.75± 486.94

19.57± 9.66

1.20 ± 0.08

20 cm 6.83± 0.53

0.16± 0.01

1.31± 0.40

56.96 ± 89.95

704.26± 436.19

18.88± 5.81

1.21 ± 0.09

2 Waghai

0 cm 6.15± 0.66

0.32± 0.19

2.03± 0.23

24.13 ± 39.55

825.81± 341.34

29.15± 3.43

1.06 ± 0.09

10 cm 6.28± 0.43

0.22± 0.12

1.61± 0.50

8.70 ± 12.84

483.84± 392.30

23.18± 7.25

1.08 ± 0.07

20 cm 6.21± 0.36

0.21± 0.12

1.58± 0.41

8.70 ± 6.68

465.92± 421.00

22.69± 5.90

1.11 ± 0.07

3 Surat

0 cm 6.05± 0.96

0.24± 0.06

1.56± 0.27

8.9 ± 3.56

322.56± 186.87

22.37± 3.92

1.11 ± 0.06

10 cm 6.34± 0.87

0.15± 0.04

1.53± 0.26

10.68 ± 6.49

255.36± 108.07

22 ± 3.77

1.15 ± 0.07

20 cm 6.65± 0.70

0.18± 0.05

1.68± 0.34

8.9 ± 6.16

332.64± 118.38

24.24± 4.89

1.17 ± 0.06

4 Shoolpaneshwer

0 cm 6.55± 0.77

0.21± 0.06

1.66± 0.47

53.4 ± 41.41

782.2 ± 413.17

23.87± 6.82

1.08 ± 0.12

10 cm 6.44± 0.85

0.22± 0.17

1.52± 0.53

40.58 ± 31.89

565.82± 460.91

21.88± 7.73

1.07 ± 0.10

20 cm 6.62± 0.67

0.24± 0.28

1.58± 0.42

17.44 ± 10.93

514.75± 417.77

22.71± 6.09

1.07 ± 0.05

5 Jambughoda

0 cm 6.53± 1.09

0.21± 0.04

1.47± 0.59

10.68 ± 9.55

506.24± 140.36

21.12± 8.52

1.32 ± 0.17

10 cm 6.55± 1.09

0.17± 0.05

1.25± 0.66

12.46 ± 9.21

504 ± 192.47

17.96± 9.52

1.33 ± 0.16

20 cm 6.5 ± 1.01

0.17± 0.06

1.43± 0.60

19.58 ± 27.73

568.96± 287.71

20.60± 8.74

1.34 ± 0.13

6 Ratanmahal

0 cm 7.14± 0.64

0.28± 0.09

1.71± 0.57

33.82 ± 21.52

705.6 ± 402.04

24.50± 8.32

1.11 ± 0.17

10 cm 7.05± 0.45

0.17± 0.05

1.05± 0.56

15.57 ± 20.48

475.44± 311.98

15.08± 8.17

1.21 ± 0.07

20 cm 6.59± 0.67

0.16± 0.05

1.02± 0.59

31.15 ± 46.05

483.84± 314.86

14.66± 8.53

1.23 ± 0.07

7 Balaram

0 cm 7.38± 0.30

0.64± 0.21

1.33± 0.40

72.38 ± 19.89

1137.92 ± 271.43

19.20± 5.87

1.35 ± 0.09


139

10 cm 7.53± 0.27

0.51± 0.61

0.86± 0.36

97.01 ± 34.17

1067.36 ± 351.62

12.29± 5.29

1.42 ± 0.10

20 cm 7.59± 0.17

0.26± 0.08

0.70± 0.13

77.72 ± 21.06

1104.32 ± 427.62

10.09± 2.01

1.45 ± 0.07

8 Jessore

0 cm 7.2 ± 0.27

0.97± 1.27

1.44± 0.48

74.76 ± 77.27

1296.06 ± 368.30

20.73± 6.90

1.28 ± 0.11

10 cm 7.22± 0.52

0.57± 0.56

1.06± 0.41

95.65 ± 55.68

1126.72 ± 176.87

15.27± 5.92

1.36 ± 0.13

20 cm 7.27± 0.56

0.39± 0.20

1.03± 0.43

73.45 ± 32.75

991.42± 164.69

14.76± 6.27

1.37 ± 0.13

9 Ahmedabad

0 cm 7.42± 0.51

0.94± 1.00

1.29± 0.52

18.12 ± 8.78

712.32± 296.65

18.53± 7.58

1.15 ± 0.25

10 cm 7.97± 0.86

0.59± 0.71

0.97± 0.58

20.39 ± 11.81

574.25± 259.08

13.92± 8.43

1.18 ± 0.14

20 cm 8.01± 0.82

0.62± 0.85

0.92± 0.66

13.59 ± 10.77

527.83± 304.94

13.24± 9.61

1.22 ± 0.21

10 Amreli

0 cm 7.81± 0.30

0.55± 0.55

1.38± 0.53

30.62 ± 33.54

946.18± 533.94

19.86± 7.74

1.19 ± 0.17

10 cm 7.98± 0.18

0.49± 0.65

0.95± 0.32

26.34 ± 24.22

631.68± 405.43

13.62± 4.66

1.20 ± 0.19

20 cm 8.03± 0.15

0.42± 0.50

0.907± 0.21

22.07 ± 20.04

774.14± 407.61

13.03± 3.08

1.23 ± 0.18

11 Hingolgadh

0 cm 7.71± 0.59

0.26± 0.08

1.34± 0.54

29.90 ± 44.12

802.37± 510.32

19.23± 7.77

1.28 ± 0.24

10 cm 8.05± 0.32

0.21± 0.05

1.17± 0.42

16.38 ± 9.37

694.85± 463.15

16.88± 6.17

1.31 ± 0.15

20 cm 8.08± 0.33

0.19± 0.07

1.01± 0.31

14.95 ± 10.04

710.97± 505.92

14.49± 4.47

1.36 ± 0.11

12 Rampara

0 cm 7.59± 0.46

0.61± 0.47

1.41± 0.54

31.25 ± 22.14

834.77± 386.58

20.25± 7.89

1.19 ± 0.14

10 cm 7.71± 0.53

0.44± 0.30

1.16± 0.69

20.57 ± 16.67

822.83± 456.35

16.72± 9.95

1.2 ± 0.14

20 cm 7.83± 0.55

0.37± 0.22

1.15± 0.57

19.38 ± 13.91

761.6 ± 443.31

16.48± 8.30

1.21 ± 0.09

13 Porbander

0 cm 7.64± 0.39

0.47± 0.22

1.78± 0.31

14.83 ± 6.13

871.36± 529.43

25.53± 4.52

1.03 ± 0.16

10 cm 7.81± 0.33

0.56± 0.25

1.67± 0.36

23.14 ± 5.84

647.36± 432.96

24.02± 5.19

1.08 ± 0.07

20 cm 7.85± 0.38

0.51± 0.29

1.52± 0.52

14.83 ± 8.54

721.28± 405.67

21.80± 7.47

1.06 ± 0.05

14 Gir

0 cm 7.38± 0.60

0.25± 0.07

1.53± 0.48

29.45 ± 29.66

948.13± 543.06

21.91± 6.93

1.17 ± 0.12

10 cm 7.45± 0.64

0.18± 0.07

1.27± 0.56

25.89 ± 28.26

921.25± 528.77

18.22± 8.08

1.18 ± 0.11

20 cm 7.44± 0.59

0.17± 0.06

1.11± 0.50

21.03 ± 13.07

1011.66 ± 449.59

15.87± 7.25

1.20 ± 0.14

Discussion:

The ability of lands to store or sequester carbon depends on several factors, including

climate, parent material, soil type, topography, type of vegetation cover, C content,


140

bulk density, depth of soil and soil management and time (Jeff and Hill, 2009;

Chandran et al., 2009; Luske & Kamp, 2009; Rathore and Jasrai, 2013).

Climate

In cooler climates, decomposition happens more slowly, so the plant residue has a

greater chance of becoming humus, which is a stable part of soil with high organic

carbon content (Dinakaran and Krishnayya, 2008; Misra et al., 2008; Jeff and Hill,

2009; Luske & Kamp, 2009). Hence the SOC in South Gujarat, Central Gujarat and

Saurashtra is more with equable climate and good annual rainfall, as compared to

North Gujarat as the climate here is more arid and dry with high temperatures and

drought conditions.

Soil type

Another reason for the variation in SOC is the type of soil. Soil in South Gujarat and

South Saurashtra is black and clayey and in central Gujarat is brownish in colour and

has a high SOC. While in North Gujarat the soil is sandy and alluvial and with low

SOC. Poorly-drained soil types have the capacity to store carbon more readily than

others (Farage et al., 2003; Dinakaran and Krishnayya, 2008; Jeff and Hill, 2009).

Type of vegetation

The vegetation in forest of North Gujarat and North Saurashtra is sparse and shrubby

type with more Acacia sps, showing a typical arid climate. Hence the SOC is low.

While in South Gujarat, Central Gujarat and South Saurashtra the SOC is high. The

vegetation in forest here is of moist deciduous and dry deciduous type, where the

SOC is enhanced as a result of litter accumulation on soil surface, thus affecting

long-term soil fertility and carbon storage (Kumar et al., 2006). SOC content in soils

with natural vegetal cover (trees) is sufficiently large, indicating their sink capacity.

The soil organic carbon content is more under dense tree cover, while it will be less

under grass/herb cover. Difference in vegetal cover not only influences SOC content

of the top layer, but also of the deeper layers. SOC decomposition is significantly


141

different across different vegetal covers due to substrate availability (Dinakaran and

Krishnayya, 2008).

Carbon content/ depth of soil and soil management/ land use pattern

In all the sites, except for Surat, the SOC decreased as the depth of the soil increased.

This result is in accordance with the work of Wang et al., (2003, 2004); Shrestha et

al., (2004); Chen et al., (2005); Dinakaran and Krishnayya, (2008); Chandran et al.,

(2009); and Rathore and Jasrai (2013) which reported that soils under natural

vegetation had high SOC content compared to other land-use systems. The SOC was

less in case of Surat as it was an agricultural field, while all other sites chosen are

sanctuaries under forest cover. Large scale disruption or changes on land drastically

alter the harmonious movement of carbon (Sampson, 2000; Resh et al., 2002;

Ramachandran et al., 2007; Jeff and Hill, 2009; Luske & Kamp, 2009; Scherr and

Sthapit, 2009). Changes in land-use pattern severely reduced sink capacity of soils.

Land- use alteration can convert a soil system from a sink to a source of carbon

(Dinakaran and Krishnayya, 2008).

Soil may be considered as an important sink for the carbon storage in the form of soil

organic carbon (Kumar et al., 2006). In case of the various agroclimatic zones of

Gujarat, the maximum SOC content is in the soil of South Gujarat followed by

Central Gujarat, South Saurashtra, North Saurashtra and least in North Gujarat. The

soil organic carbon content is found to be more under dense tree cover, while it will

be less under grass and shrubby vegetation of North Saurashtra and North Gujarat.

So, the area of North Saurashtra and North Gujarat with least SOC can be considered

to me most effective future sinks of organic carbon as the soil under dense forest

would soon become saturated. This is in accordance with the work of Dinakaran and

Krishnayya, (2008). The size of soil organic matter pools in natural ecosystems

decreases exponentially with temperature (Lal, 2004). Drier soil is less likely to lose

carbon (Glenn et al, 1993) and consequently the residence time of carbon in dryland

soils is much longer than forest soils (Gifford et al, 1992). A soils’ potential to

function as a carbon sink is highly dependent on the initial carbon stock of the soil,


142

as well as land use practices. Compared to other soils, arid desert soils have a

relatively high potential to act as a carbon sink, as their initial carbon stock is usually

minimal (Chandran et al., 2009; Luske & Kamp, 2009).

Hence, North Saurashtra and North Gujarat being the most arid zones of the present

study with least SOC content can be considered as potential future carbon sinks.


143

Conclusion

The factors like climate, vegetation cover, soil type, depth of soil and land

management practices influence the SOC content of the soil. The soil samples of the

six agro-climatic zones of Gujarat studied prove that the above factors do influence

the SOC content of the soil. The areas with moderate climate (South Gujarat, Central

Gujarat and South Saurashtra) show more amount of SOC than the one with arid

climate (North Saurashtra and North Gujarat). The areas with natural vegetation

cover show more SOC than other areas. All areas except for Surat are forest areas.

The SOC content was found to decrease as the depth increases. The only exceptional

case was of Surat where the SOC in surface soil was less showing depletion due to

agricultural practice. The soil in South Gujarat and South Saurashtra was dark and

clayey and hence had a high SOC than the soil at Central Gujarat followed by at

North Saurashtra and least in the forest soil of North Gujarat.

The maximum SOC content is in the soil of South Gujarat followed by Central

Gujarat, South Saurashtra, North Saurashtra and least in North Gujarat.

Considering soil as an important sink of carbon the area of North Saurashtra and

North Gujarat with least SOC can be considered to me most effective future sinks of

organic carbon as the soil under dense forest would soon become saturated.

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