~ 2362 ~

Journal of Pharmacognosy and Phytochemistry 2018; 7(2): 2362-2390

E-ISSN: 2278-4136

P-ISSN: 2349-8234

JPP 2018; 7(2): 2362-2390

Received: 01-01-2018

Accepted: 02-02-2018 RK Naresh

Department of Agronomy

Sardar Vallabhbhai Patel University of

Agriculture & Technology, Meerut, Uttar

Pradesh, India

Arvind Kumar

Rani Lakshmi Bai Central Agricultural

University, Jhansi- Uttar Pradesh, India

RK Gupta

Borlaug Institute for South Asia (BISA),

New Delhi, India

AK Shukla

Indian Institute of Soil Science Nabibagh,

Berasia Road, Bhopal, Madhya Pradesh,

India

SS Dhaliwal

Department of Soil Science; Punjab

Agricultural University, Ludhiana, Punjab,

India

RS Rathore

Uttar Pradesh Council of Agricultural

Research, (UPDASP), Lucknow- Uttar

Pradesh, India

Vivek

Department of Agronomy

Sardar Vallabhbhai Patel University of

Agriculture & Technology, Meerut, Uttar

Pradesh, India

Mukesh Kumar

Department of Horticulture, Sardar

Vallabhbhai Patel University of Agriculture

& Technology, Meerut, Uttar Pradesh, India

SP Singh

Department of Soil Science, Sardar

Vallabhbhai Patel University of Agriculture

& Technology, Meerut, Uttar Pradesh, India

Satyaveer Singh

Department of Agronomy,BAC, Sabour,

Bhagalpur, Bihar, India

SS Tomar

RVSKVV, ZARS-A, B. Road, Morena,

Madhya Pradesh, India

Hans Raj

K.V.K. Ghaziabad, Sardar Vallabhbhai

Patel University of Agriculture &

Technology, Meerut, Uttar Pradesh, India

SP Singh

K.V.K. Baghpat, Sardar Vallabhbhai Patel

University of Agriculture & Technology,

Meerut, Uttar Pradesh, India

RC Rathi

K.V.K. Beghra, Sardar Vallabhbhai Patel

University of Agriculture & Technology,

Meerut, Uttar Pradesh, India

NC Mahajan

Department of Agronomy

Sardar Vallabhbhai Patel University of

Agriculture & Technology, Meerut, Uttar

Pradesh, India

Rajendra Kumar

Department of Agronomy

Sardar Vallabhbhai Patel University of

Agriculture & Technology, Meerut, Uttar

Pradesh, India Correspondence

RK Naresh

Department of Agronomy

Sardar Vallabhbhai Patel University of

Agriculture & Technology, Meerut, Uttar

Pradesh, India

Organic and conservation systems enhanced

carbon sequestration potential and soil carbon

stock dynamics: A review

RK Naresh, Arvind Kumar, RK Gupta, AK Shukla, SS Dhaliwal, RS

Rathore, Vivek, Mukesh Kumar, SP Singh, Satyaveer Singh, SS Tomar,

Hans Raj, SP Singh, RC Rathi, NC Mahajan and Rajendra Kumar

Abstract

The study aims to elucidate the impact of organic inputs and conservation systems on soil carbon

sequestration and carbon stock dynamics in an Inceptisol of Indo-Gangetic Plain Zone of India. The

management of soil organic carbon (SOC) has now been identified as the most imperative dimension for

managing the global climate change as well as soil fertility. Long-term fertilization significantly

influenced SOC concentrations and storage to 60 cm depth. Below 60 cm, SOC concentrations and

storages were statistically not significant between all treatments. Organic manure plus inorganic fertilizer

application also increased labile soil organic carbon pools in 0–60 cm depth. The average concentration

of particulate organic carbon (POC), dissolved organic carbon (DOC) and microbial biomass carbon

(MBC) in organic manure plus inorganic fertilizer treatments (NP+S and NP+FYM) in 0–60 cm depth

were increased by 64.9–91.9%, 42.5–56.9%, and 74.7–99.4%, respectively, over the CK

treatment.Average SOC concentration of the control treatment was 0.54%, which increased to 0.65% in

the RDF treatment and 0.82% in the RDF+FYM treatment and increased enzyme activities, which

potentially influence soil nutrients dynamics under field condition. Compared to F1 control treatment the

RDF+FYM treatment sequestered 0.28 Mg C ha-1 yr-1 whereas the NPK treatment sequestered 0.13 Mg C

ha-1 yr-1. As tillage intensity increased there was a redistribution of SOC in the profile, but it occurred

only between ZT and PRB since under CT, SOC stock decreased even below the plow layer. Increased

SOC stock in the surface 50 kg m-2 under ZT and PRB was compensated by greater SOC stocks in the

50-200 and 200-400 kg m-2 interval under residue retained, but SOC stocks under CT were consistently

lower in the surface 400 kg m-2. Over the last 16 years, CT lost 0.83 ±0.2 kg of C m-2 while ZT gain 1.98

±0.3 and PRB gain 0.97±0.2 kg of C m-2 in the 1200 kg of soil m-2 profile. These results indicate that

long-term adoption of organic and conservation systems have the most beneficial effects in building

carbon sequestration potential and carbon stock pools among the investigated types of fertilization.

Keywords: Soil organic carbon fractions, C sequestration, soil aggregates, carbon dynamics

Introduction

Soil carbon sequestration at a global scale is considered the mechanism responsible for the

greatest mitigation potential within the agricultural sector, with an estimated 90%contribution

to the potential of what is technically feasible (Smith et al., 2008) [119]. However, global soil

carbon stocks of agricultural land have decreased historically and continue to decline (Lal,

2004a) [65]. Thus, improved agronomic practices that could lead to reduced carbon losses or

even increased soil carbon storage are highly desired. This includes improved crop varieties,

extending crop rotations, notably those with grass–clover or forage legume leys that allocate

more carbon below- ground, avoiding or reducing use of bare (unplanted) fallow (4), and the

application of organic fertilizer such as compost or waste products from livestock husbandry in

the form of slurry or stacked manure (5). Although these practices are not common in current

modern agriculture, they are core practices of organic agriculture, where crop production relies

in large part on closed nutrient cycles by returning plant residues and manures from livestock

back to the land and/or by integrating perennial plants, mainly grass–clover mixtures, into the

system. It is therefore hypothesized that the adoption of organic agriculture will lead to a

reduction in soil carbon losses or even to higher soil carbon concentrations and net carbon

sequestration over time (Niggli et al., 2009) [88].

With increasing global concerns over impacts of toxic chemicals, energy crisis and

environmental protection, it is becoming more alarming to rely on local abundant agricultural

bio resources than on chemical fertilizers. Recent studies have focused on reconsidering

cowpathy practices to enhance soil organic input, fostering agricultural sustainability by

promoting soil microbial biomass and activity. Conventional agro ecosystems have been

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Journal of Pharmacognosy and Phytochemistry characterized by high input of chemical fertilizer, leading to

deterioration of soil quality due to reductions in soil organic

matter and nutrients (Wu, 2009) [140]. Studies in comparison

with conventional agriculture systems reveals that organically

farmed soils showed improved soil quality with higher

microbiological activity, higher pH, organic C, N

mineralization potential, soil micro-organisms (30-40%), and

higher biological activity (30-100%).

Aggregate-size distribution and total organic carbon

Beare et al. (1994) [11] shown that conservationist soil

management practices can result in larger soil aggregation,

leading to increase in TOC stocks in the surface soil layer

when compared to conventional management practices, like

CT. The accumulation of TOC stocks under NT introduced

after continuous CT in the surface soil layer, down to

approximately 30 cm is a well known effect of NT and similar

conservation tillage systems. It is however subject to debate

whether NT is capable of accumulating more TOC if

investigated to larger depths. According to Baker et al. (2007)

[7] the ‘‘widespread belief that conservation tillage also favors

carbon sequestration may simply be an artifact of sampling

methodology’’ caused by shallow sampling. Sisti et al. (2004) [115] revealed that NT is in fact more efficient in organic

carbon stabilization to greater depths (to 100 cm), however

this is dependent on correct N management. Madari et al.

(2005) [76] found that the difference in SOC distribution

between aggregate-size fractions is greater under cultivation

than forest, regardless of the tillage system. Impacts of tillage

on SOC in different size fractions vary greatly because of

many factors, including climate, soil type, texture, pH and

dominant mineralogy. Adesodun et al. (2007) [1] also found

that the concentrations of SOC are higher under RNT than

CT, which implies that soil tillage management may play a

crucial role in sustaining agricultural productivity in this

system. The proportion of macro-aggregates (>1.00 mm) is

higher under RNT than CT, probably because tillage

disrupted soil macro-aggregates and reduced macro-

aggregates by 67% compared with RNT. The finding that

tillage methods do not change the distribution patterns of

SOC in aggregate-size fractions, but do change the size

distribution of aggregates, indicates that tillage influences soil

fertility through changes in soil structure. Onweremadu et al.

(2007) [91] reported that SOC in aggregates vary according to

tillage method. They found that the highest SOC was

distributed in 4.75–2.0 mm aggregates under MT, whereas

1.0–0.5 mm had the highest SOC under CT. Razafimbelo et

al. (2008) [107] report that SOC is mainly associated with

micro-aggregates (<0.02 mm) under NT with no significant

differences apparent for CT among macro-, meso- (0.02–0.2

mm), and micro-aggregates (<0.02 mm).

Source: Jiang et al. (2011)

Fig 1: Soil organic carbon and total N distribution in aggregates under different tillage regimes (RNT, combination of ridge with no tillage in a

rice rotation ecosystem; CT, conventional tillage in a rice rotation ecosystem)

Jiang et al. (2011) revealed that the highest SOC was

observed in the 1.00–0.25 mm size fraction (35.7 and 30.4

mg⁄ kg for RNT and CT, respectively), while the lowest SOC

was in the micro-aggregates and silt + clay fractions (19.5 and

15.7 mg⁄ kg for RNT and CT, respectively). While similar

distribution patterns were observed under RNT and CT, SOC

was significantly higher under RNT than CT by an average of

23.4%. One of the reasons for the significant difference may

be that the RNT system has greater crop residue production

resulting in higher residual returns to the soil each year. The

slower decomposition of this residue under RNT than CT is

due to less physical destruction during tillage and is also

likely to be responsible for the higher SOC levels under RNT.

The resulting higher crop and residue production is a response

to higher SOM levels, and higher nutrient-supplying capacity

of RNT soils compared with CT. Total N ranged from 1.3 to

3.0 mg⁄ kg, with an average of 2.3 and 2.13 mg⁄ kg for RNT

and CT, respectively. The highest total N for both RNT and

CT was in the 1.00–0.25 mm fraction while the lowest N for

both tillage methods was in the 0.25–0.053 mm fraction.

Similar to total C, total N was higher under RNT than CT.

Fig 2a: SOC levels in the 0–30 cm layer by tillage system CT, conventional tillage; MT, minimum tillage; NT, no tillage

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Journal of Pharmacognosy and Phytochemistry

Fig 2b: Vertical distribution of the SOC content in 2004 by tillage system

Sombrero and de Benito, (2010) [120] reported that at a depth

of 0–10 cm, the SOC content was significantly higher with

NT than CT or MT, by 58% and 11%, respectively. SOC

values were 41% higher with MT, in turn, than with CT. At a

depth of 10–20 cm, the SOC content was 30% higher with NT

than with CT and 7% higher than with MT. And at 20–30 cm,

it was 7% higher with MT than with CT, 12% higher with NT

than CT and 9% higher with no-till than minimum-till. In

2004, at the end of the 10 years period, SOC was 25% greater

with NT than CT, 16% greater with NT than MT, and 17%

higher with MT than CT (Figure 2 a & b). Onweremadu et al.

(2007) [91] also found that the highest SOC was distributed in

4.75–2.0 mm aggregates under MT, whereas 1.0–0.5 mm had

the highest SOC under CT. Razafimbelo et al. (2008) [107]

reported that SOC is mainly associated with micro-aggregates

(<0.02 mm) under NT with no significant differences

apparent for CT among macro-, meso- (0.02–0.2 mm), and

micro-aggregates (<0.02 mm). Chen and Shrestha (2012) [25]

observed that the SOC increased with the passage of time

(year) and caused an increase in percentage of water-stable

aggregate. Higher C accumulation in macro-aggregates could

be due to the lower decomposable SOM associated with these

aggregates and also the direct contribution of SOM to the

stability of macro-aggregates resulting in only C-rich macro-

aggregates being able to withstand slaking due to zeolitic

materials in the soil. Zhou et al. (2013) [143] concluded that the

application of NPK plus OM increased the size of sub-

aggregates that comprised the macro-aggregates. Also, they

observed that long-term application of NPK plus OM

improves soil aggregation and alters the three-dimensional

microstructure of macro-aggregates, while NPK alone does

not. Land use change usually alters land cover and the

terrestrial change in carbon stocks (Bolin and Sukumar,

2000). The change from one ecosystem to another can occur

naturally or through human activity. Anthropogenic changes

are prominent in tropical rain forest, which is a diverse and

complex ecosystem occupying approximately 17 percent of

the world’s land area and is a habitat for about 40 to 50% of

the earth’s species (Meyers, 1981). Tropical Rain Forests

represent significant sources/sinks of trace gases, and the

exchange of CO2 between forest and the atmosphere is an

important component of the global carbon cycle. The

economic damage through global warming from tropical

deforestation alone is estimated at $1.4-10.3 billion per year

(Pearce and Brown, 1994). Fearnside (1996) estimated the

economic damage by global warming in the region at

approximately $1,200 - $ 8,600 ha-1. In addition to its sheer

expanse, this eco-region also presents adequate climate

conditions for plant growth, expressed by high temperatures

throughout the year and well-distributed precipitation.

Therefore, tropical rainforest has, in principle, great potential

for soil carbon sequestration, despite poor to moderate soil

fertility.

Fig 3: Version of a land use/management sequence diagram

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Journal of Pharmacognosy and Phytochemistry Mamta et al. (2011) [78] reported that the fine (0.053–0.25

mm) intra-aggregate particulate organic C (iPOM-C), in 0.25-

to 2-mm aggregates, was also higher in ZT than conventional

tillage. A higher amount of macro-aggregates along with

greater accumulation of particulate organic C indicates the

potential of ZT for improving soil C over the long-term in

rice-wheat rotation Figure 4a. However, 0-5 cm layer, ZT had

significantly higher SOC of 7.37 and 7.86 g kg−1 in T5 and T6,

respectively than those of 5.81 and 6.14 g kg−1 in

conventional tillage treatments T1 and T2, respectively Figure

4b. This indicated a greater potential for C accumulation with

ZT likely to be associated with factors such as (a) a reduction

in soil disturbance, (b) undisturbed left –over stubbles on the

surface, and their slow decomposition leading to cooler soil

temperature, and (c) increased soil water retention (Kern and

Johnson, 1993) [57]. All of these favored the formation and

stabilization of soil aggregates and their associated organic C,

which has been protected from rapid breakdown and

decomposition (Six et al., 2000). Like rice, soil C at wheat

harvest was higher in ZT than conventional tillage.

Fig 4a: Intra-aggregate particulate organic matter (iPOM) C (g kg−1 of sand-free aggregates) in aggregate-size fractions at the 0- to 5-cm soil

depth at (i) rice and (ii) wheat harvest. ‘(a)’ and ‘(b)’ in legend refer to coarse (0.25–2 mm) and fine (0.053–0.25 mm) iPOM in the respective

size of aggregates

Fig 4b: Soil organic C (g kg−1 of bulk soil) as influenced by tillage practices at (a) rice and (b) wheat harvest

The CO2 is a major greenhouse gas (GHG) because of its

atmospheric concentration (about 398 ppm) and strongest

radioactive forcing among all the known GHGs (Figure 5),

despite having relatively lower warming potential (Forster et

al. 2007). It, along with atmospheric water vapors, contributes

majorly to the greenhouse effect on the earth. Though other

GHGs such as methane (CH4), nitrous dioxide (NOX) and

chlorofluorocarbons (CFCs) are present at lower

concentrations (about 2–6 orders of magnitude) than CO2 in

the atmosphere, their per molecule absorption of infrared (IR)

radiation is many fold higher than CO2. It is now known

(Figure 5) that the major contributors of the enhanced

atmospheric GHGs are fossil-fuel combustion, land use

changes and increased use of synthetic fertilizers in the

agriculture. The deterioration of soil quality following land

use change and agro-management practices has drawn global

attention towards the soil ecosystem in general and soil

organic carbon (SOC) dynamics in particular (Srivastava et

al. 2016a) [124]. It is believed that the increased atmospheric

CO2, in which land use change and management adds

considerably in the form of soil CO2 efflux, can be

sequestered back as SOC through appropriate agro-

management practices. It may help to mitigate the change in

global carbon cycle and climate (Aswathanarayana 2012) [3].

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Journal of Pharmacognosy and Phytochemistry

Fig 5: Major greenhouse gases (a) and their economic sector-wise (b) distribution (adapted and redrawn from IPCC 2014; USEPA 2014)

Singh et al., (2007) [114] have shown that addition of various

organic manures along with inorganic fertilizers in rice-wheat

system improved the aggregation status of the soil. Aggregate

ratio varied significantly with treatments. Compared with the

control, treatments where more organic matter was added

either through FYM, CR and GM maintained a greater

fraction of macro-aggregate. Bappa Das et al., (2014) [8]

revealed that the increased amounts of large (>2 mm) macro-

aggregate fractions in NPK + GR (rice) + FYM (wheat) and

NPK + CR (rice and wheat) are associated with the very large

MWD in these treatments. Similar trends are observed in

other organic treatments, with a large amount of small macro-

aggregate fractions, along with large macro-aggregates. A

higher amount of silt- and clay-sized fractions was observed

in the control (43.84%). Mazumdar et al., (2015) [81] found

that he MWD was significantly higher in plots receiving

50%NPK+ 50% N through FYM in rice (1.36 mm), 100%

NPK in wheat or 50%NPK+ 50% N through CR in rice (1.28

mm), 100% NPK in wheat or 50%NPK+ 50% N through GM

in rice (1.29), 100% NPK in wheat (1.18mm) as compared to

control (0.89 mm. Naresh et al., (2016) [85] revealed that the

small macro-aggregates accounted for >30% of the total

aggregates (mean of both main plots) in the surface soil layer.

Silt- plus clay-sized aggregates comprised the greatest

proportion of the whole soil, followed by the small macro-

aggregates. The amount of water-stable large and small

macro-aggregates in the FIRB and ZT plots were significantly

higher than in the CT plots in the 0- to 5-cm soil layer. These

differences may be attributed to the different planting

systems. Song et al., (2016) [122] reported that compared to

conventional tillage, the percentages of >2mm macro

aggregates and water-stable macro-aggregates in rice-wheat

double- conservation tillage (zero-tillage and straw

incorporation) were increased 17.22% and 36.38% in the 0–

15 cm soil layer and 28.93% and 66.34% in the 15–30 cm soil

layer, respectively. In surface soil (0–15cm), the maximum

proportion of total aggregated carbon was retained with 0.25–

0.106mm aggregates, and rice-wheat double-conservation

tillage had the greatest ability to hold the organic carbon

(33.64g kg−1)

Soil carbon dynamics and potential carbon sequestration

Soil C dynamics comprise the study of the soil C pools, the

rate of its exchange among them (turnover) and the associated

regulatory variables. Therefore, it encompasses the kinetics as

well as the governing variables, which defines the temporal

change in SOC pools among its various compartments. SOC

dynamics generally shows nonlinearity, and several years are

required to reach a new equilibrium. Therefore, the short-term

assessments misrepresent the SOC dynamics. However, the

long-term datasets to derive the rate of change across the

various SOC pools to better understand the SOC dynamics are

often scarce (Vaccari et al. 2012) [132].

Soil organic carbon is key attribute of soil fertility and

productivity because of its influence on the physical, chemical

and biological properties of soils. Irrespective of its potential

benefits to productivity and profitability, organic carbon

might be sequestered by vegetation and soils as a possible

way of reducing the rate of CO2 enrichment of atmosphere

and moderate the global climate change. Net change in SOC

depends not only on the current management practices but

also on the management history of the soil.

The presence of a positive difference in SOC concentrations,

stocks, and C sequestration rates between organic and

nonorganic systems does not reveal whether this change goes

along with a net carbon gain due to conversion from

conventional to organic farming or whether it rather reflects a

reduced carbon loss if compared with the non-organic

treatment. Leifeld and Fuhrer (2010) [68] found that an average

annual increase of the SOC concentration in organic systems

by 2.2%, whereas in conventional systems, SOC did not

change significantly. Freibauer et al. (2004) [41] estimated a C

sequestration potential of organic farming in Europe of 0–500

kg ha−1 y−1(more than 50% uncertainty) using calculations

based on the combination of single practices such as

intensification, improved rotations, residue incorporation, and

manure use, but excluding zero and reduced tillage.

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Journal of Pharmacognosy and Phytochemistry

Source: Houghton (2007)

Fig 6: Global carbon cycle depicting various pools and fluxes of C.

Land use change (LUC), especially forest to agriculture

conversion, has been identified as a major source of historical

loss of SOC, primarily in the form of soil CO2 efflux (Poeplau

and Don 2013) [102]. It strongly influences the balance of SOC

dynamics which affects the soil CO2 efflux and subsequent C

sequestration (Lal 2003). Further, various agro-management

practices differentially affect the SOC dynamics (Srivastava

et al. 2016a) [124]. These management- induced changes in the

SOC have been already studied well in agricultural systems in

the context of conservation tillage, cropping, organic and

synthetic fertilization, and residue incorporation (Srivastava et

al. 2016a) [124]. The intensive crop production practices to

increase the crop productivity (i.e. conventional agriculture),

which involves agro-chemicals, improved irrigation, high

mechanization and high yielding seed varieties, enhance the

soil C mineralization, but induce severe environmental

problems (Pimentel et al. 1995) [101]. Consequently, it depletes

SOC with the time because of continuous harvest and

negligible organic input. Therefore, it is essential to

understand various pools and processes related with SOC

before devising the management policies.

C entering the soil is slowly transformed to humus with the

remainder being mineralized back to CO2.

Dhama et al. (2005) [31] reported that degraded soil is

improved by layer of soil and bio-mass with sprinkling of

fresh dung slurry for composting. Cow dung along with sea

water and yeast has been exploited as a

liquid catalyst. It is claimed that it is capable of greening

degraded land. Not only good compost is made but valuable

organisms like earthworms are also generated as in due course

which keep on working all through. Individually or system as

a whole, biogas slurry with Panchgavya combination is

adjudged as the best organic nutritional practice for the

sustainability of crops by positive impacts on overall

performance on growth, productivity and soil health.

Rao et al. (2013) [108] revealed that, fertilizer application could

just maintain the status of soil organic carbon in the cropping

system, with neither improving nor declining at the end of the

annual cropping cycle. While it was found gradually built up

compared to the pre-experimental level, after all the three

crops raised with the application of organic manures. Among

the organic sources tried, neem leaf manure, Panchagavya,

vermicompost and farmyard manure added more organic

carbon to the soil compared to pig manure and poultry

manure. Slow decomposition of neem leaf, vermi compost,

farmyard manure and direct relation to improved fertility over

other manures may probably the reason for the differences in

soil organic carbon. Neverthless, organics did build up the

organic content as well as nutrients there by indicating the

sustenance of soil productivity [Table 1]. Ramesh and Rao

(2009) [105] also reported that soil health could be sustained

with organic nutrition due to diversification of soil biota.

Kamp et al. (2017) [54] revealed that cultivation over the years

caused a significant decrease in soil organic carbon content by

14% in unfertilized control as compared to uncultivated soil.

The balanced fertilization with NPK, super optimal dose of

NPK and integration of balanced fertilization with FYM

increased the SOC content as well as SOC stocks over the

initial year. The carbon sequestration potential (1.77 Mg ha-1)

was highest in 100%NPK +FYM treatment.

Table 1: Effect of various organic farming practices in maize-sunflower-green gram cropping system on soil organic carbon and apparent soil

nitrogen balance over two years

Treatments Organic carbon (%) Initial status

(kg/ha)

Added over two

years (kg/ha)

Uptake over two

years (kg/ha)

Final status

(kg/ha)

soil nitrogen

balance (kg/ha) 2004 2005

T1-No manure 0.21 0.18 135.6 0 154.5 100.6 -189.5

T2- Panchagavya 0.21 0.18 135.6 0 174.5 100.2 -209.9

T3-RDF 0.23 0.20 135.6 400 427.8 150.5 -12.9

T4-RDF + Panchagavya 0.23 0.20 135.6 400 434.1 149.7 -20

T5-Farm Yard Manure 0.42 0.48 135.6 400 410.7 193.1 46.8

T6-FYM + Panchagavya 0.42 0.48 135.6 400 447.8 191.2 7.8

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Journal of Pharmacognosy and Phytochemistry T7-Vermicompost 0.45 0.50 135.6 400 403.4 210.5 71.5

T8-T7 + Panchagavya 0.45 0.50 135.6 400 439 209.6 35

T9-Neem leaf manure 0.46 0.52 135.6 400 385.3 245.2 124.3

T10-T9 + Panchagavya 0.46 0.52 135.6 400 402.1 244.1 106.4

T11-Poultry manure 0.34 0.40 135.6 400 387.8 224.7 101.3

T12-T11 + Panchagavya 0.34 0.40 135.6 400 404.8 223.8 83.4

T13-Pig manure 0.34 0.40 135.6 400 407.4 208.1 65.1

T14-T13 + Panchagavya 0.34 0.40 135.6 400 442.6 205.9 27.7

Initial 0.23 0.32 - - - - -

C.D. (P = 0.05) 0.07 0.06 - - - - -

Soil Organic Carbon stock

Earth is a major reservoir of C. The lithosphere (i.e., the

geological strata) comprises of 75,004 Eg (Exagram =1018g =

1000 gigaton) of C or 99.938% of the total terrestrial C stock

(Lal, 2010). The non-geologic C component consists of 46.46

Eg or 0.062% of the total C stock. Of this ocean consists of

42Eg (Lal, 2010). In contrast, the entire atmospheric reservoir

contains merely 0.8Eg. Thus, even small changes in soil C

stock can have a major impact on the atmospheric

concentration of CO2.

Soil organic carbon stock is one of the most important

terrestrial pools for carbon storage. Onwudike (2010) [92]

reported that combination of cow dung with NPK (15:15:15)

in the concentration of 3 t/ha and 100 kg/ha, respectively. The

organic carbon of the soil after treatment with this

combination was found to be significantly increased from

1.33 to 3.21%. The combination also improved soil organic

matter, exchangeable ions, effective cation exchange capacity

and pH in comparison to untreated soil. Akhilesh and Nandan,

(2016) [5] found that soil organic carbon stock was found

maximum in treatment Dhanicha + FYM + Vermicompost

(Split) (43.77 tha-1), and highest rate of sequestration resulted

in Dhanicha + FYM + Vermicompost (Split) (2.69 tha-1yr-1).

Both these parameters were found minimum in Dhanicha in

kharif and no manure application in summer.

Eleanor et al. (2006) [34] reported that the SOC stocks for the

three dominant classes of cropping systems are shown in

Figure 7. They include rice-wheat, double-cropping (other

than wheat) with rice, and triple-cropping with rice. Double-

cropping refers to crop rotations with two crops grown in a

single year and triple cropping refers to crop rotations with

three crops grown in a single year. The SOC in double-

cropping systems that include rice in AESR’s 9.1, 9.2, and

13.1 will drop, due to shifts into other cropping systems and

losses of soil C resulting from cropping intensification. SOC

stocks in rice-wheat systems in those AESR’s will increase

substantially. AESR’s 2.3, 4.1, and 4.2 will see substantial

decreases in SOC stocks from rice-wheat systems as lands are

shifted out of rice-wheat and into triple cropping systems that

include rice.

Fig 7: SOC stock trends in dominant cropping system classes by AESR in the IGP

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Journal of Pharmacognosy and Phytochemistry Eleanor et al. (2006) [34] revealed that SOC stocks predicted

by Century, on a Tonnes-per-hectare basis, are shown in the

maps in Figures 8a, 8b and 8c for 1990 to 2030. Geographic

analysis of the stocks and change rates indicate a number of

contrasting effects that are occurring throughout the region. In

the lower IGP, cropping intensification has led to reductions

in SOC values in sandy, poorly drained soils. In contrast to

this, the central IGP has seen an increase in SOC in more

clayey soils, as has the upper IGP.

Naresh et al. (2017) [86] found that the quantities of SOC at the

0-400 kg of soil m-2 interval decreased under ZT without

residue (T1), PRB without residue (T4) and Conventional

tillage (T7) treatments evaluated. Stocks of SOC in the top

400 kg of soil m-2 decreased from 7.46 to 7.15 kg of C m-2

represented a change of -0.31±0.03 kg of C m-2 in T1, 8.81 to

8.75 kg of C m-2 represented a change of -0.06±0.05 kg of C

m-2 in T4, and 5.92 to 5.22 of C m-2 represented a change of -

0.70 ±0.09 kg of C m-2 in T7 between 2000 and 2016.

Fig 8a: SOC stocks predicted by the Century model in the IGP in

1990

Fig 8b: SOC stocks predicted by the Century model in the IGP in

2000

Fig 8c: SOC stocks predicted by the Century model in the IGP in

2030

Jobbágy and Jackson, (2000) [52] reported that the mean SOC

density invariably decreased with depth, its vertical

distribution pattern was notably different under different

LULC types. The mean SOC density under different LULC

types ranged from 6.0–11.3 kg·m−2 (0–20 cm), 3.9–6.4

kg·m−2 (20–40 cm), 2.5–3.7 kg·m−2 (40–60 cm), 1.5–2.5

kg·m−2 (60–80 cm) and 1.1–2.5 kg·m−2 (80–100 cm) (Table

2). The mean SOC density values at 0–20 cm and 20–40 cm

depths under all LULC types were significantly different from

each other and also from the values of the last three depths

The relatively large mean SOC density in the top layers could

be attributed to higher OM inputs by litter fall causing higher

accumulation of SOC in the upper layer of the mineral soil.

Table 2: Vertical distribution of SOC density values under different

land use/land cover (LULC) types

Depth

(cm)

SOC Density (kg·m−2) (Mean ± Standard Error Mean)

Agricultural

Lands Forests Grasslands Shrublands

0-20 5.98 ± 0.32 a* 9.62 ± 0.44 a 11.34 ± 1.05 a 8.73 ± 0.64 a

20-40 3.89 ± 0.32 b 6.35 ± 0.34 b 6.23 ± 0.75 a 5.58 ± 0.54 b

40-60 2.45 ± 0.36 c 3.73 ± 0.27 c 2.86 ± 0.61 b 2.53 ± 0.50 c

60-80 2.48 ± 0.34 c 2.54 ± 0.24 d 1.90 ± 0.95 b 1.49 ± 0.39 c

80-100 2.46 ± 0.34 c 2.50 ± 0.23 d 1.12 ± 0.00 b 2.05 ± 0.43 c

* Values in the columns suffixed with different superscript letters are

significantly different (p < 0.05) from each other.

Bäumler et al. (2005) [10] found that the vertical distribution of

SOC density under forests was more homogeneous than

grassland and shrublands (Figure 9a) probably due to high

OM inputs from both above- and belowground biomass, slow

decomposition and SOC complications with andic and spodic

properties of non-volcanic andosolic soils. Begum et al.

(2010) [14] observed that the mean SOC density under

different altitudinal zones was relatively large under 4000–

5520 m (4.8–13.2 kg·m−2 for first three depths) and 3500–

4000 m zones (3.4–11.7 kg·m−2) compared to 3000–3500 m

(2.2–11.6 kg·m−2), 2500–3000 m (1.7–7.0 kg·m−2) and

1769–2500 m zones (2.0–7.1 kg·m−2) (Figure 9b). The

increase in SOC density with altitudinal zone was largely due

to increase in SOC concentration with altitude resulting from

higher OM inputs from above- and belowground biomass,

slow decomposition due to low temperature [10] and more

translocation of OC into deeper layers.

~ 2370 ~

Journal of Pharmacognosy and Phytochemistry

Fig 9a: Proportion of SOC density (kg·m−2) stored at different depth

intervals under different LULC types

Fig 9b: Proportion of SOC density (kg·m−2) stored at different

depths under different altitudinal zones

Fig 9c: Proportion of SOC density (kg·m−2) stored at different depth

intervals under different aspect directions

Egli et al. (2009) [33] reported that the mean SOC density

values were variable in their ranges under different aspect

directions, viz: 2.8–10.6 kg·m−2 (north-facing slopes), 2.6–9.0

kg·m−2 (east-facing slopes), 1.9–8.5 kg·m−2 (south-facing

slopes) and 1.5–8.5 kg·m−2 (west-facing slopes) (Figure 9c).

At all depths, the northern aspect had relatively large mean

SOC density than other aspect directions. The larger SOC

density on the north-facing slopes could be ascribed to rich

biodiversity, high OM inputs, faunal abundance and more soil

moisture on the northern aspect compared to other aspect

directions. (Gathala et al. (2011b) [43] exposing SOC to

microbial decomposition compared to CT for wheat. The

cumulative carbon input from aboveground biomass after 7 yr

was about three times greater in ZTDSR-ZTW+R and

PBDSR-PBW+R than the other treatments, which increased

total SOC by 4.7 and 3.0 tha-1 at 0–0.6 m depth, respectively.

Bhattacharyya et al. (2000a) [16] revealed that the SOC stock

of the IGP constitutes 6.45% of the total SOC stock of India,

0.30% of the tropical regions and 0.09% of the world in the

first 30 cm depth of soils. The corresponding values for SIC

are 3.20% for India, 0.17% for tropical regions and 0.06% for

world, respectively Table 3. Therefore it indicates that IGP

has only 3% SOC stock of the country. The impoverishment

of SOC in the IGP as compared to tropical regions and world

in general and to India in particular is thus apparent.

Table 3: Carbon stock in IGP, India and other regions

Region IGP, India

Soil depth range (cm)

0-30 0-100 0-150

<————————— Pg———————————>

SOC 0.63 (6.45/0.30/0.09)* 1.56 (6.23/0.39/0.10)* 2.00 (6.67/0.32/0.08)*

SIC 0.13 (3.20/0.17/0.06)* 1.96 (8.76/0.93/0.27)* 4.58 (—/—/—)*

Total 0.76 (5.50/0.27/0.0.08)* 3.52 (7.42/0.58/0.16)* 6.58 (10.28/—/—)*

India1

SOC 9.77 25.04 29.97

SIC 4.06 22.37 34.03

Total 13.83 47.41 64.00

Tropical Regions2

SOC 207 395 628

SIC 76 211 —

Total 283 604 —

World2

SOC 704 1505 2416

SIC 234 722 —

Total 938 2227 —

* Values in parentheses indicate% of stock in India, Tropical Regions and the world respectively,

- = figures not available 1Bhattacharyya et al. (2000a) [16]

~ 2371 ~

Journal of Pharmacognosy and Phytochemistry Paudel et al., (2014) [98] showed that, soil organic carbon

buildup was affected significantly by tillage and residue level

in upper depth of 0-20 cm but not in lower depth of 20-40 cm.

Higher SOC content of 19.44 g kg-1 of soil was found in zero

tilled residue retained plots followed by 18.53 g kg-1 in

permanently raised bed with residue retained plots. Whereas,

the lowest level of SOC content of 15.86 g kg-1 of soil were

found in puddled transplanted rice followed by wheat planted

under conventionally tilled plots. Pandey et al., (2014) [98]

revealed that no-tillage before sowing of rice and wheat could

increase SOC by 0.59 Mg C ha–1yr–1. The rate of SOC

sequestration due to reduced- or no-tillage management in

rice-based systems in South Asia varied from 0- to 2114 kg

ha–1 yr–1 (Bhattacharyya et al., 2012a) [19]. Naresh et al.,

(2015) [84] revealed that the highest SOC stock of 72.2Mg C

ha-1 was observed in F4 with T6 followed by that of 64Mg C

ha-1 in F6 with T2> that in F3 with T4 (57.9Mg C ha-1)> F5 with

T1 (38.4Mg Cha–1) = F7 with T5 (35.8Mg C ha-1), and the

lowest (19.9Mg C ha-1) in F1 with T7. Relatively higher

percentage increase of SOC stock was observed in F4 with T6

treatment (56.3Mg Cha-1) followed by F6 with T2 (51.4Mg

Cha-1) and F3 with T1 (48.4Mg Cha–1).

Venkanna et al. (2014) [133] reported that the soil organic

carbon (SOC) stock was highest in Alfisols (52.84 Mg ha–1)

followed by Inceptisols (51.26 Mg ha–1) and Vertisols and

associated soils (49.33 Mg ha–1), whereas soil inorganic

carbon (SIC) stock was highest in Vertisols and associated

soil (22.9 Mg ha–1) followed by Inceptisols (17.5 Mg ha–1)

and Alfisols (12.4 Mg ha–1). The total organic carbon stock

has

been estimated as 0.068 Pg for 0–60 cm soil depth and the

organic C stock with categories < 40 Mgha–1, 40– 50 Mg ha–1,

50–60 Mg ha–1 and > 60 Mg ha–1 are 5.19%, 20.36%, 57.92%

and 16.53% respectively. For inorganic carbon stock it is

estimated to be 0.02 Pg with categories < 10 Mg ha–1, 10–20

Mg ha–1, 20–30 Mg ha–1 and > 30 Mg ha–1 as 6.14%, 68.11%,

18.46% and 7.28% respectively, for 60 cm soil depth Figure

10a. Relationship between inputs of SOC with SOC stock.

The input of SOC has been estimated based on biomass yield,

input of organic residue, including FYM, fertilizers and leaf

fall to soils. The input of organic matter is also well correlated

with organic carbon stock. The C saturation level in the soil of

semiarid tropics is estimated to be 73.21 Mg ha–1 up to 60 cm

soil depth Figure 10b.

Fig 10a: Distribution of carbon stock (total, organic and inorganic) in Alfisols, Inceptisols and Vertisols and soils for 0–60 cm soil depth

Fig 10b: Soil organic carbon stock (Mg ha–1) expressed as a function of carbon input levels (Mg ha–1yr–1) for the semiarid tropical region of

South India

Naresh et al. (2015) [84] observed that compared to the RDF

treatment also, the RDF+FYM treatment had higher SOC

concentration in all the TCE. The highest increase in SOC in

the RDF+FYM treatment was observed in F4 with TCE T6

(Table 4). Organic sources of nutrient such as FYM

decompose slowly resulting in more SOC accumulation in

soil (Lu et al., 2009) [74]. In comparison with the control, the

mean rate of SOC build-up during the 12 years of cropping

was the highest in F6 with T6 (50.63%) and the lowest in F7

with T7 (16.48%). It was estimated that 30 per cent of applied

C through FYM was stabilized, and the rest (70 per cent) was

lost through oxidation. Although ploughing- induced

depletion of SOC pool is widely observed (Bhattacharyya et

al., 2011) [18], the magnitude of depletion depends upon the

geographical location, crops/ cropping systems and inherent

soil properties (Mandal et al., 2007) [79].

~ 2372 ~

Journal of Pharmacognosy and Phytochemistry Table 4: C restoration rate in soil profile as affected by 12 yr of tillage crop establishment and fertilization

Source: Naresh et al. (2015) [84]

T1- CTDSR-ZTDSW; T2- CTTPRAWD–ZTDSW; T3-

ZTDSR-ZTDSW; T4- ZTTPR-ZTDSW;

T5- WBedDSR- WBedZTDSW; T6- WBedTPR-

WBedZTDSW; T7- CTTPR-CTDSW; F1-Control (no N–P–K

fertilizers or organics; F2- 50% RDF; F3-100% RDF; F4-100%

organic as sole FYM;F5- 50% RDF+50% RDF (foliar); F6-

50% organic (FYM) + 50%RDF; F7- Farmer’s practice (180

kg N + 60 kg P2O5 ha–1 only)

Soil carbon sequestration

Carbon sequestration is the provision of long-term storage of

carbon in the terrestrial biosphere, underground, or in the

ocean so that the buildup of carbon dioxide (the principal

greenhouse gas) concentration in the atmosphere will reduce

or slow down. It is also known as carbon capture and storage.

Agriculture is defined as an anthropogenic manipulation of

carbon through uptake, fixation, emission and transfer of

carbon among different pools. Thus land use change, along

with adoption of recommended management practices can be

important instrument of soil organic carbon (SOC)

sequestration (Post and Kwon, 2006) [103]. Soil organic carbon

sequestration (SOCS) is a process in which carbon dioxide

(CO2) is removed from the atmosphere and stored in the soil

carbon pool. This process is primarily mediated by plants

through photosynthesis, with carbon stored in the form of

SOC (Ontl and Schulte, 2012) [90]. Carbons stored in soils

represent the largest terrestrial carbon pool and factors

affecting this will be vital in the understanding of future

atmospheric CO2 concentrations in the climate change arena.

After 16 years of different fertilization treatments in the crop

rotation, Liu et al. (2005) found that the profile average SOC

content (0–90 cm) was only 0.9%, 4.1%, and 8.6% higher for

manure, chemical fertilizers, and manure plus fertilizers,

respectively, than that with no fertilizer application or control.

However, SOC at the 0–15 cm soil layer was 6.2%, 7.7%, and

9.3% higher with manure, chemical fertilizers, and manure

plus fertilizers, respectively, than with no fertilizer

application. Yang et al. (2003b) indicated that the SOC

content could be maintained at a relatively stable level under

sufficient chemical fertilizer application without return of

manure and crop residue conditions, and SOC content was

increased at the combination of chemical fertilizer and

manure application. Francioso et al. (2000) also reported that

SOC and N differed significantly after 22 years for all

treatments where the amendments with cattle manure

markedly increased the SOC and N contents, while cow

slurries and crop residues reduced SOC and N contents.

Soil carbon sequestration is a process in which CO2 is

removed from the atmosphere and stored in the soil carbon

pool. This process is primarily mediated by plants through

photosynthesis, with carbon stored in the form of SOC. In arid

and semi-arid climates, soil carbon sequestration can also

occur from the conversion of CO2 from air found in soil into

inorganic forms such as secondary carbonates; however, the

rate of inorganic carbon formation is comparatively low (Lal,

2008) [66].

Fig 11a: Change in soil organic C in the NPK+FYM treatment compared to the NPK treatment in various long-term experiments

~ 2373 ~

Journal of Pharmacognosy and Phytochemistry

Fig 11b: Sequestration of C with change in net return in the NPK+FYM treatment compared to the NPK treatment in various long-term

experiments

Pathak et al. (2011) [97] revealed that compared to the NPK

treatment also, the NPK+FYM treatment had higher SOC

concentration in all the LTEs (Figure 11a). The highest

increase in SOC in the NPK+FYM treatment was observed in

LTE 14 in New Delhi (Figure 11b). Organic sources of

nutrient such as FYM decompose slowly resulting in more

SOC accumulation in soil (Mandal et al., 2007) [79]. High

lignin content in FYM resulted in greater accumulation of C

compared to other non-lignin materials (Paustian et al., 1992) [99]. Carbon sequestration in CSP NPK scenario denoted that

even without any organic matter application soils could

sequester organic carbon through balanced application of

NPK. But application of FYM along with inorganic fertilizer

led to an additional build up of SOC in soil. Average rate of

sequestration was 0.33MgC ha−1 yr−1 in the NPK+FYM

treatment whereas in the NPK treatment the rate was

0.16MgC ha−1 yr−1. The C sequestration rate was lowest in

LTE 18 in the NPK treatment (0.02MgC ha−1 yr−1) whereas it

was highest in LTE 25 (1.2MgC ha−1 yr−1) in the NPK+FYM

treatment. In the INM scenario i.e., NPK+FYM treatment

compared to the NPK treatment, the average C sequestration

rate was 0.17%. The study showed that C sequestration in

Indian agricultural soil was feasible with application of NPK

and FYM. Addition of about 10Mg FYM ha−1 sequestered

0.33 Mg C ha−1 yr−1. However, to apply this magnitude of

FYM to 147.43Mha agricultural land the country would

require 1474Mt of FYM per year (737 Mt dry weight

considering 50% moisture content). India supports the largest

bovine (cattle + buffalo) population (286.22 million) of the

world (MAC, 2006). In the country 335Mt dung is produced

per annum out of which 110Mt is lost during collection or

used for construction purposes (Pathak et al., 2009) [96].

The remaining 225Mt dung is available for use in agriculture.

This is only about 1/3rd of the FYM requirement of the

country to achieve the full potential of C sequestration. There

are, however, some other sources of organic C, which can be

used in agriculture for C sequestration. For example, total

municipal solid waste (MSW) generation from major Indian

cities (35 metro cities and 24 state capitals) is about 40

thousand Mgd−1 (CPCB, 2006). The biodegradable organic

matter in MSW is about 28% by mass. Thus MSW from

Indian cities generates 4.1Mt C yr−1 and can be an important

source of organic C (Pathak et al., 2009) [96]. Chan, (2008)

reported that globally, clearing natural vegetation for

agriculture results in large reductions in SOC levels and

further declines may occur due to management practices. In

many areas, soil carbon levels have dropped by up to 50%

compared to pre-agricultural periods. Most of the reduction in

SOC occurs in the surface soil layer, 0–10 cm. Therefore, soil

carbon levels of agricultural soils are lower than

corresponding soils under natural vegetation. This difference

in SOC indicates the potential for soil carbon storage.

Xu, (2008) [141] revealed that the estimation of total topsoil

SOC sequestration of (29.9± 61.1) to (31.3±72.4) Tg per year

for the period of 1980-2006, among which (9.15±14.0) Tg/a is

contributed by rice paddies and the other (25.7±61.4) Tg/a by

dry croplands. Depletion of SOC stocks has created a soil

carbon deficit that represents an opportunity to store carbon in

soil through a variety of land management approaches.

However, various factors impact potential soil carbon change

in the future, including climatic controls, historic land use

patterns, and current land management strategies. Continued

increases in atmospheric CO2 and global temperatures may

have a variety of different consequences for soil carbon inputs

via controls on photosynthetic rates and carbon losses through

respiration and decomposition. Carbon loss may also increase

due to increased plant respiration from greater root biomass

(Hungate et al. 1997) [47], or from accelerated decomposition

of SOM through increased microbial activity (Zak et al.

2000).

Likewise, increased temperatures may impact the carbon

balance by limiting the availability of water, and thus

reducing rates of photosynthesis. Alternatively, when water is

not limiting, increased temperatures might increase plant

productivity, which will also impact the carbon, balance

(Maracchi et al. 2005). Estimates of the global sequestration

potential of agricultural soils are typically made for

sequestration on an annual basis and range from 0.4 to 1.2

gigatons per year (Gt/yr) (Lal, 2004a) [65]. Some are more

optimistic, including Kell (2011, 2012) [55, 56] who argues that

by improving root growth in agricultural crops, soil carbon

storage could match anthropogenic emissions for the next 40

years. When multiplied across several years, these rates

produce vastly different estimates of the total potential of soil

carbon sequestration. An optimistic soil carbon accrual rate

could sequester at least 10% of the current annual emissions

of 8-10 Gt/yr (Hansen et al., 2013) [44], while a lower rate

would account for less than 5%. If deep rooted crops could be

elevated and bred, that potential might be even greater.

Hossain (2009) [45] reported that the greater SOC content

under poultry litter and cattle manure application in rice-

wheat-legume rotation compared to farmers’ practice of no

manure and fertilizer application in the rice-wheat-fallow

system in Bangladesh. Similarly, manure or straw addition

when combined with NP fertilizer increased SOC content by

0.30 Mg ha–1yr–1 in a rice-wheat rotation (Fang et al. 2005).

Majumder et al. (2008) [77] indicated that application of NPK

and organic amendments (FYM, straw, and green manure)

~ 2374 ~

Journal of Pharmacognosy and Phytochemistry could increase SOC by 24%. Jha et al. (2013) [51] also found

that an application of bio-nutrient containing Pseudomonas

mycostraw, cyanobacteria, and Azospirillum increased SOC

by 14 to 18% in a rice field in Bihar, India. Sapkota et al.

(2017) [111] revealed that after seven years, ZTDSRZTW+R

and PBDSR-PBW+R increased SOC at 0–0.6 m depth by 4.7

and 3.0 t Cha-1, respectively, whereas the CTR-CTW system

resulted in a decrease in SOC of 0.9 tC/ha. Over the same soil

depth, ZT without residue retention (ZTDSR-ZTW) only

increased SOC by 1.1tCha-1.

Table 5: SOC sequestration rates of croplands of some countries (Data calculated from the literature)

Country Contemporary/(Tg/a) Future potential

Global soil Not applicable 0.2-1.0 Tg/a Cambell, (2003), 1.2-2.6 Pg/a Lal, (1999)

Global agricultural soil 75-1140 1.3-1.5 Pg/a Smith et al. (2008) [119],0.4-0.6Pg/a Cambell, (2003)

EU agricultural soil 56 80-100 Tg/a (biophysical) Smith,(2004) [117],16-19 Tg/a (reachable) Smith et al.

(2005) [116, 118]

USA agricultural soil 67.3 83 Tg/a Sperow et al. (2003)

Indian agricultural soil Not applicable 6-7 Tg/a Lal, (2004)

China’s agricultural soil 34 66.7 Tg/a Xu, (2008) [141]

Dynamics of Soil Organic Carbon Stock

Soil organic matter is made up of four major pools—plant

residues, particulate organic carbon, humus carbon and

recalcitrant organic carbon. These pools vary in their

chemical composition, stage of decomposition and role in soil

functioning and health. Management is capable of altering not

only total organic carbon stocks, but the proportion of carbon

present in these different pools. Knowledge of how carbon

pools change in response to management can provide valuable

information on likely soil functioning and health. Naresh et

al. (2015) [84] reported that the highest SOC stock of 72.2Mg

C ha”1 was observed in F4 with T6 followed by that of 64Mg

C ha-1 in F6 with T2 > that in F3 with T4 (57.9Mg C ha–1)> F5

with T1 (38.4Mg C ha–1) = F7 with T5 (35.8Mg C ha-1), and

the lowest (19.9Mg C ha-1) in F1 with T7. Relatively higher

percentage increase of SOC stock was observed in F4 with T6

treatment (56.3Mg C ha–1) followed by F6 with T2 (51.4Mg C

ha–1) and F3 with T1 (48.4Mg C ha–1) Table 6. Majumder et

al., (2008) [77] reported 67.9% of C stabilization from FYM

applied in a rice–wheat system in the lower Indo-Gangetic

plains. It is well recognized that improved management

practices promote soil carbon sequestration, and thus increase

soil carbon storage (Lu et al., 2009) [74].

Table 6: Profile soil organic carbon (SOC) as affected by 12 yr of tillage crop establishment and Fertilization

Source: Naresh et al. (2015) [84]

Rahangdale and Pathak, (2016) [104] reported that among the

land uses, the mean SOC content was highest (0.81%) in

eucalyptus+pigeonpea agrisilviculture practice followed by

eucalyptus+paddy-wheat (0.77%), eucalyptus+moong-wheat

(0.76%), eucalyptus+soybean-mustard (0.74%), eucalyptus

sole plantation (0.71%), pigeonpea (0.68), paddywheat

(0.66%), soybean-mustard (0.65%) and mean SOC content

was lower under moong-wheat conventional cropping land

use system (0.62%) [Table 7]. The SOC content also varied

with soil depth. Significantly, highest value of 0.79% was

recorded in the top soil layer (0-15 cm) followed by mid layer

(15-30 cm) and lower layer (30-45 cm), which showed

gradually decreasing trend in soil depth. Highest SOC content

in upper most soil layer (0-15 cm) was reflecting the highest

root densities and increased biological activity (Nair and

Chamuah, 1988). The integration of tree under farming

systems always had highest SOC content over the

conventional cropping system which may be attributed to

addition of litter-fall and root residues of both crops and trees.

On account of recycling of organic matter, higher organic

carbon contents were observed in the soil under intercropped

poplar plantations than at a site without trees and the content

varied depending upon the intercrops (Moshin et al. 1996) [83].

The lower SOC content in conventional sole cropping land

use systems is attributed due to the lower amount of residues

addition to soil. This is because SOC content varies with the

extent and type of vegetative cover on the land as quoted by

Koul et al. (2011) [58].

Rahangdale and Pathak, (2016) [104] also found that the SOC

stock and CO2 sequestration (CS) potential were significantly

influenced by different land use systems and soil depth. Mean

SOC stock (16.33 t ha-1) and CS potential (59.92 t ha-1) both

were found significantly higher under eucalyptus+pigeonpea

agrisilviculture practice followed by eucalyptus+paddy-wheat

[15.66 t ha-1 (SOC stock) and 57.48 t ha-1 (CS potential)],

eucalyptus+moong-wheat [15.61 t ha-1 (SOC stock) and 57.27

t ha-1 (CS potential)], eucalyptus+soybean-mustard [15.41 t

ha-1 (SOC stock) and 56.57 t ha-1 (CS potential)], eucalyptus

sole plantation [14.74 t ha-1 (SOC stock) and 54.11 t ha-1 (CS

potential)], soybean-mustard [14.12 t ha- 1 (SOC stock) and

~ 2375 ~

Journal of Pharmacognosy and Phytochemistry 51.84 t ha-1 (CS potential)], paddy-wheat [14.19 t ha-1 (SOC

stock) and 52.06 t ha-1 (CS potential)], pigeonpea [14.39 t ha-1

(SOC stock) and 52.80 t ha-1 (CS potential)] and lower

magnitude was found under moong-wheat conventional

cropping [13.71 t ha-1 (SOC stock) and 50.30 t ha-1 (CS

potential)] [Table7]. The highest SOC stock and CS potential

under eucalyptus+pigeonpea agrisilviculture practice may

have happened because of enhanced accumulation of leaf

litter in tree based agroforestry land use systems. The

abundant litter and or pruned biomass return to soil, combined

with the decay of root, contribute to the improvement of

organic matter under complex land use systems (Beer et al.,

1990 and Kumar et al., 2001) [12, 60]. Low amount of soil

organic carbon stock under the conventional agriculture land

system can be ascribed to intensive cropping as also reported

by Lal et al., (1998) and Bhardwaj et al. (2013) [15].

It was also observed that, the SOC stock and CS potential in

the soil also varied with its depth. Maximum of 16.08 and

59.00 t ha-1 was recorded in the top layer (0-15 cm), while the

minimum of 13.71 and 50.33 t ha-1 was recorded at the lower

layer studied (30-45 cm). This gradually decreased

significantly with increasing soil depth. The increase or

decrease in SOC stock and CS potential was associated with

bulk density and organic carbon content of soil at a particular

soil depth. The higher amount of SOC stock and CS potential

in surface layer i.e., 0-15 cm may be explained in the sense

that, there is continuous accumulation of leaf litter on the

surface layer which keep on decomposing and thus enrich the

upper layer continuously. Carbon stock is also intricately

linked with site quality, nature of land use, choice of species

and other management practices adopted, which explains the

varying carbon stock in different land use management and

also at different soil depths. This in turn is due to the effect of

differential litter addition in different land uses (Swamy et al.

2003) [128]. Thus accumulation of SOC stock in different land

uses through litter fall is different that might have been

regulated due to varying organic matter decomposition and

the formation of stable and labile soil organic matter pool in

these land uses (Vitousek and Sanford, 1986) [134].

Table 7: Effect of land use systems and soil depth on soil organic carbon stock

Land Use Systems Soil organic carbon stock (t ha-1) CO2 sequestration potential (t ha-1)

0-15 15-30 30-45 Mean 0-15 15-30 30-45 Mean

Paddy-wheat conventional cropping 15.17 14.42 12.97 14.19 55.66 52.93 47.60 52.06

Soybean - mustard conventional cropping 15.26 14.15 12.97 14.12 55.99 51.94 47.58 51.84

Moong -wheat conventional cropping 14.67 13.71 12.74 13.71 53.83 50.31 46.77 50.30

Pigeonpea conventional cropping 15.37 14.59 13.21 14.39 56.39 53.55 48.47 52.80

Eucalyptus sole plantation 15.62 14.90 13.71 14.74 57.32 54.68 50.32 54.11

Eucalyptus + paddy- wheat agrisilviculture 17.26 15.42 14.31 15.66 63.33 56.61 52.51 57.48

Eucalyptus+soybean-mustard agrisilviculture 16.48 15.32 14.45 15.41 60.48 56.21 53.03 56.57

Eucalyptus + moong- wheat agrisilviculture 16.94 15.49 14.38 15.61 62.18 56.85 52.79 57.27

Eucalyptus + pigeonpea agrisilviculture 17.93 16.36 14.69 16.33 65.81 60.04 53.92 59.92

Mean 16.08 14.93 13.71 - 59.00 54.79 50.33 -

Land use system C.D. at 5% 0.42 1.55

Soil Depths C.D. at 5% 0.24 0.89

Interaction (Land use systemX Depth) C.D. at 5% NS NS

Soil organic carbon storage

An estimate of 1500 Pg SOC and about 2000 Pg SIC had been

generally accepted for world soils. Among the global

terrestrial C pools, the SOC pool of the agricultural soils has

been regarded as most prone to change and would be

modified in short term under human management practices

(FAO, 2001) [39]. The size of this pool and the capacity for

future sequestration has been one of the important baselines

for assessing global capacity of CO2 offsetting for the recent

years. Globally, the soil area under agriculture amounts to

5000 Mhm2, of which about 1400 Mha is used for crop

production in a proportion of 10.5% to the global land area

(FAO, 2001) [39]. Therefore, the C turnover of these

agricultural soils could have deep impact on global terrestrial

C cycling and climate change.

Table 8: SOC pool and storage of some representative countries (data cited or calculated from literature)

Region Whole soil/ Pg Topsoil/ Pg Topsoil storage/ (t/hm2) Reference

Globe 1500 684 46.91), 47.82) Batjes, (1996)

USA - - 50.3 US Climate Change Sci Prog. (2007)

EU - 34.6 70.8 Smith et al. (2004) [117]

Brazil - 36.4±3.4 44.1 Bernoux et al. (2002)

India 63.2 (150 cm) 21.0 63.8 Bhattacharyya et al. (2000) [16]

China 90 43.6 46.7±44.3 Song et al. (2005) [121]

Notes: 1) According to the global land area of 146.6 Mkm2; 2) According to the total exposured land area of 143.2 Mkm2

Feng and Li (2001) [37] in their 5 years study concluded that

for the same carbon input, carbon storage in soil was higher

by 1.18 t/ha C with manure application than with plant

residues. Kukal et al. (2009) [59] conducted two long term

experiments involving application of FYM and inorganic

fertilizer in rice-wheat and maize-wheat cropping systems.

They reported that the SOC sequestration rate was higher in

FYM plots in comparison to NPK plots in both the cropping

systems. Also the sequestration rate was three times higher in

rice-wheat than in maize-wheat cropping system. In rice-

wheat system, the FYM plots sequestered 0.31 Mg/ha/year

while the rate was 0.14 Mg/ha/year in maize-wheat cropping

system. This was due to that the soil in rice-wheat cropping

system was under submerged condition for three to four

~ 2376 ~

Journal of Pharmacognosy and Phytochemistry months and lack of oxygen for microbial activities resulted in

slower rate of decomposition. Secondly, the biomass

production was higher in rice in comparison to maize. They

also found that at all the sampling depth; the magnitude of

difference among treatments was greater in the top soil (0-15

cm) layer and generally decreased with soil depth. This was in

consonance with the studies conducted by Parker et al. (2002) [95] who obtained 7-20% higher organic carbon in top soil

layer (5 cm) in cotton-rye cropping system with poultry litter

as compared to fertilizer. Conservation practices such as

reduced- and no-tillage are interlinked with crop residue and

nutrient management (fertilizers, manure, and green

manures), which influences SOC accrual and C dynamics in

cropping systems (Ladha et al. 2011; Ghimire et al. 2012) [67,

42].

Soil organic carbon pool

The depletion of the SOC pool leads to a downfall in the soil

quality and productivity. SOC consists of several pools,

namely active, slow and passive, with differential turnover

rate ranging from months to over several hundred to

thousands years (Silveira et al. 2008) [113]. Active SOC pool

plays a very different role than passive does. As labile (active)

and non-labile (stable) SOC play differential roles in SOM

dynamics and nutrient cycling, the pool size and turnover time

of these two fractions in bulk soil and in aggregate size

fractions may be important to assess and evaluate the soil

management practices for the monitoring of SOC (Srivastava

et al. 2016b) [125]. Ch. Srinivasarao et al. (2011) [26] reported

that the surface 0.2m layer, 50 per cent RDN (F) + 50 per cent

RDN (FYM) contained the highest SOC concentration (2.7 g

kg-1) followed by that in 50 per cent RDN (FYM) (2.2gkg-1)

and 100 per cent RDN (F) (1.7 g kg-1). There was a significant

reduction in SOC concentration with the sole application of

inorganic fertilizers (100 per cent RDN) compared with those

in the mixed organic and inorganic or sole FYM treatments

Table 9. Ch. Srinivasarao et al. (2012) [27] also found that in

comparison with the control,% increase in SOC stock was in

the order 100% organic (FYM) treatment (55.0) > 50%

organic (FYM)+50% RDF (35.2) > 100% RDF (mineral)

(15.3).This trend was reflected in the profile SOC stock of the

respective treatments. The mean rate of change in SOC stock

followed a trend similar to that of SOC stock (Table 9). The

SOC stock declined in all but two treatments (100% FYM,

50% FYM + 50% RDF). The mean rate of SOC sequestration

in two treatments which enhanced SOC stock over 21 yr was

0.32 Mg ha–1 yr–1 for 100% FYM and 0.15 Mg ha–1 yr–1 for

50% FYM + 50% RDF. However, results showed that 13.4%

C applied as FYM was stabilized in SOC stock. Similarly,

Majumder et al. (2008) [77] reported 67.9% of C stabilization

from FYM applied in a rice–wheat system in the lower Indo-

Gangetic plains.

Table 9: Changes in concentration of soil organic carbon after 18 years of cropping and use of amendments (Mean ±SD)

Source: Ch. Srinivasarao et al. (2011) [26]

Source: Trumbore, (1997)

Fig 12: Characteristics of different soil organic C pools and soil CO2 efflux

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Journal of Pharmacognosy and Phytochemistry Table 10: Profile soil organic carbon (SOC), C restoration, C restoration rate, and C sequestered in soil profile as affected by 21 yr of cropping

and fertilization under sub-humid tropical conditions (± standard deviation from mean).

Source: Ch. Srinivasarao et al. (2012) [27]

Nayak et al. (2012) [87] reported that improved the SOC,

particulate organic carbon (POC), microbial biomass carbon

(MBC) concentration and their sequestration rate. Application

of 50% NPK + 50% N through FYM in rice and 100% NPK

in wheat, sequestered 0.39, 0.50, 0.51 and 0.62 Mg C ha−1 yr−1

over control (no N–P–K fertilizers or organics), (Figure 13 a,b

&c). Across the different agro-climatic zones of IGP, higher

SOC content was observed in Kalyani (LGP) followed by

Sabour (MGP), Kanpur (UGP) and Ludhiana (TGP),

respectively. Across all the agro climatic zones, the

sequestration rate of SOC, POC and MBC in all the four

treatments followed the order NPK + FYM > NPK + CR >

NPK + GM > NPK.

Ch. Srinivasarao et al. (2011) [26] revealed that the profile

SOC stock was the highest in 50 per cent RDN (F) + 50 per

cent RDN (FYM) (25.5MgCha_1) followed by that in the 50

per cent RDN (FYM) (23.4MgC ha_1), and the lowest in the

control (17.9MgCha_1) (Table 10). The highest rate of SOC

build-up from the C inputs was observed in treatments

receiving 50 per cent RDN (F) + 50 per cent RDN (FYM)

(42.5 per cent) followed by that in the 50 per cent RDN

(FYM) (30.7 per cent), farmer’s practice (10.6 per cent), 100

per cent RDN (F) (7.8 per cent), and the lowest in 50 per cent

RDN (F) (7.3 per cent). A similar trend was also observed in

the profile SOC stock and the rate of SOC build up in the

respective treatments.

Fig 13(a): Soil organic carbon sequestration (Mg ha−1 yr−1)

Fig 13(b): Particulate organic carbon sequestration (Mg ha−1 yr−1)

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Journal of Pharmacognosy and Phytochemistry

Fig 13(c): Microbial biomass carbon sequestration (Mg ha−1 yr−1) in different inte-grated nutrient management system over the control under

different agro-climatic situation in Indo-Gangetic Plains

Table 11: Cumulative C input, profile SOC, C build up, C build up rate and C sequestered in soil profile as affected by 18 years of cropping and

fertilization under semi-arid conditions (Mean± SD)

Source: Ch. Srinivasarao et al. (2011) [26]

Microbial Biomass

Microbial biomass is considered as a crucial parameter to

evaluate the functional status of soil. The top soil layer had

higher amount of MBC than the deeper layer, because the

amount of microbial biomass and rate of microbial activity

decline rapidly below the surface layer. Soil microbes play

crucial roles in soil ecosystems by regulating the

decomposition of organic matter, the formation of humus, and

cycling of nutrient elements, while soil enzymes catalyze or

mediate most soil biological processes; thus, soil microbes

and enzymes are key components and the main driving force

in soil nutrient cycling and energy flow. Soils with a high

functional diversity of microorganism, which occur very often

under organic agriculture practice, develop disease and insect

suppressive properties and can help to induce resistance in

plants (Fliebach et al., 2007). Since microbial biomass and its

activity plays a significant role in regulating processes of

nutrient cycling, studying the change of microbial biomass

and soil enzymes under diverse organic inputs may help us to

better understand the impact of organic amendments on

improving soil fertility.

Comparative analysis of heterotrophic bacterial counts in

organic and fertilizer fields revealed that heterotrophic count

was significantly low in fertilizer stations as compared to the

organic stations. Determination of soil microbial biomass is

generally used as a rapid indicator of change in soil

management which in turn affects the turnover of organic

matter (Nannipieri et al., 1990). A relatively rapid response to

organic amendments has been reported for microbial biomass

carbon by several workers which suggest it could be a useful

indicator in identifying positive effects of soil management

(Fauci and Dick, 1994) [36]. Axelsen and Elmholt, (1998) [4]

reported that a transition to 100% organic farming has

increased the microbial biomass by 77% as a national

average.

Collins et al. (1992) reported a greater amount of soil organic

matter and soil microbial biomass in continuous wheat than in

a wheat-fallow rotation after 58 years. Beare et al. (1994) [11]

indicated that tillage enhanced short-term CO2 evolution and

microbial biomass turnover, and accelerated organic C

oxidation to CO2 not only by improving soil aeration, but also

by increasing contact between soil and crop residues, and by

exposing aggregate-protected organic matter to microbial

attack. Witt et al. (2000) found that the replacement of dry

season rice by maize caused a reduction in soil C and N due

to a 33–41% increase

in the estimated amount of mineralized C and N during the

dry season. As a result, there was 11–12% more C

sequestration and 5–12% more N accumulation in soils

continuously cropped with rice than in the maize-rice rotation

with the greater amounts sequestered in N-fertilized

treatments. Tillage also exposes organic carbon in both the

inter- and intra-aggregate zones and that immobilized in

microbial cellular tissues to rapid oxidation (Roscoe and

Burman 2003). This is because of the improved availability of

O2 and the exposure of more decomposition surfaces, thereby

stimulating increased microbial activity (Jastrow et al., 1996).

Active microbial biomass and C mineralization were higher

under NT than under conventional tillage in the top 5 cm of

the soil profile (Alvarez and Alvarez 2000). Increased C

storage has been frequently observed in soils under

conservation tillage, particularly with NT (Zibilske et al.,

~ 2379 ~

Journal of Pharmacognosy and Phytochemistry 2002). Balota et al. (2003) showed that no-tillage increased

microbial biomass C, N, and P, and higher levels of more

labile C existed in no-tillage systems than in conventional

systems.

Li et al. (2013) showed that MBC was affected by the straw

return factor with an affecting force of 95.95% at 0–7 cm

depth and 97.83% at 7– 14 cm depth. The probable

explanation maybe that crop residue might enter the labile C

pool, provide substrate for the soil microorganisms, and

contribute to the accumulation of labile C.Panettieri et al.

(2013) revealed that TOC, β-glucosidase and, to a less extend,

dehydrogenase were useful as indicators of management

practices impact on soil quality. Additionally, dehydrogenase

and β-glucosidase were useful indicators to reflect changes in

soil total biological activity and biochemical status involved

in the carbon cycle Figure 14 (i). Ratnayake etal. (2013) [106]

revealed that microbes affect the turnover of their primary

substrates with increasing soluble carbon fractions such as

MBC and WSC, because organic matter acts as source of

nutrients and also improve greater nutrient retention. Liu et

al., (2013) [72] revealed that the average concentration of

particulate organic carbon (POC), dissolved organic carbon

(DOC) and microbial biomass carbon (MBC) in organic

manure plus inorganic fertilizer treatments (NP+S and

NP+FYM) in 0–60 cm depth were increased by 64.9–91.9%,

42.5–56.9%, and 74.7–99.4%, respectively, over the CK

treatment. Beesley et al., (2014) [13] opined that incorporation

of organic manure to the soil should substitute for lost C

which in turn should modulate the dynamics of soil C pools.

Apart from the addition of essential nutrients to the soil,

organic inputs also eradicate the problems of heavy metal

pollution to a considerable degree. Sharma et al., (2015) [112]

reported that the greatest soil quality index (1.61) was

observed with application of 25 kg nitrogen (N; compost) as

well as with application of 15 kg N (compost) + 10 kg N ha−1

(green leaf). The order of percentage contribution of key

indicators toward soil quality indices was available potassium

(K) (34%) > available phosphorus (P) (32%) > available N

(13%) > microbial biomass carbon (12%) > exchangeable

calcium (Ca) (9%) Figure 14(ii & iii). Akhilesh and Nandan,

(2016) [5] reported that the heterotrophic microbial count

showed an average highest value of 20x 106 cfu/g soils in

organic, whereas was 90x104 cfu/g soils in fertilizer applied.

Naresh et al. (2017) [86] also found that the values of MBC in

surface soil varied from 116.8 mgkg−1 in unfertilized control

plot to 424.1 mgkg−1 in integrated nutrient use of 50% RDN

as CF+50% RDN as FYM (F5) plots, respectively; while it

varied from 106.6 mgkg−1 (control) to 324.9 mgkg−1 (50%

RDN as CF+50% RDN as FYM F5) in sub-surface (5-15 cm)

soil layer. The values of MBC increased by 58.4 and 72.5%

under 75% RDN as CF+25% RDN as FYM (F3) and 50%

RDN as CF+50% RDN as FYM (F5) treatments in surface soil

over control. While, there were 14.5 and 43.4% increase of

MBC over 100% RDF as CF (F2) fertilizer, respectively. The

highest value of MBC due to integrated use of FYM and RDN

fertilizer might be due to higher turn-over of root biomass

produced under 50% RDN as CF+ 50% FYM treatment.

Fig 14(i): Projected loadings of the soil chemical and biochemical

properties MBN: microbial biomass nitrogen; MBC: microbial

biomass carbon; WSC: water soluble carbon; TOC: total organic

carbon; DHA: dehydrogenase activity; β-GLU: β-glucosidase

activity.

ii. iii

Fig 14 (ii & iii): Percentage contributions of key soil quality indicators towards soil quality indices in long term conjunctive nutrient-

management treatments under pearl millet system in Inceptisols of Agra

MBC was highest in the farmyard manure plus inorganic

fertilizer treatment in top soil, an increased MBC content after

farmyard application was also reported by (Chakraborty et al.,

2011; Marschner et al.,2003 and Liu et al., 2013) [23, 78, 80, 71].

This indicated the activation of microorganisms through

carbon source inputs consisting of organic residues. Increases

in soil organic matter are usually associated with similar

increases in microbial biomass because the SOM provides

principal substrates for the microorganisms Melero et al.

(2009) [82]. Among the investigated fertilizer treatments, straw

plus inorganic fertilizer had impact on the microbial biomass.

This effect is mainly due to the input of straw manure as an

organic carbon source. Srinivasan et al. (2012) [126] observed

that SOC protection by soil aggregates, the newly added

carbon provides physical protection and is then subjected to

chemical conversion and structural stabilization; meanwhile,

~ 2380 ~

Journal of Pharmacognosy and Phytochemistry alternation of the properties and distribution of the carbon

pool leads to both the diversification of aggregate-scale

microbial habitats and the evolution of microbial biota, along

with changes in various fertility service functions such as

functional groups and enzyme activity, which promote the

development of diverse biota and thereby stabilize ecosystem

processes. Lynch and Panting, (1980) [75] reported that eight

months after application of straw manure to a loamy arable

soil the microbial biomass was almost twice as high as

compared to a control. Also, Ocio et al. (1991) [89] have

demonstrated rapid and significant increases in microbial

biomass following straw inputs in field conditions. The MBC

was not only correlated with SOC concentration near the

surface but also at deeper depths. Though the average MBC

decreased with soil depth, the NP+FYM, NP+S and FYM

treatments resulted in significant increase in microbial

biomass C even in 60–80 cm soil layer.

Management shifts that can enhance SOC stocks and

Climate change

In general, any shift in management that increases inputs

and/or reduces losses should build SOC stocks especially in

soils that have lost significant quantities of SOC relative to

pre-clearing conditions. Given that climate and

physicochemical characteristics of a particular soil exert such

overriding controls on overall SOC dynamics, results from

one field trial under a particular set of climate and soil

conditions may not be applicable to another. There is

evidence that large-scale changes in farming practices to

cowpathy and so-called “biological” farming systems which

rely heavily on alternative soil amendments and manure

applications can decrease net GHG emissions (Stolze et al.

2000) [127] and increase SOC stocks (Wells et al., 2000) [136]

while maintaining or increasing farm profitability especially

during extreme climatic years (Lotter et al. 2003) [73]. Wells et

al. (2000) [136] found that in intensive vegetable farming, both

cowpathy and hybrid organic-best management practice

systems significantly increased SOC levels over more

traditional management systems. After 8 years SOC stocks to

15 cm were found to increase by 0.5 and 0.3 Mg C ha-1 yr-1

for cowpathy (organic) and low-input crop rotation systems,

respectively. While the conventional treatment showed no

change over the same period (Clark et al., 1998) [28].

Fig 15: Conversion of native vegetation to agriculture

Eleanor et al. (2008) reported that the adoption of no-tillage

systems, SOC stocks have shown an increase over time under

soybean cultivation (Figures 15). The effects of agriculture

expansion can also be observed by the SOC stock change

rates, where soybean shows the highest change rates among

the different land uses in the Brazilian Amazon. The increase

in soybean cultivation area associated with adoption of no-

tillage systems has led to an increase in SOC stocks. This is

illustrated in the SOC stock maps for 2000 and 2030 (Figure

16). In 1990 the agricultural expansion area was dominated by

SOC stock class of 20-40 t C ha-1. In the year 2000 some

areas started to be cultivated with soybean and finally in

2030, most of this region moved to a higher class of SOC

stock, now in the range of 40-60 t C ha-1 (Figure 17). Brown

and Lugo (1990) reported that abandoned agricultural lands

that reverted to forest accumulate carbon at rates proportional

to the initial forest biomass. Rates range from about 1.5 Mg C

ha-1 yr-1 in forests with initial biomass of < 100 Mg C ha-1 to

about 5.5 Mg C ha-1 yr-1 for forests with biomass of > 190

MgCha-1. Woomer et al. (1999) observed a rate of 6.2±1.3

Mg C ha-1 yr-1 of carbon sequestration in secondary forest re-

growth in the Brazilian Amazon. Watson et al. (2000)

suggested a range of carbon accumulation of 3.1 to 4.6 Mg C

ha-1 yr-1 for tropical regions over 40 years. Schroth et al.

(2002) reported that secondary forest on an infertile upland

soil in central Amazon accumulated carbon in above- and

belowground biomass and litter at a rate of about 4 Mg ha-1yr-1.'

Fig 16: SOC stock change rate

~ 2381 ~

Journal of Pharmacognosy and Phytochemistry

Fig 17: Estimated current and future SOC stocks in the agricultural

expansion area within the Brazilian Amazon

Chan (2001) found that 69 to 94% of changes in total SOC

stocks occurred in the particulate fraction for several diverse

management shifts. This is the SOC fraction that is most

sensitive to perturbation and could be easily lost with only

minor management or environmental change. Globally, Lal

(2004a) [65] estimated that 78 Pg of carbon have been lost due

to agricultural practices, with 26 Pg attributed to erosion and

52 Pg attributed to mineralization. If best management

practices, including reduced or no-till farming, cover crops,

nutrient management, manuring, efficient irrigation, and

setting aside marginal lands, were adopted on all agricultural

land, Lal (2004a) [65] estimates that 50-66% of historic losses

could be sequestered over the next 50 years. Globally, this

equates to 30 to 60 Pg C at a rate of 0.9 ± 0.3 Pg C yr-1 over

25 to 50 years. This sequestration rate is equivalent to

approximately 10% of current total GHG emissions due to

fossil fuel burning and land-use change (IPCC 2007) or 25 to

33% of the annual increase in atmospheric CO2 levels.

Kern and Johnson (1993) [57] concluded that the greatest

change of C occurred in the top 8 cm of soil, a lesser amount

in the 8- to 15-cm depth, and no significant amount below 15

cm. They also concluded that, unlike no-till (NT) in which

SOC had increased, no significant change in SOC was

detected in response to reduced tillage (RT). West and Post

(2002) indicated that on average, a change from CT to NT can

sequester 57 ± 14 g Cm-2yr-1, and by enhancing crop rotation

complexity it can sequester an average of 20 ± 12 g Cm-2yr-1.

Carbon sequestration rates can be expected to peak in 5–10

years with SOC reaching a new equilibrium in 15–20 years.

Liu et al. (2003) [71] showed a significant decline of total SOC

that occurred in the first 5 years of cultivation where the

average SOC loss per year was about 2300 kgha-1 for the 0–

17 cm horizon. The average annual SOC loss between 5- and

14-year cultivation was 950 kgha-1 and between 14- and 50-

year cultivation it was 290 kgha-1. These data clearly showed

a rapid reduction of SOC for the initial soil disturbance by

cultivation and a relatively gradual loss later. Compared with

organic matter in the uncultivated soil, Liu et al. (2003) [71]

also indicated that the total SOC loss (the sum of three

horizons) was 17%, 28%, and 55% in the 5-, 14- and 50-year

cultivation periods, respectively. Song et al. (2005) [121]

reported that a reduction in topsoil SOC storage at

(14.8±15.1) t/hm2, leading to a total loss of 1.7-2.0 Pg.

However, using similar approach, Wu and Cai, (2007) [138, 139]

revealed that a total topsoil SOC loss as high as 4.3 Pg.

Nevertheless, all these studies had described the SOC

reduction had happened mainly in those regions with

significant climate change and/or vulnerable ecosystems

though the estimation of the extent of SOC stock loss seemed

quite different.

Wu and Cai, (2007) [138, 139] indicated an up-rise of SOC

content between 0.05 gkg-1 and 0.29 gkg-1 under balanced or

combined inorganic and organic fertilization and a net SOC

sequestration of 0.2- 1.6 Pg during 1982-2005. Huang and

Sun, (2006) also observed that 53%-60% of croplands in SOC

enhancement, 30%-35% in decline and 4%-6% in balancing

during 1980s-2005. Hutchinson et al. (2007) revealed that the

sequestration potential for numerous management practices

and found that on average improvements to cropland resulted

in gains of 0.24 ± 0.20 Mg Cha-1yr-1 (mean ± s.d.), while

improvements to pasture lands resulted in increases of 0.44 ±

0.20 Mg Cha-1yr-1, and conversion from cropland to pasture

gained 0.82 ± 0.28 Mg C ha-1 yr-1.Smith et al. (2008) [119]

estimated that the global technical mitigation potential,

considering all greenhouse gases, from agriculture by 2030 is

5.5 to 6.0 Pg CO2-eq Yr-1 (or ~ 1.5 Pg C yr-1).

Stable organic matter and humic substances

Humic substances have been shown to contain a wide variety

of molecular components. Some typical components are:

polysaccharides; fatty acids; polypeptides; lignins; esters;

phenols;ethers; carbonyls; quinones; lipids: peroxides; various

combination of benzene, acetal, ketal, and lactol, and furan

ringed compounds; and aliphatic (carbon chains) compounds.

The oxidative degradation of some humic substances

produces aliphatic, phenolic, and benzenecarboxylic acids in

addition to n alkanes and n fatty acids. Humic Substances as

the fraction of SOM that is not composed of recognizable

biomolecules, such as carbohydrates, proteinaceous materials,

and lipids. Humic substances often represent 60 to 85% of

total SOM, with the highest values often reported for

agricultural soils with the remainder being dominated by

particulate OM which includes all plant residues.

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Journal of Pharmacognosy and Phytochemistry

Fig 18a: Diagram of interactions and negative impacts of agricultural management on soil quality

FIG. 18b: Long-term soil organic carbon level changes depending on carbon input and decomposition in agricultural ecosystems

Conant et al. (2001) [24] reported that globally, rates of C

sequestration by different types of management range from

0.11 to 3.04 Mg C ha–1 yr–1, with a mean of 0.54 Mg C ha–1yr–

1, and are highly influenced by biome type and climate. Ch.

Srinivasarao et al. (2012) [27] revealed that an annual

application of biomass C through crop residues and FYM

significantly enhanced SOC stock. A linear relationship (y =

6.340x +10.04, R2 = 0.58, P < 0.01) was observed between

SOC and the annual inputs of C as crop residues in different

treatments, indicating the latter’s influence on SOC stock

(Figure 19 i) Similarly, a significant relationship between the

crop residue C, external C, and the total C input with the total

SOC stock in the profile, indicated that the C input positively

influences SOC stock (Figure 19 ii). A significant

improvement in SOC, after 10 yr of the incorporation of a

cover crop [horsegram, Macrotyloma uniflorum (Lam.)

~ 2383 ~

Journal of Pharmacognosy and Phytochemistry Verdc.] biomass grown with off –season rainfall in a rainfed

Alfisol under semiarid tropical conditions was reported by

Venkateswarlu et al. (2007). Therefore the positive linear

relationship between the changes in SOC stock and the total

cumulative C inputs to the soils (external organics plus crop

residue) over the years (Y = 0.099X – 5.131; R2 = 0.99***, P

< 0.001) (Figure 19 iii) was highly significant and indicates

that even after 21 yr of C input, ranging from 1.13 to 5.55 Mg

C ha–1yr–1.

Fig 19(i): Crop residue C inputs influence soil organic carbon (SOC)

Fig 19(ii): cumulative C input through (a) crop residue, (b) external

C (organics) and (c) total C on total soil organic C stock

Fig 19: (iii) and the magnitude of critical C input and its influence on soil organic carbon (SOC) sequestration

Carbon balance

Cerri et al. (2004) [22] reported that in order to perform the

calculation for the carbon balance when forest is burned and

pasture established, requirements are needed concerning the

pools of carbon in the soil and in the biomass. Regarding the

fluxes, i.e. transfer of carbon between the different

compartments and the atmosphere. It is going to be shown

that although there is an eventual accumulation of C in the

soil when forest is converted to pasture, the total C balance

Figure 20 ends up with a large emission of C to the

atmosphere, indicating that clearing forest to pasture

establishment is not a good option in terms of greenhouse gas

emissions and therefore, an important contribution to

enhancing global climate change problems.

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Journal of Pharmacognosy and Phytochemistry

Fig 20: Carbon balance in the conversion of forest to pasture

Over long enough time periods, there must be an approximate

balance between inputs and losses, otherwise soils would

either be devoid of carbon or awash in the entire atmospheric

carbon pool (Richards et al., 2007) [109]. An example of the

importance of recognizing multiple pools with varying

turnover times, t, is given in Figure 21 (A). In this

hypothetical example, there is a step increase in C returns to

the soil of 2 Mg C ha-1 yr-1. Depending on the fate of this new

C, there is a 3-fold difference in the amount of new C

ultimately sequestered. If the new C remains as unprotected

particulate C (POC), only 6 Mg C ha-1 are added to the soil

with sequestration rates dropping to negligible levels after

only 10 years Figure 21 (B). If some of this POC becomes

incorporated into aggregates with decadal turnover times, then

8 Mg C ha-1 will be sequestered. If some of the POC and

aggregate-protected C becomes adsorbed to mineral surfaces

with a t of 120 yrs, then 18 Mg C ha-1 will be added to the soil

with sequestration rates >0.1 Mg C ha-1 yr-1 sustained for 30

years. An important collorary to this concept is that if the new

inputs cease Figure 21 (C), the C stocks will return to their

previous level rapidly if this new C has not become physically

protected.

Fig 21: Total new soil C (A) and sequestration rates (B) following a 2 Mg C ha-1 yr-1 increase in inputs with a cessation of the new inputs after

60 years for 3 scenarios: #1 – all new C enters and stays in soil as unprotected POC (MRT = 3 yrs); #2 – all new C enters as POC but a fraction

of the POC becomes protected within aggregates (MRT = 30 yrs); and #3 – as #2 with an additional fraction becoming stabilised by adsorption

to minerals (MRT = 120 yrs). Model structure shown in (C), with the 3 pools shown as boxes (turnover time, t, given for each pool), solid

arrows represent transfers, and wavy arrows represent losses as CO2. Steady state distribution of SOC amongst pools is ~25% as POC, ~15% as

aggregate-protected and ~60% as sorbed C. This model is mathematically very similar to Roth C and Century models, but the 3 pools are

represented by specific stabilization processes

Persson et al. 2008) [100] reported that the equilibrium SOC

levels and multiple pools lead to a second important insight

for soil C management: the state of the soil system prior to a

change in management may override any expected soil C

gains (e.g.). This is particularly true for soils that have only

been cultivated for short periods of time with significant

stocks of SOM derived from the native vegetation remaining.

The initial drop in C input rates from the native state to the

first cultivated state will likely take 50 to >100 years to be

fully expressed as losses as the more stable SOM pools adjust

to the new input levels. During this time period, a shift in

management so that more residues, but still less than the

amount prior to any cultivation, are returned to the soil may

not result in increased C levels because the soil is still losing

C as a result of the previous large drop in input rates.

However, if the soil had reached steady state with respect to

the initial management, then the new management with

increased residue returns would result in a significant gain in

SOC.

Lentz and Lehrsch, (2015) also found that the mean annual

total C input was 15.7, 10.8, and 10.4 Mg ha−1 for M,

(manure) F, (fertilizer) and NA,(no amendments)

respectively, while total C outputs for the three treatments

were similar, averaging12.2 Mg ha−1. Manure plots with a

mean net gain of 3.3 Mg C ha−1 Figure 22a&b.

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Journal of Pharmacognosy and Phytochemistry

Fig 22a: Mean annual transfers of C in Mg C ha−1 into and out of an irrigated silage corn and calcareous soil system amended with inorganic

fertilizer. The value shown in parentheses is the standard error of the mean (n = 8). DIC dissolved inorganic C; DOC, dissolved organic C; PIC,

particulate inorganic C; POC, particulate organic C.

Fig 22b: Mean annual transfers of C in Mg C ha−1 into and out of an irrigated silage corn and calcareous soil amended with stockpiled dairy

manure. The value shown in parentheses is the standard error of the mean (n = 8). DIC dissolved inorganic C; DOC, dissolved organic C; PIC,

particulate inorganic C; POC, particulate organic C.

Conclusion

It was recognized that soil organic matter levels are generally

low and are still declining except in the few instances where

appropriate management techniques have been introduced.

Conservation system (CS) proved to be highly effective in

enhancing SOC under the semi-arid conditions prevailing in

western Uttar Pradesh. CS were observed to lead to

differences in SOC beginning in the third year after a change

in management practice, followed by larger increase in

subsequent years. Long-term compost amendment

significantly increased the organic C content in soil by

increasing organic C in all aggregates, whereas the increase in

organic C in inorganic fertilizer–added soils was mainly

because of the enhancement in organic C content in macro-

aggregates and the silt + clay fraction. Low organic matter

and poor soil structure are one of the key reasons of yield

stagnation and even decline in yield of rice-wheat system of

India. Therefore, crop residue incorporation will enhance soil

organic matter and will improve soil structure. Soil organic C

is a key element in the valuation of natural resources and the

evaluation of how management affects soil quality and

ecosystem services derived from soil. A key to success will be

to consider the agronomic, ecological and environmental

constraints within a particular farm setting. The magnitude

and severity of the depletion of SOC pool are exacerbated

through decline in soil quality by accelerated erosion and

other degradation processes. Perpetual use of extractive

farming practices and mining of soil fertility also deplete the

SOC pool. Conversion to a restorative land use and adoption

of recommended agricultural management practices, which

create positive C and nutrient budgets, can enhance SOC pool

while restoring soil quality. As a living component of soil C

and N pool, microbial biomass serves as a reservoir of

nutrients and driver of nutrient cycling processes. The depth

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Journal of Pharmacognosy and Phytochemistry distribution of microbial biomass was impacted by long term

tillage, which may influence the potential nutrients supply to

crops. No till management regime which promoted

maintenance of crop residues at the soil surface may have

beneficial impacts on soil fertility through maintenance of

microbial biomass and supply of mineralizable nutrients.

Conventional tillage (CT) significantly reduces macro-

aggregates to smaller ones, thus aggregate stability was

reduced by 35% compared with conservation system (CS),

further indicating that tillage practices led to soil structural

damage. The concentrations of SOC and other nutrients are

also significantly higher under CS than CT, implying that CS

may be an ideal enhancer of soil productivity in this Inceptisol

ecosystem through improving soil structure which leads to the

protection of SOM and nutrients, and the maintenance of

higher nutrient content. The average concentration of

particulate organic carbon (POC), dissolved organic carbon

(DOC) and microbial biomass carbon (MBC) in organic

manure plus inorganic fertilizer treatments (NP+S and

NP+FYM) in 0–60 cm depth were increased by 64.9–91.9%,

42.5–56.9%, and 74.7–99.4%, respectively, over the CK

treatment.

Average SOC concentration of the control treatment was

0.54%, which increased to 0.65% in the RDF treatment and

0.82% in the RDF+FYM treatment and increased enzyme

activities, which potentially influence soil nutrients dynamics

under field condition. A regular input of biomass-C along

with chemical fertilizers is essential to improving soil quality

in the semi arid tropics of India, and for minimizing the

depletion of SOC stock under continuous cropping. Use of

organic amendments is essential to enhancing the SOC

sequestration. The minimum input of 1.1 Mg C ha−1 year−1 is

needed to maintain SOC at the initial level (with no change).

In view of the decreasing availability of FYM, however,

application of 10.7 Mg ha–1 of FYM (equivalent to 60 kg N)

on dry weight basis is difficult. Thus, conjunctive use of FYM

or other crop residues along with 50% recommended dose of

fertilizers is a viable option for curbing SOC depletion and

sustaining crop production. Hence, balanced use of NPK

fertilizer along with FYM or other crop residues, which will

take care of critical-C-input addition quantitatively, will be a

better option to stop SOC depletion and maintain and sustain

crop production.

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