Soil carbon stocks in natural and manmade agri-hortisilvipastural land use systems in dry zones of Southern India

Abstract

A study was undertaken to assess the soil carbon stocks in 0-50 cm soil depth, under natural and
man-made land use systems in the eastern dry zones of Karnataka in India. The carbon (C) stocks
in soils ranged from 26.46 t ha-1 in dry land agricultural systems (without manure) to 89.20 t ha-1 in
a mixed forest. Among natural systems, mixed forest (89.20 t ha-1) and ungrazed grassland (71.78 t
ha-1) recorded higher levels of C stock than other systems, while grazing in grassland and litter
removal in teak plantations correlated to reduced carbon stocks to 39.32 and 32.74 t ha-1, respectively.
Intensively managed horticultural systems namely, grapes plantation (85.52 t ha-1) and pomegranate
plantation (78.78 t ha-1) maintained higher levels of C stock. However, agricultural systems recorded
moderate to lower levels. Total carbon stocks in top 0-50 cm soils of agricultural systems was in the
order: irrigated lands with manure application (52.77 t ha-1) > irrigated lands without manure
application (44.47 t ha-1) > dry lands with manure application (37.79 t ha-1) > dry lands without
manure application (26.46 t ha-1). It was observed that adoption of appropriate soil and crop
management practices such as conservation tillage, good irrigation, incorporation of crop residues
and application of manure etc. could enhance soil C pool by reducing existing carbon loss and
promoting C accumulation in the soil.

Full text

258 NAGARAJA et al. [Journal of Soil & Water Conservation 15(3)
Journal of Soil and Water Conservation 15(3): 258-264, July-September 2016
ISSN: 022-457X
Soil carbon stocks in natural and man-made agri-horti-
silvipastural land use systems in dry zones of Southern India
M.S. NAGARAJA1, A.K. BHARDWAJ2 *, G.V.P. REDDY3,
V.R.R. PARAMA3 and B. KAPHALIYA4
Received: 16 May 2016; Accepted: 6 August 2016
ABSTRACT
A study was undertaken to assess the soil carbon stocks in 0-50 cm soil depth, under natural and
man-made land use systems in the eastern dry zones of Karnataka in India. The carbon (C) stocks
in soils ranged from 26.46 t ha-1 in dry land agricultural systems (without manure) to 89.20 t ha-1 in
a mixed forest. Among natural systems, mixed forest (89.20 t ha-1) and ungrazed grassland (71.78 t
ha-1) recorded higher levels of C stock than other systems, while grazing in grassland and litter
removal in teak plantations correlated to reduced carbon stocks to 39.32 and 32.74 t ha-1, respectively.
Intensively managed horticultural systems namely, grapes plantation (85.52 t ha-1) and pomegranate
plantation (78.78 t ha-1) maintained higher levels of C stock. However, agricultural systems recorded
moderate to lower levels. Total carbon stocks in top 0-50 cm soils of agricultural systems was in the
order: irrigated lands with manure application (52.77 t ha-1) > irrigated lands without manure
application (44.47 t ha-1) > dry lands with manure application (37.79 t ha-1) > dry lands without
manure application (26.46 t ha-1). It was observed that adoption of appropriate soil and crop
management practices such as conservation tillage, good irrigation, incorporation of crop residues
and application of manure etc. could enhance soil C pool by reducing existing carbon loss and
promoting C accumulation in the soil.
Key words: Soil carbon, land use systems, residue recycling, forest, horticulture, grassland.
1Associate Professor, College of Horticulture, University of Horticultural Sciences, Bagalkot-587102, Karnataka; 2Senior Scientist,
ICAR-Central Soil Salinity Research Institute, Karnal-132001, Haryana; 3Research Scholar, Department of Soil Science, University
of Agricultural Sciences, Bangalore -587165, Karnataka; 4Research Associate, ICAR-CSSRI, Karnal, Haryana, India; E-mail:
ak.bhardwaj@icar.gov.in
INTRODUCTION
Evidences are mounting that better soil
management practices could contribute
substantially to the mitigation of atmospheric
carbon dioxide emissions (Yan et al., 2005; Xu et al.,
2011). Conversion of natural ecosystems to
agriculture in the last century has contributed to
the extent of one sixth of atmospheric greenhouse
gases through reduction in standing (vegetation)
carbon (C) and soil C stocks (Tilman et al., 2002).
Soil C constitutes a major pool in global C cycle
(Scharlemann et al., 2014). It is estimated that the
Soils contain about 1550 Pg organic carbon and 950
Pg inorganic carbon in the upper 1m of soil layer
(Lal, 2004). It is also well established that these
trends could be reversed through management and
land use changes (Robertson et al., 2015). The
carbon stored in soil of an ecosystem is controlled
by the quality and quantity of biomass added and
its loss through decomposition. The rate of C
accumulation or loss from soil is determined by
the quantity of recyclable biomass-C, temperature,
rainfall, soil moisture content and management
induced disturbances (Delon et al., 2015; Mills et
al., 2014; Bhardwaj et al., 2016). The carbon content
is generally higher in the surface layer than deeper
sub-surface layers as much of the plant and animal
dead material reach the surface directly. Finally,
the rate of C accumulation in soil is significantly
controlled by the net balance between inputs and
outputs per unit time (Fang et al., 2015). Adoption
of suitable management practices viz., conservation
tillage, good irrigation practices, incorporation of
crop residues, manure application etc. can enhance
soil C pool by decreasing C losses and encouraging
its sequestration in soil (Jarecki and Lal, 2003;
Bhagat et al., 2003). Important soil functions that
are affected by agricultural land use are primary

July-September 2016] SOIL CARBON STOCKS 259
productivity, carbon storage and cycling, nutrients
cycling and water purification and regulation
(Bouma et al., 2014; Schulte et al., 2014).
Thus, soil can act as a large terrestrial sink of
atmospheric CO2 but the storage of C in soil is
affected by the land use: crops/plant species, tillage
and crop management, residue removal and
incorporation and irrigation practices. Knowing
the effect of these variables helps in land use
planning as well as in accounting of C stocks at
regional level. Keeping these in view, a study was
undertaken in the Eastern dry zone of Karnataka
in India to assess the soil carbon stocks (0-50 cm
soil) under different land use systems, both natural
and manmade, comprising of forests, grasslands,
horticultural and agricultural systems.
MATERIALS AND METHODS
Study Area and land use systems
The soils of the study area originated from
granite and gneiss, and are classified as Kaolinitic,
isohyperthermic, belonging to Typic Kandiustalf.
The study area is situated at a latitude of 12o 58’ N
and longitude of 77o 35’ E at an elevation of about
930 MSL. The climate that prevailed was cool
summer and warm winter with bimodal
distribution pattern and a mean annual rainfall of
844 mm.
The forest systems comprised of mixed forest
(>20 tree species) and a teak plantation. The
grassland systems studied consisted of two natural
grassland patches with and without grazing, and
one man made napier patch. Horticultural systems
included mango plantations with complete in situ
litter turnover, and intensively managed grapes
and pomegranate plantations. Agricultural
systems comprised of both irrigated and dryland
systems, with and without farmyard manure
(FYM) along with recommended doses of
fertilizers. Detailed descriptions of each land use
system are given in Table 1.
Quantification of biomass produced and recycled
Quantity of biomass produced, removed and
recycled were determined separately for each land
use system. In grassland systems, the above ground
biomass was harvested from one square meter
while the below ground biomass was removed by
digging and the roots were washed thoroughly and
dried. Quantity of biomass was expressed on dry
weight basis. Similarly, in grazed and napier
grasslands the stubble and root biomass left after
grazing/harvest were quantified. Biomass
quantification was restricted only to annual litter
turnover in forest systems as the methodology for
annual root biomass estimations are not available.
The litter samples were collected from one square
meter area at a regular interval to get the annual
Cultivation (C); Irrigation (IR); Weedicide (W); Pesticides (P); Fertilization (F); Manuring (M); Harvesting (H); Grazing (G).
Land use systems Vegetation System Management Practices Biomass Removed
Grassland Systems
Ungrazed Grasses Natural None None
Grazed Grasses Natural G Grasses
Napier Grasses Manmade C, F, H Grasses
Forest Systems
Mixed Trees, Bushes Natural None None
Teak Teak Manmade Litter Removal Litter
Horticultural Systems
Grapes Grapes Manmade C, IR, P, W, F, M, H Fruits + Cane
Pomegranate Pomegranate Manmade C, IR, P, W, F, M, H Fruits
Mango Mango Manmade C, P, F, H Fruits
Agricultural Systems
Irrigated Plots Finger Millet Manmade C, IR, M, F, H, W, P Grain + Straw
(Fert. + FYM) + Corn
Irrigated Plots Finger Millet + Manmade C, IR, F, H, W, P Grain + Straw
(Only Fert.) Corn
Dryland Plots Finger Millet Manmade C, M, F, H, W, P Grain +Straw
(Fert. + FYM)
Dryland Plots Finger Millet Manmade C, F, H, W, P Grain + Straw
(Only Fert.)
Table 1. Details of the studied land use systems.

260 NAGARAJA et al. [Journal of Soil & Water Conservation 15(3)
turnover (Shylaja et al., 1993).
The biomass produced in horticultural systems
was quantified by collecting the litter samples from
one square meter and recording the annual fruit
yield. Annual root biomass was not estimated in
these systems, as the destructive method of
sampling would result in large economic losses.
In agricultural systems, the quantity of fodder and
grain produced were used from the actual yield
data and the biomass left in the field after the
harvest of the crop was determined as detailed in
grasslands.
Soil sampling and estimation of soil-C stocks
Three sampling sites were chosen for each land
use system. In each site, soil samples were collected
from 3 different spots at 0-15, 15-30 and 30-50 cm
depths and the samples were pooled to get
composite samples for each depth separately.
These composite soil samples (depth wise) were
air dried and passed through 2 mm sieve for further
analyses. The soil present in 0-50 cm layer was
determined by measuring the bulk density of soils
for three depths separately and the carbon content
for the collected soil samples were determined by
adopting modified Walkley and Black (1934) wet
oxidation method. Soil carbon stock was estimated
by considering the soil bulk density and fine
fractions.
Statistical analysis
All parameters were tested using a one-way
analysis of variance (ANOVA) and separation of
means was subjected to Tukey’s honestly
significant difference test (Steel and Torrie, 1960).
Correlation analysis was conducted to identify
relationships between the measured parameters.
All tests were performed at 0.05 significance level.
RESULTS AND DISCUSSION
Biomass produced and recycled
The data on the quantity of biomass produced,
removed and recycled annually among different
land uses systems are given in Table 2.
Biomass Production: Among 12 different land
use types, pomegranate orchards recorded the least
biomass production with 3.6 t ha-1, while irrigated
agricultural systems with two crops of finger millet
and maize, supplemented with manures and
fertilizers, produced 30.0 t ha-1 of biomass. In
grassland systems, the annual biomass production
ranged from 6.0 - 13.8 t ha-1 with least production
in grazed land and the highest in napier grassland.
Irrigated agricultural systems recorded very high
biomass production compared to dryland systems.
The moisture limitations in dryland restricted the
cropping to only one crop per year, which was able
* Biomass produced included litter, fruit, grain, straw and root; ‡ biomass removed included grain, fodder, litter and fruit; § Residue
biomass recycled included roots and stubble in annuals and only litter (leaves + twigs) in perennial trees; † Net organic matter (OM)
recycled = Residue BM recycled + FYM added; # Below ground BM produced / recycled not considered.
Land use system *Biomass ‡Biomass §Residue BM FYM †Net OM
Produced Removed Recycled added Recycled
Grassland Systems
Ungrazed 6.7 0.0 6.7 0.0 6.7
Grazed 6.0 3.5 2.5 0.0 2.5
Napier 13.8 7.0 6.8 0.0 6.8
Forest Systems
Mixed#6.7 0.0 6.7 0.0 6.7
Teak#5.2 4.2 1.0 0.0 1.0
Horticultural Systems
Grape#7.2 7.1 0.1 50.0 50.1
Pomegranate#3.6 2.4 1.2 12.5 13.7
Mango#5.4 1.0 4.4 0.0 4.4
Agricultural Systems
Irrigated (FYM + Fert.) 30.0 20.0 10.0 15.0 25.0
Irrigated (Fert. Alone) 24.9 17.5 7.5 0.0 7.5
Dryland (FYM +Fert.) 17.1 10.5 6.6 10.0 16.6
Dryland (Fert. Alone) 8.2 3.4 4.8 0.0 4.8
Table 2. Quantity of in-situ and ex-situ annual biomass turnover (t ha-1) among different land use systems.

July-September 2016] SOIL CARBON STOCKS 261
to produce 8.2 and 17.1 t ha-1 of biomass. The litter
biomass (fallen leaves and stems) ranged from 3.6
- 7.2 t ha-1 among land use systems with perennial
trees. Natural mixed forest recorded 7.2 t of litter
biomass, while teak plantations produced 5.2 t of
litter per hectare. In case of horticultural systems,
the above ground biomass produced in grape and
mango orchards were 7.2 t ha-1 and 5.4 t ha-1,
respectively.
Residue biomass recycled
Land management practices adopted in a given
system determine extent of the biomass recycling.
There was no removal of biomass in the non-grazed
grasslands and mixed forests, and hence, all the
biomass produced was allowed to recycle. While
in grazed land, 3.5 t ha-1 of grass biomass were
removed as fodder and hence, only 2.5 t ha-1 of
biomass was allowed to recycle in the form of
stubble and roots. Among irrigated agricultural
systems, biomass was removed (grain and fodder)
to an extent of 20.0 t ha-1 in fertilizer and FYM
treated plots and 17.5 t ha-1 in no-FYM plots (only
fertilizer). Thus, the quantity of biomass allowed
to recycle was 10.0 and 7.5 t ha-1, respectively.
However, the moisture limitations in dryland
restricted the turnover to 6.6 and 4.8 t ha-1,
respectively in plots with fertilizer plus manure
and fertilizer alone plots. Among tree based
perennial systems, mixed forest recorded an in situ
biomass turnover of 6.7 t ha-1. Litter removal in
teak plantations, to prevent fire damages, resulted
in a biomass turnover of mere 1.0 t ha-1. Extraction
of fruits was the major source of biomass removal
in horticultural systems except in grapes, where
the biomass was also removed in the form of canes
and leaves during pruning operations. Thus, the
management practices adopted in a given system
and the quantity of biomass recycled is likely to
have an influence on the net soil carbon stocks.
Net organic matter recycled
In manmade agricultural and horticultural
systems, unlike the natural ones, organic matter
was added in the form of compost/manure to
maintain yield and quality. Thus, the net organic
matter recycled would be the sum of residue
biomass and manure. The net organic matter
recycled was as high as 50.1 t ha-1 in grape orchard
and it was low in pomegranate plots with a net
turnover of 13.7 t ha-1. However, there was no
addition of manure to mango and thus the biomass
recycled was equal to the net organic matter
recycled. In FYM treated agricultural systems,
irrigated lands recorded a net biomass turnover of
25.0 t ha-1 while, dryland system recorded 16.6 t
ha-1. However, the net biomass recycled among no-
FYM plots (only fertilizer applied), in both irrigated
and dryland agricultural systems, were equal to
that of residue biomass recycled. Application of
organic sources enhances all the pools of soil carbon
(Khursheed et al., 2013) indicating recycling of
organic matter. Similarly, the net biomass recycling
was unchanged in ungrazed grassland and forest
systems as there was no addition of organic matter
from external sources.
Soil carbon stocks
The data on seasonal changes in soil organic-C
under different land use systems at various depths
are given in Table 3. The amount of total soil carbon
stocks present in 0-50 cm of soil layer is depicted
diagrammatically in Fig. 1. The surface soils (0-15
cm) of all land use systems in all the three seasons
recorded highest soil organic-C. In general, the soil
organic-C was higher in winter season and lower
in summer.
Carbon present in these soils is mostly organic
in nature and is present in the form of humus coat
over soil particles. It decreased with depth in all
the treatments and it differed significantly among
treatments as well as seasons (Table 3). There are
no records of elemental carbon in these soils as
Fig. 1. Soil carbon stocks among different land use systems.
UG = Ungrazed grasses, GG = Grazed grasses, NG =
Napier grass, MF = Mixed forest, TF = Teak Forest, GH =
Horticultural plantation-Grape, PH = Horticultural
plantation-Pomegranate, MH = Horticultural plantation-
Mango, IR-1 = Irrigated agricultural system with FYM and
fertilizer, IR-2 = Irrigated agricultural system with fertilizer
alone, DL-1 = Dryland agricultural system with FYM and
fertilizer, and DL-2 = Dryland agricultural system with
fertilizer alone.

262 NAGARAJA et al. [Journal of Soil & Water Conservation 15(3)
there are no natural deposits of coal/coke.
Higher level of carbon was recorded in mixed
forest patches (2.91 %) during rainy season and
lowest was observed during summer in dryland
agricultural plots with no FYM. Among the
systems, based on mean depths and season, the
ungrazed control plot (1.24 %), grapes (1.36 %),
pomegranate orchards (1.24 %) and mixed forests
(1.70 %) systems recorded more than 1.0 % of soil
organic-C. Moderate levels of soil organic-C were
observed among other systems except teak
plantations (0.46 %) and dryland plots receiving
only fertilizers (0.38 %). The variations in soil
organic-C among different land use systems would
be attributed to the net biomass turnover and land
management practices adopted in the system (Post
and Kwon, 2000). Influence of management
practices and biomass addition/turnover on soil
carbon stocks is well documented (Liao et al., 2010).
The amount of soil carbon present in the form
of humus is a function of bulk density and soil
organic-C content. It was determined using the soil
volume and its corresponding soil organic-C
contents. The amount of carbon stored in the top
0-50 cm soil layer ranged from 32.7 t ha-1 in teak
plantations to 89.5 t ha-1 in mixed forest. Similarly,
the soil carbon stock in ungrazed grassland (71.8 t
ha-1) was higher than grazed (39.3 t ha-1) and napier
(42.5 t ha-1) grasslands. The data also indicate that
the quantity of carbon stored in horticultural
systems was much higher than the disturbed forest
and grassland ecosystems. The amount of soil
carbon present in top 0-50 cm soil layer was 85.5,
78.8 and 51.6 t ha-1 in grapes, pomegranate and
mango systems respectively. Interestingly, the soil
carbon stocks was almost near to that of disturbed
natural systems and lesser than horticultural
systems. Irrigated agricultural systems had stored
52.8 t ha-1 in FYM and fertilizer treated plots
compared to 44.5 t ha-1 in fertilizer alone treated
plots. Similar trend was observed in dryland
agricultural systems with much lesser quantities
of humus carbon. The corresponding values in
dryland agricultural systems were 37.8 t ha-1 (with
manure and fertilizer) and 26.5 t ha-1 (with fertilizer
alone).
Soil organic-C of any ecosystem is determined
by the quality and quantity of C-inputs through
biomass addition (Liu et al., 2014) and its loss
through decomposition (Zhu et al., 2014, Toosi
et al., 2014). Larger the biomass turnover higher
would be the soil organic carbon. Large carbon
stocks were observed in natural forest and
ungrazed grasslands and it could be attributed to
high biomass turnover and no disturbances.
However, manmade napier and grazed grasslands
recorded much lower carbon stocks than ungrazed
plots. Reduction in soil organic-C in napier
grasslands could be due to regular cultivation
practices adopted (Panagos et al., 2015) and higher
soil temperature as the surface was not covered
most of the time (Hopkins et al., 2014). Litter
removal in teak plantation to prevent fire damages
might have severely reduced the soil carbon stocks.
Table 3. Seasonal changes in soil organic carbon (per cent) under different land use systems.
Land use system Winter Summer Rainy
SOIL ORGANIC CARBON (%)
Grassland Systems
Ungrazed 1.27 1.28 1.17
Grazed 0.56 0.52 0.60
Napier 0.62 0.71 0.52
Forest Systems
Mixed 1.85 1.58 1.68
Teak 0.38 0.56 0.45
Horticultural Systems
Grape 1.41 1.39 1.28
Pomegranate 1.32 1.40 1.01
Mango 0.67 0.89 0.69
Agricultural Systems
Irrigated (FYM +Fert) 0.96 0.59 0.79
Irrigated (Fert. Alone) 0.74 0.51 0.64
Dryland (FYM +Fert) 0.62 0.52 0.54
Dryland (Fert. Alone) 0.35 0.38 0.39
The values indicated are the mean of three depths.

July-September 2016] SOIL CARBON STOCKS 263
Agroforestry system results in leaf litter fall that
recycles the C as well as nutrients to the soil
(Solanki and Arora, 2015). This suggests that the
cultivation and removal of surface cover would
reduce soil carbon through enhanced decomposition
rates (Sayer, 2006; Leff et al., 2012; Fekete et al.,
2014).
CONCLUSION
The carbon preserved in the form of humus on
soil particles could be used effectively as a mean
to sequester atmospheric CO2 and hence in
mitigating global warming effects. The amount of
carbon stored is determined by the quality and
quantity of biomass added and its loss through
decomposition. Deforestation, expansion of
agriculture, shifting cultivation, irrigation etc.
would lead to oxidation of organic matter in soil.
These processes would result in CO2 release,
leading to increased concentration of CO2 in the
atmosphere. However, substantial carbon
accumulation can also occur in soil with increase
in biomass turnover and reduction in mechanical
disturbances. Thus, adoption of conservation
tillage, good irrigation practices, crop residue
incorporation, manure application etc. could
enhance soil carbon to a great extent by decreasing
the loss of existing carbon mass and encouraging
carbon accumulation. Results of the present study
clearly indicate that there is a great scope to
mitigate atmospheric CO2 through better land
management practices.
ACKNOWLEDGEMENT
We acknowledge the help of the Department of
Soil Science, University of Agricultural Sciences,
Bangalore and Centre for Ecological Sciences,
Indian Institute of Science, Bangalore, for
providing requisite facilities to carry out this
research.
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