www.elsevier.com/locate/still
Soil & Tillage Research 92 (2007) 87–95
Carbon sequestration and relationship between carbon addition
and storage under rainfed soybean–wheat rotation in a
sandy loam soil of the Indian Himalayas
S. Kundu, Ranjan Bhattacharyya *, Ved Prakash, B.N. Ghosh 1, H.S. Gupta
Vivekananda Institute of Hill Agriculture (Indian Council of Agricultural Research), Almora 263601, Uttaranchal, India
Received 23 February 2005; received in revised form 19 January 2006; accepted 27 January 2006
Abstract
Soil organic matter (SOM) contributes to the productivity and physical properties of soils. Although crop productivity is
sustained mainly through the application of organic manure in the Indian Himalayas, no information is available on the effects of
long-term manure addition along with mineral fertilizers on C sequestration and the contribution of total C input towards soil
organic C (SOC) storage. We analyzed results of a long-term experiment, initiated in 1973 on a sandy loam soil under rainfed
conditions to determine the influence of different combinations of NPK fertilizer and fertilizer + farmyard manure (FYM) at
10 Mg ha�1 on SOC content and its changes in the 0–45 cm soil depth. Concentration of SOC increased 40 and 70% in the
NPK + FYM-treated plots as compared to NPK (43.1 Mg C ha�1) and unfertilized control plots (35.5 Mg C ha�1), respectively.
Average annual contribution of C input from soybean (Glycine max (L.) Merr.) was 29% and that from wheat (Triticum aestivum L.
Emend. Flori and Paol) was 24% of the harvestable above-ground biomass yield. Annual gross C input and annual rate of total SOC
enrichment were 4852 and 900 kg C ha�1, respectively, for the plots under NPK + FYM. It was estimated that 19% of the gross C
input contributed towards the increase in SOC content. C loss from native SOM during 30 years averaged 61 kg C ha�1 yr�1. The
estimated quantity of biomass C required to maintain equilibrium SOM content was 321 kg ha�1 yr�1. The total annual C input by
the soybean–wheat rotation in the plots under unfertilized control was 890 kg ha�1 yr�1. Thus, increase in SOC concentration under
long-term (30 years) rainfed soybean–wheat cropping was due to the fact that annual C input by the system was higher than the
required amount to maintaining equilibrium SOM content.
# 2006 Elsevier B.V. All rights reserved.
Keywords: Carbon sequestration; Carbon addition and storage; Farmyard manure; Soybean–wheat cropping; Sandy loam soil; Sub-temperate
Indian Himalayas
1. Introduction
Sustaining soil organic matter (SOM) is of paramount
importance in terms of cycling plant nutrients and
improving the soil’s physical, chemical and biological
* Corresponding author. Tel.: +91 9412996534;
fax: +91 5962 241005.
E-mail address: [email protected] (R. Bhattacharyya).1 Present address: Central Soil Water Conservation and Research
and Training Institute, Dehradoon, Uttaranchal, India.
0167-1987/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.still.2006.01.009
properties. Maintenance of soil organic C (SOC) is
essential for long-term sustainable agriculture, since
declining levels generally lead to decreased crop
productivity (Allison, 1973). Soil organic C is an
important index of soil quality because of its relationship
to crop productivity (Campbell et al., 1996; Lal et al.,
1997). Optimum levels of SOM can be managed through
crop rotation, fertility maintenance including use of
inorganic fertilizers and organic manures, tillage
methods, and other cropping system components
(Huggins et al., 1995; Janzen et al., 1998). As SOC
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–9588
Table 1
Soil properties of initial conditions
Properties Soil depth (cm)
0–15 15–30 30–45
pH (soil:water, 1:2.5) 6.2 6.1 NA
EC (dS m�1) 0.08 0.07 NA
CEC [cmol (p+) kg�1 soil] 8.7 NA NA
Bulk density (Mg m�3) 1.32 1.33 1.36
Total organic C (g kg�1 soil) 5.8 5.6 5.3
C:N 12.8 12.1 12.3
Available N (mg kg�1 soil) 127 (125) 119 88
Available P (mg kg�1) 12 (7) 10 7
Available K (mg kg�1) 65 (55) 59 48
Texture Sandy loam Sandy loam NA
Data in parentheses indicate the critical values. NA: not available.
changes are generally directly related to the quantity of
crop residues returned to the land, agronomic practices
that influence yield and affect the residues returned to soil
are likely to influence SOC (Campbell et al., 1997, 2000).
Many studies have indicated a strong positive
relationship between the amount of C incorporated
into soil, either from crop residues or from external
sources such as manure, and total SOC content
(Paustian et al., 1992; Havlin et al., 1990). Changes
in SOC were linearly related to gross C input to the soil
(Rasmussen and Collins, 1991; Buyanovsky and
Wagner, 1998). Annual C input was 22% of the
harvestable above-ground biomass of soybean in a
Vertisol in Central India (Kundu et al., 2001). However,
there are no data on quantifying rhizodeposition in
soybean using tagged C (14C), although many reports
are available on other crops including wheat. In a green
house study with 11 plant species, Shamoot et al. (1968)
reported that rhizodepositon of C from root turnover
and exudates represented 5–20% of the above-ground
biomass. However, in soybean around 13% of the total
biomass (roots and tops) was found in roots alone by
Kemper et al. (1998).
The net change in SOC depends not only on the
current management practices but also on the manage-
ment history of the soil. Long-term experiments are the
primary source of information to determine the effect of
cropping systems, continuous cropping, and retention of
residues in soils and fertilizer/manure addition on
changes in SOC (Leigh and Johnston, 1994). These
experiments are usually the only source of information
for determining agricultural sustainability (Barnett
et al., 1995) and to define land use effect on SOC
(Paul et al., 1997). For getting meaningful estimates of
the rate of added biomass incorporation into SOM and
decay rates of native SOC, it is desirable to have
experiments with full records of gross C inputs into the
soil through various sources. Therefore, quantification
of SOC in relation to various soil management practices
is of value in identifying the pathways of C sequestra-
tion in soils.
Several experiments began in the 1970s in Asian
countries under tropical conditions with rice (Oryza
sativa L.) and wheat system under irrigated conditions.
The data of many such experiments have been analyzed,
but mostly restricted to yield trends and soil nutrient
status (N, P and K) and SOC content. Several authors
suggested declining rice and wheat yields due to gradual
decline in the supply of soil nutrients and SOC (Cassman
et al., 1995; Yadav et al., 1998, 2000; Duxbury et al.,
2000). Others reported an increase in SOC due to addition
of organic sources of nutrients along with high inputs of
NPK fertilizers (Gami et al., 2001; Bhandari et al., 2002).
We found no report of C sequestration, the relationship
between C addition and storage and estimation of decay
rates of native SOC under sub-temperate climate of the
Indian Himalayas with low input agriculture. Hence our
objectives were: (i) to quantify the effects of different
combinations of mineral fertilizer application and FYM
addition along with mineral fertilizers on C sequestra-
tion, and (ii) to establish a relationship between annual C
addition and storage.
2. Materials and methods
2.1. Experimental site
A long-term field experiment was initiated in June
1973 on a Typic Haplaquept at the experimental farm of
Vivekananda Institute of Hill Agriculture, located in the
Indian Himalayan region at Hawalbagh (298360N and
798400E with 1250 m above mean sea level), in the state
of Uttaranchal, India. Initially the purpose of the
experiment was to study the effect of manure
application along with fertilizers on yield of rainfed
soybean–wheat cropping and soil nutrient status. Soil
characteristics based on analysis of preserved soil
samples taken in 1973 are given in Table 1. The climate
is sub-temperate, characterized by moderate summer
(May–June), extreme winter (December–January) and
general dryness, except during the southwest monsoon
season (June–September). Based on the records for the
period 1973–2003, average kharif (monsoon) season
rainfall was 704 mm (e.g., 68% of the average annual
rainfall). During soybean growth, average monthly
rainfall (mm) was: June (146); July (257); August (187)
and September (119), whereas, during wheat growth
average monthly rainfall (mm) was: October (27);
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–95 89
November (6); December (28); January (53); February
(56); March (48) and April (42). The mean monthly
temperature ranged from a minimum of 0.4 8C in
January to a maximum of 31.5 8C in May. The field was
newly reclaimed for cultivation in 1973. Prior to 1973,
the field was native grassland that was yearly cut and
grazed.
2.2. Experimental design
The experiment included two crops per year, soybean
(June–September) and wheat (October–April), with six
treatment combinations (in kg ha�1): no fertilizer and no
manure (unfertilized control); 20 N + 35 P (NP); 20
N + 33 K (NK); 20 N + 35 P + 33 K (NPK), 20 N +
FYM at 10 Mg ha�1 (N + FYM, commonly used by
the local farmers) and NPK + FYM at 10 Mg ha�1
(NPK + FYM). Treatments were distributed in a ran-
domized block design with six replications over three
uniformly level terraces. The net plot size was
5.4 m � 2.0 m. Fertilizers used were urea for N, single
super-phosphate for P and murate of potash for K. Based
on the chemical analysis of every fifth year, FYM had
370 g moisture kg�1 and contained 7.1–7.5 g N kg�1,
2.1–2.4 g P kg�1 and 5.3–5.8 g K kg�1 on oven-dry
weight basis.
2.3. Crop management
Farmyard manure (10 Mg ha�1 on a fresh weight
basis) and fertilizers were applied before sowing of
soybean. Soybean (80 kg seed ha�1) was sown in early
June each year after the land was tilled twice by hand
with a spade to a depth of 15 cm. Soybean cultivar
‘‘Bragg’’ was used from 1973 to 1998 and thereafter it
was replaced with VLS 2 (1999–2002). The crop was
sown in rows 40 cm apart to a depth of 4–5 cm by hand.
Propanil (3,3,4-dichloro-propionanilide) was sprayed
two days after sowing at the rate of 1.5 kg a.i. ha�1 in all
plots to control weeds. Other plant protection measures
were taken as needed to control diseases and pests for
both crops. Soybean was harvested manually just above
the ground in the first week of October using sickles and
above-ground biomass was removed from the field.
Grain yield was adjusted to 90 g moisture kg�1 for
soybean.
Wheat was grown on residual fertility. Wheat (cultivar
Sonalika from 1973–1974 to 1988–1989; VL 421 from
1989–1990 to 1998–1999; VL 616 from 1999–2000 to
2002–2003) was sown (100 kg seed ha�1) in rows
22.5 cm apart to a depth of about 5–6 cm by hand in
early October each year. Other field operations were as
with soybean. Wheat was harvested at 5 cm above the
soil surface in late April and straw was removed from the
plots and dry weights were recorded. Wheat straw below
5 cm (stubble) was incorporated into the soil during land
preparation for soybean. Grain yield was adjusted to
120 g moisture kg�1 for wheat.
2.4. Soil and plant sampling and analysis
Initial soil samples were collected in 1973 prior to
the start of the experiment. Soil was analyzed for pH in
1:2.5 soil:water suspension (Jackson, 1973), oxidizable
SOC by the method of Walkley and Black (1934), total
SOC (from the stored soil samples) by dry combustion
(Nelson and Sommers, 1982) with a CHN analyzer,
total N by standard procedure using a FOSS Tecator
(Model 2200), available P following the method of
Olsen et al. (1954), and available K by 1 N NH4OAc
using a flame photometer (Jackson, 1973). Core sampler
was used for soil bulk density determination. Soil
texture was determined by Bouyoucos hydrometer
(Bouyoucos, 1927).
After the harvest of wheat in 2003, depth-wise (0–15,
15–30 and 30–45 cm) triplicate soil samples were
collected from all plots, combined, ground, dried
(65 8C) passed through 0.2-mm sieve, and total C
content measured. Soil organic C concentrations were
converted from g kg�1 to Mg C ha�1 using measured
soil bulk density. Annual rate of change in SOC
concentration over initial soil condition was calculated.
Soil organic C sequestration in different treatments was
calculated as the net increase of SOC content
(Mg C ha�1) over the unfertilized control (Aulakh
et al., 2001).
Using biomass yield of soybean and wheat, annual
inputs of C added to the soil was computed. In case of
soybean, unmeasured biomass was through leaf-fall,
roots and nodules. Leaf-fall from all treatments was
manually collected during the last 5 years of experi-
mentation from 45 days after sowing until harvest, dried,
and dry weight recorded. Root and nodule biomass of
soybean were calculated using the root/shoot and nodule/
root biomass ratios recorded from a pot experiment
(Kundu et al., 2001). The pot experiment was conducted
using 10 kg capacity earthen pots filled with soil
collected during 1999–2002 from the field experiment.
The treatment-wise soil samples collected from the field
experiment were processed to pass through 2.0-mm sieve
and equivalent amounts of fertilizer and manure were
applied as per the treatments. After harvest of above-
ground biomass (shoot), soil was removed gently by
placing the pot on a sieve and washed slowly using a
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–9590
Table 2
Soil bulk density and organic C at 0–45 cm as affected by 30 years of
fertilizer application in a rainfed soybean–wheat rotation
Treatments Soil bulk density
(Mg m�3)a
Soil organic C
Concentration
(g kg�1 soil)
Amount
(Mg ha�1)
Initial soil 1.34 5.54 33.3
Control 1.31 6.01 35.5
NP 1.28 6.70 38.7
NK 1.30 6.45 37.6
NPK 1.28 7.51 43.1
N + FYM 1.26 9.63 54.7
NPK + FYM 1.25 10.76 60.3
L.S.D. (P = 0.05) 0.02 0.09 0.8
a Soil bulk density at 0–45 cm layer = average soil bulk density of
0–15, 15–30 and 30–45 cm soil layers.
water jet. Root biomass with entangled nodules was
recovered, dried, and dry weights of root and nodules
recorded. From dry weights, root/shoot and nodule/root
ratios were estimated.
During 1999–2002, soybean leaves were collected
after senescence, nodules were excavated on 65 days
after sowing, and roots were excavated at 85 days after
sowing. Samples were analyzed for total C content using
a CHN analyzer for calculation of C inputs. Rhizode-
position of C from root turnover and exudates was
assumed to be 10% of the harvestable above-ground
biomass of soybean (Shamoot et al., 1968). Organic C of
FYM was 22% C on oven-dry weight basis.
Wheat biomass to soil was through stubble (3–4% of
the straw yield) and roots [30% of the harvestable
above-ground biomass as observed by Chander et al.
(1997)]. Samples of stubble and roots of wheat were
collected after harvest (1999–2000 to 2002–2003) from
all the plots and C inputs through stubble and roots were
calculated based on C determination with a CHN
analyser. The contribution of C through rhizodeposition
from wheat was estimated by multiplying the values of
total root C inputs with a factor of 1.4 as observed by
Regmi (1994). During growth of soybean and wheat,
weeds were removed so that C input from roots and
rhizodeposition by the weeds were not considered.
The relationship between C addition to the soil by
different sources and storage within the soil was
determined. The rate constant of annual C inputs
incorporated into SOM (h) and decay rate constant (k)
of native SOC were calculated from the following
equation (Jenkinson, 1988) assuming a single-pool, first-
order kinetic relationship between C addition and storage
dCs
dt¼ hA� kSOC (1)
where SOC is the soil organic C, t is time, and A is
annual C input to soil. The same first order kinetic
equation was also used by Parton et al. (1996) to explain
changes in SOC in terms of C added to the soil, wherein
they termed ‘h’ as ‘carbon storage fraction constant’.
From the single-pool first-order equation we estimated
the quantity of biomass C required to maintain equili-
brium SOC content. For computing the ‘A’ value, we
assumed that whole amount of biomass C from leaf fall
and FYM, and 90% of the biomass C from roots,
nodules and rhizodeposition remained within the 0–
45 cm soil layer for soybean. For wheat, we assumed
80% of the biomass contributed by roots and exudates
remained within 0–45 cm soil depth. Not all the C from
below-ground biomass and root exudates would remain
in the 0–45 cm depth of the soil profile as some C could
leach. Kundu et al. (2001) assumed 70% of the biomass
C from roots, nodules and rhizodeposition of soybean
and 70% of biomass C from roots and rhizodeposition
of wheat remained in the 0–30 cm layer in Central
India. The basis of choosing 10% higher value in case
of soybean over wheat was that the root system of
soybean is shallower than that of wheat. Kemper
et al. (1998) reported that roots of soybean and wheat
extended as deep as 60 and 225 cm, respectively.
Statistical analyses were done using standard
analysis of variance (Gomez and Gomez, 1984).
Treatment means were compared at 5% level of
significance using least significant difference.
3. Results and discussion
3.1. Soil bulk density
Soil bulk density (BD) was lower with FYM than
with inorganic fertilizers only or the unfertilized control
(Table 2). Highest BD was under the unfertilized
treatment at 30–45 cm depth (1.33 Mg m�3) and lowest
BD (1.24 Mg m�3) was under NPK + FYM treatment at
0–15 cm depth. Application of FYM might have
impacted soil aggregation, thereby reducing BD.
Reduction in soil BD with organic matter additions is
well documented (Sharma et al., 1995). Soil BD
decreased with FYM application due to higher SOC and
increased root biomass (Halvorson et al., 1999) that
resulted in better soil aeration and improvement of soil
structural properties.
3.2. Plant derived C inputs to soil
The highest mean harvestable above-ground biomass
of soybean (Table 3) and wheat (Table 4) was observed
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–95 91
Table 3
Annual input of soybean above-ground biomass (1973–2002), leaf-fall (1998–2002) and roots and nodules (1999–2002) under different fertilizer
treatments
Treatments Havestable above-ground biomass
(shoot) yield (kg ha�1)
Annual addition of biomass to soil (kg ha�1)
Leaf-falla Rootb Nodulec
Control 1307 124 549 62
NP 2139 344 898 103
NK 1601 115 672 78
NPK 3440 757 1280 196
N + FYM 5749 1150 1748 262
NPK + FYM 7024 1271 2374 318
L.S.D. (P = 0.05) 291 48 112 15
a From the pot experiment, we estimated that under the unfertilized control, NP, NK, NPK, N + FYM and NPK + FYM-treated plots, the leaf-fall
biomass constituted 9.5, 16.1, 7.2, 22.0, 20.0 and 18.1% of the harvestable above-ground biomass, respectively.b Under unfertilized control, NP, NK, NPK, N + FYM and NPK + FYM treatments, root biomass constituted 42, 42, 42, 37, 30 and 34% of the
harvestable above-ground biomass, respectively.c Under unfertilized control, NP, NK, NPK, N + FYM and NPK + FYM treatments, nodule biomass constituted 11.3, 11.5, 11.6, 15.3, 15.0 and
13.4% of the root biomass of soybean, respectively.
Table 4
Annual input of soybean above-ground biomass (1973–74 to 2002–03), stubble (1999–2000 to 2002–2003) and roots (1973–74 to 2002–03) under
different fertilizer treatments
Treatments Havestable above-ground biomass
(shoot) yield (kg ha�1)
Annual addition of biomass to soil (kg ha�1)
Stubblea Rootb
Control 2119 85 636
NP 2473 84 742
NK 2350 94 705
NPK 3025 91 908
N + FYM 4518 140 1355
NPK + FYM 5414 173 1624
L.S.D. (P = 0.05) 276 10 85
a We estimated that under the unfertilized control, NP, NK, NPK, N + FYM and NPK + FYM-treated plots, the stubble biomass constituted 4.0,
3.4, 4.0, 3.0, 3.1 and 3.2% of the straw yield of wheat, respectively.b We assumed that root biomass constituted 30% of the harvestable above-ground biomass of wheat.
Table 5
Estimated annual C inputs to soil (0–45 cm) from soybean under different fertilizer treatments
Treatments C inputs (kg ha�1)a Annual gross C input into
soil (kg C ha�1)Leaf-fall Root Nodule Rhizodeposition FYM
Control 47 174 18 131 – 371
NP 126 276 28 214 – 643
NK 45 200 22 160 – 427
NPK 291 404 58 344 – 1097
N + FYM 426 543 72 575 1587 3204
NPK + FYM 478 708 89 702 1587 3565
L.S.D. (P = 0.05) 18 35 4 31 – –
a We assumed that entire amount of biomass through leaf fall and FYM and 90% of the biomass contributed by roots, nodule, and rhizodeposition
remained within 0–45 cm soil depth.
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–9592
in the plots under NPK + FYM and the lowest under
unfertilized control. The higher above-ground biomass
in FYM amended soils was probably associated with
other benefits apart from N, P and K supply, such as
improvements in microbial activity (Ved Prakash et al.,
unpublished data) and soil physical conditions (Bhat-
tacharyya et al., unpublished data). FYM applied to rice
had residual positive effects on the next wheat crop
(Yadvinder-Singh et al., 1995).
The average annual total C input to soil from
soybean (Table 5) and wheat (Table 6) varied with
above-ground yield responses of both crops under
different fertilizer application. Roots of soybean crop
contributed the highest amount of annual addition of
biomass to soil. Kundu et al. (1997) also estimated that
root biomass of soybean added the highest amount
(31% of the above-ground biomass) to soil.
Mean C concentration of soybean leaves, roots and
nodules was 38, 34 and 32%, respectively. The roots and
rhizodeposition were major components of estimated C
inputs from soybean (Table 5). Without fertilizer total C
input from soybean was 371 kg ha�1 yr�1. Total C was
1097 kg ha�1 yr�1 with NPK and 3565 kg ha�1 yr�1
with NPK + FYM. Apart from FYM’s own contribution
(1587 kg C ha�1 yr�1); an additional gain of 872 kg
C ha�1 yr�1 occurred under soybean with NPK + FYM
compared to NPK only.
Like soybean, roots and rhizodeposition from wheat
also contributed the highest amount of C input to soil
(Table 6). Total C input from unfertilized wheat was
520 kg ha�1 yr�1 and 1286 kg ha�1 yr�1 from wheat
grown on residual fertility of NPK + FYM. The
residual effect of FYM resulted in an additional gain
of 563 kg C ha�1 yr�1 in wheat over that under NPK
only. The harvestable above-ground biomass yield
of wheat varied due to variation in residual
fertility from different fertilizer treatments applied
to soybean.
Table 6
Estimated annual C inputs to soil (0–45 cm) from wheat under different fe
Treatments C inputs (kg ha�1)a
Stubble Root
Control 36 201
NP 37 238
NK 40 232
NPK 37 286
N + FYM 58 439
NPK + FYM 74 505
L.S.D. (P = 0.05) 4 26
a We assumed that entire amount of biomass through stubbles and 80% of th
soil depth.
Average C input from wheat to soil (Table 6) was
24% of the harvestable above-ground biomass
(R2 = 0.998*, P < 0.01). Kundu et al. (2001) reported
a value of 32%. Kemper et al. (1998) reported a root/
shoot ratio of 0.25 in wheat. In wheat, considerable
amount of C input (on average 445 kg C ha�1 yr�1) to
soil originated from rhizodeposition. Study with 14C
indicated that rhizodeposition during the growing
season of wheat was 30% of the total C accumulated
above-ground (Lucas et al., 1977; Jenkinson and
Rayner, 1977; Keith et al., 1986).
3.3. Soil carbon
Soil organic C concentrations remained positively
changed from the initial values in plots under
unfertilized control (Table 2). This was due to annual
C addition through the roots and crop residues (Ved
Prakash et al., 2002). At the end of 30 years, soils under
NPK + FYM-treated plots contained higher SOC by
43.8 and 40.1% in the 0–15 and 0–45 cm soil layers,
respectively, over NPK-treated plots (Table 2). Total
SOC stocks in the 45 cm layer were 60.3 Mg ha�1 for
NPK + FYM-treated soils compared with 43.1 Mg ha�1
for NPK-treated plots. Thus, there was
573 kg C ha�1 yr�1 increase in SOC contents in the
plots under NPK + FYM treatment as compared to
those under NPK-treated plots. Soil organic C content at
0–45 cm soil layer in the plots under NPK + FYM
treatment was 15% higher than that under N + FYM-
treated plots (Fig. 1).
At the end of 30 years, application of balanced dose
of NPK showed significantly higher SOC (7.51 g kg�1)
over the unfertilized control (6.01 g C kg�1) in 0–45 cm
soil layer. Application of NPK also showed significantly
higher SOC concentrations over either NP or NK. There
was significant improvement in SOC in NP
(6.70 g C kg�1) over NK (6.45 g C kg�1) in the same
rtilizer treatments
Annual gross C input
into soil (kg C ha�1)Rhizodeposition
282 519
333 608
324 596
401 723
614 1111
707 1286
40 69
e biomass contributed by roots and exudates remained within 0–45 cm
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–95 93
Fig. 1. Annual change in soil organic C content during 30 years as affected by different fertilizer treatment.
Fig. 2. Change in SOC content as affected by estimated gross C input
to 0–45 cm depth of soil layer.
depth. Compared with the plots under NPK, total SOC
content increased significantly in plots where N + FYM
or NPK + FYM were applied (Table 2). The plots with
NPK + FYM treatment applied to soybean accumulated
highest SOC concentration (10.76 g kg�1) in 0–45 cm
soil depth, which was 43% higher than that of NPK-
treated plots (7.51 g kg�1) and 12% higher than that of
N + FYM-treated plots (9.63 g kg�1).
The benefits of sequestering SOC to sustain crop
productivity by applying organic amendments have
been well documented in the temperate regions
(Aulakh et al., 2001). In our study, use of both
fertilizers and FYM increased SOC due to increased
yields of roots and plant residues, and the direct
application of organic matter through FYM. Fertilizer
application in the NPK + FYM-treated plots was the
same as in the NPK treated ones. The difference in
SOC, therefore, was a result of added C through entry
of FYM and increased biomass of both the crops. A
larger proportion of the higher C content or C
sequestration in FYM added plots also might have
resulted from slower breakdown rate (less and constant
mineralization rate).
3.4. Rate constant (h) of added biomass C
incorporation into soil organic matter
The annual rate of change in SOC was positively
correlated (P < 0.01) with gross C inputs (Fig. 2). The
intercept (�61.3 kg C ha�1 yr�1) of the equation would
represent the annual loss of C from native SOM.
Equating this intercept with ‘k � Cs’ of the Jenkinson
(1988) equation and setting initial SOC content at
33.3 Mg C ha�1, the decay rate of native SOC was
0.0018. This indicated that C loss from native SOC
during 30 years of cultivation was 0.18% of the initial
SOC content.
3.5. Minimum C input to maintain SOC
When addition of C input to the soil equals loss of C
(i.e, dCs/dt = 0), annual C input was 321 kg ha�1 yr�1.
This amount would be required from plant parts or
manures to be incorporated to maintain SOM content at
equilibrium. Annual loss of C from native SOM in the
Pacific North-west of the USA was 200 to
2000 kg ha�1 yr�1 (Rasmussen and Albrecht, 1998)
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–9594
and in sub-tropical Central India was 888 kg ha�1 yr�1
(Kundu et al., 2001). Our relatively low value at
61 kg ha�1 yr�1 suggests a relatively slow decomposi-
tion rate of native SOM. Under unfertilized conditions,
average productivity (grain + straw yield) of soybean
(1.31 Mg ha�1) and wheat (2.12 Mg ha�1) contributed
C input of 371 and 520 kg ha�1 yr�1, respectively. The
total annual C input under unfertilized control treatment
was nearly three times more than the amount of C input
required (321 kg ha�1 yr�1) to maintain SOM at
equilibrium. So, even removing the above-ground
biomass of both crops, these production levels on
sandy loam soils in the Indian Himalayas would be
sufficient to supply enough C input to soil (provided soil
erosion be checked), so that SOC could be maintained.
4. Conclusion
Long-term (30 years) average (all treatments) above-
ground biomass of soybean and wheat was 3543 and
3317 kg ha�1 yr�1, respectively. The proportion of
mean harvestable above-ground biomass as C input
from soybean and wheat was 29 and 24%, respectively.
Application of inorganic fertilizer resulted in higher
SOC over the unfertilized control, due to greater crop
residue and root biomass produced. The annual rate of
increase in SOC content over initial condition was 74,
328, 711 and 900 kg C ha�1 under unfertilized, NPK,
N + FYM and NPK + FYM treatments. Thus, addition
of FYM resulted in higher SOC and higher productivity
of both soybean and wheat crops.
From the relationship of C addition and storage, it was
observed that (i) 19% of the gross C input contributed to
SOC accumulation, (ii) annual C loss during 30 years
from native SOM averaged 61 kg C ha�1, (iii) C loss
from native SOC during 30 years of cultivation was
0.18% of initial SOC content, and (iv) 321 kg C ha�1 was
needed to maintain SOM at equilibrium. Total annual C
input by the soybean–wheat rotation under unfertilized
control was 890 kg ha�1 yr�1. Thus, rainfed soybean–
wheat cropping in the sub-temperate Indian Himalayas is
a system that can sequester soil organic C.
References
Allison, F.E., 1973. Soil Organic Matter and its Role in Crop Produc-
tion. Soil Sci., Elsevier, Amsterdam, p. 3.
Aulakh, M.S., Khera, T.S., Doran, J.W., Bronson, K.F., 2001. Mana-
ging crop residue with green manure, urea, and tillage in a rice–
wheat rotation. Soil Sci. Soc. Am. J. 65, 820–827.
Barnett, V., Payne, R., Steiner, R., 1995. Agricultural Sustainability.
Economic, Environmental and Statistical Considerations. John
Wiley & Sons, Chichester, UK, p. 51.
Bouyoucos, G.J., 1927. The hydrometer as a new method for the
mechanical analysis of soil. Soil Sci. 23, 343–353.
Buyanovsky, G.A., Wagner, G.H., 1998. Changing role of cultivated
land in the global carbon cycle. Biol. Fertil. Soil 27, 242–
245.
Bhandari, A.L., Ladha, J.K., Pathak, H., Padre, A.T., Dawe, D.,
Gupta, R.K., 2002. Yield and soil nutrient changes in a long-term
rice–wheat rotation in India. Soil Sci. Soc. Am. J. 66, 162–
170.
Campbell, C.A., McConkey, B.G., Zentner, R.P., Selles, F., Curtin, D.,
1996. Tillage and crop rotation effects on soil organic C and N in a
coarse-textured Typic Haploboroll in Southwestern Saskatche-
wan. Soil Till. Res. 37, 3–14.
Campbell, C.A., Janzen, H.H., Juma, N.G., 1997. Case studies of soil
quality in the Canadian prairies: long-term field experiments. In:
Gregorich, E.G., Carter, M.R. (Eds.), Soil Quality for Crop
Production. Elsevier Science Publishers, Amsterdam, The
Netherlands, pp. 351–397.
Campbell, C.A., Zentner, R.P., Liang, B.C., Roloff, G., Gregorich,
E.C., Blomert, B., 2000. Organic C accumulation in soil over 30
years in semiarid southwestern Saskatchewan—effect of crop
rotations and fertilizers. Can. J. Soil Sci. 80, 179–192.
Cassman, K.G., De Datta, S.K., Olk, D.C., Alcantara, J., Samson, M.,
Descalsota, J., Dizon, M.A., 1995. Yield decline and the nitrogen
economy of long-term experiments on continuous, irrigated rice
systems in the tropics. In: Lal, R., Stewart, B.A., (Eds.), Soil
Management: Experimental Basis for Sustainability and Environ-
mental Quality. Adv. Soil Sci., CRC Press, Boca Raton, FL, pp.
181–222.
Chander, K., Goyal, S., Kapoor, K.K., 1997. Organic matter, microbial
biomass and enzyme activity of soils under different crop rotations
in the tropics. Biol. Fertil. Soils 24, 306–310.
Duxbury, J.M., Abrol, I.P., Gupta, R.K., Bronson, K.F., 2000. Analysis
of long-term soil fertility experiments with rice–wheat rotations in
South Asia. In: Abrol, I.P., et al. (Eds.), Long-term soil fertility
experiments with rice–wheat rotations in South Asia. Rice–wheat
Consortium Paper Series No. 6. Rice–wheat Consortium for the
Indo-Gangetic Plains, New Delhi, India, pp. 7–22.
Gami, S.K., Ladha, J.K., Pathak, H., Shah, M.P., Pasuquin, E., Pandey,
S.P., Hobbs, P.R., Joshy, D., Mishra, R., 2001. Long-term changes
in yield and soil fertility in a 20-year rice–wheat experiment in
Nepal. Biol. Fertil. Soils 34, 73–78.
Gomez, A.K., Gomez, A.A., 1984. Statistical Procedures for Agri-
cultural Research, 2nd ed. John Wiley & Sons, New York, pp.
180–209.
Halvorson, A.D., Reule, C.A., Follett, R.F., 1999. Nitrogen fertiliza-
tion effects on soil carbon and nitrogen in a dryland cropping
system. Soil Sci. Soc. Am. J. 63, 912–917.
Havlin, J.L., Kissel, D.E., Maddux, L.D., Classen, M.M., Long, J.H.,
1990. Crop rotation and tillage effects on soil organic carbon and
nitrogen. Soil Sci. Soc. Am. J. 54, 448–452.
Huggins, D.R., Clapp, C.E., Allmaras, R.R., Lamb, J.A., 1995. Carbon
sequestration in corn-soybean agro-ecosystems. In: Lal, R., K-
imble, J.M., Levine, E., Stewart, B.A. (Eds.), Soil Management
and Greenhouse Effect. Lewis Publishers, Boca Raton, FL, pp.
61–68.
Jackson, M.L., 1973. Soil Chemical Analysis. Prentice Hall of India
Pvt. Ltd., New Delhi, India, pp. 38–204.
Janzen, H.H., Campbell, C.A., Gregorich, E.G., Ellert, B.H., 1998.
Soil carbon dynamics in Canadian agroecosystems. In: Lal, R.,
Kimble, J.M., Follett, R.F., Stewart, B.A. (Eds.), Soil Processes
and Carbon Cycles. CRC Press, Boca Raton, FL, pp. 57–80.
S. Kundu et al. / Soil & Tillage Research 92 (2007) 87–95 95
Jenkinson, D.S., Rayner, J.H., 1977. The turnover of soil organic
matter in some of the Rothamsted classical experiments. Soil Sci.
123, 286–305.
Jenkinson, D.S., 1988. Soil organic matter and its dynamics. In: Wild,
A. (Ed.), Russell’s Soil Conditions and Plant Growth. 11th ed.
Longman Group UK Limited, pp. 564–607.
Keith, H., Oades, J.M., Martin, J.K., 1986. Input of carbon to soil from
wheat plants. Soil Biol. Biochem. 18, 445–449.
Kemper, W.D., Alberts, E.E., Foy, C.D., Clark, R.B., Ritchie, J.C.,
Zobel, R.W., 1998. Arenchyma, acid tolerance and associative N2
fixation enhance carbon sequestration in soil. In: Lal, R., Kimble,
J.M., Follet, R.F., Stewart, B.A. (Eds.), Management of Carbon
Sequestration in Soil. CRC Press, Boca Raton, New York, pp.
221–234.
Kundu, S., Singh, M., Saha, J.K., Biswas, A., Tripathi, A.K., Acharya,
C.L., 2001. Relationship between C addition and storage in a
Vertisol under soybean–wheat cropping system in sub-tropical
central India. J. Plant Nutr. Soil Sci. 164, 483–486.
Kundu, S., Singh, M., Tripathi, A.K., Manna, M.C., Takkar, P.N.,
1997. Time-course of dinitrogen fixation in soybean grown on
Typic Haplusterts of Madhya Pradesh. J. Indian Soc. Soil Sci. 45,
274–278.
Lal, R., Kimble, J.M., Follett, R.F., Stewart, B.A., 1997. Soil Processes
and Carbon Cycles. CRC Press, Boca Raton, FL.
Leigh, R.A., Johnston, A.E., 1994. Long-term Experiments in Agri-
cultural and Ecological Sciences. CAB International, Wallingford,
UK.
Lucas, R.E., Holtman, J.B., Connor, L.J., 1977. Soil carbon dynamics
and cropping practices. In: Lockertz, W. (Ed.), Agriculture and
Energy. Academic Press, London, pp. 333–351.
Nelson, D.W., Sommers, L.E., 1982. Total carbon, organic carbon, and
organic matter. In: Page, A.L., et, al., (Eds.), Methods of soil
analysis. Part 2, 2nd ed., Agron. Monogr. 9. SSSA, Madison,
Wisconsin.
Olsen, S.R., Cole, C.V., Watanbe, F.S., Dean, L.A., 1954. Estimation
of Available Phosphorus by Extraction with Bicarbonate. Circular
939, United States Department of Agriculture, Washington, DC,
pp. 171–179.
Parton, W.J., Ojima, D.S., Schimel, D.S., 1996. Models to Evaluate
Soil Organic Matter Storage in Agricultural Soils. Adv Soil Sci.,
CRC/Lewsis Publisher, Boca Raton, FL.
Paul, E.A., Paustian, K., Elliott, E.T., Cole, C.V., 1997. Soil Organic
matter in Temperate Agro-ecosystems: Long-term Experiment in
North America. CRC Press Inc., Boca Raton, FL.
Paustian, K., Parton, W.J., Persson, J., 1992. Modelling soil organic
matter in organic amended and nitrogen fertilized long-term plots.
Soil Sci. Soc. Am. J. 56, 476–488.
Rasmussen, P.E., Collins, H.P., 1991. Long-term impacts of tillage,
fertilizer and crop residue on soil organic matter in temperate
semi-arid regions. Adv. Agron. 45, 93–134.
Rasmussen, P.E., Albrecht, S.L., 1998. Crop management effects on
organic carbon in Semi-arid pacific North West soils. In: Lal, R.,
Kimble, J.M., Follet, R.F., Stewart, B.A. (Eds.), Management of
Carbon Sequestration in Soil. CRC Press, Boca Raton, New York,
pp. 209–219.
Regmi, A.P., 1994. Long-term effects of organic amendment and
mineral fertilizer on soil fertility in a rice-rice–wheat cropping
system in Nepal. M.S. Thesis, University of Philippines, Los
Banos, pp. 58–64.
Shamoot, S.O., Mc Donald, L., Bartholomew, W.V., 1968. Rhizode-
position of organic debris in soil. Soil Sci. Soc. Am. Proc. 32, 817–
820.
Sharma, P.K., Verma, T.S., Bhagat, R.M., 1995. Soil structural
improvement with the addition of Lantana camara biomass in
rice–wheat cropping. Soil Use Manage. 11, 199–203.
Ved Prakash, Kundu, S., Ghosh, B.N., Singh, R.D., Gupta, H.S., 2002.
Annual carbon input to soil through rainfed soybean (Glycine
max)–wheat (Triticum aestivum) cropping sequence in mid-hills of
North-west Himalaya. Indian J. Agric. Sci. 72, 14–17.
Walkley, A., Black, I.A., 1934. An examination of the Degtjareff
method for determining soil organic matter and a proposed
modification of chromic acid titration method. Soil Sci. 37, 29–38.
Yadav, R.L., Dwivedi, B.S., Pandey, P.S., 2000. Rice–wheat cropping
system: assessment of sustainability under green manuring and
chemical fertilizer inputs. Field Crops Res. 65, 15–30.
Yadav, R.L., Yadav, D.S., Singh, R.M., Kumar, A., 1998. Long-term
effects of inorganic fertilizer inputs on crop productivity in a rice–
wheat cropping system. Nutr. Cycling Agroecosyst. 51, 193–
200.
Yadvinder-Singh, Bijay-Singh, Maaskina, M.S., Meelu, O.P., 1995.
Response of wetland rice to nitrogen from cattle manure and urea
in a rice–wheat rotation. Trop. Agric. (Trinidad) 72, 91–96.
Top Related