This document summarizes a study on the long-term effects of nutrient management on soil fertility and soil organic carbon pools under a 6-year pearl millet-wheat cropping system. The study found that application of farmyard manure alone or integrated with chemical fertilizers led to significant increases in soil fertility parameters like nitrogen, phosphorus, potassium, and sulfur compared to the unfertilized control. It also increased total organic carbon, labile organic carbon, and microbial biomass carbon pools, especially in surface soils. Integrated nutrient management maintaining application of farmyard manure was most effective for enhancing crop productivity, nutrient availability, and soil carbon over the long term according to the carbon management index.

1. Field Crops Research 136 (2012) 32–41
Contents lists available at SciVerse ScienceDirect
Field Crops Research
jou rnal h om epage: www.elsevier.com/locate/fcr
Long-term effect of nutrient management on soil fertility and soil organic carbon
pools under a 6-year-old pearl millet–wheat cropping system in an Inceptisol of
subtropical India
P.C. Moharana, B.M. Sharma, D.R. Biswas∗, B.S. Dwivedi, R.V. Singh
Division of Soil Science and Agricultural Chemistry, Indian Agricultural Research Institute, New Delhi 110012, India
a r t i c l e i n f o
Article history:
Received 18 May 2012
Received in revised form 29 June 2012
Accepted 2 July 2012
Keywords:
Soil fertility
Soil organic carbon pools
Nutrient management
Carbon management index
Pearl millet–wheat cropping system
a b s t r a c t
We studied the long-term effect of nutrient management on soil fertility and soil organic carbon (SOC)
pools under a 6-year-old pearl millet–wheat cropping system in an Inceptisol of subtropical India. Sig-nificant
build-up in soil fertility in terms of alkaline KMnO4-N, Olsen-P, NH4OAc-K and CaCl2-S as well
as SOC pools namely, total organic carbon (TOC), Walkley and Black organic carbon (WBC), labile organic
carbon (LBC) and microbial biomass carbon (MBC) were maintained under FYM and integrated nutrient
management involving FYM and NPK than unfertilized control plot in 0–15 and 15–30 cm soil depths. The
highest values of TOC (11.48 g kg−1) and WBC (7.86 g kg−1) were maintained in FYM treated plot, while
the highest values of LBC (1.36 g kg−1) and MBC (273 mg kg−1) were found in FYM + NPK. The magnitude of
change in pools of SOC in sub-surface (15–30 cm) soil was low as compared to the surface soil (0–15 cm).
Significant increase in all the pools of SOC in FYM treated plots indicates the importance of application of
organic manure like FYM in maintaining organic carbon in soil. Highly strong relationships were exhibited
between LBC and MBC with yield, indicating that these pools are more important for nutrient turn-over
and their availability to plants than total SOC. Carbon management index revealed that integrated nutri-ent
management could be followed for enhancing crop productivity, nutrient availability and soil carbon
pools for long-term. These results conclude that for sustainable crop production and maintaining soil
quality, input of organic manure like FYM is of major importance and should be advocated in the nutrient
management of intensive cropping system for improving soil fertility and biological properties of soils.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Soil organic carbon (SOC) is the most important component in
maintaining soil quality because of its role in improving physi-cal,
chemical and biological properties of the soil. Stagnation or
decline in yields has been observed in intensive cropping systems in
recent times all over the world and India in particular. The reasons
ascribed to this phenomenon are quality and quantity of SOC and its
impact on nutrient supply (Bhandari et al., 2002; Ladha et al., 2003).
The level of SOC at a point of time reflects the long-term balance
between addition and losses of SOC, particularly carbon and nitro-gen,
under continuous cultivation (Dalal and Mayer, 1986; Dawe
et al., 2003; Manna et al., 2005). Changes in agricultural practices
often influence both quantity and quality of SOC and its turn-over
rates. Application of manure is a common management practice
that improves the fertility status of soil and SOC level. As the turn-over
of SOC is of paramount importance for sustaining soil quality
∗ Corresponding author. Tel.: +91 11 25841494/965; fax: +91 11 25841529.
E-mail address: drb ssac@yahoo.com (D.R. Biswas).
and long-term productivity of agricultural systems, measurements
of changes in SOC under various nutrient management practices
in intensive cropping system are the need of the day. In addition
to total SOC, it is also important to determine active carbon frac-tions
in soil (Lal, 1994). Small changes in total SOC are difficult to
detect because of large background levels and natural variability
(Blair et al., 1995; Carter, 2002). Intensive cultivation can decline
both total and labile organic carbon in soil (Blair, 2000). Thus, reg-ular
additions of organic materials to soil are required to improve
and maintain SOC pools as well as to help in governing nutrient
fluxes, microbial biomass and their activities and improvement in
soil physical properties (Marinari et al., 2000).
Labile organic carbon is sensitive to soil management practices
and thus provides the better management of carbon dynamics in
short-term to medium-term effect than total carbon alone. Soil
organic carbon refers to the sum total of different heterogeneous
organic substances, which may be simply divided into stable and
labile organic carbon fractions (Wander, 2004). Stable SOC fractions
are relatively resistant to decompose, take longer time to turn-over
and do not take part in several nutrient cycling. However, labile SOC
fractions are readily accessible source of microorganisms, turn-over
0378-4290/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.fcr.2012.07.002

2. P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41 33
rapidly (weeks or months) and have impact on plant nutrient sup-ply.
Labile SOC fractions could indicate changes in soil quality due
to management practices more rapidly than measuring changes in
the magnitude of total SOC (Ding et al., 2006). Some of the impor-tant
labile pools of SOC currently used as indicators of soil quality
are microbial biomass carbon (MBC), mineralizable organic car-bon
(Cmin), particulate organic carbon (POC) and KMnO4-oxidizable
labile organic carbon (LBC). Highly recalcitrant or passive pool of
SOC is very slowly altered by microbial activities and hence hardly
serves as a good indicator for judging soil quality.
Pearl millet–wheat cropping system is the second most impor-tant
system after rice–wheat in Indo-Gangetic Plain of India (Kumar
et al., 2005). This cropping system is followed in an estimated
area of 2.26 million ha in India (Yadav and Subba Rao, 2002). It
is being increasingly realized that when crops are grown in sys-tem,
the fertilizer requirements of the cropping system as a whole
is important than that of the individual crop (Sharma and Singh,
2003). The soil fertility status and their availability to plants are
strongly affected by nutrient management practices and cropping
systems (Bhandari et al., 2002; Kundu et al., 2002). The loss of soil
fertility, in many developing countries, due to continuous nutri-ent
depletion by crops without adequate replenishment poses an
immediate threat to food and environmental securities. There is
a need to revive the age-old practice of application of farmyard
manure (FYM) to maintain soil fertility and also to supplement
many essential plant nutrients for crop productivity. The fertilizer
recommendations based on targeted yield equations have been
well established in India through number of follow-up trials and
frontline demonstrations (Subba Rao and Srivastava, 2001). How-ever,
information on long-term effect of these recommendations
used with or without FYM in a pearl millet–wheat cropping system
on soil fertility and different pools of SOC is limited. Keeping these
points in mind, the present field experiment was conducted to see
the long-term effect of soil fertility and pools of soil organic carbon
as influenced by nutrient management with FYM and chemical fer-tilizers
applied either alone or in combination under a 6-year-old
pearl millet–wheat cropping system. We hypothesized that long-term
application of carbon through FYM and N, P and K through
fertilizers will have distinct effects on the soil fertility, nutrient
availability and soil organic carbon pools under a 6-year-old pearl
millet–wheat cropping system in an Inceptisol of subtropical India.
2. Materials and methods
2.1. Site descriptions
The present field experiment on pearl millet–wheat cropping
system was initiated in monsoon 2003 at the research farm of
Indian Agricultural Research Institute (IARI), New Delhi under the
network of All India Coordinated Research Project (AICRP) on Soil
Test Crop Response (STCR) Correlation Studies. The experimental
field is located at 28.4◦N latitude, 77.1◦E longitude and at an ele-vation
of about 250 m above the mean sea level. The climate of
the experimental site is semi-arid with hot and dry summer and
severe cold winter intervened by short monsoon period of 2–3
months spreading from July to September. On the basis of 30 years
climatic data, the mean maximum temperature, minimum temper-ature
and rainfall are 31.2 ◦C, 17.0 ◦C and 821 mm, respectively. The
experimental area represents Indo-Gangetic Plains which belongs
to Mehrauli series. The soil is Inceptisol having sandy loam texture,
alkaline reaction and free from salinity occurring on nearly level to
very gently sloping land. Soil structure is sub-angular blocky. Clay
mineralogy is dominated by illite along with presence of kaolinite,
chlorite and chloritized montmorillonite. Taxonomically it belongs
to Typic Haplustept.
2.2. Experimental design and treatments
The field experiment on pearl millet–wheat cropping system
was designed under AICRP-STCR with three different nutrient man-agement
practices along with a control in a randomized block
design with four replications. The treatments selected for this study
consisted of (i) unfertilized/unmanured control (Control); (ii) FYM
alone @ 20 Mg ha−1 to each crop (FYM); (iii) STCR-based fertil-izer
NPK alone for grain yield target of 2.5 Mg ha−1 of pearl millet
and 5.0 Mg ha−1 of wheat (NPK); and (iv) STCR-based integrated
use of 10 Mg ha−1 of FYM + fertilizer NPK for grain yield target of
2.5 Mg ha−1 of pearl millet and 5.0 Mg ha−1 of wheat (FYM + NPK).
The purpose of selecting FYM alone was to investigate the long-term
use of organic manure alone on yield and soil productivity.
Application of FYM @ 20 Mg ha−1 was adopted so as to provide
100 kg N ha−1. The treatments, NPK fertilizer alone and FYM + NPK
were selected to investigate the effect of STCR-based fertilizer NPK
management (i.e. fertilizers only) and STCR-based integrated man-agement
of FYM + fertilizers NPK on soil available nutrient and
pools of SOC at the same level of targeted yield production as
established by Ramamoorthy et al. (1967). In the present field
experiment, the soil test based fertilizer adjustment equations with
and without FYM for targeted levels of grain production of pearl
millet (2.5 Mg ha−1) and wheat (5.0 Mg ha−1) grown in sequence
for 6 years as developed by Sharma and Singh (2003) under AICRP
on Soil Test Crop Response Correlation at IARI, New Delhi were
used for fertilizer management in NPK and FYM + NPK treatments,
respectively. The following fertilizer adjustment equations were
used for calculation of inputs of nutrients from fertilizers and FYM:
Fertilizer adjustment equations for pearl millet
Without FYM With FYM
FN = 69.7 T
−
0.36 SN FN = 53.5 T
−
0.29 SN
−
2.23 FYM
FP2O5 = 57.3 T
−
4.81 SP FP2O5 = 47.2 T
−
3.29 SP
−
2.48 FYM
FK2O = 39.2 T
−
0.28 SK FK2O = 28.8 T
−
0.17 SK
−
1.35 FYM
Fertilizer adjustment equations for wheat
Without FYM With FYM
FN = 43.0 T
−
0.44 SN FN = 38.5 T
−
0.41 SN
−
1.64 FYM
FP2O5 = 37.9 T
−
6.02 SP FP2O5 = 27.8 T
−
4.12 SP
−
1.72 FYM
FK2O = 23.4 T
−
0.33 SK FK2O = 20.4 T
−
0.29 SK
−
0.88 FYM
where FN, FP2O5 and FK2O stand for fertilizer rate (kg ha−1) of N,
P2O5 and K2O, respectively; SN, SP and SK stand for soil test values
(kg ha−1) for KMnO4-N (Subbiah and Asija, 1956), Olsen-P (Olsen
et al., 1954) and NH4OAc-K (Hanway and Heidel, 1952), respec-tively;
FYM stands for dose of farmyard manure (Mg ha−1) and T
denotes the targeted yield (Mg ha−1). Based on the above equa-tions,
the inputs of nutrients from fertilizers and FYM under each
treatment are presented year-wise in Table 1.
2.3. Soil sampling and crop management
Prior to start of the experiment, two exhaustive crops namely,
pearl millet during monsoon and wheat during winter season
were grown to bring the uniformity in soil fertility in the field.
After harvesting the second exhaustive crop of wheat, the com-posite
initial soil samples from surface (0–15 cm) and sub-surface
(15–30 cm) layer were collected and analyzed for physicochemical
properties. The field was divided into four equal size strips and
each strip was divided into four equal size plots of 20 m
×
4 m each.
The treatments were distributed randomly using a randomized
block design. Before application of fertilizer doses in each crop,
plot-wise soil samples from 0 to 15 cm and 15 to 30 cm depth
were collected and analyzed for available N, P and K status and
soil test based fertilizer doses for NPK and FYM + NPK treatments
were calculated from the fertilizer adjustment equations for pearl
millet and wheat as mentioned earlier. The pearl millet (cv Pusa
383) and wheat (cv HD 2687) were grown in sequence for 6 years

3. 34 P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41
Table 1
Year-wise input of nutrients from fertilizers and FYM under each treatment in a 6-year-old pearl millet–wheat cropping system using targeted yield equations.
Year Treatments
Control FYM (Mg ha−1) NPK NPK + FYM
N (kg ha−1) P2O5 (kg ha−1) K2O (kg ha−1) N (kg ha−1) P2O5 (kg ha−1) K2O (kg ha−1) FYM (Mg ha−1)
Pearl millet
2003 0 20.0 108.0 36.5 45.8 59.3 19.8 26.6 10.0
2004 0 20.0 109.8 27.8 43.5 53.6 11.9 26.5 10.0
2005 0 20.0 110.7 21.1 44.0 52.7 11.9 26.2 10.0
2006 0 20.0 111.6 15.5 42.8 50.0 7.7 23.6 10.0
2007 0 20.0 111.3 17.7 44.2 50.0 5.4 23.7 10.0
2008 0 20.0 110.9 12.3 43.4 50.0 1.4 22.7 10.0
Wheat
2003–04 0 20.0 134.9 47.3 53.1 100.7 18.0 38.0 10.0
2004–05 0 20.0 136.7 43.2 52.5 93.3 21.7 37.8 10.0
2005–06 0 20.0 137.6 33.0 51.2 93.3 20.0 25.8 10.0
2006–07 0 20.0 138.0 25.8 51.0 88.8 10.6 30.9 10.0
2007–08 0 20.0 139.3 25.8 49.8 88.4 8.9 28.2 10.0
2008–09 0 20.0 139.3 23.3 49.4 88.0 8.9 27.7 10.0
with the same treatments. Fertilizer materials used were urea,
diammonium phosphate (DAP) and muriate of potash (MOP).
Half quantity of N and full quantities of P and K were applied as
basal in both the crops by broadcasting followed by mixing by
disc plough. Remaining half of N was applied as top-dressing at
knee-height stage (45 days after sowing) in pearl millet and at
panicle emergence (55 days after sowing) in wheat. Irrigation and
other agronomic practices were carried out as and when required.
2.4. Soil analysis
The initial soil samples from surface (0–15 cm) and sub-surface
(15–30 cm) were analyzed for mechanical composition, pH, elec-tric
conductivity (EC), cation exchange capacity (CEC), bulk density
(BD), organic carbon and available nutrients (N, P, K and S) following
standard procedures. The physicochemical properties of the initial
soil under study are presented in Table 2.
After completion of six cropping cycles of pearl millet–wheat,
soil samples from surface (0–15 cm) and sub-surface (15–30 cm)
were collected. In each plot the soil was collected from ten points
randomly, and mixed into one sample. After carefully removing
the surface organic materials and fine roots, each mixed soil sam-ple
was divided into two parts. One part of the fresh soil sample
(∼100 g) was sieved through a 2-mm screen and immediately kept
in a refrigerator at 4 ◦C in plastic bags for a few days to stabilize
the microbiological activity and subsequently analyzed for biologi-cal
properties. The other part of the sample was air-dried in shade,
ground to pass through a 2-mm sieve and used for the estimation
of soil chemical properties.
The alkaline potassium permanganate oxidizable soil N
(KMnO4-N) as an index of available N was determined as per
the procedure given by Subbiah and Asija (1956). Olsen-P was
extracted with 0.5 M sodium bicarbonate (pH 8.5) as outlined by
(Olsen et al., 1954) and the P content in the extract was deter-mined
using ascorbic acid as reducing agent (Watanabe and Olsen,
1965) by a spectrophotometer. Available potassium (NH4OAc-K)
was extracted with neutral 1 N ammonium acetate (Hanway and
Heidel, 1952) and estimated by a flame photometer; while available
sulphur (CaCl2-S) was determined by extracting the soil sample
with 0.15% CaCl2 (Williams and Steinbergs, 1959) and sulphur con-tent
in the extract was estimated by turbidimetric method (Chesnin
and Yien, 1950).
Total organic carbon (TOC) in soil was determined by wet oxida-tion
method (Snyder and Trofymow, 1984). While, organic carbon
content was determined by wet oxidation method of Walkley and
Black (1934). The Walkley and Black method is based on oxidation
of organic matter by K2Cr2O7 with H2SO4 heat of dilution. Some-what
less of the total organic matter is oxidized by this method,
because the heating obtained by the H2SO4 dilution is less and
thus Walkley–Black method tends to underestimate SOC concen-trations.
Studies have shown that the recovery of organic C using
the Walkley and Black procedure ranged from 60 to 86% with a
mean recovery being 76% as a result of the incomplete oxidation
(Walkley and Black, 1934). To overcome the concern of incom-plete
digestion of the organic matter, TOC in soil is determined by
Table 2
Physicochemical properties and fertility status of the experimental soil before commencing the study.
Soil characteristics Soil depth Method followed
0–15 cm 15–30 cm
Mechanical composition Bouyoucos (1962)
Sand (%) 56.5 56.4
Silt (%) 25.0 26.0
Clay (%) 18.5 17.6
Texture Sandy loam Sandy loam
pH 8.44 8.44 Jackson (1973)
EC (dS m−1) 0.32 0.25 Jackson (1973)
Bulk density (Mg m−3) 1.59 1.72 Veihmeyer and Hendrickson (1948)
Organic carbon (g kg−1) 5.2 2.6 Walkley and Black (1934)
CEC [cmol(p+) kg−1 soil] 10.7 6.15 Jackson (1973)
KMnO4-N (kg ha−1) 183 168 Subbiah and Asija (1956)
Olsen-P (kg ha−1) 22.4 6.3 Olsen et al. (1954)
NH4OAc-K (kg ha−1) 188 134 Hanway and Heidel (1952)
CaCl2-S (kg ha−1) 10.6 8.2 Williams and Steinbergs (1959)

4. P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41 35
wet oxidation method (Snyder and Trofymow, 1984) where organic
matter in the sample is converted to CO2 which is then quantified.
For this, air-dried sample of soil (1.0 g, 1-mm sieve) was pre-treated
with 3.0 ml of 2 N HCl to remove carbonates, then soil was oxidized
with potassium dichromate (K2Cr2O7) in presence of 25 ml of mix-ture
of concentrated H2SO4 and H3PO4 in a ratio of 3:2 by heating on
a digestion block at 120
±
1 ◦C for 2 h. The evolved CO2 was trapped
in 2 N NaOH and amount of CO2 (entrapped) was measured by back
titration with 0.5 N HCl using phenolphthalein as indicator. Total
carbon content was computed based on the amount of CO2 evolved.
Microbial biomass carbon (MBC) was estimated by the
chloroform-fumigation incubation method of Jenkinson and
Powlson (1976). Sample of soil (10.0 g) rewetted to 40–60% WHC
(water holding capacity) was fumigated with ethanol-free chloro-form
(CHCl3) in a vacuum desiccator. Following fumigant removal,
the soil was extracted with 0.5 M K2SO4 (soil:solution ratio of
1:2.5) through 30 min horizontal shaking at 200 rpm and filtered. A
duplicate soil sample without fumigation (unfumigated) was also
extracted with 0.5 M K2SO4 in a similar fashion. Both the extracts
of fumigated and unfumigated soil were subjected to wet oxida-tion
separately with potassium persulphate and 0.025 N H2SO4 by
heating on a digestion block at 120
±
1 ◦C for 2 h. Evolved CO2 was
then trapped in 0.1 N NaOH solution. The amount of CO2 evolved
was determined by back titration with 0.05 N HCl. The MBC was
computed by subtracting the amount of CO2 evolved in fumigated
soil from that of unfumigated one. A sub-sample of soil was drawn
for moisture determination so as to express the data on oven dry
weight basis. The amount of the MBC in soil was calculated as fol-lows:
Microbial biomass carbon
= OCF −
OCUF
KEC
where OCF and OCUF are the organic carbon extracted from fumi-gated
and unfumigated soil, respectively (expressed on oven dry
basis), and KEC is the efficiency of extraction. A value of 0.45 is con-sidered
as a general KEC value for microbial extraction efficiency
and used for calculation.
Labile carbon (LBC) in soil was determined by following the pro-cedure
of Blair et al. (1995). Moist sample of soil (2.0 g) was taken
in centrifuge tube and oxidized with 25 ml of 333 mM KMnO4 by
shaking on a mechanical shaker for 1 h. The tubes were then cen-trifuged
for 5 min at 4000 rpm and 1.0 ml of supernatant solution
was diluted to 250 ml with double distilled water. The concen-tration
of KMnO4 was measured at 565 nm wavelength using a
spectrophotometer. The change in concentration of KMnO4 is used
to estimate the amount of carbon oxidized assuming that 1.0 mM of
MnO4
− was consumed (Mn7+→
Mn2+) in the oxidation of 0.75 mM
(9.0 mg) of carbon.
2.5. Plant and FYM analysis
Plot-wise samples of wheat grain and straw were dried at
65 ± 1 ◦C in oven and ground in a Wiley mill for chemical analy-sis.
Total nitrogen was determined after digesting the sample with
concentrated H2SO4 using digestion mixture of K2SO4 and CuSO4
(10:1) followed by steam distillation in a micro-Kjeldahl nitrogen
distillation unit (Jackson, 1973). For other nutrients, grain and straw
samples were digested with di-acid mixture of HNO3:HClO4 (10:4
mixing ratio) and subsequently used for analysis. Total phosphorus
content in the acid digest was determined by a spectrophotometer
after developing vanadomolybdo–phosphate yellow colour com-plex
as described by Jackson (1973). Potassium content in the acid
digest was determined by a flame photometer (Jackson, 1973) and
sulphur content by turbidimetric method (Chesnin and Yien, 1950).
Fresh sample of FYM was analyzed for total C, N, P, K and S as in case
of plant analysis. Moisture content was determined by gravimetric
method. The fresh sample of FYM had 0.50% N, 0.32% P, 0.46% K,
0.32% S, C/N ratio of 26.5 and 8.9% moisture content (w/w).
2.6. Carbon management index
The carbon management index (CMI) was obtained according to
the mathematical procedures used by Blair et al. (1995), which are
described below:
CMI =
CPI ×
LI ×
100 (1)
where CPI is the carbon pool index and LI is the lability index.
The CPI and the LI are calculated as follows:
Carbon pool index (CPI)
= Total C in treated sample (mg g−1)
Total C in reference soil (mg g−1)
(2)
Lability index (LI)
= Lability of C in sample soil
Lability of C in reference soil
(3)
Lability of C (L)
= C in fraction oxidized by KMnO4 (mg labile C g−1 soil)
C remaining unoxisized by KMnO4 (mg labile C g−1 soil)
= LBC (Labile C)
NLC (Non-labile C)
(4)
The native uncultivated soil near the experimental field was
used as the reference, with a CMI defined as 100. The labile C
was considered as the portion of soil organic C that was oxidized
by 333 mM KMnO4 (Blair et al., 1995). The non-labile C (NLC)
was estimated from the difference between total organic C pool
as determined by wet oxidation method (Snyder and Trofymow,
1984) and the labile C (NLC = TOC
−
LBC).
2.7. Statistical analysis
For statistical analysis of data, Microsoft Excel (Microsoft Cor-poration,
USA) and SPSS (Statistical Package for the Social Science,
SPSS, Inc., Chicago, USA) window version 16.0 were used. Analy-sis
of variance (ANOVA) was done as per the procedure outlined
by Gomez and Gomez (1984). The significant differences between
treatments were compared with the least significance (LSD) at 5%
level of probability. Pearson’s correlations matrix was used to eval-uate
the relationships between yields, nutrients uptake by wheat
and soil available nutrients and different pools of organic carbon.
Unless otherwise stated, the level of significance referred to in the
results is P < 0.05.
3. Results and discussion
3.1. Changes in soil fertility
3.1.1. Alkaline KMnO4-N
Significant increase in alkaline KMnO4-N in surface soil
(0–15 cm) was maintained in plots receiving FYM (262 kg N ha−1)
and integrated use of FYM + NPK fertilizer (270 kg N ha−1) over NPK
treated (182 kg N ha−1) and unfertilized control plots (178 kg ha−1)
(Table 3). However, increases in KMnO4-N in sub-surface soil
(15–30 cm) were observed only under plots receiving FYM and
FYM + NPK fertilizer over unfertilized control. Increase in KMnO4-N
in surface soil was 47.2 and 51.7% in FYM and FYM + NPK fertilizer
treated plots over control, respectively. The increase in KMnO4-N
in FYM amended plots is attributed to the increase in total SOC
and might have been partially due to a slow release of N from
manure, as suggested by Yadav et al. (2000), Gami et al. (2001)

5. 36 P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41
Table 3
Effect of FYM and fertilizers on KMnO4-N and Olsen-P in a 6-year-old pearl
millet–wheat cropping system.
Treatments KMnO4-N (kg ha−1) Olsen-P (kg ha−1)
0–15 cm 15–30 cm 0–15 cm 15–30 cm
Control 178 150 18.3 5.5
FYM 262(47.2)a 169(12.7) 20.7 (13.1) 8.2 (49.1)
NPK 182 (2.2) 163 (8.7) 22.4 (22.4) 7.3 (32.7)
FYM + NPK 270 (51.7) 181 (20.7) 24.9 (36.1) 7.7 (40.0)
SEM (±) 3.93 4.77 0.82 0.82
LSD (P = 0.05) 12.6 15.3 2.61 NS
a Figure in parentheses indicate percent increase over control.
and Bhandari et al. (2002). Farmyard manure is known to stimu-late
biological N2 fixation in the soil, which may also have been
responsible for the increase in soil N (Ladha et al., 1989) over
NPK treatment, apart from FYM’s own N contribution. In addition,
soils under NPK + FYM treated plots produced more biomass and,
therefore, possibly had more extensive root systems that may have
contributed to increased N levels. It is evident from this study that
higher values of KMnO4-N were observed in surface soil as com-pared
to sub-surface soil irrespective of treatments. This might be
due to higher organic carbon content observed in surface as com-pared
to sub-surface soil.
3.1.2. Olsen-P
Significantly greater amount of Olsen-P in surface soil was main-tained
in all the three treatments receiving manure and fertilizer
applied either alone or in combination over unfertilized control plot
(Table 3). The build-up of Olsen-P in surface soil (0–15 cm depth)
were 24.9, 22.4 and 20.7 kg P ha−1 in plots receiving FYM + NPK, NPK
and FYM, respectively as against 18.3 kg P ha−1 in unfertilized con-trol
plot. The Olsen-P increased by 36.1, 22.4 and 13.1% in plots
receiving FYM + NPK, NPK and FYM, respectively over unfertilized
plot. However, no significant differences were found in sub-surface
soil where Olsen-P varied from 5.5 to 8.2 kg P ha−1 in different
nutrient management practices. The increase in Olsen-P in plots
receiving FYM applied either alone or in combination with NPK pos-sibly
due to release of organically bound P during decomposition
of organic matter, solubilization of soil P by organic acids produced
during decomposition of organic matter. Continuous application of
FYM also reduced the activity of polyvalent cations such as Ca, Fe,
and Al due to chelation which, in turn, considered responsible for
reduction in P-fixation (Gupta et al., 1988). The application of FYM
increased Olsen-P because of its P content, and possibly by increas-ing
retention of P in soil. A positive effect of FYM on P availability
was also observed by Roy et al. (2001). This might be due to the
fact that the major P fraction added through FYM is in the organic
pool, which mineralized slowly with time (Yadvinder-Singh et al.,
2004). Increase in Olsen-P in NPK fertilizer is due to residual effect
of higher amount of fertilizer P applied annually in this treatment
as compared to no application of fertilizer in FYM and low appli-cation
of fertilizer P in FYM + NPK treated plots. Biswas and Benbi
(1997) reported considerable build-up of Olsen-P with application
of phosphatic fertilizer, while those not receiving phosphatic fer-tilizer
annually have shown a decline in Olsen-P. Similarly, earlier
reports suggested that long-term application of P fertilizer in excess
of crop requirement can build-up large amounts of P in soil in both
the inorganic and organic pools (Singh et al., 2007).
3.1.3. NH4OAc-extractable-K
The NH4OAc-extractable-K (NH4OAc-K) showed significant
changes in both the depths in different treatments. The NH4OAc-
K content of soil under different treatments varied from 169
to 245 kg ha−1 in surface soil and from 119 to 152 kg ha−1 in
Table 4
Effect of FYM and fertilizers on NH4OAc-K and CaCl2-S in a 6-year-old pearl
millet–wheat cropping system.
Treatments NH4OAc-K (kg ha−1) CaCl2-S (kg ha−1)
0–15 cm 15–30 cm 0–15 cm 15–30 cm
Control 169 119 13.2 8.4
FYM 245(45.0)a 152(27.7) 21.3 (61.4) 9.6 (14.3)
NPK 184 (8.9) 123 (3.4) 16.4 (24.2) 9.2 (9.5)
FYM + NPK 214 (26.6) 137 (15.1) 22.2 (68.2) 9.4 (11.9)
SEM (±) 10.3 4.70 0.54 0.41
LSD (P = 0.05) 33.1 15.1 1.71 NS
a Figure in parentheses indicate percent increase over control.
sub-surface soil (Table 4). Plots received with FYM maintained sig-nificantly
highest amount of NH4OAc-K (245 kg ha−1) followed by
integrated use of FYM + NPK (214 kg ha−1), NPK alone (184 kg ha−1)
and control (169 kg ha−1) in surface soil (0–15 cm). In contrast to
Olsen-P, NH4OAc-K declined significant in treatments that received
NPK fertilizers over 6 years, suggesting that the current rate of
K application in the plots under NPK treatment was insufficient
to sustain soil K fertility in the present pearl millet–wheat sys-tem
where crop residues, particularly wheat straw, are removed
from the fields. On the contrary, application of FYM resulted in an
increase in NH4OAc-K due to more release of non-exchangeable K
from the soil as FYM increased soil cation exchange capacity, which
might have resulted in increased NH4OAc-K and its utilization by
crops (Blake et al., 1999), besides FYM’s own K supply. The plots
under FYM treatments either alone or in combination with NPK
fertilizer showed the maximum accumulation of exchangeable K,
possibly because of the increased sorption of K following continu-ous
addition of FYM (Poonia et al., 1986; Mehta et al., 1988). This
demonstrates that inputs of K with organic materials resulted in
a build-up of soil NH4OAc-K because FYM generally contains high
amounts of K. Considerable build-up of NH4OAc-K under FYM + NPK
treatment in a long-term fertilizer experiment was reported by oth-ers
(Nand Ram, 1998; Singh et al., 2000). Similar trend in NH4OAc-K
due to different treatments was found in sub-surface soil. However,
the levels of NH4OAc-K content were lower in sub-surface than
surface soil.
3.1.4. CaCl2-extractable-S
The 0.15% CaCl2-extractable-S (CaCl2-S) content in surface
soil (0–15 cm) was significantly higher in FYM + NPK treatment
(22.2 kg ha−1) followed by FYM alone (21.3 kg ha−1) and least in
unfertilized control plot (13.2 kg ha−1) (Table 4). However, no sig-nificant
effect was observed in sub-surface soil. The increase in
CaCl2-S in 0–15 cm soil depth was 68.2 and 61.4% in FYM + NPK and
FYM treated plots over control. This increase is attributed to the
accretion of sulphur through FYM application. Sarkar et al. (1998)
reported that application of various organic sources like compost,
FYM, green manure and crop residues can supply adequate quanti-ties
of sulphur to crops. Nambiar and Abrol (1989) also reported
from the long-term fertilizer experiments conducted at several
locations that the treatment involving un-interrupted yearly appli-cation
of FYM could maintain adequate status of sulphur to guard
against its deficiency in soils.
3.2. Pools of soil organic carbon
3.2.1. Total organic carbon
Continuous application of FYM either alone or in com-bination
with NPK resulted in considerable accumulation of
total SOC in 0–15 cm soil layer than unfertilized control plots
(Table 5). Soils under the FYM + NPK treated plots resulted
in higher total SOC in the 0–15 cm soil layer over those

6. P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41 37
Table 5
Carbon management index (CMI) as affected by application of FYM and fertilizers
in a 6-year-old pearl millet–wheat cropping system.
Treatment TOC
(g kg−1)
LBC
(g kg−1)
NLC
(g kg−1)
CPI LC LI CMI
0–15 cm depth
Control 7.53 0.79 6.74 1.00 0.12 1.00 100
FYM 11.48 1.20 10.28 1.52 0.12 1.52 232
NPK 8.50 0.94 7.56 1.13 0.12 1.19 134
FYM + NPK 11.08 1.36 9.72 1.47 0.14 1.72 253
SEM (±) 0.39 0.07 0.36
LSD (P = 0.05) 1.25 0.23 1.14
15–30 cm depth
Control 5.87 0.64 5.23 1.00 0.12 1.00 100
FYM 7.86 0.84 7.02 1.34 0.12 1.31 176
NPK 6.37 0.70 5.67 1.09 0.12 1.09 119
FYM + NPK 7.85 0.87 6.98 1.34 0.12 1.36 182
SEM (±) 0.19 0.03 0.20
LSD (P = 0.05) 0.60 0.10 0.64
TOC, total organic carbon; LBC, labile organic carbon; NLC, non-labile C; CPI, carbon
pool index; LC, lability of C; LI, lability index; CMI, carbon management index.
under the NPK treated plots. The TOC in surface soil were in
the order of FYM (11.48 g kg−1) > FYM + NPK (11.08 g kg−1) > NPK
(8.50 g kg−1) > unfertilized control (7.53 g kg−1). However, increase
in TOC was more in surface as compared to sub-surface soil, which
indicate that higher accumulation of organic carbon due to appli-cation
of FYM was confined to surface soil. The increase in TOC
in FYM and FYM + NPK treatments in surface layer was 52.5 and
47.1% over unfertilized control, while they were 35.0 and 30.3%
greater over NPK treatment, respectively. No significant difference
in TOC in FYM and FYM + NPK treatments although the amount of
FYM applied during the study period in FYM treated plot was dou-ble
of the amount applied in FYM + NPK treated plot. This might
be due to more turn-over of root biomass in FYM + NPK treatment
because of better growth and higher average yields obtained during
the study period of both the crops in FYM + NPK treatment as com-pared
to FYM treatment. It is evident that irrespective of depths,
greater accumulation of TOC was observed with FYM treatment
while control plot showed the lowest value. In the present study,
the above-ground biomass was removed and there was no incor-poration
of residues to the soil. The only input of organic matter
was through root biomass. Thus, increase in TOC in optimal and
balanced application of NPK is because of greater input of root
biomass due to better crop growth. It was supported by the data
published by Manjaiah and Singh (2001) who noted an annual esti-mated
organic carbon input to the tune of 8190 and 2780 kg ha−1
in 100% NPK + FYM and 100% NPK treatments, respectively. Simi-lar
effects of manure and inorganic fertilizer applications on soil
organic C has also been reported from Rothamsted classical exper-iments
(Jenkinson, 1991) and long-term experiments elsewhere
(Kukreja et al., 1991; Campbell et al., 1996; Biswas and Benbi, 1997;
Potter et al., 1998; Rudrappa et al., 2006).
3.2.2. Walkley and Black organic carbon
Walkley and Black method mostly determines both labile and
small part of non-labile organic carbon which is the readily accessi-ble
source of carbon to microorganisms and have direct impact on
plant nutrient supply. The monitoring of soil organic carbon either
for agricultural sustainability or environmental quality has been
done in most of the studies by Walkley and Black method (Walkley
and Black, 1934). In the present study, the plots that received FYM
(7.30 g kg−1) and FYM + NPK (6.50 g kg−1) had significantly higher
build-up in WBC over NPK treated (5.10 g kg−1) and unfertilized
control plots (4.90 g kg−1) in the surface soil (Fig. 1). The increase
in build-up in WBC under FYM and FYM + NPK treatments was 43.1
and 27.5% greater over treatment receiving NPK fertilizer alone and
Fig. 1. Changes in Walkley and Black organic carbon as influenced by application of
FYM and fertilizers after wheat grown in a 6-year-old pearl millet–wheat cropping
system. Error bars represent standard deviation of the mean.
49.0 and 32.7% greater over treatment receiving no fertilizer or
manure (control). In case of sub-surface soil, the build-up in WBC
under plots receiving FYM alone (4.1 g kg−1) and FYM + NPK fertil-izer
(3.8 g kg−1) was higher than in the plots receiving only NPK
fertilizer (3.0 g kg−1) and in the control (2.5 g kg−1). In general, the
values of WBC in sub-surface soils due to application of different
treatments were low compared to surface soil. The WBC and TOC
showed similar trend with respect to the changes in soil organic car-bon
due to different treatments, however, the values of WBC were
lower as compared to TOC. The values of this pool of soil organic
carbon varied between 58.6 and 65.0% of total soil organic carbon
in surface soil.
The significantly greater SOC in the fertilized plots over the con-trol
may be explained by the greater yield and associated greater
amount of root residues and stubbles of all the crops added to the
soil (Ghosh et al., 2003). Greater SOC under complete doses of NPK
fertilizer as compared to unfertilized soil has also been reported
in long-term studies (Swarup and Wanjari, 2000). Application of
organic amendments (FYM) also increased the SOM content to a
much greater extent than that of inorganic fertilizer alone. This
may be attributed to enhanced crop growth which in turn, resulted
in increased above and below-ground organic residues (e.g. roots),
and thus raised the SOM content. The increased SOM in FYM treated
plots also due to slower breakdown rate (less and constant miner-alization
rate) of FYM in soil. Kundu et al. (2002) reported that SOC
content improved in fertilized plots as compared to the unfertil-ized
plots due to C addition through the roots and crop residues,
higher humification rate constant, and lower decay rate. Similarly,
in a long-term experiment, Masto et al. (2006) observed that the
SOC was considerably greater in soils receiving FYM or straw along
with NPK fertilizer than in plots receiving merely NPK fertilizer. In
this study, the combination of organic and inorganic fertilization
enhanced the accumulation of SOC which is consistent with many
other studies (Jenkinson, 1991; Kukreja et al., 1991; Biswas and
Benbi, 1997; Majumder et al., 2007, 2008; Hao et al., 2008; Banger
et al., 2009).
3.2.3. Labile organic carbon
The labile organic carbon (LBC) pool or KMnO4 oxidizable car-bon
is considered as a useful approach for the characterization of
SOC resulting from different soil management practices including
cropping systems and application of organic and inorganic sources
of nutrients. The values of LBC in surface soil were 1.20, 1.36, 0.94
and 0.79 g kg−1 in FYM, FYM + NPK, NPK and unfertilized control
treatments, respectively (Table 5) which were 10.5, 12.3, 11.1 and
10.5% of the TOC, respectively. Similar trend in LBC were observed

7. 38 P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41
Fig. 2. Changes in microbial biomass carbon as influenced by application of FYM and
fertilizers after wheat grown in a 6-year-old pearl millet–wheat cropping system.
Error bars represent standard deviation of the mean.
in sub-surface soil. The plots received with FYM and FYM + NPK
treatments showed significant increase in LBC over NPK and
unfertilized control treatments in both surface and sub-surface
soil depth. However, the highest value of 1.36 g kg−1 was observed
in FYM + NPK treatment in surface soil. This may be due to the
application of FYM as well as higher turn-over of root biomass
because of better growth and yield of pearl millet and wheat
crops under combined application of FYM + NPK as compared to
1.20 g kg−1 in FYM alone. The percent increase in LBC in FYM and
FYM + NPK treatments in surface soil was 27.7 and 44.7% over
NPK and 51.9 and 72.2% over unfertilized control, respectively.
Higher variations in LBC in combined application of FYM + NPK
fertilizer indicate that this pool of soil organic C is more sensitive
to change due to manuring and fertilization. Higher turn-over of
root biomass under integrated nutrient management (FYM + NPK)
also might have attributed to higher increase in this pool as
compared to other treatments. Our results are in agreement with
the values reported by others (Conteh et al., 1997; Rudrappa et al.,
2006). Labile soil organic carbon pool is considered as the readily
accessible source of microorganisms which turns over rapidly and
has direct impact on nutrient supply. Labile soil organic carbon
pool generally includes light faction of organic matter, microbial
biomass and mineralizable organic matter. Adoption of procedure
that can preferentially extract more labile soil organic carbon
might be a useful approach for characterizing soil organic carbon
and hence soil fertility and nutrient availability to plant resulting
from different management practices including cropping systems
and application of organic and inorganic sources of nutrients. The
significant increase in LBC under integrated nutrient management
system (FYM + NPK) indicates its superiority over the manage-ment
by organic and chemical fertilizer alone in sustaining crop
productivity.
3.2.4. Microbial biomass carbon
The microbial biomass carbon (MBC) is an important compo-nent
of the SOM that regulates the transformation and storage of
nutrients. The soil MBC regulates all SOM transformations and is
considered to be the chief component of the active SOM pool. It
is evident that the MBC contents in both surface and sub-surface
soil were significantly higher in plots receiving FYM + NPK and
FYM treated plots compared to NPK fertilizer and unfertilized con-trol
plots (Fig. 2). The values of MBC in surface soil varied from
155 mg kg−1 in unfertilized control plot to 273 mg kg−1 in inte-grated
nutrient use of FYM + NPK plots, respectively; while it varied
from 113 mg kg−1 (control) to 156 mg kg−1 (FYM + NPK) in sub-surface
soil. The values of MBC increased by 56.3 and 76.5% under
FYM and FYM + NPK treatments in surface soil over control. While,
there were 26.7 and 43.0% increase of MBC over NPK fertilizer,
respectively. The highest value of MBC due to integrated use of FYM
and NPK fertilizer might be due to higher turn-over of root biomass
produced under FYM + NPK treatment. Application of NPK fertilizer
is not only required for better growth of the crop but also required
for synthesis of cellular components of microorganisms. There-fore,
higher root biomass under FYM + NPK fertilizer treatment
helped in increasing MBC over other treatments. Similar increases
in integrated nutrient management with manure + fertilizer have
been reported by others (Hopkins and Shiel, 1996; Grego et al.,
1998; Dezhi et al., 2007). Although MBC content in soil repre-sent
a small fraction i.e. about 1–5% of TOC), however, variation
in this pool due to management and cropping systems indicate
about the quality of soil, because the turn-over of SOM is con-trolled
by this pool of SOC which can provide an effective early
warning of the improvement or deterioration of soil quality as
a result of different management practices (Powlson and Brooks,
1987).
In our study, MBC was highest in the FYM plus inorganic fertil-izer
treatment. The increase of MBC under FYM amended soils could
be attributed to several factors, such as higher moisture content,
greater soil aggregation and higher SOC content. The FYM amended
plots provided a steady source of organic C to support the microbial
community compared to NPK treated plots. Generally, FYM applied
to soil has long been employed to enhance favourable soil condi-tions.
Decomposition of manure in soil releases essential nutrients
such as N, P and S that are required by microorganisms. Fauci and
Dick (1994) suggested that soils with a long-term use of organic
amendments, such as animal manure, generally maintain high lev-els
of MBC. In long-term field experiments in Denmark, Powlson
et al. (1987) showed that straw manure could increase MBC up to
45%. Similar to our study, Kandeler et al. (1999) earlier reported that
FYM (30 Mg ha−1, applied every second year) doubled the microbial
biomass in a Haplic Phaeocem under spring barley. Manjaiah and
Singh (2001) reported an increase of MBC by a factor of three after
a combined application of FYM and mineral N-fertilizer in a semi-arid
Cambisol. The higher microbial biomass in FYM + NPK might be
both due to higher below ground plant residues as well as added
FYM (Grego et al., 1998). This observation is consistent with that of
Hopkins and Shiel (1996), who reported that the MBC was greater in
soils receiving annual additions of FYM for nearly 100 years in addi-tion
to inorganic NPK. However, in a different study, a significant
increase in MBC was found only in soils fertilized with compost,
while treatment with mineral fertilizers was characterized by a
small MBC, as small as in the control soil (Grego et al., 1998). Sim-ilarly,
Omay (1997) reported a significant decrease in MBC due to
fertilizer applications, particularly N. The imbalanced use of fer-tilizers
also decreased MBC due to limitation imposed by major
nutrients like P and K, which are essential for higher crop produc-tion
as well as for microbial cell synthesis. The surface soil exhibited
higher MBC compared to lower soil depths primarily because of
addition of left-over crop residues and root biomass into the top-soil.
This view is consistent with the observation of Hao et al. (2008)
who observed that the microbial biomass was considerably greater
in soils receiving FYM along with NPK fertilizer than in plots receiv-ing
merely NPK fertilizer in three subtropical paddy soils. Mandal
et al. (2007) also reported that the microbial biomass was greater in
soils due to addition of straw plus inorganic NPK for 34 years than
that of inorganic NPK fertilizers. Similarly, Kaur et al. (2005) also
observed that in general, MBC tends to be smaller in unfertilized
soils or those fertilized with chemical fertilizers compared to soil
amended with organic manures. The readily metabolizable carbon
and N in FYM in addition to increasing root biomass and root exu-dates
due to greater crop growth are the most influential factors
contributing to the increase in soil MBC.

8. P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41 39
Fig. 3. Effect of FYM and fertilizers on yield of wheat grown in a 6-year-old pearl
millet–wheat cropping system. Error bars represent standard deviation of the mean.
3.2.5. Carbon management index
The carbon management index (CMI) is derived from the total
soil organic C pool and C lability index and is useful to evaluate
the capacity of management systems to promote soil quality. This
index compares the changes that occur in total and labile carbon as
a result of agricultural practices, with an emphasis on the changes
in labile carbon, as opposed to non-labile carbon in SOM. Therefore,
the integration of both soil organic C pool and C lability into the car-bon
management index can provide a useful parameter to assess
the capacity of management systems to promote soil quality (Blair
et al., 1995). A management system is considered sustainable, if the
value of CMI is greater than 100. In the present study, the highest
CMI values of 292 at 0–15 cm soil depth and 182 at 15–30 cm soil
depth were obtained in treatment receiving integrated use of FYM
and NPK fertilizer (Table 5). The addition of FYM alone resulted in
CMI values of 267 and 176 at 0–15 and 15–30 cm soil depth, respec-tively;
while that of NPK fertilizer resulted in CMI values of 173 and
143 at 0–15 and 15–30 cm soil depth, respectively. Improvement
in CMI value under integrated use of organic and inorganic fer-tilizer
over their sole application could be attributed to addition
of organic carbon and other nutrients through these sources. In
general, the CMI values decreased from surface soil to sub-surface
soil depth irrespective of nutrient management practices. Similar
result in higher CMI under rice–wheat cropping system amended
with Lantana spp. was reported earlier by Sharma et al. (2003).
Blair et al. (1995) reported that there was no ideal value of CMI.
However, this index provides a sensitive measure of the rate of
changes in soil carbon dynamics of the system related to the more
stable reference soil. The higher values of CMI indicate that the
system have greater soil quality than the other management sys-tems.
These results indicated that integrated use of FYM and NPK
fertilizer in intensive cropping system like pearl millet–wheat sys-tem
by using targeted yield equations could be considered as the
sustainable management option for crop production.
3.3. Yield of wheat
Grain yield of wheat obtained in different nutrient management
varied from 1.67 Mg ha−1 in unfertilized control to 5.33 Mg ha−1
in integrated use of FYM and inorganic fertilizers (FYM + NPK) and
straw from 2.29 (unfertilized control) to 7.49 Mg ha−1 (FYM + NPK)
(Fig. 3). The highest grain and straw yields were obtained in inte-grated
treatment (FYM + NPK) and lowest in control. This showed
the superiority of integrated nutrient management over either
fertilizers or FYM alone. Significantly higher yield was obtained
in FYM + NPK as compared to FYM, which revealed that FYM
alone cannot be a substitute for fertilizers. The highest grain yield
recorded under the application of inorganic sources of nutrient
may have been due to the immediate release and availability of
nutrients as compared to organic sources of nutrient, which release
the nutrient slowly. The yield advantage on application of organic
sources of nutrients was due to addition of secondary and micronu-trients
(Nambiar, 1997; Nayar and Chhibba, 2000; Manna et al.,
2005; Banik et al., 2006) along with the major nutrients, increased
nutrient absorption capacity due to the higher root density. It also
improved soil physical (Boparai et al., 1992) and biological prop-erties
by increasing the soil pore space, water holding capacity
(Biswas et al., 1971; Wallace, 1996; Lehmann et al., 1999) and
improving the soil structure (Biswas et al., 1971; Prasad and Singh,
1980). Combined use of organic and inorganic sources of nutri-ent
could be attributed to better synchrony of nutrient availability
to the wheat crop, which was reflected in higher grain yield and
biomass production and also the higher nutrient use efficiency. The
higher wheat yield obtained on FYM + NPK fertilizer-treated plots
was possibly caused by other benefits of organic matter such as
improvements in microbial activities, better supply of secondary
and micronutrients which are not supplied by inorganic fertilizers,
and lower losses of nutrients from the soil besides supply of N, P
and K (Abrol et al., 1997; Yadav et al., 2000; Yadvinder-Singh et al.,
2004). The improved soil physical properties in the FYM-treated
plots as observed in the present study might have also contributed
to the improvement in crop yields. The present study corroborates
the findings of other workers (Banger et al., 2009), where increased
yield of wheat due to integrated use of manures and fertilizers over
fertilizers alone were reported. It is also reported that application
of FYM along with chemical fertilizer enhances the activities of N
fixers (Ladha et al., 1989), improves the availability of the nutrients
for a longer period (Rani and Srivastava, 1997), increases nutrients
use efficiency of the crops (Narwal and Chaudhary, 2006), and bet-ter
availability of native nutrients to the plants resulting in a higher
yield (Bhandari et al., 2002). Improvement in the efficiency of fer-tilizers
when used in conjunction with manure might be due to
the enhanced inherent nutrient supplying capacity of the soil and
improved soil physical properties (Hati et al., 2006), which might
have promoted better rooting, higher nutrient and water absorp-tion
by crops (Reicosky and Deaton, 1979; Zhang et al., 1998).
3.4. Correlation matrix
Data on Pearson’s correlation matrix revealed that yield of
wheat was significantly (P < 0.01) and positively correlated with
KMnO4-N (r = 0.564*), Olsen-P (r = 0.819**) and CaCl2-S (r = 0.734**)
in soil (Table 6). Similarly, significant and positive correlation
between yield and TOC (r = 0.775**), LBC (r = 0.689**) and MBC
(r = 0.682**) were observed. A strong relationship between crop
yields with different pools of carbon indicates that there appears
to be a significant influence of SOC in enhancing crop yields. Differ-ent
pools of SOC showed significant and positive relationship with
each other indicating a dynamic relationship of different pools of
carbon in soil. The results also revealed that changes in pools of
organic carbon namely, WBC, LBC and MBC were affected signifi-cantly
by total organic carbon content in soil. The highest value of
correlation coefficient between LBC with TOC (r = 0.828**) and MBC
with TOC (r = 0.738**) indicates that these pools are most affected
by change management practices in soils. The results indicate that it
is not only the change in TOC under different treatment is important
but also the change in LBC and MBC pools which are more impor-tant
form the point of quality of soil organic carbon and availability
of nutrients to crops are concerned. Although the quantity of LBC
and MBC pools are very low as compared to TOC but these pools
are easily accessible thus more important from the point of nutri-ent
availability during crop growth period as compared to total soil
organic carbon. Therefore, these pools are helpful in understanding
the availability of nutrients in soil for uptake by plants.

9. 40 P.C. Moharana et al. / Field Crops Research 136 (2012) 32–41
Table 6
Pearson’s correlation matrix between yield, available nutrients and pools of soil organic carbon as affected by FYM and fertilizers in a 6-year-old pearl millet–wheat system.
Parameter Yield KMnO4-N Olsen-P NH4OAc-K CaCl2-S TOC WBC LBC
KMnO4-N 0.564*
Olsen-P 0.819** 0.453*
NH4OAc-K 0.368 0.680** 0.271
CaCl2-S 0.734** 0.918** 0.595** 0.750**
TOC 0.775** 0.805** 0.530* 0.648** 0.844**
WBC 0.398 0.867** 0.247 0.718** 0.785** 0.736**
LBC 0.689** 0.841** 0.457* 0.584** 0.789** 0.828** 0.638**
MBC 0.682** 0.816** 0.592** 0.708** 0.864** 0.738** 0.648** 0.829**
* Correlation is significant at the 0.05 level (1-tailed).
** Correlation is significant at the 0.01 level (1-tailed).
4. Conclusions
The present study demonstrated that integrated use of FYM and
NPK fertilizer using STCR-based targeted yield approach increased
soil fertility and pools of soil organic carbon. Significant and pos-itive
correlations of LBC and MBC with yield indicate that these
pools are more important for nutrient turn-over and their avail-ability
to plants than TOC. Carbon management index revealed that
integrated nutrient management could be followed for enhanc-ing
crop productivity, nutrient availability and soil carbon pools
for long-term. These results conclude that for sustainable crop
production and maintaining soil quality, input of organic manure
like FYM is of major importance and should be advocated in the
nutrient management of intensive cropping system for improving
chemical and biological properties of soils. Therefore, the gov-ernment
should encourage farmers to manage nutrients and soil
fertility following soil test based integrated nutrient management
by combining organic with inorganic fertilizer to increase crop pro-ductivity,
enhancing nutrient availability and sustaining soil carbon
pools for long-term.
Acknowledgments
The senior author thanks the Indian Council of Agricultural
Research, New Delhi, India, for providing financial support as Junior
Research Fellowship during his research work and the Head, Divi-sion
of Soil Science and Agricultural Chemistry, Indian Agricultural
Research Institute, New Delhi, India, for providing facilities for suc-cessful
completion of the research work.
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