OI

Sa

b

c

d

e

a

ARRA

KSSCGPF

1

eaic(hmAeTttHti

B

0h

Agriculture, Ecosystems and Environment 156 (2012) 134– 141

Contents lists available at SciVerse ScienceDirect

Agriculture, Ecosystems and Environment

jo u r n al hom ep age: www.elsev ier .com/ locate /agee

rganic amendments influence soil quality and carbon sequestration in thendo-Gangetic plains of India

ubhadip Ghosha,b,∗, Brian Wilsonb,c, Subrata Ghoshald, Nimai Senapatib, Biswapati Mandale

Centre for Urban Greenery and Ecology, National Parks Board, Singapore 259569, SingaporeSchool of Environmental and Rural Science, University of New England, Armidale, NSW 2351, AustraliaOffice of Environment and Heritage, University of New England, Armidale, NSW 2351, AustraliaSugarcane Research Station, Govt. of West Bengal, Bethuadahari 741126, West Bengal, IndiaDirectorate of Research, Bidhan Chandra Krishi Viswavidyalaya, Kalyani 741235, West Bengal, India

r t i c l e i n f o

rticle history:eceived 1 September 2011eceived in revised form 10 May 2012ccepted 11 May 2012

eywords:oil qualityoil organic carbon

a b s t r a c t

Soil organic carbon is considered to be of central importance in maintaining soil quality. We assessed theeffects of a range of commonly applied organic and inorganic amendments on soil quality in a rice–wheatcropping system in the Indo-Gangetic plains of eastern India and evaluated the carbon sequestrationpotential of such management approaches using a 25 year old long-term fertility experiment. Resultsshowed that there were significant increases in soil nutrient availability with the application of farmyard manure (FYM @ 7.5 t ha−1), paddy straw (PS @ 10 t ha−1) and green manure (GM @ 8 t ha−1) alongwith inorganic fertilizer. Both microbial biomass C and mineralizable C increased following the addition

arbon poolreen manureaddy strawarmyard manure

of the organic inputs. Continuous cultivation, without application of organic inputs, significantly depletedtotal C content (by 39–43%) compared with treatments involving the addition of organic amendments. Asignificant increase in the non-labile C fraction resulted from both organic and inorganic amendments,but only 26, 18 and 6% of the C applied through FYM, PS and GM, respectively was sequestered in soils.A significant increase in yield of kharif rice was observed as a result of the addition of these organicamendments.

. Introduction

Agricultural ecosystems represent an estimated 11% of thearth’s land surface which include some of the most productivend carbon-rich soils. It is widely recognized that organic mattern these soils plays an essential role in a range of soil physical,hemical and biological processes and that soil organic carbonSOC) is one of the most important indicators of soil quality andealth. Maintaining or increasing SOM is critical to achieve opti-um soil functions and therefore fertility and crop production.s a component of the terrestrial carbon (C) cycle, soil can beither source or sink of atmospheric carbon dioxide (Lal, 2007).heir judicious management therefore has significant potential forhe mitigation of greenhouse gas emissions. Intensive cultivationypically results in soil carbon depletion and reduced productivity.

owever, the addition of organic waste materials is a management

echnique with the potential to increase SOC content and tomprove soil quality. This is a particularly useful option in tropical

∗ Corresponding author at: Centre for Urban Greenery and Ecology, National Parksoard, Singapore 259569, Singapore. Tel.: +65 64717391; fax: +65 64723033.

E-mail address: subhadip00@rediffmail.com (S. Ghosh).

167-8809/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.agee.2012.05.009

© 2012 Elsevier B.V. All rights reserved.

regions where inorganic fertilizer costs are high but organicwastes are plentiful. The benefits of organic amendments havebeen widely demonstrated in temperate regions of the world buttheir efficacy in tropical and subtropical regions is not believedto be as significant due to high temperatures and humidity whichfacilitate a rapid oxidation of the applied organics. Investigationsregarding the efficacy of applying recycled organic wastes on SOCand soil quality are however, limited in these regions (Sharmaet al., 2005). Research is therefore needed to assess the effect oforganic amendments on soils in the tropics and their potential topartially or fully replacing inorganic fertilizers for crop production.This work is also critical to quantify the potential of soils in theseregions to store additional carbon as a GHG mitigation strategy.

The Indo-Gangetic plains are located within the tropical andsubtropical regions of India and are among the most agriculturallyproductive areas in the country. The average SOC content of the soilsin the region is however low due to intensive cultivation along withthe prevailing high temperatures and humidity (Nambiar, 2002).Rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping is the

dominant cropping sequence in the Indo-Gangetic Plains, and occu-pies nearly 50% of its cropped area (Singh and Khan, 2000). Thereis concern in the region regarding a continuous declining trend inSOC content and crop productivity and attempts are therefore being

S. Ghosh et al. / Agriculture, Ecosystems and Environment 156 (2012) 134– 141 135

Table 1Background information for the experimental site.

Item Characteristics

Geographical location Latitude—23◦N, longitude—89◦E,altitude–9.75 m (msl)

Year of start Kharif, 1986Climate Sub-humidAverage rainfall 1500 mmMean annual temperature (◦C) Max. 29.2 and Min. 18.5Soil Aeric Haplaquept

Texture—sandy loam (49%sand, 30% silt and 20.5% clay)

mcGsstw(tpIii

taeGeso

2

2

IUWzIii21hd

2

tooo@Ntoa

Table 2Biochemical composition (% on oven-dry basis) of the organic amendments(Bandyopadhyay et al., 2011).

Composition Farmyard manure Paddy straw Green manure

C 33.3 ± 5.1 42.0 ± 3.0 41.5 ± 3.6C:N 66.6 97.7 24.3

Crop variety used Rice–IET 4094; wheat–UP 262Recommended fertilizer dose Rice—N:P:K: 120:60:60; wheat—N:P:K:

100:60:40

ade to raise the productivity in the region through more effi-ient management practices (Bhattacharyya et al., 2009; Hobbs andupta, 2003). Within such systems, the use of organic amendmentsuch as FYM, rice straw and green manure is known to improveoil productivity (Ramesh et al., 2009; Bhatia et al., 2005) and hashe capacity to increase SOC (Ghosh et al., 2010). However, littleork has quantified the long-term impact of organic amendments

with or without fertilization) on the SOC stock, the dynamics ofhe various C pools and soil quality response in relation to croproductivity in intensively managed Indian soils, especially in the

ndo-Gangetic region. In addition, little work has compared the var-ous available waste products and their effects in combination withnorganic amendments on different attributes of soil quality.

The present study was, therefore, undertaken to assess the longerm effects of different management practices on soil qualitynd carbon sequestration using a 25 year old long term fertilityxperiment (LTFE) with rice–wheat cropping systems in the Indo-angetic plains of West Bengal, India. We sought to (i) evaluate theffects of various organic and inorganic amendments on a series ofoil quality indicators and (ii) assess the role of these amendmentsn C sequestration potential in soils.

. Materials and methods

.1. Site description

A long-term field experiment was initiated in 1986 for the Allndia Coordinated Research Project on Cropping Systems at theniversity Teaching Farm, Bidhan Chandra Krishi Viswavidyalaya,est Bengal (23◦N, 89◦E, 9.5 m msl) on the new alluvial soil

one in the hot humid sub-tropic Indo-Gangetic plains of easternndia. Background information characterizing the experimental sites presented in Table 1. The experimental soil (0–0.15 m depth)s sandy loam classified as Aeric Haplaquept (Soil Survey Staff,006), with pH 7.2, oxidizable organic C 8.8 g kg−1, bulk density.13 g cm−3 and cation exchange capacity 22.0 cmolc kg−1. Due toigh annual rainfall (1500 mm), a rice-based cropping system is theominant agricultural system in the region.

.2. Experimental design and treatments

The experiment was laid out in a randomized block design withhe following treatments: fallow (no cultivation since the inceptionf the experiment) (T1), control (conventional cultivation with-ut any fertilizer or amendments) (T2), 100% recommended dosef inorganic fertilizer (NPK) (T3), NPK + farm yard manure (FYM

7.5 t ha−1) (T4), NPK + paddy straw (PS @ 10 t ha−1) (T5) and

PK + green manure (Sesbenia sesban L.) (GM @ 8 t ha−1) (T6). Each

reatment was replicated four times. The biochemical compositionf the organic amendments was summarized in Table 2 as an aver-ge for the last 5 years. Two crops, viz., rice (O. sativa L., cv IET

Cellulose 23.1 ± 0.4 35.0 ± 0.3 10.0 ± 0.2Lignin 17.5 ± 0.2 11.0 ± 0.1 8.9 ± 0.1Polyphenol 1.1 ± 0.03 0.6 ± 0.03 0.3 ± 0.02

4094) and wheat (T. aestivum L., cv UP 262) were grown annuallyfollowing standard regional practices. Land preparation was under-taken using a bullock drawn plough and the fields were kept floodedor saturated with water. Puddling was done with powertiller oneweek before transplanting of rice seedlings. After harvesting of rice,wheat is grown with specified fertilizers (Table 1) following stan-dard practices. Three representative soil samples were collectedrandomly at the same time 7 days after rice harvest from each plotincluding the fallow at three different depths (0–0.15, 0.15–0.30and 0.30–0.45 m) as the effects of inorganic and organic amend-ments on soils are typically restricted to these layers (Ghosh et al.,2010; Mandal et al., 2007). Field-moist soil samples were handcrushed and passed through a 2.0 mm sieve and stored at 4 ◦C. Thesefresh field-moist sieved samples were used for the estimation ofsoil microbial biomass C and mineralizable C. Air-dried soil samplesthat had passed through the same sieve were used for analysis of aselected suite of physico-chemical properties. In each plot, dupli-cate undisturbed soil core samples at the three depths were takenby using a 50 mm diameter core sampler to determine bulk density(BD).

2.3. Soil quality parameters

A series of soil quality parameters were analysed to evaluatethe effects of soil amendments on physical, chemical and biolog-ical properties of the soils studied. Soil pH was measured in a1:2.5 soil:water suspension. Soil available nitrogen (N) was deter-mined by alkaline permanganate method (Subbiah and Asija, 1956).Extractable phosphorus (P) was determined colorimetrically fol-lowing ascorbic acid reductant method as outlined by Watanabeand Olsen (1965) and exchangeable potassium (K) content of thesoils was determined by flame photometer using neutral normalammonium acetate as an extractant as described by Jackson (1973).Total C content of the samples were analysed by high temperature(450 ◦C) combustion weight loss on ignition method (Konen et al.,2002).

A chloroform (CHCl3) fumigation–extraction method was usedto determine microbial biomass C (MBC) (Voroney and Paul, 1984;Ghosh et al., 2010). Microbial biomass N (MBN) was estimatedusing the same principle of MBC. The filtrate extracted by K2SO4of both fumigated and unfumigated soil was digested for 1.5 h withaddition of digestion mixture and sulphuric acid. The differencebetween fumigated and unfumigated N of soil divided by a cali-bration factor (KEN) 0.45 (Jenkinson, 1988) gives the measure ofMBN in soil and expressed as �g of MBN g−1 of dry soil. Carbonmineralization (Min-C) was evaluated by incubation for twentyfour days with alkali traps containing 1.0 M NaOH (Franzluebbers,1999). The same soil (after incubation) was used to measure min-eralizable N (Min-N). 10 g of incubated soil was placed in a 250 mlconical flask and extracted by shaking with 100 ml 2.0 M KCl for30 min in an oscillating shaker at 200 rpm and then filtered throughthe filter paper and the filtrate collected for the determination of

N (both NO3 and NH4) content. Min-N was determined by sub-tracting the control from the incubated reading and expressed as�g of N mineralized g−1 of dry soil per day. Dehydrogenase activ-ity was measured based on the estimation of the magnitude of

1 s and

rmaAtoBn

2

lcatortarraAbS

2

wac0aaaddilHBCBsm

2

cl

S

wS

2

mb

S

36 S. Ghosh et al. / Agriculture, Ecosystem

eduction of triphenyl tetrazolium chloride (TTC) to triphenyl for-azan (TPF) by soil at 30 ◦C for 24 h (Thalmann, 1966) and the

ctivity was expressed in �g TPF formed g−1 of dry soil per day.cid and alkaline phosphatase activity were measured based on

he determination of p-nitrophenol released after the incubationf soil with p-nitrophenyl phosphate for 1 h at 37 ◦C (Tabatabai andremner, 1969) and the enzyme activity was expressed as �g p-itrophenol g−1 of dry soil.

.4. Cumulative C input

Cumulative C inputs, during the 25 cropping cycles, were calcu-ated from organic sources (FYM, PS and GM) as well as from cropontributions (roots, stubble and rhizodeposition) (Table 3). Themount of C inputs from FYM, PS and GM were computed by mul-iplying the total dry weight with their C concentrations (averagef last 5 years) (Table 3). The biomass yield of roots, stubble andhizodeposition of rice were assumed as 19, 2.5 and 15%, respec-ively, of the total above ground biomass harvested at maturity,nd the corresponding values for the wheat were 22, 3 and 12.6%,espectively (after Bronson et al., 1998). The C concentration in theoot, stubble and rhizodeposition were estimated to be 41.2, 31.8nd 74%, respectively for rice, and 39.1, 35.2 and 74% for wheat.n extra C input was also assumed through photosynthetic contri-ution by aquatic organisms of rice field, was accounted followingaito and Watanabe (1978) (Table 3).

.5. Carbon fractionation

The fractions of SOC present under the various treatmentsere estimated through a modified Walkely and Black method

s described by Chan et al. (2001) using 5, 10 and 20 ml of con-entrated H2SO4 resulting three acid–aqueous solution ratios of.5:1, 1:1 and 2:1 (which corresponded, respectively to 12 N, 18 Nnd 24 N of H2SO4). The amount of SOC determined using 5, 10nd 20 ml of concentrated H2SO4 when compared with total C,llowed separation of total C into the following four fractions ofecreasing oxidizability: Fraction I (Cfrac 1, very labile) organic C oxi-izable under 12 N H2SO4; Fraction II (Cfrac 2, labile) the difference

n SOC extracted between 18 N and 12 N H2SO4; Fraction III (Cfrac 3,ess labile) the difference in SOC extracted between 18 N and 24 N

2SO4 (the 24 N H2SO4 is equivalent to the standard Walkely andlack method); and Fraction IV (Cfrac 4, non-labile) residual organic

after reaction with 24 N H2SO4 when compared with total C.ecause of possible changes in bulk density as a result of croppingystem and organic fertilization, the C pools were calculated on aass per unit volume basis (Ellert and Bettany, 1995).

.6. Carbon sequestration

The amount of carbon sequestered during the last 25 years ofropping was computed in the 0–0.45 m soil layer using the fol-owing formula.

equestered C (Mg ha−1) = TOCtreatment − TOCfallow

here TOCtreatment = total SOC from the treatments; TOCfallow = totalOC from fallow.

.7. Sustainable yield index (SYI)

The sustainable yield index of rice was calculated for the treat-

ents taking into consideration the yield data for the last 25 years

y using the following formula (Singh et al., 1990):

YI = Y − �

Ymax

Environment 156 (2012) 134– 141

where Y = mean yield over the years; � = standard deviation andYmax = maximum yield of the area.

2.8. Statistical analyses

Results were analysed in R 2.5.0 (R Development Core Team,2006) using fixed effects analysis of variance (ANOVA). For eval-uation of C sequestration, two-way analysis was performed withtreatment and depth as factors. Variances were checked by plottingresidual vs. fitted values to confirm the homogeneity of the data. Notransformations were necessary. Means for significant treatmenteffects were separated using Duncan’s Multiple Range Test (DMRT)and based on least significant difference (LSD) values.

3. Results

3.1. Effects on soil quality parameters

The experimental soils had almost neutral pH (6.57–7.20)(Table 4) and BD ranging between 1.13 and 1.25 Mg m−3. Applica-tion of fertilizer with or without organic amendments, in general,resulted in significantly larger concentrations of available N, P andK in all the treatments compared with the control (Table 4). Micro-bial biomass carbon (MBC) content of the soils varied from 250 to776 �g g−1 soil and the values constituted about 3.1% of the totalSOC content of the soil. Although the addition of inorganic NPK(T3) resulted in a significant increase in MBC over the control (T2),this effect was significantly larger when fertilizer was applied alongwith the organic amendments (Table 4). Microbial biomass nitro-gen (MBN) content of the soils varied from 33.3 to 66.5 �g g−1 soil,with the relative amount under different treatments as follows:NPK + GM (T6) > NPK + PS (T5) > NPK + FYM (T4) = NPK (T3) > fallow(T1) > control (T2). The amount of Min-C in the soils varied from 0.09to 0.17 mg CO2 24 h−1 g soil−1, the relative magnitude under differ-ent treatments being as follows: fallow (T1) > NPK (T3) > NPK + FYM(T4) > NPK + PS (T5) > NPK + GM (T6) > control (T2) (Table 5). TheMin-N content of the experimental soils under different treatmentsvaried from 1.14 to 4.70 �g NH4 g soil−1 24 h−1. Soils under contin-uous cultivation without any fertilizer had a significantly smallerconcentration of Min-N compared with the fallow treatment. Thedehydrogenase activity of the soils under different treatmentsranged from 20.3 to 30.4 �g TPF g soil−1 24 h−1; whilst the acid andalkaline phosphatase varied from 69.0 to 88.0 and 47.1 to 60.1 �g p-nitrophenol g soil−1, respectively.

3.2. Effects on C sequestration

Continuous cultivation, without application of any organicor inorganic amendments (T2), had the lowest concentration oftotal SOC (Table 6). Among the different treatments, soil underNPK + FYM (T4) contained as much as 61% higher total SOCwhen compared with control (T2), followed by NPK + PS (T5)(51%) > NPK + GM (T6) (43%) > NPK (T3) (32%). All the amendmenttreatments had significantly larger quantities of Cfrac 4 comparedwith T2, with the highest increase under T4 followed by T6 > T5 > T3and the content of Cfrac 4 was higher in the sub-surface soil(Table 6). The magnitude of different fractions was as follows:Cfrac 4 > Cfrac 1 > Cfrac 3 > Cfrac 2. Both PS (T5) and GM (T6) had signif-icantly larger quantities of labile Cfrac 1, Cfrac 4 dominated with T4(FYM), whereas Cfrac 2 was significantly higher under T5 and T4when compared with control (T2).

3.2.1. C gain or lossWhen compared with fallow (T1), the amount of sequestered

C was higher (2.47 Mg ha−1) under T4 (NPK + FYM) followed by T5

S. Ghosh et al. / Agriculture, Ecosystems and Environment 156 (2012) 134– 141 137

Table 3Cumulative C inputs in soils through different treatments.

Treatment Stubble biomass C(Mg ha−1)

Root biomass C(Mg ha−1)

Rhizode-position C(Mg ha−1)

Aquatic biomass C(Mg ha−1)

Crop C input(Mg ha−1)

FYM/PS/GM C(Mg ha−1)

Cumulative C input(Mg ha−1)

Control 1.52 10.6 11.8 13.3 37.2 0.0 37.2NPK 3.04 24.5 29.6 13.3 70.4 0.0 70.4NPK + FYM 3.42 27.0 34.2 13.3 77.9 9.5 87.4NPK + PS 3.42 26.4 33.3 13.3 76.4 8.0 84.4NPK + GM 3.23 25.8 32.5 13.3 74.8 6.3 81.1

Table 4Changes in some important attributes of soil quality after 25 years of cultivation with different treatments.

Treatment pH BD(Mg m−3)

Av. N(kg ha−1)

Av. P(kg ha−1)

Av. K(kg ha−1)

MBC(�g g soil−1)

MBN(�g g soil−1)

Microbialquotient (%)

Fallow 6.57b 1.25a 132d 35.0e 162d 483d 37.7d 3.00b

Control 7.20a 1.13c 152c 48.8d 173c 250e 33.3e 2.25d

NPK 6.90a 1.25a 165ab 95.9a 199a 486d 44.3c 3.04b

NPK + FYM 7.03a 1.19b 167a 95.5a 186b 531c 44.3c 2.73c

NPK + PS 7.00a 1.19b 158bc 73.7c 159d 776a 55.4b 3.88a

NPK + GM 7.03a 1.16b 158bc 90.4b 191b 565b 66.5a 3.09b

SEm(±) 0.089 0.011 2.30 1.07 1.95 3.58 0.29 0.011

Means followed by common letter are not significantly different (p < 0.05) by Duncan’s Multiple Range Test (DMRT).BD = bulk density; Av. N = available N; Av. P = available P; Av. K = available K; MBC = microbial biomass C; MBN = microbial biomass N.

Table 5Changes in some important attributes of soil quality after 25 years of cultivation with different treatments.

Treatment Min-C(mg CO2 24 h−1 g soil)

Min-N(�g NH4 g soil−1 24 h)

Metabolic quotient(�g CO2-C 24 h−1 �g MBC)

Dehydro(�g TPF g soil−1 d)

Acid phos(�g p-nitrophenol g soil−1)

Alkaline phos (�g p-nitrophenol g soil−1)

Fallow 0.17a 3.36a 0.34a 30.4a 69.0e 56.4bc

Control 0.09b 1.14d 0.35a 22.9e 75.7d 54.5c

NPK 0.15ab 1.97bc 0.31ab 20.3f 76.1d 47.1d

NPK + FYM 0.15ab 4.70a 0.28ab 26.7c 83.1c 56.8bc

NPK + PS 0.13ab 1.57c 0.17bc 24.8d 85.0b 57.5b

NPK + GM 0.11ab 4.03a 0.20c 28.4b 88.0a 60.1a

SEm(±) 0.020 0.473 0.004 0.34 0.42 0.70

MM y; Aci

(aatAtC

eans followed by common letter are not significantly different (p < 0.05) DMRT.in-C = mineralizable C; Min-N = mineralizable N; Dehydro = dehydrogenase activit

NPK + PS) (1.41 Mg ha−1) > T6 (NPK + GM) (0.4 Mg ha−1). There was net loss of C by 5.6% due to continuous cultivation without anymendment (T2). The result showed that 26.1%, 17.7% and 6.3% of

he C applied through FYM, PS and GM were sequestered in the soil.fter 25 years of cropping, there was a strong positive linear rela-

ionship (R2 = 0.98) between stable C (C fraction 4) and cumulative input (Fig. 1).

Fig. 1. Relationship between stable C (Cfrac 4) and cu

d phos = acid phosphatase activity; Alkaline phos = alkaline phosphatase activity.

3.3. Yield and sustainable yield index

The yield of kharif rice showed wide variations among thetreatments compared. The relative performance of the dif-

ferent treatments was as follows: NPK + GM (T6) > NPK + FYM(T4) > NPK + PS (T5) > NPK (T3) > control (T2) (Table 7). With respectto sustainable yield index (SYI), application of NPK fertilizers caused

mulative C input under different treatments.

138 S. Ghosh et al. / Agriculture, Ecosystems and Environment 156 (2012) 134– 141

Tab

le

6C

han

ges

in

tota

l soi

l car

bon

(Mg

ha−1

)

and

orga

nic

C

frac

tion

s

(g

kg−1

)

un

der

dif

fere

nt

trea

tmen

ts

and

dif

fere

nt

dep

ths.

Trea

tmen

t

Tota

l soi

l org

anic

carb

on

(Mg

ha−1

)

Soil

orga

nic

carb

on

frac

tion

(Mg

ha−1

)

0–0.

15

0.15

–0.3

0

0.30

–0.4

5

Cfr

ac

1C

frac

2C

frac

3C

frac

4

0–0.

15

0.15

–0.3

0

0.30

–0.4

5

0–0.

15

0.15

–0.3

0

0.30

–0.4

5

0–0.

15

0.15

–0.3

0

0.30

–0.4

5

0–0.

15

0.15

–0.3

0

0.30

–0.4

5

Fall

ow18

.8c

18.1

b19

.6c

8.05

bc4.

50d

4.01

b3.

31c

2.63

c3.

04b

2.12

a4.

13b

0.69

a5.

29c

6.84

a11

.81e

Con

trol

14.7

a13

.4a

12.0

a6.

92a

3.78

bc2.

77a

1.53

a1.

03a

2.91

ab2.

94b

2.07

a2.

91c

3.27

a6.

56a

3.39

a

NPK

17.8

b17

.9b

17.5

b7.

65b

3.22

a2.

89a

1.90

ab2.

74c

2.96

b2.

75ab

1.76

a4.

10d

5.47

c10

.15b

7.53

b

NPK

+

FYM

21.3

e22

.4e

21.2

d7.

90bc

3.45

ab3.

18a

3.93

cd3.

70d

2.21

a3.

67b

2.39

a4.

16d

5.82

c12

.90c

11.6

6e

NPK

+

PS19

.9d

21.6

d19

.5c

7.94

b6.

44c

2.91

a4.

50d

1.83

b4.

17c

3.56

b3.

40b

1.80

b3.

88ab

9.89

b10

.59d

NPK

+

GM

18.3

bc19

.9c

19.4

c8.

31c

3.99

c4.

15b

2.69

b1.

57ab

2.49

ab2.

98b

1.69

a3.

19c

4.28

b12

.63c

9.54

c

T

×

D**

*

***

**

***

***

LSD

(0.0

5)0.

505

0.48

60.

712

0.78

20.

683

ns

=

not

sign

ifica

nt;

T

=

trea

tmen

t,

D

=

dep

th.

*p

<

0.05

.**

p

<

0.01

.**

*p

<

0.00

1.

Table 7Yield of Kharif rice and sustainable yield index after 25 years of cultivation withorganic and inorganic treatment combinations.

Treatment Yield (t ha−1) Sustainable yieldindex

Fallow – –Control 1.5c 0.234e

NPK 2.0c 0.616d

NPK + FYM 3.2a 0.684a

NPK + PS 2.6b 0.638c

NPK + GM 3.3c 0.669b

SEm(±) 0.169 –

Means followed by common letter are not significantly different (p < 0.05) by DMRT.

a significant increase (167%) in the value of SYI over the control.Results also showed that incorporation of organics with NPK fertil-izer caused a further increase in SYI and the magnitude of increasewas higher with FYM (192%) followed by GM (186%) and PS (173%)(Table 7).

4. Discussion

4.1. Effect on soil quality

The soils that had received both inorganic and organicamendments consistently showed significantly higher amounts ofavailable N, P and K. This is primarily due to the mineralizationand release of these elements contained in the organics (FYM, PS,GM) on their decomposition. Further, the intense reduced conditionfacilitated by the decomposition of these organics in the floodedsoil during rice growth enhanced the reduction of insoluble ferricphosphate in soil to soluble ferrous phosphate resulting in increasein the available P. Moreover the organic acids and ligands thatare produced during decomposition of organics help to increasethe availability of other nutrients in soil. In rice–wheat system, Kis readily displaced from the exchange complex due to increasedconcentrations of Fe(II), Mn(II) and ammonium during the floodingphase of rice. There is therefore a need to supplement cation con-tents under such conditions and organic amendments can stronglyinfluence K budgets and promote efficient management of K for asustainable rice–wheat system in the Indo-Gangetic plains (Singhet al., 2004). We also observed a significant increase in availableK content upon fertilizer and organics application over the controland the fallow excepting with PS incorporation.

Soil microbial biomass constitutes a small portion (1–4%) ofSOM (Smith and Paul, 1990), but it is more dynamic and fluctu-ates more over time than the total SOM. Therefore, measurementof soil microbial biomass may show the effect of soil managementon potential changes in SOM long before such effect can be detectedby measuring total SOC (Powlson et al., 1987). The applicationof organic amendments along with inorganic fertilizer provided amore favourable environment for rapid microbial growth, whichcaused a greater increase in MBC in these soils (Moscatelli et al.,2005). Addition of FYM is usually associated with an increase inmicrobial biomass (Kaur et al., 2008) and, Banerjee et al. (2006)similarly observed an increased MBC with addition of FYM and GMin the alluvial soils of Indo-Gangetic plains with rice–wheat crop-ping system. However, we observed a larger increase of MBC withPS compared to GM or FYM, which might be due to the presenceof decomposition resistant fibre fractions in the former (PS) com-pared with the latter two (GM, FYM). Management practices thatinclude the incorporation of organic residues into soil therefore

increase biological activity. The use of inorganic fertilizers mightalso increase plant biomass production which in turn can increasethe amount of residue return to the soil each year for the LTFE andthus stimulate biological activity.

s and

ewbeaetiomwrctitogaicdit

boMGtt

t2etaBGsiymetitdiatt

oeiliaua2ple

inputs through organic amendment as well as crop C inputs (Fig. 1)

S. Ghosh et al. / Agriculture, Ecosystem

The microbial quotient for the experimental soils under differ-nt treatments varied from 2.3 to 3.9% (Table 4) which is consistentith the findings of other researchers who also observed micro-

ial quotient to vary within a wide range from 0.27 to 7% (Insamt al., 1989; Jinbo et al., 2007). As microbial quotient of <1% is

reliable indicator for a reduced C turnover in soils (Joergensont al., 1994), the results of the present study indicate a high Curnover in the experimental soils, as is expected in soils of trop-cal and subtropical region of the world. An efficient utilizationf C by microorganisms was indicated by a significantly loweretabolic quotient (qCO2) in the organic treatments comparedith the control or fallow treatments (Table 5). Incorporation of

eadily decomposable organic matter such as GM, PS and FYMaused about 100, 66 and 33% increase in MBN over the con-rol, probably because, these organics stimulate biological activityn soils causing both an increase in microbial biomass C and Nhere (Dalal and Mayer, 1987). Microbial C:N ratio (MBC:MBN)f the experimental soils varied from 7.75 to 14.01, which sug-ested that particularly fallowing and incorporation of PS as wells FYM induced a fungal dominated microflora (Jenkinson, 1988)n soils. The higher microbial C:N ratio in soil amended with PSompared to GM and FYM might be related to the presence ofecomposition resistant fibre fractions (Sridevi et al., 2003) induc-

ng a fungal dominated microbial population in the PS amendedreatment.

There was a significant decline in Min-C in where soils hadeen intensively cultivated over the last 25 years, the magnitudef decrease in the control treatment being 48% that of the fallow.ineralizable C and N content were significantly higher in FYM andM treatments as compared to control and fallow; PS incorpora-

ion, on the other hand, did not show any differences, possibly dueo its high C:N ratio.

Long-term studies have shown that soil enzymes are sensitiveo changes in soil management systems (Dick, 1992; Roldan et al.,005), level of nutrients and organic matter addition (Katsalirout al., 2010). An increase in dehydrogenase activity due to addi-ion of organic wastes with NPK fertilizer might be due to highervailability of easily decomposable organic C in these treatments.olton et al. (1985) also expressed similar views that addition ofM to a wheat based rotation over a 30 year period caused aignificant increase in dehydrogenase activity. Phosphatases aremportant in maintaining the P-cycle because they catalyse hydrol-sis of P-ester bonds binding P to C (C O P ester bond) in organicatter and addition of organic residues with inorganic NPK fertiliz-

rs enhanced the phosphatase activity in the soils. All these resultshus indicated that on continuous cultivation without any fertil-zer and organic amendments, there was depletion in almost allhe favourable attributes of soil quality and hence the soil qualityeteriorated under such condition. Conjoint application of organ-

cs with inorganic caused an increase in these attributes and hencen improvement in the soil quality (compared to fallow) even withhe stresses of intensive double (rice–wheat) cropping system forhe last 25 years.

Although our results have demonstrated positive effects ofrganic amendments to the soils studied, caution has beenxpressed elsewhere with regard to potential excess nutrient load-ng or concentration of phytotoxic elements that might result fromong-term or over-application of organic materials to soils. Theres increasing evidence that organic amendments at high rates ofpplication can cause dramatic increases in soil nutrients, partic-larly N, P and K, leading to increased leaching of these elementsnd associated off-site impacts (Amlinger et al., 2007; Kundu et al.,

009). Other work has identified the potential for accumulation ofhytotoxic element (e.g. Cd, Pb, Cr) in soils at high rates or pro-

onged applications of various organic amendments (e.g. Neilsent al., 1998; Smith, 2009) and their potential transfer to plants and

Environment 156 (2012) 134– 141 139

grazing animals. The composition and potential threat from variousorganic materials will of course vary depending on their origin, thesoil type in question and a variety of other variables. Sustainableuse of organic amendments in agriculture will however, demandthat these potential effects are recognized and that application tosoils is undertaken at rates that mitigate these potential negativeeffects. Quantification of appropriate rates of application is rare,particularly in the region that we studied and therefore representsa significant current knowledge gap.

4.2. Effect on C sequestration

The amount of C sequestered at a site reflects the long-termbalance between C uptake and release mechanisms. Continuouscultivation affects the distribution and stability of soil aggre-gates and reduces organic C stock in soils (Six et al., 2002).Many researchers (Lal, 2004; Mandal et al., 2007) have reportedhigh levels of C depletion (30–60%) due to intensive cropping insubtropical regions of India. Application of FYM, PS and GM asa supplement with NPK not only added organic carbon in thesoil but also increased plant C inputs in the soil through rootresidue, stubble, rhizodeposition (Table 3), etc. because of anincrease in yield (Table 7). Similarly, Kukal et al. (2009) observeda higher C sequestration in a 33 year old rice–wheat system dueto application of FYM and the cropping system has greater capac-ity to sequester C because of high C input through enhancedproductivity.

The first two (labile) fractions (Cfrac 1 and Cfrac 2) constituted58% of total C in the top 0.15 m soil layer and 34% at the lowerdepth, whereas the less labile or non labile fractions (Cfrac 3 andCfrac 4) constituted 42% of total C at 0.15 m depth and 66% at lowerdepth. These indicated that along depth, a higher proportion oftotal SOC got allocated to non-labile recalcitrant forms with longerresidence time highlighting the potential to increase SOC seques-tration in soil by improving depth distribution of SOC. Plants withdeeper root system and translocation of dissolved organic C fromsurface to subsurface layers might thus contribute to higher sta-bility to SOC for enriching its levels in subsurface layers. Amongthe treatments, the higher values of labile fractions (Cfrac 1 andCfrac 2) under NPK + PS (T5) may be ascribed to the higher polysac-charides (cellulose and hemicellulose) content of PS that couldled to the higher production of that fraction as compared to thatof FYM and GM. The larger effect of NPK + FYM (T4) and NPK + PS(T5) treatments on less labile/non labile fractions (Cfrac 3 and Cfrac 4)may be attributed to the higher lignin and polyphenol content ofFYM and PS (Table 2) that could lead to formation of more sta-ble complex with protein of plant origin and thus made FYM-Cmore resistant to decomposition (Tian et al., 1992) than that ofGM.

This is reinforced by a higher allocation of C into less labile/nonlabile fractions with NPK + FYM treatments, as mentioned earlier(Table 6). Addition of these organic amendments also increasedplant C inputs in the soil (Table 3). When the plant C inputs wereincluded with C inputs through organic amendments, the percent-age of C sequestration reduced to 14.5%, 10.0% and 3.7% due tothe FYM, PS and GM application, respectively. After 25 years crop-ping cycles, the existence of a strong positive linear relationship(R2 = 0.98) between the amount of C sequestered and the cumu-lative C input values indicted that the soil of the present studystill has the capacity to sequestered more C with the increase of C

(Mandal et al., 2007). Similarly, in a long term study for 20 years,Dou et al. (2007) observed that for intensive cropping sequences,decreasing fallow periods and increasing crop residue productionincreased soil C sequestration in silty clay loam soil.

1 s and

5

cetosimflrtibeptaae

A

RWA

R

A

B

B

B

B

B

B

C

D

D

D

E

F

G

40 S. Ghosh et al. / Agriculture, Ecosystem

. Conclusion

The implementation of effective management practices such asombined application of fertilizer and organic amendments led tonhanced soil quality and associated increases in soil C sequestra-ion in rice–wheat cropping system in the Indo-Gangetic plainsf eastern India. Such applications also helped to maintain yieldustainability by improving nutrient supply and biological activityn soils. Continuous cropping without addition of organic amend-

ents resulted in a decrease in total C in both labile and non-labileractions. The labile C fractions dominated in the near surface soilayers, but decreased significantly in the deeper layers where theecalcitrant C fraction increased. Our results clearly indicate thathe application of organic amendments along with inorganic fertil-zer can improve or maintain soil quality and productivity whilstuilding SOC in these environments. Although these overall ben-fits can be viewed as an opportunity to improve soil quality androductivity, there is still a need to quantify and manage poten-ial negative effects such as excess nutrient accumulation, leachingnd phytotoxicity associated with long-term application of organicmendments. The magnitude of these threats remains a key knowl-dge gap in this region.

cknowledgement

We gratefully acknowledge the Indian Council of Agriculturalesearch (ICAR), New Delhi, for funding the work through theorld Bank assisted multi-institutional collaborative National

gricultural Technology Project.

eferences

mlinger, F., Peyr, S., Geszit, J., Dreher, P., Weinfurtner, K., Nortcliff, S., 2007. Ben-eficial Effects of Compost Application on Fertility and Productivity of Soils: ALiterature Study. Federal Ministry for Agriculture and Forestry, Environmentand Water Management, Vienna, 235 pp.

andyopadhyay, P.K., Saha, S., Mallick, S., 2011. Comparison of soil physical prop-erties between a permanent fallow and a long-term rice–wheat cropping withinorganic and organic inputs in the humid subtropics of eastern India. Commun.Soil Sci. Plant Anal. 42, 435–449.

anerjee, B., Aggarwal, P.K., Pathak, H., Singh, A.K., Chaudhury, A., 2006. Dynam-ics of organic carbon and microbial biomass in alluvial soil with tillage andamendments in rice–wheat systems. Environ. Monit. Assess. 119, 173–189.

hatia, A., Pathak, H., Jain, N., Singh, P.K., Singh, A.K., 2005. Global warming potentialof manure amended soils under rice–wheat system in the Indo-Gangetic plains.Atmos. Environ. 39, 6976–6984.

hattacharyya, R., Prakash, V., Kundu, S., Srivastva, A.K., Gupta, H.S., 2009. Soil aggre-gation and organic matter in a sandy clay loam soil of the Indian Himalayas underdifferent tillage and crop regimes. Agric. Ecosyst. Environ. 132, 126–134.

olton, H., Elliot, L.F., Papendick, R.I., Bezdicek, D.F., 1985. Soil microbial biomass andselected soil enzyme activities; effect of fertilization and cropping practices. SoilBiol. Biochem. 17, 297–302.

ronson, K.F., Cassman, K.G., Wassmann, R., Olk, D.C., Noordwijk, M.van., Garrity,D.P., 1998. Soil carbon dynamics in different cropping systems in principaleco-regions of Asia. In: Lal, R., Kimble, J.M., Follett, R.F., Stewart, B.A. (Eds.), Man-agement of Carbon Sequestration in Soil. CRC Press, Boca Raton, New York, pp.35–57.

han, K.Y., Bowman, A., Oates, A., 2001. Oxidizable organic carbon fractions and soilquality changes in an oxic paleustaff under different pastures leys. Soil Sci. 166,61–67.

alal, R.C., Mayer, R.J., 1987. Long term trend in fertility of soils under continuous cul-tivation and cereal cropping in southern Queensland. VII. Dynamics of nitrogenmineralization potentials and microbial biomass. Aust. J. Soil Res. 25, 461–472.

ick, R.P., 1992. A review: long-term effects of agricultural systems on soil biochem-ical and microbial parameters. Agric. Ecosyst. Environ. 40, 25–36.

ou, F., Wright, A., Hons, F., 2007. Depth distribution of soil organic C and N afterlong-term soybean cropping in Texas. Soil Till. Res. 94, 530–536.

llert, B.H., Bettany, J.R., 1995. Calculation of organic matter and nutrients stored insoils under contrasting management regimes. Can. J. Soil Sci. 75, 529–538.

ranzluebbers, A.J., 1999. Potential C and N mineralization and microbial biomassfrom intact and increasingly disturbed soils of varying texture. Soil Biol.

Biochem. 31, 1083–1090.

hosh, S., Wilson, B.R., Mandal, B., Ghoshal, S.K., Growns, I., 2010. Changes in soilorganic carbon pool in three long-term fertility experiments with different crop-ping systems, inorganic and organic soil amendments in the eastern cereal beltof India. Aust. J. Soil Res. 48, 413–420.

Environment 156 (2012) 134– 141

Hobbs, P.R., Gupta, R.K., 2003. Rice–wheat cropping systems in the Indo-Gangeticplains: issues of water productivity in relation to new resource-conserving tech-nologies. In: Kijne, J.W., Barker, R., Molden, D. (Eds.), Water Productivity inAgriculture: Limits and Opportunities for Improvement. , pp. 239–253.

Insam, H., Parkinson, D., Domsch, K.H., 1989. The influence of macroclimate on soilmicrobial biomass levels. Soil Biol. Biochem. 21, 211–221.

Jackson, M.L., 1973. Soil Chemical Analysis. Prentice Hall India Pvt. Ltd., New Delhi,p. 498.

Jenkinson, D.S., 1988. Determination of microbial biomass carbon and nitrogen insoil. In: Wilson, J.R. (Ed.), Advances in Nitrogen Cycling in Agricultural Systems.CAB International, Wallingford, UK, pp. 368–386.

Jinbo, Z., Changchun, S., Wenyan, Y., 2007. Effects of cultivation on soil microbiolog-ical properties in a freshwater marsh soil in Northeast China. Soil Till. Res. 93,231–235.

Joergenson, R.G., Meyer, B., Mueller, T., 1994. Time course of soil microbial biomassunder wheat: a one year field study. Soil Biol. Biochem. 26, 987–994.

Katsalirou, E., Deng, S., Nofziger, D.L., Gerakis, A., 2010. Long-term managementeffects on organic C and N pools and activities of C-transforming enzymes inprairie soils. Eur. J. Soil Biol. 46, 335–341.

Kaur, J., Choudhary, O.P., Singh, B., 2008. Microbial biomass carbon and soil prop-erties as influenced by long-term sodic water irrigation, gypsum and organicamendments. Aust. J. Soil Res. 46, 141–151.

Konen, M.E., Jacobs, P.M., Burras, C.L., Talaga, B.J., Mason, J.A., 2002. Equations forpredicting soil organic carbon using loss-on-ignition for North Central US soils.Soil Sci. Soc. Am. J. 66, 1878–1881.

Kukal, S.S., Rasool, R., Benbi, D.K., 2009. Soil organic carbon sequestration in relationto organic and inorganic fertilization in rice–wheat and maize–wheat systems.Soil Till. Res. 102, 87–92.

Kundu, M., Hazra, G.C., Mandal, B., 2009. Nitrate and fluoride contamination ingroundwater of an intensively managed agroecosystem: a functional relation-ship. Sci. Total Environ. 407, 2771–2782.

Lal, R., 2004. Soil carbon sequestration impacts on global climate change and foodsecurity. Science 304, 1623–1627.

Lal, R., 2007. Soil science and the carbon civilization. Soil Sci. Soc. Am. J. 71,1425–1437.

Mandal, B., Majumder, B., Bandyopadhyay, P.K., Hazra, G.C., Gangopadhyay, A.,Samantaray, R.N., Misra, A.K., Chaudhury, J., Saha, M.N., Kundu, S., 2007. Thepotential of cropping systems and soil amendments for carbon sequestration insoils under long-term experiments in subtropical India. Global Change Biol. 13,357–369.

Moscatelli, M.C., Lagomarsino, A., Marinari, S., De Angelis, P., Grego, S., 2005. Soilmicrobial indices as bioindicators of environmental changes in a poplar planta-tion. Ecol. Indic. 5, 171–179.

Nambiar, K.K.M., 2002. Soil Fertility and Crop Productivity Under Long-term Fer-tiliser Use in India. ICAR, New Delhi, p. 144.

Neilsen, G.H., Hogue, E.J., Neilsen, D., Zebarth, B.J., 1998. Evaluation of organic wastesas soil amendments for cultivation of carrot and chard on irrigated sandy soils.Can. J. Soil Sci. 78, 217–225.

Powlson, D.S., Brooke, P.C., Christensen, B.T., 1987. Measurement of soil microbialbiomass provides an early indication of changes in total soil organic matter dueto straw incorporation. Soil Biol. Biochem. 19, 159–164.

R Development Core Team, 2006. A Language and Environment for Statistical Com-puting. R Foundation for Statistical Computing, Vienna.

Ramesh, P., Panwar, N.R., Singh, A.B., Ramana, S., Rao, A.S., 2009. Impact of organic-manure combinations on the productivity and soil quality in different croppingsystems in central India. J. Plant Nutr. Soil Sci. 172, 577–585.

Roldan, A., Salinas-Garcia, J.R., Alguacil, M.M., Diaz, E., Caravaca, F., 2005. Soil enzymeactivities suggest advantages of conservation tillage practices in sorghum culti-vation under subtropical conditions. Geoderma 129, 178–185.

Saito, M., Watanabe, I., 1978. Organic matter production in rice field flood water.Soil Sci. Plant Nutr. 24, 427–440.

Sharma, K.L., Mandal, U.K., Srinivas, K., Vittal, K.P.R., Mandal, B., Kusuma, G.J.,Ramesh, V., 2005. Long-term soil management effects on crop yields and soilquality in a dryland Alfisol. Soil Till. Res. 83, 246–259.

Singh, B., Singh, Y., Imas, P., Jian-chang, X., 2004. Potassium nutrition of therice–wheat cropping system. Adv. Agron. 81, 203–259.

Singh, P., Khan, R.A., 2000. Long-term effects of fertiliser practice on yield and prof-itability of rice–wheat cropping system. In: Abrol, I.P., Bronson, K.F., Duxbury,J.M., Gupta, R.K. (Eds.), Long-term Soil Fertility Experiments in Rice–Wheat Crop-ping Systems. Rice–Wheat Consortium Paper Series 6. Rice–Wheat Consortiumfor the Indo-Gangetic Plains, New Delhi, India, pp. 7–13.

Singh, R.P., Das, S.K., Bhaskara Rao, U.M., Narayana Reddy, M., 1990. SustainabilityIndex Under Different Management. Annual Report. CRIDA, Hyderabad, India, p.106.

Six, J., Conant, R.T., Paul, E.A., 2002. Stabilization mechanisms of soil organic matter:implications for C-saturation of soils. Plant Soil 241, 155–176.

Smith, J.L., Paul, E.A., 1990. The significance of soil microbial biomass estimation. In:Ballag, J.M., Stotzky, G. (Eds.), Soil Biochemistry, vol. 6. Marcel Dekker, Inc., NewYork, pp. 357–396.

Smith, S.R., 2009. A critical review of the bioavailability and impacts of heavy metalsin municipal solid waste composts compared to sewage sludge. Environ. Int. 35,

142–156.

Soil Survey Staff, 2006. Keys to Soil Taxonomy (Washington, DC, U.S.A.).Sridevi, S., Katyal, J.C., Srinivas, K., Sharma, K.L., 2003. Carbon mineralisation and

microbial biomass dynamics in soil amended with plant residues and residuefractions. J. Indian Soc. Soil Sci. 51, 133–139.

s and

S

T

T

T

S. Ghosh et al. / Agriculture, Ecosystem

ubbiah, B.V., Asija, G.L., 1956. A rapid procedure for the determination of availablenitrogen in soils. Curr. Sci. 25, 259–260.

abatabai, M.A., Bremner, J.M., 1969. Use of p-nitrophenylphosphate for assay of soil

phosphatase activity. Soil Biol. Biochem. 1, 301–307.

halmann, A., 1966. The determination of dehydrogenase activity in soil by meansof T.T.C. (tryphenyl tetrazolium chloride). Soil Biol. 6, 46–47.

ian, G., Kang, B.T., Brussaard, T., 1992. Biological effects of plantresidues with contrasting chemical compositions under humid tropical

Environment 156 (2012) 134– 141 141

conditions-decomposition and nutrient release. Soil Biol. Biochem. 24,1051–1060.

Voroney, R.P., Paul, E.A., 1984. Determination of kC and kN in situ for calibra-

tion of the chloroform fumigation-incubation method. Soil Biol. Biochem. 16,9–14.

Watanabe, F.S., Olsen, S.R., 1965. Test of an ascorbic acid method for determiningphosphorus in water and NaHCO3 extracts from soil. Soil Sci. Soc. Am. Proc. 29,677–678.