RESEARCH ARTICLE

Productivity, Organic Carbon and Residual Soil Fertilityof Pigeonpea–Wheat Cropping System Under Varying Tillageand Residue Management

Seema Sepat • U. K. Behera • A. R. Sharma •

T. K. Das • Ranjan Bhattacharyya

Received: 10 September 2013 / Revised: 20 February 2014 / Accepted: 16 April 2014

� The National Academy of Sciences, India 2014

Abstract Conservation agriculture improves productivity

and soil quality, but most of the research results are only

confined to the rice–wheat system. Hence, a long term field

experiment was conducted at Indian Agricultural Research

Institute, New Delhi during 2008–2009 to 2011–2012 on a

sandy loam soil to study the effect of tillage and crop

establishment techniques, and residue management prac-

tices on system productivity, residual nutrient status,

microbial biomass carbon, microbial biomass nitrogen and

enzymatic activities under a pigeonpea–wheat cropping

system. It was observed that zero tillage gave 5.4 and

2.3 % higher pigeonpea and wheat yield, respectively, over

conventional tillage. Similarly, it resulted in 9.6 and 4.9 %

higher Kjeldahl N and extractable K, respectively and the

plots under zero tillage had 20.6, 8.0 and 6.1 % higher

dehydrogenase and acid and alkaline phosphatase activi-

ties, respectively, over conventional tillage. Application of

crop residue at 3 t/ha provided 14.3 and 34.4 % higher

pigeonpea and wheat grain yield, respectively, over no

residue. Further, organic C, Kjeldahl N and Olsen’s P in

soil were enhanced by 7.4, 6.9 and 7.5 %, respectively, due

to residue compared to no residue plots. Combined appli-

cation of pigeonpea ? wheat residue at 3 t/ha resulted in

higher dehydrogenase (20.9 lg triphenylformazan/g/h), b-

glucosidase (145 lg p-nitrophenol/g/h), and acid phos-

phatase activities (24.5 lg p-nitrophenol/g/h) than the

single application of wheat or pigeonpea residue in either

season or no residue control.

Keywords Dehydrogenase � Enzyme �Indo-Gangetic Plains � Pigeonpea–wheat �Residue � System productivity � Zero-tillage

Introduction

The area of the Indo-Gangetic Plains (IGP) is nearly 13 %

of the total geographical area of India, and it produces

about 50 % of the total food grains to feed 40 % population

of the country [1]. In IGP, the crop residue burning

accompanying intensive tillage with an additional disking

and harrowing is the most common farmers’ practice for

seed bed preparation. Under these circumstances, quality of

soil, in general, and soil organic matter (SOM) in partic-

ular, has deteriorated considerably, although it was con-

sidered once the most fertile region of the country. Soil

biological properties are important parameters to judge the

quality of soil as microbes are living part of SOM. Fur-

thermore, their enzymatic activities play a critical role in

nutrient cycling [2]. It is reported that conventional tillage

(CT) and residue burning has led to a loss of 8.2 t/ha soil

organic carbon (SOC), and considerable decline in activity

of microbial population in cereal production. In developing

countries like India, increasing SOC by 1 t/ha/year can

S. Sepat (&)

Scientist, Division of Agronomy, Indian Agricultural Research

Institute, New Delhi 110012, India

e-mail: seemasepat12@gmail.com

U. K. Behera � T. K. Das

Division of Agronomy, Indian Agricultural Research Institute,

New Delhi 110012, India

A. R. Sharma

Directorate of Weed Science Research, Jabalpur,

Madhya Pradesh, India

R. Bhattacharyya

Centre for Environment Science and Climate Resilient

Agriculture, Indian Agricultural Research Institute, New Delhi

110012, India

123

Proc. Natl. Acad. Sci., India, Sect. B Biol. Sci.

DOI 10.1007/s40011-014-0359-y

increase food grain production by 32 million t/year [3]. So,

there is an urgent need to adopt such practices which can

build up SOC pool in improvised Indian soils. Conserva-

tion agriculture (CA) has drawn considerable attention

worldwide as it has potential to improve resource use

efficiency, productivity and soil health, besides many

environmental benefits [4]. CA, defined as minimal soil

disturbance, permanent soil cover combined with crop

rotation, is a more sustainable cultivation system for future

[5]. Through adoption of CA, productivity and soil quality

is improved by build-up of SOC pool over the conventional

practices [6]. Globally, CA occupies 124.8 m ha, but in

India, area under zero tillage is approximately 2.2 m ha,

which is mostly confined to the rice–wheat system [7].

Continuous growing of rice–wheat in the IGP has

encountered a host of problems like higher nutrient

depletion including micro-nutrients, water scarcity, pest

and diseases and weed infestation, particularly that of

Phalaris minor [8]. This necessities the diversification of

the cereal–cereal system through replacement of rice with

legumes or equally remunerative crops like cotton and

maize. In this context, pigeonpea (Cajanus cajan L)–wheat

(Triticum aestivum L. emend Fiori and Paol) cropping

system is a viable option, covering 3.58 m ha area in India.

Again adoption of conventional system for growing these

crops may not be that much productive and sustainable [9].

Keeping this in view, a long term field experiment was

conducted to assess the effects of different tillage and crop

establishment techniques, and crop residue management

practices on system productivity, residual soil fertility and

microbial properties of soil under a pigeonpea–wheat

cropping system in the western IGP.

Material and Methods

Experimental Site

The field experiment was conducted for four consecutive

years (2008–2009, 2009–2010, 2010–2011 and

2011–2012) in a pigeonpea–wheat cropping system at

research farm of the Indian Agricultural Research Institute

(IARI), New Delhi, India located at 28 �370N latitude and

77 �090E longitude (228.7 m above mean sea level). The

experimental area was characterized as semi-arid, sub-

tropical region having hot summers and cold winters with a

mean annual maximum and minimum air temperature of

40.5 and 6.5 �C, respectively. The mean annual rainfall in

this part is about 670 mm, the distribution of which is

unimodel and about 70–80 % rains are confined to a three

month period from July to September. The quantity of

rainfall was variable during the years of experimentation. It

was 303, 610, 990 and 730 mm during 2008–2009,

2009–2010, 2010–2011 and 2011–2012, respectively. The

rainfall in first year (2008–2009) was below normal as

compared to long-term average rainfall, whereas in other

three cropping seasons, it was favorable for crops. The

mean temperature ranged from 44 to 2.2 �C, but was

almost similar across the years. The soil was an Inceptisol

(Typic Haplustept) containing 66.2 % sand, 18.2 % silt and

15.6 % clay, pH 8.3 (1:2.5), bulk density (1.59 Mg/m3),

SOC (Walkley–Black C) 3.6 g/kg, available N 163.7 kg/ha,

0.5 M NaHCO3 available P 10.2 kg/ha and NH4OAc

extractable available K 270 kg/ha.

Treatment Details and Experimental Design

There were 16 treatments, comprising combinations of four

tillage and crop establishment techniques [viz., conven-

tional tillage—raised bed (CT-B); conventional tillage—

flat bed (CT-F); zero tillage—raised bed (ZT-B) and zero

tillage—flat bed (ZT-F)] in main plots, and four residue

management practices [no residue; sole wheat residue at

3 t/ha; sole pigeonpea residue at 3 t/ha; and combined

application of pigeonpea residue and wheat residue at 3 t/ha

in sub-plots, allocated randomly in a split-plot design with

three replications. Under CT, the plots were ploughed four

times (2 disc harrowing ? 2 cultivators) followed by

planking, while in zero-tillage (ZT) the crop was sown

without any tillage operation. The raised bed (70 cm centre

to centre width of beds) was formed with a tractor mounted

bed planter. Under CT, beds were dismantled after

ploughing with cultivator (2 times) followed by planking in

every growing season. In ZT plots, beds were reshaped

using a bed planter with minimum soil disturbance. Pi-

geonpea residue at 3 t/ha was applied to the wheat crop,

while wheat residue at 3 t/ha was applied to pigeonpea

under the sole residue application treatments. In combined

application of pigeonpea ? wheat residue, wheat residue at

1.5 t/ha was applied during kharif season in pigeonpea crop

and in the same plot pigeonpea residue at 1.5 t/ha was

added in wheat crop during rabi season. Considering wheat

residue an important fodder for the livestock in this part of

the country, roughly 33 % of the total biomass yield of

wheat, which is likely 3 t/ha, was adopted as one of the

treatments. It was thought that, even if the farmers could not

spare the whole amount of wheat residue, due to livestock

feeding, at least some amount of it, say 3 t/ha can be spared

for soil quality improvement or maintenance under CA. In

pigeonpea, woody main stems, which would hardly be

decomposed, were spared for the fuel wood usually used by

the farmers, and the tender twigs and branches of the apical

portions of pigeonpea plants was used as residue treatment

for this experiment. The amount of residue was fixed at

about 3 t/ha, whether applied during the kharif, rabi or both

the seasons, just to appraise the effect of single season or

S. Sepat et al.

123

both season residue application on crop yield and soil

parameters. The application of crop residue at 3 t/ha may

add around 30–40 kg N/ha to soil, some of this amount may

be utilized by the standing crop or may provide residual

effect to the next crop. All crop residues were applied on a

dry weight basis. Before application, residues were chem-

ically analyzed. On an average 1.3, 0.11 and 1.2 % NPK

and 0.5, 0.18 and 1.9 % NPK was found in pigeonpea and

wheat residue, respectively. The mean leaf litter fall of pi-

geonpea was 0.90–1.15 t/ha and it added about

36–52 kg N/ha and 5–7.2 kg P/ha during the experimen-

tation period. Pigeonpea (cv Pusa 991) was sown in rows at

70 cm apart, so one row was in the centre of each bed

(70 cm centre to centre spacing) while three rows of wheat

(cv HD 2895) were accommodated on the respective beds

during the rabi seasons in all years. Nutrient at

20:26:33 kg NPK/ha was applied as basal to pigeonpea,

while a dose of 120:26:33 kg/ha NPK was applied to wheat

(50 % of N and full P and K as basal and rest 50 % N at

crown root initiation stage). Pigeonpea was sown during the

first week of June and manually harvested about 10 cm

above the ground level in the third week of November each

year. Wheat was sown in the fourth week of November and

harvested in the third week of April in all years. Other

agronomic practices as recommended were followed for

raising both the crops.

Soil Sampling and Analysis

Composite surface (0–15 cm) soil samples at the beginning

of experiment from whole field, and from each plot were

taken after completion of fourth cropping cycle. The soil

samples were sieved (2 mm), homogenized and stored at

4 �C for enzymatic activity estimation, while for chemical

analysis, soil was air dried for 3 days and thereafter stored

at room temperature. The organic C in soil was determined

by wet digestion [10], total N by Kjeldahl digestion–dis-

tillation [11], available P by 0.5 M NaHCO3 [12] and

extractable K by NH4OAc [13] methods. Similarly,

microbial biomass C and microbial biomass N were esti-

mated by chloroform fumigation extraction method [14].

Soil dehydrogenase activity was estimated by measuring

the rate of triphenylformazan (TPF) from triphenyl tetra-

zolium chloride (TTC) [15] and b-glucosidase by deter-

mining the amount of p-nitrophenol released after 1 h of

incubation with p-nitrophenyl-b-D-glucopyranoside [16].

Acid and alkaline phosphatase activities were measured by

using p-nitrophenyl (PNP) [17].

Statistical Analysis

Productivity of the system was worked out by adding

wheat yield and wheat equivalent yield for respective

years. Afterwards, system productivity was pooled across

the 4 years. A two-factor analysis of variance (ANOVA)

was carried out to test the significance of treatments.

Critical difference (CD at P = 0.05) was used to determine

whether means differed significantly or not. Correlation

coefficients (r) were determined to show the degree of

association among different soil and crop parameters

studied. For statistical analysis of data and correlation

coefficient, Microsoft excel (Microsoft corporation, USA)

was used. Since there were yearly variations in grain yields

of both pigeonpea and wheat, and error variance was not

homogeneous, the pooled analysis of data was not per-

formed. However, the system productivity was subject to

the pooled analysis to find out the yearly variations and

interactions.

Results and Discussion

Results

Grain Yield and System Productivity

There was no significant (P \ 0.05) variation in grain yield

of pigeonpea and wheat, but system productivity was sig-

nificantly influenced over the years. The tillage and crop

establishment techniques significantly influenced pigeon-

pea yield, wheat yield and system productivity (Fig. 1;

Table 1). Averaged over 4 years, the grain yield of pi-

geonpea and wheat varied from 1.6 to 1.8 and 3.8 to 4.4 t/ha,

respectively. Under ZT, the average yield of pigeonpea and

wheat was 1.8 and 4.1 t/ha, respectively. Likewise, corre-

sponding grain yield for CT was 1.7 and 4.0 t/ha, respec-

tively. Hence, the grain yield of pigeonpea and wheat in ZT

was 5.4 and 2.5 % (P [ 0.05) higher over CT, respec-

tively. Similarly, the average system productivity across

the years ranged from 7.5 to 9.0 t/ha. The highest system

productivity was recorded in the 4th year (2011–2012),

which was 20, 15.4 and 4.5 % higher over the 1st

(2008–2009), 2nd (2009–2010) and 3rd years (2010–2011),

respectively. Zero tillage on an average gave 8.2 %

increased system productivity over the CT. Further, plots

under zero tillage—raised bed (ZT-B) and zero tillage—

flat bed (ZT-F) were found comparable to each other, but

both showed significantly better results over the plots with

conventional tillage—flat bed (CT-F) and conventional

tillage—raised bed (CT-B). In ZT-B and CT-B plots,

combined application of pigeonpea ? wheat residue

resulted in significantly higher system productivity than

pigeonpea residue and other residue management practices

(Table 1). However, there was no significant difference in

pigeonpea residue and combined application of pigeon-

pea ? wheat residue in CT-F and ZT-F. Further, wheat

Pigeonpea–Wheat Rotation in Varying Tillage and Residue Management

123

residue gave highest system productivity under ZT-F,

which was significantly higher as compared to other tillage

practices, but pigeonpea residue had similar system pro-

ductivity at ZT-B and ZT-F. Similarly, in no residue plots,

ZT-F gave significantly higher system productivity than the

other tillage practices. In the case of pigeonpea and wheat

grain yield, application of crop residues was found superior

to no residue during all years (Fig. 1). Application of crop

residue gave 14.4 and 28.2 % higher pigeonpea and wheat

grain yield over no residue. Additionally, among the crop

residue treatments, combined application of pigeon-

pea ? wheat residue was found comparable with pigeon-

pea residue, but remained significantly higher over wheat

residue. However, wheat residue was found superior over

no residue plots.

Soil Bulk Density

Among tillage and crop establishment methods, plots under

ZT-F had about 3 % higher soil bulk density than CT-B

plots (1.57 Mg/m) in the 0–15 cm soil layer (Table 2). In

the same soil depth layer, ZT-B plots had also significantly

higher bulk density than CT-B plots. Residue management

had greater impacts on soil bulk density (Table 2). Plots

under pigeonpea ? wheat residue had *4 % less soil bulk

density in the 0–15 cm soil layer as compared with no

residue added (either surface retained or buried) plots. All

residue added plots had similar soil bulk densities in that

layer after 4 years of cropping.

Residual Soil Fertility

Different tillage and crop residue management practices

affected the Kjeldahl N and NH4OAc extractable K sig-

nificantly, but no significant effects on SOC and Olsen’s P

(Table 3) at the end of 4th year. Zero tillage caused a 9.6

and 4.9 % increase in Kjeldahl N and extractable K,

respectively, over the conventionally tilled plots. Likewise,

Kjeldahl N and extractable K increased by 22.7 and

29.9 %, respectively, over the initial N and K status of soil.

Zero tillage—raised bed (ZT-B) plots had highest Kjeldahl

N (215.6 kg/ha) in the soil, while ZT-B, zero tillage—flat

bed (ZT-F) and conventional tillage—raised bed (CT-B)

plots were found at par in terms of extractable K. The

lowest Kjeldahl N and extractable K were found in con-

ventional tillage—flat bed (CT-F) treatment. Application of

crop residue significantly increased organic carbon, Kjel-

dahl N, Olsen’s P and extractable K over no residue across

the years (Table 3). The organic carbon, Kjeldahl N, Ol-

sen’s P and extractable K in soil varied from 0.416 to

0.452 %, 190 to 205, 13.2 to 14.3 and 234 to 239 kg/ha,

respectively. Application of crop residue increased organic

C, Kjeldahl N, Olsen’s P and extractable K in soil by 7.5,

6.9, 7.5 and 8.0 %, respectively, over no residue plots.

Plots under pigeon pea or wheat residues were found

comparable to each other in terms of soil quality, but

remained significantly superior to no residue. Over the

initial values, 22.0, 22.7, 37.2 and 29.8 % higher SOC,

Kjeldahl N, Olsen’s P and extractable K, respectively, were

recorded in the soil. Further, correlation analysis showed a

positive and significant (P B 0.01) values of linear corre-

lation coefficient viz. 0.993 and 0.992 for SOC and Kjel-

dahl N, and SOC and Olsen’s P, respectively as influenced

by crop residues (Figs. 2, 3). R2 value of 0.993 and 0.992

suggests that 99.3 and 99.2 % variation in Kjeldahl N and

Olsen’s P, respectively could be adequately explained by

SOC as fitted by the linear regression equation. Although,

in the case of SOC and extractable K, R2 value was 0.921,

which suggests that 92.1 % variation was due to SOC only

and correlation analysis was significant at P B 0.05

(Fig. 4).

Microbial Biomass Carbon and Nitrogen

Zero tillage increased the microbial biomass carbon (MBC)

and microbial biomass nitrogen (MBN) by 15.0 and

18.3 %, respectively, over CT (Table 4). Plots under zero

tillage—raised bed (ZT-B) recorded highest soil MBC,

while in the case of MBN, ZT-B remained comparable

with zero tillage—flat bed (ZT-F) and conventional till-

age—raised bed (CT-B). Plots under conventional tillage—

flat bed (CT-F) recorded 17.4 and 19.4 % lower values of

MBC and MBN, respectively over ZT-B plots. Crop

a a b ba

b b b

ab b

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ab

c c

0

0.5

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1.5

2

2.5

3

3.5

4

4.5

5

CT-B CT-F ZT-B ZT-F R0 R1 R2 R3

Pigeonpea Wheat

Fig. 1 Yield of pigeonpea and wheat as influenced by tillage and

crop establishment, and residue management practices (data pooled

over 4 years); CT-B conventional tillage—raised bed, CT-F conven-

tional tillage—flat bed, ZT-B zero tillage—raised bed, ZT-F zero

tillage—flat bed, R0 no residue, R1 wheat residue at 3 t/ha, R2

pigeonpea residue at 3 t/ha, R3 pigeonpea ? wheat residue at 3 t/ha.

Bars sharing the same letter are not significantly different (P \ 0.05).

Error bars represent standard deviation

S. Sepat et al.

123

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Pigeonpea–Wheat Rotation in Varying Tillage and Residue Management

123

residue application recorded 41.0 and 39.8 % higher MBC

and MBN, respectively than no residue plots (Table 4).

Furthermore, among the crop residues, combined applica-

tion of pigeonpea ? wheat residues gave highest MBC and

MBN followed by pigeonpea residue alone and wheat

residue alone.

Soil Enzymatic Activities

Tillage and crop establishment techniques significantly

influenced the dehydrogenase activity (DHA) and phos-

phatase activity in the surface soil, but not the b-glucosidase

activity (Table 5). DHA in soil varied from 14 to 21 lg 2, 3,

5-triphenylformazan (TPF) /g/h. Likewise, acid and alkaline

phosphatase activities ranged from 16 to 24.5 and 113.5 to

156.9 lg þ- nitrophenol/g/h, respectively. Zero tillage

caused an increase of 20.6, 8.0 and 6.1 % in DHA, acid and

alkaline phosphatase activities, respectively, over CT. Plots

under ZT-B recorded highest DHA and alkaline phosphatase

activity, which was found comparable with ZT-F and CT-B

plots, but remained significantly higher over CT-F plots.

Table 2 Bulk density of soil (0–15 cm) as influenced by tillage, crop

establishment and residue management practices (data pooled over

4 years)

Treatment Soil bulk density (Mg/m3)

Tillage and crop establishment

CT-B 1.57

CT-F 1.57

ZT-B 1.59

ZT-F 1.61

CD (P = 0.05) 0.02

Residue management

No residue 1.63

Wheat residue 1.57

Pigeonpea residue 1.58

Pigeonpea ? wheat 1.56

CD (P = 0.05) 0.02

Table 3 Soil organic C (SOC), Kjeldahl N, available P and ammonium-acetate-extractable K content as influenced by tillage and crop

establishment, and residue management practices (data pooled over 4 years)

Parameters Soil organic C (%) Kjeldahl-N (kg/ha) Olsen’s P (kg/ha) NH4OAc-extractable K (kg/ha)

Tillage and crop establishment

CT-B 0.434 197.1 14.0 347.1

CT-F 0.430 184.5 13.7 342.9

ZT-B 0.452 215.6 14.4 361.2

ZT-F 0.440 202.8 13.9 351.3

SEm? 0.008 3.5 0.3 2.9

CD (P = 0.05) NS 12.2 NS 10.0

Residue management

No residue 0.416 190.2 13.3 330.7

Wheat residue 0.441 200.0 14.1 354.6

Pigeonpea residue 0.448 204.4 14.3 352.4

Pigeonpea ? wheat 0.452 205.4 14.3 364.6

SEm? 0.008 3.6 0.2 3.3

CD (P = 0.05) 0.024 10.4 0.7 9.7

CT-B conventional tillage—raised bed, CT-F conventional tillage—flat bed, ZT-B zero tillage—raised bed, ZT-F zero tillage—flat bed, NS not

significant,

Initial values for Organic C, Kjeldahl-N, Olsen’s P and NH4OAc-extractable K was 0.36 %, 163, 10.2 and 270 kg/ha, respectively

y = 428.23x + 11.898

R² = 0.993

188

190

192

194

196

198

200

202

204

206

208

0.41 0.42 0.43 0.44 0.45 0.46

Kje

ldah

l-N

kg/

ha

Organic C (%)

Fig. 2 Relationship between soil organic carbon and Kjeldahl-N as

influenced by residue application under pigeonpea–wheat cropping

system

S. Sepat et al.

123

Similarly, plots under ZT-F and ZT-B had similar acid

phosphatase activity that was significantly higher than CT-B

and CT-F plots. Both CT-F and CT-B plots had similar acid

phosphatase activities. Enzymatic activities were signifi-

cantly influenced by application of crop residues over no

residue (Table 5). Crop residue application recorded about

35, 48 and 33 % higher DHA, b-glucosidase, acid and

alkaline phosphatase activities, respectively, over control.

Further, all crop residue treated plots were found compara-

ble in case of b-glucosidase and acid phosphatase activities.

Contrarily, DHA was lowest (among residue treated plots) in

wheat residue treated plots, but remained significantly

higher over control plots. With regard to alkaline phospha-

tase activity, pigeonpea residue recorded highest value,

while pigeonpea ? wheat residue treated plots had similar

values to wheat residue at plots.

Correlation among System Productivity, Organic Carbon

and Soil Enzymatic Activities

Different tillage and crop establishment practices signifi-

cantly influenced the correlation matrices of different soil

enzyme activities, microbial biomass carbon (MBC),

microbial biomass nitrogen (MBN) and system productiv-

ity (Table 5). The organic carbon content in soil had a

positive and significant (P \ 0.05) correlation with MBC

(r = 0.93), MBN (r = 0.90) and alkaline phosphatase

(ALP). Similarly, MBC had a positive and significant

(P \ 0.05) correlation with MBN and ALP. The correla-

tion coefficient (r) between dehydrogenase (DHA) and acid

phosphatase (AP) was r = 0.98. The correlation matrix of

different soil enzyme activities, MBC, MBN and system

productivity was also significantly influenced by applica-

tion of crop residues. System productivity had a positive

and significant correlation with organic carbon, MBC,

MBN, DHA, glucosidase (GLC), AP and ALP. Likewise,

organic carbon had a positive correlation with MBC, MBN,

DHA, GLC, AP and ALP. Similarly, MBC had a positive

and significant (P \ 0.05) correlation with MBN, DHA,

GLC and AP. MBN had a positive and significant

(P \ 0.05) correlation with DHA, GLC, AP and ALP.

DHA had a highly significant (P [ 0.01) correlation with

GLC, AP and ALP. Further, GLC had a positive and sig-

nificant correlation (P [ 0.01) with AP and ALP.

Discussion

Tillage and crop establishment techniques significantly

influenced the grain yield of pigeonpea and wheat and also

the system productivity over the years. The grain yields of

pigeonpea and wheat in ZT was almost similar to CT plots.

It is evident that under ZT the additional C improves the

soil structure, especially in macro-aggregates, which is

active site for holding labile C [18]. Hence, the increased

organic C content and better soil structure may have

occurred under ZT plots. Despite these improvements, ZT

plots had a trivial increase in crop productivity over CT

plots after 4 years of cropping. This could be due to has-

tening of organic matter decomposition and higher nutrient

availability [19], reduction in surface bulk density and

enhanced root growth [20] under CT. Significantly lower

bulk densities under CT-B in the surface soil layer were

caused by the loosening of soils by tillage implements and

the mixing of crop residues into the plow layer. There was

y = 31.46x + 0.1764R² = 0.9926

13

13.2

13.4

13.6

13.8

14

14.2

14.4

14.6

0.41 0.42 0.43 0.44 0.45 0.46

Ols

en's

P k

g/ha

Organic C (%)

Fig. 3 Relationship between soil organic carbon and Olsen’s P as

influenced by residue application under pigeonpea–wheat cropping

system

y = 848.2x - 21.995R² = 0.9213

325

330

335

340

345

350

355

360

365

370

0.41 0.42 0.43 0.44 0.45 0.46

NH

4Oac

-ext

ract

able

K k

g/ha

Organic C (%)

Fig. 4 Relationship between soil organic carbon and NH4OAc-

extractable K as influenced by residue application under pigeonpea–

wheat cropping system

Pigeonpea–Wheat Rotation in Varying Tillage and Residue Management

123

a definite tendency of the ZT plots of having higher soil

bulk density in the surface layer, as soils inherently had a

low SOC content to counterbalance the compactness that

might have caused by surface residue retention in the ZT

plots. Bed planting under CT led to decreased bulk density

in the 0–15 soil layer, mainly due to soil loosening.

The average system productivity across the years ranged

from 7.5 to 9.0 t/ha. The highest system productivity was

recorded in the 4th year (2011–2012) indicating the better

role of ZT in the advancing years of cultivation. Zero

tillage—flat bed (ZT-F) with combined application of pi-

geonpea ? wheat residue at 3 t/ha gave highest system

productivity over the years. This may be ascribed to the

cumulative effect of improved soil quality parameters. For

instance, ZT resulted in 9.6 and 4.9 % higher Kjeldahl N

and extractable K, respectively, over CT after 4 years of

pigeonpea–wheat cropping. This could be due to a number

of factors. The major one could be the nature of residue

management. In CT and residue treated plots, the crop

residues were incorporated into the soil (so buried) as

compared to spreading of the residue on the surface (so

surface retained) in ZT and residue treated plots. Hence,

oxidation process was faster in CT, which resulted into

enhanced organic matter decomposition and mineralization

Table 4 Microbial properties of soil as influenced by tillage and crop establishment and residue management practices (data pooled over

4 years)

Parameters MBC (mg C/kg) MBN (mg N/kg) DHA (lg TPF/g/h) GLC (lg PNP/g/h) AP (lg PNP/g/h) ALP (lg PNP/h

Tillage and crop establishment

CT-B 371.4 62.8 18.0 136.1 21.9 140.1

CT-F 353.0 59.9 16.0 135.0 20.5 134.0

ZT-B 427.8 74.3 20.0 129.8 22.7 148.8

ZT-F 405.4 70.8 21.0 128.1 23.1 142.1

SEm± 4.2 1.6 0.9 3.6 0.5 3.6

CD (P = 0.05) 12.4 5.7 3.2 NS 1.7 10.5

Residue management

No residue 297.8 51.5 14.8 103.9 16.2 113.4

Wheat residue 385.0 67.0 18.9 136.3 23.1 145.3

Pigeonpea residue 420.0 72.7 20.4 143.4 24.3 156.9

Pigeonpea ? wheat 454.8 76.6 20.9 145.4 24.5 149.4

SEm± 3.3 1.2 0.6 3.9 0.4 2.0

CD (P = 0.05) 11.6 3.6 1.7 11.5 1.2 6.8

CT-B conventional tillage—raised bed, CT-F conventional tillage—flat bed, ZT-B zero tillage—raised bed, ZT-F zero tillage—flat bed, MBC

microbial biomass C, MBN microbial biomass N, DHA dehydrogenase, GLC glucosidase, AP acid phosphatase, ALP alkaline phosphatase, TPF

triphenylformazan, PNP þ- nitrophenol

Table 5 Correlation (r values) matrix for system, organic C, MBC, MBN and soil enzyme activities under pigeonpea–wheat cropping system

Variables System

productivity

Organic C MBC MBN DHA GLC AP ALP

a b a b a b a b a b a b a b a b

System

productivity

1.00 1.00 0.16NS 0.99* 0.33NS 0.97* 0.40NS 0.99* 0.51NS 0.99* 0.85NS 0.99** 0.38NS 0.98** 0.10NS 0.94*

Organic C 1.00 1.00 0.93* 0.97** 0.90* 0.97** 0.54NS 0.99** 0.51NS 0.99** 0.52NS 0.98** 0.94* 0.93*

MBC 1.00 1.00 0.99** 0.99** 0.78NS 0.98** 0.71NS 0.94* 0.75NS 0.91* 0.92* 0.92NS

MBN 1.00 1.00 0.81NS 0.99** 0.78NS 0.97** 0.76NS 0.95* 0.87NS 0.89*

DHA 1.00 1.00 0.78NS 0.99** 0.98** 0.97** 0.62NS 0.93*

GLC 1.00 1.00 0.62NS 0.99** 0.43NS 0.99**

AP 1.00 1.00 0.65NS 0.97**

ALP 1.00 1.00

a Tillage and crop establishment, b residue management at 3 t/ha, organic C organic carbon, MBC microbial biomass C, MBN microbial biomass

N, DHA dehydrogenase, GLC glucosidase, AP acid phosphatase, ALP alkaline phosphatase, NS not significant at P [ 0.05

*,** Marked correlation are significant at P = 0.05 and 0.01, respectively (n = 3)

S. Sepat et al.

123

rates. This oxidation process is perceived to be accelerated

due to higher contact between soil micro-organisms and

crop residues. Contrarily, a soil under no tillage is not

disturbed, so organic N mineralization is significantly

reduced. This could be one of the main reasons behind

increased availability of Kjeldahl N [21] in the 0–15 cm

soil layer. Although, in the present experiment SOC was

not significantly influenced by tillage, hence the authors

infer that in the long term, it would increase [22] as

compared to the initial soils. Thus, the residue retention

under ZT did not result in appreciable SOC increase over

CT plots (with residue incorporation) within 4 years in this

region under a pigeonpea–wheat cropping system. In con-

trast Das et al. [23] observed a significant increase in total

SOC under ZT plots over CT plots after 4 years of cotton/

maize–wheat cropping in this region. This could be due to

difference in residue quality. The C/N ratio of pigeonpea

residues is lower than that of cotton or maize residues.

Higher C/N residues resulted in less mineralization of

native and added C (and thus had better potential to be

retained in soils under ZT), which was perceived to be the

major factor for differences in C retention under these two

contrasting cropping systems in this region and is of tre-

mendous value regarding C sequestration under changing

climatic conditions [24].

Zero tillage recorded 15.0 and 18.3 % higher MBC and

MBN than CT after 4 years of cropping. Although the

microbial biomass comprises only a small portion of the

total SOC, it has a great importance as it acts as a repos-

itory of nutrients for plants as it is more labile than the total

soil organic matter. So, any agronomic manipulation in the

organic C pools will have corresponding changes in

microbial pool [25]. Conventional tillage enhances oxida-

tion of organic C and impairment of soil pore networks

including mycorrhizal hyphae, which gave low MBC and

consequently MBN, while reverse is true for ZT. Higher

MBC causes an increase in enzymatic activities viz.

dehydrogenase activity (DHA), phosphatase and b-glu-

cosidea activities under ZT. DHA is an oxidoreductase

enzyme present in viable cells only. This enzyme has been

considered as a suitable indicator of soil quality and a valid

biomarker to indicate changes in total microbial activity

due to change in soil management [26]. Enhanced DHA in

ZT plots confirmed that not only organic C, but quality of

organic C was also improved [27]. Similarly, b-glucosidase

and phosphatase enzyme play an active role in C and P

cycling, respectively. Besides higher MBC, minimal soil

movement and subsequently continuously supply of C in

ZT led to higher enzymatic activity [28].

One of the prerequisites in CA is to retain crop residues

on soil surface. Here, crop residues were applied at 3 t/ha

and recorded higher values of pigeonpea and wheat grain

yields, system productivity, SOC, Kjeldahl N and Olsen’s

P over no residue plots. Application of crop residue at 3 t/

ha gave 14.4, 28.2 and 2.1 % higher pigeonpea grain yield,

wheat grain yield and system productivity, respectively,

over no residue control. Crop residue application reduces

water loss from the soil by evaporation and also moderates

soil temperature. This also might have led to higher labile

C formation is soil, which might have improved soil

structure and acquisition of nutrients by plants and finally

reflected in higher yield [29]. Residue retained plots had

about 22.0, 22.7, 37.2 and 29.8 % higher SOC, Kjeldahl N,

Olsen’s P and extractable K, respectively, over the initial

soils, Addition of crop residues along with leaf-litter fall

have recycled about 30–52 kg N/ha. Further, mineraliza-

tion process was expedited (and more so in presence of

pigeonpea residues) and released N quickly enters into the

soil over no residue plots. This could be one of the main

reasons for higher available N present in soil [30]. Bhat-

tacharyya et al. [31] also observed a higher total N accu-

mulation under residue retained plots as compared to

residue incorporated plots. Further, a positive and strong

correlation between SOC and Kjeldahl N, Olsen’s P and

extractable K signifies availability of nutrients from

enhanced SOC. It is reported that application of crop res-

idues leads to reduced soil compaction, which facilitates

deeper growth of pigeonpea roots, thus recycling of nutri-

ents occur from deeper soil surface. Furthermore, pigeon-

pea roots secret psidic acid which stimulates phosphatase

enzyme activity and recycles fixed form of P from the soil

[32]. Crop residue application at 3 t/ha recorded 41.0 and

39.8 % higher MBC and MBN, respectively than no resi-

due. Enhanced SOC with C input from crop residues at 3 t/ha

increased the amount of microbial biomass and enzymatic

activities in the soil. Furthermore, combined application of

pigeonpea ? wheat residue at 3 t/ha gave higher MBC and

MBN over no residue control, which could be due to

simultaneous C and N supply from the residues. The high

C:N ratio of wheat residue temporally blocks N supply, this

effect is probably masked by pigeonpea residue that has

low C:N ratio. Crop residue application at 3 t/ha gave 35.3,

36.3, 47.6 and 32.7 % increased DHA, b-glucosidase, acid

and alkaline activity, respectively over no residue control

plots. This may be linked to moderation of soil temperature

and lower moisture fluctuations under crop residue treated

plots, which promoted prolific growth of microbes and

enzymatic activities in the soil. Besides these, one of the

important reasons is also a complementary interaction

between pigeonpea root system and rhizobacteria.

Pigeonpea, being a legume, have prolific root system,

which releases an array of organic compounds viz. psidic

acid and oxalic acid. Gloumalin content is perceived to be

increased in the rhizosphere [33]. These compounds stim-

ulate and diversify the growth of the microbial biota and

enzymatic activity, and thus, increase nutrient cycling and

Pigeonpea–Wheat Rotation in Varying Tillage and Residue Management

123

their acquisition, especially N and P to the crop [34]. So,

retention of crop residues at 3 t/ha under ZT and an asso-

ciation of pigeonpea leaf litter fall stimulate the growth of

microbial population by providing continuous supply of

food.

Conclusions

From the present study it can be concluded that zero-tillage

with either raised bed or flat bed, combined with applica-

tion of pigeonpea ? wheat residue at 3 t/ha is a suitable

option to enhance the pigeonpea–wheat system productiv-

ity over a long run in the western Indo-Gangetic plains of

India. This was mainly due to improvement in soil quality.

Furthermore, irrespective of residue treatment, Kjeldahl N,

extractable K and enzymatic activities in soil were higher

with zero tillage as compared to conventional tillage. ZT

plots also maintained the initial soil organic C concentra-

tion. However, under both ZT and CT plots, application of

crop residues at 3 t/ha increased soil organic C, Kjeldahl N,

extractable K and enzyme activities over no residue treated

plots.

Acknowledgment The authors gratefully acknowledge the support

received from the Director, Indian Agricultural Research Institute

(IARI), New Delhi for successful conduct of this research work.

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