Influence of long term Nitrogen and Potassium fertilization on the biochemistry of Tea Soil

Influence of Long Term Nitrogen and Potassium Fertilization on the

Biochemistry of Tea Soil

Keywords: Soil enzymes, urease, cellulase, Tea, Soil pH, nitrogen and potassium fertilizers

ABSTRACT: As the tea plantation in hilly tracts are located in slopes, the management of

fertilizer regimes is somewhat challengeable due to leaching which in turn affect the quality of tea soil. In light of this fact the present study was focused to determine the quality of tea soil in terms of the evaluation of certain physical and biological characteristics as influenced by various dosage of fertilizer applications. The impact of long term nitrogen and potassium fertilization on biochemical characteristics and microbial activities in tea soil has been analyzed in the present study. Different sources and rates of nitrogen (ammonium sulphate and urea), and potassium (muriate of potash) were tested at two soil depths (0-10 cm and 10-20 cm) and for two seasons (premonsoon and monsoon). The acidic tea soil was further acidified with nitrogen application and the extent of acidification varied with the fertilizer type and season. Soil respiration rates were higher in 0-10 cm soils and were positively related to soil nitrogen and potassium concentrations. Among the soil enzymes analyzed, urease activity exhibited different trends in the two soil depths at different seasons. Urease activity tended to increase with increasing potassium application rates, whereas higher cellulase activity was associated with lower nitrogen application rates. This study clearly indicates that the soil quality depends on the fertilizer application rates and season.

124-135 | JRA | 2012 | Vol 1 | No 2

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www.jagri.info

Journal of Research in

Agriculture An International Scientific

Research Journal

Authors:

Thenmozhi K1, Manian S2

and Paulsamy S1.

Institution:

1.Department of Botany,

Kongunadu Arts and Science

College, Coimbatore

641 029, Tamil Nadu, India.

2. Department of Botany,

Bharathiar University,

Coimbatore 641 046, Tamil

Nadu, India.

Corresponding author:

Thenmozhi K.

Email: [email protected]

Phone No:

+91- 9942474703.

Web Address:

http://www.jagri.info

documents/AG0029.pdf.

Dates: Received: 14 Sep 2012 Accepted: 01 Oct 2012 Published: 06 Oct 2012

Article Citation: Thenmozhi K, Manian S and Paulsamy S. Influence of Long Term Nitrogen and Potassium Fertilization on the Biochemistry of Tea Soil. Journal of Research in Agriculture (2012) 1(2): 124-135

Original Research

Journal of Research in Agriculture

Jou

rn

al of R

esearch

in

A

gricu

ltu

re

An International Scientific Research Journal

mailto:[email protected]

INTRODUCTION

Tea (Camellia sinensis (L.) O. Kuntz), a

perennial shrub, cultivated in acid soil yields one of the

most popular non-alcoholic beverage tea which is

consumed world-wide for its taste, aroma and health

effects. South India contributes about 24% of India’s

total tea production. Being a foliage crop, nutrient

requirements for commercial tea production are

particularly high. Nitrogen and potassium are the two

major nutrients of tea without which, commercial

production levels are difficult to achieve (Verma, 1993;

Verma et al., 2001). In south Indian tea gardens, nitrogen

and potassium fertilizers are always applied in

combination. There are three different sources of

nitrogen, namely ammonium sulphate, urea and calcium

ammonium nitrate. However, the choice of potassium is

confined to muriate of potash. This soil management has

potential impact upon soil biological quality. Nitrogen

fertilizers when used on a regular basis tend to acidify

soil. Further, long-term nitrogen fertilization has been

shown to affect the distribution and the amount of

organic carbon, soil microbial biomass and soil enzyme

activities (Darusman et al., 1991; Mc Andrew and

Malhi, 1992). Thus fertilizers as nutrient sources may

have beneficial influence on plants; however, there may

be adverse effects especially on microorganisms, as a

result of soil acidification.

Enzymes catalyze all biochemical reactions and

are an integral part of nutrient cycling in soil.

Investigations are often limited to few enzymes to show

that agricultural management practices affect enzyme

activity (Dick, 1994). A wide range of enzymes have not

been systematically investigated for their potential to

reflect short and long-term soil management effects in

relation to soil quality.

Although the effect of combined application of

nitrogen and potassium fertilizers on biochemical

characteristics of tea is well reported (Venkatesan and

Ganapathy, 2004; Venkatesan et al., 2005), its effect on

soil physico-chemical and biological characteristics are

scarce (Venkatesan et al., 2004). Increasing evidence

indicates that soil biological parameters may hold

potential as early and sensitive indicators of soil health.

Microbial characteristics of acid tea soils are reported to

be qualitatively different from normal acid soils

(Nioh et al., 1993). The objective of the study was to

evaluate the long - term impact of fertilizer application

on physico-chemical and microbiological properties of

selected soil in an experimental tea field receiving

fertilizer treatment since 1994. The selection of

biological response variables was based upon their

relationship to soil function. The soil microbial

community inhabits an environment responding to

physical, chemical or biological perturbation. Soil

biological properties were chosen to represent the soil

environment in which the organism must exist (soil

organic matter and moisture), the microbial community

itself (soil respiration) and biochemical activities of these

populations (soil cellulase and urease activity). These

biochemical activities were chosen to be a representative

of nutrients that influence plant production.

MATERIALS AND METHODS

Experimental site and design

The experimental site was located at United

Planters Association of Southern India (UPASI) Tea

Research Foundation at Anamallais (10°30’N and

77°0’E, at 1050 m a.s.l.), southern India. The climatic

data collected from UPASI Tea Research

Institute - Meterological station, Valparai for the past 20

years showed that the site is experiencing an average

annual rainfall of 1100 mm and the temperature range of

11-29°C. The investigation was carried out in the long

term fertilizer trial plots (10m x 10m) established in 1994

using tea clone SA 6 with 100 bushes/ plot. The duration

of the study period was one year from Nov. 2010 to

Oct. 2011.

125 Journal of Research in Agriculture (2012) 1(2): 124-135

Thenmozhi et al.,2012

Experimental setup

The experimental plots were setup to investigate

the impacts of nitrogen and potassium fertilization on

soil biochemistry and employed a randomized complete

block design with three replicate plots for the fifteen

treatments and unfertilized control plots. The fifteen

treatments included different levels of nitrogen and

potassium (150, 300 and 450 kg ha-1y -1) individually and

in various combinations.

Fertilizers were broadcasted in four split doses in

order to avoid volatilization and leaching. Nitrogen was

applied as 25% sulphate of ammonia (containing 20%

nitrogen) and urea (containing 46% nitrogen). Potassium

was applied as muriate of potash (containing 63%

potassium). Sulphate of ammonia was broadcasted at the

rate of 7.5, 15 and 22.5 kg ha-1 between February and

November. Urea at the rate of 17.25, 34.5 and

51.75 kg ha-1 was broadcasted between May and August.

Muriate of potash was applied at the rate of 23.63, 47.25

and 70.88 kg ha-1 along with sulphate of ammonia or

urea. Other nutrients (Phosphorus, Calcium, Magnesium,

Sulphur, Zinc, Manganese and Boron) were applied at

recommended rates and regular cultural practices were

carried out uniformly in all the plots (Verma and Palani,

1997).

Sampling

Soil samples were collected during premonsoon

(March) and monsoon (June) in 2011. Ten soil cores

(5 cm in diameter) at the depths of 0-10 cm (L1 layer)

and 10-20 cm (L2 layer) were randomly taken from each

plot and bulked. Field moist samples were passed

through a 2-mm sieve and divided into two equal parts.

One part was used for the determination of soil moisture,

pH, electrical conductivity, total nitrogen, exchangeable

potassium and organic carbon. The other part was stored

at 4°C prior to microbiological assays.

Soil analysis

Soil moisture content was determined after

drying at 105°C to a constant weight. Soil pH and

Journal of Research in Agriculture (2012) 1(2): 124-135 126


Treatm

en

t M

ois

ture (

%)

pH

E

C (

dS

m-1

) S

1

S

2

S

1

S

2

S1

S 2

L

1

L2

L1

L2

L1

L2

L1

L2

L1

L2

L1

L2

N0 K

0

11

.00 b

c 1

1.6

7 d

e 1

8.0

0 d

ef

19

.00 d

e 3

.76 f

3

.36 h

4

.69 b

4

.33 d

0

.21

6 i

0

.24

8 h

0

.38

8 e

0

.33

2 e

N

0 K

15

0

6.6

7 e

-h

10

.00 d

ef

19

.67 b

-e

21

.00 b

cd

3.8

6 d

3

.65 c

4

.79 a

4

.66 a

0

.27

7 g

0

.30

9 d

e 0

.29

4 h

0

.30

4 f

N

0 K

300

8.0

0 d

e 1

2.0

0 c

d

19

.00 b

-f

21

.67 b

c 3

.89 c

3

.55 d

4

.60 c

4

.40 c

0

.18

2 j

0

.21

1 j

0

.32

0 g

0

.24

3 i

N

0 K

45

0

5.6

7 f

gh

9

.67 e

fg

20

.33 b

c 2

1.0

0 b

cd

4.3

2 a

3

.82 b

4

.59 c

4

.47 b

0

.17

8 j

0

.32

0 d

0

.23

9 i

0

.21

4 k

N

15

0 K

0

10

.00 c

d

11

.33 d

e 2

0.3

3 b

c 2

2.6

7 b

3

.55 h

3

.43 f

4

.25 d

4

.38 c

0

.32

4 e

0

.24

9 h

0

.33

5 f

0

.25

6 h

N

15

0 K

15

0

13

.00 a

b

14

.00 b

c 2

0.0

0 b

cd

21

.67 b

c 3

.68 g

3

.47 e

4

.26 d

4

.30 d

0

.32

8 e

0

.22

5 i

0

.33

8 f

0

.22

8 j

N

15

0 K

30

0

11

.00 b

c 1

5.6

7 a

b

21

.00 b

2

3.0

0 a

b

3.4

3 k

3

.39 g

4

.23 d

e 4

.33 d

0

.36

0 c

0

.22

3 i

0

.34

6 f

0

.25

7 h

N

15

0 K

45

0

14

.67 a

1

6.3

3 a

2

4.0

0 a

2

5.0

0 a

3

.82 e

3

.43 f

4

.19 f

4

.31 d

0

.36

5 c

0

.26

4 g

0

.42

1 d

0

.36

7 d

N

30

0 K

0

7.0

0 e

fg

10

.00 d

ef

18

.67 c

-f

19

.67 c

de

3.5

4 h

3

.28 i

4

.20 e

f 4

.25 e

0

.24

5 h

0

.26

9 g

0

.28

7 h

0

.29

9 f

N

30

0 K

15

0

8.0

0 d

e 1

2.0

0 c

d

17

.67 e

f 1

9.0

0 d

e 3

.50 i

3

.28 i

4

.14 g

4

.32 d

0

.38

9 b

0

.31

6 d

e 0

.34

5 f

0

.32

6 e

N

30

0 K

30

0

5.0

0 g

h

7.0

0 h

i 1

8.3

3 c

-f

18

.00 e

3

.46 j

3

.22 j

3

.86 k

4

.40 c

0

.28

0 g

0

.35

2 b

0

.49

1 a

0

.24

9 h

i N

30

0 K

45

0

4.6

7 h

6

.00 i

1

9.0

0b-f

1

9.3

3 d

e 4

.06 b

3

.97 a

4

.07 h

4

.31 d

0

.30

4 f

0

.30

8 e

0

.33

7 f

0

.42

0 b

N

45

0 K

0

7.0

0 e

fg

7.6

7 g

hi

17

.67 e

f 2

0.0

0 c

de

3.2

4 m

3

.03 k

4

.04 h

4

.14 g

0

.45

4 a

0

.43

2 a

0

.31

9 g

0

.32

5 e

N

45

0 K

15

0

7.0

0ef

g

9.6

7 e

fg

18

.00

def

1

8.0

0 e

3

.43 k

3

.36 h

3

.98 i

4

.20

f

0.2

14 i

0

.26

6 g

0

.34

3 f

0

.28

8 g

N

45

0 K

30

0

7.6

7 e

f 9

.00 f

gh

1

9.3

3 b

-e

19

.67 c

de

3.2

9 l

3

.21 j

3

.89 j

4

.23 e

f 0

.34

3 d

0

.33

9 c

0

.47

3 b

0

.38

2 c

N

45

0 K

45

0

7.3

3ef

9

.00 f

gh

1

7.0

0 f

2

0.0

0 c

de

3.2

9 l

3

.23 j

4

.05 h

4

.23 e

f 0

.38

0 b

0

.28

7 f

0

.45

2 c

0

.50

1 a

Tab

le 1

P

hy

sical

ch

aracte

rs

of

soil

for

0-1

0 c

m l

ay

er (

L1)

an

d 1

0-2

0 c

m l

ay

er (

L2)

du

rin

g p

rem

on

soon

(S

1)

an

d m

on

soon

(S

2)

sea

son

s a

s in

flu

en

ced

by

nit

rog

en

an

d p

ota

ssiu

m

ferti

lizati

on

.

Mea

ns

in a

colu

mn

for a

soil

la

yer

foll

ow

ed

by

sa

me

lett

er(s

) d

o n

ot

sig

nif

ica

ntl

y d

iffe

r (P

<0

.05

) accord

ing t

o D

un

ca

n’s

Mu

ltip

le R

an

ge

Test

.

electrical conductivity were measured using a digital pH

meter (Cyberscan 510, Singapore) and Conductivity

Bridge Meter (ORLAB 201, India). Total nitrogen was

measured using an autoanalyser (Skalar autoanalyser,

Netherlands) after Kjeldahl digestion and distillation.

Exchangeable potassium was extracted in ammonium

acetate solution (pH 7) and measured using a flame

photometer (GENWAY). Total organic carbon was

determined according to Nelson and Sommers (1982).

The titration method of Jaggi (1976) was used to

assess soil respiration. Urease activity was determined

according to Kandeler and Gerber (1988) with urea (1M)

as a substrate and the values were expressed as

µg N.g -1dm.2h -1 using the calibration curve. Cellulase

activity was determined by incubation of soil samples

with water-soluble carboxymethylcellulose (Schinner

and Von Mersi, 1990) for 24 h at 50°C, pH 5.5. Low

molecular products and sugars resulting from the

enzymatic degradation of carboxymethylcellulose were

used for the quantitative reduction of potassium

hexacyanoferrate II to potassium hexacyanoferrate III,

which reacts with Fe (III) ammonium sulfate to form a

complex known as “Prussian Blue“, which is determined

photometrically at 690 nm. Cellulase activity is

expressed as µg GE g-1 dm 24 h -1.

Statistical analysis

All data were subjected to analysis of variance

(ANOVA) (IRRISTAT, version 3/93) and Duncan’s

Multiple Range Test (P<0.05) was used to separate the

means when the differences were significant. Pearson’s

correlation analysis was used to assess the relationship

between soil and microbial variables. The latter analysis

was carried out in SPSS 9.0.

RESULTS

Soil properties

Soil in the experimental plots were clayey loam

and fertilizer application had a profound influence on

soil moisture. As expected, soil moisture was



Treatm

en

t T

ota

l n

itrogen

(%

) E

xch

an

gea

ble

pota

ssiu

m (

mg

kg

-1l)

Org

an

ic c

arb

on

(%

) S

1

S2

S1

S2

S1

S 2

L1

L2

L1

L2

L1

L2

L1

L2

L1

L2

L1

L2

N0 K

0

0.3

7 h

i 0

.29 e

f 0

.27 f

g

0.2

4 b

1

55.2

1 h

1

01.8

3 i

1

62.6

5 i

1

07.4

3 k

4

.83 h

3

.26 h

3

.99 h

3

.55 f

N

0 K

15

0

0.3

6 i

0

.31 d

e 0

.29 e

fg

0.1

4 e

2

48.4

5 d

1

86.8

8 e

2

28.2

0 d

1

97.4

3 d

5

.24 f

3

.69 e

4

.06 h

3

.63 e

N

0 K

300

0.4

0 d

ef

0.3

4 a

bc

0.2

4 h

0

.19 c

2

59.8

3 c

2

23.5

9 c

2

17.8

5 e

1

57.7

8 e

5

.07 g

3

.39 g

4

.37 g

3

.00 j

N

0 K

45

0

0.3

8 f

gh

0

.27 g

0

.27 g

0

.19 c

3

23.7

0 b

2

46.7

2 b

2

81.2

2 b

2

59.7

7 b

4

.79 h

3

.82 d

4

.91 e

4

.10 c

N

15

0 K

0

0.3

8 g

hi

0.2

8 f

g

0.2

8 f

g

0.1

6 d

e 1

36.9

5 j

9

3.3

5 j

1

23.0

2 m

1

15.3

3 i

5

.00 g

3

.32 g

4

.45 g

3

.08 i

N

15

0 K

15

0

0.4

7 a

0

.31 d

e 0

.29 e

f 0

.15 e

1

41.5

0 i

8

0.8

8 l

1

37.4

3 k

1

15.3

3 i

6

.07 a

3

.84 d

3

.90 i

3

.20 h

N

15

0 K

30

0

0.3

8 g

hi

0.2

8 f

g

0.2

7 g

0

.31 a

1

59.8

3 g

1

19.1

8 g

1

97.2

0 f

1

43.3

6 f

5

.34 e

3

.33 g

h

5.2

7 c

3

.39 g

N

15

0 K

45

0

0.4

2 b

cd

0.2

7 f

g

0.3

8 b

0

.30 a

4

42.7

1 a

3

13.2

3 a

3

70.0

1 a

2

65.1

0 a

5

.04 g

3

.80 d

5

.85 b

3

.86 d

N

30

0 K

0

0.4

2 c

de

0.3

3 b

cd

0.3

7 b

0

.25 b

7

6.8

0 n

6

0.8

6 n

6

7.2

8 p

8

8.5

3 m

5

.46 d

4

.00 c

4

.00 h

4

.02 c

N

30

0 K

15

0

0.4

2 c

d

0.2

9 e

fg

0.3

6 b

c 0

.31 a

1

06.1

2 l

8

0.8

8 l

9

2.9

0 o

1

06.2

5 l

5

.50 c

d

3.7

8 d

5

.19 c

4

.96 a

N

30

0 K

30

0

0.3

9 f

g

0.3

5 a

0

.36 b

c 0

.24 b

1

28.0

2 k

1

14.7

9 h

1

52.9

5 j

1

19.9

2 h

5

.69 b

4

.37 a

5

.93 b

3

.71 e

N

30

0 K

45

0

0.4

3 b

c 0

.31 d

e 0

.31 d

e 0

.25 b

2

17.0

2 f

2

02.4

4 d

1

92.3

9 g

1

38.6

1 g

5

.27 e

f 3

.59 f

4

.64 f

3

.28 h

N

45

0 K

0

0.4

4 b

0

.35 a

b

0.3

8 a

b

0.1

6 d

e 8

0.8

8 m

7

3.8

0 m

1

01.7

6 n

5

5.1

0 o

5

.46 d

3

.94 c

5

.03 d

3

.82 d

N

45

0 K

15

0

0.4

3 b

c 0

.32 c

d

0.3

5 c

0

.16 d

e 1

28.0

2 k

8

5.0

0 k

1

29.2

0 l

7

5.6

5 n

6

.01 a

4

.10 b

4

.37 g

3

.28 h

N

45

0 K

30

0

0.4

0 e

fg

0.3

3 a

bc

0.3

3 d

0

.24 b

1

28.0

2 k

8

0.8

8 l

1

87.3

7 h

1

10.7

7 j

5

.56 c

4

.29 a

5

.19 c

4

.33 b

N

45

0 K

45

0

0.4

4 b

c 0

.34 a

bc

0.4

0 a

0

.17 c

d

22

3.5

9 e

1

80.8

8 f

2

70.0

1 c

2

01.7

6 c

6

.08 a

4

.35 a

6

.08 a

4

.29 b

M

ea

ns

in a

colu

mn

for a

soil

la

yer

foll

ow

ed

by s

am

e le

tter

(s)

do n

ot

sig

nif

ica

ntl

y d

iffe

r (P

<0

.05

) accord

ing t

o D

un

ca

n’s

Mu

ltip

le R

an

ge

Test

.

Ta

ble

2 C

hem

ical

chara

cter

s of

soil

for

0-1

0 c

m l

ayer

(L

1)

an

d 1

0-2

0 c

m l

ayer

(L

2)

du

rin

g p

rem

on

soon

(S

1)

an

d m

on

soon

(S

2)

sea

son

s as

infl

uen

ced

by n

itro

gen

an

d

po

tass

ium

fe

rti

liza

tion

.

significantly higher during monsoon and was affected by

fertilization. Similarly, the L2 layer was moister than the

L1 layer during both the seasons. For premonsoon period,

it ranged between 4.67-14.67% (L1) and 6.00-16.33%

(L2), respectively. On the other hand, it registered

17.00-24.00% (L1) and 18.00-25.00 % (L2) of mixture

for monsoon seasons (Table 1). Soil moisture was higher

in unfertilized soils during both seasons, but

progressively decreased with fertilizer application rates,

especially nitrogen (300 and 450 kg ha-1).

A significant difference in soil pH was evident

between layers, seasons and most treatments. Soils

fertilized with potassium had higher pH values, the

exception being the 0-10 cm soils fertilized with 300 and

450 kg ha-1of potassium. In contrast, soils fertilized with

nitrogen had the lowest pH values, and this drop in pH

was more evident in the top 0-10 cm soils than in 10-20

cm soils. Soil pH correlated positively with soil moisture

levels (r = 0.737; P<0.01) (Table 1, 3). Like pH, soil

electrical conductivity also exhibited significant

differences between treatments, seasons and layers.

During premonsoon, soils fertilized with nitrogen had

either almost similar or significantly higher electrical

conductivity values. In contrast during monsoon, soil in

nitrogen fertilized plots had decreased electrical

conductivity values compared to unfertilized plots

(Table 1).

Total soil nitrogen and exchangeable potassium

significantly differed between seasons, layers and among

treatments (Tables 2 and 3). The percentage nitrogen

content of the tea soil was higher during premonsoon

period (S1) when compared to the monsoon season (S2).

Similarly, the nitrogen content of L1 layer was higher

when compared to their respective L2 layer. Further the

application of nitrogen fertilizer at different doses

enhanced the available nitrogen in L1 layer

concomitantly (Table 2). The exchangeable potassium

level was comparable between premonsoon (S1) and

monsoon (S2) seasons and it fluctuated between different



So

urce

of

va

ria

tion

df

Mois

ture (

%)

pH

E

C (

dS

m-1

)

Soil

nu

trie

nts

Tota

l n

itrog

en

(%

) E

xch

an

gea

ble

pota

ssiu

m (

mg

kg -1

l)

Org

an

ic c

arb

on

(%

)

Tre

atm

ent

(T)

15

,12

8

34

.25 *

*

15

49.1

4 *

*

74

.64 *

*

49

.53 *

*

1299822839.4

7 *

*

23

.06 *

*

Laye

r (L

) 1

,12

8

10

0.9

2 *

*

58

3.8

4 *

*

92

8.3

3 *

*

30

78

.56

**

1627574891.3

7 *

*

15

6.6

2 *

*

Sea

son

(S

) 1

,12

8

33

06.7

2 *

*

84

72

1.7

8 *

*

15

98

.55

**

2

385

.60

**

9

118

00.3

5 *

*

64

.56 *

*

T x

L

15

,12

8

1.3

9

22

8.4

8 *

*

17

5.4

9 *

*

28

.54 *

*

40106426.7

8 *

*

11

.13 *

*

T x

S

15

,12

8

7.1

6 *

*

37

9.0

4 *

*

27

5.2

1 *

*

37

.60 *

*

50173100.7

1 *

*

21

.50 *

*

L x

S

1,1

28

8.3

3 *

*

33

51.8

3 *

*

26

6.8

6 *

*

2.0

5

29

53

962.1

6 *

*

14

0.9

8 *

*

T x

L x

S

5,1

28

1.2

4

74

.64 *

*

19

6.6

5 *

*

29

.49 *

*

14858168.8

7 *

*

16

.02 *

*

Tab

le 3

F

- V

alu

es o

f vari

ou

s so

il p

hy

sico

ch

em

ical

ch

aracte

rs a

s in

flu

en

ced

by

nit

rogen

an

d p

ota

ssiu

m f

erti

liza

tio

n.

**

an

d *

** s

ign

ific

an

t a

t P

<0

.01

an

d P

<0

.00

1 r

esp

ecti

vely

.

treatment plots in the range of 55.1 and 442.7 mg/ kg dry

soil. However, the potassium content was comparably

higher in the L1 layer than the L2 layer. The application

of increasing doses of muriate of potash in the different

experimental plots resulted in the enhanced amount of

potassium content in both L1 and L2 layers (Table 2).

Generally nitrogen content in the 0-10 cm soils was

higher when compared to their respective 10-20 cm soils.

Exchangeable potassium was lower in nitrogen fertilized

soils than unfertilized soils. Soil nitrogen was

significantly (P<0.01) and negatively correlated to soil

moisture (r = -0.627) and pH (r = -0.518). In contrast,

soil potassium and pH had a significant and positive

correlation (r = 0.267; P<0.05). Organic carbon was

higher in the 0-10 cm soils than in 10-20 cm soils and

significantly varied with fertilization and seasons.

Generally, organic carbon was higher during

premonsoon than monsoon season. As organic carbon

was significantly and positively correlated to electrical

conductivity (r = 0.315; P<0.05) and nitrogen (r = 0.752;

P< 0.01), it was significantly and negatively correlated to

soil moisture (r = -0.334; P<0.01) (Table 3)

Soil respiration

Soil respiration tended to be higher in 0-10 cm

soils and significantly varied between seasons and

among treatments (Fig 1). During premonsoon,

maximum respiration rates were occurred in the 0-10 cm

soils and it was moderate (300 kg ha-1) and high

(450 kg ha-1) in potassium fertilized soils. In contrast,

maximum respiration rates in the 10-20 cm soils during



mg

CO

2.g

-1 d

m.2

4

Fig. 1 Influence of nitrogen and potassium fertilization on soil respiration in the two soil layers (L1, L2)

during premonsoon (S1) and monsoon (S2) seasons. Points bearing same letter(s) for a season do not

significantly differ (P<0.05) according to Duncan’s Multiple Range Test

L1

L2

Treatments (Fertilizer dose in kg/ha/y)

premonsoon occurred in soils fertilized with high

nitrogen (450 kg ha-1). During monsoon, maximum

respiration rates were occurred in the 0-10 cm soils of

treatment involving moderate potassium and high

nitrogen levels (K300 and N450). The respiration rates in

10-20 cm soils during monsoon in fertilized plots were

generally lower compared to unfertilized soils. Soil

respiration was significantly and positively correlated to

soil nitrogen (r=0.325; P<0.001) and potassium

(r =0.309; P<0.05).

Enzyme activities

Application of nitrogen and potassium either

individually or in combinations significantly affected soil

urease activity (Fig 2). Urease activity exhibited different

trends in the two soil layers at different seasons. High

urease activity occurred during premonsoon in 0-10 cm

soils and during monsoon in the 10-20 cm soils.

However, maximum urease activity occurred in soils

fertilized with higher doses of nitrogen and potassium

(N450 and K450) during both the seasons and layers except

in 0-10 cm soils where maximum urease activity was

detected in soils fertilized with low nitrogen and

moderate potassium (N150 and K300). Soil urease activity

was significantly and positively correlated to organic

carbon (r=0.265; P<0.05) and negatively to soil

respiration (r =-0.347; P< 0.01).



Fig. 2 Influence of nitrogen and potassium fertilization on soil urease activity in the two soil layers (L1, L2)



μg

N.g

-1d

m.2

h-1

L1

n p

L1

L2


Cellulase activity in the soil differed

significantly among treatments and between seasons and

soil layers (Fig 3). Cellulase activity was higher in 0-10

cm soils during premonsoon season. There was a greater

cellulase activity in both soil layers during both the

seasons at low nitrogen application rates (N150).

However, increasing concentration of nitrogen

fertilization affected cellulase activity to a greater extent

in the 0-10 cm soils than in 10-20 cm soils. A significant

(P<0.05) positive correlation existed between soil

cellulase activity and total soil nitrogen (r = 0.283).

DISCUSSION

Regular nitrogen fertilization of the acid

soil further acidified the soils. The acidification was

more in sulphate of ammonia application during

premonsoon, than in urea application during monsoon.

These are in accordance with the fact that regular

nitrogen fertilization tend to acidify soils (Khonje et al.,

1989; Darusman et al., 1991). Biederbeck et al., (1996)

indicated that application of anhydrous ammonia

lowered soil pH more than urea, which clearly indicates

varied levels of soil acidification by different nitrogen

sources. Furthermore, soil total nitrogen levels were

lower in plots during urea application than sulphate of




μg

GE

.g-1

dm

.24 h

-1

Fig. 3 Influence of nitrogen and potassium fertilization on soil cellulase activity in the two soil layers (L1, L2)



L1

L2

ammonia. Most of the broadcasted urea might have

leached out in heavy monsoon showers, as considerable

loss (10-25%) of nitrogen has been reported to occur due

to leaching or volatilization, if urea was not incorporated

into soil soon after its application (Yang, 1991; Byrnes

and Freney, 1995).

The physico-chemical complexity of soil

contributes significantly to underlying variability in

K+ levels with soil pH, moisture and chemical

composition, all having marked effects (e.g. Maathuis

and Sanders, 1996). In particular, acidic pH leads to

desorption of K+ from anionic binding sites in the soil,

and accounts for the tendency towards higher K+ levels

in acidic soils (Gassmann et al., 1993). The

exchangeable potassium increased with increasing

potassium application rates. It has been thought for a

long time that exchangeable potassium do not built up in

the tea soils of south India, because of the dominance of

Kaolinite clay mineral (Verma, 1997; Venkatesan et al.,

2003). However the presence of other minerals other

than Kaolinitic might contribute to the build up of

potassium in the soil (Venkatesan et al., 2004). In this

study, exchangeable potassium was not related to pH,

moisture or chemical composition of the soil. However,

application of nitrogen significantly reduced soil

potassium which ranged from 18-55% in the 0-10cm

soils and 0-38% in 10-20 cm soils. Application of

nitrogen is known to enhance the growth of tea plants.

An increased plant growth resulting from nitrogen

fertilization tends to increase potassium uptake from the

soil. Studies by The Chinese Tea Research Institute

showed that tea leaves contain 1.2-2.5% potassium (TRI,

1997). So a large amount of potassium is being mined

from the soil system by the tea plants as a result of

increased growth response to nitrogen fertilization

(Tchienkoua and Zech, 2004).

The existence of a significant positive correlation

between soil organic carbon and soil nitrogen indicates

an increasing soil organic carbon content with increasing

nitrogen application rates. This is in accordance with

Venkatesan et al., (2004) who has also reported higher

organic carbon in soils fertilized with nitrogen. Further,

Venkatesan et al., (2004), indicated that natural organic

carbon reserves of tea soil would be lost due to no or

inadequate supply of nitrogen because tea plants tended

to mineralize and absorb nutrients from organic matter in

the soil under nutrient stress conditions. In addition,

other studies indicate an increase in soil organic carbon

with increasing soil acidity (Willett et al., 2004; Kemmitt

et al., 2006). Results from this study tended to indicate

that soil pH and organic carbon were negatively

correlated to each other; but this relation is not

statistically significant. However, when the correlation

analysis was staggered between layers, a significant

negative correlation existed between soil pH and organic

carbon in 0-10 cm soils (r = -0.667; P<0.000), but not in

10-20 cm soils (r = -0.193; P>0.05). This varied relation

between soil organic carbon and pH between layers

could be attributed to soil nitrogen which tended to

strongly influence soil pH than soil potassium.

Correlation coefficient values for soil pH and nitrogen in

0-10 cm soils were higher (r= -0.773) compared to

10-20 cm soils (r = -0.734). These observations are in

line with results of Mc Andrew and Malhi (1992) who

reported an increase in soil organic matter with

increasing soil nitrogen.

Soil respiration rates were within normal ranges

reported for natural soils (Srivastava and Singh, 1991;

Maxwell and Coleman, 1995). Results from this study

tended to show that nitrogen and potassium fertilization

affected soil respiration in 0-10 cm soils more than in the

10-20 cm soils. Results of Chen et al., (2002), also

indicate that nitrogen fertilization reduced soil

respiration in 0-10 cm soils. The low respiration rate

with fertilizer application might be attributable to lower

availability of carbon with decreasing soil pH induced by

the nitrogen application (Thirukkumaran and Parkinson,

2000).



Soil urease activity has been reported to follow

changes in soil factors (Cookson and Lepiece, 1996). In

the present study, fertilizer application generally

increased soil urease activity. This is in agreement with

Venkatesan and Senthurpandian (2006), who also

reported an increased urease activity in fertilized tea

soils. However these observations contrasts the studies of

Dick et al., (1988) and Bandick and Dick (1999) where

soil urease activity was reported to decrease with

increasing application of ammonia based nitrogen

fertilizers. Since urease is a substrate inducible enzyme,

the application of fertilizers especially urea could have

resulted in higher urease activity. Further, the binding of

the urease to organic matter insulating itself from

denaturation and biological degradation by soil humic

polymers (Beri et al., 1978; Baligar and Wright, 1991)

could also attribute to increased level of urease as this

urease could be released from these protected sites by

acid sensitive ammonia oxidizers in response to

fertilization (Martikainen, 1985).

Cellulase activity was higher in the surface layer

(0-10 cm soils) than in the subsoils (10-20 cm soils) and

was positively correlated to soil organic matter.

Fertilization increased soil cellulase activity, which are

in accordance with studies of Aescht and Foissner

(1992).

CONCLUSION

Results from the present study revealed that long

term application of nitrogen and potassium fertilizers

affected soil nutrients and pH. Further these fertilizers

can interact with soil microbial communities in a variety

of ways and consequently disturb their normal

functioning. The use of nitrogenous fertilizers is

inevitable and an essential part of agricultural practices.

In the present study, we determined that long–term

application of higher doses of urea or ammonium

sulphate fertilizers had an inverse effect on pH, moisture,

soil respiration and enzyme activities. Therefore the

maintenance of low rates of nitrogen and potassium

(i.e., < 300 kg-1ha-1y-1) are vital for preserving the soil

quality, as higher doses of nitrogen and potassium

(i.e., > 300 kg-1ha-1y-1), adversely affects the soil quality.

However, the actual mechanisms behind these changes

are difficult to infer and needs further investigation.

ACKNOWLEDGEMENTS

I express my sincere thanks to

Dr. N. Muraleedharan, Director, UPASI Tea Research

Institute, Valparai, Coimbatore District, Tamil Nadu,

India for kind permission to use their experimental plots,

which formed vital foundation for this work. I

acknowledge the invaluable help and support rendered

by Dr. S. Premkumar Samuel Asir, Dr. U.I. Baby and

Dr. S. Venkatesan, Dr. R. Selvasundaram, UPASI Tea

Research Institute, Valparai, Coimbatore District, Tamil

Nadu, India during the course of this study.

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Influence of long term Nitrogen and Potassium fertilization on the biochemistry of Tea Soil

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