soil organic carbon and nitrogen pools in poplar based agroforestry system

110 Pages·2014·1.48 MB·English

SOIL ORGANIC CARBON AND NITROGEN POOLS IN

POPLAR BASED AGROFORESTRY SYSTEM

Thesis

Submitted to the Punjab Agricultural University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
in
SOIL SCIENCE
(Minor Subject: Chemistry)

By

Shehnaz
(L-2012-A-127-M)

Department of Soil Science
College of Agriculture
 PUNJAB AGRICULTURAL UNIVERSITY
LUDHIANA-141004

2014
CERTIFICATE I
This is to certify that the thesis entitled, “Soil organic carbon and nitrogen pools in
poplar based agroforestry system” submitted for the degree of M.Sc. in the subject of Soil
Science (Minor subject: Chemistry) of the Punjab Agricultural University, Ludhiana, is a
bonafide research work carried out by Shehnaz (L-2012-A-127-M) under my supervision and
that no part of this thesis has been submitted for any other degree.
The assistance and help received during the course of investigation have been fully
acknowledged.

__________________________
Dr. Baljit Singh
(Major Advisor)
Scientist (Soil Conservation)
Department of Forestry and N. R.
Punjab Agricultural University
Ludhiana- 141004 (India)
CERTIFICATE II
This is to certify that the thesis entitled, “Soil organic carbon and nitrogen pools in
poplar based agroforestry system” submitted by Shehnaz (L-2012-A-127-M) to the Punjab
Agricultural University, Ludhiana, in partial fulfillment of the requirements for the degree of
M.Sc. in the subject of Soil Science (Minor subject: Chemistry) has been approved by the
Student’s Advisory Committee along with the Head of the Department after an oral examination
on the same.

_________________ ____________________
(Dr. Baljit Singh) (Dr. K. N. Sharma)
Major Advisor External Examiner
Professor of Soils (Retd.)
Department of Soil Science
Punjab Agricultural University
Ludhiana-141-004

____________________
(Dr. J. S. Dhiman)
Head of the Department

_______________________
(Dr. Gursharan Singh)
Dean, Postgraduate Studies
Acknowledgements
First of all I would like to offer my sincere reverence to the Almighty and my dear parents
whose blessings have enabled me to complete a very important phase of my life. I feel proud
to be a part of the esteemed Soil Science Department of Punjab Agricultural University.
I wish to express my heartfelt thanks to my major advisor Dr. Baljit Singh, Scientist
(Soil Conservation), who shaped my efforts and helped in every possible way in achievement
of my objectives. I thank him for his invaluable guidance, constant encouragement, immense
patience, stead-fast support, peerless criticisms and dedication to ensuring my success in
every single step of my masters.
I feel great pride and privilege to express my thanks to Dr. Rajeev Sikka, Dr. M. S.
Hadda and Dr. (Mrs.) Anita Garg for their encouragement and invaluable suggestions
endowed during the course of my research work as well as for reviewing the thesis drafts. I
would also like to express my gratitude to Dr. D. K. Benbi (ICAR National Professor) for his
guidance and support during my research work. A Sincere thanks to Dr. Pritpal Singh for
clearing the statistical doubts and rendering great help whenever I needed.
I owe my profound thanks to Dr. U. S. Sadana, Former Head and Dr. J. S. Dhiman
Present Head, Department of Soil Science for providing the necessary facilities and a great
work environment throughout the course of this study.
No words can express my sense of gratitude to my parents Mr. Ramesh Sharma and
Mrs. Shashi Sharma, my sister, brother and family whose love, care and affection has always
stood by me through the good and the bad times and given me direction in my life. I am
grateful to my friends for their constant support and unwavering faith in me. They were
always supporting, giving suggestions, cheering me up and encouraging me with their best
wishes. Thanks to my classmates and seniors who helped in one way or the other in
completion of this venture.
My sincere thanks to PG laboratory assistant Mr. Raj Kumar and other laboratory
staff who were always available for help during my research work.
I feel proud to be a part of Punjab Agricultural University. This institution has helped
me to explore nature and made me truly love science.

Date: 24-07-2014
Place: Ludhiana Shehnaz Sharma
Title of the Thesis : Soil organic carbon and nitrogen pools in poplar
based agroforestry system
Name of the Student : Shehnaz
and Admission No. (L-2012-A-127-M)
Major Subject : Soil Science
Minor Subject : Chemistry
Name and Designation : Dr. Baljit Singh
of Major Advisor Scientist (Soil Conservation)
Degree to be Awarded : Master of Science
Year of award of Degree : 2014
Total pages in Thesis : 102+Vita

Name of University : Punjab Agricultural University, Ludhiana

ABSTRACT
Soil samples were collected from 0-15, 15-30 and 30-45 cm soil depths from farmers’
fields of two villages namely Khehra Bet and Nurpur in Ludhiana district to investigate the
effects of cutting cycles (rotations) of poplar (Populus deltoides Bartr.) plantations and
paddy-wheat sequence on soil organic carbon and nitrogen pools, available macro and
micronutrients and physico-chemical characteristics of soils. Soil organic carbon (SOC), total
organic carbon (TOC) and total carbon (TC) content and stock increased significantly from 1
to 4 cutting cycles up to 30 cm depth. Maximum content of SOC, TOC and TC was observed
under paddy-wheat sequence. Higher contents of hot water soluble carbon, very labile, less
labile and recalcitrant carbon were found under 4 cutting cycles than 1 cutting cycle. The N
pools viz. NH +-N, NO --N, available N and total N were also higher in the 4 cutting cycles.
4 3
No significant variation in available K occurred but available P was significantly higher in 3
and 4 over 1 cutting cycle. Among micronutrients, an increase of 85, 77, 119 and 133% was
observed for Fe, Mn, Zn and Cu, respectively in 4 cutting cycles over 1 cutting cycle in the
surface soil depth. Water holding capacity and CEC increased linearly with increase in cutting
cycles but no change in soil bulk density and particle density was observed. A decrease in soil
pH with increase in cutting cycles was observed. Thus, the long term adoption of poplar based
agroforestry improved SOC, N and their pools, available nutrients and physico-chemical
properties of soil.
Keywords: Carbon pools, nitrogen pools, cutting cycles, available nutrients, physico-
chemical properties

______________________ ____________________
Signature of Major Advisor Signature of the Student
Koj gRMQ dw isrlyK : poplr AwDwirq vx KyqI iv`c BmU I ivclI jYivk
kwrbn Aq y nweItRojn dy AMS
ividAwrQI dw nwm Aqy : S i h nwz
dwKlw nM. (AYl-2012-ey-127-AYm)
pRmu`K ivSw : BUmI ivigAwn
sihXogI ivSw : rswiex ivigAwn
pRmu`K slwhkwr dw nwm Aqy Ahudw : fw. bljIq isMG
ivigAwnI (BmU I r`iKAw)
ifgrI : AYm.AYs.sI (BmU I ivigAwn)
ifgrI nwl snmwinq krn dw swl : 2014
Koj p`qr iv`c kul pMny : 102+vItw
XUnIvristI dw nwm : pMjwb KyqIbwVI XUnIvristI, luiDAwxw

swr
mOjUdw AiDAYn dOrwn BUmI iv`clI jYivk kwrbn Aqy nweItRojn dy AMS, auplbD mkY Ro Aqy
sUKm pOSitk q`qW Aqy im`tI dy BOiqk-rswiexk guxW apu r poplr (popUls fyltoAwiefs bwrt.)
Aqy Jonw-kxk &slI ck`r dI kwSq dw pRBwv vyKx leI luiDAwxw dy do ipMfW Kihrw byt Aqy
nUrpur dy ikswnW dy KyqW ’coN 0-15, 15-30 Aqy 30-45 sYNtImItr fUMGweI qoN im`tI dy nmUny ley
gey[ AiDAYn dOrwn pwieAw igAw ik 30 sYNtImItr fUMGweI aupr 1 qoN 4 kitMg sweIkl q`k
BUmI iv`clI jYivk kwrbn (AYs.E.sI.), ku`l jYivk kwrbn (tI.E.sI.) Aqy ku`l kwrbn (tI.sI.)
dI imkdwr Aqy BMfwr iv`c ArQpUrn vwDw hoieAw[ AYs.E.sI., eI.E.sI. Aqy tI.sI. dI sB qoN
vDyry imkdwr Jonw-kxk AnukRm iv`c vyKx nUM imlI[ grm pwxI iv`c GulxSIl, vDyry auqrdweI,
G`t auqrdweI Aqy nSt nw hox vwlI kwrbn dI imkdwr 1 kitMg sweIkl dy mukwbly 4 kitMg
sweIkl ADIn vDyry sI[ nweItRozn dy AMS ijvyN ik NH +-N, NO --N, auplbD nweItRojn Aqy
4 3
ku`l nweItRojn dI imkdwr 4 kitMg sweIkls iv`c vDyry pweI geI[ auplbD potwSIAm iv`c
koeI ArQpUrn Prk vyKx nUM nhIN imilAw jdoN ik auplbD &ws&ors dI imkdwr 1 kitMg
sweIkl dy mku wbly 3 Aqy 4 kitMg sweIkls iv`c ArQpUrn qOr q y vDyry pweI geI[ ie`k kitMg
sweIkl dy mukwbl y 4 kitMg sweIkls iv`c sUKm pOSitk q`qW ijvyN ik Awiern, mNYgnIz, izMk
Aqy kwpr dI imkdwr iv`c kRmvwr 85, 77, 119 Aq y 133 pRqISq dw vwDw hoieAw[ kitMg
sweIkls dI sMiKAw vDx nwl BUmI dI pwxI nUM smw ky r`Kx dI smr`Qw Aqy sI.eI.sI. iv`c
ie`kswr vwDw hoieAw jdoNik ies nwl im`tI dI Gxqw Aqy kxW dI Gxqw iv`c koeI bdlwA dyKx
iv`c nhIN AwieAw[ kitMg sweIkls dI sMiKAw vDx nwl BUmI dI pI.AY~c. iv`c igrwvt AweI[
ies leI, AiDAYn qoN ieh q`Q swhmxy Awey ik poplr nUM lMby smyN q`k KyqW iv`c augwaux nwl
BUmI dI AYs.E.sI., nweItRojn, auplbD pOSitk q`qW dI imkdwr Aqy BUmI dy BOiqk-rswiexk
guxW iv`c suDwr hoieAw[

mu`K Sbd: kwrbn dy AMS, nweItRojn dy AMS, kitMg sweIkls, aulpbD pOSitk q`q, BOiqk-
rswiexk gux

__________________ _______________
pRmu`K slwhkwr dy hsqwKr ividAwrQI dy hsqwKr
CONTENTS

CHAPTER TOPIC PAGE(S)
I INTRODUCTION 1-4
II REVIEW OF LITERATURE 5-28
III MATERIALS AND METHODS 29-35
IV RESULTS AND DISCUSSION 36-85
V SUMMARY 86-89
REFERENCES 90-102
VITA
CHAPTER I
INTRODUCTION
With the onset of human evolution hunger has always been a great threat to human
survival. The threat is not due to reduced capacity of the world to supply food but is because
of the rapid rate at which world population is increasing and more particularly in developing
countries like India. In the times to come, soil and their response to management will hold the
key to food production. There are three routes to increase food production viz., clear more
land from forests for arable crops, increase cropping intensity and intensive production on
lands already under cultivation. But there are certain environmental quality concerns like
removal of native vegetation and replacement with agricultural crops leading to higher runoff
and erosion, destruction of forests worldwide resulting in release of vast quantities of CO into
2
the atmosphere that has led to global warming. The CO concentration in the atmosphere has
2
increased from 280 ppm in pre-industrialized period to >385 ppm at present due to
deforestation, industrialization and intensive cultivation. This has generated greatest global
interest in the carbon cycle. A considerable part of the current carbon atmospheric pool comes
from the terrestrial ecosystem of which soil is the largest terrestrial pool (Lal 2004).
In recent years, the awareness of the ecological and environmental health of our
surrounding ecosystems has been increasing. As a consequence there has been a growing
interest in sustainable agricultural alternative practices such as agroforestry. Agroforestry can
be defined as “a collective name for land use systems and technologies where woody
perennials (trees, shrubs, palms, bamboos etc.) are deliberately used on the same land
management unit as agricultural crops and/or animals, either in some form of spatial
arrangement or temporal sequence”. In agroforestry systems, there are both ecological and
economic interactions between the different components (Gordon et al 1997). Agroforestry is
believed to increase the soil organic carbon through litterfall and has also been proposed as a
strategy to mitigate increasing CO levels in the atmosphere (IPCC 1995). Compared with
2
monocropping systems, trees in agroforestry systems can enhance the soil organic matter
level by adding the quantity of aboveground and belowground organic matter inputs to soils
(Jose 2009, Nair et al 2009b). Agroforestry has been associated with an increasing amount of
environmental and ecological benefits such as enhancement of microclimatic conditions,
improved use and cycling of soil organic carbon and nutrients, improved soil and water
quality, creation of suitable habitats for insect and animal species, protection from erosion,
and protection from wind and rains (Jose et al 2004). The alternative practice has the potential
to alleviate both economic and ecological stress on farms. The changes in micro-environment
under tree canopy (soil moisture, temperature etc.), proliferation of root system and enhanced
biological activity also favour the carbon stock in the soil. However, the continuity in the
system is essential; otherwise the build-up in organic carbon may revert back to its original
under commercial agriculture (Sierra et al 2013). It has been said that the ecological benefits
provided by agroforestry systems along with the yields of trees and crops combined puts the
alternative practice above conventional agriculture in terms of long-term productivity
(Thevathasan and Gordon 2004).
Poplar (Populus deltoides Bartr.) is one of the important trees used under agroforestry
and preferred by the farmers of Punjab. It can be harvested at a short rotation of 6-7 years.
Hybrid poplar and eucalyptus have shown the greatest potential for very high growth rates in
USA also (Zsuffa et al 1996). Poplar is raised in agricultural fields along with the crops like
wheat, sugarcane, turmeric, pearlmillet, vegetables etc. It has very fast growth rate, high
productivity, high market value, less competition with associated crops and pruning tolerant
nature. It is a deciduous tree and sheds major portion of its leaves during winter, thus
improving the physico-chemical properties of soil through addition of organic matter in the
soil. The litter production and nutrient return through poplar litterfall vary with the age of the
tree, intercrop, spacing and other management practices. Because of economic benefits
associated with poplar-based agroforestry systems and their role in preventing land
degradation, this land-use has been proposed as a viable option for irrigated agroecosystems
of India (Pandey 2007). Plant litter decomposition plays a key role in nutrient cycling,
determining the productivity of natural and agro ecosystems. The qualities of soil organic
matter and nutrient pools mainly depend on physico-chemical quality of litter and
environmental factors.
Soil organic matter affects soil physical, chemical and biological properties and hence
is regarded as a key attribute of soil fertility (Paustian et al 1997, Verma et al 2010). Different
approaches have been used to understand soil organic matter (SOM) dynamics, such as
partitioning SOM into fractions based on biological lability with different turnover rates
related to certain ecosystem functions (Schroth and Lehman 2003). Differences in the rate of
litter decomposition can lead to large differences in organic matter accumulation and the C
and N content of soils (Parton et al 1987). In agricultural soils, land use change or
management practices can disrupt SOM dynamic equilibrium and produce a marked effect on
soil organic C stock (Lal 2004, Leifeld and Kögel-Knabner 2005). Paustian et al (1997)
estimated that global cultivated soils released about 50 Pg C through the mineralization of
SOM. Depletion of the SOM caused a decline in soil fertility and crop productivity and
increased atmospheric CO concentration (Lal 2004, Banerjee et al 2006).
2
Soil organic carbon and nitrogen contribute mainly to the soil organic matter. Their
dynamics are not only important to both productivity and sustainability but also are options to
reduce the enrichment of atmospheric CO . Soil organic carbon (SOC) is divided into three
2
major pools: active, slow and recalcitrant based on the decomposition turn over time. Active
2
or labile C pool, with rapid turnover rate is an important energy source for the soil food web
and thus influences nutrient cycling for maintaining soil quality and its productivity (Chan et
al 2001). Recalcitrant or passive pool is very slowly altered by microbial activities (Sherrod et
al 2005). Thus the labile pool is mainly associated with soil fertility and productivity and the
recalcitrant pool is associated with the sequestration of atmospheric carbon dioxide. But
agroforestry must be practiced for a long period of time for effective carbon sequestration.
Similarly, there are different pools of N like ammonical N, nitrate N which are important in
supplying N to plants and determining rate of organic matter decomposition. Some C pools
like microbial biomass C, mineralizable C, water extractable organic C and oxidisable organic
C are used as indicators of soil quality. These respond to agricultural management and land-
use changes more rapidly than the total organic carbon and thus could be used as sensitive
indicators of soil quality. Therefore, identifying the changes in these labile SOM fractions
may provide information about the effects of agroforestry practices on SOM dynamics.
The SOM added through decomposing litterfall improves both physical and chemical
properties of soil as well as the available nutrient content. There are several studies on the
improvement in aggregation, water holding capacity and CEC of the soil (Li et al 2007,
Sartori et al 2007). Soil physical properties such as clay content and mineralogy control soil
carbon pools by influencing the susceptibility of soil C to microbial attack (Percival et al
2000). Improvement in soil structure through formation of organomineral complexes is an
important mechanism of C sequestration in soils (Emerson 1995).The available macronutrient
(N, P and K) as well as micronutrient status is also reported to improve under tree species
(Singh and Sharma 2012). The higher content of available N, P and K on the surface layer
under poplar is attributed to accumulation and decomposition of litterfall on the soil surface.
Bhola and Mishra (1998) and Singh et al (2002) observed higher content of micronutrients
under tree species as compared to control. The differences in various micronutrients’ content
under different tree species may be attributed to variation in concentration, varying rates of
their release through decomposition of organic residues and rate of decomposition of these
nutrients in litterfall as well as the quantity of litterfall added.
In the North Indian state of Punjab, rice-wheat is the major cropping system
occupying an area of 2.6 million hectares; ensuring regional food security. There are reports
of stagnating or declining rice and wheat yields in the Indo-Gangetic plains (Ladha et al
2003), which have presumably been related to declining SOM content and decreased soil
fertility (Bhandari et al 2002, Regmi et al 2002). Benbi et al (2009) evaluated soil data for 25
years to investigate the impact of intensive agriculture on C sequestration and soil properties
on a regional scale in Punjab. Unexpectedly, intensive agriculture resulted in improved soil
organic carbon status. As a weighted average for the whole state, SOC increased from 2.9 g
kg−1 in 1981/82 to 4.0 g kg−1 in 2005/06, an increase of 38%. Increased productivity of rice
3