AGRICULTURAL NITROGEN USE & ITS ENVIRONMENTAL … · I am very happy that this comprehensive book...

AGRICULTURAL NITROGEN USE & ITS

ENVIRONMENTAL IMPLICATIONS

EDITORS

AGRICULTURAL NITROGEN USE & ITS

ENVIRONMENTAL IMPLICATIONS

Y.P. Abrol

Former Head

Division of Plant Physiology

Indian Agricultural Research Institute

New Delhi

N. Raghuram

Reader

School of Biotechnology

Guru Gobind Singh Indraprastha University

New Delhi

M.S. Sachdev

Principal Scientist

Indian Agricultural Research Institute

New Delhi

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I am very happy that this comprehensive book on “Agricultural Nitrogen Use and its Environmental

Implications” has been prepared by Professor YP Abrol along with his colleagues, Dr. N. Raghuram and

Dr. MS Sachdev. Nitrogen is the primary input in Indian agriculture, and its management holds the key

for quantitative and qualitative improvement of various crops. This book contains chapters written by

leading experts in the field. It provides a comprehensive, interdisciplinary description of the problems of

N use efficiency in Indian agriculture in the overall context of nitrogen cycle, its environmental and

health implications, as well as various approaches to N use efficiency. The topics vary from plant molecular

biology to agronomic management, and include issues related to the role of legumes in nitrogen nutrition,

groundwater and air pollution, and human health.

Following the rise in the cost of urea and other sources of nitrogenous fertilizers, there has been growing

interest in developing and promoting integrated nutrient management systems consisting of an optimal

blend of green manure crops, organic manures, biofertilizers, and mineral fertilizers. This book will be

useful for all interested in strategies for rational and effective nitrogen use and in addressing the issues

related to environmental degradation.

I congratulate the editors for getting such a valuable book prepared and published.

M.S. SwaminathanFRS, President,

National Academy of Agricultural Sciences,

New Delhi

Foreword

This book is one of the outcomes of a long and continuing process of consultations in India (and abroad,

lately) to develop an integrated approach for nitrogen research and policy. These efforts were necessitated

by the increasing realisation that while majority of the Indian agricultural soils are deficient in usable

forms of nitrogen (N), uneven/excessive/improper/inappropriate use of N fertilizers, coupled with

contributions from industrial effluents/ exhausts, animal wastes and geo-deposits have led to widespread

pollution of ground water and eutrophication of surface waters, posing a severe problem for the public

health and ecosystem. The ozone-depleting and greenhouse effects of NOx gases from various farm and

non-farm sources may pose new concerns for nitrogen-carbon balance.

The natural processes of producing reactive N from atmospheric N2 gas, as well as its reversal by

denitrification have been dramatically altered by fertilizer production and consumption in agriculture,

cultivation of legumes, animal husbandry, transport and other fossil fuel-consuming industries that produce

N wastes. The resulting accumulation of reactive N in the environment has adverse impacts on biodiversity,

global warming, water quality, human health etc. Unlike many other human activities in which it is a by-

product, reactive N is an essential input for agriculture, constituting upto 70 per cent of the total fertilizer

material and is manufactured and consumed on a massive scale. There is no escape from the use of

fertilizers to sustain food production, and the environmental consequences of accumulation of reactive

N are the same, regardless of whether the fertilizers are of chemical or biological origin. Therefore, the

challenge now facing Indian agriculture is to further enhance the productivity of our agricultural system

without adversely impacting our environment and ecology. This necessitates an integrated understanding

of nitrogen in India’s agriculture, industry and environment, so as to identify the appropriate sites for

intervention towards a more sustainable N management regime.

Preface

This perspective led us to begin a process of consultation with the researchers and others working on

various aspects of nitrogen research and policy across the country onto a common platform under the

auspices of the Society for Conservation of Nature. The first concrete outcome of this process was a

brain storming session sponsored by the National Academy of Agricultural Sciences (NAAS) during

October 4-5, 2005, at NAAS, New Delhi, under Prof. YP Abrol, INSA Senior Scientist and Editor,

NAAS, as convenor and Dr. S.M. Virmani, Foreign Secretary, NAAS as co-convenor. A background

paper on N in agriculture and environment was circulated in advance to over 80 scientists and specialists

from agricultural, environmental and industrial sectors, based on which over 50 papers on specific

aspects were received. These were integrated into a few position papers that were presented and discussed

during the brainstorming session attended by more than 35 participants. Their recommendations formed

the basis for a policy paper titled “Policy Options for Efficient N Use”. One of the most important

realizations that emerged from this exercise is that the problems related to N in agriculture, industry and

environment are multidimensional. The sheer diversity of research areas / expertise / approaches it

encompasses and the various levels at which the problems need to be identified / tackled calls for an

integrated network approach to harness our intellectual, financial and infrastructural resources effectively.

In order to further expand the nitrogen network beyond agriculture, the Society for Conservation of

Nature (SCON, New Delhi) organized a workshop in March 2006 on “Nitrogen in Environment Industry

and Agriculture”, at INSA. It was sponsored by INSA, DBT, MOEF and CSIR. Over 50 delegates

attended the workshop, including 26 speakers and 8 poster presenters, representing diverse specialisations

on various aspects of N, from institutes, universities, and industry. A network of Nitrogen research

workers in various sectors in India referred to as “Indian Nitrogen Group” has also been formalized as

an outcome of this workshop. In the meantime, we also came into contact with the International Nitrogen

Network (INI), which evolved in the recent years to address similar concerns and bring about international

coordination. This year, an organization called “Nitrogen in Europe” emerged to address similar concerns

at the level of the member countries of the European Union. These emerging networks highlight the

growing concerns related to nitrogen at the national, regional or international level.

This book is the first ever attempt to distill the current thinking in India with regards to various aspects

of nitrogen, based on the above process of consultation and networking. It encompasses all aspects of

the nitrogen cycle with special reference to reactive N in the Indian context to summarise the current

knowledge as well as identify the gaps in it for informed decisions on further research and policy. The

authors have been chosen for their expertise, strong and long presence in the field, and commitment to

interdisciplinary understanding on various aspects of nitrogen. The articles provide state-of-the-art reviews

in their respective disciplines integrating global literature and India-specific information as appropriate.

In this sense, apart from being a unique reference source at the national level, this book is also meant to

be of reference value for an international readership, especially those who wish to understand country-

specific issues in the wider international context.

viii Preface

Naturally, the authors of this book had a major responsibility to serve the larger purpose behind this

book while contributing their articles, and their efforts are greatly appreciated. We also gratefully

acknowledge the rich inputs from all the scientists who have been a part of our consultative process and

now constitute the Indian Nitrogen Group. The financial support we received from NAAS, DBT, INSA,

MOEF and CSIR for the two brainstorming sessions has greatly facilitated the entire process and

emboldened us to embark on the ambitious task of putting together this book.

Finally, I would like to thank I.K. International for their cooperation and support.

Y.P. Abrol

N. Raghuram

M.S. Sachdev

Preface ix

Foreword ........................................................................................................................................ v

Preface .......................................................................................................................................... vii

1. Towards an Integrative Understanding of Reactive Nitrogen .................................... 1-6

N. Raghuram, M.S. Sachdev and Y.P. Abrol

NITROGEN USE, FLOWS AND CYCLING IN AGRICULTURAL SYSTEMS

2. Indian Agriculture and Nitrogen Cycle ........................................................................ 9-28

A. Vel Murugan and V.K. Dadhwal

3. Nitrogen in Indian Agriculture .................................................................................... 29-54

Rajendra Prasad

4. Nitrogen Transformations and Flows in Agro-Ecosystems—An Overview .......... 55-74

Bijay Singh, Yadvinder Singh and R.K. Gupta

5. Geospatial Approach to Understand Nitrogen Cycle in India ................................ 75-96

V.K. Dadhwal and A. Vel Murugan

NITROGEN USE EFFICIENCY IN CROP ECOSYSTEMS

6. Nitrogen Use Efficiency in Rice Ecosystems ........................................................... 99-120

D. Panda, D.K. Kundu, A. Ghosh, N.B. Prakash and D.D. Patra

Contents

xii Contents

7. Fertilizer Use Constraints and Management in Rainfed

Areas with Special Emphasis on Nitrogen Use Efficiency .................................. 121-138

K.L. Sharma, K.P.R. Vittal, Y.S. Ramakrishna, K. Srinivas,

B. Venkateswarlu and J. Kusuma Grace

8. Enhancing Nitrogen Use Efficiency for Sustainable Rice-Wheat

Production System in the Indo-Gangetic Plains of India.................................... 139-164

Yadvinder Singh, Bijay Singh, J.K. Ladha, J.P. Singh and O.P. Choudhary

9. 15N Studies in Relation to Nitrogen Balance in Cropping Systems ................... 165-194

M.S. Sachdev and P. Sachdev

MANAGEMENT OPTIONS AND STRATEGIES FOR ENHANCING NITROGEN USE EFFICIENCY

10. Management Options for Increasing Nitrogen Use Efficiency ........................... 197-226

C.L. Acharya and A.R. Sharma

11. Importance of Interactions of Nitrogen with Primary and

Secondary Micronutrients in Crop Production and

Environmental Safety—Indian Perspectives .......................................................... 227-248

S. Joginder Manchanda and Milkha S. Aulakh

12. Nitrogen Use Efficiency Improvement through USG and NCU:

Initiative of the Indian Industry ............................................................................. 249-262

Ramendra Singh, Virendra Kumar and B.N. Vyas

13. Nitrogen from Industrial Wastes as Soil

Amendment in Agriculture ....................................................................................... 263-278

Deepak Pant and Alok Adholeya

14. Improving Nitrogen Use Efficiency: Strategies, Tools,

Management and Policy Options ............................................................................ 279-302

H. Pathak and J.K. Ladha

PLANT PHYSIOLOGICAL AND MOLECULAR ASPECTS OF ENHANCING NITROGEN USE EFFICIENCY

15. Physiological and Biochemical Aspects of Nitrogen

Use Efficiency in Crop Plants .................................................................................. 305-326

Altaf Ahmad, Vanita Jain, Y.P. Abrol

Contents xiii

16. Molecular Approaches for Enhancement of Nitrogen

Use Efficiency in Plants ............................................................................................ 327-350

Sunila Lochab, Ravi Ramesh Pathak and N. Raghuram

ROLE OF LEGUMES AND BIOFERTILIZERS IN AGRICULTURAL NITROGEN ECONOMY

17. Role of Legumes in Nitrogen Economy of Cereals/

Cropping Systems—The Indian Scenario .............................................................. 353-368

M.S. Venkatesh and Masood Ali

18. Biological Nitrogen Fixation: From Fundamentals to

Field Considerations .................................................................................................. 369-394

Anil Kumar Tripathi, Soumitra Paul Chowdhury and Vyom Parashar

19. Biological Nitrogen Fixation and Biofertilizers: Status and Prospects ............. 395-414

D.L.N. Rao

20. Nitrogen Fixation in Arid and Semi-arid Agriculture:

Opportunities and Constraints ................................................................................ 415-436

B. Venkateswarlu

ENVIRONMENTAL AND HUMAN HEALTH IMPLICATIONS

21. Nitrate Pollution of Ground Water Vis-a-Via Nitrogen Fertilizer

Use in India ................................................................................................................ 439-458

Bijay Singh, E.V.S. Prakasa Rao, Yadvinder Singh and K. Puttanna

22. N-Fertilizers and Gaseous-N Emission from Rice-Based

Cropping Systems ...................................................................................................... 459-476

T.K. Adhya, H. Pathak and A. Chhabra

23. N-Pool Size, its Reuse and Sustainability Issues of a Developing

City—Bangalore ......................................................................................................... 477-498

H.N. Chanakya and H.C. Sharatchandra

24. Nitrogen Cycling and Fluxes in Coastal Ecosystems ........................................... 499-516

K. Amrtha, R. Purvaja and R. Ramesh

25. Nitrate Toxicity and Human Health ....................................................................... 517-548

Sunil Gupta, R.C. Gupta and A.B. Gupta

Index ............................................................................................................................ 549-552

List of Contributors

Abrol YP, Society for Conservation of Nature,

40 SFS Hauz Khas Apartments,

New Delhi—110 012.

Email: [email protected]

Acharya CL, Formerly at CSK Himachal Pradesh

Agricultural University, Palampur—176 062.


Adholeya Alok, Biotechnology and Management

of Bioresources Division, TERI, India Habitat

Centre, Lodhi Road, New Delhi—110 003.


Adhya Tapan Kumar, Division of Soil Science

and Microbiology, Central Rice Research Institute,

Cuttack—753 006.


Ahmad Altaf, Department of Botany, Faculty of

Science, Jamia Hamdard, New Delhi—110 062.

Ali Masood, Indian Institute of Pulses Research,

Kanpur—208 024.


Amrtha K, Institute for Ocean Management,

Anna University, Chennai—600 025.

Aulakh Milkha S, Department of Soils,

Punjab Agricultural University, Ludhiana—141 004.


Chanakya HN, Centre for Sustainable

Technologies, Indian Institute of Science,

Bangalore—560 012


Chhabra Abha, Space Applications Centre,

Indian Space Research Organization,

Ahmedabad—380 015.

Choudhary OP, Department of Soils,


Dadhwal VK, Indian Institute of Remote Sensing

(NRSA), Dehradun—248 001.


Ghosh A, Central Rice Research Institute,

Cuttack—753 006.

Gupta AB, Department of Environmental

Engineering, Malviya National Institute of

Technology, Jaipur—302 017.

Gupta RC, Department of Physiology,

SMS Medical College, Jaipur—302 004.

Gupta RK, Department of Soils,


Gupta Sunil, Environmental Medicine

Department, Krishna Ram Ayurvigyan Shodh

Sansthan, Jaipur—302 015.


xvi Contents

Jain Vanita, Division of Plant Physiology,

Indian Agricultural Research Institute,


Kumar Virendra, Advisor, IFFCO Foundation,

New Delhi.

Kundu DK, Water Technology Centre for Eastern

Region, Bhubaneswar—753 023.

Kusuma Grace J, Central Research Institute for

Dryland Agriculture, Santoshnagar,

Hyderabad—500 059.

Ladha JK, International Rice Research Institute,

India Office, NASC Complex, DP Shastri Marg,

Pusa, New Delhi—110 012.


Lochab Sunila, School of Biotechnology,

Guru Gobind Singh Indraprastha University,

Kashmiri Gate, Delhi—110 006.

Manchanda Joginder S, Department of Soils,

Punjab Agricultural University,

Ludhiana—141 004.

Panda D, Central Rice Research Institute,

Cuttack—753 006.


Pant Deepak, Centre of Bioresources and

Biotechnology, TERI School of Advanced Studies,

India Habitat Centre, Lodhi Road,


Parashar Vyom, School of Biotechnology,

Faculty of Science, Banaras Hindu University,

Varanasi—221 005.

Pathak H, International Rice Research Institute,

India Office, NASC Complex, DP Shastri Marg,

Pusa, New Delhi—110 012.

Pathak Ravi Ramesh, School of Biotechnology,



Patra DD, Central Institute of Medicinal and

Aromatic Plants, Lucknow—226 016.

Paul Chowdhury Soumitra, School of

Biotechnology, Faculty of Science,

Banaras Hindu University, Varanasi—221 005.

Prakasa Rao, E.V.S., Central Institute of

Medicinal and Aromatic Plants,

Resource Center, Allalasandra,

Bangalore—560 065

Prakash NB, University of Agricultural Sciences,

Bangalore—560 065.

Prasad Rajendra, Division of Agronomy,




Purvaja R, Institute for Ocean Management,


Puttanna K, Central Institute of Medicinal and

Aromatic Plants, Resource Center,

Allalasandra, Bangalore—560 065.

Raghuram N, School of Biotechnology,




Ramakrishna YS, Central Research Institute for



Ramesh R, Institute for Ocean Management,



Rao DLN, All India Network Project on

Biofertilizers, Indian Institute of Soil Science,

Bhopal—462 038.


Sachdev MS, Nuclear Research Laboratory,




Sachdev Pamila, Nuclear Research Laboratory,



Contents xvii

Sharatchandra HC, Centre for Research on

Environment, Development Innovations,

Technology and Trade, Bangalore—560 024.

Sharma AR, Division of Agronomy,



Sharma KL, Central Research Institute for




Singh Bijay, Department of Soils,



Singh JP, Department of Soils, CCS Haryana

Agricultural University, Hisar—135 021.

Singh Ramendra, Tata Chemicals Ltd.,

Somdatt Tower, 3rd Floor, Sector 18, NOIDA.


Singh Yadvinder, Department of Soils,

Punjab Agricultural University,

Ludhiana—141 004.


Srinivas K, Central Research Institute for



Tripathi Anil Kumar, School of Biotechnology,

Faculty of Science, Banaras Hindu University,

Varanasi—221 005.


Vel Murugan A, Indian Institute of Remote

Sensing (NRSA), Dehradun—248 001.

Venkatesh MS, Indian Institute of Pulses

Research, Kanpur—208 024.

Venkateswarlu B, Central Research Institute for




Vittal KPR, Central Research Institute for



Vyas BN, Research & Technical Development

Division, Godrej Agrovet Ltd., Mumbai.

Towards an Integrative Understanding

of Reactive Nitrogen

Contents

r INTRODUCTION

r NITROGEN PARADOX

r AGRICULTURAL NITROGEN USE

r NITROGEN USE EFFICIENCY IN AGRICULTURE

r OTHER ANTHROPOGENIC SOURCES OF REACTIVE NITROGEN

r ENVIRONMENTAL CONCERNS

r INTEGRATIVE APPROACH

r RESEARCH AND POLICY

1

N. Raghuram1, M.S. Sachdev2 and Y.P. Abrol3

1School of Biotechnology, Guru Gobind Singh Indraprastha University, Kashmiri Gate, Delhi—110 006.2Nuclear Research Laboratory, IARI, New Delhi—110 012.

3Society for Conservation of Nature 40 SFS, Hauz Khas, New Delhi—110 016.

Summary: Nitrogen is an essential input to meet our ever growing needs for food, feed and

fiber, but it can be used only in its reactive forms, which include inorganic forms such as NH3,

NH4

+, NOx, HNO

3, N

2O, NO

3–, and organic forms like urea, amines, proteins and nucleic acids,

that constitute the global N cycle. While their natural formation is too little to meet our needs,

their natural removal is too little for our comfort. Anthropogenic perturbations of the natural N

Agricultural Nitrogen Use & Its Environmental Implications

Editors: Y.P. Abrol, N. Raghuram, M.S. Sachdev

© 2007 I.K. International Publishing House Pvt. Ltd., New Delhi, pp 1-6

17-09-07

2 Agricultural Nitrogen Use & Its Environmental Implications

17-09-07

1. INTRODUCTION

Nitrogen (N) has a great impact on our food security, economy, development and environment. It is

necessary for all forms of life. In many ecosystems on land and sea, the supply of nitrogen controls

the nature and diversity of plant life, the population dynamics of both grazing animals and their

predators, and vital ecological processes such as plant productivity and the cycling of carbon and

soil minerals. This is true not only in wild or unmanaged systems, but also in most croplands and

forestry plantations as well.

2. NITROGEN PARADOX

We live in a world surrounded by gaseous nitrogen (N2), but more than 99% of this nitrogen is not

available to more than 99% of the living organisms, due to its relatively unreactive nature. Therefore,

barring a few N2-fixing microorganisms and legume crops that harbour them as symbionts, the

entire living world depends on reactive forms of N compounds. While plants are capable of utilizing

inorganic N compounds such as nitrate and ammonium ions, animals acquire them through the food

chain in readily usable organic forms (amino acids, nucleotides etc.). The natural processes of

producing reactive N compounds from atmospheric N2 gas by lightning or N

2-fixing microorganisms

cannot meet the agricultural demands for food, feed and fiber production for the continuously

increasing human population. Artificial or anthropogenic production by any means, whether chemical

fertilizers, biofertilizers, or organic N manures must ensure their adequate utilization, failing which

reactive N compounds tend to accumulate in the environment, as the natural processes of their

denitrification (back to inert N2) cannot cope with the scale of their accumulation. In addition to the

N compounds produced deliberately for use as fertilizers, reactive N species are also formed as by-

products of anthropogenic domestic sewage, dairy effluents, as well as fossil fuel-consuming industries

and vehicles. In the last 150 years, the annual inputs of reactive nitrogen primarily from anthropogenic

sources to the earth’s soil and water bodies have nearly doubled. In some places, excessive pollution

of the ground, water, and air with reactive N compounds has already begun to adversely affect the

public health and ecology. While some of these concerns may be regional or national in nature, the

ozone depleting and greenhouse effects of NOx gases are an issue of global concern. This is sum

and substance of the nitrogen paradox: We can’t use what exists naturally in abundance (N2). What

we produce in abundance either deliberately (N fertilizers) or as by-products (of other industries) is

cycle over the last several decades have led to the increasing accumulation of inorganic forms

of reactive N in the soil, water and air, intentionally through agriculture and unintentionally through

fossil fuel consumption and other activities, adversely affecting human health, biodiversity,

environment and climate change. Fertilizers, whether chemical, biological or organic, constitute a

major source of reactive N in areas of input-intensive agriculture, primarily due to low N-use

efficiency of most crops. One of the major challenges facing us is to ensure adequate availability

and rational use of appropriate fertilizers for agriculture, while preventing the unwanted

accumulation of reactive N from agricultural and industrial sources. This article provides an

overview of the emerging issues related to reactive N in the Indian context, and underscores the

need for an integrated approach to research and policy in order to tackle them in a timely and

effective manner.

Towards an Integrated Understanding of Reactive Nitrogen 3

17-09-07

not fully usable or available for agriculture, and we can’t get rid of the unused excess to avoid

adverse consequences.

3. AGRICULTURAL NITROGEN USE

Nitrogen fertilizers give large economic gains in modern farming systems, and therefore, their

application has been steadily increased to meet the increasing food demand. The dramatic increase

in food production during the era of green revolution was accomplished mainly by using improved

seed varieties and hybrids with better responsiveness to water and fertilizers, particularly nitrogenous

fertilizers. Nitrogen fertilizers constitute nearly 70% of the total fertilizer material used for this

purpose. It is currently estimated that as much as 40% of the world’s food production has become

possible because of the application of fertilizers produced using the Haber-Bosch process of converting

N2 and H

2 to NH

3. In India, the increase in fertilizer N use in the last 3-4 decades has resulted in

unprecedented increase in agricultural production in the northwestern India leading to food security

of the country. With 6 million tonnes N-fertilizer in 1989-90 to 10.4 million tonnes in 1998-99,

every million tonnes N-fertilizer used resulted in 10 million tonnes of cereal production. The per

hectare use of nutrients from fertilizers increased from less than a kilogram in the 1950’s to more

than 100 kg per hectare of gross cropped area by 2000. Accordingly, the all India annual consumption

of fertilizers increased from 70,000 tonnes in 1950-51 to nearly 18 million tonnes at present. India

is currently the third largest producer and consumer of fertilizers (after China and USA), and fertilizer

usage is bound to increase with further intensification of agriculture. In the process, agricultural N

use has become the primary source of injecting excessive amounts of reactive N into different

ecosystems.

However, the expansion of fertilizer use has not been uniform. While chronic N-deficiency

continues to be a problem in majority of the Indian soils, the fertilizer N use may be as high as

300 kg ha–1 yr–1 in the intensively cropped regions of northwestern India. This has led to a peculiar

situation in which demands for the expansion of fertilizer N-use in some areas coexist with the

concerns over the environmental hazards of excessive and inefficient N fertilizers use in other areas.

While the interest in organic manures and biofertilizers is increasing (and rightly so), these can at

best meet only a fraction of the total demand for fertilizers, at least in the next few decades. In any

case, the environmental consequences of the accumulation of reactive N are the same, regardless of

its chemical or biological origin.

4. NITROGEN USE EFFICIENCY IN AGRICULTURE

Worldwide, NUE for cereal production (wheat, rice, maize, barley, sorghum, millet, oat and rye) is

as low as 33%. The unaccounted 67% represents an annual waste of upto Rs. 72,000 crores. The

manufacture of N fertilizers involves huge investments, import dependence, and foreign exchange

and also consumes large quantities of non-renewable energy resources such as naptha, natural gas,

coal etc. Waste of N fertilizers due to their poor utilization by plants also adds to the pressure on

these finite resources. Low NUE for crops also implies higher costs to producers and consumers

and therefore reduced competitiveness. Loss of N from soil plant system results from gaseous plant

emission, nitrification, denitrification, surface runoff, volatilization and leaching and beyond rooting

zones of crops. Many 15N recovery experiments conducted in the country on different crops have


17-09-07

reported unaccounted losses of fertilizer N from 20 to 50% depending on the local conditions.

Therefore, the losses/ leakages of the reactive N from the agricultural systems are a cause of serious

concern for both economic and environmental reasons.

The problems of N-use efficiency are often compounded in Indian agriculture due to the neglect

or insufficiency of other nutrients, water, and other critical inputs including better crop varieties and

protection from biotic/abiotic stresses. Harvesting high yields with N-fertilizer (especially urea) alone

as the major input is at best a short-lived phenomenon. It has been clearly shown that “N-driven

systems” are not sustainable, as N becomes a “shovel” to mine the soil of other nutrients, with the

result that soils initially well supplied in other nutrients become deficient in them and productivity

declines. Scientists have been working at different levels to improve N-use efficiency: improving

fertilizer formulations for more balanced plant nutrition and/or prolonged retention of N in the plant

rhizosphere, better N management practices such as localized placement, foliar sprays, repeated split

doses, integrated nutrient and water management, as well as selection/breeding cultivars for better

N-use efficiency, either by conventional or marker-assisted breeding, molecular breeding, or transgenic

crops for better N response. The current state of development in each of these aspects has been

reviewed in separate chapters of this book.

5. OTHER ANTHROPOGENIC SOURCES OF REACTIVE NITROGEN

Animal husbandry effluents also contribute significantly to the loading of local environments with

reactive N compounds. Depending on the local conditions, they may spread to both surface waters

and ground waters, as well as contribute to gaseous emissions due to volatilization. Other industrial

effluents and domestic sewage also contribute widely to the anthropogenic N-loading to varying

degrees, while natural geodeposits rich in nitrogenous compounds contribute to some local concerns.

The contribution of gaseous emissions of reactive N compounds from fossil fuel consuming industries

and automobile exhausts is becoming an increasingly significant factor not only in the developed

countries but also in the rapidly developing countries such as China and India. The burning of fossil

fuels such as coal and oil releases previously fixed nitrogen from long-term storage in geological

formations back to the atmosphere in the form of nitrogen-based trace gases such as nitric oxide.

High-temperature combustion also fixes a small amount of atmospheric nitrogen directly. It is also

estimated that by 2020, India alone will be contributing NOx to the tune of 7.1 million tons annually

from road and rail transport sectors.

6. ENVIRONMENTAL CONCERNS

Since the beginning of the last century, mankind has injected increasing amounts of reactive nitrogen

into the environment, intentionally as fertilizer and unintentionally as a by-product of combusting

fossil fuels. As a result, the global nitrogen cycle is being altered, perhaps more than any other basic

element cycle, with grave impacts on biodiversity, global warming, water quality and human health

in several parts of the world. Accumulation of reactive N adversely affects the soil, water, as well as

air quality. On the surface, they include, soil acidification, widespread N pollution of groundwater

and eutrophication of surface waters (including potable water), posing a public health problem and

Towards an Integrated Understanding of Reactive Nitrogen 5

17-09-07

the ecosystem imbalance. The transport of surface reactive N from unused fertilizers, animal wastes

and other domestic and industrial sources into streams and rivers and eventually into estuaries and

coastal waters is becoming a matter of great concern, as reports are already pouring in regarding O2

deficiency in Indian coastal waters due to enhanced nitrogen loading from the land.

Human activities are also responsible for affecting air quality due to the accumulation of nitrogen-

containing trace gases, including 40% of the nitrous oxide, 80% or more of nitric oxide, and 70%

of ammonia releases on a global basis. According to an estimate, out of total emission of NOx in

Asia, China and India accounted for 42% and 17% of the emissions during the year 2000, respectively.

In addition to the health impacts of N-loaded air, the ozone depleting and greenhouse effects of

NOx gases from various farm and non-farm sources may pose new concerns for N-C balance,

especially for environment and sustainable agriculture. Moreover, while the global C cycle is being

perturbed by less than 10% due to anthropogenic activities, the global reactive N cycle is being

perturbed by over 90%. The accumulation of NOx gases has global consequences that cannot be

constrained by political boundaries or explained away by local policies.

7. INTEGRATIVE APPROACH

The global nitrogen cycle is now attracting increased attention from scientists, environmentalists,

governments, and industry. Industrial emissions of nitric oxide to the atmosphere must be reduced as

soon as possible. The problem of excess nitrogen can be addressed by more judicious and efficient

applications of nitrogen fertilizers in agriculture, and by the better management of wetland ecosystems

that return nitrogen to the atmosphere in its nearly inert or unreactive form—N2. In fact, it is the

ultimate goal of the scientific community to provide policy-makers with reliable estimates of reactive

nitrogen transfers to different ecosystems, and to describe balanced, cost-effective, and feasible

strategies and policies to reduce the amount of reactive nitrogen where it is not wanted.

In order to prepare ourselves for this challenge, we need a precise understanding of the scale of

nitrogen use/misuse/release through various agricultural, industrial, vehicular and other activities

and their contribution to the pollution of water and air, with special reference to various point and

non-point sources and the biogeochemical N cycle. While well-coordinated nationwide surveys on

N in our environment are lacking in India, indications from a few sample studies point to the

alarmingly high levels of nitrates in some areas of the country, especially in ground/surface waters.

The rise of NOx levels in the polluted air of our cities often makes eye-catching graphics in the

media. We need to clearly integrate the information from various studies, account for their

methodological differences, and identify the underlying issues/sources of concern, options for

mitigation, and areas that need further study.

One of the most important realizations that emerged from an integrative view of the various

aspects of reactive N in the broader developmental context is that the problems of reactive N in

agriculture, industry and environment are multidimensional and interconnected. The sheer diversity

of research areas/expertise/approaches it encompasses, and the various levels at which the problems

need to be identified/tackled calls for an integrated network approach to harness our intellectual,

financial, and infrastructural resources effectively.


17-09-07

8. RESEARCH AND POLICY

Considering that N is an essential part of our developmental paradigm, the options for reduction of

the accumulation of reactive N in our environment will have to be addressed at many different

levels, such as establishing/updating national N information systems; improvements in fertilizer

formulations; promotion of biofertilizers while improving the strains for biological N fixation,

enhancement of the N use efficiency of our crops and farming systems/practices; reduced dependence

on non-renewable energy sources; improvements in fossil fuel quality, fuel-use efficiency and reduction

of fossil fuel use/abuse; reduction in NOx emissions from farming, industrial and vehicular sources,

minimizing anthropogenic (including agri-industrial) reactive N load in naturally overloaded areas

(e.g., geodeposits) and fragile ecosystems, etc. Many chapters in this book are devoted to reviewing

the current level of understanding on various aspects of the nitrogen cycle, with special reference to

reactive N in the Indian context in order to highlight the importance of this field, as well as identify

the gaps in our knowledge for informed decisions on further research and policy. For example,

while many groups are working on biofertilizers, there is a very little understanding of the biology

of the nitrogen cycle in the Indian environment. Similarly, emerging research trends abroad to find

an environmentally benign alternative to the Haber-Bosch process by developing suitable catalysts

from transition metals has not yet been explored in India. In some other areas such as leaf colour

sensors, the prohibitive cost of imported equipment makes them unaffordable even for research labs,

let alone for farmers. Indigenous development of simple and cost-effective optical sensors can go a

long way to inculcate the habit of rational and demand-driven use of N fertilizers. Only an integrative

and interdisciplinary understanding of our strengths and weaknesses in tackling the tricky problem

of reactive N of our environment would enable us to think of such “out of the box” approaches for

research and policy.

REFERENCES

Bothe H, Ferguson S and Newton WE (Eds.) (2006). Biology of the Nitrogen Cycle, Elsevier.

Goyal SS, Tischner R, Basra AS (Eds.) (2005) Enhancing the efficiency of nitrogen utilization in plants.

Food Products Press, Binghamton, USA.

Mosier AR, Syers JK, Freney JR (Eds.) (2004) Agriculture and the nitrogen cycle: Assessing the impacts

of fertilizer use on food production and the environment. SCOPE Series 65, Island Press, Washington,

USA.

NAAS (2005) Policy options for Efficient Nitrogen Use. Policy Paper no. 33, National Academy of Agricultural

Sciences, New Delhi.

Singh RP and Jaiwal PK (Eds.) (2006) Biotechnological approaches to improve nitrogen use efficiency in

plants, Studium Press LLC, Houston, Texas, USA.

Agricultural Nitrogen Use And ItsEnvironmental Implications

Publisher : IK International ISBN : 9788189866334 Author : Y.P. Abrol, N.Raghuram & M.S. Sachdev

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