Understanding Climate Change Impacts on Crop Productivity and Water Balance

By S. K. Jalota, B. B. Vashisht, Sandeep Sharma and Samanpreet Kaur

Understanding Climate Change Impacts on Crop Productivity and Water examines the greenhouse gas emissions and their warming effect, climate change projections, crop productivity and water. The book explores the most important greenhouse gases that influence the climate system, technical terms associated with climate projections, and the different mechanisms impacting crop productivity and water balance. Adaptive and mitigative strategies are proposed to cope with negative effects of climate change in particular domains. This book will help researchers interested in climate change impacts on the atmosphere, soil and plants.

• Uncovers links between climate change and its impact on crop and water outputs
• Integrates information on greenhouse gas cycles and mathematical equations into climate/crop models for analysis and seasonal prediction systems
• Provides strategies for efficient resource management and sustainable crop production in future
• Helps researchers interested in climate change impacts on the atmosphere, soil and plants

• Language: English
• Publisher: Academic Press
• Release date: Feb 19, 2018
• ISBN: 9780128097212

S. K. Jalota

Dr. Jalota specializes in soil physics, water management and climate change impact on crop and water productivity. Dr. Jalota has authored three books and 68 research papers in this area. He is a Fellow National Academy of Agricultural Sciences.

Book preview

Preface

At present, climate change is a reality. In many parts of the world, increased temperature has already reduced the crop productivity; increased CO2 has increased water-use efficiency by enhancing photosynthesis and reducing transpiration in plants; changed precipitation has influenced the status and quality of groundwater by altering snow melt, drought and floods, rise in sea level, and intrusion of salt water in the coastal areas from the ocean. More or less, all the existing climate change scenarios indicate higher magnitude of climate change in the future than the present, which may further exacerbate the adverse effect on crop productivity, available water resources, and food security for the burgeoning population. It warrants proper understanding of the fundamentals of climate variability and change; their effects on physical, chemical, and biological processes in soil-plant-atmosphere continuum; crop productivity; and water balance of root zone and groundwater. Although abundant advancement on these aspects has been made, yet, the information is scattered hither and thither separately and needs synthesis to (i) make that accessible at one source and (ii) understand the interactions of changed climate variables with different processes in soil, plant, and atmosphere in a better way. Such synthesis can help the climate change personnel to comprehend the role of atmosphere, soil, and plants in greenhouse gas (GHG) emission and design adaptation technologies and mitigation strategies to combat climate change impact and secure food and water resources for the upcoming. In view of that, a book entitled Understanding Climate Change Impacts on Crop Productivity and Water Balance comprising of five chapters has been written.

Chapter 1 highlights the sources, processes, and factors controlling formation and escape of main greenhouse gases (GHGs) such as nitrous oxide, carbon dioxide, and methane and methods of their measurements. The role of atmospheric, plant, and soil parameters and management interventions in GHG emission and its feedback on climate change are also elucidated besides the potential global warming, radiative forcing, and lifetime of GHGs in the atmosphere. Chapter 2 illustrates global climate models, their downscaling (statistical and dynamic), different emission scenarios from Special Report on Emission Scenarios (SRES) to Representative Concentration Pathways (RCPs) and uncertainties for better understanding of climate change projections, ways to minimize bias in the projected climate data by bias correction methods, and uncertainties by performing ensemble simulations to have a more robust estimate of the climate change. Chapter 3 covers the fundamentals of direct and interactive effects of climate variables in the changing climate scenario on soil environment (carbon pools, microbial population and diversity, nutrient availability, and soil water) and processes in plant (photosynthesis, respiration, transpiration, crop duration, and phenology) to comprehend their impact on yield and quality of agricultural crops, field water balance components, and water-use efficiency. Climate change effect as modified by photosynthetic pathway (C3 and C4) and N-fixing capability (legumes and nonlegumes) of the crops, water regime, and nitrogen level in the soil is also discussed. Chapter 4 comprises the impact of climate change, land use and land cover, vegetation and geology of the aquifer on recharge and discharge, fluxes across boundaries, and consequently change in groundwater status. The emission of gases due to energy expended for pumping the groundwater; groundwater modeling by coupling climate, soil-water-plant, and groundwater models through geographic information system (GIS); and management interventions to protect the groundwater resources from the impact of climate change are also discussed. Chapter 5 covers the basics of adaptation technologies to combat the climate change impact on crop production and mitigation strategies to minimize GHG (nitrous oxide, carbon dioxide, and methane) emission in agriculture.

The book written systematically in lucid and friendly way will be of great use to both under- and postgraduate students and researchers in various universities and other institutions in disciplines of climate change, agrometeorology, soil science, soil and water engineering, and environmental science.

S.K. Jalota; B.B. Vashisht; Sandeep Sharma; Samanpreet Kaur

Chapter 1

Emission of Greenhouse Gases and Their Warming Effect

Abstract

This chapter covers the main sources, processes, and factors controlling formation and emission of greenhouse gases (GHGs) from agricultural system, methods of their measurement in the field (static and closed chambers and micrometeorological methods), and estimation (from empirical relations and mechanistic models). It provides the details of the processes like mineralization and mobilization, nitrification, denitrification, volatilization, leaching, and runoff for nitrous oxide emission; biomass burning, tillage and soil disturbance, deforestation, draining of wetlands, uncontrolled grazing, and manufacturing fertilizers and pesticide for carbon dioxide emission; and methanogenesis of methane gas emission and its transport by diffusion, ebullition, and plant mediation along with their cycles in soil-plant-atmosphere continuum. The role of atmospheric, plant, and soil parameters and management interventions and feedback of climate change on GHG emission are also elucidated besides the potential global warming, radiative forcing, and lifetime of GHGs in the atmosphere.

Keywords

Nitrogen cycle; Carbon cycle; Methane formation; Emission and measurement of greenhouse gases; Impact of greenhouse gases emission on climate change and vice versa; Warming potential

Contents

1.1Introduction

1.2Nitrogen Cycle

1.2.1Biochemical Processes

1.2.2Physical Processes

1.2.3Nitrous Oxide Emission

1.2.4Effect of Climate Change on Nitrous Oxide Emission

1.3Carbon Cycle

1.3.1Soil Organic Carbon and Its Pools

1.3.2Carbon Dioxide Emission

1.3.3Effect of Climate Change on Carbon Dioxide Emission

1.4.Methane Formation and Emission

1.4.1Factors Affecting Methane Emission

1.5.Simultaneous Emission of Carbon and Nitrogen Gases

1.6.Measurement and Estimation of Greenhouse Gases

1.6.1Field Measurements

1.6.2Estimation From Empirical Relationships and Models

1.7.Past and Future Trends of Greenhouse Gases Emission

1.8.Warming Effect of Greenhouse Gases

Exercises

Fill in the blanks

References

1.1 Introduction

The atmospheric concentration of greenhouse gases (GHGs) such as nitrous oxide (N2O), nitric oxide (NO), carbon dioxide (CO2), methane (CH4), ozone (O3), and halocarbons is increasing significantly over time as a result of biotic (plants, animals, fungi, bacteria, etc.) and anthropogenic (industry, mining, transportation, construction, habitations, deforestation, etc.) activities. These gases are going to increase further in the future with rise in population, crop production, and changing consumption patterns for food including increasing demand for ruminant meats and are likely to bring major changes in global environment. The main sources contributing to GHGs are combustion of fossil fuels and industrial processes. Agricultural sector and land use also contribute noticeably.

Emission of different GHGs and their contribution to the total emission at global level varies with the land use. At global level, N2O, CO2, and CH4 contribute 8%, 77%, and 15%, respectively, to the total emission. The agriculture sector contributes 32% of total global emissions, of which 6%, 18%, and 8% are by N2O, CO2, and CH4, respectively (De la Chesnaye, Delhotal, DeAngelo, Ottinger Schaefer, & Godwin, 2006). Among the different sources of N2O emission, 67% is natural, and 33% is anthropogenic (Davidson & David, 2014). Out of the total anthropogenic sources of N2O emission, 66% is from agricultural lands; 11% from biomass burning; 15% by industry, energy, and transport; and the rest from other sources (Fig. 1.1). Likewise, 65% of N2O emission from soil (Mosier, 1998) and 12%, 11%, and 7% from biomass burning, rice agriculture, and manure management, respectively, are documented (US-EPA, 2006). The agriculture sector accounts for about 10%–12% of global anthropogenic GHG emissions, of which 54% is as N2O (Smith et al., 2007).

Fig. 1.1 N 2 O emission inventory.

The emission of CO2 is mainly from burning of fossil fuel, industry, and transport, which constitutes about 70% of the total emissions (GOI, 2015). From agricultural lands, CO2 is emitted from burning of biomass and fossil fuels, tillage and soil disturbance, decomposition of organic matter (OM), deforestation, draining of wetlands, uncontrolled grazing, manufacturing of fertilizers and pesticides, etc. But it is < 1% of global anthropogenic CO2 emission.

The atmospheric CH4 instigates from natural (wetlands, oceans, forests, wildfires, termites, geologic sources, and gas hydrates) and anthropogenic (agriculture, energy production and transmission, and waste and landfills) sources. In 2004, the anthropogenic contributions to CH4 emission by agriculture, energy production and transmission, and waste and landfills were 43%, 36%, and 18%, respectively (IEA, 2006). The emission of CH4 in agricultural sector is from rice fields and enteric fermentation in ruminant, which constitute 30% and 18%, respectively, of the total anthropogenic emissions (Bodelier, Roslev, Henckel, & Frenzel, 2000). The CH4 emission of 6% from manure management, 10% from rice, and 40% from enteric fermentation has been reported as well (Kasterine & Vanzetti, 2010).

In the future, these capricious contributions are going to change at temporal and spatial scales depending upon the adaptation technologies and mitigation strategies followed under the changed land use at regional scale to manage the amount and type of increasing food demand for the increased population. There may be more emission of GHGs from (i) increased demand of livestock products and resulting intensification of agriculture, especially in unexploited areas; (ii) more use of N fertilizers owing to change in land use, that is, rapid conversion of forests to croplands and increasing cattle population; and (iii) non-CO2 manure management and N2O emission from soils. However, in Western Europe, emission of GHGs has reduced and projected to decrease in 2020 due to adoption of climate and other environmental policies.

From agriculture sector, the emissions of N2O, CO2, and CH4 together account for approximately one-fifth of the annual increase in radiative forcing of climate change (Cole et al., 1997). However, the contribution of an individual GHG depends upon its radiative forcing (i.e., change in the balance between incoming and outgoing radiation to the atmosphere), lifetime in the atmosphere, and consequential total emission, which decide the warming impact. The emitted GHGs in the atmosphere keep the earth warm by acting as a shield around the earth and maintaining temperature by absorbing the reflected infrared radiations (long wave), known as greenhouse effect. This effect is being continuously enhanced by increasing level of GHGs in the atmosphere and results in rise of temperature and acid deposition at global level. Among different GHGs, N2O not only causes warming but also is responsible for destructing the stratospheric ozone too.

For understanding the emission of GHGs and their warming effect, it is prerequisite to have knowledge of sources, processes, and factors influencing formation and emission of GHGs drawn in the nitrogen (N), carbon (C), and methane (CH4) cycles in soil-plant-atmosphere continuum (SPAC), lifetime of GHGs in the atmosphere, and radiative forcing. In this chapter, all the aspects that include the role of atmospheric, plant, and soil parameters and management interventions and feedback of climate change on GHGs are also discussed besides the potential global warming, radiative forcing, and lifetime of GHGs in the atmosphere. Measurements by different methods and estimation by empirical relations and mechanistic models are also described.

1.2 Nitrogen Cycle

N), which does not allow the N2 molecules easily enter into chemical reactions. Once the bond is broken, N2 becomes reactive in the form of organic (urea and amines) and inorganic N compounds of reduced (NH3 and NH4+) and oxidized (N2O, NO2, and HNO3) forms. In the soil, N exists in various forms having different oxidative states (Table 1.1).

Table 1.1

and volatilized NH3 are changed to N gas, N2O, and NO that escape into the atmosphere. The N removed from the field in crop is taken by animals, which generate manure (urine and feces). In this process, about 20% of N in the manure is volatilized as ammonia (NH3) gas. The manure (organic N) is returned in croplands to fertilize the next crop, thereby completing the N cycle. In the N cycle, there are a number of biochemical processes in soil, which transform one form of N to another through physical (nonbiological) processes and are cycled in SPAC. The biological transformations mediated by microorganisms are N mineralization and immobilization, N fixation, nitrification, and denitrification (Fig. 1.2).

Fig. 1.2 Nitrogen cycle.

1.2.1 Biochemical Processes

Nitrogen Mineralization and Immobilization

that can be again taken by plants and other microbes. Soil fauna also plays an important role in these processes by regulating populations of bacteria and fungi. The microorganisms themselves have a need for nutrients, especially N, to assemble proteins, nucleic acid, and other cellular components. If plant detritus is rich in N, microbial needs are met easily, and N releases or mineralization proceeds through reactions of aminization and ammonification. In aminization, freshly added organic materials like proteins and other complex compounds (amino acids, amines, amides, urea, chitin, and amino sugars) are attacked by a group of organisms, which break down the protein structure by enzymatic digestion process and release amino-N (Eq. NH2) are changed to NH3 by another group of heterotrophs (Eq. 1.1b):

  

(1.1a)

  

(1.1b)

) and even organic N (amino acids) are consumed by diverse groups of microorganisms to synthesize their protein and get multiplied. Thus, release of inorganic N during decomposition and demand on the soil N pool made by decomposer organisms for assimilating N into microbial tissues depend upon the C:N ratio of the substrate. Microbial N need is also affected by organism's growth efficiency. For example, fungi have less N needs and grow more efficiently on low N substrates than bacteria owing to wider C:N ratios. In general, the materials with a C:N ratio < 25:1 stimulate mineralization, while those with a C:N ratio > 25:1 stimulate immobilization. For instance, wheat straw (with C:N ratio 80–100:1) leads to net N immobilization, whereas legumes (with C:N ratio 12–15:1) lead to net mineralization. Actually, it is the C:N ratio that provides an opportunity to manage the synchrony of N supply to plants or to immobilize inorganic N from the soil pool so that the chances of N loss by denitrification and leaching are reduced. Thus, to manage N losses, it is imperative to manage C:N ratio to an optimum level depending upon the substrate quality and composition of the decomposer community.

Nitrogen Fixation

N) so that N can bond with C, hydrogen (H), and oxygen (O). In this process, a lot of energy is required. The energy to fix N occurs in three main places, that is, atmosphere, tiny microbial bacteria, and industry. In the atmosphere, N fixation occurs when the enormous energy of lightning breaks apart the N molecules allowing them to bond with oxygen in the air, forming nitrogen oxides (NO + NO2) and N2O forms. These forms of N dissolve easily into rain that is then carried down to the earth. In microbial N fixation, inert N present in atmosphere is fixed by only a very selective few bacteria and archaea (the most primitive living single-celled organisms, similar in size to bacteria, but different in molecular organization) through their specialized enzymes, nitrogenases. The nitrogenase enzyme has two keyholes, one for N and one for H. When the two elements fit into the keyholes, the nitrogenase enzymes break the bond between the two N molecules and connect them with H. Using tremendous amount of energy, namely, adenosine triphosphate (ATP), nitrogenase squeezes together one N molecule and three H molecules forming two weak NH3 molecules, given away in Eq. (1.2), representing the biological N fixation:

  

(1.2)

During microbial N fixation, archaea and bacteria use diverse energy sources, for example, sunlight by phototrophs, reduced inorganic elements and compounds by lithotrophs, and a glut of different organic substrates by heterotrophs. The phototrophs, lithotrophs, and heterotrophs correspond to obligate aerobes, facultative anaerobes, and obligate anaerobes, respectively. Biological N fixation with the nitrogenase enzyme complex (dinitrogenase and nitrogenase reductase) is carried out exclusively by different types of microorganisms, that is, those that (i) live symbiotically in nodules on the roots of leguminous plants; (ii) fix N in root nodules of some nonleguminous plants; (iii) live on or close to the soil surface and are photosynthetic; and (iv) live in association with plant roots, but nonsymbiotically. Approximately 100–140 Tg N year− 1 enters the biosphere by biological N fixation and during lightning discharges (Galloway, Schlesinger, Levy, Michaels, & Schnoor, 1995). In industrial N fixation, N2 gases are forced to react under huge pressure (500 atm) and temperature (1200°C) in the presence of finely divided Fe2O3 catalyst to break the triple covalent bond and form ammonia. The ammonia so produced is directly used as fertilizer in soil. Sometimes burning of fossil fuels also makes the NH3 so hot that the N2 molecules break apart and add N to the