Soil biochemical property response to drought effects under land use change in the context of climate change

VIETNAM NATIONAL UNIVERSITY, HANOIVIETNAM JAPAN UNIVERSITY BUI HANH MAI SOIL BIOCHEMICAL PROPERTY RESPONSE TO DROUGHT EFFECTS UNDER LAND-USE CHANGE IN THE CONTEXT OF CLIMATE CHANGE MASTE

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

BUI HANH MAI

SOIL BIOCHEMICAL PROPERTY RESPONSE TO DROUGHT EFFECTS UNDER LAND-USE CHANGE IN THE CONTEXT OF CLIMATE CHANGE

MASTER’S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

BUI HANH MAI

SOIL BIOCHEMICAL PROPERTY RESPONSE TO DROUGHT EFFECTS UNDER LAND-USE CHANGE IN THE CONTEXT OF CLIMATE CHANGE

MAJOR: CLIMATE CHANGE AND DEVELOPMENT

CODE: 8900201.02QTD

RESEARCH SUPERVISOR:

Dr HOANG THI THU DUYEN

Hanoi, 2020

I assure that this thesis is the result of my own research and has not beenpublished The use of results of other research and other documents mustcomply with regulations The citations and references to documents, books,research papers, and websites must be in the list of references of the thesis

Author of the thesis

Bui Hanh Mai

TABLE OF CONTENT

LIST OF TABLES i

LIST OF FIGURES ii

LIST OF ABBREVIATIONS iii

ACKNOWLEDGMENT iv

CHAPTER 1: INTRODUCTION 1

1.1 Background and motivation of the study 1

1.2 Research framework 5

1.3 Drought in the world 6

1.4 Drought in Vietnam 8

1.5 Impact of drought and land use change on soil properties 10

1.5.1 Impacts of drought on soil microbial activities and biochemical properties 10

1.5.2 Impacts of land use change on soil microbial activities and biochemical properties 11

1.6 Objects and scope of the research 13

1.7 Research questions and hypothesis 17

1.7.1 Research questions 17

1.7.2 Hypothesis 17

CHAPTER 2 METHODOLOGY 18

2.1 Data collection 18

2.1.1 Meteorological data 18

2.1.2 Remote sensing data 18

2.2 Methods of identifying and calculating drought indicators 20

2.3 Soil sampling and processing 21

2.4 Experiment setup 22

2.5 Determination of MBC and MBN 24

2.6 Identification of microbial basal respiration 24

2.7 Statistical analysis 25

CHAPTER 3: RESULTS AND DISCUSSION 26

3.1 Results 26

3.1.1 Land use and land cover maps 26

3.1.2 Drought progress characteristic 27

3.1.3 Basic soil properties 30

3.1.4 Microbial activities 31

3.2 Discussion 37

3.2.1 Land use and land cover maps 37

3.2.2 Drought progress characteristics 37

3.2.3 Soil properties and microbial activities 37

CHAPTER 4 CONCLUSIONS AND RECOMMENDATIONS 42

4.1 Conclusions 42

4.2 Recommendations for future research 43

REFERENCES 45

APPENDIX 53

LIST OF TABLES

Table 2.1 Land cover types description 189

Table 2.2 Classification used for K indices 21

Table 2.3 Methodologies to analyze soil physic-chemical properties 22

Table 3.1 The basic properties of forest soil and pineapple soil 30

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LIST OF FIGURES

Figure 1.1 Drought concept relevant to climate change Drought releases

ecological and socio-economic impacts 2

Figure 1.2 Research framework 6

Figure 1.3 Average monthly sunshine hours (2000 - 2019) in Quang Nam 14

Figure 1.4 Average monthly temperature (2000 - 2019) in Quang Nam 15

Figure 1.5 Average monthly precipitation (2000 - 2019) in Quang Nam 16

Figure 1.6 Average monthly evaporation (2000 - 2019) in Quang Nam 16

Figure 2.1 Soil sampling locations at Phiem Ai Village, Dai Nghia Commune, Dai Loc District, Quang Nam Province 231

Figure 2.2 Experiment setup for drought condition 23

Figure 2.3 Design experiment to analyze soil respiration 24

Figure 3.1 Land-use and land cover maps in Quang Nam (2003 – 2018) 26

Figure 3.2 The total area of each type of land use and land cover in Quang Nam 2003 – 2018 27

Figure 3.3 Drought frequency month during 2000 – 2019 28

Figure 3.4 K indices of mean drought months in dry season 28

Figure 3.5 K indices of drought months during dry season (2000 – 2019) 29

Figure 3.6 MBC of forest soil and pineapple soil 31

Figure 3.7 MBN of forest soil and pineapple soil 32

Figure 3.8 MBC:MBN ratio of two soil types and three treatments 33

Figure 3.9 The ratios of MBC to SOC and MBN to TN of both soils 33

Figure 3.10 The microbial basal respiration in the difference soil moistures of both soil 35

Figure 3.11 The amount of CO2 after three periods incubators at three treatments 35

Figure 3.12 The correlation between MBN and soil respiration of forest soil in incubated with 10% WHC 36

Soil organic carbonSoil organic matterTotal carbon

Total nitrogenWater holding capacity

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To complete this thesis, I would like to express my sincere thanks to thelecturers and staff of Program of Climate Change and Development, VietnamJapan University, Vietnam National University, Hanoi, and other lecturersand students of Soil Sciences Department of Vietnam National University ofwho guided and facilitated me to complete my thesis on time

I would like to express my deepest and most sincere thanks to my supervisor

-Dr Hoang Thi Thu Duyen, advisor - -Dr Kotera Akihiko, Prof Phan Van Tanand Dr Nguyen Van Quang - Lecturers of Climate Change and Developmentprogram, Vietnam Japan University, VNU for their dedication and valuablecomments on thesis

In addition, the research has also received support and help from leaders andstaff of Quang Nam Crop Production and Plant Protection Subdepartment andDepartment of Agriculture and Rural Development Dai Loc District so that Icould collect information related to the thesis

Last but not least, the author also appreciates financial support of VNUproject (code QG.20.63, No 1086/QĐ-ĐHQGHN), without this support theimplementation is impossible

Finally, I would like to dedicate this thesis to my parents and friends as agesture of my thanks for their constant support and belief in me

CHAPTER 1 INTRODUCTION

1.1 Background and motivation of the study

Climate change is a natural process but it is boosted by anthropogenicactivities (IPCC, 2012) and the rapid increases in CO2 concentrations over thelast few centuries, which leads to a series of unpredictable weather events.Drought/severe drought is one of the consequences of climate change, which

is projected to increase unprecedentedly in prone areas (IPCC, 2019) Theworld temperature is supposed to increase over 1.5 to 2oC in the period of

2081 to 2100 (Collins et al., 2013) Each increase of atmospheric temperatureresults in 7% increase of atmospheric moisture holding capacity (Sun et al.,1996) Therefore, precipitation becomes more condensed, and hence,prolonged dry season over a year In drought-sensitive areas, such as theMediterranean, north-eastern Asia, West Asia, many regions of SouthAmerica and the majority of Africa (IPCC, 2019), global warmingexacerbates drought severity by accelerating evaporation, enhancing shortage

of soil moisture (Figure 1.1)

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Figure 1.1 Drought concept relevant to climate change Drought releases

ecological and socio-economic impacts (Wilhite, 2000)

Excessive extraction of surface and underground water under drought contextfor agricultural production will proceed desertification in cultivated areas As

a consequence, land-use change occurs in response to the high demand forexpanded cropland due to population growth, and the reduction of soilmoisture and quality During 1990 – 2005, 13 million hectares forestdestroyed per year (FAO, 2006) to convert from forest land to cropland,which reduces soil C sequestration and a rapid biomass C loss, releasing up to

180 – 200 Pg (pentagrams) C emissions in the last two centuries (Ramesh et

Land-use change, as well as drought, have an impact on the biochemicalproperties of the soil Increasing frequency, intensity and timing of drought ispredicted to lead to reduce the functions of microorganism, which is essential

of ecosystem sustainability (McHugh et al., 2017) Moreover, the structure ofthe soil microorganisms is greatly influenced by land use, land cover, andagricultural activities Those factors impact on SOM and lead to regulatingthe microbial structure appropriately (Moon et al., 2016; Bissett et al., 2011).Thus, it could impact on soil microbial biomass and the usage C efficiency ofmicroorganism (Bauhus et al., 1998) Terrestrial plants are the main sources

of soil organic matter (SOM) which retains moisture in different soil horizons.However, during 20 years (1980 – 2000), more than 80% of newly cultivatedland came from the intact and disturbed forests (Gibbs et al., 2010) Landconversion from forest to cultivated land reduces SOM content, leading to adecline in soil moisture content and lowering resistance and resiliencecapacity of the terrestrial ecosystem to drought impacts (de Vries et al., 2012).This land-use change also triggers potential drought events as the soil is over-exploited for intensive agricultural production, which causes exhaustion insoil nutrients, bio-balance and hence soil WHC

In tropical dry land ecosystems, studies in land-use change under drought arestill restricted when compared with the total coverage of wet ecosystemsaround the world (Ramesh et al., 2019) Therefore, the study “Soilbiochemical property response to drought effects under the land-use change inthe context of climate change” is conducted in Quang Nam, Vietnam toelucidate the relationship between abiotic factor (soil moisture) and bioticfactor (microbial biomass and activity)

During the period 1999 – 2018, Vietnam ranks 6th among 10 countries mostaffected by the extreme weather events in the table of Long-term Climate

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Risk Indices (CRI) (Eckstein et al., 2019), especially the increase of droughtfrequency causes negative impacts on the production activities of localpeople Quang Nam, where is located in the South Central region with diverseterrain conditions and harsh climate, severely impacted by drought Due todrought in the Southern sub-regions and South Central are highly sensitive toENSO (Le et al., 2018) According to the People's Committee of Quang Namprovince (2010) and IMHEN (2009), the prolonged drought damaged,4,841/44,500 hectares of summer-autumn rice in plain districts; 660 hectares

of rice were lost due to saline intrusion In addition, there are over 3,000hectares of rice that cannot be sown due to aridity, along with 5,000 hectares

of crops lacking irrigation water and nearly 5,000 people suffer from watershortages in the midland and mountainous districts of Quang Nam From thebeginning of the Summer-Autumn season in 2019, the weather was abnormaland the hot and sunny situation happened continuously and lasted for manydays The storage capacity in many irrigation and hydropower reservoirs isonly about 20 – 60% of the designed capacity, lower than the average manyyears Many small reservoirs have dried up (EVN, 2019)

This study was conducted to provide a general overview of the biochemicaland microbiological activity of two different land-use types, namely forestand pineapple land in Quang Nam, under drought conditions The findingswill provide stakeholders in Quang Nam with scientific background foradaptation strategy to climate change while maintaining soil health.Moreover, in order to mitigate the effect of climate change, the identification

of management practices and appropriate land-use in each location is one ofthe necessary methods Thus, this study performs with three main objectives:

1 To define areas under drought impacts in Quang Nam in recent years

2 To demonstrate the effect of drought on microbial activities includingmicrobial biomass C and N (MBC and MBN) and microbial communitycomposition in different land-use.

3 To evaluate nutrient mineralization under drought impacts in different land-use

1.2 Research framework

Thesis is built around three main research objectives and follows aninterdisciplinary approach using remote sensing, field methods, laboratorymethods, and comprehensive analysis of collected data (Figure 1.2) The threemain factors (drought, land-use change, soil microorganism activities) areclosely intertwined The first objective uses MODIS data, field-survey anddrought indicess to estimate the change of land-use, especially forest land andcropland, as a basis for drought area, frequency, and severity droughtidentification The second and third objective involves laboratory methods toestimate microbial biomass and microbial respiration based on a commonly-applied approach used in global studies and their interaction with thechanging of climate in Quang Nam

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Biological properties MBN and MBC Soil respiration

Figure 1.2 Research framework

1.3 Drought in the world

As mention above, drought directly affects agriculture Droughts often causeloss of agricultural land, crop structure changes and crop yields decline Thatimpacts the lives of people and national food security Besides, drought alsoaffects forest resources Increased temperature and evaporation causeprolonged drought, which will affect the growth ability of forest plants andanimals Some regions in the world have occurred a trend to more longer and

severe droughts since the 1950s, especially in West Africa and southernEurope (IPCC, 2012).

Drought studies around the world through drought indices based on historicalrainfall, temperature, and humidity data show the number of drought spells,duration, severity and frequency drought in some places has increasedsignificantly Many studies show that more severe drought, due to anincreased temperature combined with a decreased precipitation will increaseevaporation (Loukas and Vasiliades, 2004) The drought frequency tends toincrease and become more severe at any season of the year in the globalwarming trend In the Mediterranean region, increased drought frequencyafter about 1970 (Hoerling et al., 2012) During period 1957 – 2016 in India,there has large frequency drought with over 10 events severe droughtoccurred in highly populated and agriculturally intense Indo-Gangetic Plain,North, South, and Eastern parts of India The most severe droughts in the last

60 years were in 1965, 1972, and 2002 with more than 35% area under severedrought for the 12-month time-scale (Aadhar and Mishra, 2018) Since thelate 1990s in China, extreme droughts have become more regular In the pastfive decades, the drought areas were reported to increase by around 3.72% perdecade (Yu et al., 2014) Zou et al (2005) also indicated that since the 1990sdrought in northern China has been on an upward trend, in particular, someareas occurred drought lasting 4 – 5 years from 1997 to 2003 In fact, in 1997,severe drought in northern China caused nearly 226 days of continuous zeroflow in the Yellow River (Cong et al., 2009) Thus, besides the increaseddrought frequency and severity, the duration of drought periods has alsosignificantly increased Drought events can last months to years in manycountries

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In addition to using observational meteorological data to study drought,drought estimates by simulation results of climate factors from dynamicmodels have also been strongly developed in many countries In warmerfuture climates, most atmospheric circulation models anticipate increasedsummer drought and winter wetness in most of the medium latitudes and highlatitudes in the north It is the summer drought that will lead to a greaterdrought disaster, especially in areas where rainfall decreases (IPCC, 2007).Kim and Byun (2009) estimated the effects of global warming on droughtconditions in Asia in the late 21st century under the A1B scenario The resultsindicate that rainfall rates decrease the highest in North Asia in all seasons, inWest Asia average rainfall plummets from winter to summer, leading tofuture droughts in these two areas have more frequency, stronger intensity,longer drought cycle than in the past, especially in summer The severity ofdrought in India is projected to increase under wetter and warmer futureclimate (Aadhar and Mishra, 2018) Due to there is an increase inprecipitation, and more than 2 degree rise in temperature leads to moreatmospheric water demand and an increase in drought severity by the end ofthe 21st century Under the RCP 8.5, almost all of India shows high-frequency

of severe drought events in the end period, more than three severe events perdecades The area affected by severe drought is predicted to increase by 150%with warming by the end of the 21st century

1.4 Drought in Vietnam

The trends of drought in Vietnam had changed recently According to Le et al.(2019), the historical trends of drought, during 1980 – 2014, changed betweensub-regions In northern sub-regions, drought trend to decrease of seasonal,except during summer months By contrast, in the central coastal, drought

the Central sub-regions often occurred drought more severe than in otherareas The periods of drought events were typically longer So, the frequency

of drought was also larger Moreover, the severity drought showed events,which have a very high drought intensity, in these sub-regions The variability

of drought in the South Central and Southern has been highly sensitive toENSO Besides the increasing temperature, decrease precipitation and soilmoisture deficit in the summer, climate seasonality, large-scale drivers, andtopography conditions also impacted on drought in Vietnam

In addition to studies on Vietnam's drought history, there have been studies ondrought prediction in Vietnam based on scenarios A1B and A2 According toNgo Thi Thanh Huong (2011), the results of drought estimates under the A1Bscenario for climatic regions in Vietnam showed that droughts are more likely

to occur in the future, especially in the period 2011 – 2030 in the Northwestclimatic region and the period 2031 – 2050 in the three climatic regions of theSouth Central, Central Highlands and Southern regions Future lighter droughtoccurs in the Northeast and North Central regions

The estimated results of drought over time through Ped indicator under A2scenario show that the drought trend in the period 2011-2030 decreased in theNorthwest, Northeast climate regions and almost no change in the NorthCentral climate region but increased significantly during the period 2031 –

2050 In the remaining climate regions, drought increased markedly in bothperiods, especially the Central Highlands and the South

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1.5 Impact of drought and land use change on soil properties

1.5.1 Impacts of drought on soil microbial activities and biochemical properties

IPCC (2019) emphasized that "Climate change, including increases infrequency and intensity of extremes, has adversely impacted food security andterrestrial ecosystems as well as contributed to desertification and landdegradation in many regions" In the fact, extremes of arid conditions reducethe growth of most plants and microbial decomposition Moreover, microbialfunctions are important for ecosystem sustainability McHugh et al (2017)stated that increasing drought prediction lead to decline in microbialfunctions When soil drier, less SOC in the soil is decomposed and respired toCO2, due to in soil pores have less water, thus resources in the soil cannot linktogether (Schimmel, 2018) In addition, these factors interact with thereduction loss of C through suppressed respiration (Heimann and Reichstein,2008) In grassland ecosystems, the soil micro-biome can be impacted long-lasting by drought, due to the dominance of drought-tolerant plant speciescause the changes in vegetation and root microorganisms also change (deVries et al., 2018)

Also, in the soil pores, the microbial distribution becomes more restrictedwhen soil becomes drier (Carson et al., 2010 and Dechesne et al., 2010).Besides, the dry situation kills many microbes However, many microbialspecies tolerate dryness due to they developed resistant strains or entered into

an inert stage The reason disruption of soil C and N cycling is the recovery ofmicrobial communities that could not occur immediately after drought (Sheik

et al., 2011) However, fungi potentially maintain C and N cycling whenwater in the soil become scarce (Treseder et al., 2018) because fungal hyphae

Conditions that favor microorganism growth will favor fast decompositionrates The product of complete decomposition are CO2, NH4+, NO3-, SO42-,

H2PO4-, H2O resistant residues, and multiple other necessary nutrientelements for plants in smaller quantities Chemical soil degradation is likelynutrient decreased because of the imbalance of nutrient extraction resultingfrom harvested products and fertilization Excessive N fertilization and export

in harvested biomass increase acidification in croplands because of thedepletion of cation like calcium, magnesium or potassium in the soil (Guo etal., 2010) In the context of climate change, the depletion of organic matterpool causes soil chemical degradation processes Tillage and the belowgroundplant biomass inputs reduction cause the increase of respiration rates, whichreduced organic matter in agricultural soils The warming directly impacts onthe decline of SOM pools in both under natural vegetation and cultivated land(Bond-Lamberty et al., 2018) Creating energy from harvesting residues alsocould lead to reducing organic matter in the forest (Achat et al., 2015) A

“hub” of degradation processes could be SOM, which also is an importantconnection with the climate system (Minasny et al., 2017) Zhao et al (2017)stated that interaction between temperature and precipitation influences notonly terrestrial ecosystem productivity but also the decomposition rate ofSOC That is the reason why those environmental factors are the mostaffecting soil CO2 efflux rates

1.5.2 Impacts of land use change on soil microbial activities and biochemical properties

Land-use change contributes to global warming because the land-use changeaffects CO2 emission to the atmosphere (Ramesh et al., 2019) Moreover, thesoil is one of the global C sinks Soil stores C higher than atmosphere andvegetation, about two times and three times, respectively (Zomer et al., 2002)

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The processes, namely the oxidation of superficial soil C stocks, enhancinggas emissions (COz and other gases) to the atmosphere, are markedlyimpacted by the changes from forest to agriculture and grassland (IPCC,1992) That conversion also causes soil organic C loss (Kasel and Bennett,2007; Guo and Gifford, 2002) According to IPCC (1992), land-use changeand deforestation emitted about 55±30 Gt CO2.

In the tropical land, the land conversion from forest land to other lands causedbig SOC losses in the soil, such as 25% SOC losses in cropland, 30% SOClosses in perennial crops and 12% SOC losses in grasslands (Don et al.,2011) The land-use change causes loss SOC not only in the surface soils butalso in the sub-surface soils Deforestation and change to agriculture causedrapidly SOC initial decreased, which lead to the active SOC pool loss or thelabile C pool loss (Motavalli et al., 2000) Besides, land clearing also makesthe loss of SOC The losses SOC could lead to soil erosion, increased rate ofSOM decomposition, and alteration of the components of plant residue (Fellerand Beare, 1997) Tillage, such as aerating the soil, disturbing soil aggregates,concealing surface residues, and revealing new surfaces for microbialpervaded, make the SOM decomposition rate increased (Indoria et al., 2017).According to Ramesh et al (2019), declining CO2 emission to the atmosphereand increasing SOC sequestration is the best way to mitigate global warming.The rapid decomposition activities of microorganisms intensify the rate ofCO2 emission to the atmosphere The accumulation rate of organic C in soildepends on many factors in specific places, including plant species, soilproperties, and climate Perennial vegetation or forests, which are convertedfrom vegetation on barren, abandoned agriculture, or degraded lands, couldimprove C storage capacity in the soil (Choudhury et al., 2014) In addition,

forest land converted to croplands may sequester less C than when converted

to grasslands

He also proved that improving agroecosystems sustainability and increasingSOC storage based on conservation management practices, namely integratednutrient management practices, manure application, residue incorporation, use

of cover crops, and no-tillage However, the organic manure application andresidues enhance CO2 emission to the atmosphere Thus, the utmost crucialfactor to mitigate the changing of climate is C sequestration in soil fromidentification appropriate management practices and land-use

1.6 Objects and scope of the research

- Study site: Quang Nam province

Quang Nam is located in the central region of Vietnam, is a region withrelatively complex topography, lower from the West to the East, formingthree ecological regions: high mountains, midlands, and coastal plains Theprovince is divided by the Vu Gia and Thu Bon river basins

Quang Nam is located in the typical tropical climate region, with only twoseasons: the dry season (from January to August) and the rainy season (fromSeptember to December) However, there still influence by the cold winter inthe North

At present, there are two meteorological stations in the province, which fullyobserve meteorological factors for a long time (starting from 1976), namelyTam Ky and Tra My stations Tam Ky station located in Hoa Thuan Ward,Tam Ky City The meteorology data was collected in Tam Ky station is used

to calculate the relevant meteorological factors for the eastern delta of theprovince Tra My station located in Tra My town, Bac Tra My district The

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meteorology data was collected in Tra My station is used to calculate therelevant meteorological factors for the western mountainous region of theprovince.

In general, the number of sunshine hours in Quang Nam was quite high(Figure 1.3) The mean sunshine hours (2000 – 2019) of Quang Nam provincewere 1850 hours in mountainous area and 2000 hours in coastal plain In May,the highest number of sunshine hours was from 227 to 242 hours Decemberwas the least sunshine hours in a year, from 55 – 68 hours

Coastal plain MountainousFigure 1.3 Average monthly sunshine hours (2000 – 2019) in Quang NamTemperature: The annual mean temperature in Quang Nam area was quitehigh, about 25.4oC in mountainous and 26.6oC in coastal plain The meantemperature of the months in winter has not exceeded the 20oC The coldestmonth was January with a mean temperature of 21.3oC (mountainous) and

22oC (coastal plain) The hottest month was June, with a mean temperature ofabout 29.5 – 31.5oC (Figure 1.4) The minimum temperature in Quang Namwas 12oC (mountainous) – 13.6oC (coastal plain) and the highest can be over40.1oC (mountainous) – 41oC (coastal plain)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Coastal plain MountainousFigure 1.4 Average monthly temperature (2000 – 2019) in Quang NamRainfall: Rain was not evenly distributed according to space, rainfall inmountainous areas was more than plain Mountainous was the center of heavyrainfall in Quang Nam, the total annual rainfall during 2000 – 2019 reaches

4311 mm, while the average annual rainfall measured at coastal plain station

is 2840 mm (Figure 1.5) The rainy months were from September to the end

of December, the peak was October to November with rainfall of about 899 –1058mm (mountainous), 601 – 693mm (coastal plain), and accounting for45.6 – 54.5% of the total mean rainfall of 19 years The lowest rainfall a yearwas from February to April, accounting for only about 5.7 – 7% of the totalmean rainfall of 19 years

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0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 1.5 Average monthly precipitation (2000 – 2019) in Quang Nam

Evaporation: The average evaporation in many years in Quang Nam was 568

– 825 mm in both monitoring stations In the dry season, due to the high air

temperature, low humidity, high winds, the evaporation in the dry months can

be twice compared with the rainy months It can be seen from Figure 1.6, the

amount of evaporation in April – August was the most, while the rainfall was

Figure 1.6 Average monthly evaporation (2000 – 2019) in Quang Nam

Humidity: The annual average humidity was 85.6% in the lowlands (coastal

fluctuation between the months of dry and rainy seasons, the month with thelowest humidity was June (78 – 84%), and the highest humidity wasDecember from 91 – 93%.

- Time performed the research: From January to end of May, 2020

- Objects of the research: Forest soil and pineapple soil have the same topographic characteristics and soil types

1.7 Research questions and hypothesis

1.7.1 Research questions

1 How has the drought situation been changing in Quang Nam in recentyears?

2 How does drought situation impact on microbial activities and

microbial community composition in different land use?

3 How is the nutrient mineralization in different land use under water limitation?

2.1.2 Remote sensing data

The MODIS image data used in this study is the MODIS Land Cover TypeProduct (MCD12Q1) From 2001 until now, MCD12Q1 provides the annualmap of global land cover at 500 meters spatial resolution with six differentland cover legends This study was used Classification schemes of TheInternational Geosphere-Biosphere Programme (IGBP) Type 1 land coverscheme identifies was chosen with 17 land cover classes (0 – 16), whichinclude 11 natural vegetation classes, 3 developed and mosaicked land classesand three non-vegetated land classes (Sulla-Menashe and Friedl, 2018).Information about all of the data layers, including Quality Control is shown inTable 2.1 The image MODIS is analyzed to create land use and land covermaps in Quang Nam province from classifications of spectro-temporalfeatures derived of data during 2003, 2008, 2013, 2018 by QGIS 3.4.6software

Table 2.1 Land cover types description (Sulla-Menashe and Friedl, 2018)

Evergreen

1 Dominated by evergreen conifer treesNeedleleaf Forests (canopy >2m) Tree cover >60%

Evergreen Broadleaf Dominated by evergreen broadleaf and

2 palmate trees (canopy >2m) Tree coverForests

>60%

Deciduous

3 Dominated by deciduous needleleaf (larch)Needleleaf Forests trees (canopy >2m) Tree cover >60%.Deciduous Broadleaf

4 Dominated by deciduous broadleaf treesForests (canopy >2m) Tree cover >60%

Dominated by neither deciduous norMixed Forests 5 evergreen (40-60% of each) tree type

(canopy >2m) Tree cover >60%

Closed Shrublands 6 Dominated by woody perennials (1-2m

height) >60% cover

Open Shrublands 7 Dominated by woody perennials (1-2m

height) 10-60% cover

Woody Savannas 8 Tree cover 30-60% (canopy >2m)

Savannas 9 Tree cover 10-30% (canopy >2m)

Grasslands 10 Dominated by herbaceous annuals (<2m)

Permanent Wetlands 11 Permanently inundated lands with 30-60%

water cover and >10% vegetated cover.Croplands 12 At least 60% of area is cultivated cropland

Urban and Built-up At least 30% impervious surface area

13 including building materials, asphalt, andLands

Cropland/Natural Mosaics of small-scale cultivation 40-60%

14 with natural tree, shrub, or herbaceousVegetation Mosaics

vegetation

Permanent Snow and 15 At least 60% of area is covered by snow

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Name Value Description

At least 60% of area is non-vegetatedBarren 16 barren (sand, rock, soil) areas with less than

10% vegetation

Water Bodies 17 At least 60% of area is covered by

permanent water bodies

Unclassified 255 Has not received a map label because of

missing inputs

2.2 Methods of identifying and calculating drought indicators.

The drought extension over time is determined by rainfall as follows(Vietnam Meteorological and Hydrological Administration, 2014):

- Drought occurs when the amount of rainfall per month is less (equal) than 30mm

- Drought frequency month caculated by:

P =Where: m is drought frequency observation month

n is frequency of rainfall observation month

- To describe the general situation of drought in the areas and their evolutionsover time, the drought indices (Nguyen Trong Hieu, 1998) of months and yearswas used:

Km =Where: Km: Drought indices month (year)

Pm: Evaporation amount according to Piche month (year)

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Rm: Monthly (annual) rainfall

Table 2.2 Classification used for K indices

2.3 Soil sampling and processing

Soil was sampled from topsoil (0 – 30cm) of pineapple and neighboring forest

in Dai Loc district Quang Nam province where drought happens annually

The sample collection time was the beginning of the dry season (3rd January

2020)

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Figure 2.1 Soil sampling locations at Phiem Ai Village, Dai Nghia

Commune, Dai Loc District, Quang Nam ProvinceThe samples were preserved in laboratory under 5oC and sieved through 2mmmesh to remove plant litter, roots and gravels larger than 2mm A subsamplewas detached to measure basic soil properties Table 2.3

Table 2.3 Methodologies to analyze soil physic-chemical properties

WHC (%) = (Water saturated soil weight dry weight)

300g of sieved soil (oven-dry equivalent) of each land use type was separatelyweighed in a plastic box and the soil moisture was adjusted to 60% WHCusing sterilized water The amount of added sterilized water to attain 60% or10% WHC:

Soil dry constant (k) = ( )

The boxes were divided into 3 sets (Figure 2.2): set 1 containing soil at 60%WHC at the initial experiment stage, set 2 containing soil at 10% WHC andset 3 was control soil (60% WHC) at the time of drought All the soilcontainers are kept at 28oC for 1 week to stabilize microbial growthconditions During the pre-incubation, soil weight was gravimetricallychecked MBC, MBN, and basal respiration were measured for each set ofsoil container including:

 Set 1 – harvested right after pre-incubation (60% WHC)

 Set 2 – harvested as soil moisture reduced to 10% WHC

 Set 3 – harvested as a control for set 2 (60% WHC)

Figure 2.2 Experiment setup for drought conditionEach treatment setup with 4 replicates (Figure 2.3)

a) Forest soil

ControlDry

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b) Pineapple soil

ControlDry

Figure 2.3 Design experiment to analyze soil respiration

2.5 Determination of MBC and MBN

Microbial biomass was defined using the chloroform fumigation extractionaccording to Brookes and Joergensen (2006) Accordingly, for each sample,5g soil fumigated with CHCl3 for 24 hours (FT) and the dissolved organic Cextracted with 20ml K2SO4 0.5M Another 5g soil subsample extractedimmediately with 20ml K2SO4 0.5M, non-fumigation (NFT) MBC and MBNwere calculated by differences between fumigated and non-fumigated sampleswith a conversion factor of 0.45 for MBC (Beck et al., 1997) and 0.54 forMBN (Brookes et al., 1985)

2.6 Identification of microbial basal respiration

50g soil subsample was incubated in Mason Jars for 6 hours, 18 hours and 24hours at a fixed temperature and atmosphere pressure (28oC) A small vialcontaining 10ml NaOH 1N was placed in the jar to trap CO2 The vial wasmeasured every 6 hours, 18 hours and 24 hours The trapped CO2 definedusing titration with HCl 0.1N against the phenolphthalein endpoint (Zibilske,1994) CO2 trapped was the net emissions of CO2 for soil, which wascalculated as follows:

(g.mol-1)/2/dry weight of bulk sample (kg)

The microbial basal respiration was calculated by dividing sum of trapped

CO2 by 48 hours (mg.kg−1) (Qiao et al., 2013)

2.7 Statistical analysis

Data were analyzed using SPSS 20.0 software (SPSS Inc., Chicago, IL, USA).Independent sample t-test was conducted to test the differences between thetwo land-use types in the soil properties Effects of soil WHC treatments onsoil respiration were analyzed in the forest soil and pineapple soil,respectively, considering the dependent differences in the initial soil anddrought soil Effects of soil WHC treatments on average values of soilrespiration during constant moisture period were tested using one-wayanalysis of variance (ANOVA) In order to understand the effect of soilbiochemical properties (explanatory variables) on soil microbial biomass(response variables), we used Pearson’s correlation analysis Significance forall statistical analyses was accepted at the level of p<0.05

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CHAPTER 3 RESULTS AND DISCUSSION

3.1 Results

3.1.1 Land use and land cover maps

The interpretation of the MODIS satellite image (MCD12Q1) from 2003 to

2018 (Figure 3.1) shows that the forest area is largest, account for60.27±1.77% total area The agriculture area just is 5.89±0.23% andconcentrated on the coastal plain

Figure 3.1 Land use and land cover maps in Quang Nam (2003 – 2018)The change of land-use area occurred at most different land-use types (Figure3.2) Land-use types tended to increase from 2003 to 2018, except for non-

about 0.83% of the total agriculture area The forest area gradually decreased

from 2003 to 2013, about 8.34% of the total forest area However, until 2018,

the forest area increased by up to 5.86% compared with 2013 By contrast,

non-vegetated land tended to be the complete opposite of forest land

Non-vegetated areas increased by about 7.93% from 2003 to 2013 and decreased

Croplands Urban and built-up

Figure 3.2 The total area of each land-use type and land cover in Quang Nam

2003 – 2018

3.1.2 Drought progress characteristic

The calculated drought frequency by observed rainfall at two monitoring

stations showed a similar trend during 2000 – 2019 in two areas, namely

mountainous and coastal plain The drought frequency month trended to

increase (Figure 3.3) In particular, the drought frequency month in 2010 and

2013 of the coastal plain was highest In general, the drought frequency of

mountainous was lower than the drought frequency of coastal plain However,

the drought frequency was similar in both areas in 2005 and 2019

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Linear (Coastal plain) Linear (Mountainous)Figure 3.3 Drought frequency month during 2000 – 2019

The K indices of dry season months is used to assess the drought severity

level The K indices calculated results showed that the drought severity level

has decreased slightly during 2003 - 2019 Figure 3.4 revealed that the

severity drought concentrated in the coastal plain The drought years appeared

11 times (out of 19 years of observation) and the highest K indices in 2003

showed that this was the most severe drought

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