1. F A C U L T Y O F S C I E N C E
U N IV E R S I T Y O F C O P E N H A G E N
Master’s Thesis
Catherine M Hepp
The Ecological Sustainability of Short Fallow Shifting
Cultivation in Upland Systems
A Study in Northern Lao PDR, Southeast Asia
Academic Advisor: Thilde Bech Bruun, Assistant Professor
Department of Plant and Environmental Sciences
University of Copenhagen
Submitted: 31/07/13

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Photograph Credits: Catherine M. Hepp

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Name of department: Department of Plant and Environmental Sciences
Author: Catherine M Hepp
Title / Subtitle: The Ecological Sustainability of Short Fallow Shifting Cultivation in
Upland Systems / A study in Northern Lao PDR in Southeast Asia
Subject description: The impact of shorter fallow lengths on the ecological sustainability of
shifting cultivation in Lao PDR, specifically in terms of soil quality and
upland rice yields. The drivers of the decreasing fallow length are also
discussed and how such changes will affect the livelihood strategies of
upland populations.
Academic advisor: Thilde Bech Bruun, Assistant Professor
Submitted: 31. July, 2013

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5. ǁ Abstract
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Abstract
The Ecological Sustainability of Short Fallow Shifting Cultivation in Upland Systems
A Study in Northern Lao PDR, Southeast Asia
C. M. Hepp
Dept. of Plant and Envrionmental Sciences, Faculty of Science, University of Copenhagen, Denmark
Shifting cultivation in Southeast Asia is rapidly transforming due to increased land pressure,
governmental policies and improved access to infrastructure and markets. The forced use of
shortened fallow lengths questions its ecological sustainability, a concern as the livelihoods of
resource-poor farmers may be affected. The objective of the study was to assess the ecological
sustainability of short fallow shifting cultivation systems in Lao PDR; specifically, how fallow length
and topography influence soil quality and upland rice yields. Upland fields of 2-, 3-, 5-, 10- and 11-
year fallows of similar topography, parent soil and land use history were selected; the 5-year fields
were used to assess topographical influence. Soil organic carbon and permanganate oxidisable
carbon were identified as key indicators of soil quality as they were positively correlated to the soil
nutrients, N, P and K, and led to higher upland rice yields. Although fields of longer fallows were
associated with higher yields, no such correlations were found with soil quality; the positive
association between fallow length and upland rice yields may rather reflect weed suppression, less
pest or disease infestation or a combination. The results indicate that a length of five years for fallow
will give the greatest return to the soil; the increase in upland rice yields when fallowed for longer
than five years will depend on the technical skill and management practices of the farmer. Soil
quality or upland rice yields were not significantly influenced by slope position, thus erosion is not a
major constraint; nitrogen and potassium show an accumulation at the bottom of the slope possibly
due to leaching effects and the downward movement of ash. It appears the use of appropriate scales
in such studies whereby soil quality and yields are both measured from marked plots will improve
accuracy. The impact of fallow length on soil quality and upland rice yields remains ambiguous;
more future studies at the plot level are required as such findings will have implications for
governmental policy reforms and the livelihoods of the rural poor.
Key Words: Lao PDR, shifting cultivation,ecological sustainability, upland rice, soil quality, fallow length,
slope position, Pox C, SOC

6. Preface ǁ
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Preface
This thesis is for the completion of a M.Sc. in Agricultural Development from the Faculty of Science
at the University of Copenhagen, Denmark. The study was partially funded by the University of
Copenhagen. It is written from an agricultural development perspective with the intention of
assessing the ecological impacts of intensification on traditional upland systems.
Mandatory field work in a developing country was carried out in Northern Lao PDR from September
to the end of November 2012. The host institution was the National University of Lao PDR. Field
sites were located in the Ban Navene area, a relatively remote village located in the Viengkham
District of the Louangphabang province. The duration of field work was spent in Ban Navene and
thus exposure to and involvement in everyday life activities occurred. Data was collected with the
help of a translator who spoke both Lao and Khamu.
Soil analysis was completed at three different institutions: the Pox C analysis was done at the
Department of Soil and Environmental Resources of the Faculty of Agricultural Production at Maejo
University in Chiang Mai, Thailand; soil samples were sent to the Soils and Fertilizers Research
Institute (SFRI) in Hanoi, Vietnam for textural and chemical analysis; and finally, pH and carbon and
nitrogen content measurements were completed at the Dept of Plant and Environmental Sciences,
Faculty of Science of the University of Copenhagen.

7. ǁ Acknowledgements
vii
Acknowledgements
This thesis would not have been possible without the support and assistance of numerous people
and institutions. I would first like to express my sincere gratitude to my academic advisor, Thilde
Bech Bruun, for her support and guidance throughout the study. Her invaluable insight, experience
and knowledge were a continuous source of encouragement and what led me to undertake this
study in the first place. Furthermore I would like to extend my appreciation for the Agricultural
Development programme (Faculty of Science, University of Copenhagen) and its programme
director, Andreas de Neergaard, for the supportive academic environment. Additionally, I would like
to thank the staff and peers from the Dept of Plant and Environmental Sciences for their assistance
with numerous aspects of the soil analysis and final stages of the study.
I would like to thank Ms. Somvilay Chanthalounnavong at the Faculty of Forestry of the National
University of Laos as her guidance made my stay in Lao PDR possible. Special thanks go out to Ms.
Supathida Aumtong, Assist. Prof., and the Department of Soil and Environmental Resources (Faculty
of Agricultural Production, Maejo University, Thailand) for generously making their facilities and
expertise available to me. I would furthermore like to extend my gratitude to Mr. Kronpech Srisoy
and his fellow peers for hosting me during the week and making my stay at Maejo truly enjoyable.
My sincere thanks go to Mr. Phaeng Xaphokhame, my interpreter, and DAFO (Viengkham district,
Lao PDR). Without Mr. Xaphokhame’s guidance and valuable knowledge, the study and data
collection would not have been attainable.
Last but not least, I would like to express my eternal gratitude to the Headman, Thong Phouy, his
family and the people of Ban Navene who graciously welcomed me into their community for the
duration of my field work. I feel privileged to have been given such an honour and opportunity as to
share in their daily life activities and Khamu culture. My stay is an experience I will truly treasure and
I hold the memories dear to my heart.
Catherine M. Hepp
July 31, 2013

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Table of Contents
Abstract ...............................................................................................................................................v
The Ecological Sustainability of Short Fallow Shifting Cultivation in Upland Systems..........v
A Study in Northern Lao PDR, Southeast Asia.......................................................................................v
Preface ............................................................................................................................................... vi
Acknowledgements ......................................................................................................................vii
List of Tables...................................................................................................................................xii
List of Figures ................................................................................................................................xiii
Appendices ....................................................................................................................................xiv
1 Introduction ............................................................................................................................. 1
1.1 Research Objective............................................................................................................................... 1
2 Theoretical Background ...................................................................................................... 3
2.1 Soil Quality: Indicators and their Significance........................................................................... 3
2.1.1 Inherent Physical Properties..................................................................................................................3
2.1.2 Dynamic Properties....................................................................................................................................3
2.2 Shifting Cultivation: a description .................................................................................................. 5
2.2.1 The Role of Burning....................................................................................................................................6
2.2.2 The Importance of Fallow Length.........................................................................................................6
2.2.3 The Impact of Shortened Fallows.........................................................................................................7
2.2.4 Topography: Does it have an Influencing Role?..............................................................................8
2.3 The Drivers of Decreasing Fallow Lengths .................................................................................. 8
2.3.1 Demographical Change .............................................................................................................................8
2.3.2 Political Influence........................................................................................................................................9
2.3.3 The Development and Expansion of Commercial Agriculture..................................................9
2.4 Livelihood Strategy Implications ..................................................................................................10

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3 Methodology...........................................................................................................................11
3.1 Study Site Description.......................................................................................................................11
3.2 Identification of Fields ......................................................................................................................13
3.3 General Plot Layout............................................................................................................................13
3.3.1 Soil Sampling and Analysis................................................................................................................... 14
3.3.2 Yield Assessments.................................................................................................................................... 15
3.4 Calculations and Statistical Analysis............................................................................................15
3.5 Constraints of Upland Rice Production.......................................................................................17
3.6 Farmers’ Perception ..........................................................................................................................17
3.7 Future Perspectives ...........................................................................................................................18
4 Results......................................................................................................................................19
4.1 Soil Quality Analysis...........................................................................................................................19
4.1.1 General Soil Description........................................................................................................................ 19
4.1.2 Soil Parameter Interactions ................................................................................................................. 20
4.2 Implications of the Soil Quality on the Yield of Upland Rice ...............................................27
4.2.1 Soil Parameter Influences on Yield ................................................................................................... 27
4.2.2 Stock Values and Yield............................................................................................................................ 31
4.3 System Influences ...............................................................................................................................32
4.3.1 Topographical Influence........................................................................................................................ 32
4.3.2 Fallow Length Impact............................................................................................................................. 34
4.3.3 Alternative Measures of Land Use Intensity ................................................................................. 39
4.4 From the Farmers’ Perspective......................................................................................................40
4.4.1 Historical and Socioeconomic Context for Ban Navene............................................................ 40
4.4.2 The Establishment of the NEPL NPA................................................................................................ 42
4.4.3 The Constraints of Upland Rice Production.................................................................................. 42
5 Discussion ...............................................................................................................................45
5.1 Ban Navene- a village in transition...............................................................................................45
5.2 The Ecological Sustainability..........................................................................................................45
5.2.1 Soil Quality: the Parameters and Their Interactions ................................................................. 46
5.2.2 The Link between Soil Quality and Upland Rice Yield .............................................................. 49
5.2.3 System Influence: the topography of a field.................................................................................. 51

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5.2.4 System Influence: the fallow length.................................................................................................. 52
5.2.5 Quantitative Experimental Design: a reflection........................................................................... 56
5.3 What is Driving the Decrease of Fallow Lengths in Ban Navene?......................................58
5.3.1 Demographical Changes........................................................................................................................ 58
5.3.2 Political influences................................................................................................................................... 59
5.3.3 The Development and Expansion of Commercial Agriculture............................................... 61
5.4 The Implications for Upland Rice Productivity: From the Farmers’ Perspective........62
5.4.1 The Constraints to Upland Rice Production.................................................................................. 62
5.5 The Implications for Livelihood Strategies ...............................................................................64
5.5.1 Livelihood Security.................................................................................................................................. 64
5.6 Future Prospects for Ban Navene..................................................................................................66
6 Conclusion...............................................................................................................................67
7 Personal Reflection..............................................................................................................69
8 References..............................................................................................................................71
9 Appendices .............................................................................................................................75

12. List of Tables ǁ
xii
List of Tables
Table 1: The range and correlations of soil parameters at the soil surface of fields............................21
Table 2: The range and correlations of soil parameters at a 10 cm depth of fields.............................22
Table 3: The range in soil parameters at depths of thirty cm of fields.................................................23
Table 4: Multiple stepwise regression results for the dependent factor, yield, for the soil surface at a
confidence level of 99% (p<0.05).............................................................................................30
Table 5 The clay and carbon content (0-5 cm) at the top, middle and bottom of a continuous slope.
..................................................................................................................................................32
Table 6:The nutrient stocks at the soil surface and at a depth of 10 cm according to the
topographical positions within a slope: top, middle and bottom. ..........................................33
Table 7: The yield in upland rice assessed directly from plots placed at the top, middle and bottom
of a continuous slope...............................................................................................................34
Table 8: The carbon concentrations of fields grouped according to the duration of the preceding
fallow¹.......................................................................................................................................35
Table 9: The C:N and SOC:Pox C ratios of fields grouped according to the duration of the preceding
fallow¹.......................................................................................................................................35
Table 10: The stocks of Pox C, N, P Avail and K Exch of the upper 10 cm in an eqv mass according to
fallow lenght.............................................................................................................................37
Table 11: The major pre-determined constraints to upland rice production for shifting cultivators in
Ban Navenea
.............................................................................................................................43

13. ǁ List of Figures
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List of Figures
Figure 1: The nutrient availability as a function of soil pH. ....................................................................3
Figure 2: Landscape typical for shifting cultivation ................................................................................5
Figure 3: Theoretical illustration of the relationship between fallow length (x-axis) and soil
productivity (y-axis).................................................................................................................6
Figure 4: The location map of Lao PDR and approximate location of the study site ...........................11
Figure 5 : A schematic drawing representing Ban Navene and its surrounding area..........................12
Figure 6: (a) Diagram depicting the plot design and (b) layout ............................................................14
Figure 7: The flashcards used for the pairwise ranking method ..........................................................17
Figure 8: Sheang’s father, a key informant ..........................................................................................17
Figure 9: The participants of the group meeting held at the Ban Navene School................................18
Figure 10: Soil profile of the ultisol typical for the Ban Navene area...................................................19
Figure 11: Relationship between carbon and nitrogen soil content depicted by SOC % and N%........24
Figure 12: Relationship between SOC % and a) P Avail and b) K Exch..................................................25
Figure 13: The relationship between SOC % and Pox C.......................................................................26
Figure 14: Relationship between Pox C and N%...................................................................................27
Figure 15: The relationship between upland rice yield and pH...........................................................28
Figure 16: The relationship between upland rice yield and Pox C.......................................................28
Figure 17: The relationship between upland rice yield, Pox C and a) N% and b) C:N ..........................29
Figure 18: The relationship between upland rice yield (kg·ha¯¹) and the upper 10 cm quantities, in
equivalent masses of soil, 81 kg, of a) SOC, b) N, c) P Avail and d) K Exch............................31
Figure 19: The relationship between SOC stocks of the upper 10 cm in an equivalent mass of soil,
88.24 kg, and fallow length ...................................................................................................36
Figure 20: The yield (kg · ha-1
) in upland rice after a preceding fallow of 2, 3, 5, 10 or 11 years.........37
Figure 21: Relationship between SOC stock and Stock N.....................................................................38
Figure 22: The relationship between yield (kg · ha-1
) in upland rice and alternative land use intensity
measures ...............................................................................................................................39
Figure 23: The historical timeline of Ban Navene from its establishment in 1910 to the present date,
2012.......................................................................................................................................40
Figure 24: The population growth of Ban Navene from 1985 - 2012..................................................41
Figure 25: Rice with a dead panicle of unfilled grains, termed ‘whitehead’ and indicative of stem
borer infestation or rice blast (IRRI, 2009)............................................................................42
Figure 26: The impressed tortoise (M. impressa), a vulnerable species found in the NEPL NPA illegally
trapped..................................................................................................................................60
Figure 27: Thong La, the maize company, husking the stored maize, 11/12 ......................................61

14. Appendices ǁ
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Appendices
1 Methodolgy................................................................................................................. 75
1.1 Survey for Field Identification................................................................................................................75
1.2 Visual Observations/ Characteristics for Field........................................................................................76
1.4 Protocol for Pox C..................................................................................................................................77
1.5 Standard Curve of Pox C Analysis...........................................................................................................78
1.6 Guiding Questions for In-Depth Farmer Interviews................................................................................79
1.7 Guiding Questions for NEPL NPA Land loss Effects.................................................................................81
1.8 Guiding Questions for Group Interview .................................................................................................82
2 Field Record Sheet..................................................................................................... 83
3 Map of Field Locations Depicting Area (ha) ............................................................. 84
4 Soil Data Summaries.................................................................................................. 85
4.1 Physical and Chemical Parameters at the Surface, 10 cm and 30 cm of the Fallow Length Study...........85
4.2 The Carbon and Nitrogen Parameters of the Fallow Length Study.........................................................86
4.3 The Carbon and Nutrient Upper 10 cm Stocks (kg m
-2
) using a fixed depth or mass equivalent approach
of the Fallow Length Study ....................................................................................................................87
4.4 Pox C levels (mg kg
-1
) at the Soil Surface and 10 cm depth of the Fallow Length Study..........................87
4.5 Physical and Chemical Parameters at the Surface, 10 cm and 30 cm of the Topographical Study ..........88
4.6 The Carbon and Nitrogen Parameters of the Topographical Study ........................................................89
4.7 The Carbon and Nutrient Upper 10 cm Stocks (kg m
-2
) using a fixed depth or mass equivalent approach
of the Topographical Study....................................................................................................................90
4.8 Pox C levels (mg kg
-1
) at the Soil Surface and 10 cm depth of the Topographical Study .........................91
5 Results........................................................................................................................ 92
5.1 Interactions between Soil Quality and Upland Rice Yield.......................................................................92
5.2 System Influence: Topographical Influence on Upland Rice Yield ..........................................................93
6 List of Interviewees and Informants ......................................................................... 94
7 Ranking of the Constraints to Upland Rice Production .......................................... 95

15. Research Objective ǁ Introduction
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1 Introduction
Agricultural systems in developing regions are shifting from subsistence farming to more specialised
and commercialised types, a goal of many national policies as this is often seen as a necessary step
for economic growth and development. The process is a step-wise transition where traditional
shifting cultivation, a once widespread form of subsistence farming in the upland areas of Southeast
Asia (Ziegler et al., 2011), is slowly replaced by permanent cropping systems, commonly with cash
crops such as maize, oil palm or rubber (Cramb et al., 2009; Ziegler et al., 2011).
The replacement of traditional shifting cultivation as a livelihood strategy, where upland rice is
commonly the dominant crop, is accelerated by demographical changes, governmental policies and
reform, the development and improved access to markets and sociocultural trends (Cramb et al.,
2009; Roder, 1997; Ziegler et al., 2011). The consequences on livelihood strategies are poorly
understood and will depend greatly on the resource endowment of the affected rural villages, often
of ethnic minority (Roder, 1997). A livelihood strategy change, in turn, will affect food security and
will have repercussions for the ecological sustainability (Cramb et al., 2009).
Where shifting cultivation is retained, intensification will lead to the implementation of shorter
fallows, a trend that has been widely observed in Southeast Asia (Schmidt-vogt et al., 2009); shorter
fallows are often the only viable intensification strategy as the adoption of alternatives, such as
permanent cropping, is difficult in upland areas as they are steep, exposed to high precipitation
levels and have generally poor soils (Cramb et al., 2009). The decline in fallow length, the central
ecological principal through which soil fertility is restored (Bruun et al., 2009), is thought to lower
upland rice yields, increase weeds, degrade soil and result in a lower return to labour (Bruun et al.,
2006; Mertz, 2002; Mertz et al., 2013); this is often termed the ‘downward spiral’ of shifting
cultivation and has negatively influenced the policies of developing countries as it is thought as
unsustainable (Cramb et al., 2009; Lestrelin & Giordano, 2007).
However, a direct causal link between the decline in fallow length and the assumed downward spiral
has been difficult to prove and the effects remain somewhat ambiguous. As shifting cultivation
supports the livelihoods of the majority of the poor upland populations in Southeast Asia, a clearer
understanding of the full impacts of the intensification is preeminent.
1.1 Research Objective
Considering this lack of understanding, the main objective of the study is to investigate the impact
short-fallow shifting cultivation, an intensification strategy, will have on the livelihoods of upland
populations, specifically from an ecological perspective. Emphasis is placed on the consequence of
short fallow lengths on upland rice yields and soil quality, both intricately-linked to the ecological
sustainability of the system and, in a broader sense, to food security.
The assessment is made difficult as there are numerous parameters that will play an influencing role;
upland rice yields are a product of both socioeconomic, i.e. land use history and fertilizer inputs, and

16. Introduction ǁ Research Objective
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ecological parameters, i.e. inherent soil properties or the burn quality. Past studies are not
consistent in which parameters have been controlled hence it is difficult to isolate the actual impacts
caused by shorter fallow lengths and to compare results. A major challenge for past studies has
been to find areas where external inputs such as fertilizers are not used and how to account for their
effect on soil quality.
Any circumstance therefore in which the parameters can be better controlled would facilitate the
study. This was a strong point for why a relatively isolated village in Northern Lao PDR was the
selected study location; it is a country with a high proportion of its population dependent on shifting
cultivation thus systems of various intensities can be found and, furthermore, farmers lack the
resources for external soil inputs. This helps lower the possibility that any ecological impact
observed is a mere consequence of an unrelated parameter.
The objective will be achieved through the following research question:
How does the fallow length affect the soil quality and upland rice yield in a shifting cultivation
system of Northeastern Lao PDR?
i. How have the fallow lengths changed in Ban Navene, a village of Khamu ethnicity
since 1985, and what are the drivers?
ii. What are the major constraints to upland rice production? Have the farmers
perceived a change in soil quality and upland rice yields?
iii. How do the soil’s properties, specifically the total carbon and nitrogen content,
plant-available minerals and nutrients, pH and cation exchange capacity, interact to
give an overall impression of soil quality? How are soil quality and upland rice yield
linked?
iv. How does the topography of a cultivated field affect the soil quality and upland rice
yield?
v. Is the fallow length correlated to soil quality, specifically the total carbon and
nitrogen content, plant-available minerals and nutrients, pH and cation exchange
capacity?
vi. What impact does the fallow length have on the yield of hill rice, without the
addition of chemical or organic fertilizers?

17. Soil Quality: Indicators and their Significance ǁ Theoretical Background
3
2 Theoretical Background
2.1 Soil Quality: Indicators and their Significance
Soil quality in this context is defined as the ability of the soil to support and maintain crop
production and incorporates physical, chemical and biological parameters (Bruun et al., 2009; Brady
and Weil, 1999). Management practices will influence soil parameters of varying sensitivities (Brady
and Weil, 1999); it is thus important that suitable soil parameters are chosen as indicators of soil
quality to determine the extent of soil degradation, if any. The parameters selected to explore soil
quality are the inherent physical properties (CEC and clay content), bulk density, soil organic carbon
(SOC) and permanganate oxidisable carbon (Pox C) content, and the nutrient levels of total nitrogen
(N), available phosphorus (P Avail) and exchangeable potassium (K Exch). Additional calculations
using the listed parameters can give further insight into soil quality levels; i.e. C:N ratio, SOC:Pox C
ratio and carbon and nutrient stocks.
2.1.1 Inherent Physical Properties
One of the defining characteristics of a highly weathered tropical
soil is its acidity and the consequential implications (Brady and Weil,
1999). At low pH, soil colloids will preferentially adsorb soluble iron
and aluminum ions; when hydrolysed, the adsorbed iron and
aluminum ions will produce hydrogen ions thereby contributing to
the acidity (Brady and Weil, 1999). The implication of pH on the soil
quality is considerable as it is strongly tied to nutrient availability
and will thus influence crop yield levels (Figure 1).
The clay content of a soil will have considerable implications for the
soil quality; clay colloids are influential determinants of the
chemical properties of a soil due to their unbalanced negative
charges (Weil and Brady, 1999).
2.1.2 Dynamic Properties
The dynamic properties of a soil are insightful as they will react to
agricultural management practices however in varying degrees of sensitivity. Nevertheless, the
sustainability of a shift in management practices can be assessed through such parameters.
2.1.2.1 Soil Organic Carbon Content
SOC, in primary association with soil organic matter (58%), is a commonly measured soil parameter
because of its key role in the global carbon cycle and its response to anthropogenic activities. The
SOC content of a soil has significant implications for soil quality; it is an important source of plant
nutrients (N,P,K) and CEC, acts as a buffer against acidity and Al- toxicity, improves soil aggregation
Figure 1: The nutrient availability
as a function of soil pH
Source: University of Minnesota (2009)

18. Theoretical Background ǁ Soil Quality: Indicators and their Significance
4
and stability, and it enhances the water holding capacity and infiltration (Bruun et al., 2009). Hence
it is intricately-linked to the other investigated parameters.
Bulk density is defined as the mass per unit volume of dry soil whereby the volume includes the
solids and pores (Brady and Weil, 1999); a greater proportion of pore space will correlate to a lower
bulk density. Bulk density is a function of both soil organic matter and the clay content of a soil due
to their positive influence on pores between and within the soil granules (Brady and Weil, 1999). A
fine-textured soil, characterized by higher clay content, will have aggregates of porous granules and
hence, the total pore volume be greater. This translates to a lower bulk density and indicates
favourable physical conditions for crop growth.
Funakawa et al. (1997) found soil organic matter to be a determinant of plant-available nitrogen.
The mineralization of nitrogen by soil microbes is the main source for plant uptake and is heavily
reliant on the C:N ratio. Nitrogen immobilization, i.e. its incorporation into the cells of
microorganisms, will be determined by the C:N ratio and will occur if it is greater than 25 (Brady and
Weil, 1999).
Likewise, P Avail and K Exch levels are influenced by the SOC. The mineralization of organic
phosphorus to its inorganic plant-available form is important as the added phosphorus will become
quickly fixed by the Al- and Fe-oxides (Brady and Weil, 1999). SOC degradation supplies K Exch as it
is largely determined by the plant and animal residues that are returned to the soil; K Exch will
quickly leach through a soil and can be a limiting factor in production (Brady and Weil, 1999).
2.1.2.2 Permanganate Oxidisable Carbon
Studies suggest that SOC levels of a soil are too insensitive to land use changes to be of any use in
detecting soil degradation (Aumtong et al., 2009). As a result, a magnitude of varying methods have
been proposed of which target different fractions of the SOC pool higher in sensitivity, one of which
is the Pox C method (Aumtong et al., 2009).
The use of Pox C as a sensitive indicator of the effects land use changes may have on the soil quality
has been proposed by several studies (Aumtong et al., 2009; Culman et al., 2012); however the
exact fraction of the carbon pool it reflects is not well understood (Aumtong et al., 2009; Culman et
al., 2012; Tirol-Padre & Ladha, 2004). It is commonly said to represent the most readily oxidisable
carbon such as plant litter, microbial biomass and non-humic substances that are not bound to
minerals (Tirol-Padre & Ladha, 2004; Weil et al., 2003). The Pox C content of a soil will influence soil
quality considerably and in a similar matter to that of SOC; as soil microbes readily degrade the labile
carbon, nutrients will be converted to plant-available forms with obvious implications for crop yields.
It is important to assess the changes in the various carbon pools as their sensitivities towards change
and activity levels are different; a greater change in the labile carbon pool will have larger
implications for soil fertility when compared to non-labile carbon (Blair et al., 2001). This has led to
the development of a carbon management index (CMI) by Blair et al. (2001) in which the changes in
the various carbon pools, relative to one another, can be compared to reference levels; the index
will give a clearer picture of the full impacts of management practices seen sooner than if only SOC

19. Shifting Cultivation: a description ǁ Theoretical Background
5
content was measured. Alternatively, if no reference soil is available, the similar parameter, SOC:Pox
C, may reflect the respective carbon pool changes.
2.2 Shifting Cultivation: a description
The definition of shifting cultivation is debated but the majority agree that it refers to a smallholder
agricultural system that implores the use of fallow as a means to restore productivity, usually with
no addition of external inputs such as fertilizers (Lestrelin et al., 2012; Mertz, 2002; Mertz et al.,
2009). The farmers will rotate between their upland fields usually in a cyclic manner (Cramb et al.,
2009). Commonly, local varieties of upland rice are the main crop of shifting cultivation produced
for subsistence needs; upland rice may be sold or exchanged for labour, market food, goods such as
clothes or fuel, or when health supplements or services are required (Seidenberg et al., 2003).
The fallow phase, the central ecological
principle, works to repress weeds and restores
soil quality (Bruun et al., 2006; Mertz, 2002;
Mertz et al., 2008). The regenerating fallow
vegetation will absorb nutrients and return
them to the soil surface as litter or, when cut
and burned, in a biologically active form
(Bruun, et. al., 2009). Essentially it counteracts
the tendency for the decline in nutrient
availability caused by crop export, leaching and
volatilisation of nitrogen and sulphur during the
burning (Bruun et al., 2006; Mertz, 2002).
Furthermore, the biodiversity of the fallow
vegetation is an important source of NTFPs and
account for 40 – 60% of the income of rural
households (Moore et al., 2011)
Shifting cultivation is often the main land use strategy of ethnic minorities who live in remote upland
areas with poor soil and who contend with a limited access to markets, socioeconomic benefits and
communication (Figure 2; Roder, 1997). The system is often the only available livelihood strategy
and is thus seen as environmentally and economically sound for such populations, especially when
compared to other intensified and commercialised systems (Nielsen et al., 2006; Roder, 1997; Vien
et al., 2006).
Figure 2: Landscape typical for shifting cultivation
where a mosaic of upland rice plots and regenerating
fallow of variable age are seen. Taken in the upland
area of Northern Lao PDR.

20. Theoretical Background ǁ Shifting Cultivation: a description
6
2.2.1 The Role of Burning
The slash-and-burning of fallow vegetation is meant to resupply the soil with nutrients lost to crop
uptake. The amount of nutrients returned to the soil is highly dependent on the ash, directly linked
to the burn success of a field, and hence should be taken into account when considering the soil
quality (Andriesse & Schelhaas, 1987). The burn quality, in terms of moisture and fuel content, the
nutrient content of the fallow vegetation and the temperature thresholds of the respective nutrient
will determine the mineral nutrient content found in the ash (Andriesse & Schelhaas, 1987).
The levels of nitrogen in a soil are important when considering soil quality as it is commonly a
limiting factor in upland rice production (Roder et al., 1995) as the volatilisation losses during the
burning of fallow vegetation are high due to its low temperature threshold (Bruun et al., 2006). The
microbial biomass is a source of soil nitrogen both in regards to the mortality that occurs during the
burn and the enhanced microbial activity after burning, a consequence of the warm temperature
and increased carbon and nutrient content (Bruun et al., 2006).
Though the ash will contain some phosphorus due to its relatively high temperature threshold, the
mineralization is still important as any additional supply is beneficial since phosphorus will be quickly
fixed by the Al- and Fe-oxides (Andriesse & Koopmans, 1984; Brady & Weil, 1999). Phosphorus
content of the soil in a shifting cultivation system is thus determined in a similar manner to that of
nitrogen: by the soil organic matter concentration, the microbial mortality during burning and the
enhanced microbial activity thereafter (Bruun et al., 2006). Potassium availability for plant uptake is
dependent on the amount stored in the aboveground fallow vegetation, which will be transferred to
the soil via ash deposit (Bruun et al., 2006).
2.2.2 The Importance of Fallow Length
The length of fallow will impact the nutrients returned
to the soil as it influences the species composition and
biomass of the fallow vegetation (Bruun et al., 2009).
In the tropics, the biomass accumulation rate of the
secondary vegetation will be the greatest during the
first ten years and will then start to slow (Jepsen,
2006).
These factors, as discussed, will in turn affect the
levels of nutrients returned to the soil during burning.
Some suggest a minimum fallow length requirement
to maintain crop and soil productivity (Cramb et al.,
2009; Mertz, 2002; Mertz et al., 2009; Nielsen et al.,
2006); however the exact length is difficult to
pinpoint. Studies have found different lengths
necessary, as depicted in Figure 3 (Mertz, 2002), and
will vary according to climate and management
Figure 3: Theoretical illustration of the relationship
between fallow length (x-axis) and soil productivity (y-
axis); a and b both represent sustainable systems. From
Mertz, 2002.

21. Shifting Cultivation: a description ǁ Theoretical Background
7
(Bruun et al., 2009); in some areas, fallow lengths of 8-20 years with two or three years of successive
cropping are adequate in maintaining soil quality however it is largely dependent on the initial
condition of the soil (Mertz, 2002). Furthermore, the number of cultivation cycles, length of
cropping periods or field size will reduce biomass accumulation and, thus, the nutrients available to
the subsequent crop (Bruun, et. al., 2009).
2.2.3 The Impact of Shortened Fallows
Although the impacts still remain ambiguous, the general theory that shortened fallow lengths will
lead to a system breakdown has been widely accepted and taken for granted (Mertz et al., 2009).
With no external inputs, it is thought that shorter fallow lengths will lead to lower yield levels
because of a decline in nutrient availability, higher rates of weed infestation and poorer soil physical
properties (Mertz, 2002).
The difficulty lies in that ‘real life’ situations are diverse. To accurately assess if fallow length affects
soil quality and upland rice yields, the investigated parameters must be kept identical across study
sites; this is difficult due to variations in the physical and spatial environment, inherent soil
properties and farmers’ land use decisions and management practices as they contribute to the
productivity of the system (Aumtong et al., 2009; Mertz et al., 2008; Roder et al., 1995).
The effect of fallow length on soil quality has been difficult to quantify and results from studies have
been inconsistent as to which parameters are significantly affected. Roder et al. (1995) found a
weak positive association between SOC content and fallow length, while Bruun et al. (2006) found
plant available nitrogen to be positively correlated with fallow length instead. SOC content does
appear to be an important indicator of soil quality in general as it does respond to different land use
strategies and is influenced by a soil’s clay content and CEC (Aumtong et al., 2009).
The theoretical relationship between fallow length and upland rice yields has been difficult to prove.
Bruun et al. (2006) found fallow length to be an indicator of upland rice yield levels in Sarawak
Malaysia; however the rice density and degree of intercropping were not considered and
management practices were assumed to be constant, weaknesses of the study.
Whether fallow length has a larger function in restoring soil fertility or suppressing weed populations
also remains ambiguous; studies that have found accurate links between fallow length and weed
density are lacking. A study by Roder et al. (1995) found no links between fallow length and weed
density in Northern Lao PDR. However suggestions have been made stating that the higher yields
observed are rather a function of the fallow length’s influence on weed density and not on soil
quality (Mertz, 2002).

22. Theoretical Background ǁ The Drivers of Decreasing Fallow Lengths
8
2.2.4 Topography: Does it have an Influencing Role?
Many studies refer to the hilly topography characteristic of upland areas as a major limitation to
production(Bruun et al., 2009; Mertz et al., 2008; Roder, 1997; van Vliet et al., 2012) and will
accelerate land degradation especially in light of the decreasing fallow lengths; however the
influence of topography remains ambiguous as there are few studies. Of these studies, the majority
have investigated the degree of erosion through the measurements of sediment runoff; fewer still
have looked at soil quality in relation to slope position or its implications for upland rice yields.
It appears erosion is not as limiting as theoretically expected when measuring sediment runoff in Lao
PDR (Lestrelin et al., 2012). This is reflected in the finding by Roder et al. (1995) where erosion was
not identified as a major constraint to upland rice production.
The general soil quality does not appear to be significantly influenced by slope position (Aumtong et
al., 2009; de Neergaard et al., 2008). Aumtong et al. (2009) found carbon stocks to be unaffected by
slope position in Northern Thailand. The same result was found in Sarawak Malaysia by de
Neergaard et al. (2008) however there does appear to be an accumulation of base cations at the
slope bottoms. It was suggested that this pattern is not due to erosion per se but rather to the
downward movement of ash by wind and water and leaching (de Neergaard et al., 2008).
2.3 The Drivers of Decreasing Fallow Lengths
Cramb, et al. (2009) have defined three main causes for the trend of intensification: demographical
change, the development and expansion of markets for commercial agriculture, i.e. cash crop
integration, and policy reform. Each will increase pressure on the traditional shifting cultivation
system whereby a reduction in fallow lengths will occur (Cramb et al., 2009); in remote upland areas
with poor soils, a reduction in fallow length is often the only viable option as no alternative
livelihood strategy is available (Roder, 1997).
2.3.1 Demographical Change
Boserup’s (1965) model for agrarian change stipulates that the main driver of the change from
shifting cultivation to permanent cropping systems is population pressure; an increase in population
will add strain to the traditional system whereby the principle change is an increase in intensification
either through a decrease in fallow length or the cultivation of permanent crops. Population growth
will cause additional changes in land use strategies, agricultural technology, village locations and
land tenure systems (Boserup, 1965).

23. The Drivers of Decreasing Fallow Lengths ǁ Theoretical Background
9
The out-migration of younger generations to urban areas is a widespread trend in Southeast Asia,
one that will further promote the intensification of shifting cultivation (Cramb et al., 2009; Hansen &
Mertz, 2006; Ziegler et al, 2011). This trend will place added pressure on the labour availability; if
labour supply is limited, upland fields in close proximity to villages will be more intensively cropped
and long fallows will no longer be favoured due to the high labour requirement of falling large trees
(Nielsen, et. al., 2006; Roder, 1997).
2.3.2 Political Influence
The general notion that the system is ‘backwards’ and must be replaced if modern development is to
occur has been pushed by governmental representatives and has hastened the demise of shifting
cultivation (Cramb et al., 2009). Governmental policy reform and programmes have strained
extensive shifting cultivation as they have involved land use classification, resettlement of villages
and land privatization (Fox et al., 2009). The regulations are often restrictive in nature and thus
discourage shifting cultivation as a suitable land use form (Cramb et al., 2009). Shifting cultivation
has been mandated to specific land classes, meaning that it has been restricted to certain areas
outside defined forest reserves, protected areas and community forests (Cramb et al., 2009; Fox et
al., 2009). It is hoped that this will ultimately lead to the discouragement of shifting cultivation as
the required intensification will be deemed unsustainable (Moore et al., 2011).
2.3.3 The Development and Expansion of Commercial Agriculture
Often the commercialisation of agriculture will include the integration of cash crop cultivation and
livestock; both trends are seen in Southeast Asia and lower the reliance on shifting cultivation. Cash
crops such as the oil palm, maize, pepper and rubber are increasingly integrated with the upland
agricultural systems (Cramb et al., 2009; Ziegler et al., 2011). The livelihoods of the farmers can be
improved however they will also become more exposed to market vulnerability as the prices of such
crops are known to fluctuate (Roder, 1997). Not do they only become more vulnerable but their
continuous cropping will accelerate land degradation (Cramb et al., 2009). Furthermore, the
cultivation of permanent cash crops removes land from the cyclic rotation of shifting traditional and
thereby reduces the fallow length.
Livestock may be of benefit to villages in the upland areas as they have a high market value per unit
weight and are somewhat mobile, an important trait if road facilities are lacking (Roder, 1997). A
study found that there are cases whereby villages with poor market access built successful networks
by walking for as long as three days to bring their livestock to markets (Vien et al., 2006).
Furthermore, they can act as an insurance of some type, sold during times of illnesses or food
shortages. However livestock integration requires a basic fundamental level of infrastructure
development to avoid conflict with crops and humans, i.e. fences.

24. Theoretical Background ǁ Livelihood Strategy Implications
10
2.4 Livelihood Strategy Implications
Where the transformation of shifting cultivation has occurred, the process has involved multiple
steps and system variations. The progressive integration of padi rice in response to intensification
occurs if suitable areas, i.e. flat valley bottoms, are available (Roder, 1997); Rambo (2006) coined the
term ‘composite swidden agriculture (CSA)’ for such systems and claims it has a higher sustainability
than traditional shifting cultivation. Cramb, et al. (2009) further defines a ‘partial swiddening’
system where the inclusion of cash crops increases gradually at the expense of subsistence crops.
The cultivation of maize for the livestock feed sector is becoming widespread in Southeast Asia
where upland farmers sign contract agreements with maize companies who offer support services in
varying degrees. Published studies of this trend are scarce and farmer benefits will be dependent on
the contract conditions and the extension services provided.
On the other hand, traditional shifting cultivation is still maintained in some upland areas despite the
aforementioned drivers and challenges; it has been suggested that its maintenance as a livelihood
strategy is due to the lack of feasible alternatives (Hansen and Mertz, 2006). Governmental polices
thus have been criticised as only placing extra strain on the livelihoods of the rural poor and
accelerating land degradation.
The intensification of shifting cultivation by means of decreasing fallow length will have implications
for livelihood strategies. Food security of the upland communities is expected to be negatively
influenced as a consequence of lower rice yields and availability of NTFPs (Rerkasem et al., 2009).
Furthermore, the environmental and socioeconomic constraints in the cultivation of upland rice will
increasingly become more prominent. Roder et al. (1995) found farmers in Northern Lao PDR
identified weeds, rodents and insufficient rainfall as the three most limiting constraints to upland
rice production; the other constraints found were land availability (which included the short fallow
constraint), insects, labour, soil suitability, erosion, domestic animals, wild animals and disease and
were ranked by the farmers in this order (Roder et al., 1995).

25. Study Site Description ǁ Methodology
11
3 Methodology
To investigate the study objective, a methodology with a mix of qualitative and quantitative
methods was employed. This allowed for triangulation and a better understanding of the overall
agricultural management practices as socio-economic influences are often lost in strictly quantitative
studies. Living within the community as an active participant gave deeper insight and was an
enriching experience. Interviews were communicated through the help of a translator.
3.1 Study Site Description
The study was carried out in Lao PDR (Figure 4), a
developing country where shifting cultivation is the
main land use strategy of the rural villages in the
upland areas (Roder, 1997). Lao PDR has the greatest
extent of shifting cultivation than any other country in
Southeast Asia where an estimated 6.5 million
hectares of upland area is used (Schmidt-vogt et al.,
2009).
Fieldwork was conducted in Ban Navene, a remote
village located in the northern province of
Louangphabang (20°22’48”N, 103°10’85”E; Figure 4).
Ban Navene consists of 76 ethnic Khamu households
that are characterised by subsistence farming (Figure
5). Both upland and padi rice are cultivated in the area
and are the principal components in their diets; 27
households exclusively rely on upland rice cultivation
while the remaining rely on a combination of the two.
Each household additionally cultivates a small
vegetable garden to supplement food products found in the surrounding forest. Maize cultivation
as a cash crop is gaining momentum among the farmers; at the time of fieldwork, 45 households
were under a contract agreement with the maize company, Thong La, to whom they exclusively sold
to.
Figure 4: The location map of Lao PDR indicating
approximate location of the study site (red square)
and Ban Navene, a village in the Viengkham district of
the northern province of Louangphabang (shaded
pink). Adapted from Hett et al. (2012)

26. Methodology ǁ Study Site Description
12
Figure 5 : A schematic drawing representing Ban Navene and its surrounding fields and crop types.
Original land use map was drawn at the introductory meeting with the Headman, Assistant Headman
and key village elders (20/09/2012). Past DAFO boundary maps were used as references. The locations
of the upland rice fields used in the study are labeled.
There are a total of 60 ha of padi rice in Ban Navene, a quality that sets the village apart from its
equally-impoverished neighbours and is the major driving force for the influx of new families. Water
is supplied to a proportion of the fields by a large-scale irrigation system built by the District
Agricultural and Forestry Office (DAFO) in compensation for the land lost with the establishment of
the Nam Et – Phou Louey National Protected Area (NEPL NPA) in 2001. In addition to the irrigation
system, a dirt road from Nam Xoy was built, fish ponds were established and families were given
‘replacement’ fields if any were lost to the NEPL NPA. Policy changes were invoked to restrict or
minimise resource extraction from the NEPL NPA; hunting and cultivation within the boundary is
illegal and non-timber forest products can only be collected within specified months.
Shifting cultivation is still practiced by the villagers whereby one cropping of upland rice is cultivated
after the area is slashed-and-burned and then left for fallow. There are numerous local varieties of
upland rice grown in the area and all are of the ‘middle-season’ harvest type. Additional crops, such
as local varieties of squash, sesame, green bean, Job’s tears (Coix lacryma-jobi), pigeon pea (Cajanus
cajan) and ‘man pao (Pachyrhizus erosis)’ are scattered amid the upland rice. In the 1980s, fallow
lengths were of longer durations of those employed now; lengths were upwards of 15 years but
many are now in the range of two to eight years. This trend is largely due to the Lao government
policy whereby a family is restricted to three or four upland fields, shortening the possible length of
the entire cycle.

27. Identification of Fields ǁ Methodology
13
3.2 Identification of Fields
Prior to field selection, an introductory meeting was held with the Headman, Thong Phouy, and
village elders to obtain a general overview of the area, farming strategies and trends. Furthermore, a
land use village map was drawn (Figure 5); this map was used as a basis to where suitable fields may
be located and to ensure the fields were spatially distributed. An exception is the five-year fallow
fields wherein two are situated in close proximity of one another due to time constraint and low
field numbers. The fallow categories defined were based from the discussion which also helped to
ensure all three parties, meaning the village members, the translator and the researcher had the
same definition of the term ‘fallow length.’
Upland rice fields with various lengths of preceding fallow were needed to investigate the effects on
soil quality and rice yield; three fields for each fallow category (two to three years, five years and ten
to eleven years) were identified by conducting short surveys with households using convenience
sampling; respondents were selected on the basis of whether they were present in the village, had
the time and owned upland rice fields (Appendix 1.1).
The purpose of the short survey was not only to identify the fallow lengths of the field but also to
collect data on variables such as family size (linked to available labour), land use history and the
general economic standing of the farmer (i.e. what other crops they grow as this will affect the
available labour and time). The short survey also ensured that all the fields used had a good quality
burn. If there was some degree of uncertainty in the ownership and the length of the preceding
fallow, it was then excluded. The slope gradient and base soil type were assessed of potential fields
to ensure similarity before selection; the altitudes ranged between 600 – 843 m ± 5 m with slope
gradients between 51 – 93% and were of the ultisol soil order. In total, nine fields were identified: a
two-year fallow (2F3), 2 three-year fallows (3F1 and 3F2), 3 five-year fallows (5F1, 5F2 and 5F3), 2
ten-year fallows (10F2 and 10F3) and an eleven-year fallow (11F1). Please refer to Appendix 2 for a
full field record of characteristics and harvest data and Appendix 3 for a field area map.
3.3 General Plot Layout
A visual survey was completed for each field where details such as aspect, topography, indications of
erosion and weed coverage were noted (Appendix 1.1). In each of the fields, a 15 m by 15 m plot
was established in the middle of the slope from which soil samples were collected. The five year
fallow fields had two additional plots made at the top and bottom to investigate the influence of
topography on soil quality and yield. The distance between the plots, however, could not be fulfilled
as depicted in Figure 6 (b); the five-year fallow fields had a length of approximately 70 meters thus
restricting the distance between the plots to only 5 meters, a weakness in the design.

28. Methodology ǁ General Plot Layout
14
a) b)
Figure 6: (a) Diagram depicting the plot design; red circles represent full soil pit sampling sites (down to 50
cm) whereas the ‘x’ represents the micro sampling sites (to 10 cm). Numbering scheme is from left to right
with ‘1’ at the top left and ‘9’ at the bottom right. For the five year fallows, three plots were placed down
the slope and plot yields were also assessed, as depicted in (b).
3.3.1 Soil Sampling and Analysis
Soil samples were collected at the soil surface, 10 cm and, for the pit profiles, also at 30cm with 100
cmᶟ cores. Pit profile descriptions (i.e. colour according to the 7.5 YR Munsell Colour Chart, texture
via the feel method as described by the FAO Soil Description Guidelines, 2006, and descriptive
remarks) were recorded. Sampling depths were adjusted if a horizon boundary transected at the
desired depth and occurrences were noted. Samples were dried, weighed and crushed. If a sample
contained more than 5% of its weight in stones, they were then weighed separately and bulk density
was corrected using a value of 2.6 g cm¯ᶟ for the stones.
The pit samples were analysed for a total of seven parameters: pH, cation exchange capacity (CEC),
total carbon, total nitrogen, plant-available phosphorus (P Avail), exchangeable potassium (K Exch)
and permanganate oxidisable carbon (Pox C). Clay content (%) and texture were measured for only
one complete pit profile in each plot. The micro samples were analysed for pH, total carbon, total
nitrogen and Pox C.
The dried crushed pit samples were forwarded to the Soils and Fertilizers Research Institute (SFRI) in
Hanoi, Vietnam for analysis: the ammonium acetate method (at a pH of 7) was used to find CEC, P
Avail was detected by the Bray II method and K Exch was found by extracting with 1M ammonium
acetate and measured by flame photometry (pers. comm. Tran Tien 15/03/13). The texture of one
pit profile from each plot was also characterised.
The analyses for Pox C and pH were carried out at the Department of Soil and Environmental
Resources of the Faculty of Agricultural Production at Maejo University in Chiang Mai, Thailand1
. pH
was determined in a 1:2.5 soil:water solution. Pox C concentrations of the surface and 10 cm
samples were determined by using the method as described by Weil et al. (2003): 2.5 g of crushed
soil was weighed in a 50 ml Falcon tube, to which 18 ml of milli Q water and 2 ml of 0.2 M KMnO₄
11
With the exception of the 30 cm samples where pH was measured in a 1:2.5 soil:water solution at the
Dept of Plant and Environmental Sciences in the Faculty of Science at the University of Copenhagen.

29. Calculations and Statistical Analysis ǁ Methodology
15
were added. Due to previous observations, shaking time was doubled from two to four minutes.
After a settling time of 10 minutes, 1 mL of the supernatant was transferred to a new Falcon tube
with 19 ml of milli Q water. Absorbance was measured at 550 nm by spectrophotometry. Samples
were analysed in batches of five to maintain consistency. Please refer to Appendix 1.3 for full
protocol and Appendix 1.4 for the standard curve found for the reduction of KMnO4.
The total carbon and nitrogen content of all samples were determined using the Isotope Ratio Mass
Spectrometer at the Department of Agriculture and Ecology in the Faculty of Science at the
University of Copenhagen.
3.3.2 Yield Assessments
Upland rice yield was assessed directly from the 15 m by 15 m plots of the three five-year fallows (a
total of nine plots) in order to investigate if there is an influence from slope position. The plots were
harvested and weighed separately. Other yield assessments were based on the entire harvest where
the number of bags and average weight of a bag, based on three bags, were recorded in the field.
Plot-specific yield measurement was not done for these fields as it was deemed unnecessary as
separate harvesting did result in a certain degree of crop destruction; the three farmers of the five-
year fallows were compensated with two bags of rice each. The field perimeters, defined by the
farmers themselves, were tracked with a Garmin GPS to determine the area with Google Earth Pro
7.0. In order to determine the yield in terms of processed rice, 1 kg subsamples were dried in the
sun, milled and weighed.
3.4 Calculations and Statistical Analysis
The upland rice yield (kg ha¯¹) was calculated by:
[(No. of Bags x Weight (kg))-(No. of Bags x Weight of casing (kg))] / Area (ha)
Processed rice yields were found by multiplying the above equation with the weight of the milled
subsample.
The stock concentrations were calculated by multiplying the elemental concentration, bulk density
and the soil depth. As analysis was not done according to soil horizons, the surface stocks were
extrapolated to a depth of 5 cm and the 10 cm stocks from 5 – 10 cm.
An equivalent mass approach was used to calculate the stocks of the upper 10 cm using the
following formula as described by Ellert (2001):
Upper 10 cm X = (BDSurface x ConcentrationSurface x 0.05 m)+ (BD10 cm x Concentration10 cm x T add(depth))
Where T add is the new depth if all samples are an equivalent mass, i.e. the average mass of the
upper 10 cm for the entire data set:

30. Methodology ǁ Calculations and Statistical Analysis
16
T add = [ Avg Mass 10 cm – ((BDSurface x 0.05 m) + (BD 10 cm x 0.05 m)) / BD 10 cm ]
A standard curve for the KMnO₄ reaction was first plotted using initial concentrations of 0.02M, 0.01
M and 0.005 M and was used to determine the final concentrations of MnO₄ in all of the reactions
(Appendix 1.4). To determine the concentration of Pox C, the following formula was then used:
Pox C (mg kg¯¹) = (0.02 mol l¯¹ - [MnO₄ Final]) x 9000 mg C mol
-1
x (0.02 l solution / 0.0025 kg soil)
Where 0.02 mol l-1
is the initial concentration of the MnO4, [MnO4 Final] is the final concentration
interpolated from the standard curve and 9000 mg in the amount of Carbon (mg) that is oxidized by
1 mol of MnO4.
The data set generated from the fallow length study was used to investigate the interactions
between parameters, the influence of fallow length on soil quality and yield levels. The
topographical study provided the data set used to analyse the effect soil quality has on yield levels,
as the specific plots were harvested, and the influence of slope position on soil quality and yield
levels. Statistical analyses were conducted using SPSS 16.0 for Windows. One-way ANOVAs, with
the Levene’s test for equality, were performed to assess for any differences in the measured soil
parameters. Least Significant Difference (LSD) post hoc tests, or Games-Howell Tests if homogeneity
in variance was not observed, revealed where the significant differences lied, if any. Independent t-
tests were used to assess differences in yields between the fallows due to the group size (there was
only one site for both the 2 and 11 year fallow). Multiple regression analyses were performed to
identify the factors affecting yield, where all parameter but the stock values were included as
independent factors. Pearson’s correlation tests were also applied.
Using the land use history obtained from the short survey, it was possible to calculate an adapted
Ruthenberg Index (R Index), a measure of land use intensity developed by Ruthenberg (1971), via
the following equation:
[Years cultivated / (Years cultivated + Years fallow)] x 100
In this adapted R Index, (Years cultivated + Years fallow) always equaled ten years as this history was
available for all fields. The fields were then assessed as above but according to their R Index, which
meant that two 3-year fallows increased in their level of intensity to match those of the 5-year while
one 5-year fallow decreased to an intensity equal of the 2-year fallow.
The Accumulated Cropping index (ACi), a second measure of land use intensity, was adapted from
the Accumulated Farming Index developed by Birch-Thomsen et al.( 2007). Here each year was
assigned a value, i.e. the present year would be assigned a value of 10, the preceding year a value of
9 and so on, which would only be included in the calculated sum if it was a year of cropping. In this
way, more recent years have a bigger influence over the land use intensity. To clarify, the equation
is:
ACi = [Value cultivation yrs (10 present + 7if 2 year fallow+…)]

31. Constraints of Upland Rice Production ǁ Methodology
17
3.5 Constraints of Upland Rice Production
Roder (1995) has identified constraints of upland rice
production and, of these, ten were picked based on initial
findings to which would be of relevance to Ban Navene
(domestic livestock was not included, for example, as the
majority of farmers did not own grazing livestock): weeds,
pests (insects), disease, wild animals (i.e. wild boar), land
availability (includes shortened fallow length), rainfall, soil
suitability, labour availability, soil erosion and rodents.
Pair-wise ranking was conducted with twenty villagers at
random to investigate which identified factor was most
limiting in upland rice production in Ban Navene.
To alleviate miscommunication, flashcards for each factor
were made with a representational image and translated
both in Lao and Khamu (Figure 7). Flashcards were
presented two at a time whereupon the informant was
asked to identify which was the most constraining.
Responses were recorded in a matrix from which total
scores for each factor were calculated by summing up the
individual scores.
3.6 Farmers’ Perception
To gain a deeper insight into management practices and for
triangulation purposes, in-depth interviews were conducted with
the farmers of the nine chosen fields. Questions pertaining to
cycle management, assets (labour, financial), challenges and their
perspective on any changes in yields or soil quality were asked
(full guideline in Appendix 1.5). Their outlook on the soil quality
of their own fields and the attributes that make them suitable for
upland rice production led to a better understanding of the soil
and yield results. Overall, the interviews allowed for a holistic
perspective of the links within an agricultural system and how an
individual’s unique life story will shape management practices. To
understand the consequences of land allocation for conservation
projects, interviews were conducted with three families who
had lost land to NEPL NPA establishment (Appendix 1.6 for
question guideline).Figure 8: Sheang’s father, a key
informant for what characteristics,
physical and biological, are indicative
of a field with high quality for upland
rice production
Figure 7: The flashcards used for the
pairwise ranking method to assess
which factors constrain upland rice
production

32. Methodology ǁ Future Perspectives
18
A field walk with a key informant, Sheang’s father, was carried out with focus placed on what singles
out a field of higher quality (Figure 8). Sheang’s father was chosen as a key informant because he
appeared to have extensive knowledge on this topic from a prior informal discussion. The walk was
through the surrounding upland fields of Ban Navene during which Sheang’s father identified fields
with fertile soil, indicated by the presence of specific plants and soil characteristics (i.e. colour), and
the general physical properties that reflect suitability for upland rice (i.e. slope gradient).
As mentioned, every day discussions and observations enhanced results by allowing for a better
understanding of how such developing villages respond to change, be it in policy or the
environment. General discussions were had with many informants; some of which are the
Headman, Thong Phouy, a volunteer forest officer, and an officer from DAFO, Phaeng Xaphokhame
(who also acted as a translator).
3.7 Future Perspectives
Thong Phouy, the Headman, was a valuable resource
in understanding how the villagers of Ban Navene
perceive their future. He was involved in the
introductory meeting, where the community map was
drawn, the timeline exercise and the group meeting.
General discussions with him touched upon many
subjects of which include but are not restricted to
policy changes, future endeavors, maize production
and community forest management.
A group meeting was held with Thong Phouy, the
assistant headman, Siphet, the women’s group head,
Von Shaeng, and the nine selected farmers to discuss
two main topics: the decreasing trend in labour supply in Ban Navene and governmental policies,
specifically the restriction of three to four upland fields per family and the 2020 policy in which the
Lao Government hopes to stop all slash-and-burn activity (Figure 9). These two topics very much
touched upon the future of Ban Navene and how the challenges may be overcome. Additionally, the
participants were asked what they feel is required for Ban Navene to develop further and what
social programmes would help in reaching their goals. Please refer to Appendix 1.7. for guiding
questions of the group interview.
Figure 9: The participants of the group
meeting held at the Ban Navene School;
some attendees are missing from the
picture

33. Soil Quality Analysis ǁ Results
19
4 Results
4.1 Soil Quality Analysis
There are two sets of quantitative data:
1. Soil and yield data from nine fields of fallow lengths from 2-11 years.
2. Soil and yield data from three 5-year fallow fields whereby each had three sampling plots,
giving a total of nine plots.
The first set of data is used to investigate the interactions between soil parameters and the overall
influence of fallow length. The second set of data better represents the links between yield and soil
parameters as yield measurements are taken directly from the marked plots, hence it is used to
identify the influence of the soil quality on yield. Additionally, topographical influence on soil quality
and yield is also explored using this set. Refer to 3.3 General Plot Layout in the Methodology section
for full details of experimental set-up, collection and assessment.
Please refer to Appendix 2 for an inventory of the field codes and their characteristics, i.e. area,
slope gradient. For the map of the areas of each field site, please refer to Appendix 3. The soil
parameter averages are organised in tables according to the two studies, fallow length and
topographical, and can be found in Appendix 4.
4.1.1 General Soil Description
The ranges found for the soil parameters are typical of a tropical ultisol
with kandic horizons (Table 1, 2 and 3) and fall within those found by
Roder et al (1995) in a study also conducted in Northern Lao P.D.R.
Ultisols are extensively found in humid forested areas (Weil and Brady,
1999).
The soils in the Ban Navene area are quite acidic (4.60 – 5.05), clay or
clay loam in texture and with clay in the upper 10 cm ranging between
363 – 487 g ∙ kg¯¹. The topsoil is thin, fine and is either a deep
brown/black colour or bleached (Figure 10). The accumulation of Fe-
and Al-oxides, characteristic of kandic horizons (Weil and Brady, 1999),
is evident by the red colour of the subsurface horizons (Figure 10). The
soils contain charcoal and quartz fragments (Figure 10).
Conventionally, ultisols can be quite productive with adequate fertilizer
and liming (Weil and Brady, 1999); however, the farmers in Ban
Navene do not use any fertilizer or lime, removing chemical additives
as a possible influencing factor.
Figure 10: Soil profile of the ultisol
typical for the Ban Navene area

34. Results ǁ Soil Quality Analysis
20
4.1.2 Soil Parameter Interactions
The Pearson’s correlation coefficient test revealed the linear relationships between the parameters
and how they may interact. Results involving the physical soil parameters are presented first
followed by those involving SOC. It should be noted that CEC and pH display minimal or no
correlations with the investigated soil parameters, a surprising result as they are known to
theoretically influence the nutrient availability (i.e. K Exch, P Avail) in a soil. Only two significant
correlations were found: pH and stock K Exch show a positive medium-strength correlation
(r=0.578**) at the surface, and pH and bulk density exhibit a weak positive correlation at the surface
and at 30 cm (Table 1 and 3).
The results may not be fully indicative of the true links between the soil parameters as relationships
may not be linear and, thus, would be deemed insignificant. In general, it must be kept in mind that
the overall sample size is quite small, especially when interpreting the correlations found involving
clay.
4.1.2.1 Interactions of Physical Soil Parameters
Many of the correlations at 10 cm parallel those found at the soil surface though to a lesser degree
as the soil will be less exposed to environmental and management effects. Therefore, the soil
parameters are influenced by soil depth: they decrease with soil depth except for bulk density, clay
content and SOC:Pox C depicted by Table 1 (soil surface), 2(10 cm) and 3(30 cm).
The soil physical parameters, bulk density and clay content, show a significant correlation to each
other and to those pertaining to carbon and nitrogen content (Table 1, 2 and3). Bulk density and
clay are positively correlated (Table 1 and 2). Both show an inverse relationship with carbon (SOC %
and Pox C) and nitrogen (N %) content (Table 1 and 2). At 10 cm, however, clay content is only
negatively correlated to N % (Table 2). Only bulk density interacts with potassium and phosphorus;
at the surface, P Avail shows a weak negative correlation (Table 1), while at 10 cm, K Exch has a
strong negative correlation to bulk density (Table 2).
Significant correlations between the soil parameters at 30 cm are few, evident from Table 3 where
all significant correlations are shown. Bulk density is positively correlated with pH and negatively
correlated with both SOC % and N % (Table 3). Clay content is correlated to SOC% (Table 3), N% (r=-
0.575**) and stock N (r=-0.498**).

35. Soil Quality Analysis ǁ Results
21
Table 1: The range and correlations of soil parameters at the soil surface of fields under shifting cultivation management and after one harvest of upland rice; based on nine
fields with fallow lengths from two to eleven years.
Correlation Coefficient (r)¹
Soil Parameter Range Clay Bulk Density CEC pH SOC % SOC Stock Pox C SOC: Pox C N % Stock N SOC : N P Avail K Exch
Clay (g·kg¯
1
) 367 - 450
Bulk Density (g∙m¯ᶟ) 558 - 934 0.716**
CEC (cmol(+) kg¯¹) 11.5 - 14.0 ns ns
pH 4.64 - 5.05 ns 0.445* ns -
SOC % 3.00 - 4.59 -0.631** -0.627** ns ns
SOC Stock (kg · m¯²) 1.27 - 1.79 ns 0.330** ns ns 0.490**
Pox C (mg·kg soil¯¹) 808 - 1143 -0.595** -0.728** ns ns 0.792** ns
SOC : Pox C 36.6 - 41.5 ns ns ns ns 0.683** 0.618** ns
N % 0.28 - 0.39 -0.687** -0.592** ns ns 0.835** 0.424** 0.779** 0.502**
Stock N (g · m¯²) 105 - 160 ns 0.523** ns ns ns 0.851** ns 0.347** 0.353**
SOC : N 10.8 - 12.1 ns -0.331** ns ns 0.677** 0.331** 0.383** 0.557** ns ns
P Avail (mg·100g soil¯¹)
0.409 - 3.38 ns -0.433* ns ns 0.389* ns 0.540** ns 0.443* ns ns
K Exch (mg·100g soil¯¹) 12.6 - 32.1 ns ns ns ns ns ns 0.415* ns ns ns 0.516** ns
¹Analysed by the Pearson’s Correlation Test via SPSS 16.0 at a confidence level of 95%,(*) or of 99% (**). n = 81 for bulk density, Pox C, SOC %, N%, SOC : Pox C, SOC Stock, SOC:N, Stock
N and pH; n = 27 for CEC, P Avail, K Exch; n = 9 for clay

36. Results ǁ Soil Quality Analysis
22
Table 2: The range and correlations of soil parameters at a 10 cm depth of fields under shifting cultivation management and after one harvest of upland rice; based on nine
fields with fallow lengths from two to eleven years.
Correlation Coefficient (r)¹
Soil Parameter Range Clay Bulk Density CEC pH SOC % SOC Stock Pox C SOC : Pox C N % Stock N SOC : N P Avail K Exch
Clay (g·kg¯
1
) 363 – 521
Bulk Density (g∙m¯ᶟ) 818 - 1102 0.532**
CEC (cmol(+) kg¯¹) 11.5 – 15.5 ns ns
pH 4.60 – 4.86 ns ns ns -
SOC % 2.07 – 3.58 ns -0.680** ns ns
SOC Stock(kg · m¯²) 1.12 – 1.46 ns ns ns ns 0.732**
Pox C (mg·kg soil¯¹) 556 - 770 ns -0.363** -0.461** ns 0.830** 0.592**
SOC : Pox C 37.6 – 47.6 ns -0.321** ns ns 0.422** 0.325** ns
N % 0.22 – 0.31 -0.539** -0.696** ns ns 0.907** 0.646** 0.743** 0.439**
Stock N (g · m¯²) 119 - 141 ns 0.258* ns ns 0.345** 0.793** 0.248* 0.235** 0.494**
SOC : N 9.25 – 11.39 ns -0.390** ns ns 0.758** 0.604** 0.656** 0.230* 0.423** ns
P Avail (mg· 100g soil¯¹)
0.201 -0.376 ns ns ns ns 0.420* ns ns ns ns ns ns
K Exch (mg·100g soil¯¹) 6.42 – 15.3 ns -0.640** ns ns 0.439* ns 0.431* ns 0.420* ns ns ns
¹Analysed by the Pearson’s Correlation Test via SPSS 16.0 at a confidence level of 95%,(*) or of 99% (**). n = 81 for bulk density, Pox C, SOC %, N%, SOC STOCK : Pox C, SOC Stock,
SOC:N, Stock N and pH; n = 27 for CEC, P Avail, K Exch; n = 9 for clay

37. Soil Quality Analysisǁ Results
23
Table 3: The range in soil parameters at depths of thirty cm of fields under shifting
cultivation management and after one harvest of upland rice; based on nine fields with
fallow lengths from two to eleven years
Correlation Coefficient
(r)¹
Soil Parameter Range Bulk Density SOC %
Clay (g·kg¯¹)² 333 - 526 ⁿ⁼
7
ns -0.512**
pH 4.77 - 4.95 0.427* ns
CEC (cmol(+) kg¯¹) 11.4 - 13.7 ns ns
P Avail (mg·100g soil¯¹) 0.06 - 0.22 ns ns
K Exch (mg·100g soil¯¹) 3.67 - 6.90 ns ns
Bulk Density (g∙m¯ᶟ) 990 - 1192 - -
SOC % 1.24 - 1.93 -0.488** -
N % 0.16 - 0.29 -0.556** 0.843**
¹Analysed by the Pearsons Correlation Test via SPSS 16.0 at a confidence level of 95%
(*) or of 99% (**). n = 81 for bulk density, SOC %, N%, pH; n = 27 for CEC, P Avail, K
Exch; n = 9 for clay, ²Range in clay content for surface and 10 cm samples; 3F1 was
237 & 11F1 was 184, both excluded
4.1.2.2 SOC Influence on Soil Parameters
The Pearson’s correlation coefficient test revealed that SOC is correlated with the majority of the soil
parameters investigated at both the soil surface and at a 10 cm depth (Table 1 and 2). This indicates
the high degree of influence SOC has on soil quality and thus will be discussed as a key variable. SOC
is negatively correlated with the physical properties of a soil (i.e. bulk density and clay content) while
showing no correlation with CEC and pH (Table 1 and 2).
SOC is correlated with the nutrient levels (N, P, K) found in soil (Table 1 and 2). SOC % and N%
appear to be covariates, evident from their strong correlation at all three depths and a mirroring in
their general interactions to the other soil parameters (Table 1 and 2, Figure 11). The average C:N
ratio at the surface is 11.4, slightly higher than that of 10 cm but is still generally quite low (Figure
11). SOC % has a weak positive correlation with P Avail and K Exch; P Avail is correlated at both soil
depths while K Exch is only at 10 cm (Table 1, Figure 12). Figure 12 points to possible outliers:
1. The P Avail outlier depicted in 12a is a sample from 11F3, a low-yielding field,
and was re-tested.
2. 12b indicates three K Exch outliers: two are from 2F3 and one is from 11F3, both
low-yield fields. Unfortunately re-tests were not done as decisions were based
on whether the results followed the general observed pattern (or ratio, when
compared to P Avail for instance) and cost.

38. Results ǁ Soil Quality Analysis
24
.
Figure 11: Relationship between carbon and nitrogen soil content at the surface and at a depth of 10 cm,
depicted by SOC % and N%. Individual points colour-coded according to fallow length and yield level
(kg∙ha¯¹): blue is 2, 3 or 11-year fallow and below 1000, red/pink is 5 or 10-year fallow and above 1000 and
green is 10F3, a 10-year fallow with the highest yield, 1552; lighter colours represent data points
corresponding to levels at 10 cm. Soil samples were taken after the harvest of one cropping of upland rice.
Analysed using the Pearson’s correlation coefficient test at a confidence level of 99% (**). n=81
11.4
9.94
0,00
0,10
0,20
0,30
0,40
0,50
0,60
0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00
N%
SOC %
Surface
10 cm
Surface C:N
10 cm C:N
r S
= 0.835**
r 10
= 0.907**

39. Soil Quality Analysisǁ Results
25
Figure 12: Relationship between SOC % and a) P Avail and b) K Exch at the soil surface and at a depth
of 10 cm. Individual points colour-coded according to fallow length and yield level (kg∙ha¯¹): blue is 2,
3 or 11-year fallow and below 1000, red/pink is 5 or 10-year fallow and above 1000 and green is 10F3,
a 10-year fallow with the highest yield, 1552; lighter colours represent data points corresponding to
levels at 10 cm. Soil samples were taken after the harvest of one cropping of upland rice from fields.
Analysed using the Pearson’s correlation coefficient test at a confidence level of 95%. n = 27
0,00
1,00
2,00
3,00
4,00
5,00
6,00
7,00
0,00 1,00 2,00 3,00 4,00 5,00 6,00
PAvail(mg·100gsoil¯¹)
SOC %
r S
= 0.389*
r 10
= 0.420*
a)
b)
0,00
10,00
20,00
30,00
40,00
50,00
60,00
0,00 1,00 2,00 3,00 4,00 5,00 6,00
KExch(mg·100gsoil¯¹)
SOC %
Surface
10 cm
Surface
10 cm
r 10
= 0.439*

40. Results ǁ Soil Quality Analysis
26
4.1.2.3 A Closer Look at Pox C
At 10 cm CEC shows an inverse relationship with Pox C levels (Table 2). Pox C has a strong positive
correlation with SOC % at both depths; the correlation is stronger at a depth of 10 cm than at the
soil surface (Table 1 and 2, Figure 13). The ratio between SOC and Pox C is 39.6 at the soil surface
and 44.0 at 10 cm, indicating the relative pool sizes (Figure 13).
Pox C displays similar correlations with soil nutrients (i.e. N%, P Avail and K Exch) as SOC % (Table 1
and 2, Figure 14). Pox C is stronlgy positively correlated with N % at both depths (Figure 14). It has
a weak relationship with the SOC:N ratio (Table 1 and2).
At the soil surface P Avail has a stronger positive correlation to Pox C than to SOC%; however this
relationship disappears at 10 cm (Table 1 and 2). K Exch displays positive correlations with Pox C at
both depths; a trend which SOC% does not follow as it displays no significant relationship with K
Exch at the soil surface (Table 1 and 2).
39.6
44.0
0
200
400
600
800
1.000
1.200
1.400
1.600
0,00 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00
PoxC(mg·kgsoil¯¹)
SOC %
Surface
10 cm
Surface SOC:Pox C
10 cm SOC:Pox C
Figure 13: The relationship between SOC % and Pox C at the soil surface and at a depth of 10 cm. Individual
points colour-coded according to fallow length and yield level (kg∙ha¯¹): blue is 2, 3 or 11-year fallow and
below 1000, red is 5 or 10-year fallow and above 1000 and green is 10F3, a 10-year fallow with the highest
yield, 1552; lighter colours represent data points corresponding to levels at 10 cm. Soil samples were taken
after the harvest of one cropping of upland rice. Analysed by the Pearson’s correlation test at a confidence
level of 99% (**), n = 81
r S
= 0.792**
r 10
= 0.830**

41. Implications of the Soil Quality on the Yield of Upland Riceǁ Results
27
4.2 Implications of the Soil Quality on the Yield of Upland Rice
The yield in the local, mid-season varieties of upland rice ranged from 517.35 – 1552.22 kg · ha¯¹.
The processing of rice grains resulted in a loss of 40% in weight, i.e. 1 kg of un-milled and un-
threshed grain gave approximately 600 g of finished rice.
4.2.1 Soil Parameter Influences on Yield
Statistical analysis, via Pearson’s correlation coefficient test, revealed links between soil parameters
and yield, indicating that the overall soil quality does influence upland rice yield. Soil parameters
that are directly correlated to yield are pH, bulk density, SOC %, Pox C and N%.
There is a strong negative correlation between both yield and pH, depicted by Figure 15, and yield
and bulk density.
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
0,50
0 200 400 600 800 1000 1200 1400 1600
N%
Pox C (mg ∙ kg soil¯¹)
Surface
10 cm
Surface
10 cm
r S
= 0.779**
r 10
= 0.743**
Figure 14: Relationship between Pox C and N% at the soil surface and at a depth of 10 cm. Individual
points colour-coded according to fallow length and yield levels (kg∙ha¯¹): blue is 2, 3 and 11-year fallow
and below 1000, red/pink is 5 or 10-year fallow and above 1000 and green is 10F3, a 10-year fallow with
the highest yield, 1552; lighter colours represent data points corresponding to levels at 10 cm. Soil
samples were taken after the harvest of one cropping of upland rice from fields. Analysed using the
Pearson’s correlation test at a confidence level of 95%. n = 81

42. Results ǁ Implications of the Soil Quality on the Yield of Upland Rice
28
The significant correlations between Pox C and yield will be of focus as it has a stronger correlation
to yield than SOC% (Pox C rSurface = 0.517** and r10 = 0.554**, SOC % rSurface = 0.497** and r 10 = 436*)
(Figure 16).
Figure 16: The relationship between upland rice yield and Pox C at the soil surface and at depth of
10cm of fields with five-year preceding fallows. Soil samples were taken after the harvest of one
cropping of upland rice. Analysed by the Pearson’s Correlation Coefficient test at a confidence
level of 99% (**), n=27
0
200
400
600
800
1.000
1.200
1.400
1.600
3,50 3,70 3,90 4,10 4,30 4,50 4,70 4,90 5,10 5,30
Yield(kg·ha¯¹)
pH
Surface
10 cm
30 cm
rS= -0.635**
r10= -0.716**
r30= -0.515**
0
200
400
600
800
1000
1200
1400
1600
1800
0 250 500 750 1000 1250 1500
Yield(kg∙ha¯¹)
Pox C (mg · kg¯¹)
Surface
10 cm
Surface
10 cm
rS = 0.517**
r10 = 0.554**
Figure 15: The relationship between upland rice yield and pH at the soil surface and at depths of 10cm
and 30 cm of fields with five-year preceding fallows. Soil samples were taken after the harvest of one
cropping of upland rice. Analysed by the Pearson’s Correlation Coefficient test at a confidence level of
99% (**), n=27

43. Implications of the Soil Quality on the Yield of Upland Riceǁ Results
29
Pox C and N % have a strong positive correlation at both depths. When paired with yield data, it
appears that a Pox C level above 1000 mg ∙ kg soil¯¹ with a N % above 0.35% leads to a higher yield in
upland rice; the majority of the data points from the field with the highest yield are above 1000 mg
Pox C ∙ kg soil¯¹ and all have at least 0.35% N (Figure 17a, red outline). The C:N ratio appears to also
influence yield to some degree; a C:N ratio of 11 will result in a higher yield of upland rice (Figure
17b, red line).
The links between upland rice yield, Pox C and P Avail are not clear (Appendix 5.1, Fig. B (a)) though
Pox C and P Avail do have a strong positive correlation. The same pattern is observed with K Exch
Figure 17: The relationship between upland rice yield, Pox C and a) N% and b) C:N at the soil surface and
at a depth of 10cm of fields with five-year preceding fallows. Soil samples were taken after the harvest
of one cropping of upland rice. Individual points are colour coded according to yield levels (kg ∙ ha¯¹):
below 1000 is depicted with blue, above 1000 is red/pink and the highest yield (1432) is coded green;
lighter colours represent data points corresponding to levels at 10 cm. Analysed by the Pearson’s
Correlation coefficient test at a confidence level of 99% (**), n=81
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0,40
0,45
0,50
0 200 400 600 800 1.000 1.200 1.400 1.600
N%
Pox C (mg · kg soil¯¹)
r10
= 0.870**
r N%-yield
= 0.549**
rS
= 0.698**
0,0
2,0
4,0
6,0
8,0
10,0
12,0
14,0
16,0
18,0
0 200 400 600 800 1.000 1.200 1.400 1.600
SOC:N
Pox C (mg ∙ kg soil¯¹)
Surface
10 cm
Surface
10 cm
rS
= 0.508**
r10
= 0.594**
a)
b)

44. Results ǁ Implications of the Soil Quality on the Yield of Upland Rice
30
(Appendix 5.1, Fig. B (b)). There is a larger degree of variation in the data points whereby some high-
yielding fields have low P Avail or K Exch levels. It does appear, however, that once again a level
above 1000 mg Pox C ∙ kg soil¯¹ will translate to a higher yield (Appendix 5.1, Fig. B).
4.2.1.1 Regression Analysis
Table 4: Multiple stepwise regression results for the dependent factor,
yield, at the soil surface at a confidence level of 99% (p<0.05).
Independent factors included: bulk density, pH, Pox C, SOC:N, N% and
SOC %.
Variable Model 1 Model 2
pH -0.635 -0.515
Pox C 0.329
R² 0.403 0.497
R²Adjusted 0.379 0.456
n 27 27
Significant parameters found via the Pearson’s correlation coefficient test were then applied to a
multiple stepwise regression analysis to investigate which were explanatory factors for yield
variance. Two possible models explain the variance found in the yield of upland rice when using the
soil surface data (Table 4). In both, pH is a significant contributor. 40.3% (37.9% if adjusted) of the
variance observed is due to pH alone and, when coupled with Pox C, 49.7% of the variance (adjusted
45.6%) is accounted for (Table 4). The equations are: for Model 1, y =-610(pH) +3985, and for Model
2, y = 0.487(PoxC) – 495(pH) +2996.
Multiple stepwise regression analysis with the 10 cm data indicates that pH is the sole contribute to
the variance observed in yield, where R²= 0.513 (Adjusted R²=0.494, p= 0.000). Independent
variables included were: bulk density, pH, Pox C, C:N, N% and SOC %. There were no significant
models found at 30 cm. The equation for the model is y = -702 (pH) + 4347.

45. Implications of the Soil Quality on the Yield of Upland Riceǁ Results
31
4.2.2 Stock Values and Yield
A mass equivalent approach was used to calculate the upper 10 cm quantities of carbon and the
nutrients (N,P Avail and K Exch) due to the variation in bulk density; furthermore, Pearson’s
correlation coefficient test revealed stronger significant differences when the mass equivalent values
were used.
The mass equivalent (81 kg) in carbon stocks of the upper 10 cm was positively correlated with yield
(r=0.560, p<0.005) (Figure 18a). The strongest correlation was found between yield and nitrogen
stocks of the upper 10 cm (mass equivalent) where r=0.587 (p<0.005) (Figure 18b). No significant
relationship was found between yield and P Avail or K Exch; results appear to indicate there may be
a negative tendency between yield and P Avail (Figure 18c, d).
0
200
400
600
800
1000
1200
1400
1600
0,00 1,00 2,00 3,00 4,00 5,00
SOC (kg ∙ m¯²)
0
200
400
600
800
1000
1200
1400
1600
1800
0,00 0,10 0,20 0,30 0,40
N (kg ∙ m¯²)
0,00 0,20 0,40 0,60 0,80 1,00 1,20
P Avail (g ∙ m¯²)
0,00 5,00 10,00 15,00
K Exch (g ∙ m¯²)
Yield(kg∙ha¯¹)
a) c)
b) d)
r = 0.587**
r = 0.560**
Figure 18: The relationship between upland rice yield (kg·ha¯¹) and the upper 10 cm quantities, in equivalent
masses of soil, 81 kg, of a) SOC, b) N, c) P Avail and d) K Exch. Soil samples and yield measurements were
taken after the harvest of one cropping of upland rice from fields with a preceding fallow length of 5 years.
Analysed by Pearson’s correlation coefficient test at a confidence level of 95%. SOC and N, n=81; P Avail and
K Exch, n=27

46. Results ǁ System Influences
32
4.3 System Influences
4.3.1 Topographical Influence
Distances between the plots on the same slope were restricted to approximately 5 meters due to
total slope lengths of approximately 70 meters- a weakness mentioned in the plot layout design
(Refer to Methodology, 3.3 General Plot Layout). It was thought that the plots were placed too
closely to accurately reflect the relationship between the soil parameters and slope position. The
soil parameters in question were SOC, N and Pox C as the sampling spanned across three rows
within each plot; in other words, sampling was done at least every 5 meters down the slope (Refer
to Methodology, 3.3 General Plot Layout for sampling sites). However, this does not appear to have
skewed the soil results as ANOVA whereby each individual row was compared found no
contradicting results.
4.3.1.1 Impact on Soil Parameters
To investigate the influence slope position, or indirectly erosion, may have on soil quality, focus was
placed on the following parameters as it is thought they would be most likely affected: clay stock,
SOC stock, Pox C, N stock, P Avail stock and K Exch stock. Of those soil parameters, the clay content,
SOC stocks, N stocks and P Avail stocks were significantly influenced by slope position (Table 5 and
6).
Table 5 The clay and carbon content (0-5 cm) at the top, middle and bottom of a continuous slope. Samples
are from three fields with five-year preceding fallows and taken after the harvest of one cropping of upland
rice
Slope Position
Soil Parameter Top Middle Bottom
Clay (kg ∙ m¯²) 23.8 ± 2.0ᵃ 15.7 ± 2.5ᵇ 20.4 ±1.6ᶜ
SOC Stock (kg · m¯²) 1.50 ± 0.32ᵃ 1.43 ± 0.20ᵃᵇ 1.30 ± 0.25ᵇ
Pox C (mg·kg soil¯¹) 938 ± 192 978 ± 151 1004 ± 240
*Different letters within parameter categories indicate a significant difference,
analysed by ANOVA at a confidence level of 95%
Clay content displays a negative relationship with slope position; this specific dataset indicates that
the middle of a slope will have the least clay (Table 5). This pattern is reflected in bulk density as
samples with lower clay content appear to have lower bulk densities, although this result was not
significant.
The results indicate that carbon content is significantly affected by slope position as a negative
correlation was found; the top of a slope will have the largest SOC stock (Table 5). Pox C, although
not statistically significant due to the large standard deviation, interestingly depicts the opposite
trend with slope position (Table 5).