Long-term water modelling of the Soil-Plant-Atmosphere System

67 Pages·2013·7.9 MB·English

by  Julia Cavell

Long-term water modelling of the
Soil-Plant-Atmosphere System
- A study conducted for the growing of Grape Leaves with drip
irrigation in the Binh Thuan Province, Vietnam

S A R A A N D E R S S O N

J U L I A C A V E L L

S u p e r v i s o r

P r o f . P e r - E r i k J a n s s o n

C o - s u p e r v i s o r s
P r o f . V o K h a c T r i

M S c . T r a n T h a i H u n g

MJ153x Bachelor Degree Project in Energy and Environment
Stockholm 2013
Bachelor Degree Project by Sara Andersson and Julia Cavell

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Preface

This study has been carried out within the framework of the Minor Field Studies Scholarship
Programme, MFS, which is funded by the Swedish International Development Cooperation
Agency, Sida.

The MFS Scholarship Programme offers Swedish university students an opportunity to carry out
two months’ field work, usually the student’s final degree project, in a country in Africa, Asia or
Latin America. The results of the work are presented in an MFS report which is also the student’s
Bachelor Degree Project. Minor Field Studies are primarily conducted within subject areas of
importance from a development perspective and in a country where Swedish international
cooperation is ongoing.

The main purpose of the MFS Programme is to enhance Swedish university students’ knowledge
and understanding of these countries and their problems and opportunities. MFS should provide
the student with initial experience of conditions in such a country. The overall goals are to widen
the Swedish human resources cadre for engagement in international development cooperation as
well as to promote scientific exchange between unversities, research institutes and similar
authorities as well as NGOs in developing countries and in Sweden.

The International Relations Office at KTH the Royal Institute of Technology, Stockholm,
Sweden, administers the MFS Programme within engineering and applied natural sciences.

Lennart Johansson
Programme Officer
MFS Programme, KTH International Relations Office

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Bachelor Degree Project by Sara Andersson and Julia Cavell

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Long-term modelling of the Soil-Plant-Atmosphere System

Abstract
The main objective was to set up models of the soil-plant-atmosphere system for the growing
of Grape Leaves with drip irrigation in the Binh Thuan Province, Vietnam. The computer
software tool CoupModel was used in this modelling process. The focus of the model was the
systems soil hydraulics and the water balance between its components. When running several
21 years simulations it could be seen that slight variations in soil texture inputs resulted in
relatively big output changes. For example, by either using the soil texture laboratory results
or the soil water retention inputs gained from tensiometers and moisture meters in the field,
gave an annual irrigation amount difference of 100 mm. However, it can be questioned if the
models reached the goal of simulating an efficient irrigation schedule due to the soil
evaporation output being high throughout the year. For further research, longer time series of
field measurements together with more knowledge about the plant would be preferable in
order to validate and improve the model.

Keywords: Minor Field Study, CoupModel, Drip irrigation, Soil-Plant-Atmosphere System,
Vietnam, Grape Leaves, Hydrology.

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Bachelor Degree Project by Sara Andersson and Julia Cavell

Sammanfattning
Målet med denna studie var att upprätta modeller över mark-växt-atmosfär-systemet i
programmet CoupModel. Modellerna skulle anpassas för odlingen av vinblad med hjälp av
droppbevattning i Binh Thuan-provinsen i Vietnam. Fokus i denna studie var vattenflöden
och vattenbalansen mellan systemets komponenter. Efter att ha kört flera 21 år långa
simuleringar var det tydligt att små variationer i indata resulterade i relativt stora skillnader i
utdata. Om till exempel värden angående jordartens struktur erhållna från laboratoriet
användes istället för fältmätningar från tensiometrar och fuktmätare blev det en årlig
bevattningsskillnad på 100 mm. Det kan ifrågasättas huruvida målet att simulera en
vatteneffektiv bevattning blev nått då jordavdunstningen var hög året runt. För vidare studier
skulle längre tidsserier av fältmätningar tillsammans med mer kunskap om plantan vara
nyttigt för att kunna validera och förbättra modellen.

Nyckelord: Minor Field Study, CoupModel, Droppbevattning, Mark-växt-atmosfär-system,
Vietnam, Vinblad, Hydrologi.

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Long-term modelling of the Soil-Plant-Atmosphere System

Acknowledgement
First of all we wish to thank SIDA for granting us the Minor Field Study Scholarship. The
funding made it possible to carry out this project at location in Vietnam, turning this degree
project into an invaluable once in a lifetime experience.

We also wish to thank our supervisor Professor Per-Erik Jansson, from the department of
Land and Water Resources Engineering at the Royal Institute of Technology, for being so
supportive throughout the whole project. Providing us with everything from the contacts in
Vietnam to answering technical questions he has been of great help to us.

Last but not least, we wish to show the deepest gratitude to Professor Vo Khac Tri and
Msc. Tran Thai Hung, from Sothern Institute of Water Recourses Research, for being so
welcoming and helpful during our two months stay in Vietnam. All the results from the
laboratory and field site would have been impossible to obtain if it was not for them.

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Bachelor Degree Project by Sara Andersson and Julia Cavell

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Long-term modelling of the Soil-Plant-Atmosphere System

Table of Contents
Preface .................................................................................................................................... III

Abstract .................................................................................................................................... V

Sammanfattning ..................................................................................................................... VI

Acknowledgement ................................................................................................................ VII

1
  Introduction ........................................................................................................................ 1

1.1
  Literature overview .................................................................................................................. 2

1.1.1
  The basics of hydrology ...................................................................................................... 2

1.1.2
  The soil-plant-atmosphere system ....................................................................................... 3

1.1.3
  Unsaturated soils ................................................................................................................. 6

1.1.4
  Drip irrigation technique ..................................................................................................... 7

1.2
  Main objective and specific objectives .................................................................................... 8

2
  Methods ............................................................................................................................... 9

2.1
  Site description .......................................................................................................................... 9

2.2
  Meteorological data ................................................................................................................ 11

2.3
  Field studies ............................................................................................................................. 13

2.3.1
  Tensiometers ..................................................................................................................... 13

2.3.2
  Moisture Meter .................................................................................................................. 14

2.3.3
  Infiltration test ................................................................................................................... 14

2.4
  Laboratory ............................................................................................................................... 15

2.5
  Computer simulations ............................................................................................................ 16

2.5.1
  Soil profile ......................................................................................................................... 18

2.5.2
  Soil hydraulics ................................................................................................................... 19

2.5.3
  Plant physiology ................................................................................................................ 21

2.5.4
  Irrigation ............................................................................................................................ 22

2.5.5
  Soil evaporation ................................................................................................................. 23

3
  Results ............................................................................................................................... 25

3.1
  Field study results ................................................................................................................... 25

3.2
  Simulation Results .................................................................................................................. 26

4
  Discussion .......................................................................................................................... 39

4.1
  Differences between the two simulations Soil Water Retention Curves ............................ 39

4.2
  Changes in simulated soil evaporation ................................................................................. 40

4.3
  Possible Simulation Faults ..................................................................................................... 41

4.4
  Modelling approaches ............................................................................................................ 43

5
  Conclusion ......................................................................................................................... 45

References ............................................................................................................................... 47
Appendix A…………………………………………………………………………………………. I
Appendix B………………………………………………………………………………………… II
Appendix C………………………………………………………………………………………… V

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