Soil water repellency in red pine and hevea brasiliensis forest in thanh hoa province, viet nam

The priority of this research is simply describe method for determining the presence of water repellency in a soil by using a metal corer and applying Water drop penetration time WDPT te

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT

VIETNAM FORESTRY UNIVERSITY

STUDENT THESIS

SOIL WATER REPELLENCY IN RED PINE AND HEVEA BRASILIENSIS

FOREST IN THANH HOA PROVINCE, VIETNAM

Major: Natural Resources Management (Advanced Curriculum)

Code: D850101

Faculty: Forest Resources and Environmental Management

Class: K56 Natural Resources Management Course: 2011 - 2015

Advanced Education Program

Developed in Collaboration with Colorado State University, USA

Supervisor: Adjunct Associate Professor Dr Phung Van Khoa

Co-advisor: Professor Lee MacDonald

22Tr

Hanoi, October 2015

Firstly, I would like to express my sincere gratitude to my advisor Ph.DPhung Van Khoa for constant support and valuable guidance during the time of research and writing of this thesis

Secondly, I would also thank various professors of Forestry University and Colorado State University, especially professor MacDonald for providing classes and guidance for this project

Thirdly, I would like to thank people who working in Ha Trung and BaiChanh They provided good conditions when I conducted my research

Finally, I would like to thank my family for giving birth to me and supporting me spiritually throughout my life

Hanoi, November 2015

TABLE OF CONTENTS

ACKNOWLEDGEMENT 1

ABSTRACT 4

I INTRODUCTION 1

II GOAL AND OBJECTIVES 3

2.1 Goal 3

2.2 Specific objectives 3

III METHODS 4

3.1 Study sites 4

3.2 Sample sites 6

3.3 Water repellency assessment 6

3.4 Soil moisture 7

3.5 Data analysis 7

IV RESULTS AND DISCUSSIONS 8

4.1 Evidence of Water repellency (WDPT) 8

4.2 Soil moisture vs WDPT 11

V RECOMMENDATION 14

5.1 Effects of slight water repellency in study sites 14

5.2 Soil moisture 15

5.3 Research limitation 15

5.4 Further study 16

VI CONCLUSION 17

VII REFERENCES 18

There are evidences of water repellency in variety of soil conditions The priority of this research is simply describe method for determining the presence of water repellency in a soil by using a metal corer and applying Water drop penetration time (WDPT) test at different depths of soil samples Published study has showed that organic matter, burn severity, soil texture and soil moisture are some main factor that affect the severity of water repellency In this research, observations were made in order to identify the relationship between soil moisture, bulk density and WDPT WDPT presents strongest at the top soil and rarely appear at other depths The data suggest soil moisture threshold of approximately 2% for red pine forest and up to 16% for Heveabrasiliensis forest All data were collected under dry conditions from July, 8 to July,13, 2015 Each plantation type was assessed by 4 sample sites

I INTRODUCTION

Water repellencyis a natural occurring phenomenon that can be understood as the soil ability to prohibit water from wetting or infiltrating dry soil It has been described since 1910 when Schreiner and Shorey found some soils in California that could not be wetted and unsuitable for agriculture Since then, there was a remarkedly increase concern in water repellency, over 100 papers have been published It is of considerable interest because its presence can cause a marked reduction in infiltration rate which commonly presumed the primarily cause of the increase in runoff and erosion A number of factors are believed to control the strength of soil water repellency such as fire, vegetation type, soil texture, soil

moisture and time since burning (DeBano, 1981; de Jongeet al., 1999; DeBano, 2000a,

2000b; Doerr and Thomas, 2010) It is widely accepted that water repellency is caused by the presence of organic compounds with hydrophobic properties on soil particle surfaces

(Doerret al., 2000) Water repellency in soils has been reported worldwide in grasslands (Dekker and Ritsema, 1994), shrublands (Ferreira et al., 2005), croplands (Bisdom et al., 1993), areas burned by widefires (Huffman et al., 2001; MacDonald and Huffman, 2004),

golf greens (Miller and Wilkinson., 1997) and forests The forest vegetation types most

commonly associated with water repellency are evergreen tree species such as pine (Wahl et al., 2003; Keizer et al., 2005), as well as oak (Cedraet al., 1998) and eucalypt (Crockfordet al., 1991; Doerret al., 2002) species and tree with a considerable amount of resins, waxes or

aromatic oils are well presented (Doerr et al., 2000)

Given the background above and base on the fact that there is still little study about water repellency in Vietnam, this paper aims to find evidence of water repellency in some vegetation types in Vietnam Because of the limited time and money, this study just focus on vegetation types that provision a potential of water repellency in unburned area As mentioned above, water repellency are well presented in site that has a considerable amount

of resins, waxes and aromatic oils, therefore red pine forest and euphorbia forest were selected to be the study sites because those species produce a great amount of waxes and oils

to the surface layer Note that soil can be wetted after raining, therefore all the measurements were conducted under dry conditions, if there was any occurrance of rainfall then the measurement would be delayed by 4-5 days until the soil got dry again There are many techniques for measuring water repellency, this study apply the most common method called Water Drop Penetration Time (WDPT) In the WDPT test water drops are applied to the soil being tested and the investigator simply notes how long it takes until these water drops are absorbed into the soil ( Doerr, Shakesby and MacDonald, 2007) The samples were also taken and brought to lab in order to measeure moisture content and using graph to illustrate how soil moisture and WDPT interact The appropiate forest that can match the requirement of evidence of water repellency is red pine and hevea brasiliensis forest Thus, this study were conducted in Thanh Hoa province where available for a potential amount of those forests Experiments were taken place in July, 2015 under dry conditions

II GOAL AND OBJECTIVES 2.1 Goal

Assessing the soil water repellency in red pine forest and hevea brasiliensis forest

III METHODS 3.1 Study sites

Ha Trung district

The first investigation relating to soil water repellency in red pine forest took place in

Ha Trung Scientific research and forestry technology application center Ha Trungdistrict lies in the North part of ThanhHoa province, with the coordination: 19059 – 20009 N and

105045 – 105058 E The terrain gradually tilted from northwest to southeast The northwestern area is surrounded by many high hills which made the Ha Trung district, though plain but more diversity As the result, in rainy season, there's often flooding that put locals in many difficulties The average annualtemperature is 23oC in which the maximum temperature

is 41oC and and the minimum temperature is 6oC Average humidity range from 85% to 87% with highest peak 92% fall in January, February, in contrast, June and July record the lowest humidity The average annualprecipitation over the district is 1.700 mm It is reported that the highestannual precipitation peak at 2.800 mm and the lowest one is 1.100 mm Due to the unequal distribution of precipitation among months of the year, crop productivity has been strongly affected Rainy season often last from May to October with average 250-270 mm per month, precipitation with greater amount mainly appear in August, September and October,

in some particular year, it is up to 800 mm for just one month Dry season occurs from November to April of the next year [ ] Ha Trung district offers a fairly large forested area with variety of plants Total forestry area up to 2009 is 5.430,78 hectares in which 60% of those is productive forest land (3.436,39 hectares), 20% reserved forest and special forest accounted for 2%

Figure 3.1 Ha Trung Scientific research and forestry technology application center

(Google map)

Bãi Trành commune

Research on soil water repellency of hevea brasiliensis forestwas conducted in

BãiTrành, a village of NhưThanh district Longitude of NhưXuân: 109.141924 Latitude of NhưXuân: 12.287020

Figure 3.2 Bai Tranh commune, Thanh Hoa (Goole map)

3.2 Sample sites

At each plantation type, 4 separated sites were established in order to take soil sample and measure WDPT To take soil sample, a metal corer were used and soil sample were collected from the surface to the depth of 6 cm vertically after sweeping out all the dead leaves and others coverage materials , at deeper elevation, soil were taken horizontally The volume of a cylindrical cup is 100 ml Total of 8 samples from two plantations were surveyed from July, 8th to July, 12th, 2015 It is very important to preserve all soil samples before conducting experiment in lab, the collected soil then will be packaged in black plastics in order to prevent sunlight effect

3.3 Water repellency assessment

Water repellency test was taken in the field by using the WDPT test A set of 8 study sites were identified in July 2015 WDPT test was assessed at the mineral soil surface and depths of 3, 6, 9, 12 and 15 cm At each depth the WDPT was determined by applying at least five drops of water Drop penetration time was recorded using a stopwatch For field collection purposes, I used the following drop penetration time classification scheme: 0s - 1s

= not repellent, 1s - 5s = very low repellency, 5s - 30s = slight repellency, 30s - 180s = moderate repellency, and >180s = high repellency (Robichaud 1996) These water repellency indices were further modified by combining 0s to 1s and 1s to 5s, 30s to 180s and >180s to give the following classification scheme: 0s to 5s = wettable, 5s - 30s = slight water repellency and >30s = moderate and high repellency (Hubbert and Oriol 2005) The measurement was replicated 10 times at each depth and if the water repellency was found consistently from depth to depth, the measurement would be continued until 15 cm depth In contrast, if there was no water repellency at 3 cm, then 6 cm, we can decide not to test WDPT for the next depth The median time was used as the WDPT for that depth because it is less sensitive to extreme values ( MacDonald and Huffman, 2007)

3.4 Soil moisture

At each pit one soil sample is taken from 0-5 cm and another from 9-12 cm then weighted, dried and weighted again to detemine percent moisture The effect of soil moisture was analyzed by plotting surface soil moisture content against the WDPT values from 0 - 5

cm The WDPT data from 0 - 5 cm were used because these depths exhibited the strongest water repellency and were more accurately characterized by the 0 - 5 cm samples used to determine soil moisture Visual examination of these scatter plots was used to determine thehighest moisture content associated with evidence of soil water repellency The highest moisture content with evidence of soil water repellency was assumed to represent the soil moisture threshold for that burn severity class In this research, only soil from 0-5 cm depth was analysed and then plotted against WDPT in order to identify the relationship between those factors

3.5 Data analysis

The soil water repellency was first compared by depth at each plantation if evidence

of water repellency was found The first step is identify the relationship between WDPT and soil moisture in red pine forest Plot median of WDPT against soil moisture brought a graphical outcome that show how soil moisture has affected the time of a drop being absorbed into soil The second step is similarly plot WDPT agaisnt soil moisture in hevea brasiliensis forest in order to identify the relationship of them Then see if any similarity between these plantations It is advised that the surface soil would display the most significance of water repellency rather than other depths

IV RESULTS AND DISCUSSIONS 4.1 Evidence of Water repellency (WDPT)

Table 4.1 Median WDPT of red pine and he ea brasi iensis s

Site

Forest status

Figure 4.1 WDPT at different depth

surface 3cm depth 6 cm depth

0 10 20

0 5 10 15 20

Depth (cm)

Median WDPT

0 2 4 6 8 10

Depth (cm)

Median WDPT

0 2 4 6 8 10

Depth (cm)

Median WDPT

0 5 10 15

Depth (cm)

Median WDPT

It is clear that water repellency are well-presented at the surface of all sample sites However, there is a wide difference among time absorptions While site 1, 3, 4 (red pine) and

7, 8 (hevea brasiliensis ), time for penetrating a water drop can last for 58, 117, 50 and 96,

176 seconds respectively, other sites report much faster time for a drop penetration as just under 5 seconds Due to this wide difference, the median value of WDPT was put into consideration because it provides the most accurate index of soil water repellency, unlike the mean value which can be greatly affected by one or few drops with very long penetration times In addition, WDPT rarely exist at other depths, most of the data showed that there is a very weak water repellency that present at the depth of 3 cm , 6 cm and downward, it took only 1 to 3 seconds to absorb every drop This can easily be explained as in general, the top centimeters or decimeters of soil always contain organic molecules with hydrophobic properties According to Huffman, 2001, under unburned conditions, the soil water repellency is typically strongest at the surface of the mineral soil and drops off rapidly with depth In this observation, both type of plantations showed evidence of water repellency and indicated the strongest water repellency at the top soil minerals Median WDPT ranges from 5.5 - 17.5 seconds, the severity of water repellency in both forests is concluded as: slight water repellency

Figure 4.3 Water droplets resisting infiltration into soil due to water repellency

4.2 Soil moisture vs WDPT

Table 4.2 Median WDPT and Soil moisture

Site

Forest status

Soil moisture

Median WDPT (3cm depth)

Median WDPT (surface)

as about 15% in hevea brasiliensis forest and much lower with just about 2% in average in

red pine forest The results from soil moisture measurementsintwo plantations showed that when soil moisture increases, time required for a drop to be absorbed increases as well, this also means that the wetted soiled that caused by temporal weather condition such as rain or night-time fog will lead to a decline in the strength of soil water repellency However, other studies suggested that soils become less or even completely lose their water repellency as soil moisture increases According to Dekker, at a certain soil moisture, the soil changes from being water repellent to wettable, there is also evidence that soil moisture increase with increasing burn severity (MacDonald, Huffman, 2004)