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

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 Student: Le Huy Cong Student ID: 1153090917 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 ACKNOWLEDGEMENT 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 ABSTRACT I INTRODUCTION II GOAL AND OBJECTIVES 2.1 Goal 2.2 Specific objectives III METHODS 3.1 Study sites 3.2 Sample sites 3.3 Water repellency assessment 3.4 Soil moisture 3.5 Data analysis IV RESULTS AND DISCUSSIONS 4.1 Evidence of Water repellency (WDPT) 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 ABSTRACT 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, to July,13, 2015 Each plantation type was assessed by 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 * Hypothesis: - Soilwaterrepellency of the observed plantations is at slight severity ( with regard of median WDPT ranges from 5-30s) - Water repellency is indirect proportion to soil moisture II GOAL AND OBJECTIVES 2.1 Goal Assessing the soil water repellency in red pine forest and hevea brasiliensis forest 2.2 Specific objectives (i) measure the strength of soil water repellency at different soils depth in red pine, hevea brasiliensis forest (ii) relate the observed water repellency to vegetation type, soil moisture 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, 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 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 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 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 cm, then 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 - cm The WDPT data from - cm were used because these depths exhibited the strongest water repellency and were more accurately characterized by the - 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 hevea brasiliensis Forest Median WDPT Site status surface cm cm cm Red pine 10 x Red pine 8,5 1 x Red pine 1,5 x Red pine 17,5 1,5 x hevea brasiliensis 10 2,5 x hevea brasiliensis 2,5 x hevea brasiliensis 5,5 2 x hevea brasiliensis 11,5 x Red pine WDPT vs Depth hevea brasiliensis forest WDPT vs Depth 20 20 10 10 0 P1 surface P2 P3 3cm depth P4 P5 cm depth surface Figure 4.1 WDPT at different depth P6 P7 3cm depth P8 cm depth 20 12 10 15 10 Median WDPT Median WDPT 0 Depth (cm) Depth (cm) Plot Plot 20 15 10 Median WDPT 0 10 Median WDPT 9 Depth (cm) Depth (cm) Plot Plot 10 15 10 Median WDPT Median WDPT 0 Depth (cm) Depth (cm) Plot Plot 6 15 10 Median WDPT Median WDPT 0 Depth (cm) Depth (cm) Plot Plot Figure 4.2 WDPT at different depth in each plot 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, (red pine) and 7, (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 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 cm , cm and downward, it took only to 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 10 4.2 Soil moisture vs WDPT Table 4.2 Median WDPT and Soil moisture Forest Site Median WDPT Median WDPT (3cm depth) (surface) Soil moisture status Red pine 2,7 10 Red pine 1,0 8,5 Red pine 1,4 1,5 Red pine 3,1 17,5 hevea brasiliensis 16,9 2,5 10 hevea brasiliensis 15,9 2,5 hevea brasiliensis 13,4 5,5 hevea brasiliensis 19,9 11,5 In general, the soil moisture of these two forest types are fairly low, just under 20% With this soil moisture content, it is predicted that there would be very low water repellency because normally, water is highly attracted by dry soil Soil moisture of sites are fairly low 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) 11 Relationship between WDPT and soil moisture in red pine forest MEDIAN WDPT (S) 15 10 17.5 3,2 3.5 Soil moisture 2.5 2,6 10 8.5 1,0 1,4 1.5 1.5 2 SOIL MOISTURE (%) 20 Median WDPT 0.5 Median WDPT Relationship between WDPT and soil moisture in hevea brasiliensis forest 14 25 19,9 10 16,9 10 13,4 15 20 11.5 15,9 5.5 2.5 2.5 10 SOIL MOISTURE (%) MEDIAN WDPT (S) 12 0 Figure 4.4 Relationship between median WDPT and soil moisture At the beginning of this research, it was aimed to find the connection between soil moisture and water repellency at different depths According to the observation, water repellency was only performed at the surface layer, therefore it is not necessary to take soil from every depths (only need from 0-5 cm depth) for the measurement of moisture content In this case, the results indicated how soil moisture content interact with median WDPT of the soil surface from Euphorbia plots, as well as for red pine plots There was similarity in the absorption time at the depth of cm while more significant difference has shown for the topsoil With higher soil moisture, the drops need more time to be completely absorbed 12 * Correlation: Soil moisture vs.WDPT Correlation Soil moisture vs WDPT (red pine forest) 20 Median WDPT Median WDPT 15 y = 3.5018x + 3.7402 R² = 0.683 15 y = 0.9484x - 6.9635 R² = 0.9442 10 10 y = 0.432x + 0.7295 R² = 0.8843 Correlation Soil moisture vs WDPT( hevea brasiliensis forest ) WDPT (surface) Linear (WDPT (3cm)) y = 0.1513x - 0.0063 R² = 0.9729 Linear (WDPT (surface)) 0 soil moisture WDPT (3cm) 20 40 soil moisture Figure 6a: Correlation of soil moisture Figure 6b:Correlation of soil moisture and median WDPT in red pine forest and median WDPT in hevea brasiliensis forest These scatterplots illustrate how connect between soil moisture and WDPT at two different depths (3cm depth and topsoil layer) In both cases, it is more correlated at 3cm depth than at the surface The standard deviation were all greater than 0.6 which means the soil moisture in the surveyed forests were strongly connected with water repellency follow the upward linear function (y = ax + b) Clearly, a comparision of figure it is understood as when soil moisture content increases, the strength of water repellency increases as well This means soil with greater humid will absorb water slower than dry soil The soil moisture were up to 20% in dry condition, yet the lack of WDPT data at higher soil moisture content precludes the identification of soil moisture threshold at higher severity 13 V RECOMMENDATION 5.1 Effects of slight water repellency in study sites Clearly, the capacity of soil to infiltrate water in two plantations are still strong with very slight water repellent existance Therefore, its impact will be small which means the appearance of water repellency does not really matter to runoff and erosion in these two plantations Besides, by observation, water repellency was not an isolated factor to control infiltration rate, in Ha Trung centre, for example, the surface cover plays an important role in reducing the intention of waterdrops before reaching the surface Figure 5.1 Dead leaves and grasses to cover the surface of red pine forest In contrast, human disturbance in Bai Tranh must be noted as a real effect to the soil water repellency In hevea brasiliensis forest, trees were planted in line and the workers came there to take the sap twice a week In addition, in almost hevea forest, there were no surface cover and it all exposed to the sun and the rain To combine, workers' activities can cause compaction to the soil, sunlight can burn out the organic compounds easily and rainfall with high intensity can cause some detachment of soil particles 14 Figure 5.2 Hevea brasiliensis forest in Bai Tranh commune 5.2 Soil moisture The results showed for soil moisture were controversy to other studes and still need discussion Currents idea on soil moisture is that it can break down under prolonged contact with water and does not re-establish above a soil-specific moisture threshold The undone is whether in two plantations there was any threshold that could not found during the fieldwork 5.3 Research limitation First, it would be better if we study on both soil texture and soil moisture so that more conviniences can be made in comparision to water repellency Second, the study need to put emphasis on the effects of water repellency rather than just observe the norm In addition, the aims of this study is to find evidence of soil water repellency in different vegetation types especially forests, then two plantations is still an inappropriate number However, due to the limitation of time and money, this study can only made for two palntations 15 5.4 Further study In the future, study should be made in variety of plantations that available in Vietnam and from that we can draw a map of water repellent distribution in Vietnam plantations From this map we will know in which location, water repellency are strong or low then more emphasis would be devoted for plantations with high severity of water repellency To reduce it effects, what approach should be done is another key questions and it required our experts to get involve 16 VI CONCLUSION Water repellency was found in red pine forest and hevea brasiliensis forest in Thanh Hoa province with slight severity under dry condition It is clear that water repellency was well-presented at the topsoil layer and almost disappear at other depths Isolating from other effects, with slight severity of water repellency, the impacts are not significant Regarding to soil moisture content, as soil moisture content increases, there was also an increase in time of soil water absorption The average soil moisture is approximately 2% for red pine forest, 20% for hevea brasiliensis forest Overall, it is also needed to study how these water repellency influent the soil preventative under wet conditions, especially in rainy season 17 VII REFERENCES DeBano LF 1981 Water repellant soils: a state-of-the-art Gen Tech Rep PSW46, illus Pacific Southwest Forest and Range Exp Stn.,Forest Serv., US Dep Agric.: Berkley, CA; 21 Doerr SH, Shakesby RA and MacDonald LH, 2001 Chapter I.7 Soil water repellency: A key factor in Post-fire Erosion? Doerr SH, Shakesby RA, Wash RPD, 2000 Soil water repellency: its causes, characteristics and hydro-geomorphological significance Earth-Science Reviews 51(2000) 33-65 Doerr, SH., and A.D Thomas 2000 The role of soil moisture in controlling water repellency: New evidence from forest soils in Portugal J Hydrol (Amsterdam) 231-232:134147 Huffman EL, MacDonald LH, Stednick JD, 2001 Strength and persistence of fire-induced soil hydrophobicity under ponderosa and lodgepole pine, Colorado Front range Http://geography.swansea.ac.uk/hydrophobicity/publications.htm Hallett PD, 2007: An introduction to soil water repellency MacDonald LH, Huffman EL, Post-fire Soil Water Repellency: Persistence and Soil Moisture Thresholds Shakesby, R.A., S.H Doerr, and R.P.D Wash 2000 The erosional impact of soil hydrophobicity: Current problems and future research directions J Hydrol (Amsterdam) 231-232: 178-191 Wladitchensky, S.A 1966 Moisture content and hydrophobicity as related to the water capillary rise in soils Symp Int Assoc Sci Hydrol 82:360-365 18 ... Assessing the soil water repellency in red pine forest and hevea brasiliensis forest 2.2 Specific objectives (i) measure the strength of soil water repellency at different soils depth in red pine, ... status Red pine 2,7 10 Red pine 1,0 8,5 Red pine 1,4 1,5 Red pine 3,1 17,5 hevea brasiliensis 16,9 2,5 10 hevea brasiliensis 15,9 2,5 hevea brasiliensis 13,4 5,5 hevea brasiliensis 19,9 11,5 In general,... and hevea brasiliensis Forest Median WDPT Site status surface cm cm cm Red pine 10 x Red pine 8,5 1 x Red pine 1,5 x Red pine 17,5 1,5 x hevea brasiliensis 10 2,5 x hevea brasiliensis 2,5 x hevea