Temporal infiltration characteristics of soil under different ages of acacia plantation forest in luong son headwater, hoa binh, viet nam

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM NATIONAL UNIVERSITY OF FORESTRY STUDENT THESIS TEMPORAL INFILTRATION CHARACTERISTICS OF SOIL UNDER DIFFERENT AGES OF ACACIA PLANTATION FOREST IN LUONG SON HEADWATER, HOA BINH, VIETNAM Major: Advanced Curriculum in Natural Resources Management Code: D850101 Faculty: Forest Resources & Environmental Management Student: Dang Thi Thanh Hoa Student ID: 1553090300 Class: K60A - Natural Resources Management Course: 2015 – 2019 Advanced Education Program Developed in Collaboration with Colorado State University, USA Supervisor: Assoc Prof Bui Xuan Dung Hanoi, 2019 ACKNOWLEDGEMENT First of all, I would like to express my trustworthy respect to my supervisor – Assoc Prof Dr Bui Xuan Dung for his enthusiastic support with invaluable comments Additionally, I appreciated the support of other lectures during the time I analyzed the data Furthermore, I also thank to my friends when I started to set up in the field to collect and during the time I analyzed data They always give me the support whenever I needed regardless of hardship Finally, I respected local people who own the Acacia plantation model for allowing and provided me detailed information to conduct this research in this site and Hanoi, September 2019 i TABLE OF CONTENT ACKNOWLEDGEMENT i TABLE OF CONTENT ii LIST OF TABLE iv LIST OF FIGURE v ABSTRACT CHAPTER I INTRODUCTION CHAPTER II GOALS AND OBJECTIVES 2.1 Goal 2.2 Objectives CHAPTER III STUDY SITE AND METHODS 3.1 Study site 3.2 Methods 10 3.2.1 Temporal infiltration measurement 10 3.2.3 Soil properties 13 CHAPTER IV 16 RESULTS AND DISCUSSIONS 16 ii 4.1 Soil infiltration characteristics at different ages of Acacia plantation 16 4.1.1 Infiltration rate at different ages of Acacia plantation forest 16 4.1.2 Initial and stable infiltration rate of soil under six conditions 23 4.1.3 Total water infiltration in hour 28 4.2 Impact factors on Infiltration characteristics at different ages of Acacia plantation 30 4.2.1 Soil physical and vegetation characteristics at different ages of Acacia plantation 30 4.2.2 Affecting factors on soil infiltration at different ages of Acacia plantation 38 CHAPTER V 45 CONCLUSION 45 5.1 Conclusion 45 5.2 Limitations 46 5.3 Recommendations 46 REFERENCES 48 APENDIX 51 iii LIST OF TABLE Table 3.1 Data of infiltration in different ages Acacia Forest……………………… ……… 12 Table 3.2 Information of Survey plots ……………………………………………….……12 Table 4.1 Summary of the paired mean comparison of initial rate and stable rate at different ages of Acacia plantation……………………………………………………………….…… 27 Table 4.2 Vegetation characteristics at different ages of Acacia Plantation… …………… 29 iv LIST OF FIGURE Figure 3.1 The map of study site: a) Location of Hoa Binh province on Vietnam map; b) Location of Luong Son district on Hoa Binh map; c) Location of Truong Son commune on Luong Son map Figure 3.2 Contour map of study site: Figure 3.3 Morpholygy of Acacia mangium Figure 3.4 Infiltration measurement in Acacia plantation 11 Figure 3.5 Dry Bulk Density Tube 14 Figure 3.6 Soil analysis in laboratory by using oven 15 Figure 3.7 Determine slope, coordinate system and understory vegetation cover 15 Figure 3.8 Data analysis 15 Figure 4.1 Infiltration rate of bare land 16 Figure 4.2 Infiltration rate of 1-year-old Acacia plantation 17 Figure 4.3 Infiltration rate of 2-year-old Acacia plantation 18 Figure 4.4 Infiltration rate of 3-year-old Acacia plantation 19 Figure 4.5 Infiltration rate of 4-year-old Acacia plantation 20 Figure 4.6 Infiltration rate of 5-year-old Acacia plantation 21 Figure 4.7 Average infiltration rate at different ages Acacia plantation 22 Figure 4.8 Initial infiltration rate of different condition covers 23 Figure 4.9 Stable infiltration rate of different condition covers 25 Figure 4.10 Correlation between Stable rate and Initial rate 26 Figure 4.11 Total infiltration in hour under different vegetation cover types 28 Figure 4.12 Total infiltration in hour of other studies (Dung, 2015; Dung et al, 2016; Linh, 2017; Lan, 2018; Dung et al., 2019) 29 Figure 4.13 Dry bulk density of different ages Acacia plantation 31 v Figure 4.14 Porosity of different ages Acacia plantation 33 Figure 4.15 Soil moisture of different ages Acacia plantation 35 Figure 4.16 Understory vegetation coverage of different ages Acacia plantation 36 Figure 4.17 Affecting factors on infiltration of soil 38 Figure 4.18 Correlation between initial rate and soil moisture 39 Figure 4.19 Correlation between initial rate and porosity 39 Figure 4.20 Correlation between initial rate and understory vegetation coverage 40 Figure 4.21 Correlation between: a) Stable rate and porosity; b) Stable rate and dry bulk density 41 Figure 4.22 Correlation between Stable rate and Understory vegetation cover 42 Figure 4.23 Storm events of study site (Dung et al., 2019) 43 vi ABSTRACT To determine the temporal infiltration characteristics of soil under different ages of Acacia plantation forest in Luong Son head water, Hoa Binh Province, Vietnam The field experiment for infiltration measurement was established at different vegetation cover conditions (including bare land after burning, years-old Acacia trees, 2-year-old Acacia trees, 3-year-old Acacia trees, 4-year-old Acacia trees and 5-year-old Acacia trees) from July to September 2019 A number of affecting factors were determined, including soil physical characteristics and vegetation characteristics of Acacia plantation in Truong Son Commune, Luong Son district, Hoa Binh Province The main findings included: (1) Temporal infiltration rate in six different ages of Acacia plantation tended to be decreased over time Both initial and stable rate are increase from bare land after burning to 5-year-old of Acacia Mangium forest; (2) Temporal infiltration rate has a strong relationship with soil physical characteristics and understory vegetation cover Initial infiltration rate of soil has a strong relationship with understory vegetation, porosity and soil moisture, but not have significant relationship dry bulk density While stable rate has a moderate relationship with understory vegetation, it has a weak relationship with porosity, dry bulk density and soil moisture; (3) The findings implied that infiltration rate under Acacia plantation forest has been higher than bare land after burning It can be explained that the root and understory vegetation have important impacts on infiltration characteristics of soil Key words: Acacia plantation model, bare land after burning, infiltration, headwater, porosity vegetation cover conditions CHAPTER I INTRODUCTION Infiltration is the process by which water on the ground surface enter the soil or other materials and it is commonly used in both the field of hydrology and soil science in term of watershed management (Horton, 1933) The characteristics of infiltration can determine the establishment of surface and subsurface flow, which can control the hydrological processes and factors, including peak flow rates, runoff volumes, soil erosion and plant-available water capacity In terms of the location which has higher infiltration rate, there is no chance or little of generating overland flow (Horton, 1933) Therefore, the frequency of phenomenon of soil erosion is low or even not occurring if the infiltration of soil is high and soil will absorb water rapidly On the other hand, there will be frequently degrading issues, including landslide and soil erosion caused by overland flow and low infiltration capacity (Hai, 1993) Regarding surface flow, infiltration is indicative of the capability of the most significant regulator factor in forest hydrology, after rainfall has passed through the atmosphere, vegetation coverage and fallen cover (Sharma el al, 1980) Therefore, it is easier to effectively manage land and water resources, infiltration rate plays an important role in watershed management Many researches have focus on the key influencing objects of infiltration rate, including soil characteristics, rainfall and vegetation covers to emphasize the importance of infiltration (Dien et al, 2006) It can be said that a number of factors affecting infiltration rate of soil, such as precipitation characteristics, soil characteristics, terrain and vegetation and combine the amount of rain, intensity and frequency of rainfall (Dien el al, 2006), especially the role of vegetation in improving the infiltration rate of soil (Hiraoka, 2010) With the respect to heavy rainfall and intensity of rainfall, the infiltration of the soil witnessed the trend to be small Regarding precipitation and intensity of rainy season, the infiltration capacity will be higher (Haws el al, 2014) Soil factors that control infiltration rate are vegetation cover, root development, organic content (Dune et al, 1991) Additionally, some factors such as soil moisture, bulk density, porosity, soil texture and structure also have significant effects on infiltration rate Among three factors that influence the infiltration of soil, we can manage two factors including soil characteristics and vegetation Therefore, management approaches are also concentrated on these two factors Previous studies on surface runoff and soil erosion by Lung and Hai (1997) show that the thicker the forest is, the more water is absorbed into the soil and turned into the underground flow In addition, the study research of Lung et al (1995) show that permeability is considered to be a major factor in erosion and flow The authors affirmed that in Vietnam, forest trees are capable of consuming a large amount of water At the same time, affirmation of forest land is also a factor that influences the infiltration velocity Differences in soil properties, mainly the physical properties of soils, will directly affect the soil's infiltration Lung (1992) relies on permeability, transpiration and degradation of soils for scoring and evaluates the role of soil factors on infiltration In terms of vegetation cover factor, plantation forest is very popular these days In Vietnam, about 24% of the forest area is planted forest, in which Acacia Mangium is a popular crop Acacia Mangium Wild., also known as Mangium, is a species of indigenous plants to Northern Queensland (Australia), found in Indonesia's Irian Jaya, Maluku (Doran and Skelton, 1982) This is a fast-growing species, which is widely used for various purposes such as timber, firewood, agroforestry, land improvement (Turnbull et.al, 1983 Acacia belong to Fabaceae family, which is believed to have nitrate fixation ability and make soil become better (May et al, 2003) Thus it helps to conserve soil, promote vegetation development (Brockwell et al, 2005) Some hypotheses have supposed that the oil fallen leaves of Acacia Mangium has negative effects on understory vegetation The loss of understory vegetation can reduce infiltration capacity of soil and lead to the increase of overland flow and soil erosion Therefore, in this research, experiment on infiltration can observe the infiltration capacity of soil under 4.2.2 Affecting factors on soil infiltration at different ages of Acacia plantation Figure 4.17 Affecting factors on infiltration of soil (1): Initial and Stable infiltration rate (2): Initial infiltration rate and Moisture (3): Stable infiltration rate and Moisture (4): Initial infiltration rate and Porosity (5): Stable infiltration rate and Porosity (6): Initial infiltration rate and Dry bulk density (7): Stable infiltration rate and Dry bulk density (8): Initial infiltration rate and Understory vegetation cover (9): Stable infiltration rate and Understory vegetation cover 38 40 Initial rate (mm/min) 35 30 25 y = -1.9905x + 50.499 R² = 0.76 20 15 10 10 12 14 16 18 20 Soil moisture (%) Figure 4.18 Correlation between initial rate and soil moisture Soil moisture have relationship with initial rate with the correlation coefficient R 2=0.76 (Figure 4.18) This correlation has statistically significance with p=0.00 The initial rate of soil tends to increase when the initial rate is decreasing Otherwise, the stable rate does not have a significant relationship with soil moisture with the R2=0.19 60 Initial rate (mm/min) 55 50 45 40 y = 1.743x + 16.822 R² = 0.75 35 30 25 20 11 13 15 17 19 21 Porosity (%) Figure 4.19 Correlation between initial rate and porosity 39 Porosity has positive relationship with initial rate with the correlation coefficient R2=0.75 (Figure 4.19) This correlation has statistically significance with p=0.00 The initial rate of soil tends to increase when porosity increases Otherwise, the stable rate has weak relationship with porosity with R2=0.28 70 y = 4.9374x - 29.429 R² = 0.71 Initial rate (mm/min) 60 50 40 30 20 10 11 13 15 17 19 21 Understory vegetation (%) Figure 4.20 Correlation between initial rate and understory vegetation coverage Initial rate has a strong positive relationship with understory vegetation with the correlation coefficient and R2= 0.71, p value=0.00 Initial rate increases when the understory vegetation increase (Figure 4.20) 40 3.5 Stable rate (mm/min) 2.5 a) y = 0.0441x + 0.2728 R² = 0.28 1.5 25 30 35 40 45 50 55 60 Porosity (%) 3.6 Stable rate (mm/min) 3.1 b) y = -1.5561x + 4.1369 2.6 R² = 0.26 2.1 1.6 1.1 0.6 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Dry bulk density (g/cm3) Figure 4.21 Correlation between: a) Stable rate and porosity; b) Stable rate and dry bulk density Stable rate of soil does not significantly depend on porosity and dry bulk density Correlation coefficient R2= 0.25 and R2= 0.28 with the p-value of 0.00 show the weak 41 relationship between stable rate and porosity and dry bulk density (Figure 4.21) Stable rate increases when porosity increases and the dry bulk density decreases 80 y = 24.224x - 8.7833 R² = 0.49 Stable rate (mm/min) 70 60 50 40 30 20 10 1.5 2.5 3.5 Understory vegetation (%) Figure 4.22 Correlation between Stable rate and Understory vegetation cover Stable rate has a positive relationship with understory vegetation coverage in moderate level with the correlation coefficient and R2= 0.49, p value=0.00 Stable rate increases when the understory vegetation cover increases (Figure 4.22) Comparing with other researches, they have the same results that vegetation has a critical impact on infiltration characteristic of soil and it also can be the reason to reduce rain plash With the same low understory coverage, the soil may be detached by rain drop and it can lead to overland flow and soil erosion 42 4.3 Suggestions for better management Acacia plantation in process of forming overland flow and soil erosion Figure 4.23 Storm events of study site (Dung et al., 2019) The rainfall events graph shows the total precipitation in one storm from 29 September, 2017 to 28 August, 2018, nearly during one year in Luong Son headwater, Hoa Binh, Vietnam During 2017 to August 2018, there was a fluctuation in the amount of precipitation The lowest rainfall was 0.5 mm on 29/10/2017, the highest storm was 197 mm on 19/07/2018 Over a period, the average precipitation was 33.71 mm/storm During the dry season, there are still some storms which can cause the overland flow and soil erosion The result of the research illustrates infiltration capacity of soil has strong relationship with porosity, soil moisture and understory vegetation cover; and higher age of Acacia trees tends to increase of infiltration capacity due to the increase of canopy cover, understory vegetation cover and the ability to enhance the soil quality of the roots As a result, there should be practical and effective approaches to intensify the infiltration characteristics of soil 43 - Keeping and saving litter fall under the forest canopy The litter fall plays an important role in increasing the capability to save and keep water Furthermore, the cover of fallen leaves can assist in reducing the influence of rain drops Hence, nutrients and infiltration capability of soil surface will further improve the quality - Growing trees along contour lines or terrace The data implies that the higher age of Acacia trees tends to increase of infiltration capacity As a consequence, planting tree saves soil from erosion and support to improve soil fertility In terms of storms, which generate overland flow, water tends to flow perpendicularly with contour lines, therefore, planting trees with contour line model would have the impacts on increasing the division of the flow Consequently, the soil erosion by flow will be controlled effectively - Developing and keeping understory vegetation suitably Regarding the same positive effects of litter fall, understory vegetation also plays essential function in reducing the impact of rain drops Additionally, understory vegetation can increase infiltration capacity since their roots system can be considered to make soil create more pores for water to leak in In addition, it also brings detachment of raindrop down during storms and creates a significant amount of litter fall - Combining different types of trees, shrubs and herbs The chart of total water in hour compared to other land uses (Dung et al, 2016) show that the soil of mixed forest has better infiltration capacity than Acacia forest only As a result, we should consider these approaches, for example, we can plant Acacia Mangium alternately with Pines and Eucalyptus 44 CHAPTER V CONCLUSION 5.1 Conclusion After doing experiments in different ages of Acacia plantation in 30 different locations at different times, the main conclusions included: Higher age of Acacia trees tends to increase of infiltration capacity due to the increase of canopy cover and understory vegetation Average initial infiltration rate of bare land; 1-yearold; 2-year-old; 3-year-old; 4-year-old and 5-year-old is 7.9mm/min; 15.2mm/min; 15.8mm/min; 16.5mm/min; 16.1mm/min and 16.7mm/min, respectively Average stable infiltration rate of bare land; 1-year-old; 2-year-old; 3-year-old; 4-year-old and 5-year-old is 1.3mm/min; 1.8mm/min; 2.0mm/min; 2.2mm/min; 2.6mm/min and 2.9mm/min, respectively Total infiltration for hour in bare land after burning; 1-year-old; 2-year-old; 3-year-old; 4year-old and 5-year-old of Acacia plantation forest are 212mm/hour; 227mm/hour; 236mm/hour; 310mm/hour; 301mm/hour and 310mm/hour, respectively Infiltration rate of the soil follows the law of the highest value at the beginning and decreases over time Time to reach the stable rate of the type of oscillation range from 95-97 minutes In addition, the total infiltration for hour of soil very large, range from 212 mm/hour (bare land after burning) to 310 mm/hour (3-year-old Acacia tree and 5-year-old Acacia tree) Both initial and stable rate have positive relationship with understory vegetation cover Initial infiltration rate of soil has a strong relationship with understory vegetation, porosity and soil moisture, but not have significant relationship dry bulk density While stable rate has a moderate relationship with understory vegetation, it has a weak relationship with porosity, dry bulk density and soil moisture Relationships exist primarily with relation coefficients R2=0.4 to R2=0.7 45 Some recommendations to improve soil quality and temporal infiltration rate: maintaining and growing understory vegetation and litter fall; planting trees along the contour line and combining different plants with some types of trees which have the role of enhancing soil quality 5.2 Limitations After conducting the research, there have been some limitations that need to point out: - The results of research might reflect the soil infiltration characteristics under different ages of Acacia plantation forest in Luong Son head water, Hoa Binh, Vietnam This also reflects the ability to protect soil and regulate water However, the use of double-ring equipment may result in low accuracy because of no consider about force of raindrop like rain simulation and edge effect - In addition, the range of ages under different Acacia vegetation cover is just year, therefore, it is difficult to evaluate the difference of the ability to infiltrate water of soil - Because of limitation in time and budget, there have been still some influencing factors of temporal infiltration characteristics which they are not analyzed in this research 5.3 Recommendations Infiltration process is a complicated process which can be flexible by time and space Field experiment on temporal infiltration depends on a variety of factors, such as soil moisture, porosity, slope, litter fall, understory vegetation, canopy cover and precipitation However, the study was conducted without considering several influencing factors among them Therefore, the following research in the near future on infiltration might analyzed more clarify in correlation of other factors with temporal infiltration rate to find out characteristics of infiltration In addition, the following research can continue conducting the spatial infiltration of soil under different ages of Acacia plantation forest With the respect to this consideration, we can apply better management approaches to soil erosion and water quality in this area 46 In addition, because the age group is not significant different, therefore, to evaluate the ability of infiltration capacity of different age groups under Acacia plantation forest, the following research would choose age group of Acacia plantation forest, for example, 1-yearold Acacia trees, 5-year-old Acacia trees, 10-year-old Acacia trees as possible 47 REFERENCES May, P.M Attiwill P.M, 2014 Nitrogen-fixation by Acacia dealbata and changes in soil properties years after mechanical disturbance or slash-burning following timber harvest Dien, P.V, 1998, Initially studying the hydrological characteristics of some forest vegetation as a basis for establishing the standards of water retention in the critical area of Hoa Binh Hydropower Plant Master thesis on forestry science Forestry 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