Soil infiltration characteristics at different age of acacia plantation forest in luong son headwater hoa binh vietnam

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM NATIONAL UNIVERSITY OF FORESTRY STUDENT THESIS SOIL INFILTRATION CHARACTERISTICS AT DIFFERENT AGE 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: Tran Ngoc Lan Student ID: 1453090551 Class: K59A - Natural Resources Management Course: 2014 – 2018 Advanced Education Program Developed in Collaboration with Colorado State University, USA Supervisor: Assoc.Prof Bui Xuan Dung Ha Noi, 2018 ACKNOWLEDGEMENT First and foremost, I would like to express our sincere respect to our supervisor Assoc Prof Dr Bui Xuan Dung for his enthusiastic and patient support with invaluable comments In addition, I appreciated the support of other lectures during the time we analyzed the data Not only that, many thanks are due to my friends when I started to collect and analyze data They always give me the support whenever I needed Lastly, I express my gratitude to local people who own the Acacia plantation model for allowing me to conduct this research in this site Hanoi, August 2018 i TABLE OF CONTEND ACKNOWLEDGEMENT i TABLE OF CONTEND 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 3.2.1 Infiltration measurement 3.2.2 Soil properties 10 CHAPTER IV 13 RESULTS AND DISCUSSIONS 13 4.1 Soil infiltration characteristics at different ages of Acacia plantation 13 4.1.1 Infiltration rate at different ages of Acacia plantation forest 13 4.1.2 Initial and stable infiltration rate 19 4.1.3 Total water infiltrate in hour 22 ii 4.2 Impact factors on Infiltration characteristics at different ages of Acacia plantation 23 4.2.1 Soil physical and vegetation characteristics at different ages of Acacia plantation 23 4.2.2 Affecting factors on soil infiltration at different ages of Acacia plantation 29 CHAPTER V 36 CONCLUSION, LIMITATIONS AND RECOMMENDATIONS 36 5.1 Conclusion 36 5.2 Limitations 37 5.3 Recommendations 37 REFERENCES APENDIX iii LIST OF TABLE TABLE 3.1 DATA OF INFILTRATION IN DIFFERENT AGES ACACIA FOREST TABLE 4.1 VEGETATION CHARACTERISTICS AT DIFFERENT AGES OF ACACIA PLANTATION 23 TABLE 4.2 SOIL PROPERTIES AND INFILTRATION CHARACTERISTIC 29 iv LIST OF FIGURE Figure 3.1 The map of study site: a) Location of Hoa Binh province on Viet Nam 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 Infiltration measurement in Acacia plantation Figure 3.4 Dry Bulk Density Tube 11 Figure 3.5.Soil analysis in laboratory by using oven 12 Figure 3.6 Determine slope, coordinate system and vegetation cover 12 Figure 3.7 Data analysis 12 Figure 4.1 Infiltration rate of bare land 13 Figure 4.2 Infiltration rate of 1-year-old Acacia plantation 14 Figure 4.3 Infiltration rate of 3-years-old Acacia plantation 15 Figure 4.4 Infiltration rate of 4-years-old Acacia plantation 16 Figure 4.5 Average infiltration rate at different ages Acacia plantation 17 Figure 4.6 Infiltration rate in type of soil (Horton, 1933) 18 Figure 4.7 Initial infiltration rate of different ages Acacia plantation 19 Figure 4.8 Stable Infiltration rate of different ages Acacia plantation 20 Figure 4.9 Correlation between Stable rate and Initial rate 21 Figure 4.10 Total water infiltrate in hour in different ages of Acacia plantation 22 Figure 4.11 Total water in hour compared with other land uses (Source: Dung et al, 2016, Soil infiltration characteristics of different land use at Luot mountain, Xuan Mai, Hanoi) 22 Figure 4.12 Bulk density of different ages Acacia plantation 24 Figure 4.13 Porosity of different ages Acacia plantation 25 v Figure 4.14 Soil moisture of different ages Acacia plantation 27 Figure 4.15 Understory vegetation coverage of different ages Acacia plantation 28 Figure 4.16 Affecting factors on infiltration 30 Figure 4.17 Correlation between initial rate and soil moisture 31 Figure 4.18 Correlation between initial rate and understory vegetation coverage 31 Figure 4.19 Correlation between a) Stable rate and porosity, b) Stable rate and dry bulk density 32 Figure 4.20 Correlation between Stable rate and Understory vegetation cover 33 Figure 4.21 Storm events from September 29th to October 24th, 2018 in study site (Source: D.Hoa, P.Trang, V.Thu, T.Lan, N.Cong, 2018, Evaluating effects of Acacia Plantation forest on overland flow and soil erosion in Luong Son headwater of Vietnam 34 vi ABSTRACT To determine the soil infiltration characteristics in different ages of acacia plantation forest in Luong Son-Hoa Binh head water of Vietnam I choose to a field experiment for infiltration measurement at different vegetation cover conditions (bare land, years-old Acacia trees, 3-year-old Acacia trees and 4-year-old Acacia trees) from July to August 2018 I also determine a number of affecting factors such as soil physical and vegetation characteristics of Acacia plantation in Truong Son Commune, Luong Son district, Hoa Binh Province The main findings include: (1) Infiltration rate in four different ages of Acacia plantation tended to be decreased over time Both initial and stable rate are increase from bare land to years old of Acacia Mangium forest (2) Infiltration rate has a strong relationship with soil physical and vegetation coverage of study site Initial infiltration rate of soil has strong negative relationship with soil moisture and but not has significant relationship with porosity and dry bulk density Meanwhile, stable rate does not has relationship with soil moisture but has strong relationship with porosity and dry bulk density (3)The findings implied that infiltration rate under Acacia plantation forest has been higher than bare land Maybe the root and understory have important impacts on infiltration characteristics of soil Key words: Acacia plantation model, bare land, infiltration, headwater, porosity vegetation cover conditions CHAPTER I INTRODUCTION Infiltration is the process in which water entries downward into the immediate surface of soil or other materials (Horton, 1933) It is one of the issues studied extensively in the field of hydrology From the theory of surface flow, infiltration is indicative of the ability of the most important regulator stage in forest hydrology, after rainfall has passed through the atmosphere, vegetation coverage and fallen cover (Sharma el al, 1980) Infiltration capacity of soil is very important in forming the mechanism of surface flow, subsurface flow and soil erosion Thus in the area that has high infiltration rate, soil has high infiltration capacity, there will be little or no overland flows (Horton, 1933) So surface erosion does not occur or occurs with very low frequency In contrast, soil has low infiltration rate leads to more overland flows (Hai, 1993) So there may be occur erosion with higher frequency Therefore, it is easy to effectively manage land and water resources, infiltration rate plays an important role in watershed management There are many factors affecting infiltration rate of soil, include precipitation, soil texture and structure, terrain and vegetation and precipitation characteristics combine the amount of rain, intensity and frequency of rainfall (Dien el al, 2016) In the case of heavy rainfall and intensity of rainfall, the infiltration of the soil tends to be small In case of precipitation and intensity of rainy season, the infiltration capacity will be higher (Haws el al, 2016) Soil factors that control infiltration rate are vegetation cover, root development, organic content (Dune et al, 1991) In general, soil with high vegetation cover has high infiltration rate (Hiraoka, 2010) Furthermore, some factors such as soil moisture, bulk density, porosity, soil texture and structure also have significant effects on infiltration rate In three factors that affect the infiltration of soil, we can manage two factors including soil characteristics and vegetation Therefore, management solutions are also focused on these two factors Studies on surface runoff and soil erosion by Lung and Hai (1997) show that the thicker the forest, the more water is absorbed into the soil and converted into the underground flow , the greater the ability to reduce erosion Research of Lung et al (1995) show that permeability is considered to be a major factor in erosion and flow Other works also mention the effect of vegetation type on the infiltration of forest land such as Pho (1992), Dung (1993) 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 different ages of Acacia trees compare with infiltration characteristics of different age of Acacia forest to conclude whether this hypothesis is right or not In general, the study of infiltration characteristic of soil in Vietnam Acacia forest whose value was 21.9%, but lower than soil moisture of bare land whose value was 30% Soil moisture in 4-years-old of Acacia forest varied from 19.6 to 33.41 % which the highest value was the 7th soil sample and the lowest was the 1st soil sample Average soil moisture of 4-years-old of Acacia forest was 25.9%, higher than soil moisture of 1-year-old Acacia forest and 3-years-old Acacia forest, but lower than soil moisture of bare land whose value was 30% (Figure 4.14) 4.2.1.5 Understory vegetation coverage 70 Understory Vegetation Coverage (%) Bare land 60 1-year-old 3-year-old 50 4-year-old 40 30 20 10 Location Figure 4.15 Understory vegetation coverage of different ages Acacia plantation Understory vegetation in bare land areas ranged from to 44.3%, the 5th location had the highest vegetation cover and the 1st, 2nd, 3rd, 7th and 9th have 0% of vegetation coverage The average vegetation coverage of locations in bare land areas was 7.7% Vegetation in 1-year-old Acacia forest ranged from 2.4 to 48.7%, the 8th location had the highest vegetation cover and the 6th location have lowest The average understory vegetation coverage of locations in year old Acacia plantation areas was 20.5% 28 Understory vegetation in 3-years-old Acacia forest ranged from 25.1 to 65.3%, the 6th location had the highest vegetation cover and the 2nd location have lowest The average understory vegetation coverage of locations in 3-year-old Acacia plantation areas was 40.7% Understory vegetation cover in 4-years-old Acacia forest varied from 10.2 to 37.6%, the 9th location had the highest vegetation cover and the 3th location have lowest The average understory vegetation coverage of locations in years old-Acacia-plantation was 29.5% (Figure 4.15) 4.2.2 Affecting factors on soil infiltration at different ages of Acacia plantation Table 4.2 Soil properties and infiltration characteristic Dry Bulk Porosity Moisture (%) Stable Rate Rate Veg Density (%) Initial cover (%) (g/cm3) (mm/min) (mm/min) Mean 1.30 51.08 24.98 25.1 14.20 1.91 Maximum 1.56 72.00 37.87 65.30 19.10 2.80 Minimum 0.74 41.00 12.10 0.00 6.20 0.70 Std Deviation 0.18 6.70 6.50 16.56 3.85 0.57 29 Figure 4.16 Affecting factors on infiltration 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 30 Initial Rate (mm/min) 25 y = -0,3092x + 21,92 R² = 0,2722 20 15 10 10 15 20 25 30 35 40 Moisture (%) Figure 4.17 Correlation between initial rate and soil moisture Initial Rate (mm/min) 25 20 15 10 y = 0,1432x + 10,604 R² = 0,3789 0 10 20 30 40 50 60 70 Vegetation Coverage (%) Figure 4.18 Correlation between initial rate and understory vegetation coverage Soil moisture have relationship with initial rate with the correlation coefficient R=0.52 (Figure 4.18) This correlation have statistically significance with p=0.001 The initial rate of soil tend to increase when the initial rate is decreasing Otherwise, the stable rate does not have a significant relationship with soil moisture The correlation coefficient R=0.22 show the weak relationship (Figure 4.17) 31 Initial rate have a positive relationship with understory vegetation coverage in medium level with the correlation coefficient and R= 0.63, p value=0.000 Initial rate increase when the vegetable increase (Figure 4.20) Figure 4.19 Correlation between a) Stable rate and porosity, b) Stable rate and dry bulk density Initial rate of soil does not depend on porosity and dry bulk density Correlation coefficient R= 0.25 show the weak relationship (Figure 4.17) The initial rate can be affected more by the surface moisture and the ground component of the soil Otherwise, the stable rate has relationship with porosity and dry bulk density with the correlation coefficient R= 48.6 (Figure 4.19) with p value=0.003 Stable rate increases when porosity increases and the dry bulk density decreases However, the coefficient R=48.6 is only moderately correlated 32 Therefore, the stable rate is not only affected by the porosity and dry bulk density, but also it depends on other factors, such as soil depth, soil structure and others Stable Rate (mm/min) 2,5 1,5 y = 0,0174x + 1,4751 R² = 0,2517 0,5 0 10 20 30 40 50 60 70 Vegetation Coverage (%) Figure 4.20 Correlation between Stable rate and Understory vegetation cover Stable rate have a positive relationship with understory vegetation coverage in medium level with the correlation coefficient and R= 0.50, p value=0.002 Stable rate increase when the vegetable increase (Figure 4.20) Comparing with other research, they have the same results that vegetation has a critical impact on infiltration characteristic of soil It also reduce rain plash With such low coverage, the soil may be detached by rain drop and it can lead to overland flow and soil erosion 33 4.3 Suggestions for better management Acacia plantation in process of forming overland flow and soil erosion 200 180 Precipitation (mm) 160 140 120 100 80 60 40 20 24/11/2017 20/11/2017 19/11/2017 15/11/2017 12/11/2017 9/11/2017 8/11/2017 6/11/2017 29/10/2017 25/10/2017 19/10/2017 17/10/2017 12/10/2017 9/10/2017 8/10/2017 7/10/2017 5/10/2017 4/10/2017 3/10/2017 30/9/2017 29/9/2017 Rainfall events Figure 4.21 Storm events from September 29th to October 24th, 2018 in study site (Source: D.Hoa, P.Trang, V.Thu, T.Lan, N.Cong, 2018, Evaluating effects of Acacia Plantation forest on overland flow and soil erosion in Luong Son headwater of Vietnam The rainfall events graph in our research in 2018 show the total precipitation in one storm The lowest rainfall was 0.5 mm on 29/10/2017, the highest storm was 182 mm on 12/10/2017 Average precipitation is 17.73 mm Meanwhile, the average infiltration in bare land, 1-year- old, 3-year-old, 4-year-old of Acacia plantation are 2.79, 3.19, 4.25, 4.12 mm/min, respectively During the dry season, there are still some storms which can cause the overland flow and soil erosion (Figure 4.3) The result in this thesis illustrates infiltration capacity of soil has strong relationship with porosity and soil moisture and higher age of Acacia trees tends to increase of infiltration capacity due to the increase of canopy cover and the ability to improve the soil of the roots Therefore, there should be suitable solutions to improve the infiltration characteristics of soil 34 - Protecting litter fall under the forest canopy The litter fall increases the ability to hold water Moreover, the cover of fallen leaves helps to reduce the impact of rain drops Therefore, nutrients and infiltration capability of soil surface will be protected - Planting trees along contour lines or terrace The data indicates that the higher age of Acacia trees tends to increase of infiltration capacity Therefore, planting tree prevents soil erosion and to improves soil fertility In the case of storms which lead to overland flow, water tends to flow perpendicularly with contour lines, so contour line planting would have the effects on increasing the division of the flow Therefore, the soil erosion by flow will decrease and be protected - Maintaining understory vegetation Like the benefits of litter fall, understory vegetation also helps to reduce the impact of rain drops Besides, understory vegetation can increase infiltration rate because their roots system make soil have more pores for water to leak in It also reduces detachment of raindrop during storm and produces some litter fall - Mixing planting with some kinds of trees or shrubs and herbs The graph total water in hour compared to other land uses (Dung et al, 2016) show that the soil of mixed forest have better infiltration capacity than Acacia forest Therefore, we can plant Acacia Mangium alternately with Pines and Eucalyptus 35 CHAPTER V CONCLUSION, LIMITATIONS AND RECOMMENDATIONS 5.1 Conclusion After doing experiments in different ages of Acacia plantation in 36 different locations at different times, the final conclusions were pointed out: Higher age of Acacia trees tends to increase of infiltration capacity due to the increase of canopy cover Average initial infiltration rate of bare land, 1-year-old, 3-year-old, 4-year-old is 7.94, 15.02, 16.98 and 16.84, respectively Average stable infiltration rate of bare land, 1-year-old, 3-year-old, 4-year-old is 1.11, 1.81, 2.24, 2.48, respectively Total infiltration for hour in land 1-year-old, 3-years-old and 4-year-old of plantation are 207 mm/hour, 225 mm/hour, 304 mm/hour, 286 mm/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 93-97 minutes In addition, the total infiltration for hour of soil very large, range from 207.0 mm/hour (bare land) to 304.2 mm/hour (3 years old) Both initial and stable rate have positive relationship with understory vegetation cover Initial infiltration rate of soil has strong negative relationship with soil moisture but not has significant relationship with porosity and dry bulk density Meanwhile, stable rate does not have relationship with soil moisture but has strong relationship with porosity and dry bulk density Relationships exist primarily with relation coefficients R=0.4 to R=0.7 Some suggested solutions to enhance soil quality and infiltration rate: developing understory vegetation and litter fall; planting trees along the contour line and mixing plant with some kind of trees help to enhance soil quality 36 5.2 Limitations After conducting the research, there have been some limitations that need to point out: - Research results reflect the soil infiltration characteristics in different ages of acacia plantation forest in Luong Son-Hoa Binh head water of Vietnam This also reflects the ability to protect soil and regulate water However, the use of single ring may result in low accuracy because of no consider about force of raindrop like rain simulation and edge effect - In addition to humidity and porosity, the infiltration characteristics of soil depend on many factors, but because of limitation in time and budget, they are not analyzed in my thesis - Soil analysis process: the particle density was not analyzed in laboratory may lead to some errors in calculation Moreover, some other factors of soil were not considered such as slope, soil texture and soil depth 5.3 Recommendations Infiltration process is a complex process that flexible by time and space Experiment on infiltration depends on a number of factors such as soil moisture, porosity, slope, litter fall, understory vegetation, canopy cover and precipitation and API7 The research was conducted without considering some factors of them Therefore, the following research on infiltration might analyzed more clarify in relationship of those factors with infiltration rate to find out characteristics of infiltration By this consideration, we can better manage soil erosion and water quality 37 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 Bui Xuan Dung, 2006 “Effect of vegetation cover on flow generation and soil erosion at Luot mountain, Vietnam National University of Forestry” Report Technology Scientific results granted: 48-56 Bui Xuan Dung, Pham Thuy Linh, Tran Thi Thuy, Nguyen Thi My Linh, Le Nguyen Kha, Pham Thi Thu Trang, 2016, Infiltration characteristics of soil under Eucalyptus plantation forest in headwater of Viet Nam Forestry Science and Technology Journal of Vietnam University of Forestry No2-2007: 72-73 Doran J.C., and Skelton D.J 1982, Acacia mangium seed collections for international provenance trials Forest Genetic Resources information No 11, FAO, Rome Do Thi Lan, 2011, Study on potential infiltration and retention of forest soil to contribute to limiting erosion and forest flood forecasting for Dinh Hoa district, Thai Nguyen province Master thesis 2011, Thai Nguyen University: 28-41 Dune T, Zhang W, Aubry BF 1991, Effects of rainfall, vegetation and microtopographyon infiltration and runoff Water Resources Research 1991: 2371-2285 Haws NW, Liu B, Boast CW, Rao PSC, Kladivko EJ, Franzmeier DP 2014 Spatial variability and measurement scale of infiltration rate on agriculture landscape, Soil Science Society of American Journal: 1818-1826 Hiraoka et al, 2010, Effect of understory vegetation on infiltration capacity in Japanese cypress plantation Journal of Japanese Forest: 145-150 Horton RE 1933 The role of infiltration in the hydrological cycle Transactions, American Geophysical Union: 446-460 10 John Brockwell, Suzette D Searle, Alison C Jeavons and Meigan Waayers, Nitrogen Fixation in Acacias: an Untapped Resource for Sustainable Plantations, Farm Forestry and Land Reclamation, 2005, Australian Centre for International Agricultural Research 11 Nguyen Ngoc Lung, 1992, Hierarchical methods critical watershed Vietnam national research project 1992 12 Nguyen Ngoc Lung, 1995, Apply scientific technical and economic solutions to the planning of protective river basins, building protection forests for protection of water sources and forests against coastal storms Vietnam national research project 1992 13 Nguyen Ngoc Lung, Vo Dai Hai, 1997, Initial results of research on the effects of water source protection of some major vegetation and construction of water protection forest, Agricultural Publishing House 14 Nguyen Viet Pho, 1992, Hydrological issues and tropical forests, Forestry magazine 15 Vo Dai Hai, 1993, Effect of forests on water regulation and soil erosion control PhD thesis on agricultural science Forest Science Institute of Vietnam, Hanoi 16 Pham Van Dien (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 1998 Forestry University 17 Pham Thuy Linh, 2017, Infiltration Characteristics of soil under Cinnamon and Acacia plantation forest in Mau A town, Van Yen district, Yen Bai province Student thesis 2017, Vietnam National University of Forestry: 16-17 18 Pham Quynh Trang, Vu Thi Hoai Thu, Tran Ngoc Lan, Dang Thi Thanh Hoa, Nguyen Van Cong, 2017, Evaluating effects of Acacia Plantation forest on overland flow and soil erosion in Luong Son headwater of Vietnam Scientific research 2017, Vietnam National University of Forestry: 12-13 19 Sharma ML, Gander GA, Hunt CG ,1980 Spatial variability of infiltration in a watershed Journal of Hydrolog 45: 110-122 20 Turnbull, J.W., Boland, D.J, Doran, J.C., and Gunn, B.V 1983 “Handbook on Seeds of Dry-Zone Acacias” FAO, Rome APENDIX Initial Stable Soil Locatio Bulk Porosity rate rate moisture n Veg.cove density (%) (mm/min) (mm/min) (%) r (%) (g/cm3) A1 7.4 1.5 37.6 55 1.1925 A2 8.6 1.4 24.2 60 1.06 A3 8.2 1.2 21.3 41 1.5635 A4 8.5 1.1 32.8 43 1.5105 12.6 A5 8.9 1.3 31.0 46 1.431 44.3 A6 7.7 0.9 31.1 51 1.2985 25.4 A7 7.9 34.9 44 1.484 A8 8.1 0.9 19.5 46 1.431 5.3 A9 6.2 0.7 37.9 42 1.537 A1-1 14.8 1.8 17.5 44 1.484 14 A1-2 14 1.9 29.8 54 1.219 21 A1-3 15.7 1.7 14.3 52 1.272 15.9 A1-4 17.9 2.1 17.7 55 1.1925 24.5 A1-5 16.5 1.7 14.9 46 1.431 7.6 A1-6 14.9 1.8 29.9 51 1.2985 2.4 A1-7 13.3 1.7 24.3 49 1.3515 33.1 A1-8 13.9 1.8 24.6 50 1.325 48.7 A1-9 14.2 1.8 24.1 55 1.1925 17.5 A3-1 17.8 2.5 17.9 56 1.166 36.9 A3-2 15.8 2.4 30.1 53 1.2455 25.1 A3-3 16.9 2.5 19.4 48 1.378 34.2 A3-4 15.4 27.0 61 1.0335 41.2 A3-5 18.1 2.6 29.0 49 1.3515 45.4 A3-6 17.4 1.8 12.1 43 1.5105 65.3 A3-7 19.1 2.1 18.0 42 1.537 45.9 A3-8 16 1.8 25.0 58 1.113 30.1 A3-9 16.3 2.5 20.5 49 1.3515 42.3 A4-1 16.8 19.6 50 1.325 33.6 A4-2 16.3 2.7 29.2 52 1.272 24.1 A4-3 15 2.8 31.1 72 0.742 10.2 A4-4 15.8 2.6 21.3 52 1.272 36.5 A4-5 17.5 2.1 25.2 49 1.3515 28.7 A4-6 18.6 2.5 22.3 53 1.2455 35.2 A4-7 16.6 2.4 33.4 49 1.3515 23.1 A4-8 17.2 2.5 26.7 52 1.272 36 A4-9 17.8 2.7 24.0 67 0.8745 37.6 ... Time (min) Figure 4.5 Average infiltration rate at different ages Acacia plantation Infiltration rate at different ages Acacia plantation have a similar trend Infiltration rate of the soil follows... characteristics of Acacia plantation in Truong Son Commune, Luong Son district, Hoa Binh Province The main findings include: (1) Infiltration rate in four different ages of Acacia plantation tended... Total water infiltrate in hour in different ages of Acacia plantation Average of total infiltration in locations in first hour in each different age of Acacia plantation is 168 mm/hr in bare