1. Progress Report on Activities relating to RAS/5/055 in Vietnam
By Phan Son Hai
Project Co-ordinator

2. Participating in events of RAS/5/055 (Meeting, workshop, etc.)
First Meeting in Colombo, Sri Lanka, August 2012 (Phan S. Hai)
Meeting in Dhaka, Bangladesh, June, 2013 (Trinh C. Tu)
Workshop in Xinxiang, China, December, 2012 (Missing)
Training Course in China (Missing)
Second Meeting in Dalat, Vietnam (4 persons)
Meeting in Kathmandu, Nepal (Phan Son Hai)

3. Case studies and outputs
First study
Assessment of soil erosion rates for different land uses in the region of Lamdong province using fallout radionuclides
Purpose of the study
Assessment of soil erosion rates for different farming practices
Identifying good farming practices, which can conserve soil and are familiar to local farmers
Popularizing optimal models and encouraging farmers to imitate these models

4. Study area
Study area located in the southern part of Central Highlands

5. Soil erosion problem at the study area
Lamdong province is a mountainous region
Total area: ~ km2
Percentages of the area by the slope:
< 250 : ~ 50%
> 250 : ~ 50%
Agricultural production land: ~ 30%
Mean annual rainfall: ~ 2000 mm.
Land is susceptible to erosion

6. Soil conservation
Many soil conservation models have been set up and examined in plot scale (for example hedgerows using green-manure plants or Vetiver, contour farming, terracing farming, etc.).
Such soil conservation techniques could reduce soil loss up to 96% in comparison with control plots.
Though tested soil conservation models have high effectiveness in retaining soil, putting these models into practice has had difficulties.
During running time of soil conservation projects, many farmers voluntarily adopted soil conservation models with their own fields. However, few years afterwards some of the established models were removed or they are not effective anymore.
The cost of maintenance of the models and the lost of cropland due to hedgerows are main reasons resulting in the above mentioned consequence.

7. Sampling sites

8. Pineapple, cashew intermixture S-4 30 Tea, contour farming S-5 7
Code
Slope (%)
Crops
S-1 45
Old cashew
S-2 35
Coffee, basin
S-3
Pineapple, cashew intermixture
S-4 30
Tea, contour farming
S-5 7
Tea monoculture
S-6 25
Tea and durian intermixture
S-7 15
S-8
S-9

9. Tea, contour farming, basin* S-11 25
Code
Slope (%)
Crops
S-10 15
Tea, contour farming, basin*
S-11 25
Coffee and jack intermixture, basin*
S-12 20
Alternate mulberry and corn, contour
S-13
Coffee
S-14
Mulberry
S-15
S-16 10
Vegetables, 15m terraced field

10. The study site Code Slope (%) Crops S-17 5 Vegetables S-18 10
Flowers, 105m terraced field
S-19
Flowers, net house farming
S-20
Vegetables, 90m terraced field
S-21 7
Corn and vegetables rotation
S-22 15
Vegetables, net house farming
S-23
S-24
Vegetables, 140m terraced field
S-25
Corn, 40m terraced field
S-26
Bean, 38m terraced field
S-27
Corn, 83m terraced field
The study site

11. Sampling

12. Analysis of samples Analysis of Cs-137 and Be-7
Gamma spectometry method (Be-7 should be completely analysed for 40 days since sampling time)
Analysis of soil chemical properties
OM was determined by Walkley Black method (TCVN 8941 : 2011)
Total nitrogen was determined by Kjeldahl method (TCVN 6498 : 1999)
Total phosphor was determined by photometric method (TCVN 8940 : 2011)
Total potassium was determined by flame spectrophotometry (TCVN : 2011)
Particle size analysis
Particle size distribution of soil and sediment samples was determined by wet sieving and Robinson method (TCVN 8567:2010)

13. Conversion models
The Proportional Model for Cs-137 (He and Walling, 1996):
The Empirical Model for Cs-137 (P.S. Hai, 2005)
Cultivation layer (m)
Bulk density (t.m-3)
137Cs loss (%)
Erosion rate (t.ha-1.y-1)
Hệ số HC cấp hạt
Time elapsed since 1963
Erosion rate (t.ha-1)
137Cs loss (%)

14. Conversion models
Profile-Distribution Model (Q. He, D.E. Walling and P.J. Wallbrink, 2002):
Relaxation mass depth (kg.m-2)
Erosion rate (kg.m-2)
Particle size correction factor
7Be reference inventory (Bq.m-2)
7Be inventory (Bq.m-2)
P is the ratio of the 7Be concentration of mobilized sediment to that of the original soil

15. Soil erosion rate at 27 study sites
Soil erosion rates: 5  42 t/ha/yr depending on slope, rainfall, crops and farming practices

16. Ratio of long-term soil erosion rate to short-term soil erosion rate
R(Cs)/R(Be) ratio at 27 study sites varies from 0.55 to 1.75 (mean = 0.95)
Variation in R(Cs)/R(Be) ratio reflects the change in land use and farimg practice at study sites.
Investigative areas having very low R(Cs)/R(Be) ratio implicated that they have been reclaimed for recent years.
Mean = 0.95

17. Soil erosion rates for different farming practices
R = 42 t/ha/y
R = 27 t/ha/y S3
Pineapple, cashew intermixture
Soil loss reduces by 36%
(The same slope 45% and rainfall) S1
Old cashew monoculture S2
Coffee, basin created at the base of trees
R = 34 t/ha/y
R = 24 t/ha/y S4
Tea, 1.2m contour rows
Soil loss reduces by %
(The same slope 35% and rainfall) S9
Tea, 1.4m-1.6m contour rows

18. Soil erosion rates for different farming practices
Coffee, basins created at the base of trees
R = 16 t/ha/y
R = 28 t/ha/y
Soil loss reduces by 42%
(The same slope 25% and rainfall)
S13
Coffee, no basins
S12
Mulberry contour rows alternately intercroped by corns
S14
Mulberry monoculture without contour farming
Soil loss reduces by 54%
(The same slope 20% and rainfall)
R = 11 t/ha/y
R = 23 t/ha/y

19. Soil erosion rates for different farming practices
R = 11 t/ha/y
R = 21 t/ha/y
S10
Tea, contour farming, basin
Soil loss reduces by 50%
(The same slope 15% and rainfall) S8
Tea monoculture
R = 7 t/ha/y
R = 17 t/ha/y
S22
Vegetables, net house farming
Soil loss reduces by 59%
(The same slope 12% and rainfall)
S23
Vegetables

20. Soil erosion rates for different farming practices
R = 13 t/ha/y
R = 23 t/ha/y
S20
Vegetables, 90m terraces
Soil loss reduces by 44%
(The same slope 10% and rainfall)
S16
Vegetables, 15m terraces
R = 22 t/ha/y
R = 14 t/ha/y
S27
Corns, 80m terraces
S25
Corns, 40m terraces
Soil loss reduces by 35%
(The same slope 15% and rainfall)

21. Case studies and outputs
Second study
Assessment of soil erosion rates for a large catchment using fallout radionuclides
Purpose of the study
Assessment of soil erosion rates/ soil loss for the whole watershed
Assessment of soil erosion rates for different farming practices
Soil erosion impacts (on site & off site)
Main factors affecting soil erosion in the study catchment

22. Study area Feature of study area
A 270 km2 catchment in the Central Highlands of Vietnam
Slope: from 0o to more than 45º
Annual rainfall: 2500 – 3000 mm
Annual crops: corn, beans, vegetables, etc.
Perennial crops: Tea, coffee, strawberry, cashew, fruit trees
Forest: Natural forest, artificial forest

23. Study area
Loss of capacity: 418,000 m3 y-1
(523,700 t y-1)

24. Combination of features
Study catchment
Classification of catchment area according to the slope
Classification of catchment area according to plantations
Classification of catchment area according to rainfall
Combination of features
Selection of representative study areas
Collecting samples at representative areas
Analysis of 7Be, 137Cs
Analysis of chemical properties
Analysis of particle size
Soil erosion rates at study areas
Impact of soil erosion (on-site/ off-site)
Soil erosion rates/ soil loss for whole catchment

25. The area of catchment by slope
Materials:
Topographic map (5m contour-line)
Mapinfo, Microstation, Vertical Mapper
Output:
Digital Elevation Model - DEM
Classification of catch. area by slope:
0 - 5º: 36,4%
5-15o: 40,6%
15-25o: 18,1%
25-35o : 4,7%
> 35º: 0,12%

26. The area of catchment by plantation
Materials:
Digital map of land use
Mapinfo, Microstation
Output:
Natural forest: 31,76%
Artificial forest: 6,15%
Annual crop: 1,35%
Perennial crops: 60,74%
Tea: 16,60%;
Coffee: 78,08%
Mulberry: 0,54%;
Cashew: 0,02%
Fruit trees: 4,76%

27. Selection of representative study areas
Selecting 90 representative areas (Each sampling area has at least one of the features of the slope, rainfall, crops, farming practice different from others)
Natural forest: 7 sites
Production forest: 7 sites
Perennial crops: 58 sites
Annual crops: 18 sites

28. Sampling Sampling at reference sites 3 – 5 samples at each sites
Sampling at study sites
Taking samples along sloping lines
445 samples for Cs-137 ( = 10cm)
445 samples for Be-7 (20 x 40 x 4 cm)

29. Sampling at forest land
Natural forest
Artificial forest

30. Sampling at perennial crop land

31. Sampling at annual crops land

32. Reference inventories
Ir (Cs-137): Bq/m2
Ir (Cs-137) varies with rainfall (rainfall: 2400 – 2980 mm)
Ir (Be-7): Bq/m2
Ir (Be-7) varies with rainfall and the time elapsed since the end of rainy season to sampling time

33. Soil erosion rates for perennial crops
Soil erosion rates: 5 ÷ 34 t ha-1 y-1
Soil erosion rate is in the order: tea, coffee < mulberry < cashew

34. Soil erosion rate averaging over slope

35. Soil erosion rate for perennial crops
Soil loss:  t/y
Soil loss t ha-1 y-1
Distribution of soil erosion rates for perennial crops within the catchment

36. Soil loss structure by slope
Soil loss structure by the slope for each plantation type

37. Loss of plant nutrients
OM loss up to 1,700 kg ha-1 y-1
Total N loss up to 90 kg ha-1 y-1
Total P loss up to 65 kg ha-1 y-1
Total K loss up to 40 kg ha-1 y-1

38. Change in physical property of surface soil
Ratio of sand, silt and clay in 0 – 3.5 cm layer to those in 0 – 30cm layer
Coarse fractions like sand and silt in the 0 – 3.5 cm soil layer are higher than those in the 0 – 30cm soil layer for most sampling points.

39. CSSI Data

40. Annual crops (corn, beans)
CSSI Data
Bulk C δ13C
C14
C16
C18
C20
C22
C24
Natural forest
-20,61
-28,81
-22,00
-24,95
-21,92
-33,37
-32,63
-21,88
-28,40
-24,83
-23,15
-23,07
-28,24
-30,18
Production forestry
-29,01
-32,44
-29,04
-29,79
-27,78
-29,37
-28,70
Tea plantation
-22,80
-31,66
-27,29
-29,70
-26,97
-31,55
-27,63
-25,14
-27,74
-24,62
-23,72
-26,35
-26,55
-24,68
Coffee plantation
-23,95
-31,33
-26,21
-27,91
-27,68
-27,80
-31,73
-25,82
-32,06
-29,96
-30,51
-27,51
-39,36
-38,71
-25,24
-30,65
-21,25
-18,63
-28,18
-27,41
-26,37
Annual crops (corn, beans)
-22,89
-27,75 -
-25,27
-25,78
-25,46
-23,70
Sediment - 1
-26,05
-32,50
-29,06
-30,05
-33,88
-29,17
-33,93
Sediment - 2
-28,63
-30,46
-29,77
-29,69
-25,74
Sediment - 3
-27,22
-31,15
-25,23
-27,61
-26,78
-32,97
-32,36

41. Works in progress
Analysis of FRNs, soil chemical properties and particle size for soil samples collected in natural forest land within the watershed
Analysis of FRNs, soil chemical properties and particle size for soil samples collected in production forest land within the watershed
Analysis of FRNs, soil chemical properties and particle size for soil samples collected in annual crop land within the watershed
Assessment of soil erosion rates/ soil loss for individual sampling areas
Assessment of soil erosion rates/ soil loss for the whole watershed
Using CSSI technique for assessment of sediment sources
Comparing data obtained by CSSI and FRNs techniques.

42. Thank you for your attention!