2017 SWCS Annual Conference July 30-August 2, 2017 Monona Terrace Convention Center

1. Quantifying Soil Loss and Re-
deposition in Field Experiments
Y. Ping Hsieh
Center for Water and Air Quality
College of Agriculture and Food Sciences
Florida A&M University

2. • Soil erosion is an ubiquitous watershed process yet
its observation under true field conditions is still a
challenge.
• Basically, we don’t have a practical good field
technology that can quantify soil erosion, especially
those occur in “normal” croplands (soil loss <40
t/h/y, or 3 mm/y ).

3. A critical issue in soil erosion
research: lack of quality field
data.

4. Trimble and Crosson (Science, 2000): “The soil
loss estimates, by USLE or its derivatives, in the
US is in the order of 2-8 billion tons/y but the
observed sediment yield is less than 0.5 billion
tons/y, in which a large portion is from bank
erosion….” “…..it was all based on models. Little
physical, field-based evidence has been offered to
verify the high estimate.
In response to this criticism, soil conservation
community represented by Nearing et al (2000)
said “soil loss is the amount that moved on the
field (re-deposition?), not necessarily out of the
field.”

5. Other discrepancies of the current soil erosion
measurement technology
Cited in Michael Stocking (1992) paper:
“…at the Makaweli Catchment, Sri Lanka soil loss
had been estimated ranging from 1026 t/ha/y using
USLE (El-Swaify et al., 1985) to 4 t/ha using
sediment measures and sediment transport
formulae (NEDECO, 1984) to 0.13 t/ha using 0.5
ha small plots (Krishnarajah, 1985)…”

6. Almost all soil erosion model are
runoff-plot based. Runoff plots
use physical boundaries to
enclose a small area (<0.01 ha)
and redirect runoff into a
collector for soil loss
measurements. Runoff plots are
too small in comparison to a real
field, they also obstruct natural
runoff and, therefore, biases soil
erosion observations.

7. There are a few methods,
e.g. erosion pins and 137
Cs
tracer methods that do not
obstruct natural runoff
and can be applied to
field-scale observation of
soil erosion but they are
not sensitive (uncertainty
>100 t/ha.) nor cost
effective for most cropland
studies.

8. How about soil re-deposition in field?
Soil loss from a field is only part of a soil
erosion process. Soil re-deposition, a precursor
of soil loss, has been largely ignored in the past
due to lack of a proper technology.

9. A good soil erosion field method should satisfy
the following criteria: it
1) should not obstruct the natural field runoff pattern;
2) can be conveniently and cost-effectively applied to
field-scale experiments, with or without vegetation;
3) can quantify both soil loss and soil re-deposition;
4) can provide chemical and physical properties of
the eroded soil particles;
5) is sensitive enough (detection limit 1 t/h) for
“normal” cropland sustainability assessments.

10. The mesh-pad method
Mesh-pad method (or called the mesh-bag or
mesh-sheet method) has been introduced
(Hsieh, 1992; Hsieh et al., 2009) but it hasn’t
been adequately evaluated or applied.

11. A mesh pad (10 cm x 10 cm) is made of a top nylon mesh (≈ 4
mm openings) and a bottom fine nylon mesh (≈ 0.1 mm
openings). The two meshes are aligned and installed on a bare
soil surface using bamboo pegs.

12. Mesh pads conform to the contour of the bare soil surface.
(The vegetation directly underneath a mesh pad needs to be
removed.) Water can infiltrate through the meshes but soil
particles can’t because there is little space underneath them.
*MPs mark soil surface; they don’t trap soil particles.

13. 2m
2m
Mesh pads
Mesh pads are
laid out in 2 – 4 m
random or regular
grid pattern.

14. After one or several rain events, the soil rest on and in
between the mesh sheets are harvested and brought
back to the laboratory for analysis.

15. Soil re-deposition in a field
Mesh pads don’t “trap” soil particles but “mark” the
original soil surface so that the “re-deposited” soil
particles can be conveniently sampled.
The amount of soil re-deposition (SRD) in a field is
estimated by the weight/area ratio of the mesh pads:
SRD (ton/ha) = (weight of soil on MPs)/(area of MPs)

16. Soil loss by MP: Direct method
1) First, define a “soil retention area” at the bottom
of the slope using silt fences.
2) Then, install a nylon liner on the retention area to
prevent local soil redistribution to be sampled by
MPs.
3) Install MPs on the mesh liners to quantify the soil
re-deposition in the retention area (i.e., soil loss
from the slope).
4) Calculate soil loss.

18. Soil loss by MP: Indirect method
First, one needs to observe two consecutive soil re-
deposition periods (R1 and R2) respectively and
collectively (R) over the entire two periods in the
same plot, which located at the bottom of the slope.

19. The re-deposition R over the two periods should contain
all the R2 plus the remaining of R1, or (R1- R1lost ), where
R1lost is the portion of R1 lost during the second runoff
period:
R = R2 + (R1 – R1lost) (1)
or,
R1lost = R1 + R2 – R (2)

20. But R1lost was only part of the soil loss from the plot during
the second period. There was the soil loss associated with R2
too, i.e., R2lost. (The counter part of R1 during the second
period is R2 + R2lost . )
The value of R2lost is unknown but we can deduce it by
assuming the following relationship during the second
period:
R2lost/(R2 + R2lost) = R1lost/(R1) (3)
Rearrange Eq. (3) and substitute the relationships in Eq. (2),
R2lost = R2(R1+R2-R)/(R- R2) (4)

21. Total soil loss during the second runoff period
= R1lost + R2lost
= (R1+R2-R) + R2(R1+R2-R)/(R-R2)
= R(R1+R2-R)/(R-R2)
The soil loss from the plot, therefore, can be
deduced from the soil re-deposition of R1, R2
and R, which are all observable.

22. The Mear’s Farm (Grand Ridge, FL)
field experiments

23. Objectives
• Testing the sensitivity and accuracy of the MP
method.
• Quantify soil re-deposition and soil loss in a
large filed and evaluate their significance in
sustainable crop production.

24. IV
III
silt fence
SEDA
I
II
NEDA
silt fence
NEDA

25. 6 8 5 6 5 06 8 5 7 0 06 8 5 7 5 06 8 5 8 0 0
3 4 0 4 4 5 0
3 4 0 4 5 0 0
3 4 0 4 5 5 0
3 4 0 4 6 0 0
3 4 0 4 6 5 0
3 4 0 4 7 0 0
3 5
3 5 .5
3 6
3 6 .5
3 7
3 7 .5
3 8
3 8 .5
3 9
3 9 .5
4 0
4 0 .5
4 1
4 1 .5
4 2
4 2 .5
4 3
4 3 .5
4 4
0 2 0 4 0 6 0 8 0
m
XV
XIV
XIII
I
II
III
IV
V
VI
VII VIII
IX
XII
X XI
Slope: 2-5%
Contour of the landscape
3.4ha

26. May

27. June

28. July

29. Results

30. Sensitivity analysis: soil re-deposition
due to irrigation

31. t/h
10 m

32. Effects of MP placements: random vs.
regular grids and density of placement

33. A2 2.6-m grid
A2 – 3.7-m grid grid A2 3.7-m random
10 m

34. Soil re-distribution vs. soil loss

35. Soilre-distributionorloss,tons
0
20
40
60
80
100
120
140 Re-distributed, top (2.6 ha)
Re-distributed, mid (2.6 ha)
Re-distributed, bottom (2.1 ha)
Loss from the slope
6/10-6/25 6/25-7/15 7/15-8/11 8/11-8/27

36. Soil, mT Si+Cl, mT TKN, kg TP, kg
0
10
20
30
40
50
60
Top slope
Mid slope
Bottom slope
Loss from slopes
157

37. Peanut cultivation 0-4 week 5-12 week
Eroded soil Re-deposition, t/h 11.5 28.2
Soil loss by MP method, t/h 0.5 0.16
Soil loss by SWAT model, t/h 9.8 1.5
Total rainfall, mm 150.1 196.6

38. Some remarks about quantifying soil
loss and soil redistribution:
• Soil losses are additive in multiple collections but
soil re-depositions are not because the re-deposited
soil could be re-counted multiple times.
• The amount of soil re-deposition in the field is far
greater than soil loss from the field (1 % of soil re-
deposition).

39. Spatial and temporal patterns of
soil re-deposition

40. t/h

41. Soil re-depo, t/h (average 32.2 t/h)
Organic matter re-depo conc., g/kg (average 14.1 g/kg)
Total organic matter re-depo, soil x OM conc. kg/h (average
443.5 kg/h, or 23.5 kg N/h, or 221.8 C kg/h re-depo)
June 25 – July 15

42. Conclusion I
• Soil loss from Mears Farm was not significant but
soil re-deposition was.
• Soil organic C, N and P were mostly re-deposited in
the mid slope implying short mean transport distance
of detached soil particles in one season.
• The re-deposited and lost soil was found much
enriched in fine particles, N and P. Those results
must have significance on cropland management and
sustainability. The exactly interpretation of those
results, however, requires further investigations.

43. Conclusions II
We found that the MP method can fill a critical gap in soil
conservation research because it
1. does not obstruct the natural runoff pattern of a field.
2. can be conveniently and cost-effectively applied to a large
field with or without vegetative cover.
3. quantifies both soil re-deposition and soil loss.
4. provides properties of eroded soil particals.
5. is very sensitive (DL 1 t/h).
6. provides both spatial and temporal distribution
information of eroded soil and nutrients, which is
valuable for verification and calibration of soil erosion
models.

44. Thank you!