IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Research article
erd

Soil Erosion Control by Coconut Husk Buffer Strip inBohol Island of Philippines
JULIAN TORILLO JR.
Graduate School of Agriculture, Tokyo University of Agriculture, Japan
Email: juliantorillo@yahoo.com

MACHITO MIHARA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Received 9 December 2010

Accepted 9 February 2011

Abstract Soil erosion causes serious environmental problems in Bohol Island, Philippines.
Considering the agricultural socio-economic situation in the island, utilizing available
materials in the region to mitigate soil erosion particularly in the upland fields have been
focused. Thus, slope modeling experiments were conducted to evaluate the effects ofcoconut husk buffer strip on mitigating the losses of soil and nutrients. Based on theexperimental results, the coconut husk buffer was effective to trap transported soils,
however the nutrient losses from the plots with the coconut husk buffer were slightly
higher than that from control plot without any treatments in the initial stage of rainfall
events after the installation of coconut husk buffer strip.
Keywords coconut husk, buffer strip, trapping capability, soil and nutrient losses

INTRODUCTION
Parts of the land areas with 8-18% slopes in Bohol Province of the Philippines are covered withupland fields. Even in the mountainous areas with more than 18% in slopes, some portions havebeen exploited particularly for subsistence agriculture. Along with the higher intensity rainfalls in
the interior mountainous areas, upland fields and other less vegetated areas on slopes aresusceptible to soil erosion that causes rapid degradation of land (OIDC, 2006).
Upland fields with protruding stones and rocks on ground surfaces as well as abandoned
farmlands are now dominant particularly in the southwestern part of the island. Thus, the strategies
for rehabilitating and conserving these land resources are necessary where soil erosion is the prime
problem to be mitigated. This study dealt with the strategic soil erosion control by utilizing coconut
husk which is biodegradable, renewable and locally available material in the region. Considering
the agricultural socio-economic situation in the island of Bohol, economical and easy applicationwith high efficiency is also one of important scopes that should be focused. So, the objectives ofthis study are to observe the capability of coconut husk buffer to trap soil and nutrient losses withmeasuring the particle sizes that were trapped by buffer medium.
MEHODOLOGY
In order to evaluate the effects of coconut husk buffer on mitigating soil erosion, modelingexperiments were carried out in the laboratory with artificial rainfall facilities at Tokyo Universityof Agriculture, Tokyo, Japan. The soil with clay percentage at 63.8%, silt at 8.1% and sand at
28.1% obtained from abandoned corn field in Tiptip District, Tagbilaran City of Bohol was used inthe experiment.
Coconut husk was pounded by hammer to make it into a fibrous material and installed at thelower end of the slope model plots (130 cm long and 11 cm wide) in which around 7.5 kg of thesoil was filled. Three plots were prepared as Plot I, Plot II and Plot III as the plot of control, the© ISERD

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

plot with 2 rows of husk buffer and the plot with 2 rows of husk buffer in addition to 25 cm husk
mulch, respectively as shown in Fig. 1. The prepared slope model plots were set up at 8 degrees inslope and simulated by artificial rainfall. Rainfall simulation was carried out for 2 hours at theintensity of 60 mm/h. The experiment was replicated 3 times in separate days. Surface water
discharge (Point 1) from each plot was measured and the surface water was collected at every 15
minutes for the first hour and at every 30 minutes for the second hour.

2plyHusk
huskbufferbuffer
Point 3HuskHuskmulch
mulch

Point 1

Point 2Fig. 1 Stainless slope model plots and installation ofcoconut husk buffer at slope toe
The amount of percolation water (Point 2) was measured and sampled after 24 hours from theend of each rainfall simulation. Both collected water samples at Point 1 and Point 2 were analyzed
for total nitrogen (T-N) and total phosphorous (T-P). Also, the amount of soil losses were measured
for collected water samples at Point 1. After the decomposition of water samples with sodiumhydroxide (NaOH) and potassium peroxodisulfate (K2S2O8), the concentrations of T-N and T-P
were measured by spectrometric method (Mihara et al, 2000). Oven drying method was used tomeasure the soil loss concentration in the suspended water of surface runoff.
For comparing the particle sizes of soils eroded from each plot, the wet sieving method wasapplied using 106, 250, 500 and 1000 μm sieves (Ghadiri et al., 2001). One liter of suspended
water was collected after passing through the sieves to determine the amount of <106 μm indiameters. Then the collected one liter suspended water was sampled by pipette method then filled
into the weighing can and dried by oven together with the sieved soils from 106, 250, 500 and 1000μm sieves.
RESULTS AND DISCUSSION
Soil losses
As shown in Fig. 2, the amounts of soil losses at Plot I as control dramatically increased with therepetition of rainfall simulation compared to that at Plots II and III with husk buffer. Also, there
was a significant difference at 99% level between the amounts of soil losses at Plot I as control andthat at Plots II and III with husk buffer in the second rainfall simulation test. During the first,second and third rainfall simulation tests, the 2 rows of husk buffer at Plot II could mitigate 36, 45and 53% of soil losses at Plot I as control while the 2 rows of husk buffer with 25 cm husk mulch at
Plot III could mitigate 50, 61 and 54%, respectively.

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Third rainfall simulation

Second rainfall simulation

First rainfall simulation

250250A**

20015010050150

B**
B**

100500306060

Time (min)9090120120100000Plot I: controlled plot

15050000

250200

軸ラベル

200

軸ラベル

Cumulative soil losses(g/m2)

It was clearly observed that the coconut husk buffer worked to mitigate about 50% of soillosses. Meanwhile, the 2 rows husk buffered with mulch at Plot III had no significant difference inthe amounts of soil losses with the 2 rows husk buffered at Plot II.

306060Time (min)909012012000

306060Time (min)9090120120

Plot III: 2 rows husk buffered with mulch plot

Plot II: 2 rows husk buffered plot**significant difference at 99%

Fig. 2 Cumulative soil losses from Plots I, II and III in eachrainfall simulation test
First rainfall simulation

Second rainfall simulation

180.00120.00
90.00

60.00
30.00

Plot I
Plot II
Plot III

0.00

Particle size (µm)

150.00120.00
90.00

60.00
30.00

Plot I
Plot II
Plot III

0.00

Particle size (µm)

Soil loss (g/m2)

180.00150.00

Soil loss (g/m2)

Soil loss (g/m2)

180.00Third rainfall simulation
150.00120.00
90.00
60.00
30.00

Plot I
Plot II
Plot III

0.00

Particle size (µm)

Fig. 3 Particle sizes of eroded soils from Plots I, II and III
at first, second and third rainfall simulation tests

Coconut husk buffer strip trapping capability
The amounts of eroded soils from the plots in particle sizes of <106 μm in diameter weredramatically higher compared to the particle sizes of >106 μm (106 to 1000 μm) as shown in Fig. 3.
Although coconut husk buffer could mitigate only around 25% to 35% of eroded fine soils inparticle sizes of <106 μm, coconut husk buffer trapped 99% of eroded soils in particle sizes of>106 μm (106 to 1000 μm).
The experimental results showed the coconut husk buffer was highly capable to trap erodedsoils larger than 106 μm in diameter, however less capable to trap fine soils in particle sizes of<106 μm.
Total nitrogen losses
As shown in Fig.4, the amounts of total nitrogen (T-N) losses through surface discharge from Plots
II and III with husk buffer were slightly higher than that from Plot I as control in the first rainfall
simulation test. It showed that coconut husk set in the plots released total nitrogen components.
However, the amounts of total nitrogen (T-N) losses through surface discharge from Plots II and III
became lower than that from Plot I in the second and third rainfall simulation tests.

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

0.60

0.40
0.20
0.00
03060

90120

Second rainfall simulation

0.80
0.60

0.40
0.20
0.00

03060

90120

Total nitrogen loss (g/m2)

First rainfall simulation

0.80

Total nitrogen loss (g/m2)

Cumulative total nitrogenloss (g/m2)

Higher amounts of total nitrogen losses through percolation were observed at the husk
buffered plots, particularly in Plot II (Table 1). The results clearly indicated that coconut husk set in
the plots released total nitrogen components not only through surface runoff but also throughpercolation. In addition, there was a tendency for the amounts of total nitrogen losses throughpercolation to decrease with the repetition of rainfall simulation.
Third rainfall simulation

0.80
0.60
0.40

0.20
0.00
03060

90120

Time (min)Time (min)Time (min)Plot I: controlled plot

Plot II: 2 rows husk buffered plot

Plot III: 2 rows husk buffered with mulch plot

Fig. 4 Cumulative total nitrogen (T-N) losses through surface discharge from Plots I,
II and III in each rainfall simulation test
Table 1 Total nitrogen losses through percolation (x10-2 g/m2)
First rainfall simulation
2.889
3.066
1.615

Plot I
Plot II
Plot III

Second rainfall simulation
1.561
1.983
1.235

Third rainfall simulation
0.955
2.500
1.209

Total phosphorus losses
As shown in Fig. 5, there was a tendency that the amounts of total phosphorus (T-P) losses
increased with the repetition of rainfall simulation. Also, the amounts of total phosphorus (T-P)
losses from Plots II and III with husk buffer tended to be lower than that from Plot I as control,
although a significant difference was not recorded.
As shown in Table 2, the amount of total phosphorus losses through percolation tended toincrease with the repetition of rainfall simulation, although some fluctuations in amounts of T-P
losses were observed.
Second rainfall simulation

0.03

0.02
0.01
0.00
03060

Time (min)90

Plot I: controlled plot

120

0.04

Total phosphorus loss(g/m2)

Total phosphorus loss(g/m2)

Culmulative totalphosphorus loss (g/m2)

First rainfall simulation
0.04

0.03
0.02
0.01

0.00
03060

90120

Time (min)Plot II: 2 rows husk buffered plot

Third rainfall simulation

0.04
0.03

0.02
0.01
0.00

03060

Time (min)90

Plot III: 2 rows husk buffered with mulch plot

Fig. 5 Total phosphorus (T-P) losses through surface discharge from Plots I, IIand III in each rainfall simulation test© ISERD28120

IJERD – International Journal of Environmental and Rural Development (2011) 2–1

Table 2 Total phosphorus losses through percolation (x10-2 g/m2)
First rainfall simulation
0.039
0.052
0.031

Plot I
Plot II
Plot III

Second rainfall simulation
0.090
0.058
0.161

Third rainfall simulation
0.120
0.054
0.048

Relationship between soil and nutrient component losses
As shown in Fig. 6, the relationship between total nitrogen and soil losses changed remarkably
during the first to third rainfall simulation tests. During the first rainfall simulation test, theamounts of total nitrogen losses rapidly increased with the amounts of soil losses. In the second andthird rainfall simulation tests, the trend in the first rainfall simulation test became gentler, as theamounts of total nitrogen losses gradually increased with the amounts of soil losses.
The amounts of total phosphorus losses increased with the amounts of soil losses (Fig. 7). The
increasing tendencies of total phosphorus losses from each plot changed slightly during the first to
third rainfall simulation tests. However, there was a tendency that the amounts of total phosphorus
losses from Plots II and III with husk buffer became higher than that from Plot I of control,
especially in the first and second rainfall simulation tests. In the third rainfall simulation test, thedifference in the amounts of total phosphorus losses among plots became small.

0.40
0.20
0.00
0.00

100.00200.00

Cumulative soil loss (g/m2)
Plot I

Plot II

Cumulative nitrogen loss (g/m2)

Cumulative T-N losses (g/m2)

0.60

0.60
0.40
0.20
0.00
0.00

y = 0.0061x + 0.1292

y = 0.0061x + 0.1959

R² = 0.9691**

R² = 0.9212**

R² = 0.848*

100.00200.00

Cumulative soil loss (g/m2)
Plot I

Plot IIIy = 0.003x + 0.1038

Second rainfall simulation

0.80

Plot IIy = 0.002x - 0.0834 y = 0.0023x + 0.0271

R² = 0.9957**

R² = 0.9815**

Cumulative nitrogen loss (g/m2)

First rainfall simulation

0.80

Third rainfall simulation

0.80
0.60

0.40
0.20
0.00
0.00

100.00200.00

Cumulative soil loss (g/m2)

Plot IIIPlot I

Plot IIy = 0.0023x + 0.0489

y = 0.0012x + 0.0407

R² = 0.9396**

R² = 0.9795**

y = 0.0018x + 0.0242

Plot IIIy = 0.002x + 0.0009

R² = 0.9767**
R² = 0.9773***confidence* confidence intervalinterval at
at 95%
95%**confidence**confidenceintervalinterval at
at 99%
99%

Fig. 6 Relationship between T-N losses and soil losses

Second rainfall simulation

0.02
0.01
0.00

0.00

100.00200.00

Cumulative soil loss (g/m2)
Plot Iy = 0.0002x - 0.0007

R² = 0.9945**

Plot II

Plot IIIy = 0.0002x - 0.0018 y = 0.0003x - 0.0014

R² = 0.9917**

R² = 0.9713**

0.04

0.03
0.02
0.01
0.00
0.00

100.00200.00

Cumulative soil loss (g/m2)
Plot I

Plot II

Plot IIIy = 0.0002x - 0.0119

y = 0.0002x - 0.001

y = 0.0003x + 0.0004

R² = 0.9749**

R² = 0.9995**

R² = 0.996**

Third rainfall simulation
Cumulative phosphorus loss(g/m2)

0.03

Cumulative phosphorus loss(g/m2)

Cumulative T-P losses (g/m2)

First rainfall simulation
0.04

0.04

0.030.02
0.01
0.00
0.00

100.00200.00

Cumulative soil loss (g/m2)
Plot II

Plot IIIy = 0.0001x + 0.0015

Plot Iy = 0.0003x + 0.0003

y = 0.0002x - 0.0019

R² = 0.9959**

R² = 0.9943**

R² = 0.9595****confidence**confidenceintervalintervalat
at99%
99%

Fig. 7 Relationship between T-P losses and soil losses© ISERD

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IJERD – International Journal of Environmental and Rural Development (2011) 2–1

CONCLUSION
In Bohol Island of Philippines, soil erosion causes serious environmental problems. Considering
the agricultural socio-economic situation in the island, utilizing available materials in the region tomitigate soil erosion particularly in the upland fields have been focused. So, this study dealt withthe evaluation of the effects of coconut husk buffer strip on mitigating the losses of soil andnutrients.
The experimental results indicated that coconut husk buffer could trap 99% of eroded soils inparticle sizes of >106 μm (106 to 1000μm), however less capable to trap eroded fine soils inparticle sizes of <106 μm. In addition, the nutrient losses from the plots with the coconut husk
buffer were slightly higher than that from control plot without any treatments in the initial stage ofrainfall events after the installation of coconut husk buffer strip. It was considered that coconut
husk set in the plots released nutrient components.
ACKNOWLEDGEMENT
I would like to acknowledge the support of President Dr. Elpidio T. Magante of Bohol Island State
University for his meaningful guidance and advices.
REFERENCES
Hussein, J., Yu, B., Ghadiri, H. and Rose, C. (2007) Prediction of surface flow hydrology and sediment
retention upslope of a vetiver buffer strip, Journal of Hydrology, 338, 261-272.
Mihara, M. and Ueno, T. (2000) Nitrogen and phosphorus transfer in soil erosion processes, IAHS
Publication, No. 263.
Orient Integrated Development Consultants Inc. (2006) Bohol Agriculture Master Plan, CY 2006-2026.

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