IJERD – International Journal of Environmental and Rural Development (2013) 4-2

Research article
erd

Effects of Retting Treatment on Coconut Husk Buffer
Strips for Eliminating Nutrient Losses
JULIAN E. TORILLO, JR.
Graduate School of Agriculture, Tokyo University of Agriculture, Japan

MACHITO MIHARA*
Faculty of Regional Environment Science, Tokyo University of Agriculture, Japan
Email: m-mihara@nodai.ac.jp
Received 20 June 2013

Accepted 24 September 2013(*Corresponding Author)

Abstract Coconut husk has been applied as buffer strips for soil erosion control on slope
upland fields in Bohol of the Philippines. However, attention has been paid to the losses ofnitrogen and phosphorus components not only those leached from synthetic fertilizer
applied in upland fields but also those components released from coconut husk buffer
strips. Thus, pretreatment of coconut husk by retting before its installation into the fieldhas been proposed. The objective of this study is to find out the effect of ret treating thecoconut husk utilized as buffer strips on eliminating its releasing nitrogen and phosphorus
components. Coconut husks were trimmed then minor pounding by hammer were applied
to meet the desired porosity of the material as buffer. Retting treatment of 41.34 g in dry
mass of coconut husk was carried out by soaking into 1,300 ml of distilled water for 10
days to extract its nitrogen and phosphorus components. Ret treated coconut husk were
installed into stainless slope model plot filled with Philippine soil and set at 8 degrees inslope. Another plot was also prepared and installed with untreated coconut husk thenrainfall simulation was carried out into both plots. The experimental results showed thatthe amount of nitrogen released from the plot installed with ret treated coconut husk buffer
strip was significantly lower than that of untreated husk buffer strip at 99% significant
level. Therefore, it was concluded that 10 days retting treatment of coconut husk for buffer
strips was effective on eliminating the release of nutrient particularly on nitrogen fromleaching.
Keywords coconut husk, retting, nitrogen, phosphorus, bio-fertilizer

INTRODUCTION
Upland fields with protruding stones and rocks on ground surfaces as well as abandoned farmland
are dominant particularly in the southwestern part of Bohol, Philipines (Torillo and Mihara, 2011).
Moreover, these lands are mostly located on sloped-areas with 8-18% and even some portions withmore than 18% slope, particularly for subsistence agriculture (OIDCI, 2006). Together with highsqualls, uplands in the island are susceptible to soil erosion causing rapid degradation of land.
Meanwhile, about 5 million coconut trees are cultivated in the island of Bohol (OIDCI, 2006)
producing large amount of coconut husk. These coconut husks were considered as waste residue
and left rotten in the site. In this study, utilizing coconut husk, a locally available material has been
focused from a view point of conservation agriculture in Bohol. However, coconut husk that were
installed as buffer strips for soil erosion control tended to release nitrogen and phosphorus. Thistendency was observed during the slope modeling under artificial rainfall simulator (Torillo andMihara, 2011). Those nutrients released from the coconut husk may leach through percolation andsurface runoff resulting water pollution into downstream. Therefore, treating of coconut husk
before its installation as buffer strips through retting has been recommended.
The objective in this study is to find out the effect of retting treatment of coconut husk for
buffer strips on eliminating its nitrogen and phosphorus release.

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MEHODOLOGY
Retting treatment of coconut husks
Nutrient component particularly on phosphorus can be extracted from the coconut husk by retting
method (Torillo and Mihara, 2012). Thus, retting treatment of coconut husks has been applied bysoaking into distilled water.
Coconut husks were cut and trimmed into 5 cm wide and 12 cm length then minor poundingby hammer was done to make into a porous material similar to that being installed into the site asbuffer strips. Four pieces of pounded coconut husks were prepared while two of them wereintended for retting treatment and the other two pieces were retained as untreated coconut husks.
Small amount of coconut husk`s sample was taken for analyzing total nitrogen (T-N) and total
phosphorus (T-P) component after the decomposition with sodium hydroxide (NaOH) andpotassium peroxodisulfate (K2S2O8). Concentrations of T-N and T-P were measured by spectrometric methods (Mihara and Ueno, 2000).
Pounded two pieces of coconut husks weighing 41.34 g in dry mass for retting treatment werethen soaked into 1,300 ml of distilled water. Retting treatment was carried out up to ten days as
Torillo and Mihara (2012) reported that the optimum period of releasing nutrient components fromcoconut husk was at the tenth day of retting. After ten days passed of soaking, coconut husks weretaken out and ret liquor was sampled for analyzing the released amount of T-N and T-P from thecoconut husk.

Fifth dayof rettingFirst dayof retting

a)

b)

c)

Fig. 1 Procedures in preparing the coconut husks for retting treatment such asa) cutting, b) pounding and c) retting

Control

Untreated

Treateda)b)

Fig. 2 Slope model plots in a) controlled, untreated husk buffered and treated husk
buffered plots and b) slope model plots under artificial rainfall simulator© ISERD
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Slope modeling with coconut husks buffer strip
It was proven that there was no significant difference between the two rows of coconut husk buffer
strip and the two rows coconut husks buffer strip with 25 cm husk mulch on mitigating soil losses(Torillo and Mihara, 2011). Therefore, in this study two rows of coconut husk buffer strips havebeen installed into slope model plots.
Three stainless slope model plots were prepared as controlled plot, treated coconut husk
buffered plot and untreated coconut husk buffered plot. Each slope model plot (130 cm long and 11
cm wide) were filled up with Philippine soil having clay percentage at 63.8%, silt at 8.1% and sandat 28.1% (Torillo and Mihara, 2011) of around 7.5 kilograms. Ret treated and untreated coconut
husks were installed at the lower toe of the plots as treated coconut husk buffered plot anduntreated coconut husk buffered plot, respectively. Those two slope model plots along with
controlled plot were set at degrees in slope. Rainfall simulation was carried out at rainfall intensityof 60 mm/h within two hours. Suspended water samples from surface discharge were collected
every 15 minutes for the first hour then every 30 minutes for the second hour. Percolation water
was collected at each plot after 24 hours from the end of rainfall simulation. Surface water
discharge and percolated water samples were analyzed for total nitrogen (T-N) and total
phosphorus (T-P). Surface water discharge samples were also measured for soil losses by ovendrying method. Three repetitions of rainfall simulation were carried out in separate days.
RESULTS AND DISCUSSION
Total nitrogen and total phosphorus released from coconut husk during retting treatment
Minor pounded coconut husks of 41.34 g in dry mass were soaked into 1,300 ml of distilled water
within ten days. In the tenth day of soaking, distilled water soaked with coconut husks or called ret
liquor (Fig. 1-c) were sampled then analyzed for total nitrogen (T-N) and total phosphorus (T-P).
The amounts of T-N and T-P in coconut husk before soaking into the distilled water were also
analyzed to determine the released amounts of these nutrients from coconut husk by retting.
Analysis data showed that the amounts of T-N and T-P in raw coconut husk were 0.792
mgN/g and 0.863 mgP/g, respectively (Table 1). During the tenth day of soaking or retting, theamount of T-N in ret liquor was 0.119 mgN/g and 0.729 mgP/g of T-P. Those values indicated that
15.02% of T-N component and 84.47% of T-P component from coconut husks were released into
ret liquor within ten days of retting. The tendency of high released of T-P from coconut husk was
supported by Havis and Alberts (1993) which nutrient leaching dynamics from partiallydecomposed corn residue was examined in a laboratory simulation experiment. They found out that
more PO4-P leached than NO3-N and NH4-N.
Table 1 Amounts of T-N and T-P in coconut husks and in ret liquor

Total nitrogen (T-N)
Total phosphorus (T-P)

Amounts of nutrientsin coconut husk
0.792 ± 0.045 mgN/g
0.863 ± 0.011 mgP/g

Amounts of nutrientsreleased into ret liquor
0.119 ± 0.028 mgN/g
0.729 ± 0.188 mgP/g

Percentage of nutrient
released from coconut husk
15.02%
84.47%

Effects of coconut husk buffer strips on mitigating soil losses
Two pieces of coconut husks at 41.34 g in dry mass were ret treated while other two pieces wereretained as untreated coconut husk. To observe the effects of retting treatment on eliminating total
nitrogen (T-N) and total phosphorus (T-P) in coconut husks for buffer strips, those pieces ofcoconut husk were installed into slope model plots then simulated under artificial rainfall.
Mihara (2001) reported that nitrogen and phosphorus components were transported by
sediment and suspended solids which was observed in USLE plots under natural rainfall. In thisconnection, the amount of soil losses was also observed in this study. As shown in Fig. 3 that the© ISERD
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trend of cumulative amount of soil losses is increasing with the repetition of rainfall simulation
among slope plots. This tendency is due to the accumulation of transported soil with the repetitionof rainfall at the lower toe of the plots. Hence, the depth of the sediment deposited at buffer strip
increases with time and substantially altering the geometry and gradient of the surface (Rose et al.,2003). This trend results smaller soil particles to be runoff and passes through voids in buffer strips.
The results showed that the amount of soil losses at treated and untreated coconut husk
buffered plots were lower at an average of 29, 35 and 42% than that of controlled plot during thefirst, second and third rainfall simulation, respectively (Fig. 3). It was clearly indicated that coconut
husk buffer strips mitigated soil losses which significant differences at p<0.01 were observed.

200
150

a**
b**
c**

100
50
0
0

30

60

90

300
250
200

a**

150

b**
c**

100
50

120

Time (min)

0
0

30

60

90

Time (min)Controlled plot,

120

Third rainfall simulation
Cumulative amount of soil losses(g/m2)

250

Second rainfall simulation
Cumulative amount of soil losses(g/m2)

Cumulative amount of soil
losses (g/m2)

First rainfall simulation
300

300

a**

250
200

b**
c**

150

100
50
0
0

30

60

90

120

Time (min)Untreated husk buffered plot,
Treated husk buffered plot** Significant difference at p<0.01

Fig. 3 Cumulative amount of soil losses with time during the first, second andthird rainfall simulation
Effects of retting treatment on eliminating total nitrogen and total phosphorus in coconut
husk utilized as buffer strips
Fig. 4 shows the amounts of T-N and T-P losses through surface discharge and percolation. It is
indicated in the diagram at the right side of the figure showing the values plotted in histogram fromzero x-axis and up is the amount of T-N losses. Meanwhile, values plotted in histogram from zero
x-axis and down is the amount of T-P losses. Darker colors in histogram are the amounts of T-N
and T-P losses through percolation and lighter colors are the amount of T-N and T-P losses throughsurface discharge.
The amount of T-N losses through percolation and surface discharge are shown both (Fig. 4)
to observe the balance losses of this nutrient. However, the amount of T-N losses throughpercolation was averagely 95 times lower than that of T-N losses through surface discharge. For
instance in the case of (T) treated coconut husk buffered plot during the first rainfall simulation, TN losses through percolation was 0.004 g/m2 compared to 0.817 g/m2 of T-N losses through surface
discharge. Thus, T-N losses through percolation were insignificant that it did not affect in thestatistical quantification of T-N losses.
During the first rainfall simulation, the (U) untreated coconut husk buffered plot showed
higher amount at 0.378 g/m2 accounting 31.62% of T-N losses higher than that of (T) treatedcoconut husk with a significant difference at p<0.01. This trend indicated that T-N component incoconut husk has been eliminated by retting treatment. However, (T) treated coconut husk buffered
plot showed no significant difference than that of (C) controlled plot. This signifies that treatedcoconut husk buffer showed less effective on mitigating T-N losses from the plot.
A sudden decrease of T-N losses among three plots was observed from first rainfall simulation
to second rainfall simulation test. This might be due to most of T-N component in soil that aresusceptible for runoff had been transported during the initial rainfall simulation. During the second
rainfall simulation, (U) untreated coconut husk buffered plot also showed higher amount at 0.161
g/m2 accounting 36.84% of T-N losses higher than that of (T) treated coconut husk buffered plot.
Although, only p<0.05 of significant difference was observed. It was also showed that treated© ISERD
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coconut husk buffer were able to mitigate T-N losses since (T) treated coconut husk buffered plot
has 0.173 g/m2 of T-N lower than that of (C) controlled plot with significant difference at p<0.01.
During the third rainfall simulation, although (T) treated coconut husk buffered plot appeared
to be higher losses of T-N than that of (U) untreated coconut husk buffered plot, it was indicatedthat there was no significant difference between the two plots. Therefore, based on theexperimental results, retting treatment of coconut husk influences in eliminating T-N losses.
1.4

a**

1.2

Amount of T-N losses through surface
discharge and percolation(g/m2)

Second rainfall simulation

First rainfall simulation

31.62%

1.0b**

Third rainfall simulation

1.225

1.225

1.05

1.05

0.875

0.875

0.7

0.7

b**

0.8

0.6

0.525

0.4

Amount of T-N losses (g/m2)

Amount of T-N losses (g/m2)

Loss of T-N
0.525

a**

a*

36.84%

0.35

a*
a,b

0.35

b*

b*,**
0.2

0.175

0.175

0.0

0

0

Surfacedischarge

U

0.4(0.350)0.6(0.525)

U

T

a*,*
*

C

U

c**

b*

c*,**

b**

a**

b**
-0.175-0.175

-0.35

-0.35

0.0 axis

T

0

0

b**
0.2
(0.175)C

T

Amount of T-N losses (g/m2)

0.0
0.000

C

Amount of T-N losses (g/m2)

Amount of T-P losses through surface
discharge and percolation(g/m2)

Percolation

Percolation

0.0 axisb*,**
Surfacedischarge

Loss of T-P-0.525-0.525

C:Controlled plot U:Untreated coconut husk buffered plot T:Treated coconut husk buffered plot
* Significant difference at p<0.05, ** Significant difference at p<0.01

Fig. 4 Amounts of total nitrogen (T-N) and total phosphorus (T-P) losses throughsurface discharge and percolation
The amount of T-P losses are also shown in Fig. 4 which is below the zero x-axes. It was also
observed that the amount of T-P losses through percolation is significantly lower than that of T-P
losses through surface discharge. For instance, the amount of T-P losses through percolation from(T) treated coconut husk buffered plot was 1×10-4 g/m2 accounting 450 times lower than that of its
surface discharge which is 0.045 g/m2. Thus, the amount of T-P losses through percolation is also
very insignificant to affect the statistical quantification of T-P losses.
The trend of T-P losses from all of the plots showed almost no changes from first to third
rainfall simulation test. Although coconut husk buffered plots (U and T) had lower amounts of T-P
losses than that of (C) controlled plot, T-P losses from (T) treated coconut husk buffered plottended to be higher than that of (U) untreated coconut husk buffered plot where in significant
differences at p<0.01 and p<0.05 were observed during the second and third rainfall simulation
tests, respectively. This tendency might be due to the longer contact time of coconut husk with© ISERD
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distilled water during retting treatment. As Cermark et al. (2004) reported that more amount of
PO4-P was leached from corn residue with longer time of immersing into the solution of distilledwater and inorganic salt. Thus, leaching of T-P from coconut husk residue has similar trend to thatof corn residue which releases more amount of phosphorus component. The experimental results
signified that with and without ret treating of coconut husk have less influence on eliminating T-P
losses.
On the other hand, even though retting treatment of coconut husk tended to be less effective on
eliminating T-P losses, it was observed that quantitatively the amount of T-P losses were verymuch lower than that of T-N losses. As shown in Fig. 4 that the amount of T-P losses from (T)treated coconut husk buffered plot were 18, 6, and 8 times lower than that of T-N losses during thefirst, second and third rainfall simulation tests, respectively. In addition, the amount of T-P at 0.863
mgP/g (Table 1) being released into the distilled water during the retting treatment is significantly
larger than that of T-P which loss from treated coconut husk buffered plot at an average amount of
0.046 g/m2.
CONCLUSION
This study dealt with the effect of retting treatment of coconut husk for buffer strips on eliminating
its nitrogen and phosphorus components. It was indicated that around 15% of total nitrogen (T-N)
and 85% of total phosphorus (T-P) component from coconut husk were released into distilled water
within 10-day period of retting treatment. It was also proven that retting treatment was able toeliminate T-N losses at 31.62% and 36.84% during the first and second rainfall simulation tests,
respectively. Thus, this amounts of T-N that were eliminated is important to taken into
consideration as a benefit of retting treatment. In addition, although retting treatment tended to beless effective in eliminating T-P losses during the slope modeling test, the amount of T-P that was
released into the distilled water during the retting was very high than that of T-P being loss fromtreated coconut husk buffer. The amount of T-P released into the distilled can be efficiently utilized
for liquid bio-fertilizer. Therefore, retting treatment of coconut husk not only eliminates T-N losses
but also it is an effective method to extract T-P component in the coconut husk.
ACKNOWLEDGEMENT
The authors would like to express our gratitude to the Institute of Environment Rehabilitation andConservation and to the Nodai Research Institute which partly supported this research. It is also
very much appreciated the generous efforts of Mr. Hayato Iinuma for collaborating and assisting
throughout the experiment.
REFERENCES
Cermark, J.D., Gilley, J.E., Eghball, B. and Weinhold, B.J. 2004. Leaching and sorption of nitrogen andphosphorus by crop residue. Biological Systems Engineering, University of Nebraska, 47-1, 113-118.
Havis, R.N. and Alberts, E.E. 1993. Nutrient leaching from field decomposed corn and soybean residue
under simulated rainfall. Soil Science Society of America Journal, 57(1), 211-218.
Mihara, M. 2001. Nitrogen and phosphorus losses due to soil erosion during a typhoon, Japan. Journal of
Agricultural Engineering Research, 78(2), 209-216.
Mihara, M. and Ueno, T. 2000. Nitrogen and phosphorus transfer in soil erosion processes. IAHS Publication,
No. 263, 109-115.
Orient Integrated Development Consultants Inc. 2006. Bohol Agriculture Master Plan, CY2006-2026.
Rose, W.C., Yu, B., Hogarth, L.W., Okom, E.A. and Ghadiri, H. 2003. Sediment deposition from flow at low
gradients into a buffer strip - a critical test of re-entrainment theory. Journal of Hydrology, 280, 33-51.
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