IJERD – International Journal of Environmental and Rural Development (2015) 6-1

Research article
erd

Mitigating Splash Erosion with Applying Bacillus subtilis
Natto
AYA KANEKO IKAWA
Research Center, Institute of Environmental Rehabilitation and Conservation, Tokyo, Japan

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

YUTA ISHIKAWA
Research Center, Institute of Environmental Rehabilitation and Conservation, Tokyo, JapanSERGIO AZAEL MAY CUEVAS
Graduate School of Agriculture, Tokyo University of Agriculture, Tokyo, Japan
Received 20 December 2014

Accepted 25 April2015(*Corresponding Author)

Abstract Soil erosion from upland fields affects not only soil productivity but also water
environment. From the viewpoints of soil and water conservation, many strategies for
mitigation of soil erosion were discussed. Especially, conservation strategy for mitigatingsplash erosion which is the first process of soil erosion should be considered. Moreover,biological crust mixing with microorganisms has been focused as one of the treatments forsplash erosion. Therefore, two objectives were determined in this study. The first is toevaluate the effect of Bacillus subtilis Natto adding on mitigating splash erosion, and thesecond is to investigate the kinetic energy of raindrop to break the binding force of soil
particles with hyphae of Bacillus subtilis Natto. Raindrop experiment was carried out withstainless cans and Mariotte bottle of splash erosion apparatus. Stainless cans were filledwith soil, and then Bacillus subtilis Natto was applied. In addition, raindrop energy waschanged through controlling the height of Mariotte bottle. Based on the experimentalresults, there was a tendency that soil loss from the cans applied Bacillus subtilis Natto wassignificantly lower than controlled cans. In addition, it was observed that Bacillus subtilis
Natto mitigated splash erosion until kinetic energy of raindrop at 4.86×10-5 J/drop.
Therefore, it was concluded that Bacillus subtilis Natto is applicable for mitigation ofsplash erosion.
Keywords splash erosion, Bacillus subtilis Natto, biological crust

INTRODUCTION
Large amounts of soils were released from upland fields by rainfall and surface runoff. Soil erosion
is a cause of decreasing soil productivity. Moreover, soil erosion causes water pollution such as
eutrophication in watersheds. Therefore, some conservation strategies for soil erosion such as
buffer strips installation (Kawai et al., 2007; Gopal and Mihara, 2008; Siriwattananon et al., 2009,
Torillo and Mihara, 2011, 2014) have been discussed.
On the other hand, conservation strategies for mitigating splash erosion which is the firstprocess of soil erosion should been considered. In this connection, making soil crust has been
considered as a proper treatment for mitigating splash erosion. Soil crust formation was affected bymicroorganism activity, root growing, soil animal activity or mineral interaction (Six et al., 2002).
Therefore, microorganism growing is important for mitigating soil loss. There was a report byShimomura et al. (2007) that growing microorganisms in soil is able to reduce soil loss. However,it was not discussed about specific species of microorganism for mitigate raindrop erosion.
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So, this study focused on Bacillus subtilis Natto which is a kind of Gram-positive bacteria.
Bacillus subtilis Natto can make spore which has tolerance for acid, ultraviolet or heat (Hosoi,2003). In addition, Bacillus subtilis Natto creates hyphae which contain viscous material as γ-polyglutamic acid (Hara, 1990).
In this study, two objectives were determined. One is to evaluate the effect of Bacillus subtilis
Natto adding on mitigating splash erosion and the other is to investigate the kinetic energy ofraindrop to break the binding force of soil particles with hyphae of Bacillus subtilis Natto.
METHODOLOGY
In this study two experiments were conducted, the evaluation of Bacillus subtilis Natto addition on
mitigating splash erosion, and the investigation of the kinetic energy of raindrop to break thebinding force of soil particles with hyphae of Bacillus subtilis Natto.
Evaluation of Bacillus subtilis Natto Addition on Mitigating Splash Erosion
Bacillus subtilis Natto used in this experiment was laboratory made (Fig. 1). It consists of a dry
powder which contained 1.08×107 colonies formed units per gram (cfu/g) of Bacillus subtilis Natto.
Soil properties are shown in Table 1. Stainless cans of 1.1 cm diameter and 1.0 cm deep werefilled up with Andosol soil. Then Bacillus subtilis Natto powder at 1 g/cm2 was applied to soil.
After applying Bacillus subtilis Natto, stainless cans were put in incubator set at 37 ºC for 2 weeks.
Every day, physiological saline solution at 0.8 ml was applied to each can.

Fig. 1 Bacillus subtilis Natto powder

Fig. 2 Stainless canTable 1 Characteristics of the soil (volcanic ash soil)
Specificgravity

Gravel2.63

1.97

Particle size distribution %Coarse
FineSiltsandsand12.327.80ClaySoiltexturepHEC
μS/cm

39.3

CL

5.74

155

Mariotte bottle

Steinless canFig. 3 Apparatus for raindrop experimentFig. 4 Outline of raindrop experiment

Raindrop experiments were carried out with a Mariotte bottle as shown in Figs. 3-4. A needleof DIK-6000 artificial rainfall simulator was attached with Mariotte bottle. Water was dripped fromⒸ ISERD87

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a height of 18.0 cm. Based on the observation and calculation, kinetic energy of raindrops was
2.36×10-5 J. For an experiment, 50 raindrops were applied to soil sample of each can.
Kinetic Energy of Raindrop to Break Binding Force of Soil Particles with Hyphae
Bacillus subtilis Natto powder and soil sample used in this experiment were the same as the firstexperiment. Bacillus subtilis Natto at 1.01×107 colonies were observed in the powder.
Raindrop experiments were conducted employing Mariotte bottle as well as the firstexperiment. Raindrop was applied at the heights of 20, 40, 60 and 80 cm. Kinetic energies ofraindrop in each height were observed and calculated based on the Eq. (1). Raindrop mass wasmeasured with dried filter paper and raindrop velocities of each height was measured byphotographs shuttered at 1/100 second. The results of observed and calculated kinetic energy ofraindrops are indicated in Table 2.
Kinetic energies of raindrop, Ek (J) =1× 𝑀 × 𝑣22(1)Where M is raindrop mass (kg), v is raindrop velocities of each height measured byphotographs at 1/100 second (m/s).
Table 2 Raindrop energies in each height
Kinetic energy
×10-5 J3.26
4.86
9.66
13.8

Height of raindrop
cm
2040
60
80
Analysis of Soil Loss

After raindrop experiments, the mass of soil particles splashed out from the samples was measured.
Then soil loss rate was calculated with Eq. (2).
Soil loss rate (%) = (1 −Remained soil mass in the stainless can (g)) × 100
Initial soil mass in the stainless can (g)(2)

RESULTS AND DISCUSSION
Bacillus subtilis Natto Addition on Mitigating Splash Erosion
Fig. 5 shows the rate of soil loss in stainless cans. In control cans, about 20% of soil was released
from cans. On the other hand, in case of stainless cans with Bacillus subtilis Natto, the rate of soil
loss was reduced to 13%. Moreover, based on the results of statistical analysis, significant
difference at p≦0.01 was observed between the rate of soil loss of control and that of Bacillus
subtilis Natto added.
In addition, as a result of microscope observation, hyphae of Bacillus subtilis Natto wasobserved in soil applied with Bacillus subtilis Natto as shown in Fig. 6. So, it was considered thatBacillus subtilis Natto formed biological crust with hyphae growing.
Therefore, it was considered that Bacillus subtilis Natto is applicable to mitigate splasherosion.

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Rate of soil loss (%)

30

A**

20
B**

100ControlBacillus subtilis NattoaddedHyphae**Significant difference at p≦0.01

Fig. 5 Rate of soil loss

Fig. 6 Hyphae in soil

Kinetic Energy of Raindrop to Break Binding Force of Soil Particles with Hyphae
Figure 7 shows the relationship between the rate of soil loss and the kinetic energy of raindrop.
According to the results, the rate of soil loss increased with the kinetic energy of raindrop in bothcans of control and Bacillus subtilis Natto added. As a result of statistical analysis, confidence
interval at 99% was observed for both regression lines of the rate of soil loss of control and that ofBacillus subtilis Natto added.
The changes in soil loss rate were shown in Fig. 8. Bacillus subtilis Natto reduced the soil loss
rate at kinetic energy of raindrop from 3.46 to 4.86×10-5 J. In addition, significant difference wasobserved between the rate of soil loss of control and Bacillus subtilis Natto added. However, when
the kinetic energy of raindrop was larger than 9.66×10-5 J, significant difference was not observed.
Therefore, it was considered that biological crust formed by Bacillus subtilis Natto was notbroken by splash erosion until 4.86×10-5 J of kinetic energy.
25
A

Rate of soil loss (%)

20

Rate of soil loss (%)

25

A A
A

15105A**

a*

B**

b*

03.26
Control

4.86
9.66
Kinetic energy (×105 J/drop)

2015Bacillus Subtilis Natto added

y = 1.7295x - 1.0745
R = 0.9835**

10Control

5y = 1.4547x + 2.5968
R = 0.9953**

013.8

0Significant
difference
at **p<0.01, * p<0.05
Bacillus
Subtilis
Natto added
Significant difference at **p≦0.01,*p≦0.05

Fig. 7 Relationship between rate of soil
loss and kinetic energy of raindrop

510Kinetic energy (×10-5 J)

15**Confidence interval at p≦0.01

Fig. 8 Changes in soil loss rate

CONCLUSION
In this study, two experiments were carried out to investigate the effect of Bacillus subtilis Nattoaddition for mitigating splash erosion. Based on the experimental results, the rate of soil loss wasdecreased by Bacillus subtilis Natto addition. Moreover, hyphae of Bacillus subtilis Natto wereobserved in the soil which Bacillus subtilis Natto was applied. So, it was considered that Bacillus
subtilis Natto is able to form biological crust with growing hyphae.
In addition, there was a tendency that Bacillus subtilis Natto mitigated splash erosion until
kinetic energy of raindrop at 4.86×10-5 J/drop.
Therefore, it was concluded that Bacillus subtilis Natto is applicable to mitigate splasherosion. In addition, it was found out that biological crust formed with Bacillus subtilis Natto startedⒸ ISERD

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to break at kinetic energy of raindrop 4.86×10-5 J/drop.
The results of this study showed that microorganisms which create viscid hyphae such asBacillus sp. may be applicable to mitigate splash erosion.
ACKNOWLEDGEMENTS
We would like to express our gratitude to the members of Lab. of Land and Water Use Engineeringin Tokyo University of Agriculture, Japan for the meaningful discussion.
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Gopal, T. and Mihara, M. 2008. Palm shell filter strips as a conservation strategy in mitigating soil andnutrient losses. Eco-Engineering, 20 (2), 59-65.
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