Environmental Concerns 41

1. INTRODUCTION Indonesia produces over 350Mt of clean coal in

2012 and is the second largest coal exporter to Japan, accounting for 30 Mt/y. Over 99% of clean coal is produced from open cut mines in Indonesia. As the demand of coal not only in Indonesia but also in the rest of the world is increased dramatically due to increasing the energy supply in the world, the development of coal mining is advanced in order to meet the demand of coal [1]. However, a mining operation of open cut mines has some disadvantages for surrounding environment such as disturbance of the tropical rainforest, the pollution of surface and/or ground water, subsidence and erosion. Under such situations, rehabilitation is one of the important and considerable topics for an environment protection. Adequate rehabilitation program will improve these environmental conditions and recover the nature and ecosystem.

Rehabilitation is not only the considerable topic for environment reconstruction but also one of effective solution for environment pollution such as erosion, slide of slope and drainage issue. If rehabilitation is conducted adequately in post mine surface area, it is possible to restore almost the original environment before development of open cut mining (see Fig. 1) [2]. However, the soil condition of mined out area is very severe for revegetation and

planting. In order to conduct revegetation in post mine area efficiently, appropriate rehabilitation program including the soil management and the selection of adequate species of plant has to be considered. 2. SITE DESCRIPTION

2.1 KPC coal mine

KPC coal mine is the biggest open cut coal mine in Indonesia and located in East Kalimantan. The mine site belongs to tropical rainforest climate and the average annual rainfall shows 2,000~4,000mm/year and the average temperature varies from 26 to 32℃. Currently, the demand of rehabilitation is increasing dramatically in this coal mine since the contract term will be expired in 2021. Therefore, new project to promote rehabilitation activity named of “Mine Closure Project” commenced in several years ago. The purpose of this project is not only the restoration of a forest ecosystem in all disturbed land but also the utilization of these lands as other potential economic and use options (see Fig. 2).

2.2 Soil management

This mine is working rehabilitation program with reference to “REHABILITATION SPECIFICATIONS” based on site and industry experience. It is difficult to establish vegetation

ABSTRACT Open cut mining is the typical mining method to produce coal in Indonesia and it gives serious impacts

on surrounding environment. Therefore, an appropriate rehabilitation program has to be designed. The basic concept of rehabilitation in open cut mines is the creation of a stable and self-sustaining land surface. Hence, the soil characteristics and adequate selection of species to plant in rehabilitation area have to be considered. This paper describes the current situations in rehabilitation area at one of open cut coal mine in Indonesia and then discusses the effect of soil composition for growth of Paper Mulberry as one of effective species planted in post mine surface based on the laboratory tests. KEY WORDS: Indonesia / Open cut mine /Rehabilitaiton/ Paper Mulberry/ Soil composition

PPaappeerr IIDD 2244

Effect of Soil Composition on Growth of Paper Mulberry at Post Mine Surface in Open Cut Coal Mine

N. Inoue1*, A. Hamanaka1, H. Shimada1, T. Sasaoka1, K. Matsui1and I. Miyajima2 1 Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan

2Institute of Tropical Agriculture, Kyushu University, Fukuoka 812-8581, Japan *Authors to correspondence should be addressed via e-mail: n_inoue12r@mine.kyushu-u.ac.jp

Fig. 1 Overview of rehabilitation

Environmental Concerns 42

association in the disturbed land without the proper rehabilitation process for revegetation because post mine surface shows poor conditions as planting base in usual. A lot of open cut mine keep the topsoil in the natural forest individually during soil stripping process and spread the topsoil to rehabilitation area before revegetation process in order to form good quality of planting base (see Fig. 3). The proper management of topsoil can be provided a suitable medium for plant growth. However, some areas face the shortage of topsoil due to shallow of topsoil layer. Topsoil management have to be paid more attention for establishment of vegetation in post mine surface under such situation.

Fig. 2 Cow husbandry in rehabilitation area

Fig. 3 Topsoil stripping and placement

2.3 Basic characteristics of topsoil spread to rehabilitation area

Topsoil spread to rehabilitation area has important role for establishing suitable plant base. In this research, the soil samples were collected from natural forest area and rehabilitation area (Fig. 4) and the determining the basic characteristics of the topsoil was carried out by the distribution of particle size analysis and Atterberg limits test. From these tests, the typical soil properties can be estimated such as soil permeability and water retention capacity. Basically, warter holding capacity decreases with increasing sand rate in the soil and permeability decreases with increasing clay content.

Tab. 1 shows the results of laboratory tests. From these results, the soil spread to rehabilitation area shows different soil composition with natural forest despite topsoil in natural forest backfills to rehabilitaion area. This is caused by mixing overburden as contamination during soil stripping and soil stockpiling process. Furthermore, the different

soil component affects soil characteristics. Fig. 5 shows plasticity chart that is convenience for comparing a variety of soils. It can be estimated that rehabilitation area 2 has different soil characteristics compared with rehabilitation area 1 and natural forest because the position of plot is quite different with others in this chart [3]. Considering soil characteristics in rehabilitation area, as the different soil composition may affect plant growth, appropriate soil manegement considering selection of species have to be discussed in order to conduct revegetation efficiently.

Fig. 4 Soil sampling area

Tab.1 The result of soil analysis

Fig. 5 Plasticity chart 3. PAPER MULBERRY

It can be thought that Paper Mulberry is one of efficient species to plant rehabilitation area. This species is fast growing tree and can grow under warm temperature, subtropical and tropical regions and various soil conditions. Therefore, it can be said that

Soil sample Sand (%)

Silt (%)

Clay (%)

Liquid limit

WL %

Plastic limit

WP %

Plasticity index IP

Natural forest 10 30 60 62.0 25.3 36.7

Rehabilitation area 1 75 8 17 26.9 19.1 7.9

Rehabilitation area 2 22 30 48 53.9 24.3 29.6

Environmental Concerns 43

Paper Mulberry has wide range of application and potential to be able to apply in post mine area. Additionally there are a lot of usages in Paper Mulberry such as making paper, clothing items and medicine. If Paper Mulberry can be applied in post mine area, the fibre resources can be provided continually instead of coal resources from this area not just revegetation [4].

3.1 The characteristics of paper mulberry

Paper Mulberry is deciduous and soft woody tree, which can grow up to 12-35m in height. The stems of Paper Mulberry are brown-green to dark-gray and twigs are hairy brown-green to dark-gray. The bark is thick, contains milky sap and small conical buds. The leaves are broadly, jagged, hairy and roughly, especially lower surface. The male flowers are yellow-white with 10 to 15cm long catkin spikes, but the inflorescences are 1.2-1.8cm in diameter, ball shaped. Fruit are sweet and edible with diameter of 1-3cm consist of light-red hair. The fruits contain 200-350 small hard dark-red seeds (Fig. 6).

Paper Mulberry can grow up under the wide range of climate conditions. It had been found in warm temperature, subtropical and tropical regions. This plant is a fast pioneer tree and it grows up to 4-9 m within one year. It grows fast under moist sandy loam soil in lowland areas, which close to stream and river valleys. However, Paper Mulberry can also be grown in upland areas as well for instance, upland rice field, hillside fallow, but the growth rates on the upland fields are lower.

The inner bark of Paper Mulberry has been utilized to produce paper and textile fabric for clothing for centuries, particularly in Japan, China, Indo-China, Thailand, Myanmar, the Philippines, Java and Madura. The paper which is made in Japan is used for writing, lampshades and umbrellas; however, the paper made in Thailand is mainly used for handicrafts and wrapping. Paper Mulberry textile fabric, which is called Tapa cloth, has used to make several clothing items for instance, head-clothing, sarongs, bed clothing and bags. Moreover, leaves are considered as medicine for children and diaphoretic, fruits are for stomachic and tonic, bark is laxative for

dysentery and haemorrhage and milk-sap is external use for against dog and snake bites and bee stings [5].

Fig. 6 Paper Mulberry

3.2 Laboratory vegetation test

Considering field situation in rehabilitaion area, laboratory vegetation test about Paper Mulberry was implemented under the various soil conditions. The seedlings of Paper Mulberry are planted to pots one by one filled soil mixed with sand and clay artificially. This vegetation test continued in 2 month and measured height, diameter and total leave number every a week. All pots were supplied with 500mL water every 3~4 day, while liquid fertilizer HYPONeX○R fomula 6-10-5 at the concentrate of 2mL per liter of water applied weekly. The experiment was carried out in constant temperature and humidity room, which was controlled temperature and humidity at 30℃ and 70% respectively. In the end of this vegetation test, dry root weight was measured to evaluate the root growth.

Tab. 2 shows the soil composition and basic soil characteristicics used in this test and Fig. 7 shows plasticity chart in each soil samples. It can be understood that permeability decreases and CEC represented fertilizer holding capacity increases with increasing clay content. Furthermore, the various type of soil can be expressed in plasticity chart by mixing with sand and clay.

Tab. 2 Soil compositions and basic characteristics

Soil Sample Sand(%) Clay(%) Liquid limit

WL % Plastic limit

WP % Plasticity index IP

Coefficient of permeability (cm/sec)

CEC (cmol/kg)

Soil1 100 0 28.3 NP - 8.770×10-4 10.55

Soil2 85 15 33.7 14.8 18.9 3.491×10-4 11.12

Soil3 75 25 40.7 22.6 18.1 2.431×10-4 13.07

Soil4 65 35 45.2 18.2 27.0 1.443×10-4 15.42

Soil5 55 45 52.3 20.1 32.3 8.250×10-5 16.48

Soil6 40 60 57.1 22.5 34.6 3.450×10-6 20.70

Soil7 0 100 67.2 23.6 43.6 1.000×10-7> 26.39

Environmental Concerns 44

Fig. 7 Plasticity chart (labolatory vegetation test)

3.3 Results and discussion

The results and the experiment show that there is a good correlation between the height and the diameter of seedling, and soil 4 and 5 gave higher height and diameter value than other soil compositions whereas the height and diameter of seedling in soil 1 and 7 was lower than them in the end of test (see Fig. 8 and Fig. 9). The different alphabets in these figures show a significant difference obtained by Tukey-kramer method [6]. This method is one of the statistical test and used to show the clear differences among the each results. From this result, the growth of the seedling of Paper Mulberry is different by the soil compositions because a significant difference is obserbed with elapsed time. Moreover, the growth of Paper Mulberry can be improved by arranging soil composition since soil formed in appropriate mixing rate with sand and clay has suitable permeability and water and fertilizer holding capacity as plant base.

Fig.8 Height of seedlings

Fig. 9 Diameter of seedlings

The leave has important role for plant growing to create nutrient by photosynthesis. The total leaf production tends to increase with clay contents and it shows high value especially in soil 5 and 7 in the end of this test (see Fig. 10). Therefore, it can be considered that the leaf production has correlation with CEC that is value to relate clay contents strongly.

Fig. 10 Total leaf production

The dry weight of roots tend to increase with

increasing the sand content (see Fig. 11). From this result, the dry weight of roots have a good correlation with the soil permeability. Therefore, it can be considered that the growth of root is mainly affected by the soil permeability of plant base. In addition, the dry weight of roots are heavier than that of aerial parts in soil 1, 2 and 3. On the other hand, the dry weight of aerial parts are heavier than that of roots in soil 4, 5, 6 and 7 in the end of this test. From this result, the growth balance of aerial parts and roots can be also controlled by arranging soil composition. The root system of vegetation have a role for preventing the landslide and the growth and expansion of root contributes to improve the slope stability [7]. Thus, from the aspect of root growth, it is important to control the soil composition which spread to rehabilitation area adequately.

Fig.11 Dry weight of root and aerial part

Moreover, the figure of plant growth in soil 1 and 7 can be found clear differences as shown Fig. 12. The plant on sandy soil grows up to axial direction because the plant can be easy to expand their roots in sandy soil due to high permeability though the number of leaf decreases beause of lower CEC. On

Environmental Concerns 45

the contrary, the plant on clay soil grows up to horizontal direction due to opposite soil characteristics with sandy soil. The growth of plant can be promoted by not only growing up to axial direction but also horizontal direction for increasing photosynthesis. It can be considered that growth form of Paper Mulberry can be expected under the appropriate soil condition.

Fig. 12 Difference of growth form

From a comprehensive point of view, soil 5 can

be expected the proper soil composition for growth of Paper Mulberry. Besides, the recovery rate of fibre resources from Paper Mulberry can be also improved by promoting the growth rate. Furthermore, the results of soil composition in the field indicates that the topsoil in natural forest contains larger clay contents. Therefore, it can be considered that the soil management for growth of Paper Mulberry can be achieved by mixing with overburden properly. Futhermore, to mix with topsoil and overburden can be one of solution for the lack of topsoil not only improving soil characteristics for plant growth. However, some of overburden may give adverse effect to plant growth by virtue of high salinity, potential for acid formation and ion toxicity such as Aluminum or heavy metal. In order to use overburden as improvement of soil quality, more detailed evaluations for chemical properties such as acidity, salinity, elution characteristics of toxic ion and excangeable cations have to be discussed and achieved primary.

4. CONCLUSION

Paper Mulberry is one of efficient species to plant rehabilitation area in Indonesia due to its growth characteristics and usage. From the result of soil analysis, the soil spread to rehabilitation area shows different soil composition caused by mixing overburden as contamination during soil stripping and soil stockpiling process despite topsoil in natural forest backfills to rehabilitaion area. Thus, vegetation test was conducted in order to reveal the effect of soil compositions for Paper Mulberry growth by using Paper Mulberry seedlings based on the result of soil

analysis. From the result of this test, it was found as follows : (1) The growth of Paper Mulberry seedlings can be

improved by arranging soil composition adequately.

(2) The total leaf production has a good correlation with fertilizer holding capacity of plant base.

(3) The dry weight of roots are mainly affected by soil permeability.

(4) Growth form of Paper Mulberry can be expected under the appropriate soil condition.

Furthermore, it is indicated that the growth rate of Paper Mulberry can be promoted by mixing with topsoil and overburden properly. In order to clarify and verify this consideration, more detailed research including chemical aspect have to be implemented.

ACKNOWLEDGMENT The first author wishs to extend their grateful

thanks to PT Kaltim Prima Coal in Indonesia for the acceptance of visiting mine sites and cooperation in providing the samples and materials used in this study.

REFERENCES [1] K. Matsui, “Control of Environmental Impacts

from Opencut Coal Mining in Indonesia for Sustainable Development,” Proceedings of 2005 East Asia Symposium on Rock Enginnering, pp. 3–14, 2005.

[2] A. J. Hargraves et al, “Australian Coal Mining Practice,” 1993, pp.260–279.

[3] The Japanese Geotechnical Society, “Geotechnical Handbook,” in Japanese, vol. II, 2004

[4] A. Hamanaka et al, “Fundamental Study on Application of Paper Mulberry for Rehabilitation of Surface Coal Mine in Indonesia,” Proc. of International Symposium on Earth Science and Technology 2011, pp. 419–422, 2011.

[5] A. NEEF et al, “Can Paper Mulberry Contribute to Building Sustainable Rural Livelihoods in Northern Laos?”, Souteast Asian Studies, Vol.47, No4, pp. 403–425, 2010

[6] Y. Nagata and M. Yoshida, “The Basis of Statistical Multiple Comparison,” in Japanese, Vol. III, 2001

[7] Wu, T.H. et al, “Strength of tree roots and landslides on Prince of Wales Island,” Alaska Canadian, Geotechnical Journal, 16, pp19-33,1979