Short-term effects of organic waste amendments on soil biota: responses of soil food web under eggplant cultivation.
The disposal of organic waste from households and the food industry results in both economic cost and environmental problems. Many organic wastes contain nutrients that can be reused for crop cultivation. As a result, the amendment of soil with these materials is good for the environment and sustainable agriculture (Jeng et al. 2006; Nelson and Janke 2007; Lee et al. 2008). A steady decomposition of organic waste is needed to ensure the stable supply of nutrients to crops, and many studies have investigated the effect of organic waste on nutrient and chemical changes in soil (Nelson and Janke 2007; Castro et al. 2009). Organic waste amendment is profitable for the production of crops that have a long growth period. Eggplant (Solanum melongena L.) is a solanaceous plant that has long vegetative and reproductive stages, and its fruit yield is greater with the use of slow-release fertilisers than synthetic fertilisers (Gezerel and Donmez 1988).
Soil organisms are critical for the decomposition of organic matter and for nutrient cycling. Microorganisms play important roles in the chemical breakdown of organic materials, and their biomass constitutes a source of nutrients (Coleman et al. 2004). Soil fauna directly participate in the mechanical breakdown of litter through the fragmentation of organic materials (Mikola and Sulkava 2001; Filser 2002), and indirectly alter the decomposition rate of secondary decomposers (Cragg and Bardgett 2001). The speed and efficiency of organic matter decomposition can be affected by the population density and diversity of soil biota (Bettiol et al. 2002).
Organic amendment is a major component of agricultural practice and has significant effects on the soil ecosystem. During decomposition, energy and material move through soil food webs (Polis and Strong 1996). The structure of food webs is organised by linkages between different trophic groups composed of decomposers and predators (Griffiths 1994). Bottom-up control determines the decomposition process by regulating the direction and strength of the linkages between the prey and the consumers (Lenoir et al. 2007). The soil food web can be used as a monitoring tool for external material inputs (Wardle et al. 1995). However, most studies on organic waste amendment have focused on microbial activity (Wong et al. 1998; Crecchio et al. 2001), and little is known about its effects on soil food webs. Information concerning the mechanism by which food webs can change will be helpful in understanding the control and movement of nutrients in relation to organic waste inputs.
The objective of this study was to assess the effects of organic amendments on soil food webs by monitoring the responses of microflora and fauna. We tested the effects of three types of reusable wastes: bone meal, de-oiled cake, and oyster shell. These materials are good sources of nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca). Bone meal and de-oiled cake are rich in N and P, respectively (Jeng et al. 2006; Nelson and Janke 2007). Oyster shell, in contrast, provides Ca and has a liming effect on acid soils (Lee et al. 2008). We also examined the responses of soil biota to amendment-induced soil chemical characteristics. We investigated the responses of microflora and fauna to soil amendment by categorising them into three functional groups. In terms of the primary consumers, focus was placed on the bacteria and fungi. Secondary consumers included the microfauna (protozoa and microbivorous nematodes) and mesofauna (Collembola, Oribatida, and Enchytraeida). Predators were represented by predatory nematodes and Gamasida.
Materials and methods
The study was conducted at an experimental field in Eumseong, Republic of Korea (37.05N, 127.40E). The mean annual temperature at the site was 11.2[degrees]C and precipitation 1212mm [year.sup.-1] (1981-2010). The soil was a sandy loam, and the field was used for the conventional production of sesame (Sesamum indicum L.) before the study. Organic amendments were applied separately in three replicated plots (3 m by 5 m) using a randomised block design. Bone meal, de-oiled cake of mixed, and powdered oyster shell were purchased from manufacturers; their chemical properties and nutrient contents are shown in Table 1. After the organic wastes were applied at 5 t ha l, the soil was tilled with a rotary plough on 1 June 2010. Eggplant (cv. Jangokdaejang) seedlings were grown in commercial soil for 40 days and then transplanted into an area of 0.5 m by 0.5 m in the experimental plots on 4 June 2010. The seedlings were irrigated immediately after transplantation. Plots were weeded by hand in July and August 2010. No pesticides or herbicides were used on the plots during the experimental period.
Plant growth was measured at 4 and 9 weeks after treatments reached the vegetative and fruiting stages, respectively. On each sampling day, five plants were collected per plot by cutting their bases, and their fresh weights and shoot lengths were measured. Harvesting of fruits was conducted every 2 weeks until 15 September 2010.
Soil sampling was conducted three times: 4, 8, and 13 weeks after treatment. Soil samples were obtained from a depth of 0-10cm by using a soil sampler (3.5cm in diameter). We collected four or five soil samples from each plot and mixed them to make a composite sample. Soil samples were taken to the laboratory immediately, and root fragments were removed. For microbial phospholipid fatty acid (PLFA) analysis, soils were freeze-dried and passed through a 2-mm mesh sieve.
Soil chemical analysis
Soil pH in a saturation extract (1 : 5 w/v, suspension of solid in water) was measured using a pH meter. Organic matter content was measured according to the Tyurin method. Carbon and N were analysed in a C/N analyser (Vario Max CN, Elementar, Germany). Nitrate concentration was determined on an auto analyser (Auto-Analyser 3, Bran Luebbe, Germany). Available phosphate was analysed using the Lancaster method. Exchangeable cations in the soil and nutrient contents of the organic wastes were extracted with 1 N NH4OAc (pH 7.0) and measured using inductively coupled plasma analysis (Integra XMP, GBC, Australia).
The microbial community structure was described by PLFA analysis according to Li et al. (2006). Lipids were extracted from 5 g of soil with a solvent (chloroform : methanol : citrate buffer, 1:2:0.8 v/v/v) and separated into neutral lipids, glycolipids, and phospholipids by using a silica column. Fatty acids were identified and quantified using the Sherlock Microbial Identification System (MIDI Inc., Newark, DE, USA). The fatty acid methyl ester 19:0, at a concentration of 150 ng [micro][L.sup.-1], was used as an internal standard. The ratio of monounsaturated fatty acids (16 : 1 [omega]5c, 17 : 1 [omega]8c, and 18 : 1 [omega]7c) and saturated fatty acids (14 : 00, 15 : 00, 16 : 00, 17 : 00, 18 : 00, and 20 : 00) was used as an indicator of stress. Gram-negative bacteria were measured as a sum of 18 : 1 [omega]7c, 19 : 0cy [omega]8c, and 17 : 1 [omega]8c, and Gram-positive bacteria as a sum of i14 : 0, i15 : 0, al5 : 0, i16 : 0, i17 : 0, and a17 : 0. The fatty acid 18 : 2 [omega]6, 9c was chosen to represent the biomass of fungi. Actinomycetes were determined by 10Me 16 : 0, 10Me 17 : 0, and 10Mel8:0 (Kaur et al. 2005).
The culturable microbial population was estimated using the soil dilution plate method. Triptic soy agar was used to grow bacteria. Fungi were grown on sabouraud dextrose agar with 100 [micro]g [g.sup.-1] streptomycin to suppress bacterial growth. Nematodes were extracted from 20 g of fresh soil over 48 h by using a Baermann funnel and fixed in triethanolamin-formalin fixative before classification. All individuals from each plot were categorised into one of four trophic groups: bacterivores, fungivores, herbivores, or predators (Yeates et al. 1993). Microarthropods were extracted over 96 h by using a Tullgren funnel and classified into Collembola, Oribatida, or Mesostigmata (Aoki 1999). Enchytraeids were extracted from 50 g of fresh soil over 24 h by using a modified Baermann funnel under conditions of light and heat.
Differences among treatments with regard to chemical properties of the soil, PLFA, and abundance of microarthropods were analysed by repeated-measures analysis of variance (ANOVA), followed by Fisher's protected least significant difference (1.s.d.) test. Plant growth and the time course of changes in nematode abundance were analysed by Fisher's protected l.s.d, test on each sampling day. Correlation analysis was used to evaluate the associations between soil organisms, and correlation coefficients between the different trophic groups were calculated. All tests were conducted using StatView (SAS Institute Inc., Cary, NC, USA).
Analysis of the chemical properties of the soil showed an overall treatment effect of the organic wastes applied (Table 2). Soil pH was increased by the bone meal and oyster shell treatments. Nitrate concentration was, in general, higher in soils treated with organic wastes than in control soils. The concentration of available P was 1.4 times greater in the treatment with bone meal than under control conditions. The highest levels of K and Ca were observed in soils treated with de-oiled cake and oyster shell, respectively.
Growth and fruit harvesting of eggplant
Plant growth and fruit harvest were significantly affected by the application of organic wastes (Table 3). The fresh weight and shoot length of plants were the greatest under the bone meal and de-oiled cake treatments, and this trend was significant from the vegetative stage through to the reproductive stage. Fruit yield was 3.7 and 4.7 times greater under the bone meal and de-oiled cake treatments, respectively, than under control conditions.
The ratio of cyclopropyl fatty acids to their precursors, a PLFA indicator of stress, decreased in the treatments with bone meal and oyster shell (Table 4). However, another indicator of stress, the ratio of saturated to unsaturated fatty acids, was not significantly affected. To compare these results with abundance of microorganisms, the amounts of culturable bacteria were determined using a dilution method. Bacterial abundance was the greatest under the bone meal treatment, but fungal abundance did not differ significantly between the different treatments (Table 5). The level of PLFA indicators for actinomycetes and protozoa tended to be higher under the bone meal treatment, although these differences were not statistically significant (Table 4).
Soil microfauna and mesofauna
There were differences in the responses of four trophic groups of nematodes to the application of organic materials (Table 6). The bacterivorous nematodes were the dominant trophic group, accounting for 51 91% of the total abundance. Fungivorous nematodes were the second most abundant group, accounting for 5 23% of the total abundance, but there was no apparent change in their abundance over time. The average ratio of bacterivores to fungivores was significantly greater under bone meal (7.6) and de-oiled cake (10.6) treatments than under control conditions (3.2), according to repeated-measures ANOVA followed by Fisher's protected l.s.d, test (P<0.01). Among the microarthropods, the Collembola and Oribatida were the groups most affected by treatment; the abundance of these secondary consumers was greater in the bone meal and de-oiled cake treatments (Table 5). Changes in the abundance of the predaceous Gamasida were not significant.
Soil food web
The trophic relationships between the organisms were analysed by correlation analysis (Fig. 1). There was a positive correlation between the primary and secondary consumers. In the bacteria-based food web, protozoa, bacterivorous nematodes, and collembolans showed a significant correlation with bacteria.
In the fungi-based food web, collembolans, oribatids, and fungivorous nematodes were positively correlated with fungi. However, predators were not correlated with secondary consumers in either food web.
Plant growth and soil organisms
The bioactivity of soil organisms may affect plant growth by increasing mineralisation (Bettiol et al. 2002; De Deyn et al. 2004). Increased levels of available nutrients in the soils treated with bone meal and de-oiled cake may result from increased mineralisation via the decomposition processes carried out by decomposers. However, we did not find a correlation between microorganism abundance and plant growth. We assume that this finding could be attributed to a difference in the nutrient contents of the organic materials applied. The results suggested that plant growth may not reflect amendment-induced changes in soil biota in the short term.
Bone meal, de-oiled cake, and oyster shell are all reported to have a positive effect on microbial activity (Lee et al. 2004; Mondini et al. 2008; Gougoulias et al. 2010), and decomposer abundance is affected by the C/N ratio of organic matter (Marschner et al. 2003). We assumed that amendment with bone meal and de-oiled cake would lead to bacteria-dominated decomposition because of the low C/N ratio of these wastes. However, contrary to expectations, both bacteria and fungi tended to increase in treatments with bone meal and de-oiled cake. The results showed that fungal communities were also influenced by the organic amendments. The ratio of cyclopropyl to its precursors is indicative of nutrient levels (Kaur et al. 2005), and a decrease in this ratio under the bone meal treatment might have been caused by an increase in nutrient supply. Meanwhile, we suggest that the oyster shell treatment decreased this ratio through a change in the pH, considering both the limited increase in soil nutrient content and the great liming effect of this material. The decrease in the ratio of Gram-negative to Gram-positive bacteria confirmed this suggestion, because dominance of Gram-positive bacteria can indicate a progressive change to oligotrophic conditions (Yao et al. 2000; Kaur et al. 2005).
In agro-ecosystems with a high level of disturbance, the soil ecosystem is dominated by fauna that reproduce rapidly and have short life cycles (Berkelmans et al. 2003). The present study showed that the number of bacterivorous nematodes and collembolans increased quickly in response to external input. Many of the organisms in these groups are classified as enrichment opportunists, characterised by short generation times and high fecundities (Filser 2002; Fen-is and Matute 2003). The results indicate that the input of organic waste is associated with a rapid response of secondary consumers. A high abundance of collembolans in the bone meal treatment was also noticeable, and their population seemed to be affected by the increased bacterial abundance. The difference observed in the PLFA indicator for microbial biomass between the bone meal treatment and the control was <l.3-fold, which was a much smaller difference than that observed in collembolan abundance (3.5-fold). An increase in the food source can trigger population growth because Collembola may reproduce rapidly in response to a disturbance (Domene et al. 2007).
Predators represent tertiary consumers in the decomposition process and affect nutrient mineralisation through the top-down control of other organisms (Lenoir et al. 2007). Predatory nematodes are known to feed on other animals, including protozoa and nematodes (Bilgrami and Gaugler 2005; Eo et al. 2009). Similarly, Gamasida feed on other invertebrates, including nematodes, mites, and Collembola (Heckmann et al. 2007; Schneider and Maraun 2009). We found little difference in the abundance of these predators between the different treatments, despite the changes observed in the secondary consumers. It is possible that this experiment was not of a sufficient duration for a population response to the organic waste amendments. Among the predatory nematodes, mononchids may take several weeks to complete a life cycle, and the generation time of dorylaimids is 3-6 months (Khan and Kim 2007). Gamasida also may take several weeks to complete a life cycle (Minor and Cianciolo 2007).
Bottom-up trophic effects of organic wastes
Decomposed materials and nutrients flow from microorganisms to microbivorous fauna through bacteria- or fungi-based channels. We expected that the input of organic waste would promote a bacteria-based food web, and this was apparently observed in the case of bacterivorous nematodes. Ferris and Matute (2003) suggested that the succession from bacterivores to fungivores is related to the properties of the organic sources applied. If the material is readily decomposed by bacteria, the succession to fungal decomposition can proceed, leading to an increase in the abundance of fungivorous nematodes. However, no changes in the abundance of fungivorous nematodes were apparent in our study. Meanwhile, correlations were observed between abundance of fungi and their consumers. These results suggest that bacteria- and fungi-based food webs developed simultaneously. Bottom-up control is a driving force in the structure of the food web, which is composed of linkages between the different trophic groups (Polis and Strong 1996). Correlation analyses identified a possible bottom-up regulation between the primary and secondary consumers. This process might have occurred in two steps. First, decomposers were affected by the addition of organic wastes. Second, as a consequence of the first step, secondary consumers responded through trophic linkages. Tertiary consumers showed a limited response. Our results imply that a bottom-up effect is a critical component of food web response to organic waste amendment.
We showed that organic waste amendments, especially the addition of bone meal and de-oiled cake, can increase soil biota abundance and nutrient availability of the soil, and that soil microflora and fauna were affected by the quality of organic wastes. In addition, we demonstrated that the application of organic wastes influenced soil organisms via bacteria- and fungi-based channels between primary and secondary consumers. This study suggests that stimulation of soil biota occurred only at the bottom of the soil food web, and that the impact was not transferred to higher trophic levels after 13 weeks.
Received 19 January 2012, accepted 18 April 2012, published online 20 July 2012
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Jinu Eo (A), Kee-Choon Park (A), and Byung-Bae Park (B,C)
(A) Department of Herbal Crop Research, Rural Development Administration, 80 Bisanri, Eumseong, Chungbuk 369-873, Republic of Korea.
(B) Division of Forest Ecology, Korea Forest Research Institute, Seoul 130-172, Republic of Korea.
(C) Corresponding author. Email: firstname.lastname@example.org
Table 1. Carbon/nitrogen ratios and nutrient concentrations of the organic wastes used in the experiment Data are presented as the mean [+ or -] standard deviation. Within a column, means followed by the same letter are not significantly different at [sigma] = 0.05 Treatment C/N C (%) Bone meal 4.9 [+ or -] 0.2c 25.2 [+ or -] 1.2b De-oiled cake 7.9 [+ or -] 0.3b 48.3 [+ or -] 0.2a Oyster shell 18.2 [+ or -] 1.7a 11.7 [+ or -] 0. 1c N P (%) (g [kg.sup.-1]) Bone meal 5.1 [+ or -] 0.1 b 94.8 [+ or -] 3.6a De-oiled cake 6.1 [+ or -] 0.2a 12.9 [+ or -] 0.8b Oyster shell 0.6 [+ or -] 0.1 c 0.6 [+ or -] 0.1c K Ca (g [kg.sup.-1]) (g [kg.sup.-1]) Bone meal 0.9 [+ or -] 3.4b 143.1 [+ or -] 6.2a De-oiled cake 14.0 [+ or -] 0.4a 9.9 [+ or -] 0.2c Oyster shell 0.2 [+ or -] 0.2b 111.8 [+ or -] 2.2b Table 2. Chemical properties of the soils amended with organic wastes Data are averages of three samples collected 4, 8, and 13 weeks after treatment. Within a column, means followed by the same letter are not significantly different at [sigma] = 0.05 Treatment pH OM (g [kg.sup.-1]) Control 5.4 [+ or -] 0.1c 15.6 [+ or -] 2.2a Bone meal 5.6 [+ or -] 0.1b 19.1 [+ or -] 3.0a De-oiled cake 5.4 [+ or -] 0.2bc 18.7 [+ or -] 3.9a Oyster shell 6.2 [+ or -] 0.2a 16.8 [+ or -] 2.5a Treatment N[O.sub.3] [P.sub.2][O.sub.5] (mg [kg.sup.-1]) (mg [kg.sup.-1]) Control 4.3 [+ or -] 1.3a 419.3 [+ or -] 19.9b Bone meal 13.2 [+ or -] 6.4a 589.7 [+ or -] 27.4a De-oiled cake 14.9 [+ or -] 12.4a 497.7 [+ or -] 53.7ab Oyster shell 10.9 [+ or -] 8.3a 428.8 [+ or -] 56.4b Treatment K Ca (cmol(4) [kg.sup.-1]) Control 0.3 [+ or -] 0.1a 2.1 [+ or -] 0.3b Bone meal 0.4 [+ or -] 0.1 a 3.1 [+ or -] 0.2b De-oiled cake 0.5 [+ or -] 0.3a 2.5 [+ or -] 0.4b Oyster shell 0.4 [+ or -] 0.1 a 5.5 [+ or -] 0.8a Table 3. Effects of application of organic wastes on the growth and fruit harvest of eggplant Data are presented as the mean [+ or -] standard deviation. Within a column, means followed by the same letter are not significantly different at [sigma] = 0.05 Treatment Aboveground weight (g/plant) Vegetative Reproductive stage (7 July) stage (14 Sept.) Control 33.1 [+ or -] 14.5b 137.9 [+ or -] 58.7b Bone meal 83.7 [+ or -] 21.9a 463.2 [+ or -] 22.7a De-oiled cake 109.6 [+ or -] 6.5a 453.5 [+ or -] 88.0a Oyster shell 34.8 [+ or -] 20.1b 254.5 [+ or -] 135.8ab Treatment Shoot length (cm) Vegetative Reproductive stage (7 July) stage (14 Sept.) Control 50.5 [+ or -] 7.8b 86.3 [+ or -] 16.8b Bone meal 67.2 [+ or -] 2.6a 119.0 [+ or -] 7.2ab De-oiled cake 73.9 [+ or -] 0.9a 120.4 [+ or -] 2.7a Oyster shell 52.6 [+ or -] 11.3b 96.8 [+ or -] 23.0ab Treatment Fruit harvest (gplant-1) Control 127.3 [+ or -] 59.00b Bone meal 471.3 [+ or -] 76.7a De-oiled cake 595.6 [+ or -] 118.0a Oyster shell 147.7 [+ or -] 85.5b Table 4. Phospholipid fatty acid (PLFA) characteristics of the soil after application of organic wastes Data are presented as the average of three samples collected 4, 8, and 13 weeks after treatment. Within a column, means followed by the same letter are not significantly different at [sigma]=0.05. G-, Gram-negative bacteria; G+, Gram-positive bacteria; Aero, aerobic bacteria; anaero, anaerobic bacteria; sat, saturated fatty acids; unsat, unsaturated fatty acids; eye], cyclo fatty acids; pre, precursors of cyclo fatty acids; Act, actinomycetes Treatment G-/G+ Aero/anaero Control 0.7 [+ or -] 0.04ab 1.0 [+ or -] 0.2b Bone meal 0.7 [+ or -] 0.03a 1.2 [+ or -] 0.1a De-oiled cake 0.7 [+ or -] 0.03ab 1.0 [+ or -] 0.1b Oyster shell 0.6 [+ or -] 0.02b 1.1 [+ or -] 0.1ab Treatment Sat/unsat Cycl/pre Control 2.5 [+ or -] 0.4a 0.9 [+ or -] 0.2a Bone meal 2.4 [+ or -] 0.2a 0.8 [+ or -] 0.1b De-oiled cake 2.4 [+ or -] 0.3a 0.9 [+ or -] 0.1ab Oyster shell 2.5 [+ or -] 0.3a 0.8 [+ or -] 0.1b Treatment Bacteria Fungi (nmol PLFA g [soil.sup.-1]) Control 12.0 [+ or -] 1.5a 1.7 [+ or -] 0.4a Bone meal 15.2 [+ or -] 3.1a 2.4 [+ or -] 0.3a De-oiled cake 13.2 [+ or -] 1.5a 2.1 [+ or -] 0.3a Oyster shell 12.1 [+ or -] 2.4a 1.9 [+ or -] 0.4a Treatment Act Protozoa (nmol PLFA g [soil.sup.-1]) Control 3.2 [+ or -] 0.4a 0.4 [+ or -] 0.1a Bone meal 4.0 [+ or -] 0.9a 0.5 [+ or -] 0.1a De-oiled cake 3.4 [+ or -] 0.4a 0.4 [+ or -] 0.1a Oyster shell 3.1 [+ or -] 0.4a 0.4 [+ or -] 0.1a Table 5. Abundance of culturable microorganisms and fauna Data for soil organisms from the three samples collected 4, 8, and 13 weeks after treatment were averaged before calculation. Values are means f standard deviation. Within a column, means followed by the same letter are not significantly different at [sigma] = 0.05 Treatment Bacteria Fungi cfu ([10.sup.5] [g.sup.-1]) Control 9.4 [+ or -] 1.46 0.8 [+ or -] 0.1a Bone meal 20.0 [+ or -] 5.5a 1.1 [+ or -] 0.1a De-oiled cake 14.7 [+ or -] 3.3ab 1.1 [+ or -] 0.3a Oyster shell 14.5 [+ or -] 3.8ab 0.8 [+ or -] 0.2a Treatment Collembola Oribatida N ([10.sup.3] [m.sup.-2]) Control 2.0 [+ or -] 0.86 13.3 [+ or -] 4.6bc Bone meal 7.0 [+ or -] 2.1 a 24.6 [+ or -] 7.9a De-oiled cake 3.5 [+ or -] 1.3b 22.6 [+ or -] 5.5ab Oyster shell 3.0 [+ or -] 1.3b 10.2 [+ or -] 4.5c Treatment Gamasida Enchytraeida N ([kg.sub.-1]) Control 1.8 [+ or -] 0.6a 48.9 [+ or -] 21.1a Bone meal 2.1 [+ or -] 0.9a 64.4 [+ or -] 26.4a De-oiled cake 2.0 [+ or -] 0.8a 68.9 [+ or -] 10.3a Oyster shell 1.1 [+ or -] 0.2a 53.3 [+ or -] 17.6a Table 6. Abundance of nematodes belonging to four different trophic groups Data for soil properties from the three samples collected 4, 8, and 13 weeks after treatment were averaged before the calculation. Within a column, means followed by the same letter are not significantly different at 6=0.05 Treatment Bacterivores Fungivores N ([g.sup.-1] Control 2.3 [+ or -] 0.5b 0.7 [+ or -] 0.1a Bone meal 6.3 [+ or -] 1.3a 0.8 [+ or -] 0.la De-oiled cake 7.0 [+ or -] 1.5a 0.7 [+ or -] 0.1a Oyster shell 3.6 [+ or -] 0.8b 0.6 [+ or -] 0.1a Treatment Herbivores Predators N ([g.sup.-1] Control 0.8 [+ or -] 0.1a 0.3 [+ or -] 0.1a Bone meal 0.5 [+ or -] 0.2a 0.5 [+ or -] 0.2a De-oiled cake 0.5 [+ or -] 0.1a 0.5 [+ or -] 0.1a Oyster shell 0.5 [+ or -] 0.1a 0.3 [+ or -] 0.1a
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|Author:||Eo, Jinu; Park, Kee-Choon; Park, Byung-Bae|
|Date:||Aug 1, 2012|
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