EFFECT OF YOUNG WOODY PLANTATIONS ON CARBON AND NUTRIENT ACCRETION RATES IN A REDEVELOPING SOIL ON COALMINE SPOIL IN A DRY TROPICAL ENVIRONMENT, INDIA

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1 land degradation & development Land Degrad. Develop. 17: (2006) Published online in Wiley InterScience ( DOI: /ldr.690 EFFECT OF YOUNG WOODY PLANTATIONS ON CARBON AND NUTRIENT ACCRETION RATES IN A REDEVELOPING SOIL ON COALMINE SPOIL IN A DRY TROPICAL ENVIRONMENT, INDIA A. N. SINGH, 1,2 * D. H. ZENG 1 AND F. S. CHEN 1 1 Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang , China 2 Department of Botany, Banaras Hindu University, Varanasi , India Received 12 July 2004; Revised 16 August 2004; Accepted 21 February 2005 ABSTRACT We compared the effects of young high-density plantations of three native trees (legumes: Albizia lebbeck, A. procera and a non-legume: Tectona grandis) and one fast growing woody grass species (Dendrocalamus strictus) on carbon and nutrients stock and their accretion rates in a redeveloping soil. This soil was the early phase of mine spoil restoration in a dry tropical environment. The soil bulk density and accumulation rates of C, N and P at 0 10 and cm soil depth were determined in 4- to 5-year-old plantations. The total nutrient stock of soil C, N, P significantly varied in redeveloping soil according to plantation type, plantation age and soil depth. A. lebbeck greatly improved C and N content followed by D. strictus, A. procera and T. grandis plantations. However, accretion rates of C and N were substantially high in the D. strictus plantation. Therefore, D. strictus, contributed significantly to the redevelopment of mine spoil soils. In the case of total P nutrient, A. procera showed the greatest amount among the plantations but the accretion rate was also high for T. grandis followed by A. procera, A. lebbeck and D. strictus. This study indicates that all N-fixing species may not be equally efficient in improving soil qualities especially N in the soil. Copyright # 2006 John Wiley & Sons, Ltd. key words: Albizia lebbeck; Albizia procera; Dendrocalamus strictus; Tectona grandis; accretion; mine spoil; soil redevelopment; India; carbon and nutrient accretion INTRODUCTION The heavy pressure of the human population and its activities has caused significant alterations in the terrestrial biosphere. To meet the ever-increasing demand, a huge quantity of coal has been extracted through mining, causing extensive damage to ecosystems (Bradshaw, 2000). Coal extraction drastically alters the physical and biological nature of the mined area. Opencast mining, particularly, destroys vegetation, causes extensive soil damage, and alters microbial communities (Singh et al., 1995; Bradshaw, 1997a). Opencast coal mining waste materials coalmine spoil, dumps or overburden remain an impoverished medium for any vegetation development unless rehabilitated (Singh et al., 1995; Singh et al., 2004a). Correspondence to: A. N. Singh, Laboratory of Forest Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang , China. ansingh@iae.ac.cn Contract/grant sponsor: Ministry of Coal, Government of India. Contract/grant sponsor: Institute of Applied Ecology, Chinese Academy of Sciences; contract/grant number: SLYQY0409. Copyright # 2006 John Wiley & Sons, Ltd.

2 14 A. N. SINGH ET AL. The soil of young mine spoils is very poor in physico-chemical properties (low C, N, P, poor soil structure, poor drainage, low water-holding capacity and compaction) and microbial activity (Davies et al., 1992; Singh et al., 2004a). Therefore, plant growth is less vigorous than on adjacent undisturbed sites (Bradshaw, 1997b). In mine spoils the effects of soil disturbance are markedly adverse, because many beneficial soil characteristics require a very long time ( years) to develop into something like the original state. Besides, natural recovery in mine spoils is a very slow process and depends on time, and the ecological conditions of the site (Singh et al., 1995; Bradshaw, 1997a). Although the immediate goal of rehabilitation programmes is to establish a vegetation cover that will prevent soil erosion, the long-term goal should always be soil ecosystem development (Singh et al., 1995). Thus, for the reconstruction of ecosystems and ecological function in post-mining landscapes, the reconstruction of soil is essential. The formation of upper soil layers, especially the horizons of organo-minerals, is affected by the vegetation cover, which is the main source of soil organic matter for the soil, and is of prime importance (Frouz et al., 2001). Soil organic matter, an essential component of the soil, plays a major role in determining the structure and functioning of an ecosystem by acting as an energy source for non-autotrophic soil organisms and as a nutrient reservoir for intra-system cycling (Singh et al., 1995). The accumulation of soil organic carbon and nitrogen to a critical level is a vital prerequisite for subsequent colonization of the site by suitable plants. A suitable species for planting on mine spoils should possess the ability: (1) to grow on poor and dry soils; (2) to develop the vegetation cover in a short time and to accumulate biomass rapidly; (3) to bind soil to arrest soil erosion and check nutrient loss; and (4) to improve the soil organic matter status and soil microbial biomass, thereby enhancing the supply of plant nutrients available (Singh and Singh, 1999). In addition, the species should be of economic importance. Taking into account these facts, four species were selected for this study: Albizia lebbeck (L.) Benth.; A. procera (Roxb.) Benth.; Tectona grandis L.f.; and Dendrocalamus strictus (Roxb.) Nees. The selected species are indigenous and possess varied ecological characteristics, such as short-stature leguminous trees (A. lebbeck and A. procera), slow-growing timber tree (T. grandis) and fast growing woody grass (D. strictus). In this study, we assess the effect of 4- and 5-year-old planted species on carbon and nutrient stock and their accumulation rate in redeveloping soil derived from mine spoil. We address three main questions: (1) Can the level of soil carbon and nutrients of mine spoil be substantially accumulated within a short period? (2) Is accumulating efficiency of nutrients in the soil a species-specific effect? (3) Do the two leguminous species (A. lebbeck and A. procera) differ substantially from the non-leguminous species in improving nutrients stock (C, N and P) and in their accretion rates for redeveloping soil from mine spoil? MATERIALS AND METHODS Study Site The present study focused on young plantations of three native tree species (A. lebbeck, A. procera and T. grandis) raised on a mine-spoil dump in 1990 and one woody bamboo species (D. strictus), planted in All plantations were situated in the east section of Jayant Block, located in the northeastern part of the Singrauli Coalfield in the District of Sidhi, Madhya Pradesh, India ( N, E). The stocking density at the time of planting was 2500 individuals ha 1 for all species. About per cent of these individuals survived after three years. The climate of the area is tropical monsoonal and the year is divisible into a mild winter (November February), a hot summer (April June) and a warm rainy season (July September). Data collected at a meteorological station present on the site showed that the mean monthly minimum temperature within the annual cycle ranged from 6 28 C and the mean monthly maximum from C. The annual rainfall averaged 1069 mm, of which about 90 per cent occured during late June to early September (Singh et al., 1995; Singh and Singh, 1999). The physico-chemical characteristics of the fresh mine spoils is reported in Singh et al. (2004a); briefly, they have neutral ph, high bulk density, low water-holding capacity (WHC) and poor soil nutrient (C, N and P) content. Soils under all planted species had neutral ph ( ), slightly lower bulk density than fresh mine soils and a

3 NUTRIENT ACCRETION RATE IN A REDEVELOPING SOIL ON MINE SPOIL 15 WHC of per cent. The potential natural vegetation adjacent to the present research area is a dry tropical deciduous forest, therefore the species selected for plantation were preferably deciduous in nature (Singh et al., 1995). Plantations and Sample Plots All the plantations were established in the months of July and August by planting nursery-raised seedlings in previously dug pits of 40 cm 40 cm 40 cm size at a spacing of 2 m 2 m. Each plantation plot was prepared by seeding in 1994 at the rate of 6 kg ha 1 with Pennisetum pedicellatum Trin. for the purpose of preventing soil erosion and loss of nutrients by runoff. The total planted area for both A. lebbeck and A. procera was 15 ha, whereas for T. grandis and D. strictus it was about 05 ha. For sampling, three permanent plots were established for each species. The size of the sample plots was 25 m 25 m for A. lebbeck and A. procera, and m for T. grandis and D. strictus. Sample Collection and Analyses Soil sampling was done once in September 1994 and Each time, six soil samples were collected at random from each of the three permanent plots of each species using cm monoliths for 0 20 cm soil depth at 10 cm intervals. The six soil samples within a plot were thoroughly mixed to yield one composite sample per plot for each soil depth. This yielded six samples for each plantation species on each sampling date. Large pieces of plant material were removed and the field-moist soil was air-dried, sieved through a 2 mm mesh screen, and then used for the analysis of soil organic carbon (SOC), Kjeldahl N and total P. Soil organic carbon was determined by dichromate oxidation and titration with ferrous ammonium sulfate (Allen et al., 1986). Kjeldahl N was determined by the microkjeldahl method (Jackson, 1958), and samples were analysed for P by a phosphomolybdic acid blue colour method (Jackson, 1958) after triple acid digestion. Soil bulk density was determined using a soil corer and measuring the weight of the dry soil (Piper, 1944) of a unit volume collected separately from 0 10 and cm soil depths. The site used for the present study had a distinctly higher content of fine soils, < 2 mm particles, (50 per cent of the total mine spoil material) compared to the other monoculture site (25 per cent of the total) at the same research area (Singh et al., 1996). Due to the high gravel content, the gravel-free bulk density was corrected on the basis of the fine-soil contents in each soil sample. Total carbon and nutrient stock in the soil (0 10 and cm) was estimated by corrected bulk density, soil volume and nutrient concentration values by using the following formula (Singh and Singh, 1991): Total carbon and nutrient stock in < 2 mm soil aggregates size ðkg C ha 1 Þ ¼½C ðgkg 1 Þcorrected BD ðkg m 3 ÞdðmÞ10 4 ðm 2 ha 1 ÞŠ=1000 Where, C ¼ concentration of carbon nutrient, BD ¼ corrected bulk density, and d ¼ the specific thickness layer of the soil sample. Similarly, other nutrient stocks (N and P) were calculated on the basis of same formula. Statistical Analyses SPSS-PC 1 statistical software was used for all statistical analyses. To observe the effects of variables, such as age, species and spoil depth, the data were subjected to the general linear model (GLM) for analysis of variance (ANOVA). Mean values of total nutrient stocks (C, N and P) and their accretion rates at different soil depths and ages were tested for difference between plantation species with Tukey s honestly significant difference (HSD) mean separation test (SPSS, 2001, Version 100). RESULTS AND DISCUSSION We do not have data from the initial stage of the plantations. However, in this study, climate, relief, parent material and time were same for all plantations. Therefore, we emphasize only the plantations effect on bulk density, nutrient stocks and their accretion rates.

4 16 A. N. SINGH ET AL. Table I. Soil bulk density (g cm 3 ) in redeveloping soil under plantations of native woody species on coalmine spoils Species/age (y) Soil depth (cm) Four years-old A. lebbeck a a A. procera a a T. grandis a a D. strictus a a Five years-old A. lebbeck a a A. procera a a T. grandis a a D. strictus a a Values in a row suffixed with different letters are significantly different from each other at p < 005. Values are means 1 standard error. Soil Bulk Density In 4- to 5-year-old plantations of all species, there were slight changes in bulk density at 0 20 cm spoil depth (Table I). The differences in bulk density at 0 10 cm spoil depth were non-significant ( g cm 3 ) between the species and were greatest for D. strictus (167 g cm 3 ) and least for the A. lebbeck (160 g cm 3 ) and T. grandis plantations (160 g cm 3 ). Bulk density is important in reclaimed areas due to compaction by heavy equipment during leveling of spoil or applying topsoil (Bradshaw, 2000). The bulk density ranged from g cm 3 in clay, clay-loam, and silt-loam soils and from g cm 3 in sand and sandy-loams. Generally, low bulk densities in soils indicate high organic matter content, good granulation, high infiltration, and good aeration, resulting in a good rooting medium (NRC, 1981). The old mine spoils are similar in bulk density to natural soils (Schafer et al., 1980), while new mine spoils are compacted producing higher bulk densities (Bending and Moffat, 1999). Root growth is restricted in soils with a bulk density higher than 160 g cm 3 (Russell, 1977). We have also reported 175 g cm 3 bulk density in fresh mine spoil, which was above the threshold for root growth (Singh et al., 2004a). However, after the establishment of plantations, this value was similar to our values in A. lebbeck and T. grandis plantations. In A. procera and D. strictus plantations, the value was lower than for fresh mine spoil, but was still higher than the threshold value (160) for better root growth. On the other hand, bulk density was slightly lower in all plantations than fresh mine spoil; this could be because no heavy machinery was used after tree planting, or be due to the effect of the tree species perhaps the tree roots increased the soil porosity (Bradshaw, 1997b; Bradshaw, 2000; Akala and Lal, 2000). A chronosequence of reclaimed mine lands under two land uses in Ohio (USA) was studied to determine bulk density and the potential of mine spoil reclamation to sequester carbon (Akala and Lal, 2001). The study reported that reclamation of mined lands decreased bulk density over a period of 20 to 30 years. In conformity with this, in our study an indistinct change was found in bulk density in 4- to 5-yearold plantations of all species at cm spoil depth. C and Nutrient Stocks and Their Accretion Rates in Redeveloping Soil In the present study, total C stock at 0 20 cm spoil depth in 4- to 5-year-old plantations varied significantly from 8649 to kg ha 1 in A. lebbeck, from 4294 to 6582 kg ha 1 in A. procera, from 3674 to 3808 kg ha 1 in T. grandis and from 7516 to kg ha 1 in D. strictus, respectively (Table II). Analysis of variance indicated significant differences due to age, species and depth, while their interactions (age depth, species depth and species depth age) were non-significant except for species age (see Table VI). Corresponding values

5 NUTRIENT ACCRETION RATE IN A REDEVELOPING SOIL ON MINE SPOIL 17 Table II. Organic carbon nutrient stock (kg ha 1 ) in redeveloping soil under plantations of native woody species on coalmine spoils Soil depth (cm) Species A. lebbeck A. procera T. grandis D. strictus Four years-old b a a b b a a b Total b a a b Five years-old c b a c c b a c Total c b a c Values in a row suffixed with different letters are significantly different from each other at p < 005. Values are means 1 standard deviation. reflected greater C contents in 0 10 cm spoil layer in all species under 4- to 5-year-old plantations than from cm spoil depth, indicating that sequestration of carbon in mineral soil layer is regulated by vegetation development. Richter et al. (1999) reported rapid accumulation and turnover of soil carbon in a 75 cm upper mineral soil layer of re-establishing forest in the USA. Further, they suggested that aggrading forest ecosystems are a strong carbon sink and the increasing demand by the aggrading plant biomass may not permit the mineral N and P to accumulate in deeper soil. Therefore, accumulation of carbon is greater in the tree biomass and the forest floor than in the mineral soil. Despite the high level of carbon inputs to the mineral soil, carbon sequestration is limited by rapid decomposition and facilitated by coarse soil texture and the low cation exchange capacity of clay (Richter et al., 1999). This is particularly true for soil development on mine spoils, where biological processes are more important as breakdown of clay minerals and other physical processes have already played their role (Bradshaw, 1997a, 1997b; Bradshaw, 2000). Accretion rates were calculated as the differences in nutrient stocks between two consecutive ages of plantation (4 and 5 years old) of each species. Accretion rates of organic C in the present study varied significantly due to species, being greatest in 5-year-old D. strictus (14599kgha 1 y 1 ) and least in T. grandis plantations (1534kgha 1 y 1 ) at 0 10 cm soil depth. Although the effect of soil depth was non-significant, corresponding values were higher at cm soil depth in all species except T. grandis (see Tables V and VI). Perhaps, this might be due to a species-specific effect involving the high quantity of litter fall and the associated deposition of nutrients in the soil through decomposition. Below-ground C allocation in trees was correlated to litter fall and the below-ground C allocation increased with the increase of litter fall (Raich and Nadelhoffer, 1989). In conformity with this, the highest amount of litter fall was reported in D. strictus and the lowest in T. grandis plantations. However, concentration of SOC was higher under A. lebbeck (60 73gkg 1 ), followed by D. strictus (50 67gkg 1 ), A. procera (30 42gkg 1 ) and T. grandis plantations (23 25gkg 1 ), a pattern that is governed by the decomposition rate of litter (Singh and Singh, 1999; Singh et al., 2004a, 2004b). However, in our study, values of C concentration between different plantations were high compared with nearby similar age (5-year-old) naturally vegetated sites (23gkg 1 ) (Singh et al., 1995), indicating a positive effect of plantations on C accretion in redeveloping mine spoil. However, these concentrations were considerably lower than those in natural deciduous forests (47 210gkg 1 ) (Singh and Singh 1991). Carbon accretion rates in the present study are similar in range to those in young soils at 0 10 cm soil depth from several other places reported as 1130 kg ha 1 y 1 (Roberts et al., 1988) to 1350 kg ha 1 y 1 (Schafer et al., 1980). However, Schwenke et al. (2000) reported average values of C accumulation rate of kg ha 1 y 1 in 5- to 10-year-old rehabilitated bauxite mine sites that included indigenous planted species at Weipa, Australia. They concluded that greater accretion rates of C were to be found in sites planned with native species. Gonzalez-Sangregorio et al. (1991) reported an increase in total organic C content from 20 to140gkg 1 in spoils; mostly during the first year after

6 18 A. N. SINGH ET AL. Table III. Total nitrogen nutrient stock (kg ha 1 ) in redeveloping soil under plantations of native woody species on coalmine spoils Soil depth (cm) Species A. lebbeck A. procera T. grandis D. strictus Four years-old c b a b c b b a b Total c b a b Five years-old c b a c b b a b Total c b a c Values in a row suffixed with different letters are significantly different from each other at p < 005. Values are means 1 standard deviation. seeding of lignite mine spoil in Spain. In the following years, C continued to increase, though at a slower rate, reaching a value of 230gkg 1 at the end of the third year. The increased C is because the vegetation was not harvested; it was left to increase the organic matter content of the soil (Gonzalez-Sangregorio et al., 1991). Nitrogen stocks in our study varied significantly among species due to plantation age and spoil depth (see Table VI). Substantial amounts of N were estimated in the upper soil layer (0 10 cm) for all species at 4 to 5 years old (Table III). Of the total N stock, 528 per cent under A. lebbeck, 520 per cent under A. procera, 510 per cent under T. grandis and 550 per cent under D. strictus was found at 0 10 cm depth, respectively. Although the deposition and release of N through litter fall and its decomposition was highest in A. lebbeck and A. procera plantations (Singh et al., 2004b), slow N releases from decomposing litter of D. strictus plantation indicated more N accumulation in soil than N-fixing species (A. lebbeck and A. procera) (Singh and Singh, 1999). Therefore, N accretion rates were significantly higher under D. strictus (1056kgha 1 y 1 ) at 0 10 cm spoil depth followed by A. procera (803kgha 1 y 1 ), A. lebbeck (237kgha 1 y 1 ) and T. grandis (70kgha 1 y 1 ), respectively, at 5-years-of age (see Tables V and VI), indicating a significant amount of N accumulation in redeveloping soils of mine spoil during a short period of plantation. In conformity with this, Jencks et al. (1982) found increasing soil N concentrations with age and estimated annual rates of N accretion under N-fixing black locust (Robinia pseudoacacia) of 222 kg ha 1 at 5 7-years old, 146 kg ha 1 at years old and 171 kg ha 1 at years old. Vimmerstedt et al. (1989) also studied N accretion in surface soils of black locust plantations, where the total N value increased from 04 to23gkg 1 in the 30 years since tree establishment, i.e., 475 per cent more N than the initial status at plantation establishment. However, when N-fixing species (either legumes or other species, such as Alnus, with symbiotic N-fixing microorganisms) appear in the succession, development accelerates (Bradshaw, 1997a). These species can readily contribute over 100 kg N ha 1 per year, more than the annual requirement of developing vegetation. The progress of many natural primary successions is linked with the arrival of such species, while slow development can be associated with their non-arrival. The significant end point will be the accumulation of a soil nitrogen capital of 1000 kg N ha 1 or more, which will be significant for a self-sustaining ecosystem without any further major nitrogen inputs being necessary (Bradshaw, 1997a, 1997b; Bradshaw, 2000). Evidently, in the present study, N-fixing species (A. lebbeck and A. procera) played a key role in accelerating the N capital in redeveloping soil, as reported by Bradshaw (2000), but the steady state has yet to be achieved. However, D. strictus, a non-leguminous species, performed much better in soil redevelopment and restoration, its foliage contributed 36 per cent of the ecosystem function resulting in a heavy deposition of organic matter on the soil surface (Singh and Singh, 1999), while the contribution of T. grandis to N accumulation in the soil was poor due to its deposition of less organic matter in the soil (Singh, 1999; Singh et al., 2004a). Phosphorus stocks at 0 20 cm spoil depth increased with increasing plantation age for all planted species except D. strictus, being greatest under A. procera ( kgha 1 ) and A. lebbeck ( kgha 1 ) and least

7 NUTRIENT ACCRETION RATE IN A REDEVELOPING SOIL ON MINE SPOIL 19 Table IV. Total phosphorous nutrient stock (kg ha 1 ) in redeveloping soil under plantations of native woody species on coalmine spoils Soil depth (cm) Species A. lebbeck A. procera T. grandis D. strictus Four years-old a a a a a a a a Total a a a a Five years-old a a a a a a a a Total a a a a Values in a row suffixed with different letters are significantly different from each other at p < 005. Values are means 1 standard deviation. under D. strictus ( kgha 1 ) (Table IV). However, these increases were only statistically significant due to species and soil depth while plantation age and their interactions (age depth, species age, species depth and species depth age) were non-significant (see Table VI). In developing ecosystems on waste dumps, both organic matter and the major plant nutrients accumulate steadily (Roberts et al., 1988). However, in the present study, an increasing trend for P nutrient stocks was observed across the plantation age in all species except D. strictus, which showed a more or less constant rate in a 4- to 5-year-old plantation. Accretion rates of total P in this study varied significantly due to species; being greatest under 5-year-old T. grandis (558kgha 1 y 1 ) and least under D. strictus plantation (08kgha 1 y 1 ) at 0 20 cm spoil depth. Effect of spoil depth was not significant, but values were also high at cm spoil depth in T. grandis followed by A. procera, A. lebbeck and D. strictus (Tables V and VI). Thus, there was a remarkable finding that leguminous species (A. lebbeck, A. procera) were not very efficient in accumulating more P in the cm soil horizon, as was also the case for C and N accumulation. Perhaps, N fixers have a greater requirement for P, which is essential at high levels during N fixation (Gressel et al., 1996). Table V. Accretion rates of organic carbon and nutrients (kg ha 1 y 1 ) in redeveloping soil under 5-year-old plantations of native woody species on coalmine spoils Soil depths (cm) Species A. lebbeck A. procera T. grandis D. strictus Carbon bc ab a c b ab a b Total b b a b Nitrogen a a a a ab ab a b Total a ab a b Phosphorus a a a a a ab b a Total ab b b a Values in a row suffixed with different letters are significantly different from each other at p < 005. Values are means 1 standard deviation.

8 20 A. N. SINGH ET AL. Table VI. ANOVA results for total carbon, nutrient stocks and accretion rate in redeveloping soil of mine spoil under woody plantations of native species Source df Carbon Nitrogen Phosphorus Nutrient stock Age *** 13235** 4133 NS Species *** *** 3071* Depth *** 15039** 5082* Species Age *** 2484 NS 0615 NS Species Depth NS 1534 NS 0049 NS Age Depth NS 0310 NS 001 NS Species Depth Age NS 0208 NS 0276 NS Residual 32 Nutrient accretion rate Species *** 6667*** 7539* Depth NS 0801 NS 0015 NS Species Depth NS 0559 NS 3407* Residual 16 *, **, ***significant at the < 005, < 001 and < 0001 probability levels, respectively. NS, non-significant at p < 005. In our study, the total P concentration in the soil was more or less similar under both N-fixing species ( g kg 1 under A. lebbeck and g kg 1 under A. procera) and in non-leguminous species ( g kg 1 under T. grandis and g kg 1 under D. strictus). However, total return and deposition of P through litter fall under T. grandis was similar to A. lebbeck, A. procera and D. strictus plantations (Singh, 1999). Thus, in the case of P, the availability and accumulation rate may vary due to vegetation, species soil and site conditions and thus a general prediction cannot be made. Notwithstanding, some trees might also differ in their influence on soil biological activities, such as the presence of mycorrhizae or the composition of microbial communities, which in turn may affect soil chemistry (Spears et al., 2001). However, in this study, roots of all plantation species were infected more or less (30 per cent) with vesicular arbuscular mycorrhizal fungi (Singh et al., 1995). Using either leguminous or non-leguminous species for rehabilitating any degraded ecosystem requires a good knowledge of their biology, soil preferences and interactions (Singh et al., 2004b). Therefore, it is recommended that further study is necessary to clarify the spatial and temporal extent of species effects on essential nutrients (C, N and P) in redeveloping mine spoil, at least during the initial stage of restoration especially for P, because information on it is not well documented. CONCLUSIONS In this study, soil bulk density values were distinct only for 4-year-old plantations at 0 10 cm spoil depth. Therefore, effect of spoil depth and plantation age on bulk density was non-significant. The highest amount of soil organic C and N were found under A. lebbeck followed by D. strictus, A. procera and T. grandis plantations at both depths (0 10 and cm) in redeveloping mine spoil. Whereas, the highest total P was found under A. procera followed by T. grandis, A. lebbeck and D. strictus plantations at 5 years of age. Although, the highest accretion rates of carbon and nitrogen were found under D. strictus plots followed by A. lebbeck, A. procera and T. grandis, the accretion rate of total P was highest in T. grandis plots followed by A. procera, A. lebbeck and D. strictus plantations. Therefore, this study clearly indicates that a non-legume (D. strictus) can also play a significant role in restoring mine spoil habitats, in the same way that has been specially reported for leguminous species. In conclusion, a continued increase in C and N stock and their accumulation rates under all species along with plantation age indicated a progressive development of nutrient accretion in the organo-mineral horizons of redeveloping soil. However, in case of total P, neither age nor a species-related trend was found. Therefore, greater knowledge of the species-specific effects on ecosystem restoration is required.

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