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Keywords:

  • gypsum amended;
  • plant colonization;
  • restoration;
  • soil nutrients

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

The current study was undertaken to evaluate the success of a revegetation program on three sites within the Bauxite Residue Disposal Area at the Aughinish Alumina Ltd. refinery. This was achieved by determining botanical diversity, substrate conditions, and plant uptake. Two sites revegetated in 1999, with and without the use of gypsum, were assessed and compared to a site revegetated in 1997. Compared to an initial 6 species used in seeding, a total of 47 species were recorded growing on the three sites with greatest diversity on the 1997 site. There was limited variation in the residue properties of the three treatments indicating that diversity was most influenced by succession and not substrate conditions. Limited available manganese was found in all treatments and significantly lower exchangeable magnesium in the gypsum-amended treatment. Exchangeable sodium, aluminum, and pH in the substrate were not at levels of concern. Appreciable nitrogen, phosphorus, and potassium were found as a result of a fertilizing program. Dominant species in the 1999 treatments, Holcus lanatus and Trifolium pratense, were analyzed for elemental composition. Compared to previous studies, foliar nitrogen, phosphorus, potassium, and calcium were adequate and sodium levels were low. Manganese and magnesium levels were low, and availability should be assessed as part of the monitoring program. Furthermore, the effect of a fertilizing regime on plant uptake and substrate conditions needs to be assessed.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

An estimated 70 million metric dry tons of bauxite residues, produced during the extraction of alumina from bauxite ore through the Bayer Process, are produced globally per year. Two distinct fractions, coarse (process sand) and fine (red mud) residues, are normally contained in disposal areas (TAA 2000). Revegetation of the residues is an issue of concern to alumina producers worldwide (Gherardi & Rengel 2001). Establishment of vegetation on amended bauxite residue has been demonstrated in a number of studies (Fuller et al. 1982; Marschner 1983; Wong & Ho 1993; Courtney & Timpson 2005; Wehr et al. 2006).

The establishment of plant cover on tailings is only part of the revegetation objective. The main aim of any restoration process is to create sustainable plant communities representative of the composition and diversity of the surrounding natural plant communities (Jefferson 2004). Most studies on revegetation of processing residues or tailings have focused on techniques for vegetation establishment, whereas little attention has been paid to the processes of soil development and natural recruitment (Shu et al. 2005). A major shortcoming of the published information on bauxite residue revegetation is that all studies reported were conducted for a short duration (a few months to 1 year), and it is not known how the vegetation cover would have survived over longer periods with minimal or no further input (Wehr et al. 2006).

Successful revegetation is dependent on many factors. Soil properties identified as indicators of soil quality include soil organic matter, total organic nitrogen, total organic carbon, nutrient availability, pH, and electrical conductivity (EC). Many characteristics of bauxite residue can limit soil and plant productivity. The success of bauxite residue rehabilitation is “far from satisfactory because of a characteristically slow release of Na+ and resulting high pH due to its associated bicarbonate environment” (Wong & Ho 1995). Levels of organic carbon in unamended bauxite residue are low with reported values ranging from trace amounts (Fortin & Karam 1998) to 0.3% (Wong & Ho 1993). Total nitrogen levels of 0.02% have been reported for red mud, together with high pH (11–12) and EC (60–350 dS/m) (Wong & Ho 1994). Phosphorus nutrition can be limited due to high P adsorption of sesquioxides in the residue (Barrow 1982; Snars et al. 2004). Manganese availability rapidly decreases in coarse fraction residue “process sand” (Gherardi & Rengel 2001). Low foliar N, P, K, Mg, Zn, and Cu values were observed in most treatments growing on amended bauxite residue (Eastham et al. 2006). Additionally, herbage levels for manganese, calcium, magnesium, potassium, phosphorus, and nitrogen were significantly decreased after a second year’s growing season on amended bauxite residue (Courtney & Timpson 2004).

Ecological succession has been demonstrated on metalliferous mine tailings (Skousen et al. 1994; O’Neill et al. 1998; Bagattto & Shorthouse 1999; Shu et al. 2005) and alkaline wastes (Lee & Greenwood 1976; Ash et al. 1994). Similarly, accumulation of nutrients has been identified as a critical issue in the development of stable vegetation cover in reclamation of tailings (Bradshaw 1983; Bendfeldt et al. 2001). Seaker and Sopper (1988) stressed the importance of soil organic matter accumulation, decomposition, and minimum levels of organic C and N contents for productive mine soils. To date, there is little information on the long-term integrity of vegetation established on bauxite residues.

Revegetation trials (1997–2005) have been established on the Aughinish Alumina Ltd. bauxite residue disposal area (BRDA) in Limerick, southwest Ireland. The objective of the current study was to evaluate the current status of revegetated areas through the comparison of species diversity, substrate conditions, and plant uptake characteristics of three sites on the BRDA, which had been revegetated in the period 1997–2001.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

An evaluation was made of ecological status and soil quality from revegetated areas on the Aughinish Alumina Ltd. BRDA (lat 52°37.05′N, long 9°04.18′W) in Co. Limerick, southwest Ireland. Annual rainfall is about 930 mm with November–January typically being the wettest months.

An upstream system is used in the disposal and management of the residues. Consequently, available space for revegetation work is restricted to terraced areas between raises. A series of revegetated areas have been implemented on these terraced areas during 1997–2006. Three test sites were selected on the basis of contrasting trial area preparation. Each of the three sites was approximately 60 m2.

Site 1 (RM’97) was situated in a terraced area of the BRDA where revegetation was carried out in 1997 on weathered red mud, which had been deposited some 3+ years previously and amended with 25% process sand and spent mushroom compost at 80 t/ha. Site 2 (RMG’99) was situated in a terraced area of the BRDA, which had red mud residue deposited circa 1995. Amendment of the site in 1999 involved the application of 3% gypsum w/w and 25% process sand w/w and spent mushroom compost at 80 t/ha. Site 3 (RM’99) was situated in a terraced area of the BRDA, with red mud residue deposited circa 1995. Amendment of the site in 1999 involved application of 25% process sand w/w and spent mushroom compost at 80 t/ha.

Amendments for all treatments were broadcast and incorporated by rotavation. A 4-month period of leaching was observed, and all sites were seeded with a mixture of Agrostis stolonifera, Fescue longifolia, Holcus lanatus, Lolium perenne, Trifolium repens, and Trifolium pratense at rates of 100 kg/ha.

The composition of the vegetation cover on the sites was assessed in August 2005. Species cover was recorded using a 6-point scale, 1 = 1–10% cover, 2 = 1–25% cover, 3 = 25–50% cover, 4 = 50–75% cover, 5 = 75–100% cover, += present, employed. Nomenclature for plants follows Stace (1991).

Random samples of the two dominant species, T. pratense and H. lanatus, were taken from sites RMG’99 and RM’99 to investigate the long-term effect of gypsum application on foliar nutrient content and for comparison with values obtained in a survey in 2001/2002 (Courtney & Timpson 2005). All three sites received fertilizer in the form of N:P:K (18:6:12) in 2004 and 2005, as previous foliar analysis had showed nutrient deficiencies.

Samples of amended bauxite residue were collected from sites immediately after the vegetation sampling and from areas where foliage samples were taken. Samples 0–10 cm were taken using a soil corer. The samples were allowed to dry at air temperature and were sieved through 2-mm aperture. Soil pH and EC were measured in an aqueous extract (1:5). Organic matter content was determined by loss on ignition at 500°C for 24 hours, and organic carbon was determined using the rapid dichromate oxidation technique (Nelson & Sommers 1982). Available cations were determined using the ammonium acetate extraction (Thomas 1982). Exchangeable aluminum was determined in KCl extract based on the method reported by Bertsch and Bloom (1996). Plant-available manganese was determined by DTPA extraction (Lindsay & Norvell 1978). Available phosphorus was determined using UV spectrophotometry following extraction with sodium bicarbonate (Olsen et al. 1954). Total nitrogen content was determined using the Kjeldahl method (Bremner & Mulvaney 1982).

Vegetation was rinsed thoroughly with deionized water and oven-dried to a constant dry weight prior to grinding. Samples were then digested on an open hot block for 3 hours, filtered, and analyzed by atomic absorption.

Data were statistically analyzed using SPSS version 11.0 for Windows. Analysis of variance was used to compare soil treatments with post hoc comparison of means using Tukey’s test with a significance of p < 0.05. Pearson correlations were employed for determining the strength of relationship between soil properties. The significance level reported (p <0.05 and p <0.01) is based on the Pearson coefficients.

Foliar nutrient levels were compared in the RM’99 and RMG’99 sites using t tests.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

The plant species recorded on the three rehabilitated bauxite residue sites are listed in Table 1. There were 47 species belonging to 38 genera and 15 families. Asteraceae and Poaceae were the dominant families with 14 and 9 species, respectively. In the initial seeding of the plots, six species (four Poaceae and two Fabaceae) were used. The dominant grass species were Holcus lanatus with Festuca rubra and Agrostis stolonifera, each of which was present in the original seed mixture. Lolium perenne, which was also present in the original seeding mixture, was also recorded but was not dominant. Five new grass species have invaded the revegetated area.

Table 1.  Plants growing on the three different amended bauxite residue treatments.
 RM’99RMG’99RM’97
  1. Scoring index: 1 = 1–10% cover, 2 = 1–25% cover, 3 = 25–50% cover, 4 = 50–75% cover, 5 = 75–100% cover, += present.

Apiaceae
 Angelica sylvestrisWild angelica+++
 Daucus carotaWild carrot+++
Asteraceae
 Achillea millefoliumYarrow1 +
 Centaurea nigraCommon knapweed ++
 Chrysanthemum leucanthemumOxeye daisy+ +
 Cirsium arvenseCreeping thistle+++
 Ci. vulgareCommon thistle1++
 Hypochaeris radicataCat’s ear+ 
 Lapsana communisNipplewort++ 
 Leontodon autumnalisAutmun hawkbit + 
 L. hispidusRough hawkbit+ 
 L. saxatilisLesser hawkbit +
 Senecio jacobaeaRagwort+++
 Sonchus arvensisPerennial sow-thistle ++
 Taraxacum sp.Dandelion++ 
 Tussilago farfaraColt’s-foot+++
Betulaceae
 Alnus glutinosaAlder +
 Betula sp.Birch +
Caryophyllaceae
 Cerastium fontanumCommon mouse-ear+++
Clusiaceae
 Hypericum perforatumPerforate St. John’s wort++ 
Cyperaceae
 Carex flaccaGlaucous sedge +
Fabaceae
 Lathyrus pratensisMeadow vetchling +
 Lotus corniculatusCommon bird’s-foot-trefoil++ 
 Medicago lupulinaBlack medic + 
 Trifolium pratenseRed clover2–33+
 T. repensWhite clover2–3++
 Vicia sepiumBush vetch + 
Gentianaceae
 Blackstonia perfoliataYellow-wort +
Onagraceae
 Chamerion angustifoliumRosebay willowherb + 
 Epilobium hirsutumGreat willowherb 1 
 E. parviflorumHoary willowherb++ 
Poaceae
 Agrostis stoloniferaCreeping bent222
 Anthoxanthum odoratumSweet vernal grass +
 Arrhenatherum elatiusFalse oat-grass11 
 Dactylis glomerataCock’s-foot+++
 Elymus repensCommon couch+1 
 Festuca rubraRed fescue322
 Holcus lanatusYorkshire-fog443
 Lolium perennePerennial rye-grass1++
 Phleum pratenseTimothy+++
Polygonaceae
 Rumex acetosaCommon sorrel + 
 Ru. crispusCurled dock +
Ranunculaceae
 Ranunculus acrisMeadow buttercup+1+
 Ra. repensCreeping buttercup+1+
Rubiaceae
 Galium palustreCommon marsh-bedstraw +
Salicaceae
 Salix sp.Willow ++
Urticaceae
 Urtica dioicaCommon nettle+++
Total
 Family: 15 91113
 Genus: 39 272828
 Species: 48 293232

Typical values for the unamended bauxite residue and properties of revegetated amended residue are shown in Table 2. Marked reductions in pH (8.02–8.14) and sodium content were recorded compared to unamended residue. Also, levels of total kjeldahl nitrogen and organic carbon are significantly increased. Available levels of phosphorus are low and manganese is deficient. The long-term effect of gypsum on residue chemical properties is apparent for cation behavior, with significantly lower magnesium (p < 0.05) most noticeable along with soil conductivity (Table 2). Available levels of aluminum are much lower than levels previously recorded but did not differ significantly between treatments.

Table 2.  Surface properties (0–10 cm) of bauxite residue treatments.
 pHmS/cm%g/kgmg/kg
ECOCOMNNaMgCaKAlMnP
  • n.d., not determined. Results are presented as means of eight replicates ± SE. Mean values in rows not sharing the same letter are significantly different at p = 0.05.

  • *

     Typical values for unamended residue from trial area.

RM’998.12 ± 0.02a0.362 ± 0.02ab1.52 ± 0.153a5.26 ± 0.41a1.27 ± 0.028a415 ± 17a46.8 ± 4.9a1,849 ± 64a194 ± 33.1a0.32 ± 0.0140.37 ± 0.07a9.3 ± 1.0 a
RMG’998.02 ± 0.07a0.518 ± 0.14a1.56 ± 0.110a5.18 ± 0.14a1.33 ± 0.019a368 ± 15b31.4 ± 1.9b2,627 ± 180b186 ± 15.5a0.31 ± 0.0270.37 ± 0.06a6.6 ± 1.4 a
RM’978.14 ± 0.05a0.281 ± 0.01b1.53 ± 0.177a5.35 ± 0.39a1.25 ± 0.010a318 ± 13ab46.1 ± 7.1a1,662 ± 108a161 ± 23.2a0.31 ± 0.0330.36 ± 0.07a7.6 ± 1.0 a
Unamended residue*10.91.930.1n.d.0.023,5006.4235n.d.10.2n.d.<1.5

Organic matter content in the three different sites did not differ significantly but was higher compared to unamended residue. Organic carbon, total kjeldahl nitrogen, and available phosphorus were all positively correlated with organic matter content (Table 3). Organic carbon values have increased compared to values for unamended residue with no significant differences between the treatments. Exchangeable sodium and pH were positively correlated (p < 0.05) indicating the effect of residual caustic bayer liquor on both properties.

Table 3.  Correlation matrix for amended residue properties.
 OCNOMpHECPhosCaMgNaK
  • n.s., not significant.

  • a 

    Correlation is significant at the 0.01 level.

  • b 

    Correlation is significant at the 0.05 level.

OC 0.778a0.780an.s.n.s.n.s.n.s.n.s.n.s.n.s.
N0.778a 0.755an.s.n.s.n.s.n.s.n.s.n.s.n.s.
OM0.780a0.755a n.s.n.s.0.369bn.s.n.s.n.s.n.s.
pHn.s.n.s.n.s. –0.868an.s.–0.797an.s.0.547an.s.
ECn.s.n.s.n.s.–0.856a n.s.0.862an.s.–0.374bn.s.
Phosn.s.n.s.0.369bn.s.n.s. n.s.n.s.n.s.n.s.
Can.s.n.s.n.s.–0.797a0.862an.s. n.s.−0.425bn.s.
Mgn.s.n.s.n.s.n.s.n.s.n.s.n.s. n.s.n.s.
Nan.s.n.s.n.s.0.582a–0.374bn.s.–0.425an.s. −0.454b
Kn.s.n.s.n.s.n.s.n.s.0.454bn.s.n.s.n.s. 

The mean total kjeldahl nitrogen concentration after 6 years for the amended bauxite residues was 1.27 (RM’99), 1.33 (RMG’99), and 1.25 g/kg (RM’97). Soil nitrogen content was highly correlated with organic matter content (r = 0.755) and organic carbon (r = 0.778) (Table 3).

The gypsum-amended site had significantly higher levels of calcium (p < 0.05) indicating that, even 6 years after application, calcium exists in exchangeable form on the exchange complex of the residue/soil system. High occurrence of exchangeable calcium in this site may also explain the slightly lower level of magnesium recorded. Mn DTPA was low in all treatments with no significant differences found (p > 0.05).

Of the 45 species recorded growing on the bauxite residue sites, H. lanatus and Trifolium pratense were dominant (Table 1). Furthermore, these species were included in the initial seeding of sites. Consequently, foliar analysis of these two species was undertaken to determine the long-term effect of gypsum analysis and how concentrations for critical parameters have changed since 1999 (Courtney & Timpson 2005).

Nitrogen has increased in H. lanatus to levels that are close to Irish mean values with no difference between treatments. For both treatments, T. pratense nitrogen levels compare favorably to recommended adequacy values (Table 4). Both grasses and legumes show potentially large differences in sodium concentration between species. No significant differences (p > 0.05) were recorded for each species between treatments. The other nutrients determined were close to the reported adequacy levels with lower magnesium (p < 0.05) content in the gypsum treatments.

Table 4.  Foliar nutrient concentrations for Holcus lanatus and Trifolium pratense.
 %mg/kg
NCaMgKPNaMn
Holcus lanatus
 RM’992.1 ± 0.08a0.62 ± 0.02a0.20 ± 0.02a2.6 ± 0.17a0.39 ± 0.01a0.39 ± 0.06a17.1 ± 0.8a
 RMG’991.9 ± 0.04a0.58 ± 0.03a0.16 ± 0.01b2.6 ± 0.17a0.41 ± 0.03a0.31 ± 0.04a18.6 ± 1.1a
 2.5a0.64a0.20a2.82a0.40a0.29a20b
Trifolium pratense
 RM’993.2 ± 0.11a1.47 ± 0.04a0.26 ± 0.01a2.9 ± 0.08a0.27 ± 0.01a0.15 ± 0.02a17.8 ± 2.1a
 RMG’993.0 ± 0.11a1.54 ± 0.03a0.23 ± 0.005b2.8 ± 0.20a0.24 ± 0.01a0.11 ± 0.01a18.2 ± 0.64a
Adequacy levelsc2.5–4.001.0–2.00.25–0.61.8–3.00.3–0.6>0.5d35–100

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

The dominance of Asteraceae (Compositae) and Poaceae (Gramineae) on colonized tailings has been reported previously. Forty species, belonging to 27 genera from 9 families, mostly graminaceous and composite, were found colonizing a 10-year-old copper tailings pond after human-assisted revegetation. On a 10-year-old coal mine spoil, 97 wild species from 67 genera and 21 families, mostly composite and grasses, successfully invaded the reclaimed area (Li 2006). Of 54 species colonizing five Pb/Zn mine tailings, 13 species belonged to the gramineae and 10 to the Asteraceae (Compositae) (Shu et al. 2005).

Legume and nonlegume nitrogen fixation have been identified as the critical components of the process of soil and vegetation development (Roberts et al. 1981). O’Neill et al. (1998) reported leguminous species, Trifolium repens, Vicia sepium, and Lotus pendunculatus, with T. repens the most common, on pyritic tailings site in Ireland, 8 years after rehabilitation. In the current study, Medicago sp. and Lathyrus pratensis were also recorded, with T. pratense the most common. Only Trifolium sp. was used in the initial seeding mixture.

Species that invade mine lands are often those with effective seed dispersal mechanisms, high seed production rates, local availability, and tolerance of mine soil conditions (Ashby 1984). Seed sources for Cirsium arvense, Sonchus arvensis, Taraxacum officinale, and Tussilago farfara on revegetated opencast coal sites have been attributed to wind dispersal (Chapman & Younger 1995). Spreading of hay on the surface of red mud was practiced on the BRDA as a method for dust suppression until 2001 and may have provided the seed source for much of the established species on the BRDA.

Age may be an important factor in the botanical diversity of the rehabilitated residue with highest recordings for family, genus, and species in the older site (RM’97). As there is limited variation for the soil parameters, the vegetation types associated with the older plot may represent a successional stage. Establishment of woody species on rehabilitated areas can vary, with 5 years on lignite waste (Skousen et al. 1994) to greater than 15 years for Salix scrub on calcareous alkaline waste (Lee & Greenwood 1976). In the current study, the presence of Alnus, Betula, and Salix in the older site and Salix on site RMG’99 shows that the process of natural scrub succession has commenced.

Gypsum amendment and leaching from 4 years of precipitation reduced residue pH from 10 to 8.8 (Gherardi & Rengel 2003). In the current study, substrate pH values recorded in the three treatments have similar reductions and are within the range in which plants can achieve normal growth (Williamson et al. 1982) and may not require further amendment. Conversely, in another study, within 5 years of planting, the pH of the red mud under vegetation had decreased from 10.5 to 9.5 (Hinz 1982). However, all recordings in the current study are well below 9.5 and may indicate that maximum reduction of pH has occurred in the residue.

The importance of incorporating organic matter into mine residues to improve nutrient availability and soil physical properties is well established. Organic carbon values are much greater than 0.071 g/kg reported in 4-year-old residue that had received both gypsum and organic matter (Gherardi & Rengel 2001) but are in the 0.58–1.88% range reported by Ye et al. (2002) for sparsely and densely vegetated tailings.

Nitrogen is usually deficient in mine soils, which limits vegetation establishment and sustained productivity. Nitrogen contents of unamended bauxite residues are low with levels ranging from trace (Krishna et al. 2005) to 0.02% (Wong & Ho 1993). Values found in the current study show a significant increase in total Kjeldahl nitrogen levels.

Available phosphorus was low in all treatments, with values corresponding to index 0 in the phosphorus availability indices (Rowell 1994). Bauxite residue contains large amounts of sesquioxides, and thus has a very high phosphorus retention capacity (Snars et al. 2004). Analysis with acidic extracting reagent (pH 4.8) showed high values of greater than 150 mg/kg phosphorus (Data not shown). Similarly, Meecham and Bell (1977) found available levels of 8.2 mg/kg phosphorus with an 8-fold increase in acid extract. These results indicate that although phosphorus reserves may be high, available amounts are low.

Availability of major cations is a concern in revegetating bauxite residues due to excessive levels of exchangeable sodium. Calcium and potassium levels in the amended residue are within the satisfactory limits reported for mine soils (Monterroso et al. 1999). Previous studies indicated deficient levels of potassium in amended residue (Courtney & Timpson 2004). Satisfactory levels currently existing in the residue reflect the effect of annual applications of inorganic NPK on the treatment area. Available magnesium levels recorded for all treatments are within the slight to severe deficiency range reported by Monterroso et al. (1999) for mine soils.

Manganese nutrition on bauxite residues is limited and added supplements are readily transformed to a plant-unavailable form (Gherardi & Rengel 2001). Wong and Ho (1992) reported values of 0.25 mg/kg in unamended residue with significant increases being observed at sewage sludge addition of 16% w/w. Although organic content in the residues in the current study have increased from unamended values, manganese deficiency is still an issue.

Aluminum levels in bauxite residue are closely correlated with pH (Fuller et al. 1982), with solubility increasing above pH 9.2. Wong and Ho (1993) reported soluble aluminum levels of 1.04 mg/kg (pH 10.5) in unamended residue with reductions to 0.08–0.24 mg/kg (pH 8.56–9.98) with increasing gypsum addition. Levels of 20 mg/kg are reported to be toxic to red clover and other legumes (Alam & Adams 1979). Results reported in the current study are much lower than this value, probably as a result of the significant reductions in pH.

Foliar nutrient deficiency in Lolium perenne and Holcus lanatus was observed after a 1-year growing season on amended bauxite with further decreases in the second year having previously been recorded (Courtney & Timpson 2004). Nutrients that decreased include manganese, calcium, magnesium, potassium, phosphorus, and nitrogen.

Levels recorded for the two species show that satisfactory nitrogen nutrition can be achieved in revegetated bauxite residue. Plant phosphorus nutrition on bauxite residue is anticipated to be a limiting factor due to the high phosphorus adsorption capacity of the residue (Snars et al. 2004). The current study shows foliar phosphorus to be only marginally deficient, and values in the current study have improved from values recorded previously (Courtney & Timpson 2005). Application of inorganic fertilizer phosphorus has increased plant uptake and nutrition. Phosphorus availability in amended residue as influenced by the inherent high adsorption capacity and emerging properties of the substrate needs to be further evaluated.

Whitehead (2000) reported that of 10 common grassland species, H. lanatus had the greatest foliar sodium concentration and, of three legumes species, T. pratense accumulated the least sodium. The much lower sodium content in T. pratense than in H. lanatus reflects this tendency for sodium accumulation. Sodium levels for both species are lower than those recorded previously (Courtney & Timpson 2004, 2005). There is evidence that the application of potassium fertilizers suppresses the uptake of sodium and may be attributable to a change in the ratio of available potassium to sodium in the soil (Chiy & Phillips 1995).

Impaired uptake of calcium is an important nutritional disorder associated with sodic soils (Curtin & Naidu 1998). In the current study, adequate levels of foliar calcium for both T. pratense and H. lanatus indicate that sodium soil concentrations are not affecting plant uptake. This is not surprising because satisfactory levels of exchangeable calcium were recorded for both treatments.

Previous studies have illustrated low foliar potassium in plants growing on bauxite residue (Courtney & Timpson 2005; Eastham et al. 2006). Low foliar magnesium and potassium in vegetation growing in bauxite residue have been attributed to high levels of entrained sodium from the refining process and calcium from gypsum amendment (Eastham et al. 2006). In the current study, levels of T. pratense foliar potassium are adequate and levels for H. lanatus are greater than the average critical range for temperate grasses of 1.2–1.6% (Whitehead 2000). The findings in the current study show that the deficiency can be overcome with fertilizing. The necessity for fertilizer application as part of the revegetation program is being further monitored.

Reuter and Robinson (1997) cite 0.15% magnesium as the critical threshold for many grasses and 0.25% for T. pratense. Significantly lower foliar magnesium was recorded in the present study for both species in gypsum-amended treatments. This reflects the lower levels of exchangeable magnesium in these treatments and supports the statement of Eastham et al. (2006) above.

Levels of foliar manganese in H. lanatus and L. perenne decreased after a second-year growing season on the bauxite residue (Courtney & Timpson 2004). Values recorded in the current study show an increase in foliar manganese but levels are still deficient for both H. lanatus and T. pratense. Marginally higher manganese levels in gypsum-amended treatments may be due to the lower pH in these treatments. Manganese deficiency in residue-grown plants is primarily a consequence of the highly alkaline nature of the residue (Fuller et al. 1982). Overall, foliar manganese is low and reflects the low levels of extractable manganese in the amended residue.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

Ecological surveys indicate that successful colonization is taking place on the rehabilitated areas on the BRDA. Although 6 species were initially seeded, a total of 47 species were recorded on the revegetated BRDA. Encouragingly, woody shrub species, Betula and Salix, were recorded growing on the BRDA. As there was limited variation in properties of the substrate, the increased diversity of species on the older BRDA vegetated area is attributed to age and succession.

Satisfactory levels of substrate nitrogen and potassium with only slightly deficient levels of phosphorus were recorded. Improved levels are attributed to application of inorganic fertilizer. However, deficiency in manganese and magnesium was evident in the substrate. Encouragingly, levels of exchangeable sodium and aluminum in the substrate were low, and analysis showed promising signs of organic matter and nutrient buildup.

Similarly, plant analysis showed sufficient quantities for most nutrients but with deficiencies in magnesium and manganese. Sodium levels were not considered to be excessive, and gypsum-amended treatments displayed lower sodium and significantly lower magnesium concentrations.

Due to high adsorption capacity, phosphorus nutrition may be a long-term issue. The possibility of long-term success of vegetation on bauxite residue is promising but management of the system may be necessary.

Although initially beneficial in rehabilitating alkaline and sodic residues, there may be a long-term issue with magnesium and other cation imbalance induced by the calcium supply in gypsum.

The impact of fertilizer application on nutrient content and cation behavior needs to be further monitored.

Implications for Practice

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED
  • • 
    Bauxite residues exhibit characteristics that can significantly inhibit satisfactory plant growth.
  • • 
    Successfully amended bauxite residue can support a diverse groups of plant species that will be naturally colonized by others.
  • • 
    No evidence of excessive sodium or aluminum uptake was found. Additionally, only some nutrients elements were recorded as deficient.
  • • 
    Long term, there appears to be no regression in residue chemical properties such as release of alkalinity.
  • • 
    Sufficient levels of nutrients can be achieved with minimum management, and demonstration of nutrient cycling is seen as a desirable aim.
  • • 
    Buildup of an organic matter in the residue is seen as a beneficial method to supply adequate phosphorus nutrition in the long term.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED

The authors would like to thank Aughinish Alumina for their financial support for this research.

LITERATURE CITED

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Conclusions
  8. Implications for Practice
  9. Acknowledgments
  10. LITERATURE CITED
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