Phytoremediation of Contaminated Soil and Water - Chapter 3 potx

3 FACTORS INFLUENCING FIELD PHYTOREMEDIATION OF SELENIUM-LADEN SOILS Gary S. Bañuelos CONTENTS Introduction General Observations on Reported Field Studies Influential Factors in Field Phytoremediation Crop Rotation Water Management Water Reuse Predators (Insects and Wildlife) Selenium Inventory Utilization of Plants in Phytoremediation Conclusion References INTRODUCTION In California’s San Joaquin Valley and in numerous other irrigated agricultural areas in the western U.S., irrigation effluent may accumulate in confined shallow aquifers, eventually rising to levels that adversely affect crops (Ayars et al., 1994). To sustain long-term agricultural productivity in these regions, subsurface drainage systems for the removal of this effluent must be installed (Mercer and Morgan, 1991; Ayars, 1996). On the western side of San Joaquin Valley, there are several thousand hectares of irrigated land (possessing subsurface drains) with high water tables resulting from over irrigation. Because the drainage system was never completed, the saline effluent produced in this region was eventually routed and discharged into Kesterson National Wildlife Refuge. The wetlands receiving the drainage water, in the course of being used as wildlife habitat, were also operated as evaporation ponds to reduce the volume of agricultural wastewater. Deleterious effects on birds and fish were doc- umented on biological systems inhabitating or frequenting Kesterson Reservoir (Ohlendorf and Hothem, 1995). Selenium was identified as the element of primary Copyright © 2000 by Taylor & Francis concern. Studies showed exposure to high Se diets resulted in high tissue Se con- centrations in waterfowl (Presser and Ohlendorf, 1987; Tanji et al., 1986; Ohlendorf and Hothem, 1995; Sylvester et al., 1991; U.S. Department of the Interior, 1986). These findings resulted in closing of the Kesterson Reservoir for receiving drainage effluent from agricultural lands. Growers on the west side of the San Joaquin Valley have tried alternative practices to reduce their production of Se-laden effluent and thus sustain their agricultural land. After more than a decade of extensive research on Se remediation in California, several strategies to reduce loads of Se from entering the effluent have been proposed by the Salinity Drainage Task Force Committee in California (UC Salinity/Drainage Program, 1993). Some of these include improvement of irrigation and drainage management practices (Grattan, 1994; Mercer and Morgan, 1991), microbial volatilization (Frankenberger and Karlson, 1994), and vegetation manage- ment (phytoremediation) with perennial and annual crops (Bañuelos and Meek, 1990; Wu et al., 1988; Parker et al., 1991; Parker and Page, 1994). Phytoremediation is a plant-based technology that is being considered for man- aging Se in central California soils (Bañuelos and Meek, 1990; Terry and Zayed, 1994, 1998; Parker and Page, 1994; Wu and Huang, 1991) and for removing other toxic trace elements in soils (Baker et al., 1994; Chaney et al., 1994; McGrath et al., 1993; Salt et al., 1995; Cunningham and Lee, 1995; Blaylock et al., 1997). The phytoremediation technology for Se implies the use of plants in conjunction with microbial activity to extract, accumulate, and volatilize Se. Any one or a combination of these plant responses may lead to lower concentrations of soluble Se in the soil and thus lower amounts entering the effluent. Most greenhouse studies on phytore- mediation of Se have shown that Se added as soluble selenate can be extracted and/or volatilized from soil, translocated to shoot tissue, and removed as Se-laden plant material. Studies are needed, however, that demonstrate the effectiveness of phy- toremediation for reducing the amount of naturally occurring Se entering effluent (Martens and Suarez, 1997), since options for disposing of Se-laden effluent are still unclear. Field research on Se phytoremediation is still in the nascent stage (Bañuelos et al., 1993); however, field studies are crucial to develop sound phytoremediation strategies for remediating soils and sediments (Schnoor et al., 1995). Growing crops to manage soluble Se by field phytoremediation requires the application of a wide range of knowledge about the chemistry and transformation of Se in soil, Se uptake and its toxicity in plants and animals, and sustainable agronomical practices neces- sary for long-term crop production. The successful implementation of phytoreme- diation requires growing selected crops in Se-containing soils as part of a crop rotation and simultaneously reducing amounts of soil Se primarily by plant uptake. Factors to consider for phytoremediation under field conditions in central California include: (1) soil salinity and high concentrations of toxic elements, (2) presence of competitive ions affecting Se uptake, (3) adverse climatic conditions, (4) water management strategies that produce less effluent, (5) unwanted consumption of high Se plants by wildlife and insects, and (6) acceptance of phytoremediation as a remediation technology by the public and growers in regions known to have Se. Copyright © 2000 by Taylor & Francis The objective of this chapter is to summarize results from recent field studies conducted by the USDA–ARS, Fresno, and the University of California on managing levels of naturally occurring Se in west side soils of central California. GENERAL OBSERVATIONS ON REPORTED FIELD STUDIES Field sites with moderate levels of naturally occurring Se near Los Baños, CA were selected for evaluating crops used in phytoremediation. The soils at these sites contained very little plant-available Se (soluble forms of Se). Because of regulatory restrictions placed upon growers in water districts of the west side of the San Joaquin Valley, the load of soluble Se leaving these soils via drainage effluent is closely controlled. Thus, Se concentrations in drainage water produced from all west side soils must be constantly monitored. Cropping, irrigation, cultivation of the soil, and organic matter (Neal and Sposito, 1991) contribute to the solubilization and movement of immobile or complexed soil Se. For this reason, some growers are committed to planting crops considered for phytoremediation as a preventative measure for reducing the amount of soluble Se entering their effluent. Information regarding growth performance and uptake of naturally occurring Se under field conditions, e.g., high salinity, boron, and sulfate, for these crops is limited, however. Moreover, there is no information available on managing Se in the soil with selected phytoremediation crops. INFLUENTIAL FACTORS IN FIELD PHYTOREMEDIATION Crop Rotation Crop selection is an important factor for successful field phytoremediation of Se. Phytoremediation strategies should initially consider rotations among phytoremedi- ation crops under field conditions. This practice will likely contribute to a constant production of biomass and to a reduction of plant disease (e.g., Fusarium, Rhizoc- tonia root rot, Alternaria block spot), insect population, and weed buildup. Different crops used in rotation may extract Se from different zones of the soil profile and deposit it at more accessible depths for eventual uptake by subsequent crops used in phytoremediation. For long-term maintenance of Se-containing soils in Se-sensi- tive areas of the west side of central California, selected crops should be tried in rotation with other agronomic crops, e.g., cotton, wheat, tomatoes, etc., typically grown in these saline soils (Shennan et al., 1995). Bañuelos and colleagues (1997) evaluated a rotation of selected crops as a preventative measure for reducing amounts of naturally occurring Se entering efflu- ent from soils located near Kesterson Reservoir. The following crops that can reduce soil Se levels were evaluated near Los Baños, CA on 15 10 x 10 m plots: Indian mustard (Brassica juncea Czern L.), tall fescue (Festuca arundinacae), birdsfoot trefoil (Lotus corniculatus), kenaf (Hibiscus cannibinus), and bare plots (without plants). The four different phytorotations used from 1992 to 1995 consisted of the following: (I) bare plots; (II) Indian mustard, Indian mustard, tall fescue, tall fescue; Copyright © 2000 by Taylor & Francis (III) birdsfoot trefoil, birdsfoot trefoil/tall fescue mixture, birdsfoot trefoil/tall fescue mixture, tall fescue; and (IV) kenaf, kenaf, tall fescue, tall fescue. Table 3.1 presents the dry matter of the above-ground biomass production for the tested crops, including two annual clippings for tall fescue, birdsfoot trefoil, tall fescue, and birdsfoot trefoil mixture on an area (m 2 ) basis for each year. Kenaf produced the greatest amount of biomass among the tested species. Tissue Se concentrations were all under 1 mg Se kg -1 DM, except for Indian mustard which exceeded 2 mg Se kg -1 DM (Table 3.1). Plots from crop rotation II, which had Indian mustard for the first 2 years, had the greatest reduction of total soil Se compared to all plots after 4 years (Table 3.1). Total soil Se concentrations between 0 to 60 cm were lower in all cropped plots than the bare plots after 4 years. Overall, the cropped plots were more effective in lowering total soil Se in years 1992 and 1993 than in 1994 and 1995. The percentage changes between preplant and post-harvest soil Se concentrations (lost Se) after 4 years for each crop rotation is as follows: I – 17%, II – 60%, III – 34%, and IV – 41%. In another multiyear field study conducted near Los Baños, Bañuelos and col- leagues (1995) planted tall fescue on six 17 x 17 m plots and left six plots bare. Table 3.2 shows that, despite the low tissue Se concentrations, the cropped plots had 25% lower soil Se concentrations after 4 years from 0 to 45 cm vs. 11% in bare plots and 25% lower in cropped plots from 45 to 90 cm vs. 3% in bare plots, respectively. Tall fescue is a perennial grass with an extensive root system and a high transpiration rate. The species appears to be moderately effective at reducing soil Se concentrations near the soil surface, as well as in the subsurface profiles. Moreover, tall fescue is salt tolerant and thus a likely candidate for use on soils with relatively high levels of salinity. Although such perennial crops as tall fescue may take up less Se, their compatibility with conventional fodder crop equipment (e.g., mechanical swather and baler) make them ideal candidates as low-maintenance crops used for phytoremediation. Selenium inventory of lost Se under field conditions will be discussed later in this chapter. Water Management Water requirements are not known for crops used in phytoremediation, yet water management strategies are essential for growing Se-accumulating plants in irrigated regions of the west side of central California regions to produce the greatest amount of biomass with the minimum application of water. Efficient irrigation reduces percolation losses and the production of Se-laden effluent. Bañuelos et al. (1993, 1995) used data collected weekly by neutron probe to a depth of 1.5 m and data collected from the California Irrigation Management Information System (CIMIS) weather station (Howell et al., 1983) to estimate crop water use and schedule irrigation on crops used in phytoremediation. Responses of such crops as canola and kenaf cultivars to different regimens of irrigation are presently being evaluated in a multiyear field study conducted in central California (Tables 3.3 and 3.4). Based on the preliminary data, production of biomass increased with the amount of water applied up to reference evapotranspiration (Et r ). The greater the yields, the more Se Copyright © 2000 by Taylor & Francis TABLE 3.1 Changes in Naturally Occurring Se Concentrations from 0 to 60 cm Depth and Mean Tissue Concentrations of Se in Crops Grown in Different Rotations for Phytoremediation Total Soil Se Concentration at: Year Plant Species a Rotation # Preplant Post-Harvest Change b Shoot Se DM Yield (mg kg -1 soil) (%) (mg kg -1 DM) (g m -2 ) 1992 K° (bare plot) I 1.32(.08) c 1.27(.06) 4 NA NA Indian mustard II 1.20(.06) 0.90(.09) 25 2.15(.06) 1328 Birdsfoot trefoil III 1.18(.12) 1.06(.09) 10 0.58(.01) 435 Kenaf IV 1.41(.09) 1.29(.10) 9 0.70(.02) 3125 1993 K° (bare plot) I 1.22(.10) 1.16(.08) 5 NA NA Indian mustard II 0.85(.09) 0.69(.06) 19 1.70(.06) 1212 Birdsfoot trefoil/ III 1.09(.06) 0.92(.05) 16 0.61(.02) 721 tall fescue Kenaf IV 1.26(.13) 1.09(.10) 13 0.59(.03) 3450 1994 K° (bare plot) I 1.18(.09) 1.13(.09) 4 NA NA Tall fescue II 0.66(.07) 0.58(.07) 12 0.41(.01) 400 Birdsfoot trefoil/ III 0.86(.07) 0.77(.09) 10 0.56(.02) 902 tall fescue Tall fescue IV 1.13(.09) 1.01(.08) 11 0.52(.03) 350 1995 K° (bare plot) I 1.15(.10) 1.10(.12) 4 NA NA Tall fescue II 0.56(.06) 0.51(.08) 9 0.39(.01) 705 Birdsfoot trefoil/ tall fescue III 0.81(.07) 0.78(.07) 4 0.36(.01) 1121 Tall fescue IV 0.95(.08) 0.83(.06) 13 0.42(.01) 802 Note: NA = Not applicable. a Indian mustard and kenaf were planted and harvested and then replanted the following year. Tall fescue and birdsfoot trefoil were only planted once in their respective plots. b Percent change of total Se concentrations between preplant and post-harvest soil sampling for each respective year. c Values represent the mean from six replicates followed by the standard error in parenthesis. Copyright © 2000 by Taylor & Francis TABLE 3.2 Annual Changes in Naturally Occurring Se Concentrations from 0 to 90 cm Depth Planted to Tall Fescue or Allowed to Remain as Bare Plot a,b Total Se Concentrations Year Treatment Soil Depth Preplant Post-Harvest Change Shoot Se DM Yield (cm) (mg kg -1 soil) (%) (mg kg -1 DM) (kg m -2 ) 1992 Bare Plot 0–45 1.65(.12) 1.61(.14) 2 NA 45–90 1.59(.09) 1.65(.13) 4 Planted 0–45 1.47(.10) 1.32(.09) 10 1.02 4.4 45–90 1.63(.04) 1.49(.09) 9 1993 Bare Plot 0–45 1.71(.14) 1.63(.09) 5 NA 45–90 1.72(.12) 1.67(.13) 3 Planted 0–45 1.37(.10) 1.24(.08) 9 1.25 4.5 45–90 1.43(.11) 1.41(.09) 1 1994 Bare Plot 0–45 1.58(.13) 1.55(.12) 3 NA 45–90 1.60(.10) 1.63(.09) 2 Planted 0–45 1.31(.14) 1.20(.13) 8 2.10 5.4 45–90 1.30(.10) 1.34(.09) 3 1995 Bare Plot 0–45 1.57(.10) 1.53(.10) 3 NA 45–90 1.58(.13) 1.62(.12) 2 Planted 0–45 1.19(.08) 1.15(.09) 3 1.95 6.3 45–90 1.25(.12) 1.17(.09) 6 1996 Bare Plot 0–45 1.49(.13) 1.47(.11) 5 NA 45–90 1.49(.14) 1.55(.15) 4 Planted 0–45 1.20(.12) 1.09(.11) 9 2.41 6.9 45–90 1.34(.10) 1.23(.09) 8 Note: NA = not applicable. a Values are means from 24 samples collected each year followed by standard error in parenthesis. b Values are means from three clippings collected each year. Copyright © 2000 by Taylor & Francis that can be extracted from the soil. If a minimum amount of water will grow a successful crop, then the acceptance and use of phytoremediation by growers in water districts where water supplies are stringently regulated might be greater. Other studies have shown the effect of field irrigation practices on biomass and Se accumulation using various plant species on a two-acre field plot by Lawrence Berkeley Laboratory and University of California (Wu, 1994). Generally, water applied efficiently contributed to an increase in biomass. Wu reported that irrigation increased biomass plant tissue Se concentrations in Brassica hyssopifola Kuntze (summer weed) and in Melilotus indica (winter weed). Irrigation scheduling influ- ences growth of the rooting system. Thus, encouraging deeper root development with planned water deficits may permit some plant species to access bioavailable Se in the deeper subsoil horizons. Information is needed to evaluate the influence of soil water levels on promoting volatilization of Se by the plant or soil microbes, as well as whether sequential drying and rewetting cycles promote microbial activity (Frankenberger and Karlson, 1994). Water Reuse Se-laden drainage effluent that contains dissolved salts and other constituents must be managed to minimize its detrimental effects on the ecology of the water or land where it is discharged (van Schilfgaarde, 1990; Shennan et al., 1995). Field studies were conducted in central California by Watson and colleagues (Watson and O’Leary, 1993; Watson et al., 1994; Bañuelos et al., 1993) with Se-laden effluent used as a source of irrigation water on Atriplex (saltbush) spp. and B. juncea (Indian mustard). The Atriplex species were grown on 30 x 124 m plots, while the B. juncea was planted three successive times on 5 x 15 m plots and replicated 4 times, respectively. The agricultural effluent used as the source of irrigation water had an electrical conductivity (EC) of 19 dS m -1 and a Se concentration ranging from 150 to 200 μg l -1 . Mustard plants accumulated Se up to 3.1 mg Se kg -1 DM, whereas the Atriplex species did not exceed 0.6 mg Se kg -1 DM (Table 3.5). If water reuse is to be considered as a disposal option for Se-laden effluent, long-term feasibility of reusing Se-laden drainage water is dependent not only on crop selection (e.g., Indian mustard, saltbush), but also on well planned strategies related to managing chemical and physical changes of the soil (Shennan et al 1995; Ayars et al., 1994; Grattan, 1994). Management strategies should include: (1) maintaining a favorable salt bal- ance — the mass of salts leaving the area must be greater than or equal to that entering the area; (2) maintaining good soil physical conditions; (3) considering the mobility and retention of specific elements within the soil that can be toxic to the plant (e.g., B) or to biological consumers (e.g., Cd, Se); and (4) finding economically viable salt-tolerant crops that accumulate Se. Brassica species may be a suitable candidate to receive Se-laden effluent. However, unless plants take up Se faster than evapotranspiration, the net effect of irrigating land with Se-enriched water may increase the soil Se level (Parker and Page, 1994), unless leaching or volatilization by plants and microorganisms is occurring. Copyright © 2000 by Taylor & Francis Predators (Insects and Wildlife) Identification of insects frequenting crops and soils used in phytoremediation is important in agriculture-producing regions like central California, especially with flowering plant species, i.e., Indian mustard, birdsfoot trefoil; Tables 3.6 and 3.7. Flowering plants tend to attract greater numbers of potential predators which could be harmful or beneficial to other near-growing agricultural crops. In addition, the transfer of Se from soil to crop, from crop to insect, from insect to insect, and from insect to animal, is a biological Se cycle (bioaccumulation) that should be monitored in long-term field phytoremediation of Se-laden soils. There has been contradictory evidence as to whether biomagnification of Se exists in the food chain (Kay, 1984; Lemly, 1985). Research is needed to examine the dynamics of Se bioaccumulation in insects frequenting field sites. Factors affecting bioaccumulation depend upon the availability of soil Se, plant species, the feeding behavior of the food chain consum- ers, and mobility of insects. A herbivore may have a choice in the quality of its diet. For example, grasshoppers (Dissosteria pictipennis Brunner) may reject plants that accumulated higher tissue Se concentrations, whereas mantises (Litaneutria minor Scudder) have little choice if they rely on grasshoppers (Table 3.6; Wu et al., 1995). Unpublished data by Bañuelos and colleagues have shown that aphids (Aphididae spp.) prefer feeding upon non-Se-containing Brassica species compared to Se- containing plants. Plants that have accumulated high concentrations of Se may inadvertantly discourage the infestation by some insect species. High tissue Se concentrations by Brassica plants and subsequent bioaccumulation by insects and animals are concerns because of the deleterious effects Se may exert on birds and mammals that eat the insects. Ohlendorf and Santolo (1994) have illustrated in great detail exposure pathways and projected Se concentrations in biota at Kesterson Reservoir. Strategies that are used in fruit production (e.g., metal reflectors and noise guns) may be useful in frightening off certain animals from field-grown Brassica planted for phytoremediation. In field experiments, Bañuelos and colleagues (1997; TABLE 3.3 Parameters Used for Approximating Water Application Rate for Kenaf with Subsurface Irrigation Under Field Conditions Treatment Total Applied Water a Net Soil Water Depletion Calculated Crop Et c Potential Et r Actual (% Et c ) (mm) (mm) (mm) (mm) Et c /Et r 25 95 125 220 418 0.23 50 190 141 331 418 0.45 100 379 175 554 418 0.91 125 473 49 522 418 1.13 150 593 78 671 418 1.47 a Effective precipitation was 0 mm during crop year and assumes no deep percolation losses. Copyright © 2000 by Taylor & Francis TABLE 3.4 Biomass of Canola and Cultivars of Kenaf Exposed to Different Water Application Rates Given in Table 3.3 with Subsurface Irrigation Under Field Conditions a Treatment % Et c 7-N C-531 Kenaf cultivars: C-533 EU-41 TA-2 Canola Leaves Stem Leaves Stem Leaves Stem Leaves Stem Leaves Stem Leaves Stem (Mg ha -1 ) (Mg ha -1 ) 25 9.4 12.7 11.4 17.4 10.1 14.8 8.4 13.0 10.5 17.7 0.86 3.9 50 10.7 13.2 12.0 24.0 10.9 22.3 10.9 23.9 17.9 21.6 1.83 5.3 100 12.9 23.5 15.5 36.6 16.2 28.9 12.9 26.6 13.9 28.3 2.36 8.3 125 12.2 2.25 15.6 30.1 15.2 26.7 11.3 21.3 12.3 26.5 4.33 7.5 150 13.7 26.2 16.0 28.8 12.2 27.6 11.2 25.4 19.2 28.2 3.10 9.3 a Based on a plant population of 160,000 plants ha -1 . Copyright © 2000 by Taylor & Francis TABLE 3.5 Shoot Tissue Concentrations of Se and Other Selected Elements in Brassica juncea and Atriplex Species Irrigated with Se-Laden Saline Effluent Tissue Concentrations of Plant Species Se B Fe Mn Zn Cu S (mg kg -1 DM) Brassica juncea a 3.1(.10) 275(.10) 250(.04) 177(.08) 55(.03) 2(.01) 20400(.11) Atriplex canescens b 0.5(00) 126(.07) 411(.09) 60(.02) 36(.04) 6(.01) 10400(.12) A. undulata 0.6(00) 131(.05) 348(.09) 68(.01) 37(.02) 7(.01) 7500(.10) A. deserticola 0.6(00) 121(.03) 388(.07) 53(.02) 35(.03) 6(.01) 10900(.09) A. nummularia 0.6(00) 142(.04) 391(.05) 44(.01) 30(.01) 5(.01) 9260(1.1) A. polycarpa 0.6(00) 135(.03) 401(.08) 70(.02) 39(.02) 6(.01) 9960(.07) a Values for B. juncea are the means from three plantings followed by the coefficients of variation. b Values from the Atriplex species are the means from three harvests followed by the coefficients of variation. (From Watson et al., J. Environ. Qual. 48: 157-162, 1994.) Copyright © 2000 by Taylor & Francis [...]... Pub No 43: 14 5-1 56, 1995 Doran, J.W Microorganisms and the biological cycling of selenium Adv Microbial Ecol 6: 1 -3 1, 1982 Frankenberger Jr., W.T and U Karlson Environmental factors affecting microbial production of dimethylselenide in a selenium -contaminated sediment Soil Sci Soc Am J 53: 1 43 5-1 442, 1990 Frankenberger Jr., W.T and U Karlson Microbial volatilization of selenium from soils and sediments,... species J Environ Qual 21: 34 1 -3 44, 1992 Terry, N and A.M Zayed Selenium volatilization by plants, in Selenium in the Environment W.T Frankenberger, Jr and S Benson, Eds., Marcel Dekker, New York, 34 3- 3 69, 1994 Terry, N and A.M Zayed Phytoremediation of selenium, in Environmental Chemistry of Selenium W.T Frankenberger, Jr and R.A Engberg, Eds., Marcel Dekker, New York, 63 3- 6 56, 1998 UC Salinity/Drainage... Evaluation of different plant species used for phytoremediation of high soil selenium J Environ Qual 26: 63 9-6 46, 1997 Bañuelos, G.S., B Mackey, L Wu, S Zambrzuski, and S Akohoue Bioextraction of soil boron by tall fescue Ecotoxicol Environ Safety 31 : 11 0-1 16, 1995 Bañuelos, G.S., R Mead, and G Hoffman Mineral composition of wild mustard grown under adverse saline conditions Agri Ecosys Environ 43: 11 9-1 26,... 11 9-1 26, 19 93 Bañuelos, G.S and D.W Meek Accumulation of selenium in plants grown on seleniumtreated soil J Environ Qual 19: 77 2-7 77, 1990 Biggar, J.W and G.R Jayaweera Measurement of selenium volatilization in the field Soil Sci 155: 3 1 -3 5, 19 93 Blaylock, M.J., D.E Salt, S Dushenkov, O Zakharova, C Gussman, Y Kopulnik, B.D Ensley, and I Raskin Enhanced accumulation of Pb in Indian mustard by soil- applied...TABLE 3. 6 Tissue Selenium Concentrations Found in Grasshoppers and Mantis from Different Sites at Kesterson Reservoir Soil Se Site # Total (mg kg -1 soil) 1 2 3 4 0.6 ± 03c 53. 7 ± 17.5 0.1 ± 09 4.2 ± 2 .3 Range of Se in Extractable (mg l-1) 0.05 0.72 0.02 0.16 ± ± ± ± 02 63 01 04 Mantis b Grasshopper a -1 insect) (mg kg 1.2–9.8 9.1–27.5 3. 1–7.0 1.0–4.6 9–22 31 –52 10.2–18.0 5.5–10 .3 a Dissosteria... New York, 12 9-1 42, 1998 Parker, D.R and A.L Page Vegetation management strategies for remediation of selenium contaminated soils, in Selenium in the Environment W.T Frankenberger, Jr and S Benson, Eds., Marcel Dekker, New York, 32 7 -3 42, 1994 Parker, D.R., A.L Page, and D.N Thomas Salinity and boron tolerances of candidate plants for the removal of selenium from soils J Environ Qual 20: 15 7-1 64, 1991... 48(2) 30 (3) 46 (3) 22(1) 37 (2) 36 (2) a Fe Al (mg kg-1 DM) 35 4(12) 1268(52)b 162(12) 7 73( 39) 84(6) 497(12) 97(4) 477(16) 420(15) 133 5(70)b 177( 13) 1045(50)b 77(4) 941(44) 80 (3) 980(57)b Cu Mo B 11(.4) 6(.2) 5(.2) 4(.2) 1(.1) 4(.2) 6(.1) 5(.1) 1(.1) 1(.1) 4(.1) 3( .1) . 12.0 24.0 10.9 22 .3 10.9 23. 9 17.9 21.6 1. 83 5 .3 100 12.9 23. 5 15.5 36 .6 16.2 28.9 12.9 26.6 13. 9 28 .3 2 .36 8 .3 125 12.2 2.25 15.6 30 .1 15.2 26.7 11 .3 21 .3 12 .3 26.5 4 .33 7.5 150 13. 7 26.2 16.0 28.8. 1.58(. 13) 1.55(.12) 3 NA 45–90 1.60(.10) 1. 63( .09) 2 Planted 0–45 1 .31 (.14) 1.20(. 13) 8 2.10 5.4 45–90 1 .30 (.10) 1 .34 (.09) 3 1995 Bare Plot 0–45 1.57(.10) 1. 53( .10) 3 NA 45–90 1.58(. 13) 1.62(.12). cultivars: C- 533 EU-41 TA-2 Canola Leaves Stem Leaves Stem Leaves Stem Leaves Stem Leaves Stem Leaves Stem (Mg ha -1 ) (Mg ha -1 ) 25 9.4 12.7 11.4 17.4 10.1 14.8 8.4 13. 0 10.5 17.7 0.86 3. 9 50 10.7 13. 2