REGULAR ARTICLE

The effects of a permanently elevated water table in an acidsulphate soil on reed canary grass for combustion

Kenedy E. Epie & Seija Virtanen & Arja Santanen &

Asko Simojoki & Frederick L. Stoddard

Received: 6 June 2013 /Accepted: 27 September 2013 /Published online: 28 October 2013# Springer Science+Business Media Dordrecht 2013

AbstractAims and background Acid sulphate (AS) soils requirecareful management to prevent the environmental haz-ards that result from the oxidation of sulphide-bearingdeep soil layers and the consequent acidification of soiland waters. Management with a high water table pre-cludes many food crops, so their suitability for peren-nial energy cropping was investigated in a 3-year studyusing reed canary grass (Phalaris arundinacea L.,RCG).Methods Monolithic lysimeters made of undisturbedAS soil and equipped with ground-water level controland measurement instruments were planted with 1-year-old RCG turfs taken from a non-AS field. Twowater tables were imposed, high (HWT, 20 cm belowsoil surface) and low (LWT, 70 cm below soil surface,considered normal for agriculturally managed ASsoils) for a 3 year period. Growth and physiologicalcharacters of RCG were determined and its ash contentand the elemental composition of its dry biomass (Ca,Cl, K, Mg, and S) were analysed.

Results The level of the water table had significanteffects on crop growth and quality. Shoots were 25 to29 % taller, consequently yielding more dry matter inHWT than in LWT lysimeters. Concentrations of K,Mg and S that can affect the combustion process werehigher in biomass harvested from LWT lysimeters thanfrom the HWT plants. At the end of the experiment, thespatial distribution of roots within the soil profile dif-fered between treatments. Roots penetrated to the bot-tom of LWT lysimeters with total root dry mass nearlytwice that in HWT.Conclusions RCG intended for burning grows andperforms well in acid sulphate soils managed with araised water table. This management option minimizesthe risk of acid flows from oxidized soils, and allowsfarmers to harvest a non-food crop from soils thatwould have to be drained to provide a food or feedcrop.

Keywords Phalaris . Acid sulphate soil .Watertable . Biomass . Ash content . Element composition

Introduction

Bioenergy cropping presents a number of questionsabout its ecological implications. Concerns remainabout the choice of feedstock, the land where it isgrown, and the use of cropland for energy productionparticularly when world food production needs to beincreased. About 3.2 % of the total arable land in theEU-27, corresponding to about 5.5 million ha of

Plant Soil (2014) 375:149–158DOI 10.1007/s11104-013-1925-4

Responsible Editor: Juan Barcelo.

K. E. Epie (*) :A. Santanen : F. L. StoddardDepartment of Agricultural Sciences, University of Helsinki,P.O. Box 27, FI-00014 Helsinki, Finlande-mail: epie.kenedy@helsinki.fi

S. Virtanen :A. SimojokiDepartment of Food and Environmental Sciences,University of Helsinki,P.O. Box 27, FI-00014 Helsinki, Finland

agricultural land, is used to grow biomass for energy(Dworak et al. 2008), although 20 million ha of poten-tial land for bioenergy exists (EEA 2006). In Finland, itwas predicted that up to 500,000 ha of arable landcould be dedicated to energy crops by 2012 (Vainio-Mattila et al. 2005), but not even one-tenth of thisfigure was achieved (TIKE 2012). Other land, consid-ered unsuitable for food or feed cropping, offers asolution to the energy/food crop dilemma. Acid sul-phate (AS) soils are one such case. These soils can beclassified as marginal land for agricultural use becausedraining them for cultivation causes oxidation ofsulfidic material and consequently an acid load in thesub soil which may cause hazardous off-site environ-mental effects (Dent and Pons 1995; Sullivan 2012).Furthermore, potentially toxic metal concentrations infood crops cultivated on AS soils have given rise toconcern (Fältmarsch 2010). Alternative managementsystems are thus required and growing non-food cropssuch as perennial bioenergy crops may be appropriate.

It is estimated that 17 million ha of actual andpotential AS soils exist worldwide (Andriesse andvan Mensvoort 2002). The Baltic basin contains mostof Europe’s AS soils, with 130,000 ha in agriculturaluse in Finland according to soil taxonomy criteria(Yli-Halla et al. 1999). Besides the formation of severeacidity and toxic aluminium concentrations in soils,reclamation of AS soil, especially by improved drain-age, also provides very productive fields when theacidity is neutralized by either liming or ploughing intothe under-lying carbonate-rich horizon (Elisa et al.2012). Without liming, plant growth is restricted dueto either low pH (Moore et al. 1990) or sulphide injuryof roots (Mathew et al. 2001). Unfortunately, limingfor agricultural purposes does not mitigate the environ-mental hazards of AS soils (Åström et al. 2007). Forexample in Finland, acidic leachates from cultivatedAS soils have decreased water quality downstream(Åström et al. 2005) and either impaired fish reproduc-tion or killed aquatic organisms (Hudd and Leskelä1998; Hudd and Kjellman 2002). AS soils may haveother ecological impacts, such as serving as a signifi-cant source of greenhouse gases (GHG) (Simek et al.2011). Although many different management optionshave been proposed for these soils, including controlleddrainage, liming, adding N and P fertilizer, and strawamendment, the most effective tool is maintenance of ahigh water table, which keeps the sulphidic materialsubmerged and prevents its oxidation to sulphuric acid,

and may reduce the oxidized and acidified soil horizons(Ward et al. 2004). Virtanen et al. (2013) reported that ahigh water table caused reduced conditions in AS soillysimeters. The cultivation of a water-tolerant energycrop could be an option to maintain a high water tableand temporarily allow water-logged conditions in theseareas.

Reed canary grass (RCG; Phalaris arundinacea L.),a perennial cool-climate C3 grass, was chosen for thisstudy because its cultivation requires few inputs. Sinceone round of land preparation and sowing leads tomany more harvests than is the case with annual crops,perennials are associated with low GHG emissions(Sanderson et al. 2006; Adler et al. 2007) and theirnet energy production (output–input) can be greater(Mikkola and Ahokas 2009).

This grass, already used as a bioenergy crop inFinland and Northern Europe (Lewandowski et al.2003) where it is native, tolerates both drought andwaterlogging conditions, and thrives in areas of peri-odic fluctuations in water levels (Galatowitsch et al.1999). It is a non-food crop, and under Finnish condi-tions, where its production area has stabilised around20,000 ha since 2007 (TIKE 2012), its dry biomass hasgood combustion quality (Pahkala and Pihala 2000)and energy content of 4.5 MWh t−1 (Komulainen et al.2008). Its use for production of bioethanol and biogashas been studied as well (Kallioinen et al. 2012). Lownutrient and ash contents in dry biomass improve thecombustion properties of RCG, reduce the corrosion ofcombustion vessels in Combined Heat and Power(CHP) systems (Jenkins et al. 1998), and reduce emis-sions of toxic gases and dioxin (Clarke and Preto 2011).

There is little comparable data on the potential ofcool-climate energy grasses in general or RCG in par-ticular to tolerate AS soils with a high content of freemetal ions or managed with a high water table. Somewarm-climate C4 energy grasses are, however, consid-ered acid-tolerant (Krizek et al. 2003).

Converting cropland to bioenergy cropping may in-crease C sequestration in the soil and contribute toreducing atmospheric CO2, especially when it displacesannual crop production or a lower yielding system.While root biomass is a critical component of total soilorganic carbon, its measurement in field conditions isdifficult and often neglected, and its contributions havenot been extensively quantified (Gale and Cambardella2000). Therefore, this study was aimed at determiningwhether high water table AS soils could 1) enhance the

150 Plant Soil (2014) 375:149–158

growth, development and biomass yield of RCG, 2)improve its combustion qualities, and 3) support morecarbon sequestration in the root zone of the soil.

Materials and methods

Experimental design

Lysimeters comprised of PVC tubes (height 1.0 m,diameter 0.5 m, sealed from the bottom) were filledwith AS soil monoliths excavated from the ViikkiExperimental Farm of the University of Helsinki insouthern Finland (60°13′ N, 25°0′ E) (Virtanen et al.2010). The soil was a Sulfic Cryaquept (Yli-Halla et al.2008) with an acid sulphate soil in the B horizon and atransition horizon (BC) located at the depth of thesubsurface drainage pipes, underlain by a constantlywater-logged and reduced C horizon (potential acidsulphate soil) (Virtanen et al. 2010). The 3-year exper-iment was set up in a glass-roofed shelter with open,wire-netted “walls” on three sides that provided pro-tection from precipitation, including snowfall, andmarginal protection from radiation frosts, but had fewother effects on the aerial environment. The lysimeters,equipped with ground water level control and othermeasurement instruments, were insulated to ensurethat soil temperatures differed little from those in thefield during winter, but were 2–3 °C higher in summer(Virtanen et al. 2013).

In May 2008, eight large turf pieces of 1-year-oldRCG, 15 cm thick were excavated from the ploughlayer of fine sandy soil elsewhere on the Viikki Exper-imental Farm, trimmed to 50 cm diameter, transplantedonto the top 20 cm of the lysimeters, and wateredaccording to the long-term average precipitation. Thenumber of crowns in each lysimeter was counted,lysimeters with nearly identical crown numbers werepaired, and one member of each pair was assigned toeach of the two treatments, in order to give a structurewith four blocks to the experiment. Each year at theend of May or the beginning of June (calendar week21–22), the lysimeters were fertilised with recom-mended amounts of nutrients (N 90, P 5 and K40 kg ha−1) and 1 week later, two treatments wereimplemented: high water table (HWT, 20 cm belowsoil surface) and low water table (LWT, 70 cm belowsoil surface and considered normal for AS soil inagricultural use). During winter, however, the water

table was allowed to rise to the bottom of the topsoilin LWT as well, and only after the harvest in spring itwas adjusted back to the depth of 70 cm. This winterpractice was designed to mimic variations in the watertable in natural field conditions. There was a total of 8lysimeters, each treatment replicated four times in arandomised complete block design but one of the LWTlysimeters was left out of statistical analyses as anoutlier due to technical problems in controlling thewater level.

Growth and development measurements

At the start in year 1, the mean number of tillers wasequal in both treatments. Flowering tillers, along withintact and shattering panicles were counted in eachlysimeter 8 weeks after water levels were adjustedand the percentage of shattered panicles was calculat-ed. At 12–16 weeks after water levels were adjusted,plant height (cm) was measured. The rate of net pho-tosynthesis and other gas exchange characteristicswere measured in each of the 3 years of the experimentfrom the youngest fully expanded leaf, starting 4 weeksafter treatment was implemented and then at 4-weekintervals, except when technical difficulties preventedmeasurement. These measurements were taken using aportable LI 6400 photosynthesis system according tothe manufacturer’s instructions (LI-COR Inc. USA)between 10.00 and 14.00 h on sunny days. This equip-ment used a LED light source (6400-02B, 90 % red and10 % blue) giving 2,000 μmol m−2 s−1 of light intensityand a CO2-injection cartridge attached to control ref-erence CO2 concentration at 400 μmol mol−1 at a flowrate of 400 μmol s−1. Water use efficiency was calcu-lated according to Paez and Gonzalez (1995) as theratio of the rate of photosynthesis to transpiration rate.

Biomass harvesting and element composition

Above-ground biomass was harvested the followingspring in April of every year, after each growing sea-son, according to normal management procedures forthis crop. The number of tillers was counted and theywere dried in an oven at 65 to 70 °C for 72 h, weighed,crushed and milled in a Retsch Rotor Beater 120(Retsch GmbH, Germany) to pass a 0.25 mm sieve.The mill and sieve were cleaned before milling andbetween samples of different lysimeters using 15 %ethanol. The milled samples were stored in small

Plant Soil (2014) 375:149–158 151

plastic bags and subsamples of 200 mg were acid-digested in a microwave oven (Mars Express, CEM,USA) according to EPA 3052 (9 ml 70 % HNO3 and1 ml 30 % H2O2, power 1,600 W, temperature 175 °C).Ca, K, Mg, and S contents were determined using ICP-OES (Thermo Scientific, ICAP 6000). The quality ofthe ICP analysis was controlled every 20 samples withknown samples. Total carbon (C) and nitrogen (N)contents of the dried plant samples were determinedby the Dumas combustion method in a Vario Max CNAnalyser (Elementar Analysensysteme GmbH, Ger-many). Extracts for chloride analysis were made bymixing about 500 mg of dry sample with 10 ml ofwater and shaking for 3 h in a water bath at 60 °C, thentesting the extract in a Chloride analyzer Model 926(Sherwood Scientific Ltd., Cambridge, England). Ashcontent was determined by burning samples in a mufflefurnace at 575 °C for 12 h.

Three years after the start of the experiment, dupli-cate 1 dm−3 soil cores were taken from each of the fivesoil horizons of every lysimeter in the course of dis-mantling of the monoliths. Soil was then washed offthe roots with a root washing device (Gillison 714,Gillison’s Variety Fabrics, USA) and after organicdebris was manually removed, the root masses weredried at 60 to 70 °C for 48 h to obtain dry mattercontent. Total C content of the roots were determinedusing Vario Max CN Analyser and total C sequesteredin the soil profile was determined.

Statistics

Data collected were subjected to t-tests and repeatedmeasures analysis of variance using SPSS 15 (SPSSInc., Chicago, USA). Unless otherwise mentioned,means were considered to be statistically significantwhen at P<0.05. After the establishment of the exper-iment, the “blocks” term was not significant.

Results

The two water table treatments affected growth, bio-mass quantity and quality of RCG, clearly in years 2and 3, but not in year 1 when the treatments wereimposed late in the growing season, at the end of July.Eight weeks after water levels were adjusted, tillersgrew 29 % taller in the HWT lysimeters than in LWTlysimeters in year 2 and 25 % taller in year 3 (Table 1).

Panicle shattering was significantly greater in LWTthan HWT in both years 2 and 3 (P<0.05).

In years 2 and 3, net photosynthesis in the twotreatments progressively diverged through the growingseason (Fig. 1), and was significantly higher in theLWT treatment than in the HWT (Table 4). Transpira-tion rate was higher in the HWT treatment than in theLWT treatment (Fig. 1) and significantly so only inyear 2 (Table 4), and conversely water use efficiencywas significantly higher in LWT in all 3 years, shortlyafter the water level difference was implemented(Fig. 1).

Dry matter yields following year 1 were almost thesame in both treatments (Table 2), but in years 2 and 3,HWT grasses yielded 37 % and 36 % more than LWT(P≤0.01 in both years), respectively. Ash, K, Cl and Scontents of dry biomass in the LWT treatment weresignificantly higher than in the HWT treatment, con-versely the concentration of Ca was lower in the3 years. The C:N ratio was more than 70 % higher inHWT than in LWT biomass in years 2 and 3.

The spatial distribution of roots within the soil pro-file differed between treatments. In LWT, the rootspenetrated through the whole soil monolith down tothe bottom of the lysimeter at 90 cm, whereas in HWT,the roots were concentrated in the uppermost horizonsand no roots were virtually found deeper than 50 cm(Table 3). The total dry mass of roots in LWT wasnearly twice that in HWT, as was the amount of Cpotentially sequestered in the soil profiles.

Discussion

Growth, yield and quality of RCG were affected bywater table level in AS soils. The high water tableprovided more favourable growth conditions for RCGthan the low water table, producing both higher yieldand better combustion quality. Water saturated soilhorizons in these HWT lysimeters had higher pH dueto reduced conditions (Virtanen et al. 2013), while theLWT lysimeters contained oxidized AS soils with verylow pH (Simojoki et al. 2012), and a lower degree ofsoil water saturation (Virtanen et al. 2013) especiallyduring summer. In previous studies, low soil moisturedecreased leaf number, plant height and dry matterproduction in RCG (Epie 2010), and suppressed tiller-ing in other grasses (Butler and Briske 1988). RCG isconsidered to acclimate well to wide extremes of soil

152 Plant Soil (2014) 375:149–158

moisture and nutrients (Kercher and Zedler 2004), andthe combination of tall leafy shoots and fast growthrate makes it highly productive (Wetzel and van derValk 1998). The low rate of shattering in the HWTtreatment may be attributed to the effect of the highwater content on delaying ripening, as the associationbetween late ripening and lower seed shattering inRCG has been noted before (Sahramaa and Jauhiainen2003). Growing RCG in AS soils managed with raisedwater table could be a good option for seed productionas the late ripening and low panicle shattering willreduce seed loss (Table 4).

In this study, net photosynthesis was not decreasedin the drier LWT treatment, in contrast to previousfindings on drought-stressed RCG (Bota et al. 2004;Shurpali et al. 2009; Zhou 2011). One of the reasonscould have been the higher concentration of Mg, acomponent of chlorophyll and a contributor in photo-synthesis. Reducing soil conditions, such as those inthe HWT lysimeters, may decrease photosynthesis andstomatal conductance (Pezeshki 2001) in species-specific ways (Pezeshki et al. 1996). Some flood-tolerant plants show an initial reduction in photosyn-thesis when flooded (Kozlowski 1997) and this hasbeen attributed to stomatal closure and metabolic inhi-bition (Pezeshki 1993). Water use efficiency washigher in LWT plants than HWT, largely due to highertranspiration rates in the HWT treatment that led togreater nutrient uptake and biomass production. In

practical terms, this result shows that AS soils can bemanaged with high water content to produce RCG.

Although the LWT treatment reduced overall plantbiomass production, in line with expectations (Qaderiet al. 2006), yields in both treatments far exceeded the6–8 t ha−1 reported by Pahkala et al. (2008) for theselatitudes. This is an indication that conditions in thelysimeters were conducive to good growth, in spite ofthe soil conditions earlier mentioned. While manage-ment factors such as the use of small plots, protectionfrom snow and rain damage, marginal protectionagainst frosts in autumn and spring and against highlevels of solar irradiation in summer, along with man-ual harvest at 5 cm above ground all contributed tothese differences, the 33–40 % yield margin of HWTover LWT is indicative of the yield benefit to be ob-tained when water for transpiration is always available.If the water table cannot be maintained at a consistentlyhigh level, its fluctuations may cause some minor yieldlosses. High yields achieved suggest that RCG is not asinhibited by low pH as some other species (Gilker et al.2002). The significantly higher biomass from HWTlysimeters was due to increases in both tiller numberand height in comparison with LWT lysimeters. Higherbiomass yield means higher energy yields. At yieldlevels of 5 t ha−1 of DM, RCG with energy content of4.5 MWh t−1, produces about 450 GWh yr−1 from20,000 ha in Finland (Komulainen et al. 2008). In thisstudy, yields ranged from 10 to 20 t ha−1, meaning

Table 1 Tiller and flower char-acteristics of reed canary grassgrown in acid sulphate soils ex-posed to high (HWT) or low(LWT) water tables in years 2and 3

ns (not significant) P>0.05, SEDis standard error of the difference

*,** P<0.05, 0.01, respectively

Year/Treatment Total tillers/lysimeter

Flowering tillers(%)

Shatteringpanicles (%)

Tiller height(cm)

2

HWT 227 13 39 131

LWT 222 18 75 102

SED 7 3 11 5

3

HWT 217 16 71 123

LWT 188 12 91 98

SED 15 3 8 5

P-value

Treatment ns ns * **

Year * ns ** *

Treatment ×year

ns ns ns ns

Plant Soil (2014) 375:149–158 153

more than double energy production with significantlyhigher values from HWT biomass can be predicted.Although comparable yields of 11–19 t ha−1 yr−1 werereported by Mediavilla et al. (1995) in Switzerland, thepotential to use HWT for RCG production on AS soilsremains to be tested in field conditions.

The main elements in this study contributing to ashmelting behaviour, deposition and corrosion were Ca,K, Cl and S. Excluding Ca, low content of these ele-ments is preferred in biomass intended for combustionin combined heat and power (CHP) plants (Monti et al.2004), and the HWT treatment was superior to theLWT in respect to all of these elements, so it had bettercombustion qualities. The K contents in LWT were

higher than in field-grown RCG (Pahkala and Pihala2000). Higher K concentration decreases ash meltingpoint, causing deposit formation on the furnaces andboilers of power systems (Obernberger and Thek2004). Generally, the ash content in RCG is slightlyhigher than in woody materials also used for burning(Pastorek et al. 2004) and in this study, it is higher thanthat reported in the literature. Radiotis et al. (1999), forexample, reported ash content of 6.3 % for RCG. Thehigh ash content could have been as a result of the highcontents of soil K, Cl and S and largely by the fact thatthe experiment was under a glass roof so was notwashed by precipitation and snow. Values of Cl and Swere higher than the 1.46 and 7.6 g kg−1 DM

Fig. 1 Net photosynthesis, transpiration and water use efficiency of reed canary grass grown in acid sulphate soils with low (LWT, •continuous lines) and high (HWT, □ dotted lines) water tables through three growing seasons. Error bars show standard errors of means

154 Plant Soil (2014) 375:149–158

respectively reported for this grass by Tahir et al.(2011). High ash contents in biomass lowers theheating value, creates disposal problem, increases op-erating cost of boilers (Campbell 2007) and dust emis-sions can be hazardous to health and buildings.

The high C:N ratios in this study show that the mate-rial was largely lignocellulose, a factor that confers bothhigh calorific value in combustion systems (Crutzen and

Andreae 1990; Obernberger and Thek 2004) such asthose where RCG is generally used in Finland, mixedwith peat and/or wood fuel (Vapo 2007). The high Ncontent in the LWT biomass came from the large mineralN reserves in the deep horizons of AS soils (Simek et al.2011) that were reached by the roots, and this mayincrease emissions of GHGs such as nitrous oxide duringburning process (IPCC 1997). Therefore, growing RCG

Table 2 Biomass yield, ash and element composition of reed canary grass grown in acid sulphate soil in lysimeters with low (LWT) andhigh (HWT) water tables

Year/Treatment Biomass yield (t ha−1) Ash (%) Ca (g kg−1) K (g kg−1) Mg (g kg−1) S (g kg−1) Cl (g kg−1) C:N

1

HWT 11.3 9.8 5.36 8.11 2.10 1.93 10.14 105

LWT 11.9 10.7 4.64 9.77 2.12 1.85 11.32 101

SED 0.7 0.2 0.48 0.49 0.15 0.13 0.82 13

2

HWT 20.1 6.1 3.53 7.48 1.31 1.86 6.45 162

LWT 14.7 8.5 2.86 13.24 1.50 2.48 10.39 93

SED 1.1 1.0 0.17 1.86 0.08 0.19 1.27 10

3

HWT 16.0 7.2 3.65 7.56 1.63 2.13 6.47 142

LWT 11.8 9.1 3.29 13.14 2.00 2.73 9.68 83

SED 0.9 0.5 0.37 0.76 0.16 0.19 0.84 10

P-value

Treatment ** * ** ** ns * ** **

Year *** *** *** ns *** ** * *

Treatment × year *** ns ns ns ns ** ns **

*,**,*** P<0.05, 0.01, 0.001, respectively. ns (not significant) P>0.05, SED is standard error of the difference

Table 3 Root dry matter (DM)and carbon data of reed canarygrass in different acid sulphatesoil horizons exposed to high(HWT) and low (LWT) watertable

Values are means and SEM isstandard error of mean

Treatment Soil depth (cm) Root DM(t/ha)

Root carbonconcentration (g g−1)

Total root carbon(t/ha)

HWT 10 2.74 0.44 1.21

30 1.35 0.43 0.58

50 0.33 0.42 0.14

70 0.01 0.31 0.00

90 0.06 0.43 0.02

Total 4.49 1.97

LWT 10 2.66 0.44 1.18

30 1.66 0.40 0.66

50 1.56 0.38 0.59

70 1.85 0.41 0.77

90 0.67 0.37 0.25

Total 8.41 3.44

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in AS soils with a high water table can reduce emissionsby lowering the N content of the harvested material.

In this study, the RCG root biomass in the LWTtreatment was almost the same as the 8.6 t ha−1 report-ed in cool-climate grasses by Lemus and Lal (2005)and below the 10.6–19.1 t ha−1 reported by Bolinderet al. (2002) within a depth of 0–45 cm, probably as aresult of differences in soil conditions, grass speciesand plantation age. In the HWT treatment, the total rootmass was about 4.5 t ha−1, or about 25 % of the above-ground dry matter, representing about 1.97 t ha−1 ofcarbon at the end of the growing season. Within a shortgrowing season, RCG can accumulate large amountsof atmospheric carbon in biomass (Shurpali et al.2008). Estimates for the C sequestration potential ofplants range from 0.3 to 0.8 t ha−1 yr−1 (Smith 2004),but sometimes estimates are well out of this range, as inthis study. If carbon is to be sequestered in the soil, asignificant quantity of root material needs to penetratethe saturated horizons, as was found in both the LWTtreatment and, to a lesser extent, in the HWT treatment.

Reed canary grass, an established bioenergy crop,grows well in acid sulphate soils and can performbetter when the water table is raised to reduce acidityand avoid environmental hazards. This species cansequester carbon in a saturated zone regardless of itsdepth. RCG grown in AS soil with a high water tablegrew taller and produced more biomass with betterquality for use in energy production than that grownin drained, oxidized soil. This could serve as manage-ment option and a solution to the environmental prob-lems cause by drainage of AS soils and at the sametime help to reduce the tension between food andbioenergy crop production on arable land. Like manyother energy crops, RCG has characteristics that makeit a highly invasive weed where it is not native. Outsidenorthern Europe, the principles expounded in this

paper would be better applied to comparable nativespecies rather than by importing RCG. The combina-tion of higher yields with higher combustion quality isparticularly appealing when the gross margins of RCGproduction are currently so poor and expansion of thecrop has halted.

Acknowledgments This work was supported by the Academyof Finland grant 1124435, ‘Carbon-sequestering species mix-tures for sustainable energy cropping’, and the Graduate Schoolfor Agricultural Production Sciences of the University of Hel-sinki. J. Fustec of ESAAngers, France and B. Deen of Universityof Guelph, Canada are greatly thanked for some useful sugges-tions. The authors extend appreciations to A. Lammi and M.Tykkyläinen for laboratory analyses and assistance.

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