Directory UMM :Data Elmu:jurnal:I:Industrial Crops and Products:Vol11.Issue2-3.Mar2000:

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Different plant parts as raw material for fuel and pulp

production

K. Pahkala *, M. Pihala

Agricultural Research Centre of Finland,FIN-31600Jokioinen,Finland

Accepted 8 October 1999

Abstract

Reed canary grass (Phalaris arundinacea L.), meadow fescue (Festuca pratensis Hudson), tall fescue (Festuca arundinaceaSchreber) and goat’s rue (Galega orientalisL.) were harvested at seed ripening stage and in the following spring when the plants were totally dry. The amounts of different plant parts (grasses: stem, leaf sheaths, leaf blades and panicles; goat’s rue: stem, leaf blades and pods) were measured and the composition of ash, silica (SiO2), iron

(Fe), manganese (Mn), copper (Cu) and potassium (K) was analysed for each plant fraction. Plant species, plant part and harvesting time affected the mineral composition; grasses contained more SiO2and K, but less Cu than goat’s

rue. The mineral concentrations were highest in leaf blades. In each species, stem fractions had the lowest ash, SiO2,

K, Fe, and Mn contents. The proportion of stem was highest in reed canary grass and goat’s rue when harvested in spring. The K concentration was clearly lower in plants harvested in spring than at seed ripening stage in autumn. However, the concentrations of SiO2, Fe, Cu and Mn were highest at spring harvesting. Spring harvest of reed canary

grass yielded clearly higher fibre contents for each plant fraction than harvesting in autumn. Of the species studied, reed canary grass suits best for raw material, if the leaf blades are removed and harvesting is done in spring at senescence stage of plants. © 2000 Elsevier Science B.V. All rights reserved.

Keywords:Grass species; Goat’s rue; Plant fractions; Mineral composition; Fibre

www.elsevier.com/locate/indcrop

1. Introduction

Non-wood plant species have been found to be potential sources for fibre production (Nieschlag et al., 1960; Nelson et al., 1966; van Dam and Shannon, 1994) and raw material for energy pro-duction (Burvall, 1993). In northern Europe,

espe-cially reed canary grass (Phalaris arundinacea L.) has aroused interest as an energy crop (Burvall, 1993; Leinonen et al., 1998) and in recent years as raw material for paper (Berggren, 1989; Paavi-lainen and Torgilsson, 1994). Also other grasses,

such as tall fescue (Festuca arundinacea Schr.)

(Janson et al., 1994), and cereal straw (Atchison, 1988; Lo¨nnberg et al., 1996) can be used for paper production. In central Europe, elephant grass (Miscanthus sinensisAnderss.) has been studied as a raw material for paper and energy (Walsh, 1998).

* Corresponding author. Tel.:+358-3-41881; fax: + 358-3-41882437.

E-mail address:katri.pahkala@mtt.fi (K. Pahkala)

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When herbaceous species are pulped for paper-making or used for bioenergy, most frequently, the whole plant with all plant parts is used as raw material. Except for fibrous material from cell walls, this biomass contains inorganic elements, which are essential or useful for plant growth and development. However, these mineral substances have a negative effect on the pulping and combus-tion processes, so their quantities should be as low as possible (Keitaanniemi and Virkola, 1982; Il-vessalo-Pfa¨ffli, 1995; Obernberger et al., 1997). Silicon (Si), potassium, manganese, copper and iron are harmful for the pulping process (Keitaan-niemi and Virkola, 1982) and undesirable in fuel use (Obernberger et al., 1997). In papermaking, silicon wears out the installations of a factory (Watson and Gartside, 1976), lowers the paper quality (Jeyasingam, 1988) and complicates the recovery of chemicals and energy (Ranua, 1977; Keitaanniemi and Virkola, 1982; Ulmgren et al., 1990). In combustion, high alkali metal concen-trations decrease the melting point of ash and cause deposits and damage in boilers (Burvall, 1993; Obernberger et al., 1997).

The concentration of each particular mineral substance varies depending on the plant species and the plant part (Rexen and Munck, 1984; Petersen, 1988; Theander, 1991). The plant age or stage of development when harvested and the concentration of other minerals have also a sig-nificant influence (Tyler, 1971; Gill et al., 1989; Marschner, 1995; Landstro¨m et al., 1996). The main botanical components in a grass plant are stem (nodes, internodes), leaf sheaths, leaf blades and panicles, in legumes stem, leaves and pods or flowers, respectively. The weight distribution of these components varies within and between plant species (Salo et al., 1975; Petersen, 1988). Harvest-ing at different stages of development also affects the stem to leaf ratio in the biomass. There are differences in the chemical composition of stem and leaves (Muller, 1960; Salo et al., 1975; Buxton and Hornstein, 1986; Albrecht et al., 1987; Pe-tersen, 1988) which also cause variations in the mineral content of the harvested biomass.

In the early 1990s, the Agricultural Research Centre and the University of Helsinki together with the Finnish Pulp and Paper Institute set out

to search for the most promising crop species for raw material of papermaking (Pahkala et al., 1995). In those studies, reed canary grass, tall fescue, meadow fescue and goat’s rue were chosen for further studies, including field experiments to determine the proper harvesting system and fertil-isation level for biomass production. The fibre and mineral compositions of the total yields have been reported in an earlier study (Pahkala et al., 1994). In the present study, we wanted to find out whether the quality of the raw material could be improved by screening for the plant fraction, which is most appropriate for the pulping and combustion processes.

2. Material and methods

2.1. Field experiments

In field experiments, three grass and one legu-minous species, reed canary grass (P.arundinacea

L.), meadow fescue (Festuca pratensis Hudson),

tall fescue (F. arundinacea Schreber) and goat’s rue (Galega orientalisL.), were studied. The data presented in this paper were collected from previ-ous field experiments designed to determine the proper harvesting system and fertilisation level for biomass production. The field experiment for each grass species comprised two fertilisation levels combined with four harvest times in split-plot design with 3 – 5 replicates. The fertilisation treat-ments were completely randomised into blocks. For goat’s rue, four harvest times and one fertili-sation level were used. Because Pahkala et al. (1994) showed earlier that harvesting to produce biomass for industrial purposes is best at seed ripening stage and in the following spring as senescent dry crop, we focused only on these two harvest times in this study. The results presented here are from the lower fertilisation level (100 kg N ha−1

), because the higher fertilisation level

(200 kg N ha−1_{) was shown to be too high for}

economic reasons.

The experiments were performed on farm-scale fields of sandy loam with pH values between 5.8 and 6.3. The plot size was 15 m2_{. More details of}

cultivation practices are given in Table 1 and in an earlier report (Pahkala et al., 1994).

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2.2. Har6esting and sampling

Harvest at seed ripening stage felt usually be-tween the last week of July and the second week of August, depending on the year (Table 1). Har-vest in spring was at the end of April or in the beginning of May. Delayed harvest was done in early spring after the snow and ice had melted and the soil had dried enough to carry the harvest machine (Haldrup forage plot harvester). For analysing the DM content in harvested biomass, two samples of 200 g were dried first for 2 h at 105°C and then 17 h at 60°C. For plant part

analyses, a sample of 25×50 cm (consisting

about 100 – 120 plants) was taken from each plot, cutting the plants near the soil surface. The dried grass samples were separated into stems, leaf blades, leaf sheaths and panicles. The goat’s rue samples were separated into stems, leaf blades and pods. The weight distribution of the plant parts (%) was determined after drying the samples for 17 h at 60°C.

2.3. Mineral composition and crude fibre

For grass species, chemical analyses were per-formed on samples of stem, leaf sheaths and leaf blades separately, for goat’s rue on samples of stem and leaf blades. After drying, the samples

were milled to less than 1 mm. The concentrations of K, Fe, Mn and Cu were measured by flame AAS (flame atomic absorption spectrophotome-ter), the concentration of silica (SiO2) and ash by

gravimetry, in both cases after dry ashing at 500°C. Crude fibre is the fibre fraction, which is not soluble in the acid – alkali treatment. Crude fiber was determined by using the Fibertec system M, which consists of hot and cold extraction units. The sample was boiled first in dilute acid

(H2SO4) and then in dilute alkali (KOH). The

residue, which contains cellulose, some hemicellu-lose and lignin, was measured gravimetrically af-ter ashing it at 500°C. Analyses were performed at the Chemistry Laboratory of the Agricultural Re-search Centre of Finland.

2.4. Statistical analyses

An analysis of variance was done for each

measured variable. Each plant species was

analysed separately. Statistical analysis was done for testing the harvest time effect. When testing the differences between plant parts, the plant part was handled as a repeated factor. For reed canary grass, the year was analysed as a repeated factor when analysing the total DM yield and stem proportion. The repeated measurements were cor-related. This correlation was taken into account

Table 1

Cultivation practices, varieties, localities, sowing years and harvesting dates of the experiments Sown

Variety Locality Harvested

Spring Autumn

DM yield and plant parts

Reed canary grass _Venture _Jokioinen ₁₉₉₀ 24th July 92a _{27th April 93}a Venture Jokioinen

Reed canary grass 1990 29th July 93 25th April 94

Reed canary grass Venture Jokioinen 1990 3rd August 94 11th May 95 8th May 96 Jokioinen 1990

Reed canary grass Venture 25th July 95

12th May 97 Venture

Reed canary grass Jokioinen 1990 16th August 96

11th May 98 Venture

Reed canary grass Jokioinen 1990 16th August 97

21st April 93a 28th July 92a

1988

Tall fescue Retu Helsinki

21st April 93a Helsinki 1988

Meadow fescue _Kalevi 28th July 92a

Gale Jokioinen 1990

Goat’s rue 5th August 92a _{6th May 93}a

Fibre

Venture Jokioinen 1993 19th August 96 16th May 97 Reed canary grass

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Fig. 1. Dry matter yield (kg ha−1_{) of reed canary grass in autumn 1992 – spring 1998. Relative proportion of different plant parts} in total DM (%) are given in columns.

on a selected model (1). The covariance structure of the repeated measurements was chosen by com-paring potential structures using Akaike’s infor-mation criterion (Wolfinger, 1996).

Yij=m+Ti+Bj+oij+Pk+(T×P)jk+(B×P)ik

+dijk (1)

where m, Ti, Bj and oij are equivalent in the

analysis of variance for the classical randomised complete-block design.Pkand (T×P)jkrepresent

the fixed effect of plant part (or year in reed

canary grass) and plant part (or year)×harvest

time interaction. (B×P)ikrepresents the random

effect of plant part (or year)×block interaction.

dijk are the experimental error terms.

Assumptions of the model were checked by graphical methods; box-plot for normality of er-rors and plots of residuals for constancy of error variance (Neter et al., 1996). The parameters of the models were estimated by the restricted maxi-mum likelihood (REML) estimation method us-ing the SAS system for Windows 6.12.

3. Results

3.1. Total yields and weight distributions of different plant parts

3.1.1. Reed canary grass

When harvested in spring, the total DM yield of reed canary grass was on average 2025 kg ha−1

higher than at autumn harvest (P0.0012) (Fig. 1). The age of the crop stand did not affect the harvested DM yield significantly in spring, and the yield level remained constant throughout the experiment period. In spring, the DM yield varied

between 6408 (1993) and 7716 kg ha−1

(1997). Variation in yield was greater when harvested in autumn; 3298 (1992) to 6357 kg ha−1

(1994). The variation was due to the climate and the age of the crop stand. The lowest yield was obtained in the second harvest year at both harvest times (autumn 1992 and spring 1993). The total yields of the first harvest year have been reported earlier (Pahkala et al., 1994), but then we did not frac-tionate the biomass into the different plant parts.

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The stem proportion of reed canary grass was significantly (P 0.0133) higher in spring (61.3%) than at autumn harvest (51.6%) (Fig. 1). The proportion of stem varied greatly depending on

the year (P 0.0001). Variation in stem fraction

ranged between 42.4 (1993) and 61.8% (1996) in autumn and in spring between 46.6 (1993) and

73.9% (1997). The stem yield (kg ha−1_{) varied}

yearly more than stem proportion. The stem yield

was lowest in 1992 (2269 kg ha−1_{) and it}

in-creased later, varying from 2966 to 4311 kg ha−1

in older stands. The proportion of leaf blades averaged 28.2% in autumn and 20.1% in spring, leaf sheaths 17.4 and 18.5% of the DM yield, respectively. Panicles were found only at seed stage in autumn when their proportion was 3.3% of the DM yield.

3.1.2. Fescues

The total DM yields for both tall fescue and meadow fescue over a period of several years have been presented earlier (Pahkala et al., 1994). In both fescues, the total biomass yield was lower

and variation was greater in spring than in au-tumn (Fig. 2). The harvest effect was significant in tall fescue (P0.0450). In fescues, the major part of the harvested biomass consisted of leaf blades (Fig. 2), the stem fraction being a minor part and the stem proportion even decreased during winter. In autumn, the proportion of stem varied from 24.1 to 33.1% in tall fescue and from 29.9 to 34.6% in meadow fescue and in spring from 11.1 to 39.9% and from 7.1 to 27.9%, respectively. The proportion of panicles in tall fescue was 8.2%, and in meadow fescue 11.6% of the DM yield at seed ripening stage.

3.1.3. Goat’s rue

The spring yield of goat’s rue was significantly

lower than that harvested in autumn (P 0.0299)

(Fig. 2). The proportion of stem was as high as 73.1% in spring, which was significantly higher (P

0.0250) than in autumn (48.6%). However, the

stem yield (kg ha−1_{) was comparable at both}

harvest times.

Fig. 2. Dry matter yield (kg ha−1_{) of tall fescue (a), meadow fescue (b) and goat’s rue (c) in autumn 1992 – spring 1993. Relative} proportion of different plant parts in total DM (%) are given in columns.

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Table 2

Ash, silica (SiO2) and potassium (K) contents in different plant parts of reed canary grass, tall fescue, meadow fescue and goat’s rue in autumn 1992 and in spring 1993a

SiO2(% of DM) K (g kg-1of DM) Ash (% of DM)

Harvest time Harvest time Harvest time

Spring Pvalue Autumn Spring Pvalue

Autumn Autumn Spring Pvalue

Reed canary grass

5.04 ab _0.4824 _{1.67 a}b _{4.04 a}b

Stem 4.71 ab 0.0005 _{14.47 a}b _{2.77 a}b _0.0019

9.00 b 0.2572 4.27 b 7.40 b 0.0002

8.44 b 19.73 b

Leaf sheath 3.57 a 0.0004

11.53 c

Leaf blade 13.00 c 0.0263 5.73 b 10.67 c 0.0022 21.13 b 4.30 a 0.0001

Tall fescue

4.15 a 0.0132 0.67 a 1.94 a 0.0039

6.03 a 25.93 a

Stem 8.83 a 0.0114

9.03 b

Leaf sheath 8.53 b 0.5180 3.24 b 5.06 b 0.0029 28.30 ab 13.07 b 0.0336 10.07 b 0.1931 3.54 b 7.33 c

Leaf blade 10.90 c 0.0014 30.77 b 6.33 a 0.0007

Meadow fescue

Stem 6.12 a 3.78 a 0.0077 0.53 a 2.54 a 0.0266 24.87 a 3.00 a 0.0001 7.76 b 0.1168 2.86 b 5.83 b 0.0071

Leaf sheath 8.71 b 23.90 a 4.30 a 0.0001

10.89 c 0.3735 2.63 c 8.51 c 0.0006

11.37 c 30.87 b

Leaf blade 4.47 a 0.0001

Goat’s rue

3.62 a 0.0012 0.08 a 0.48 a

Stem 4.89 a 0.0766 12.57 a 2.50 a 0.0014

11.10 b 0.0166 0.34 a 2.03 b 0.0243 14.57 a 3.37 a

10.77 b 0.0012

Leaf blade

a_The_P_{value are given for the harvest time effect.}

b_{Means for each species, which are written in columns, are not significantly different at the 0.05 probability level if they are} followed by the same letter.

3.2. Mineral and fibre contents of different plant parts

3.2.1. Ash

The ash content was lowest in the stem fraction for all species and at both harvest times, in leaf sheaths and especially in leaf blades the ash content was clearly higher (Table 2). Harvest time had not a very clear effect on the ash content. Leaf blades of reed canary grass and goat’s rue had a higher ash content in spring than in autumn, while the ash content in the stem of fescues and goat’s rue decreased in spring.

3.2.2. Silica (SiO2)

The grass species had a higher silica content than goat’s rue. In spring, the silica content was higher than in autumn in all plant parts. Silica was lowest in the stem fraction for all species at both harvest times (Table 2). The silica content in leaf sheaths and blades was almost the same in autumn, but in spring the silica content was

clearly higher in leaf blades than in leaf sheaths.

3.2.3. Potassium (K)

Harvest time had a considerable effect on the potassium content in all plant species and plant parts. The potassium content in all plant species and in all plant parts was clearly lower at spring harvest than in autumn (Table 2). Between plant parts the differences were small. In autumn, the potassium content was lower in stem than in leaves.

3.2.4. Copper (Cu), iron (Fe) and manganese

(Mn)

The copper content of leaf sheaths and blades in all plant species was higher in spring than in autumn, but the difference was not so clear in stem (Table 3). Except for tall fescue, in spring the copper content was significantly lower in stem than in leaf blades. The copper content of goat’s rue was higher than that of grasses.

The iron content was always higher in spring than in autumn (Table 3). Also the differences

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Table 3

Copper (Cu), iron (Fe) and manganese (Mn) contents in different plant parts of reed canary grass, tall fescue, meadow fescue and goat’s rue in autumn 1992 and in spring 1993a

Fe (mg kg-1_{of DM)} _{Mn (mg kg}-1_{of DM)} Cu (mg kg-1 _{of DM)}

Harvest time Harvest time Harvest time

Autumn Spring Pvalue Autumn Spring Pvalue Autumn Spring Pvalue

Reed canary grass

Stem 5.90 ab _{6.34 a}b _0.4946 _{18.70 a}b _{61.37 a}b _0.1738 _{20.00 a}b _{48.00 a}b _0.3998 4.11 b

Leaf sheath 7.33 ab 0.0055 66.67 b 267.00 b 0.0015 52.83 ab 140.33 b 0.0423 8.22 b 0.0193 110.33 b 491.00 c 0.0001

5.99 a 80.53 b

Leaf blade 213.67 c 0.0110

Tall fescue

4.65 a 0.0447 15.73 a 68.10 a

Stem 2.47 a 0.0090 35.73 a 62.67 a 0.0851

4.91 a 0.0228 48.00 a 148.33 b

2.19 a 0.0796

Leaf sheath 97.37 b 175.67 b 0.0027

3.63 a

Leaf blade 6.72 a 0.0149 91.97 a 477.33 c 0.0044 105.10 b 186.00 b 0.0024

Meadow fescue

5.73 a 0.2692 25.30 a 157.33 a

4.23 a 0.0195

Stem 42.53 a 63.43 a 0.2313

3.31 a

Leaf sheath 8.54 b 0.0110 55.50 a 391.67 b 0.0019 84.70 b 117.70 b 0.2366 6.81 b

Leaf blade 12.07 c 0.0109 131.00 a 1176.33 c 0.0007 83.53 b 149.67 c 0.1155

Goat’s rue

12.40 a 0.0096

Stem 4.09 a 44.83 a 332.00 a 0.0507 18.33 a 48.57 a 0.0009

26.07 b 0.0512 125.00 a 1192.00 b 0.0215 85.80 b 194.00 b

10.67 a 0.0062

Leaf blade

a_The_P_{value are given for the harvest time effect.}

b_{Means for each species, which are written in columns, are not significantly different at the 0.05 probability level if they are} followed by the same letter.

between plant parts were significant in spring. The lowest contents were found in stem, the highest in leaf blades. In autumn, the iron content varied greatly which is the reason why there were no significant differences between the plant parts in iron content.

The manganese content varied considerably be-tween different plant parts. It was higher in spring than in autumn (Table 3). The contents were lowest in the stem of all species, the highest in leaf blades.

3.2.5. Fibre

The fibre content in reed canary grass was always clearly higher in spring than at autumn harvest (Table 4). Even the differences between plant parts were significant. The highest fibre content was observed in stem where the harvest time effect was strongest. The amount of fibre was lowest in leaf blades.

4. Discussion

Reed canary grass, meadow fescue, tall fescue and goat’s rue had shown a high yielding capacity in earlier studies, and especially the grass species had been found to be potential fibre crops

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Crude fibre contents (% of DM) in different plant parts of reed canary grass in autumn 1996 and in spring 1997a

Harvest time

Autumn Spring Pvalue Reed canary grass

52.13 ab _0.0001 39.70 ab

Stem

Leaf sheath 36.70 b 39.83 b 0.0032

26.97 c 0.0293

Leaf blade 30.13 c

a_The_P_{value are given for the harvest time effect.} b_{Means, which are written in columns, are not significantly} different at the 0.05 probability level if they are followed by the same letter.

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son et al., 1994; Pahkala et al., 1995). In this study, the highest DM yield was obtained from reed canary grass when the crop was harvested in spring as a dry senescent crop, and the yield level remained constant from the second year through-out the experimental period of 6 years. In Swedish studies (Landstro¨m et al., 1996), the DM yield of reed canary grass increased at delayed harvest with increasing age of the crop stand during the first three ley years.

The stem proportion of plant species studied varied greatly because of different growth habit of the species. On average, more than half of the biomass of reed canary grass and goat’s rue con-sisted of stem and the proportion of stem was higher in spring than in autumn. In fescues, the major part of the harvested biomass consisted of leaf blades, and the proportion of stem even decreased during winter. Reed canary grass is a strawy rhizomatous species and its growth habit is vigorous and erect, while fescues form leafy tus-socks, which also lodge more easily during winter. The total and stem yield losses during the winter are more common in fescues than in reed canary grass or goat’s rue due to the lodging of the canopy.

The chemical composition of a plant part varies depending on the stage of development of the plant when the mobile elements are moving from organ to organ as growth proceeds (Jeffrey, 1988). The concentrations of silicon, iron, manganese and copper have proved to increase at the late stage of development (Tyler, 1971), and also in this study the highest concentrations were found in dead plants in spring. The reason for the great variation in the manganese and iron contents may be connected to the lodging of the canopy and for possible soil contamination at harvesting. The potassium content was clearly lower in spring than in autumn because of the leaching during winter. An increase of fibre fraction in spring can be explained by ageing of the plant, when the relative amount of plant cell walls increases with increasing amount of cellulose and lignin in the secondary wall, as has been described in several forage crops (Buxton and Hornstein, 1986; Bux-ton and Russel, 1988; Albrecht et al., 1987; Gill et al. 1989).

Grasses seemed to accumulate more silica than goat’s rue. This result is comparable with earlier findings which have shown high silica content typical for grass plants (Marschner, 1995; Ilves-salo-Pfa¨ffli, 1995). Grasses accumulate silicon as silica in epidermic cells where it protects the plant against herbivores and fungi (Jones and Han-dreck, 1965). Its role is different from that of potassium, copper, iron and manganese, which take part more in cell metabolism.

From plant parts, leaf blades accumulated the highest concentrations of minerals. Removing the undesirable minerals with the leaf blades would reduce the mineral content considerably and, at the same time, would increase the relative propor-tion of stem, the most fibre-rich part of the plant. On the one hand, sorting out the leaf blades would decrease the material usable for industry from 11 to 67% depending on plant species. On the other hand, using more stem fraction increases the pulp yield and improves the pulp quality (Petersen, 1989; Hemming et al., 1994; Pahkala et al., 1999). At the pulp mill, leaves, dust and dirt can be removed by air fractionation before cook-ing. However, in grasses the leaf sheath is usually tightly rolled around the stem, and it can be more difficult to remove than leaf blades. Mechanical pretreatment improves the quality of the pulp by increasing the bleachability of the pulp and de-creasing the fines and silica particles in the raw material. Silicon entering the process can be de-creased by pretreatment of the grass, removing 40% of the silica (Paavilainen et al., 1996b). The dewatering and drying ability of pure grass pulps can be improved by mechanical fractionation and blending the grass pulp with long-fibre soft wood pulp (Wisur et al., 1993; Paavilainen et al., 1996a,b).

5. Conclusion

It is possible to improve the raw material for pulping and fuel production by choosing a suit-able plant species and harvesting time and by using only the plant parts which contain low amounts of minerals, e.g. potassium and silicon. In this study, the highest stem yield was given by

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reed canary grass when harvested in spring as a senescent crop and the yield level remained con-stant for at least 6 years. The main part of the fibre in reed canary grass was found in stem, and the fibre content even increased when harvested in spring. However, the contents of ash and most of the minerals studied were also high when har-vested in spring. The mineral concentrations were highest in leaf blades. By removing the leaf blades, the ash and mineral contents would de-crease considerably and at the same time, the relative fibre content could increase, thus increas-ing the value of plant material for industrial use.

Acknowledgements

The authors wish to thank the Ministry of Agriculture and Forestry and the Agricultural Research Centre of Finland for financing this study as part of the project ‘Production and use of agrofibre in Finland’. Our special thanks are due to Biometrician Lauri Jauhiainen for the comments of the manuscript, and to the Chem-istry Laboratory of MTT for the careful labora-tory work.

References

Albrecht, K.A., Wedin, W.F., Buxton, D.R., 1987. Cell-wall composition and digestibility of alfalfa stems and leaves. Crop Sci. 27, 735 – 741.

Atchison, J.E., 1988. World wide capacities for non-wood plant fibre pulping increasing faster than wood pulping capacities. TAPPI Pulping Conference 1988. New Orleans, LA, USA, Book 1, pp. 25 – 45.

Berggren, H., 1989. Lusern och ro¨rflen i framtidens massor. Svensk papperstidning 17, 28 – 33.

Burvall, J., 1993. Production and combustion of reed canary grass powder — a full scale trial. Ro¨ba¨cksdalen meddelar. Rapport 9, 31.

Buxton, D.R., Hornstein, J.S., 1986. Cell wall concentration and components in stratified canopies of alfalfa, birdsfoot and red clover. Crop Sci. 26, 180 – 184.

Buxton, D.R., Russel, J.R., 1988. Lignin constituents and cell-wall digestibility of grass and legume stems. Crop Sci. 28, 553 – 558.

van Dam, J.E.G., Shannon, W.B., 1994. Increased application of domestically produced plant fibres in textiles, pulp and paper production. In: Industrial fibre crops. European

Commission. Science Research Development, Agro Indus-trial Division. EUR 16101 EN, pp. 133 – 150.

Gill, M., Beever, D.E., Osbourn, D.F., 1989. The feeding value of grass and grass products. In: Holmes, W. (Ed.), Grass, its Production and Utilization, 2nd edn. Blackwell Scientific Publications, Worcester, pp. 89 – 129.

Hemming, M., Ja¨rvenpa¨a¨, M., Maunu, T., 1994. On-farm handling techniques for reed canary grass to be used as a raw material in the pulp industry. Pira International/Silsoe Research Institute Joint Conference. Non-food fibres for industry. 23 – 24 March 1994. Leatherhead, UK. Confer-ence Proceedings, Vol 1., Paper 12, pp. 1 – 11.

Ilvessalo-Pfa¨ffli, M.-S., 1995. Fiber Atlas. Identification of Papermaking Fibers. Springer-Verlag, Berlin, Germany, pp. 267 – 388.

Janson, J., Jousimaa, T., Hupa, M., Backman, R., 1994. The use ofFestuca arundinacea: pulping, bleaching, papermak-ing and spent liquor recovery. Third European Workshop on Lignocellulosics and Pulp (EWLP’94), 28 – 31 August 1994, Stockholm, Sweden. Extended abstracts, p. 278. Jeffrey, D.W., 1988. Mineral nutrients and the soil

environ-ment. In: Jones, M.B., Lazenby, A. (Eds.), The Grass Crop. The Physiological Basis of Production. Chapman and Hall, London, pp. 180 – 202.

Jeyasingam, J.T., 1988. A summary of special problems and considerations related to non wood pulping world wide. TAPPI Pulping Conference 1988. New Orleans, LA, USA. Book 3, pp. 571 – 579.

Jones, L.H.P., Handreck, K.A., 1965. Studies of silica in the oat plant. III. Uptake of silica from soils by the plant. Plant Soil 23, 79 – 96.

Keitaanniemi, O., Virkola, N.-E., 1982. Undesirable elements in causticizing systems. TAPPI 65, no. 7, 89 – 92. Landstro¨m, S., Lomakka, L., Andersson, S., 1996. Harvest in

spring improves yield and quality of reed canary grass as a bioenergy crop. Biomass Bioenergy 11, 333 – 341. Leinonen, A., Lindh, T., Paappanen, T., Kallio, E., Flyktman,

M., Hakkarainen, J., 1998. Cultivation and production of reed canary grass for mixed fuel as a method for reclama-tion of a peat producreclama-tion area. An Internareclama-tional Sympo-sium Peatland Restoration and Reclamation, 14 – 18 July 1998. Duluth, Minnesota, USA. Proceedings, pp. 120 – 124. Lo¨nnberg, B., El-Sakhawy, M., Hultholm, T., 1996. Ethanol pulping of pretreated non-wood fibre materials. In: Kennedy, J.F., Phillips, G.O., Williams, P.A. (Eds.), The Chemistry and Processing of Wood and Plant Fibrous Materials. Woodhead Publishing, Great Yarmouth, Cam-bridge, pp. 99 – 109.

Marschner, H., 1995. Mineral Nutrition of Higher Plants, 2nd edn. Academic Press, London, p. 889.

Muller, F.M., 1960. On the relationship between properties of straw pulp and properties of straw. TAPPI 43, no. 2, 209A – 218A.

Nelson, G.H., Clark, T.F., Wolff, I.A., Jones, Q., 1966. A search for new fibre crops: Analytical evaluations. TAPPI 49, no. 1, 40 – 48.

(10)

Neter, J., Kutner, M., Nachtsheim, C., Wasserman, W., 1996. Applied Linear Statistical Models, 4th edn. Irwin, Chicago, USA, p. 1310.

Nieschlag, H.J., Nelson, G.H., Wolff, I.A., Perdue, R.E., 1960. A search for new fibre crops. TAPPI 43, no. 3, 193 – 201.

Obernberger, I., Biederman, F., Widman, W., Riedl, R., 1997. Concentrations of inorganic elements in biomass fuels and recovery in the different ash fractions. Biomass and Bioen-ergy 12, no. 3, 211 – 224.

Paavilainen, L., Torgilsson, R., 1994. Reed canary grass — a new Nordic papermaking fibre. TAPPI Pulping Confer-ence, November 6 – 10, 1994, San Diego, CA, USA, pp. 611 – 618.

Paavilainen, L., Cheng, Z., Tuhkanen, T. 1996a. Behaviour of special reed pulp on the paper machine. 3rd International non-wood fibre pulping and papermaking conference. Oc-tober 15 – 18, 1996, Beijing, China, pp. 577 – 582. Paavilainen, L., Tulppala, J., Varhimo, A., Ranua, M., Pere,

J., 1996b. Production and use of agrofibre in Finland. Final report of the study, IV. Reed canary grass sulphate pulp as raw material for fine paper. Maatalouden tutkimuskeskus. Maatalouden tutkimuskeskuksen julkaisuja, Jokioinen, Finland, Sarja A. 6, p. 57. Pahkala, K., Mela, T., Laamanen, L., 1994. Prospects for the

production and use of agrofibre in Finland. Final report of the preliminary study in 1990 – 1992. Maatalouden tutkimuskeskus. Finland, Tiedote 12/94, p. 55.

Pahkala, K.A., Mela, T.J.N., Laamanen, L., 1995. Mineral composition and pulping characteristics of several field crops cultivated in Finland. In: Chartier, P., Beenackers, A.A.C.M., Grassi, G. (Eds.), Biomass for Energy, Envi-ronment, Agriculture and Industry. Proceedings of the 8th EC Conference. October 3 – 5 1994, Vienna, Austria, Perga-mon Press. Vol. 1, pp. 395 – 400.

Pahkala, K.A., Eurola, M., Varhimo, A. 1999. Effect of genotype and growing conditions on fibre and mineral composition of reed canary grass (Phalaris arundinaceaL.). In: Mela, T., Topi-Hulmi, M., Pithan, K. (Eds.). Alterna-tive Crops for Sustainable Agriculture. COST 814 Work-shop, June 13 – 15, 1999. Turku, Finland (in print).

Petersen, P.B., 1988. Separation and characterization of botan-ical components of straw. Agri. Prog. 63, 8 – 23.

Petersen, P.B., 1989. Industrial applications of straw. Fifth International Symposium on Wood and Pulping Chem-istry. Raleigh, NC, USA, pp. 179 – 183.

Ranua, M., 1977. Oljen ka¨ytto¨ puunjalostusteollisuudessa. Teho 4/77, 14 – 16.

Rexen, F., Munck, L., 1984. Industrial utilization of cereal straw. In: Cereal crops for industrial use in Europe. The Commission of the European Communities. EUR9617EN, pp. 120 – 136.

Salo, M.-L., Nyka¨nen, A., Sormunen, R., 1975. Composition, pepsin-HCl solubility and in vitro digestibility of forages at different growth stages. J. Sci. Agri. Soc. Finland 47, 480 – 490.

Theander, O., 1991. Ro¨rflenets kemiska sammansa¨ttning. In: Ro¨rflen fo¨r massa och bra¨nsle. Karlstad, Sverige. p. 4.

Tyler, G., 1971. Studies in the ecology of Baltic sea-shore meadows IV. Distribution and turnover of organic matter and minerals in a shore meadow ecosystem. Oikos 22, 265 – 291.

Ulmgren, P., Lindstro¨m, R., Saltin, G., 1990. Kemikaliea˚tervinning vid framsta¨llning av kemisk massa ur etta˚rsva¨xter. In: Kan jodbruket bidra till skogsindus-trins ra˚varufo¨rso¨rjning? IVA- Symposium. Ingenjo¨rsveten-skapsakademien, 14.2.1990, Stockholm, Sweden, p. 7. Walsh, M., 1998. Miscanthus handbook. Miscanthus

produc-tivity Network (AIR-CT92-0294). Hyperion Energy Sys-tems Ltd, Cork, Ireland, pp. 225.

Watson, A.J., Gartside, G., 1976. Utilising woody fibre from agricultural crops. Aust. Forestry 39, 16 – 22.

Wisur, H., Sjo¨berg, L., Ahlgren, P., 1993. Selecting a potential Swedish fibre crop: fibres and fines in different crops as an indication of their usefulness in pulp and paper produc-tion. Ind. Crops Prod. 2, 39 – 45.

Wolfinger, R., 1996. Heterogeneous variance-covariance struc-tures for repeated measures. J. Agri. Biol. Environ. Stat. 1 2, 205 – 230.

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The stem proportion of reed canary grass was

significantly (

P

0.0133) higher in spring (61.3%)

than at autumn harvest (51.6%) (Fig. 1). The

proportion of stem varied greatly depending on

the year (

P

0.0001). Variation in stem fraction

ranged between 42.4 (1993) and 61.8% (1996) in

autumn and in spring between 46.6 (1993) and

73.9% (1997). The stem yield (kg ha

−1

_{) varied}

yearly more than stem proportion. The stem yield

was lowest in 1992 (2269 kg ha

−1

_{) and it}

in-creased later, varying from 2966 to 4311 kg ha

−1

in older stands. The proportion of leaf blades

averaged 28.2% in autumn and 20.1% in spring,

leaf sheaths 17.4 and 18.5% of the DM yield,

respectively. Panicles were found only at seed

stage in autumn when their proportion was 3.3%

of the DM yield.

3.1.2. Fescues

The total DM yields for both tall fescue and

meadow fescue over a period of several years have

been presented earlier (Pahkala et al., 1994). In

both fescues, the total biomass yield was lower

and variation was greater in spring than in

au-tumn (Fig. 2). The harvest effect was significant in

tall fescue (

P

0.0450). In fescues, the major part of

the harvested biomass consisted of leaf blades

(Fig. 2), the stem fraction being a minor part and

the stem proportion even decreased during winter.

In autumn, the proportion of stem varied from

24.1 to 33.1% in tall fescue and from 29.9 to

34.6% in meadow fescue and in spring from 11.1

to 39.9% and from 7.1 to 27.9%, respectively. The

proportion of panicles in tall fescue was 8.2%, and

in meadow fescue 11.6% of the DM yield at seed

ripening stage.

3.1.3. Goat

’

s rue

The spring yield of goat’s rue was significantly

lower than that harvested in autumn (

P

0.0299)

(Fig. 2). The proportion of stem was as high as

73.1% in spring, which was significantly higher (

P

0.0250) than in autumn (48.6%). However, the

stem yield (kg ha

−1

_{) was comparable at both}

harvest times.

Fig. 2. Dry matter yield (kg ha−1_{) of tall fescue (a), meadow fescue (b) and goat’s rue (c) in autumn 1992 – spring 1993. Relative}

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Table 2

Ash, silica (SiO2) and potassium (K) contents in different plant parts of reed canary grass, tall fescue, meadow fescue and goat’s rue

in autumn 1992 and in spring 1993a

SiO2(% of DM) K (g kg-1of DM)

Ash (% of DM)

Harvest time Harvest time Harvest time

Spring Pvalue Autumn Spring Pvalue

Autumn Autumn Spring Pvalue

Reed canary grass

5.04 ab _0.4824 _{1.67 a}b _{4.04 a}b

Stem 4.71 ab 0.0005 _{14.47 a}b _{2.77 a}b _0.0019

9.00 b 0.2572 4.27 b 7.40 b 0.0002

8.44 b 19.73 b

Leaf sheath 3.57 a 0.0004

11.53 c

Leaf blade 13.00 c 0.0263 5.73 b 10.67 c 0.0022 21.13 b 4.30 a 0.0001

Tall fescue

4.15 a 0.0132 0.67 a 1.94 a 0.0039

6.03 a 25.93 a

Stem 8.83 a 0.0114

9.03 b

Leaf sheath 8.53 b 0.5180 3.24 b 5.06 b 0.0029 28.30 ab 13.07 b 0.0336 10.07 b 0.1931 3.54 b 7.33 c

Leaf blade 10.90 c 0.0014 30.77 b 6.33 a 0.0007

Meadow fescue

Stem 6.12 a 3.78 a 0.0077 0.53 a 2.54 a 0.0266 24.87 a 3.00 a 0.0001 7.76 b 0.1168 2.86 b 5.83 b 0.0071

Leaf sheath 8.71 b 23.90 a 4.30 a 0.0001

10.89 c 0.3735 2.63 c 8.51 c 0.0006

11.37 c 30.87 b

Leaf blade 4.47 a 0.0001

Goat’s rue

3.62 a 0.0012 0.08 a 0.48 a

Stem 4.89 a 0.0766 12.57 a 2.50 a 0.0014

11.10 b 0.0166 0.34 a 2.03 b 0.0243 14.57 a 3.37 a

10.77 b 0.0012

Leaf blade

a_The_P_{value are given for the harvest time effect.}

b_{Means for each species, which are written in columns, are not significantly different at the 0.05 probability level if they are}

followed by the same letter.

3.2. Mineral and fibre contents of different plant

parts

3.2.1. Ash

The ash content was lowest in the stem fraction

for all species and at both harvest times, in leaf

sheaths and especially in leaf blades the ash content

was clearly higher (Table 2). Harvest time had not

a very clear effect on the ash content. Leaf blades

of reed canary grass and goat’s rue had a higher ash

content in spring than in autumn, while the ash

content in the stem of fescues and goat’s rue

decreased in spring.

3.2.2. Silica

(

SiO

)

The grass species had a higher silica content than

goat’s rue. In spring, the silica content was higher

than in autumn in all plant parts. Silica was lowest

in the stem fraction for all species at both

harvest times (Table 2). The silica content

in leaf sheaths and blades was almost the same

in autumn, but in spring the silica content was

clearly higher in leaf blades than in leaf sheaths.

3.2.3. Potassium

(

K

)

Harvest time had a considerable effect on the

potassium content in all plant species and plant

parts. The potassium content in all plant species

and in all plant parts was clearly lower at spring

harvest than in autumn (Table 2). Between plant

parts the differences were small. In autumn, the

potassium content was lower in stem than in leaves.

3.2.4. Copper

(

Cu

),

iron

(

Fe

)

and manganese

(

Mn

)

The copper content of leaf sheaths and blades in

all plant species was higher in spring than in

autumn, but the difference was not so clear in stem

(Table 3). Except for tall fescue, in spring the

copper content was significantly lower in stem than

in leaf blades. The copper content of goat’s rue was

higher than that of grasses.

The iron content was always higher in spring

than in autumn (Table 3). Also the differences

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Table 3

Copper (Cu), iron (Fe) and manganese (Mn) contents in different plant parts of reed canary grass, tall fescue, meadow fescue and goat’s rue in autumn 1992 and in spring 1993a

Fe (mg kg-1_{of DM)} _{Mn (mg kg}-1_{of DM)}

Cu (mg kg-1 _{of DM)}

Harvest time Harvest time Harvest time

Autumn Spring Pvalue Autumn Spring Pvalue Autumn Spring Pvalue

Reed canary grass

Stem 5.90 ab _{6.34 a}b _0.4946 _{18.70 a}b _{61.37 a}b _0.1738 _{20.00 a}b _{48.00 a}b _0.3998

4.11 b

Leaf sheath 7.33 ab 0.0055 66.67 b 267.00 b 0.0015 52.83 ab 140.33 b 0.0423 8.22 b 0.0193 110.33 b 491.00 c 0.0001

5.99 a 80.53 b

Leaf blade 213.67 c 0.0110

Tall fescue

4.65 a 0.0447 15.73 a 68.10 a

Stem 2.47 a 0.0090 35.73 a 62.67 a 0.0851

4.91 a 0.0228 48.00 a 148.33 b

2.19 a 0.0796

Leaf sheath 97.37 b 175.67 b 0.0027

3.63 a

Leaf blade 6.72 a 0.0149 91.97 a 477.33 c 0.0044 105.10 b 186.00 b 0.0024

Meadow fescue

5.73 a 0.2692 25.30 a 157.33 a

4.23 a 0.0195

Stem 42.53 a 63.43 a 0.2313

3.31 a

Leaf sheath 8.54 b 0.0110 55.50 a 391.67 b 0.0019 84.70 b 117.70 b 0.2366 6.81 b

Leaf blade 12.07 c 0.0109 131.00 a 1176.33 c 0.0007 83.53 b 149.67 c 0.1155

Goat’s rue

12.40 a 0.0096

Stem 4.09 a 44.83 a 332.00 a 0.0507 18.33 a 48.57 a 0.0009

26.07 b 0.0512 125.00 a 1192.00 b 0.0215 85.80 b 194.00 b

10.67 a 0.0062

Leaf blade

a_The_P_{value are given for the harvest time effect.}

b_{Means for each species, which are written in columns, are not significantly different at the 0.05 probability level if they are}

followed by the same letter.

between plant parts were significant in spring. The

lowest contents were found in stem, the highest in

leaf blades. In autumn, the iron content varied

greatly which is the reason why there were no

significant differences between the plant parts in

iron content.

The manganese content varied considerably

be-tween different plant parts. It was higher in spring

than in autumn (Table 3). The contents were

lowest in the stem of all species, the highest in leaf

blades.

3.2.5. Fibre

The fibre content in reed canary grass was

always clearly higher in spring than at autumn

harvest (Table 4). Even the differences between

plant parts were significant. The highest fibre

content was observed in stem where the harvest

time effect was strongest. The amount of fibre was

lowest in leaf blades.

4. Discussion

Reed canary grass, meadow fescue, tall fescue

and goat’s rue had shown a high yielding capacity

in earlier studies, and especially the grass species

had been found to be potential fibre crops

(Jan-Table 4

Crude fibre contents (% of DM) in different plant parts of reed canary grass in autumn 1996 and in spring 1997a

Harvest time

Autumn Spring Pvalue Reed canary grass

52.13 ab _0.0001

39.70 ab

Stem

Leaf sheath 36.70 b 39.83 b 0.0032

26.97 c 0.0293

Leaf blade 30.13 c

a_The_P_{value are given for the harvest time effect.} b_{Means, which are written in columns, are not significantly}

different at the 0.05 probability level if they are followed by the same letter.

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son et al., 1994; Pahkala et al., 1995). In this

study, the highest DM yield was obtained from

reed canary grass when the crop was harvested in

spring as a dry senescent crop, and the yield level

remained constant from the second year

through-out the experimental period of 6 years. In Swedish

studies (Landstro¨m et al., 1996), the DM yield of

reed canary grass increased at delayed harvest

with increasing age of the crop stand during the

first three ley years.

The stem proportion of plant species studied

varied greatly because of different growth habit of

the species. On average, more than half of the

biomass of reed canary grass and goat’s rue

con-sisted of stem and the proportion of stem was

higher in spring than in autumn. In fescues, the

major part of the harvested biomass consisted of

leaf blades, and the proportion of stem even

decreased during winter. Reed canary grass is a

strawy rhizomatous species and its growth habit is

vigorous and erect, while fescues form leafy

tus-socks, which also lodge more easily during winter.

The total and stem yield losses during the winter

are more common in fescues than in reed canary

grass or goat’s rue due to the lodging of the

canopy.

The chemical composition of a plant part varies

depending on the stage of development of the

plant when the mobile elements are moving from

organ to organ as growth proceeds (Jeffrey, 1988).

The concentrations of silicon, iron, manganese

and copper have proved to increase at the late

stage of development (Tyler, 1971), and also in

this study the highest concentrations were found

in dead plants in spring. The reason for the great

variation in the manganese and iron contents may

be connected to the lodging of the canopy and for

possible soil contamination at harvesting. The

potassium content was clearly lower in spring

than in autumn because of the leaching during

winter. An increase of fibre fraction in spring can

be explained by ageing of the plant, when the

relative amount of plant cell walls increases with

increasing amount of cellulose and lignin in the

secondary wall, as has been described in several

forage crops (Buxton and Hornstein, 1986;

Bux-ton and Russel, 1988; Albrecht et al., 1987; Gill et

al. 1989).

Grasses seemed to accumulate more silica than

goat’s rue. This result is comparable with earlier

findings which have shown high silica content

typical for grass plants (Marschner, 1995;

Ilves-salo-Pfa¨ffli, 1995). Grasses accumulate silicon as

silica in epidermic cells where it protects the plant

against herbivores and fungi (Jones and

Han-dreck, 1965). Its role is different from that of

potassium, copper, iron and manganese, which

take part more in cell metabolism.

From plant parts, leaf blades accumulated the

highest concentrations of minerals. Removing the

undesirable minerals with the leaf blades would

reduce the mineral content considerably and, at

the same time, would increase the relative

propor-tion of stem, the most fibre-rich part of the plant.

On the one hand, sorting out the leaf blades

would decrease the material usable for industry

from 11 to 67% depending on plant species. On

the other hand, using more stem fraction increases

the pulp yield and improves the pulp quality

(Petersen, 1989; Hemming et al., 1994; Pahkala et

al., 1999). At the pulp mill, leaves, dust and dirt

can be removed by air fractionation before

cook-ing. However, in grasses the leaf sheath is usually

tightly rolled around the stem, and it can be more

difficult to remove than leaf blades. Mechanical

pretreatment improves the quality of the pulp by

increasing the bleachability of the pulp and

de-creasing the fines and silica particles in the raw

material. Silicon entering the process can be

de-creased by pretreatment of the grass, removing

40% of the silica (Paavilainen et al., 1996b). The

dewatering and drying ability of pure grass pulps

can be improved by mechanical fractionation and

blending the grass pulp with long-fibre soft wood

pulp (Wisur et al., 1993; Paavilainen et al.,

1996a,b).

5. Conclusion

It is possible to improve the raw material for

pulping and fuel production by choosing a

suit-able plant species and harvesting time and by

using only the plant parts which contain low

amounts of minerals, e.g. potassium and silicon.

In this study, the highest stem yield was given by

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reed canary grass when harvested in spring as a

senescent crop and the yield level remained

con-stant for at least 6 years. The main part of the

fibre in reed canary grass was found in stem, and

the fibre content even increased when harvested in

spring. However, the contents of ash and most of

the minerals studied were also high when

har-vested in spring. The mineral concentrations were

highest in leaf blades. By removing the leaf

blades, the ash and mineral contents would

de-crease considerably and at the same time, the

relative fibre content could increase, thus

increas-ing the value of plant material for industrial use.

Acknowledgements

The authors wish to thank the Ministry of

Agriculture and Forestry and the Agricultural

Research Centre of Finland for financing this

study as part of the project ‘Production and use

of agrofibre in Finland’. Our special thanks are

due to Biometrician Lauri Jauhiainen for the

comments of the manuscript, and to the

Chem-istry Laboratory of MTT for the careful

labora-tory work.

References