B~omasv and Bioener~~~ Vol. 13, Nos. l/2. pp. 51-X 1997 8~‘ 1997 Elsevier Saence Ltd. All rights reserved Pergamon

PII: SO961-9534(97)00023-8 Printed in Great Britain

096lb9534/97 $17.00 + 0.00

HARVEST MANAGEMENT EFFECTS ON QUANTITY AND QUALITY OF ERIANTHUS PLANT MORPHOLOGICAL

COMPONENTS’

P. MISLEVY*?, F. G. MARTIN?, M. B. ADJEI* AND J. D. MILLERS

*Range Cattle Research and Education Center, University of Florida, 3401 Experiment Station, Ona, FL 33865, U.S.A.

tstatistics Department, University of Florida, Gainesville, FL 3261 l-0560, U.S.A. $USDA-ARS, Sugarcane Field Station, Canal Point, FL 33438-9702, U.S.A.

(RcTceiued 27 March 1997; revised 15 April 1997; accepted 17 April 1997)

Abstract-Lignocellulose materials can be readily produced under tropical and subtropical conditions and converted to a variety of fuels through bioconversion methods. However, biomass production and plant quality may differ between plant species and morphological components of plants. The objectives of these two experiments were to: (1) determine the influence of plant height at harvest on Erianthus arundinaceum (Retz) Jesw-IK76-1 IO dry biomass (DB) yield; and (2) monitor changes in tiller density, quantity and quality of plant components with increased plant height. Experiment (1) determined the influence of plant height when harvested at 1.2, 2.5 and 3.7 m, mature stage in October (4.9 m), mature stage in December (4.9 m, plus inflorescence), and an additional treatment harvested in October, which received half the total N (168 kg ha-‘) annually on DB yield from 1987 to 1990. Experiment (2) treatments were to monitor changes in quantity and crude protein (CP) and in citro organic matter digestion (IVOMD, estimate of soluble cell solids) of green leaf, dead leaf and stem plant components, leaf area index and tiller number at 0.6 m plant height increments to a final height of 4.3 m during 1987 and 1988. Treatments from both experiments of the study received 25 kg P and 93 kg K ha-’ in one application and 336 kg N ha-’ y’ in single or split applications applied annually prior to regrowth of each harvest. Plants repeatedly harvested at the 1.2 m height and mature stage in December (Experiment (1)) produced a 4-y average yield of 5.2 and 51.5 Mg ha-’ y-’ DB, respectively. These same two treatments had a yield reduction of 100% (plants died) and 1% between years I and 4. Leaf area index increased quadratically to a maximum of I7 at the 3.1 m plant height treatment. Percentage green leaf, total tillers and live tillers decreased quadratically. while dead leaf and dead tillers increased linearly and stem increased quadratically as plant height was delayed from 0.6 to 4.3 m. Crude protein and IVOMD of green leaf and stem decreased quadratically with plant maturity. Knowing the quantity and quality of plant components at various physiological stages can be important to biomass producers, who need to make logical field decisions regarding biomass feedstock that should be utilized immediately after a freeze or stockpiled for later use. (‘1 1997 Elsevier Science Ltd

Keywords--Tall grass; energycrop; biomass feedstock: harvest stage; crude protein; digestibility

1. INTRODUCTION

Alternative fuels can be produced from dom- estic feedstocks,’ thus, reducing our dependency on foreign oil. Favorable climates in the tropics for extended plant growth and high yields, make lignocellulosic biomass the most attractive renewable energy source. Both tropical and subtropical climates support grass plants that have an efficient C, metabolic system that returns 4-5 units of energy for each unit used,’ making C, plants like Erianthus an efficient genera in converting solar energy to biomass.

‘Florida Agric. Exp. Stn. Journal Series No. ROS403. ‘Author to whom correspondence should be addressed

(Tel: (941) 735-1314; Fax: (941) 735-1930).

Erianthus is tolerant to most above- and below-ground plant pests, and can produce high biomass yields with limited fertility and moisture.’ 5 This tall grass also tolerates saturated soil conditions, making it adaptable to soils susceptible to a high water table and occasional flooding.

Studies’ conducted in central Florida revealed Erianthus IK 76-110 had the potential to produce high biomass yields with minimal input. However, there is a need to determine the influence of harvest intervals on yield, ratoon success and change in plant leaf and stem component and quality over time. The purpose of this experiment was to determine the influence of plant height at harvest on yield,

51

52 P.MISLEVY et al.

persistence and changes in plant quantity and quality with maturity.

2. PROCEDURE

Two field experiments were conducted at the Range Cattle Research and Education Center, University of Florida, Ona, Florida (27”25’N, 81’55’W). The soil type was an Ona fine sand (sandy, siliceous, hyperthermic, Typic Hap- laquod). Both experiments were established with Erianthus rooted crowns planted 0.8 m apart within the row and 0.9 m between rows. Plants were allowed 1.5 y for establishment before harvest treatments were imposed.

Experiment (I) studied the influence of plant heights at 1.2, 2.5 and 3.7 m at harvest (plants measured at crest of the most recent fully expanded leaf), two mature stages in October (4.9 m) and a mature stage in December6 (4.9 m, plus inflorescence) on DB yield and ratoon success from 1987 to 1990. Cutting interval for the 1.2 m treatment varied between 7 and 11 weeks. However, the October and December treatments were harvested within f 1 week. All treatments received 25 kg P and 93 kg K ha-’ y-’ plus, S, Fe, Mn, Cu and B at 11.2, 2.8, 1 .O, 0.5 and 0.5 kg ha-’ in March. Nitrogen was applied in single or split applications at 336 kg ha-’ y-’ prior to growth or regrowth of each harvest (Table 1). One of the October treatments received only 168 kg N ha-’ y-‘. Field plot layout was a randomized complete block with six harvest treatments and four replications. Each plot treatment was 4.5 x 4 m with a 3 m border. Biomass from a 1 x 3.1 m strip was harvested to a lo-cm stubble and weighed. A 1 kg sub-sample was chopped into 2.0 cm pieces or less and dried at 60°C for dry matter (DM) and DB yield and analyzed for total N.‘,*

Experiment (2) was established to monitor changes in tiller density, LAI, quantity (percent- age on a DM basis) and crude protein (CP) and in vitro organic matter digestion (IVOMD) (estimate of soluble cell solids) of plant green leaf (GL), dead leaf (DL) and stem (S) at 0.6 m increments to a final height of 4.3 m.

The field plot layout was a randomized complete block with seven harvest treatments and four replications. Each plot measured 4.5 x 2 m. All treatments received 336, 25 and 93 kg ha-’ y-’ N-P-K, respectively, in one spring application. An area about 1.1 m* containing two plants was clipped to the soil

Harvest management effects on quantity and quallity of Erianthus plant morphological components 53

surface when plants attained a 0.6 m height and thereafter at 0.6 m increments to a final height of 4.3 m. At each harvest height all,tillers were clipped from the 1.1 m’ area with about 25% of the total tillers by weight separated into GL, DL and S. Both GL and DL were separated at the collar region. The leaf sheath was considered part of the S. Weights of the three plant parts were recorded and dried at 60°C to calculate percentage DB of plant parts and percentage of each plant part on a DB basis. Percentage of each plant part was calculated by dividing the dry wt of the plant part by the total dry wt of the three (GL, S and DL) plant parts. A sub-sample of dried GL, S and DL and whole plant was ground to pass a l-mm stainless steel screen and analyzed for total N (N x 6.25 = CP), and IVOMD.”

Pooled-year analyses were performed when year by treatment was not significant (P > 0.05). Polynomial equations were esti- mated for each year if the year x treatment (plant height at harvest) interaction was significant (P < 0.05).

3. RESULTS AND DISCUSSION

3.1. Dry biomass yield (Experiment (1))

Dry biomass yields were not consistent over years, resulting in a significant (P < 0.05) treatment x year interaction. Harvesting Eri- anthus at a height of 1.2 m produced lowest yields for each year and a 4-y average yield of 5.2 Mg ha-’ (Table 1). There was a 100% yield reduction and 100% stand loss, because plants died after the second ratoon year (1989). Continuously harvesting these tall growing plants at the 1.2 m frequency also tends to be detrimental to energycane and elephant- grass.‘o. Il. I3 Generally, all treatments from the 2.5 m plant height to the mature stage in December produced respectable DB yields averaged over 4 y. Delaying harvest until the mature stage in October or December (4.9 m plant height) yielded 4-y averages of 46.8 and 51.5 Mg ha-’ DB (P < 0.05) respectively. Har- vesting the tall grass at the mature stage in October and December resulted in a 2 and 0% plant stand loss after four harvest years, respectively (Table 1). Earlier studies with energycane (Sacchrum sp.) revealed that the same two mature treatments were also the most persistent after 4 y of harvest.“,” Generally, tall grasses tend to decline gradually in DB

production from initial harvest year through second or third ratoon years. However, Erianrhus IK 76110 DB yield for the 2.5 or 3.7 m harvest treatment did not decline. The maximum yield reduction was 33 and 28% for the October 336 kg N ha-’ and October 168 kg N ha-‘, respectively. Even with the 33 and 28% yield reduction average drop in DB (October) these treatments still produced a 4-y average yield of 46.8 and 34.7 Mg ha-‘. Decreasing total N rate from 336 kg ha-’ to 168 kg ha-’ y-’ for the mature stage in October resulted in a decrease (P < 0.05) in average DB from 46.8 to 34.7 Mg ha-‘, respectively (Table 1). Average dry biomass yield was 12.1 Mg ha-’ y-’ higher for the 336 kg N ha-’ compared with 168 kg N ha-’ treatment.

Nitrogen content in the above-ground biomass was 3.0 g kg-’ on a DB basis for both 336 and 168 kg N ha-’ rates. Respective N uptake in the above-ground tissue was 42 and 62% for the 336 and 168 kg N ha-’ rate (data not shown). The N uptake is much lower than that calculated for energycane US 72-l 153, which averaged 72 and 95% for the 336 and 168 kg ha-’ N rate,14 respectively and 87 and 83% for the 336 and 168 kg N ha-’ rate, respectively, applied to energycane L 79-1002.‘” Nitrogen content in DB tissue of Erianthus harvested at a 1.2 m height and fertilized annually with 336 kg ha-’ N averaged 14 g kg-’ over a 3-y period, and generally decreased as plant height at harvest increased to the mature stage. They averaged 7, 11 and 3 g kg-’ at harvest treatments of 2.5, 3.7 m and all mature stages, respectively. Harvesting Erianrhus at the mature stage in October or December, plus an annual application of 336 kg N ha-’ yielded 3.0 g kg-’ N in DB tissue. Harvesting these plants at a less mature stage (3.7 m) produced 37.5 Mg ha-’ DB with an average N tissue content of 11 g kg-‘. This Erianthus harvest treatment not only produced good DB yields but high tissue N content, which may yield additional biological methane.” Research indi- cated that by increasing N concentration in growth media, methane yield from whole plant water hyacinth [Eichhornia crassipes (Mort.) Solms] also increased.

Most tall grass species, including energycane US 72-l 153,14 L 79-1002,‘” and Erianthus, will not tolerate continuous harvesting at an immature (1.2 m) stage. Plants will survive this type of intense harvest regime for one or two ratoon crops, producing significantly lower DB

54 P.MISLEVY et al.

yields followed by death. Since the biomass -1237 y - 47.3 + 27.7H - 16.7H * R’= 0.47

industry needs a continuous supply of feed +to80 y = 75.4 + 71.3H - 30.5H2 I@= 0.68

stock, there will be times when immature Eriunthus will need to be harvested. However, if 2501 H=Plnthshht 2

the dangers from harvesting plants at the immature stage are not recognized, plant stand reductions of 87-100°~‘o (Table 1) can occur after 34 y of harvesting. Therefore, harvesting energycane”, ” and Erianthus at the mature stage in October (4.9 m) or December (4.9 m) generally results in highest DB yields, lowest

0’ 0 0.6 1.2 1.8 2.5 3.1 3.7 4.7

yield reduction (compared with the initial Plant height (m)

harvest year) and lowest plant stand loss after three ratoon years.

~1907 y = 52.8 + 16.2H - 14.1H2 R’= 0.59

3.2. Tiller density (Experiment (2)) -=-I~38 y = 58.1 + 152SH - 150.2H2+ 33.6H3 I?‘= OBQ

The influence of harvest treatments on total H-Plrvrthsioht

tiller density was not consistent over years, 150

II I 2 resulting in a year x harvest treatment (P < 0.05) interaction. Harvesting plants at increments of 0.6 m followed a quadratic response increasing in total tillers until it peaked at 1.8 m followed by a curvilinear decline for both 1987 and 1988 (Fig. I). Total tiller number 01

peaked at E 59 and 108 tillers 1.1 m-2 for 1987 0 0.6 1.2 1.8 2.5 3.1 3.7 4.3

and 1988, respectively and live tillers at a plant Plant height (m)

height of 1.2 m (57 and 103 tillers for 1987 and 1988, respectively). There was a gradual decline to an average of 25 live tillers 1.1 me2 at a 4.3 m

1088 y=-3.3+16.!3H R’= 0.43

H==Plantheiaht plant height (Fig. 1). The live tiller and total 2

tiller number were equal at the 1.2 m plant “I height, however, as plants continued growth light decreased within the canopy causing some developed tillers to become necrotic and die. Dead tiller density increased linearly as plant height at harvest was delayed from 0.6 to 4.3 m. As plants grew throughout the season a few

;I / 0

tillers became dominant, reducing the light 0.6 1.2 1.6 2.5 3.1 3.7 4.3

penetration into the canopy resulting in death of Plant height (m)

the shorter (15-30 cm) tillers. Harvesting plants Fig. 1. Change in total, live and dead tiller number 1.1 mm’

at the 0.6-1.2 m plant height have less of Erinnthus as plant height at harvest increased from 0.6 to 4.3 m, 1987 and 1988.

vegetative canopy and more solar radiation reaching the soil surface, and consequently develop and retain tiller density. the senescence of bottom leaves, since all N

(336 kg ha-’ y-‘) was applied in late March. 3.3. Leaf area index

Leaf area index was independent of year and 3.4. Quantity of plant components

increased quadratically (P < 0.05) to 17 at a Percentage GL plant component was depen- plant height of 3.1 m followed by a gradual dent on year and decreased quadratically decline to 11 at a mature plant stage of 4.3 m for (P < 0.05) as plant height increased from 0.6 to both 1987 and 1988 (Fig. 2). This decline is due 4.3 m (Fig. 3). Approximately 72% of Erianthus to the senescence of bottom leaves, partially due IK 76-l 10 consisted of GL at the 0.6 m plant to insufficient light penetrating the dense leaf height. Delaying harvest from 0.6 to 4.3 m canopy. Lack of N at this physiological stage of resulted in a 79.6% decrease in GL. The leaves development may also be partly responsible for that remained green were near the top of the

Harvest management effects on quantity and quallity of Erianfhus plant morphological components 55

plant canopy. One reason for the major decline in GL is the shading effect created by the dense tall grass (4.3 m) canopy.‘4.‘6

The S component of Erianthus depended on year and increased quadratically (P < 0.05) as plant height increased (Fig. 3). The S com- ponent increased from an average of 29% for the 0.6 m plant height to 70% of the whole plant on a DB basis for the 4.3 m plant height. These values are similar to those obtained for L 79-1002 and US 72-l 153 energycane.14,16 As plant height increased from 0.6 to 4.3 m, total leaf canopy also increased as evidenced by the increase in LAI. However, as leaf canopy continued to increase light reaching the base of the canopy was reduced, resulting in a linear increase in the DL plant component (Fig. 3). Only about 0.2% of the whole plant consists of DL at a plant height of 0.6 m. This value then increases to 16% DL of the whole plant at the 4.3 m plant height. Unlike elephantgrass (Pen- nisetum purpureum Schum.) dead leaves of Erianthus tend to cling to the standing plant allowing them to be harvested as a biomass feed stock.

3.5. Quality oj’plant components

Crude protein concentration in the GL of Erianthus was dependent on year and decreased quadratically (P < 0.05) as plant height at harvest increased from 0.6 to 4.3 m (Fig. 4). Harvesting plants initially at a 0.6 m height contained an average CP concentration in GL of 170 g kg-‘, which continued to decrease to 55 g kg-’ as plant height increased to 4.3 m. This decrease in CP of GL may be due to the gradual decrease of N content in the soil, since 336 kg N ha-’ was applied in one application 7

1987 and 1088

Y = -6.4 + 33.2H- 11.7ti Iv= o.@a H=eiaabam

18 2

18 14

12 \

-

’

10

8 6 4 2

/-

0 0 0.8 1.2 1.8 2.5 3.1 3.7 4.3

M h&W (m)

Fig. 2. Influence of plant height on leaf area index (LAI) of Erianthus during 1987 and 1988.

-cl887 y = 88.13-8l.28H + 13.3QH2 IV- 0.87 +1288 y = 90.88-(P.24H + ll.8DH2 R2 = 0.08

H=J?UtM&U 2

“0 0.6 1.2 1.8 2.8 3.1 3.7 4.3

Plant height (m)

+1Q87 y = 13.84 + 57.lOH - 14.88H2 I?= 0.88

+1988 y = 15.05 + 42.36H - 7.71H2 R’ - 0.07

H =J?bUmkU

100 2

I

:I 0 0.8 1.2 1.8 2.5 3.1 3.7 4.3

Plant height (m)

1987 md 1888

y = - 2.861 + O.OH R2 - 0.83

HaPlant 2

” -~~

0 0.6 1.2 1.8 2.5 3.1 3.7 4.3

Plant height (m)

Fig. 3. Change in percentage CL, DL, and S on a DB basis as plant height at harvest of Erianfhus increased from 0.6 to

4.3 m, 1987 and 1988.

months prior to the 4.3 m harvest for both 1987 and 1988. It also may be due to normal reduction attributed to DM increase (dilution effect).

Crude protein concentration in the S was year dependent and decreased quadratically (P < 0.05) as plant height increased (Fig. 4). Stem CP concentration averaged 166 g kg-’ when harvested at the 0.6 m plant height, and decreased 86% to 23 g kg-’ when harvest was

56 P.MISLEVY et al.

delayed to a plant height of 4.3 m. This 166 g kg-’ CP concentration at the 0.6 m plant height was 51% higher than the CP concen- tration in energycane entries14, I6 harvested at the same stage. However, the CP decline in S with maturity followed a similar pattern (79 and 86%) for Eriunthus and the energycane en- tries.14. I6

The CP concentration in the DL portion of the plant was independent of years and declined linearly (P < 0.05) as plant height at harvest was delayed (Fig. 4). The CP concentration in

--I987 y = 240.7 - 247.7H + 14Q.9H2- 3f3.7H5 d = 0.82

*lo88 y = 205.4 - 159.8H + 42.8H= Ra= o.Q3

H=Plantheiaht 2

_- 2501

d 0’ 0 0.6 1.2 1.8 2.5 3.1 3.7 4.3

Plant height (m)

+I987 y = 240.2 - 25Q.2H + 74.4l-I ’ R*= 0.96

*IQ08 y = 255.4 - 351.4H + 17Q.8H2- 31 .4H5 Fl*= 0.88

H =Plant 250

2

-I zj 1 0 0.6 1.2 1.3 2.5 3.1 3.7 4.3

Plant height (m)

IQ87 and 1988

Y = 84.77.2Q.iH Rl= 0.74 H=J?b&h&@

80 70

60 50 40 SO 20 10

0 0 0.6 1.2 1.8 2.5 3.1 3.7 4.3

Plant height (m)

4. Influence of plant height at harvest on CP concentration of GL, DL and S for Eriunthus, 1987 and

1988.

+I 987 y = 700.8 - 652.QH + S48.4H z 60.75H ’ Ra s 0.~8

+tQ88 y = 880.8 - 480.3H + i2Q.4H2 R’s 0.W

[; 7 5:

1

6 ‘frL 0 0.6 1.2 1.8 2.5 9.1 3.7 4.3

Plant height (m)

-1887 y’ 610.3-40.1H-lQ7.5H2+ 68.2H= R*=O.g7

-IQ!38 y-731.3-S40.QH+50.8H2 R*= 0.98

H=

7001 2

0 0.6 1.2 1.8 2.5 3.1 3.7 4.3

Plsnt height (m)

y = 450.3 - 224.1 H + 46.OH * R* = 0.80

y = 344.0 + 203.7H - 377.3H2+ 100.1 Ha R* = 0.82

H==lWlLWIM 600 2

500

0’ 0 0.6 1.2 1.8 2.5 3.1 3.7 4.3

Plant height (m)

Influence of plant height at harvest (1987 and 1988) on IVOMD of GL, DL and S of Erianthus.

the DL was 76 g kg-’ when harvested at the plant height of 0.6 m. Delaying harvest until plants attained maturity (4.3 m plant height), resulted in a 70% decrease in CP concentration to 23 g kg-‘. Similar results were obtained for L 79-1002 energycane.16 Results indicate the CP in DL is about 50% of the CP in GL. This may indicate about half the N content in GL is translocated from senescenesing leaves to develop GL.

The IVOMD of the GL plant component was year dependent and decreased quadratically (P < 0.05) as plant height increased from 0.6 to 4.3 m (Fig. 5). Green leaf from plants harvested

Harvest management effects on quantity and quallity of Erianthus plant morphological components 51

ise7y=251.3-24Q.1ciH+70.wHz RZ=0.E16 H=PlanthaiaM

2 f 180 5 is0 a 120

i raO d” 6a

g so L

”

0 0.6 1.2 1.8 2.5 3.1 3.7 4.3 Ptant height (m)

1087 y = 008.1 - 260.7H + 61.24HS R’= 0.95 H=PLanthdaht

2

- 0 0.6 1.2 1.8 2.5 9.1 3.7 4.3 Plant hdght (m)

Fig. 6. Change in CP concentration and IVOMD (1987) of whole plant Eriandms as plant height at harvest increased

from 0.6 to 4.3 m.

at the 0.6 m height averaged (2 y) 534 g kg-’ IVOMD. As plant height increased from 0.6 to 4.3 m IVOMD of GL decreased 50% or 44 g kg-’ for each 0.6 m increase in plant height. The GL IVOMD dropped to or below 300 g kg-’ when plants attained a height of 2.5 m or higher. These values are about 100 g kg-’ lower than those from energy- cane,‘4,‘6 which may indicate higher concen- trations of fiber in the GL tissue of Erianthus.

The IVOMD of the S, like that of the GL, depended on years and followed a quadratic decrease as plant height increased (Pig. 5). Stem IVOMD averaged 612 g kg-’ when harvested at 0.6 m plant height, which was similar to energycane entries.14. I6 At this 0.6 m stage the plant averages about 29% stem (Fig. 3). Plant height and stem percentages continue to increase to a final value of 70%; IVOMD decreases about 58 g kg-’ for each plant height increment to a low of 264 g kg-’ at the 4.3 m plant height (Fig. 5). This drastic decrease in S IVOMD was similar for L 79-1002 energycane,” however, the decrease of S IVOMD for energycane US 72- 1153 was much less averaging 35 g kg-‘.14

Dead leaf IVOMD was year dependent and decreased quadratically (P < 0.05) as plant height at harvest increased from 0.6 to 4.3 m. The DL component of the plant generally had the lowest IVOMD when compared with the GL and S plant parts (Fig. 5). Dead leaf IVOMD averaged 375 g kg-’ with 0.6 m plant heights and decreased 60% to 150 g kg-’ with 4.3 m plants. Low IVOMD values for DL may not be extremely important since only 20% of the plant consists of the DL component.

The CP concentration and IVOMD of whole plant samples both decreased quadratically (P < 0.05) as plant height increased from 0.6 to 4.3 m. The CP concentration decreased 81% between the 0.6 and 3.7 m plant height or a decrease of 30 g kg-’ for each 0.6 m increase in plant height to 3.7 m (Fig. 6). The IVOMD of whole plants also decreased as plant height rose from 0.6 to 4.3 m. This 47% decrease resulted in 42 g kg-’ decrease for each 0.6 m plant height increase. As Erianthus plants mature there is a greater decrease in whole plant CP and IVOMD when compared with energycanes.14, I6

4. SUMMARY

Erianthus harvested at the mature stage in October (46.8 Mg ha-’ y-‘) and December (51.5 Mg ha-’ y-‘) produced highest (P < 0.05) average DB yields after three ratoon harvest years. Harvesting Erianthus at a height of 1.2 m resulted in a loss of stand, therefore, a 100% yield reduction after three ratoon harvests (Table 1). The yield reduction after three ratoon years was lowest for Erianthus averaging 27% over all harvest treatments compared with 33% for US 72-l 153” and 56% for L 79-1002.” Plant stand losses for the October and December harvest treatments were 2 and O%, respectively. Leaf area index followed a similar pattern over 2 y with a maximum of 17.2 achieved at 3.1 m plant height. The stem component of the mature plant averaged 70% with the green and dead leaf portions of the plant equally divided at about 15%. Crude protein content and IVOMD of mature plant parts were generally low, ranging from 23 to 55 g kg-’ and 200 to 300 g kg-‘, respectively. Knowing the quantity and quality of plant components can be important to biomass producers who need to make logical field harvest decisions. Harvesting immature plants containing high CP and IVOMD following a freeze ( I 0°C) may be a better choice for methane production than

58 P.MISLEVY et al.

mature plants with low CP and IVOMD. 5. Mature plants containing about 70% stem may be better material for stockpiling biomass in the 6.

field. This stockpiled feedstock can be used during 7.

the cool and/or dry periods of the year. If immature biomass plants (1.2 m) must be 8, harvested, remove only 2535% of the crop land area at the immature stage allowing regrowth from those plants to become mature. This harvest technique may allow a continuous

9.

year-around supply of feed stock with minimal stockpiling. IO.

Ackno~~,led~emenrs-This research was funded in part 11. through an agreement between the Institute of Food and Agricultural Sciences (IFAS), University of Florida and the Gas Research Institute (GRI), Chicago, IL, U.S.A.

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