PERGAMON
Biomass and Bioenergy 16 (1999) 51±59
Harvesting of cotton residue for energy production
T.A. Gemtos a, *, Th. Tsiricoglou b
a
Laboratory of Farm Mechanisation, University of Thessaly, Pedio Areos, 38334 Volos, Greece
b
TEI of Larissa, 41110 Larissa, Greece
Abstract
The possibility of collecting cotton stalks in Greece and using them for energy production was investigated. The
production and properties of cotton stalks were studied and a system for collection of the aerial part is proposed as
a feasible solution to avoid wet conditions under the local climate. A successful method for collection and
packaging of the residue was applied, using conventional but highly advantageous equipment, o€ering reduced
investment cost and use of existing machinery. The energy required to harvest cotton stalks was measured by an
instrumented tractor. The tractor was able to measure the developed forces between tractor and implement, the
power absorbed through the PTO, as well as tractor velocity and fuel consumption. The energy consumed for the
operation was calculated and when compared to the energy of the biomass collected gave a positive balance. The
work proved the feasibility of harvesting cotton stalks using conventional machinery giving the possibility to collect
energy material with a total energy content of 500,000 tons of oil equivalent at national level. # 1999 Elsevier
Science Ltd. All rights reserved.
Keywords: Biomass; Cotton stalks; Residue harvesting; Energy
1. Introduction
During recent decades, biomass use for energy
production has been more and more proposed as
a substitute for fossil fuels. Biomass, as a zero
CO2 emission fuel, can o€er an immediate solution in the reduction of CO2 atmosphere content. Although energy crops can o€er a basis for
larger energy producing plants, the use of crop
residues can o€er a more immediate source of
biomass for energy production in small installations. The economics of a system which produces
* Corresponding author. Tel. 30-4216-9781; Fax: 30-42163383; E-mail: [email protected].
energy from crop residue highly depends on the
cost of collection, transportation and storage of
the raw material. It is probably true that
specially constructed machinery could give, in the
long run, the best results. However, at the initial
stages of the residue use the purchase of new
equipment would increase the cost of operation
with an unknown acceptance by the end user.
Therefore the best solution to promote biomass
utilisation is to employ, when possible, existing
equipment for the collection of the raw material.
Cotton is cultivated in Greece in more than
400,000 hectares [14]. It is harvested by cotton
pickers between the end of September and the
beginning of December leaving stalks in the ®eld.
0961-9534/99/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved.
PII: S 0 9 6 1 - 9 5 3 4 ( 9 8 ) 0 0 0 6 5 - 8
52
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
Climatic data in the cotton growing plains of
Greece show that there is considerable rainfall at
the end of the harvesting period. Greek farmers
usually chop the stalks by cotton shredders and
the residue is then incorporated into the soil by
ploughing. Only a few farmers leave the stalks
uncut and drill winter cereals without any
tillage [1]. The latter is mostly applied during
very wet years. Cotton stalks are a residue, which
is left unused for the time being, but has the potential to be used as biomass for energy production or as raw material for other industries.
Ebeling and Jenkings [2] studied the physical
and chemical properties of di€erent crop residues. For cotton stalks the following values were
obtained: higher heating value 15.83 MJ/kg; volatile 65.40%; ash 17.30%; carbon fraction
17.30%. The stoichiometric analysis of the stalks
gave C 39.47%, H 5.07%, O 39.14%, N 1.20%,
S 0.02%, residue 15.10%.
Sumner et al. [3] have reported, the gross heat
of combustion to be 18.1 MJ/kg and 18.4 MJ/kg
for dry cotton stalks and roots respectively.
Sumner et al. [4] have done a study of the parameters needed for the design of a cotton stalk
puller. They quoted from Demian an average
pulling force to uproot cotton stalks of 903 N
with maximum 1188 N and from Colwick an
average uprooting force of 489 N. They reported
that the cotton stalk mean diameter was 13 mm
(12±14 mm). The average pulling force was
found [4] to be 317 N (256±373 N). Sumner et
al. [5] measured the moisture content of the
stalks (average 42.7% wb, range 23±62.3% ) and
of the roots (average 60.8% range 53±64.4%).
Dry matter yield was 4.42 t/ha with range of 3±
7.04 t/ha. Roots were 23.2% of the whole plant
in average with the measured values ranging
between 14.3 and 29.1%. In the same experiment
the moisture content was found to drop from
50% to under 20% when the stalks were left in
the ®eld, after uprooting, for three weeks.
Sumner et al. [4±6] have suggested a method to
harvest cotton stalks by uprooting them. They
constructed a machine with two rubber wheels
turning in opposite directions. The wheels
trapped the stalks and, as they turned, uprooted
them. The stalks were then left on the ground
surface to dry and were collected after remaining
there for two weeks. The soil which remained on
the roots when uprooted was dried and mostly
removed due to the movement of the balling machinery. This drying period permitted the collection of the residue quite free of soil. However,
there was no exact estimation of the amount of
the soil collected with the residue. Similar processes were also used by Kemp and Matthews [7]
and the NIAE in Sudan and by others [4].
Coates [8] reported results of a research of cotton
stalks harvesting systems in Arizona, USA. He
used two machines that undercut the plants
before they pulled them o€ the ground, leaving
most of the root in the soil. One system chopped
the material immediately after pulling while the
other left it on the ground before chopping or
packaging it. Packaging was carried out by
round balers or seed cotton module builders.
Coates found the e€ective cotton stalks yields to
range from 2.34 (chopped by ¯ail mower) to 5.7
t/ha (for hand harvested). Soil contamination
ranged from 0.9 to 7.7% while total energy
required for harvesting ranged from 47.9±52.1
kWh/ha or 8.6±10.9 kWh/t dry matter.
In the literature cited cotton stalks were harvested by uprooting them. In most cases, the
local climate allowed sucient time for the
uprooted plants and the soil stacked on the roots
to dry. As a result of these conditions, the cotton
residue could be collected dry enough for storage
and without signi®cant soil impurities. In Greece,
however, it is unusual to experience continuous
periods of dry weather as required by the previously described procedure. In anticipation of
the wet period of the year, farmers plough their
®elds for the next crop as soon as cotton is
picked, so that their ®elds are not too wet for
ploughing. It is well known that ploughing under
wet conditions causes compaction that deteriorates the physical properties of soil and adversely
a€ects crops [9].
In order to investigate the possibility of using
cotton stalks for energy production under Greek
conditions, a research programme was undertaken. The objectives of the programme were:
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
(a) to quantify the yield of cotton stalks and its
potential in Greece;
(b) to study the physical properties of cotton
residue;
(c) to identify and propose a procedure for harvesting cotton stalks;
(d) to investigate the possibilities for storing the
material in a simple and economical way;
(e) to study the energy budget and the economics
of harvesting cotton stalks; and
(f) to investigate possible utilisation methods of
energy production by burning.
The present paper reports some of the results
obtained during the project, which was funded
by the Greek Ministry of Education.
2. Material and methods
2.1. Theoretical and preliminary tests
The size of the stalks, their distribution, their
properties in the ®eld and the yield were studied
after seed cotton picking. Rows of 2±10 m length
(cotton is cultivated in rows of 0.95 to 1.00 m
apart) were studied in di€erent ®elds in central
Greece. The diameters of the stalks at soil level
and at a height of 0.05 m from the soil level (the
height a mower cuts the stalks) and their height
were measured. The plants in a row were then
uprooted and without any disturbance of the soil
stacked on the roots were placed in bags. The
bags were weighed in a laboratory. Then the
stalks were removed from the bags and samples
were taken from di€erent plant parts for moisture content determination. They were placed in
an oven to dry at 728C for 48 h. The soil was
then removed from the roots by washing it with
water and its percentage in the total weight was
estimated. The Higher Heating Value was estimated from samples taken from freshly uprooted
plants. The measurements were made using an
IKA 400 adiabatic bomb calorimeter. The material was dried in an oven and divided into
roots, stalks and branches and bolls. Then a mill
ground it and 1 g samples were formed by a
special small, hand operated press. The material
53
was burnt in the oxygen enriched atmosphere of
the bomb of the calorimeter.
Additionally, uprooting of the stalks was carried out to study the uprooting forces. Uprooting
was performed using a small vice and the
hydraulic system of a tractor. Each stalk was
clamped in the vice and pulled out of the soil by
the upward movement of the three-point linkage
of the tractor. A mechanical balance did the
force measurement and it was recorded by a
video camera.
Based on observations of the amount of the
soil stacked on the roots during ®eld work, it
was decided to investigate the possibility of collecting only the aerial part of the residue, leaving
the roots in the ®eld. It was anticipated that the
collected material would be free of soil and with
less moisture content. These factors would make
its storage easier and its use for energy production by burning more attractive.
Based on the analysis and the measurements of
the strength of cotton stalks and the friction
properties between cotton stalks and mower
knife [10] the feasibility of using existing farm
machinery was investigated. The cutting resistance encountered by the mower during hay cutting (grasses or legumes) is estimated from
Kepner et al. [11]. They quoted from Elfes an
average PTO power for cutting mixed hay of 1.9
kW at a speed of 7.9 km/h. Part of this power,
0.89 kW, was due to cutting resistance of the
plants. From measurements of cotton stalks
strength, carried out during the present
investigation [10], the following equation giving
the energy required for cutting the stalks as a
function of their diameter was found:
WORK = 4.71 + 0.78*DCUT with r2 = 0.69
where: WORK is the energy required to cut
the stalk in J,
DCUT stalk diameter at a height 0.05 cm from
the ground in mm.
According to this equation a stalk with base
diameter of 10 mm requires 12.51 J to be cut.
Based on the plant base diameter distribution
found from the ®eld measurements and assuming
a cotton plant population of 100,000 per hectare
or 10 plants per meter on the row, the total
work which is needed for cutting 2 m of row is
54
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
approximately 750 J. Given that only two rows
can be cut down by a 1.70 m working width
mower, the total power requirements for a working speed of 2 m/s, are 1500 J/s or 1.5 kW. This
means that the mower will encounter resistance
of the same order cutting two rows of cotton as
cutting grass at a width of 1.70 m and the same
speed. The di€erence will be in the concentration
of the load, which in the case of the cotton stalks
harvesting, will be only applied on two knives. It
was concluded that a mower with reciprocating
knives could be used without the risk of any
damage, apart from a minor possibility of
damage to the knives due to the concentration of
the load. To illustrate this, a reciprocating knife
hay mower was used to cut cotton stalks of two
rows at a speed of about 2 m/s. The machine
worked well, with a slight deterioration of the
knives. That means that the mower should be
used with stronger knives, possibly with teeth.
The stalks cut by the mower were left on the soil
surface. A rotating head rake was used to collect
more material in one row. The rake worked well
and collected four rows in one, in one run.
Actually only two rows were moved on top of
the other two.
From the beginning of the project, the use of a
hay baler for small square bales which was
widely used in the area, was rejected for packaging the cotton stalks. It appeared rather dicult
for stalks with high moisture content to be fed
into the compression chamber and to be cut by
the ram knife. Additionally the material had high
density, which would cause heating and destruction of the material. Some preliminary tests
showed the diculties in using it. Two additional
possibilities were also investigated. The ®rst was
a special machine which gathered vine prunings
and packed them into round bales of 0.50 m in
diameter and length. In the ®rst experimental
year, the stalks used for the analysis of their
properties were fed into the machine.
The machine worked well and formed bales of
about 10 kg. The bales were loose enough and
the moisture content of the stalks dropped from
about 40% to under 20% w.b. in less than 20
days without any warming of the material. Bales
left outdoors proved that they absorbed water
easily after a rainfall but under Greek climatic
conditions they dried again within 10 days. These
bales could be handled easily by hand and fed
into a bunch shape biomass boiler. In the second
year, the machine was used to collect material
immediately after cutting. It proved that there
were a lot of blockages due to the high moisture
content of the stalks which blocked the pick-up
and made baling impractical.
The second machine used successfully was a
Claas Rollant 44 round baler with a ®xed
chamber and metallic rollers. The wrapping material was a plastic net. The machine worked well
during the second year just after the cutting of
the stalks, producing bales with dry matter of
about 190 Kg. The bales were 1.20 m in diameter
and in length and could be handled by a front
tractor end fork lifter and transportable by a
platform.
2.2. Field trials
A ®eld application of the method was carried
out in 1994 in order to prove the feasibility of
harvesting cotton stalks by conventional machinery, assess their performance and measure the
energy required. Harvesting was applied in a 1.4
ha ®eld using the machinery shown in Table 1.
The particular ®eld is typically representative of
the area.
During ®eld work the performance of the machinery used was monitored and their eciency
was determined. An instrumented tractor
described by Gemtos and Tsiricoglou [12] and
Tsiricoglou and Gemtos [13] was used to measure
the forces developed during the work, the power
Table 1
Farm machinery used for harvesting cotton stalks
Machinery
Speci®cation
Tractor
Mower
Raker
Round bales baler
Two wheel drive, 50 kW
Reciprocating knives, 1.70 m width
1.70 m width
Bales 1.2 m in diameter and
height, with plastic net wrapping
Mounted on tractor
Carrying up to 8 bales
Fork lifter
Platform
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
55
Table 2
Size of cotton plants and their distribution in the ®eld (in mm)
Year
Diameter
at soil
level
mm
Diameter
at
soil
level
mm
Diameter
at 0.5m
height
mm
Diameter
at
0.5m
height
mm
Distance
between
plants
mm
Distance
between
plants
mm
Height of
plants
mm
Height
of
plants
mm
1st
mean
11.7
st dev
1.9
mean
9.5
st dev
1.6
mean
NR
st dev
NR
mean
NR
st dev
NR
2nd
14
3.3
11.9
3
14.1
5.3
934
134
requirements and the fuel consumption. The tractor had six loading cells (three measuring horizontal forces, two vertical and one side forces)
measuring the forces in the space. Additionally a
torque and rotation frequency meter was
installed on the PTO shaft of the tractor to
measure the power absorbed through PTO.
Analogue signals after ampli®cation were converted to digital by an A/D converter and
recorded by a portable PC. Samples were taken
at 1000 s/s for each transducer. A fuel discharge
meter and a radar type linear velocity meter were
installed. Mean values of fuel consumption and
speed were given on a liquid crystal display as a
mean for each run. Based on the recorded
measurements the energy budget of cotton stalks
harvesting was determined.
3. Results and discussion
3.1. Theoretical and preliminary results
The results of cotton stalks size, water content
and yield, as well as the soil stacked on the roots
during uprooting, are summarised in Tables 2±4,
for two years of measurements. It is clear that
cotton stalks were quite di€erent during the two
studied years. It is also clear that large amounts
of soil were stacked on the roots when pulled by
hand. If collected immediately the movement will
remove a part of the soil caused by the harvesting equipment. Even if most of the soil is
removed a considerable amount will remain and
be collected with the plants, which would even-
Table 3
Distribution of the stalk diameter at a height of 0.05 m
Diameter range
in mm
Frequencies %
1st year
Frequencies %
2nd year
5±6
6±7
7±8
8±9
9±10
10±11
11±12
12UP
6.2
7.5
7.5
18.8
28.8
10
17.6
3.7
0
0
13.3
6.7
13.3
14.7
34.7
17.4
tually cause problems in the energy conversion
plant. This e€ect is indicated by the reported
research, where the stalks remained in the ®eld
for long periods not only for the stalks to dry
but also the soil, which then would be easily
removed. The results of the higher heating value
measurements are shown in Table 5. In Tables 5
and 6 the yield of the stalks and the roots are
presented. Total yield averaged 3,144 kg/ha, of
which 2,547 kg/ha were the aerial part. Mean
water content at the end of the harvesting period
Table 4
Amount of Soil stack on the cotton roots when uprooted
a/a
Mean
Range
Soil weight on
the root
Soil
Moisture
content
Percent of the soil
on the weight of
the whole plant-soil
g
1377
200±2419
%
23.6
22.9±24.1
69.3
58.0±79.1
56
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
Table 5
Higher heating value of cotton residue (mean values for
measurements of several years)
plant part
Dry matter
yield
kg/ha
Higher heating
value
MJ/Kg
Moisture
content
%
Bowls
Stalk and branches
Total aerial part
Roots
Total aerial part
440
2107
2547
597
3144
17.5
18.1
18.0
18.3
18.05
25.4
44.80
41.5
58.40
44.71
was 41.5% for the aerial part and 54.8% for the
root. The reported dry matter yields of cotton
stalks varied from 2.3 to 5.7 t/ha with water content mean 34.9% and range 23.3±41.4% [8].
Sumner et al. [6] reported yields ranged from 3
to 7 t/ha (including roots) with water contents
ranging from 23.2% to 62.3% for stalks and
from 53% to 64.4% for roots in the period
between mid November till end of February.
The Greek results are similar to the results of
Sumner et al. [6], showing that a considerable
amount of energy could be produced by cotton
stalks, which can give about 1250 kg of diesel
equivalent per ha or a total of 500,000 tons of oil
equivalent for the country. Total Greek energy
consumption in 1991 was 22,214,000 tons of oil
equivalent [14].
The results of the uprooting force from two
years of measurements are shown in Table 7.
According to the results obtained, when cotton
residue is harvested by uprooting the plants, a
large amount of soil will be collected with it
unless a rather long drying period in the ®eld is
available. It appears to present a problem with
Greek farmers who cannot delay soil tillage for
the next crop until the soil stacked on the roots
is dry enough to be easily removed. Although
during collection of the stalks some of the soil
will be removed at any case, a considerable
amount will remain stacked. This amount of soil
will eventually cause problems in the work of
any burner and of any system for biomass conversion.
3.2. Field trial results
During ®eld trials the experiment ®nished in
one day. Fifteen bales were formed weighing
4923 kg of fresh material (2880 kg of dry matter)
with a water content at 41.5%. During the work
the performance of the equipment was monitored
as well as their power consumption. The results
on the performance of the machinery as well as
their energy consumption during the work are
Table 7
Uprooting force for cotton stalks
Year
a/a
Mean diameter
soil level
mm
Mean diameter
05 m height
mm
Pulling
Mean
N
1st
Mean
Range
Mean
Range
11.7
11.5±11.7
14.2
13.8±14.8
9.5
9±10
11.8
11.4±12.3
333
278±389
385
376±392
2nd
Table 6
Cotton residue production. Samples collected by hand
Variable
Mean
Range
Dry matter yield of stalks kg/ha
Dry matter yield of roots kg/ha
Stalks moisture content % mid November
Root moisture content % mid November
Stalks moisture content % mid December
Root moisture content % mid December
Energy content of dry aerial part MJ/ha
Energy content of dry root MJ/ha
Energy content of total dry material MJ/ha
2578
566
50.29
60.6
41.5
54.8
45,836.7
10,925.1
56,762
1168±3391
301±690
39.7±64
52.9±69.5
36.9±52.0
47.8±62.5
21,024±61,038
5,508±12,627
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
57
Table 8
Energy consumed during cotton stalks harvesting
Machinery
Speed
km/h
Pulling
power
kW
Power in
PTO
kW
Fuel
consumption
l/h
Speci®c
consumption
g/kWh
Hay mower
Raker
Baler beginning
Baler end of cycle
Baler mean
Transportation
8.2
8.25
6.5
6.5
6.5
10.1
3.21
2.90
1.13
6.88
4.01
10.4
2.35
2.60
2.71
2.81
2.76
Ð
7.7
6.3
5.2
6.5
5.85
4.8
1100
930
1083
542
812
370
given in Tables 8 and 9. Table 8 presents the
e€ective speed of work, as measured in the ®eld.
Pulling power was calculated from the mean
horizontal force developed between tractor and
implement and the mean linear velocity of the
tractor during the run was measured by the
radar. Power from the PTO was calculated from
the torque and the rotating frequency of the
PTO shaft of the tractor. Fuel consumption was
the mean for each run. Speci®c fuel consumption
was calculated from the fuel consumption and
the total useful power produced by the tractor. It
is clear from Table 8 that a smaller tractor
should have been used for part of the work. This
underused power has caused a high speci®c fuel
consumption. This indicates the diculty of
obtaining optimum results during ®eld work
because there is rarely a close ®t between power
requirements of the equipment and the power of
the tractor. In Table 9 the performance of the
machinery is given. Field eciency coecients
are generally small. For the mower and the raker
Coates [8] found higher eciencies for the machinery used. Hunt [15] gave the eciency coecient range for mowers as 75±89%, for rakers
62±89%, for ¯ail mowers 50±76% and for balers
65±85%. The values of the present work are at
the lower end of the range of the literature which
is reasonable given the small harvested area. In
larger areas, operator experience gained during
the work would increase eciency. The eciency
of the round baler given by Coates is rather high
for conventional machines unless a non-stop
model was used which was not made clear in the
Table 9
Performance of machinery used for cotton stalk harvesting in a ®eld of 1.4 ha
Machine
working power
width
required
measured
by tractor
m
kW
mower
2
raker
4
baler mean 4
transport
full
transport
empty
Total
5.56
5.5
6.77
10.4
theoretical e€ective eciency energy consumption energy consumption energy consumption
®eld
®eld
coecient based on measured based on measured based on measured
capacity
capacity
power requirements fuel consumption
fuel consumption
ha/h
ha/h
1.64
3.3
2.6
1.1
2.3
1.3
67.7
69.70
50
MJ/1,4ha
MJ/ha
MJ/1,4ha
25.47
12.05
26.25
20.3
352.80
215.71
342.26
94.68
493.92
301.99
479.16
132.55
N/A*
84.07
1407.62
Energy of cotton stalks collected: 15 bales *192 kg of dry matter by 18 MJ/kg gives 51840 MJ.
*Measurements during return were not taken due to the high speed. Values of loaded transportation are taken for the return trip.
58
T.A. Gemtos, T. Tsiricoglou / Biomass and Bioenergy 16 (1999) 51±59
paper. In columns seven and nine of Table 9 the
energy consumed for harvesting 1.4 ha of cotton
stalks is given. In column seven the estimation is
based on the net energy consumed by the machinery while the values in column nine include
the energy consumed by the tractor and all its
parts. It is clear that much more energy is consumed to do a ®eld work than it is actually
required by the machinery. This di€erence is
much higher as tractor power is not well matched
to the equipment size. This mismatch is also
apparent from the high speci®c fuel consumption
(Table 8). In this higher fuel consumption is also
included any low eciencies of the tractor engine
due to bad maintenance or settings. However,
that energy is a more realistic estimation of the
energy consumed for any ®eld work and should
be the base for any assessment of the energy budget of cotton stalk collection. It should be noted
that transportation energy is only measured for
the loaded platform as the high speed in the
return trip could damage the instrumentation.
So, a slight overestimation was introduced.
Additionally, energy consumption was not estimated during the pre-compression of the baler by
the hydraulic system of the tractor and during
fork loading and unloading of the bales. Total
direct energy consumed for the ®eld operation is
1407 MJ. In these ®gures, the indirect energy
consumed for the machinery as well as the energy
for lubricants, repair and maintenance etc should
be added to have an exact energy balance. An
analysis of the indirect energy consumed for the
machinery used was given by Gemtos and
Tsiricoglou [16]. In this work the energy
sequested for the construction, maintenance etc,
of the machinery used ranged from 521 to 695
MJ for the 1.4 ha giving a total energy consumption of 1929±2103 MJ. The energy content of the
collected stalks was 15 bales of 192 kg dry matter/bale and heating value of 18 MJ/kg, yield
51,840 MJ, giving a net energy gain of about
49,800 MJ or 35,571 MJ/ha.
The material collected by the baler was 2,880
kg dry matter (15 bales of 192 kg each). With
theoretical yield 3565.8 kg the eciency of collection is 80.8% which is quite satisfactory. In order
to investigate the problems encountered during
storage, the bales were stored outside and inside
a barn. In both cases, the bales were dried to a
water content of less than 20% w.b. in 20 days
of outdoor storage without any heating of the
material. Cotton stalks are covered at the base
by a cork layer which prevents moisture loss. An
uprooting of the plants without the disturbance
of this layer could decrease the moisture loss
speed. In our case, the cutting of the stalks and
their bending during baling would cause damage
to that layer and thus increase moisture loss.
Detailed results of storing experiments were
given by Gemtos and Tsiricoglou [17].
4. Conclusions
From the present work it can be concluded
that under Greek conditions:
. uprooting of cotton stalks is not a feasible
method of harvesting due to the soil stacked
on the roots and the limited period available
for the plants to be left in the ®eld for drying;
. cutting of stalks is feasible with the existing
hay mowers with reciprocating knives;
. the whole work of collection, packaging and
transportation of the residue can be ful®lled by
the existing conventional hay making equipment which gives a great advantage to the
method;
. the best results were given by the use of a large
round baler;
. the harvesting operation is energy e€ective,
giving a net energy of 35,571 MJ/ha;
. the bales can be stored safely in or out of
doors without heating problems for the material and, equally importantly, with natural
drying during the initial storage period.
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