an agro-economic analysis of briquette production from fibre hemp and energy sunflower
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Highlights
Industrial Crops and Products xxx (2013) xxx–xxxAn agro-economic analysis of briquette production from fibre hemp andenergy sunflower
Maarika Alaru∗
• Energy sunflower has high potential to produce vigorous above ground biomass in north European conditions.• Regarding profitability the sewage sludge could be used as an organic fertiliser for energy crops because of high NUE and nitrogen recovery.• In most years 100 kg N ha−1 did not guarantee profitable above ground biomass production of hemp in low fertility soil.• Cattle slurry for energy crops with slow initial development is not a promising organic fertiliser.
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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Industrial Crops and Products xxx (2013) xxx– xxx
Contents lists available at ScienceDirect
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An agro-economic analysis of briquette production from fibre hempand energy sunflower
1
2
Maarika Alaru ∗Q13
Estonian University of Life Sciences, Department of Field Crop and Grassland Husbandry, Institute of Agricultural and Environmental Sciences, Fr. R.Kreutzwaldi 1, EE51014 Tartu, Estonia
4
5
6
a r t i c l e i n f o7
8
Article history:9
Received 22 February 201310
Received in revised form 18 July 201311
Accepted 21 August 201312
Available online xxx
a b s t r a c t
The current study estimated (i) the effect of mineral N fertiliser (NH4NO3), municipal sewage sludgeand cattle slurry on hemp cultivar (cv) USO-31 and sunflower cv Wielkopolski above ground biomassyield, (ii) the efficiency of nitrogen recovery of the applied amendments (nitrogen recovery, %), nitrogenuse efficiency (NUE, kg kg−1) and the profitability (%) of briquette production from hemp and sunflowerabove ground biomass. A long-term field trial was established in 2008–2011 at Estonian University of LifeSciences (58◦23′N, 26◦44′E) on Stagnic Luvisol soil (sandy loam surface texture, C 1.12%, and N 0.12%, pHKCl
5.6). The plants were grown on different N treatments: N0 (without N), N100 (mineral N fertiliser NH4NO3),sewage sludge from the city of Tartu, and cattle slurry. The applied amount of N for all treatments (withthe exception of the N0 treatment) was 100 kg N ha−1. The energy sunflower has high potential to producevigorous above ground biomass in north European conditions. But, it is necessary to continue the fieldtrials with this crop to clarify the biomass yield stability over many years. In point of profitability, thesewage sludge could be used as organic fertiliser for energy crops, because the biomass increase by 1 kgof sludge N was the highest and biomass yield over trial years more stable of the fertilisers tested. Inmost years 100 kg N ha−1 did not guarantee profitable above ground biomass production of hemp inlow fertility soil. Cattle slurry for energy crops with slow initial development is not a promising organicfertiliser.
© 2013 Published by Elsevier B.V.
1. Introduction13
Renewable energy production is one of the priorities of the14
energy policy of the European Union (Directive 2009/28/EC). The15
aim of the EU energy policy is that, by 2020, the biomass supply16
should be increased to meet 20% share of energy from renew-17
able sources. The greatest means of increasing the biomass supply18
is by growing energy crops, and by using products from agricul-19
ture and forest logging residues. To avoid competition between20
food and energy crops for arable land, energy crop cultivation21
on abandoned land is being considered. Kukk et al. (2010) indi-22
cated that abandoned areas often have low soil fertility, so energy23
crop biomass and solid fuel production potential in low soil fer-24
tility conditions should be investigated. In countries, where the25
majority of the land is covered by forests and the area of arable26
land is limited, the cultivation of annual energy crops has to be27
highly motivated. The most important criteria in suitable energy28
crop selection are their above ground biomass yield potential, their29
suitability in crop rotation and low input requirements. In northern30
∗ Corresponding author. Tel.: +372 7 313 521; fax: +372 7 313 539.E-mail address: [email protected]
Europe, high above ground biomass yield of fibre hemp (Cannabis 31
sativa L.) has been reported with quite small amounts of nitrogen 32
fertiliser application (Pakarinen et al., 2011; Prade et al., 2012b); as 33
nitrogen affects hemp yield only slightly, a relatively small amount 34
of fertiliser adequately covers the crop’s needs on comparatively 35
fertile soils (Struik et al., 2000; Malceva et al., 2011). Studies have 36
indicated that nitrogen application, which commonly limits crop 37
production, does not increase the yields of several dedicated energy 38
crops (Danalatos and Archontoulis, 2010; Zubillaga et al., 2002). 39
For example, Zubillaga et al. (2002) found that fertiliser application 40
did not affect total biomass accumulation in sunflower (Helianthus 41
annuus L.) production. Sunflower has been cultivated on a larger 42
area in Europe than fibre hemp. For example, in 2011 the harvest 43
area of sunflower for seed production in Europe was 16.7 million 44
hectares, compared to 22,246 hectares of harvest area for hemp 45
(sum of seed and tow waste; FAO, 2011). Being a short-day crop, 46
sunflower cultivation is more widespread in southern Europe, and 47
there is a lack of information about its cultivation as an energy 48
crop in Nordic conditions. However, in cool regions where tem- 49
perature limits the photosynthetic process, the investigation of 50
energy sunflower cultivars with small flower heads and potential 51
to produce vigorous above ground biomass (Kalinowski et al., 2001; 52
Kluza-Wieloch, 2005; Alaru et al., 2011) is promising. 53
0926-6690/$ – see front matter © 2013 Published by Elsevier B.V.http://dx.doi.org/10.1016/j.indcrop.2013.08.066
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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Studies have analysed nutrient use efficiency per unit of biomass54
in energy crops production (Brouder et al., 2009; Lewandowski and55
Schmidt, 2006). This can be calculated for macro- and microele-56
ments but the efficiency for N is generally analysed.57
Lewandowski and Schmidt (2006) have studied nitrogen use58
efficiency of several energy crops and found, that at an N supply of59
100 kg ha−1 yr−1 the nitrogen use efficiency of miscanthus, triticale60
and reed canary grass were relatively high (i.e. 0.35, 0.14 and 0.11 t61
dry biomass per kg N, respectively). Montemurro and De Giorgio62
(2005) have shown significant correlation between N uptake and63
nutrient use efficiency and identified N nutrition as an impor-64
tant factor in sunflower production in Mediterranean conditions.65
Sewage sludge and cattle slurry are alternative N resources for66
energy crop cultivation. In organic fertilisers, the amount of organ-67
ically bound N available for plants depends on its C:N ratio, because68
the organics must first of all undergo microbial decomposition69
unlike the mineral N fertilisers (Mutegi et al., 2012). The applica-70
tion of sewage sludge to soil as an organic fertiliser has become71
common practice in some countries due to its increased produc-72
tion, lack of available disposal sites and its potential to increase soil73
fertility (Hall, 1995). The study of Kelessidis and Stasinakis (2012)74
indicated that approximately half of the total sewage sludge pro-75
duction has been reused in EU-15 during the years of 1992–200576
whereas 44% was in agricultural use in 2005. However, in some77
European countries, such as Estonia, the use of sewage sludge as78
fertiliser is marginal and has currently no practical importance. To79
avoid the risk of soil contamination, the heavy metal concentrations80
in sewage sludge has to be under control. In energy crop cultivation81
for solid fuel production (briquettes and pellets) heavy metal con-82
centration in plants does not limit their use as bioenergy resources83
if the ash is not used as nutrient source. The ash can be used later,84
for example, in Portland cement production (Rulkens, 2008).85
Many studies have indicated the concurrent improvement of86
nutrient use efficiency and production profitability (Giller et al.,87
2004; Brouder et al., 2009). Therefore, analysing the profitability88
of potential energy crops for briquetting or different treatments in89
certain pedo-climatic conditions, the whole production cycle from90
cultivation to marketing should be included.91
The aim of this study was to investigate (i) the effect of differ-92
ent fertilisers (mineral N, sewage sludge, cattle slurry) on hemp93
and sunflower above ground biomass yield; (ii) the N availability94
of different fertilisers and nitrogen use efficiency (NUE); (iii) the95
profitability of hemp and sunflower briquette production in soil of96
low fertility in northern Europe.97
2. Materials and methods98
2.1. The field trial and experimental details99
To investigate the effect of mineral N fertiliser (NH4NO3),100
municipal sewage sludge and cattle slurry on hemp cultivar (cv)101
USO-31 and sunflower cv Wielkopolski above ground biomass yield102
in 2008–2011, a field trial was established at the Institute of Agri-103
cultural and Environmental Sciences of Estonian University of Life104
Sciences, near Tartu (58◦23′N, 26◦44′E), Estonia, on Stagnic Luvi-105
sol (WRB 1998 classification) soil (sandy loam surface texture, C106
1.12%, and N 0.12%, pHKCl 5.6). The plants were grown on different107
N treatments: N0 (without N; defined also as control treatment),108
N100 (mineral N fertiliser NH4NO3), sewage sludge from the city of109
Tartu, and cattle slurry. The applied amount of total N for all treat-110
ments (with the exception of the N0 treatment) was 100 kg N ha−1.111
In 2008–2010, the sewage sludge was aerobically composted for112
2–3 month, while that used in 2011 was aerobically composted for113
8 months. The sowing rate of hemp and sunflower was 200 and 25114
viable seeds m−2, respectively.115
Table 1The chemical composition of sewage sludge in 2008–2011.
Year pHKCl DM* (%) Ptot (%) Ktot (%) Ntot (%) C (%)
2008 6.8 18.2 1.9 0.4 5.2 31.82009 5.8 22.4 1.2 0.6 4.2 31.42010 6.4 18.6 0.5 0.4 4.9 33.12011 6.9 17.5 1.5 0.7 2.8 26.1
* DM—dry matter.
Table 2The chemical composition of slurry in 2008–2011.
Year pHKCl DM* (%) Ptot (%) Ktot (%) Ntot (%) C (%)
2008 7.0 6.6 0.9 3.2 4.5 35.82009 7.2 6.6 0.8 1.3 3.7 37.12010 6.8 9.1 0.7 2.9 2.8 34.12011 5.7 8.4 0.7 4.1 5.7 36.4
* DM—dry matter.
Seeds were sown with a plot drill (Wintersteiger) on 20, 19, 116
22 and 19 of May in 2008, 2009, 2010 and 2011, respectively, to 117
a depth of 3–5 cm, with 15-cm between rows. The experiments 118
were performed in a randomised complete block design with four 119
replications; plot size was 13 m2. Fertilisers were applied once: the 120
sewage sludge and slurry were applied and incorporated into the 121
soil prior to sowing, mineral N fertiliser (NH4NO3) was applied by 122
hand after plant emergence, which was on 6 June 2008, 2 June 123
2009, 9 June 2010 and 6 June 2011. To reduce the accumulation 124
of heavy metals through repeated application, the sewage sludge 125
was applied to the same plot in 2008 and in 2010, but in 2009 and 126
2011, the sludge was applied to an adjacent plot. The other treat- 127
ments followed the same scheme. Barley was grown on the field in 128
the intervening years. During the vegetation period no pesticides 129
were applied or no mechanical or manual weeding was done. 130
Meteorological data were collected from a meteorological 131
station approximately 2 km from the trial site. Temperatures in 132
2008 and 2009 were similar to the long-term average, but in 2010 133
and 2011, were higher than usual (in July the temperature was 134
4.7 and 2.4 ◦C higher than the long-term average). Total precipi- 135
tation during the growth period of 2008–2010 (May–September) 136
was similar to the long-term average of 351 mm, but, in 2011, was 137
75 mm lower than normal. In 2011, precipitation in June–August 138
was considerably lower than the long-term average, only 138 mm, 139
i.e. 98.2 mm lower than normal (see more in Alaru et al., 2011). 140
Above ground biomass from 1 m2 of each experimental plot with 141
4 replications was harvested by hand and measured on 11 and 18 142
September, 23 August and 15 September 2008, 2009, 2010 and 143
2011, respectively. The dry matter (DM) content in energy crops 144
was determined; the above ground biomass yield g m−2 was cal- 145
culated. Samples for the briquetting were taken from hemp and 146
sunflower above ground biomass in 2009 and 2010. 147
2.2. Chemical analyses and briquetting 148
For chemical analyses the soil and plant samples were taken 149
after harvest and samples from sewage sludge and slurry before 150
applying to the soil. The results of chemical analyses from the 151
sewage sludge and slurry are presented in Tables 1–2, respectively. 152
Acid digestion by sulphuric acid solution (Methods of Soil and 153
Plant Analysis, 1986) was used to determine P and K total content 154
in sewage sludge and slurry. After the digestion, the content of total 155
phosphorus (Ptot) was determined colorimetrically (spectrometer 156
Jenway 6300; UK). Total potassium (Ktot) content was determined 157
by flame photometry (Jenway PFP7; Bibby Scientific Ltd, UK). Total 158
nitrogen (Ntot) and carbon (C) content of oven-dried samples was 159
determined by the dry combustion method on a varioMAX CNS 160
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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Table 3Heavy metal amounts applied with sewage sludge in 2008–2011.
Element In sewage sludge in trial (mg kg−1) Permitted norms(mg kg−1)*
2008 2009 2010 2011
Cd 0.38 0.57 1.3 1.5 20Cr 51 46 49 80 1000Cu 99 150 220 260 1000Ni 19 13 27 36 300Pb 18 21 24 34 750Zn 360 510 620 920 2500
* Regulation RTL 2003.
elemental analyser (ELEMENTAR, Germany). C:N ratio was calcu-161
lated in soil, sewage sludge and cattle slurry samples.162
Heavy metals (Cd, Cr, Ni, Pb, Cu and Zn) content was measured163
from samples of sewage sludge and soil in 2008–2011; sewage164
sludge treatment was compared with N0 treatment. All heavy165
metals concentrations were determined in the Central Lab of Tartu166
Environmental Research Ltd. The following methods were used:167
for dry matter (DM) SFS 3008, for content of Cd, Cr, Ni, Pb SFS 5074168
and for Cu and Zn EVS-EN ISO 11885. The heavy metals amounts169
applied with sewage sludge did not exceed the permitted norms170
(Regulation, 2003; Table 3).171
The samples of hemp and sunflower were ground with Cutting172
Mill SM 100 comfort (Retsch GmbH) and pressed into briquettes173
without sifting. Ground hemp and sunflower plants were pressed174
into briquettes with a biomasser BS06 briquetting device.175
This device is a screw press designed for briquetting thatch176
and hay. The productivity of the device during the experiment177
was Q = 39.0 − 52.9 kg h−1. The length of Cooler-stabiliser was178
L = 3000 mm. Briquettes produced by this device were of random179
length and diameter D = 70 mm (see more in Alaru et al., 2011).180
2.3. Calculation procedures of nitrogen available from organic181
fertilisers182
The following formulas were used in calculation procedure of183
nitrogen available from organic fertilisers (www.icrisat.org/.../):184
C in organic matter (kg) = Organic matter (kg) × C content (%),(1)185
N in organic matter (kg) = C in organic matter (kg)C : N ratio of organic matter
, (2)186
As fresh organic matter is decomposed, the microbes use 75% of187
the carbon for energy and, the remaining 25% of the carbon is used188
to form their new tissue.189
The amount of carbon used by microbes for forming new tissues190
(kg):191
C for microbes (kg) = C in organic matter (kg)4 (i.e. 25% of total C)
, (3)192
Microbes use also nitrogen from the added organic matter,193
whereas they require 1 kg N for every 8 kg of carbon as the C:N194
ratio of microbes is 8:1 (www.icrisat.org/.../).195
The amount of nitrogen required for microbes (kg):196
N for microbes (kg) = C for microbes (kg)8
, (4)197
The nitrogen available for plants (kg):198
N for plants (kg) = N in organic matter (kg)199
− N for microbes (kg), (5)200
201
Table 4Costs of hemp and sunflower above ground biomass production and briquetting.
Cost and return component Unit Value
Machinery expense D ha−1 154.30Transport D Mg−1 4.80Mineral fertiliser NH4NO3 D Mg−1 325.00Sewage sludge D Mg−1 6.00Cattle slurry D Mg−1 5.75Seeds of hemp D kg−1 3.83Seeds of sunflower D kg−1 2.25Briquetting D Mg−1 80.50
2.4. Nitrogen efficiency analysis 202
In our study NUE of cattle slurry and sewage sludge were inves- 203
tigated and their effect on energy crops above ground biomass were 204
compared with the effect of mineral N fertiliser. Using total nitro- 205
gen uptake (N concentration multiplied by above ground biomass 206
yield), we calculated the mean % recovery of the applied N. 207
The efficiency of nitrogen recovery of the applied amendments, 208
i.e. percent recovery of nitrogen (or nitrogen recovery) was deter- 209
mined as follows: 210
%Recovery = Treatment uptake-control uptakeTotal amount of nitrogen applied
× 100, (6) 211
where control uptake is the uptake of N0 treatment. 212
Definition of nutrient use efficiency includes harvestable prod- 213
uct per unit of nutrient applied (Caradus, 1990). Nitrogen use 214
efficiency (NUE, kg DM kg−1 N−1), in our trial, was calculated as 215
follows (Pandey et al., 2001): 216
NUE = Treatment biomass − control biomass
Total amount of nitrogen applied, (7) 217
where control biomass is the biomass of N0 treatment 218
2.5. Economic analysis 219
The costs of hemp and sunflower production and briquetting 220
are given in Table 4. The costs of machinery, agricultural work and 221
briquetting are Estonian values in 2011; for machinery works prices 222
for a tractor with power 102 kW was used. 223
Processing costs are calculated on the basis of the cost rate of 224
different work operations. The calculation of the cost of operating 225
modes includes the cost of materials (energy, fuel), employment 226
costs, equipment depreciation, insurance costs per hour, and work 227
time needed for processing one metric tonne of dry material. 228
Machinery expense includes the following agricultural works: 229
ploughing, cultivation (twice), sowing and harvesting (cutting). Dif- 230
ferent fertilisers and fertilisation costs are calculated separately 231
for each treatment. It was assumed that the total N amount for 232
all fertilisers was 100 kg ha−1; the cost of transport was found 233
using average transportation range of 10 km. The price of briquet- 234
ting includes biomass conditioning-drying, grinding and pressing 235
into briquettes. Since the absence of herbaceous briquette prices 236
in Estonia, the price of hemp and sunflower briquettes was, in our 237
calculation, the same as that for commonly used woody briquettes, 238
which was 133D Mg−1 in 2011. 239
The profitability (%) of briquette production was calculated for 240
each treatment as follows: 241
Profitability = Profit/loss of treatment
Total costs of treatment× 100 (8) 242
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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Table 5Amount of nitrogen (kg ha−1) released from organic fertilisers into the soil andavailable to plants in 2008–2011.
Fertiliser 2008 2009 2010 2011 Average
Sludge 80.9 76.6 79.0 71.3 77.0 ± 2a*
Slurry 75.1 69.3 61.9 80.0 72.0 ± 4a
* Different letters in column denote significant difference.
2.6. Statistical analysis243
The trial data were processed using Pearson‘s correlation,244
variance analyses (ANOVA) and descriptive statistics. Normal245
distribution assumptions were checked using the Shapiro–Wilk246
normality test. Tukey test was used as a post hoc test of significance247
differences between means. The means are presented with their248
standard errors (±S.E.). Significance is presented with P < 0.05 if not249
indicated otherwise. Statistical analyses were carried out using the250
statistical software R version 2.15.2 (R Development Core Team,251
2012).252
3. Results253
3.1. The amount of nitrogen in slurry and sludge available to254
plants255
The amount of N potentially available to plants in organic fer-256
tilisers was calculated by their C:N ratio. It was assumed, that257
amount of N applied with all fertilisers was 100 kg N ha−1, but the258
amount of N available to plants from organic fertilisers depends on259
the C:N ratio of organic matter (www.icrisat.org/.../), because part260
of the nitrogen and carbon is used by microorganisms for build-261
ing up their tissues. The C:N ratio of sewage sludge over the trial262
years ranged from 6.1 to 9.3 and of cattle slurry from 6.4 to 12.2.263
The amounts of total N potentially released from organic fertilis-264
ers into the soil and therefore available to plants were calculated265
to range from 71.3 to 80.9 kg ha−1 in sewage sludge and from 61.9266
to 80 kg ha−1 in slurry (Table 5). The mean N amount available to267
plants over the trial years was statistically comparable for sewage268
sludge and slurry.269
The C:N ratios in the soils of different treatments were deter-270
mined after harvest of the crops (Fig. 1) and were significantly271
influenced by fertilisers. The mean C:N ratio in sewage sludge272
N0 N100 Sludge Slur ry
C:N
0
2
4
6
8
10
1
3
5
7
9
11
bb
c
a
Fig. 1. Mean (±S.E.) C:N ratio in soil of different N treatments over trial years;*different letters between treatments denote significant difference.
Table 6Above ground biomass (g DM m−2) of hemp in 2008–2011 (±S.E).
Year N0 N100 Sludge Slurry
2008 418 ± 60b 665 ± 71ab 870 ± 86a 505 ± 33b2009 307 ± 37b 867 ± 96a 880 ± 24a 392 ± 10b2010 193 ± 37b 542 ± 36ac 701 ± 20a 334 ± 66bc2011 111 ± 26b 288 ± 38ab 449 ± 87a 190 ± 17abCoefficient of variation (%) 52.1 41.0 27.8 36.9
*Different letters in row denote significant difference. Q12
treatment soil over trial years was significantly the lowest 273
(8.2 ± 0.2). The mean C:N of sewage sludge soil treatment 274
decreased, because the amount of C in this soil decreased while that 275
of N increased. The significantly higher C:N ratio in slurry treatment 276
soil (mean over trial years 10.0 ± 0.37) was caused by an increase 277
in the amount of C and a decrease in that of N. The C:N ratio in the 278
soil treated with mineral N fertiliser was comparable with that of 279
the control treatment. 280
3.2. The effect of fertilisers on the above ground biomass of hemp 281
and sunflower 282
The fertiliser and weather conditions affected hemp and sun- 283
flower biomass yield significantly; the proportion of variation 284
for hemp was 52.1% and 33.0%, respectively, and for sunflower 285
44.3% and 20.2%, respectively. The above ground biomass of hemp 286
increased in different trial years by sewage sludge application 287
2.1–4.1 times, compared with the control treatment. The yield of 288
hemp in slurry treatment over the trial years was the same as that of 289
the N0 treatment (Table 6). The above ground biomass of sunflower 290
increased significantly over the trial years by the application of 291
sewage sludge (2.4 times higher than in the N0 treatment), whereas 292
biomasses of slurry and N100 treatments were the same (Table 7). 293
Weather conditions (temperature and precipitation) influenced 294
also significantly (P < 0.01) hemp and sunflower above ground 295
biomass. Hemp biomass yield was negatively correlated with 296
temperature data (P < 0.001) and positively correlated with precip- 297
itation sum in June. Sunflower biomass amount was in negative 298
correlation with temperature in July and in negative correlation 299
with precipitation in May and in September (P < 0.01). Hemp above 300
ground biomass varied over trial years and treatments up to 7.9 301
times and for sunflower up to 4.8 times. The mean above ground 302
biomass of hemp and sunflower over trial years and N treatments 303
was 557 ± 69 and 879 ± 107 g m−2 in DM, respectively. The coeffi- 304
cient of variation of hemp was the highest in N0 treatment, followed 305
by the N100 treatment; generally the above ground biomass of 306
hemp varied over trial years considerably. 2008 and 2009 had 307
more favourable climatic conditions than 2011 for hemp cv USO- 308
31 above ground biomass formation; the biomass yield with N100, 309
sewage sludge and slurry treatment was 3.0-, 1.96- and 2.66-fold 310
higher, respectively, in 2008 or 2009 than in 2011. More favourable 311
climatic conditions for sunflower cv Wielkopolski above ground 312
biomass formation were in 2009 and 2011, whereas the above 313
ground biomass yield varied most over the trial years in the control 314
treatment, followed by the sewage sludge treatment (up to 2.2 and 315
2.08 times, respectively). 316
3.3. Percent recovery of N and NUE 317
The concentration of N in plant above ground biomass at harvest 318
was influenced by N treatment. The mean N content of hemp above 319
ground biomass over trial years ranged from 0.7% to 1.1%, whereas 320
the slurry treatment had a significantly lower N content (Fig. 2). 321
The mean N content of sunflower above ground biomass over the 322
trial years ranged from 0.6% to 1.0%, the control treatment had a 323
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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Table 7Above ground biomass (g DM m−2) of sunflower in 2009–2011 (±S.E).
Year N0 N100 Sludge Slurry
2009 770 ± 205b 818 ± 233b 1654 ± 233a 828 ± 39b2010 343 ± 43b 652 ± 62ab 794 ± 19a 733 ± 116ab2011 385 ± 46b 703 ± 114ab 1100 ± 111a 628 ± 57abCoefficient of variation (%) 47.1 11.7 36.9 13.7
Different letters in row denote significant difference.
significantly lower N content. In general, the above ground biomass324
quantity at harvest time did not correlate with plant N content.325
Weather conditions in the trial years also influenced the biomass326
N concentration. Hemp biomass N content was significantly nega-327
tively correlated with precipitation in August (end of flowering and328
kernels start to mature) and sunflower N concentration was signifi-329
cantly negatively correlated with temperature in July and positively330
correlated with precipitation sum in May and September (P < 0.05331
and P < 0.001, respectively).332
Using total N uptake, we calculated the mean % recovery of the333
applied N for hemp and sunflower (Table 8). Nitrogen recovery of334
different N fertilisers was significantly influenced by plant species335
and climatic conditions. That for hemp ranged from 19.2% to 53.1%336
from mineral N fertiliser and from 29.9% to 81.0% from sewage337
sludge. The highest N uptake from mineral N fertiliser and sewage338
sludge was in 2009, followed by 2010. The same data for sunflower339
ranged over trial years in N100 treatment from 35.0 to 46.7% and340
in sewage sludge treatment from 57.1% to 66.8%. The highest N341
uptake from these treatments was in 2009 and 2011. N uptake from342
slurry by hemp and sunflower plants in north European conditions343
ranged from 0% to 9.1% and from 0% to 63.0%, respectively. The344
above ground biomass yield of hemp in slurry treatment was low345
because of insufficient N uptake.346
N0 N100 Sludge Slurry
N (
%)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4HempSunfl ower
ab
ab
a
b
b
a a
a
Fig. 2. Mean (±S.E.) nitrogen concentration (%) of hemp and sunflower above groundbiomass over trial years at harvest; *different letters within species denote signifi-cant difference.
Table 8Mean (±S.E.) nitrogen recovery (%) over trial years.
Plant species N100 Sludge Slurry
Hemp 34.2 ± 7.21ab 55.7 ± 14.75a 4.5 ± 2.53bSunflower 41.5 ± 3.44a 63.2 ± 3.06a 36.8 ± 19.13a
Different letters in row denote significant difference.
The NUE of different fertilisers over the trial years differed signif- 347
icantly. The highest NUE for sunflower was with the use of sewage 348
sludge and for hemp with the use of sludge and N100 (Table 9). 349
The lowest NUE for hemp was in the slurry treatment, whereas the 350
sunflower biomass increase per 1 kg N in slurry and N100 treatment 351
was statistically the same. 352
3.4. The profitability of briquette production from hemp and 353
sunflower biomass 354
The major part of costs in hemp briquette production was from 355
the expenses of machinery works in the field for biomass produc- 356
tion and briquetting operations (Table 10). In the case of sunflower 357
biomass the highest costs were for the briquetting. In the slurry 358
treatment the costs of fertilising were much higher because of low 359
N concentration in this organic fertiliser (2.8–5.7%) and because of 360
the need to apply a large amount of wet cattle slurry to the field. The 361
relative importance of briquetting in the total budget was higher 362
in treatments with higher biomass yield. 363
The briquette price of 133D Mg−1 for hemp was too low. A prof- 364
itable price for hemp dependent on treatment would have been 365
190–240D Mg−1. Briquette production from sunflower biomass 366
was unprofitable only in the slurry treatment, because the biomass 367
yield was low, while the cost of fertilising was high. 368
Our trial showed that profitability of briquetting was in positive 369
correlation with above ground biomass (Table 11; Fig. 3; P < 0.001) 370
and NUE (P < 0.001). Briquetting was profitable, when biomass yield 371
of energy crops in this trial was over 7.6 Mg ha−1, and biomass yield 372
increase by 1 kg N over species and trial years at least 45.5 kg in 373
DM. In the current study, an increase of above ground biomass 374
by 1 Mg ha−1 increased the profitability of hemp and sunflower 375
briquette production 5.3% as an average. 376
Table 9Mean (±S.E.) nitrogen use efficiency (NUE; kg DM kg−1 N−1) of hemp and sunflowerover trial years.
Plant species N100 Sludge Slurry
Hemp 33.3 ± 8.34a 46.8 ± 4.98a 9.8 ± 1.44bSunflower 22.5 ± 8.85b 68.3 ± 12.60a 23.0 ± 9.60b
Different letters in row denote significant difference.
Table 10Mean percent proportion (±S.E.) of expenses in hemp and sunflower above groundbiomass production and briquetting.
Expenses N0 N100 Sludge Slurry
HempMachinery* 60 ± 6.3a 35 ± 4.3b 30 ± 2.6b 32 ± 1.8bFertiliser + fertilising 0a 11 ± 1.3b 13 ± 1.1b 38 ± 2.2cHarvesting 4 ± 0.2a 4 ± 0.2a 4 ± 0.1a 2 ± 0.2bBriquetting 36 ± 6.2a 50 ± 5.4b 53 ± 3.6b 28 ± 3.9a
SunflowerMachinery 39 ± 5.6a 26 ± 1.1b 19 ± 2.7c 20 ± 0.8cFertiliser + fertilising 0a 10 ± 0.4b 10 ± 1.5b 30 ± 1.2cHarvesting 5 ± 0.1a 5 ± 0.03a 5 ± 0.1a 4 ± 0.1bBriquetting 56 ± 5.5a 59 ± 1.6a 66 ± 4.1b 46 ± 1.8c
Different letters in row denote significant difference.* Machinery: includes plowing, cultivation (two times), seeds and sowing.
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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Table 11Regression model of profitability (%) depending on hemp and sunflower aboveground biomass (Mg ha−1; R2 = 0.55, P < 0.001).
Coefficient SE of coefficient* P-value
Intercept −39.966 6.505 <0.001Biomass 5.308 0.944 <0.001
* SE—standard error.
4. Discussion377
The influence of sewage sludge, cattle slurry and mineral N fer-378
tiliser on fibre hemp and energy sunflower above ground biomass379
yield was investigated. Research on the effects of soil amendment380
with sewage sludge has mainly focused on the potential risks of381
the introduction of heavy metals into the food chain (Barbarick382
et al., 1997; Logan et al., 1997) and on its action as a soil condi-383
tioner (Sastre et al., 1996; Johansson et al., 1999). Knowledge on384
crop-specific fertiliser requirements and appropriate timing and385
application strategies enable farmers to maximise crop yield and386
to reduce risks for N losses (Gutser and Ebertseder, 2002). This trial387
focused on analysing the NUE of sewage sludge and we found that388
the NUE of sewage sludge was the highest for both investigated389
energy crops. Our trial revealed that slurry was not an efficient390
fertiliser for hemp biomass production and therefore it is impor-391
tant to choose the crop-specific fertiliser type to produce higher392
and more stable biomass yields over years. In our trial the biomass393
yield of hemp decreased over the trial years consistently which394
needs to be studied in following years. It is important to study395
the cultivation of hemp in crop rotations for analysing its influ-396
ence on biomass yield stability. Zegada-Lizarazu and Monti (2011)397
argued about the importance of rotation in energy crops produc-398
tion as currently existing information about rotational systems is399
often limited and fragmented.400
The above ground biomass formation depends mostly on the401
amount of N available to plants. The availability of N from organic402
fertiliser is considerably influenced by its previous treatment403
(for example, sewage sludge composting), inorganic N content404
(Hutchings, 1984), C:N ratio (Sims, 1990), site (e.g. soil, climate),405
soil fertility (e.g. turnover rate), soil C:N ratio and crop type (length406
of the growing period during the warmer season; Whitmore and407
Fig. 3. Regression line with its corresponding 95% confidence bands (i.e the narrowbands) and the 95% prediction bands (i.e. the wide bands) of hemp and sunflowerprofitability depending on the above ground biomass (Mg ha−1).
Groot, 1997; Hadas et al., 2002). The last four factors influence the 408
availability of N also from mineral fertiliser. 409
The C:N ratio of an organic substance is the decisive factor for 410
N release from organic matter (Gutser et al., 2005). In our trial the 411
mean N amount released from sewage sludge or cattle slurry that 412
became available to plants was statistically the same. They had a 413
high amount of organic C, total N and C:N ratio. N derived from 414
organic fertilisers acts mainly via the soil N pool. The direct uti- 415
lisation in the year of application is relatively small, because of 416
the slow-release characteristics of organically bound N and the 417
medium- and long-term N immobilisation in soils (Jensen et al., 418
2000; Sørensen and Amato, 2002). Soil C:N ratio has been sug- 419
gested as a sensitive indicator of N impact on soil (Evans et al., 420
2006). In our study the C:N ratio of soil decreased significantly by 421
the application of sewage sludge in the first year of use in compar- 422
ison with the N0 treatment. García-Gil et al. (2004) found in their 423
study, that this result apparently disappears after 36 months and 424
was very similar to the control variant. Gutser et al. (2005) indicated 425
that organic fertilisers with low contents of NH4+–N and relatively 426
high C:N ratios (e.g. manure, composts) which release nutrients 427
slowly, show a strongly increased N utilisation by crops over time 428
due to the mineralisation of accumulated N in soils. The lower C:N 429
ratio indicates the increase in soil microbial biomass content and 430
its metabolic activity, the contribution of sewage sludge to the soil 431
improves soil fertility above all due to the contribution of nitrogen 432
and phosphorus (Smith et al., 1998), which promote plant growth 433
and biomass formation. By contrast to sewage sludge treatment, 434
the C:N ratio in soil of the slurry treatment increased in the first 435
year of use. Liquid organic fertilisers as cattle slurry are generally 436
rich in NH4+–N and the mineralised N is hardly immobilised in soil 437
because the remaining organic substance is highly stable (i.e. it does 438
not promote immobilisation of N), resulting in a high N availability 439
(Gutser et al., 2005; Viiralt et al., 2009). 440
The NUE was influenced by N availability during rapid growth 441
period of plants. Crop nutrient uptake rates are different at each 442
growth stage, and crop growth rates vary with crop, variety, and 443
growing conditions. In our trial both organic fertilisers were applied 444
about 10 days before sowing of hemp and sunflower. In Estonian 445
conditions the rapid growth period of hemp and sunflower is from 446
mid-June to early July (in our case 6–9 weeks after amendment of 447
organic fertilisers). The N of slurry was probably mineralised and 448
released to the soil by this time, but was not immobilised in the 449
soil and there was a lack of N for the rapid plant growth period. 450
We suppose this because we studied also the after-effect of all N 451
treatments on barley’s grain yield (data not shown) and found that 452
grain yield on slurry treatment was comparable with control treat- 453
ment. N mineralisation rate in slurry is the highest in 3–4 weeks 454
after amendment to the soil (Jenerette and Lal, 2005; Tarrasón et al., 455
2008), but in sewage sludge 6–7 weeks after amendment 25–30% 456
of organic N is not yet mineralised (Carneiro et al., 2007). 457
The study indicated that in low fertility soils the profitability of 458
briquette production from hemp and sunflower depended on their 459
ability to form high above ground biomass. In this trial, the mean 460
above ground biomass of fibre hemp over years in different N treat- 461
ments was lower than expected. For example, the above ground 462
biomass of hemp in field trials in Sweden and Finland has reached 463
up to 14.4 Mg ha−1, whereas the N amount in the Finnish trial was 464
only 60 kg ha−1 at a sowing density of 60 seeds m2. Also, it revealed 465
that the Swedish field trial was carried out on a moderately humus- 466
rich (2.7%) sandy loam (Pakarinen et al., 2011; Prade et al., 2011). In 467
our trial, the highest above ground biomass of hemp and sunflower 468
was obtained from the sewage sludge treatment, the mean biomass 469
over trial years for this treatment was 7.3 and 11.8 Mg ha−1, respec- 470
tively. Over the trial years, of the crop species used in this trial, 471
the sunflower cv Wielkopolski showed a greater potential than the 472
hemp cv USO-31 to produce higher above ground biomass. 473
Please cite this article in press as: Alaru, M., An agro-economic analysis of briquette production from fibre hemp and energy sunflower. Ind. CropsProd. (2013), http://dx.doi.org/10.1016/j.indcrop.2013.08.066
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M. Alaru / Industrial Crops and Products xxx (2013) xxx– xxx 7
Comparing the above ground biomasses and recovery of nitro-474
gen in different treatments it appears that the slurry treatment did475
not cater for the needs of the plants. Dale et al. (2011) found, that476
the efficiency of slurry N utilisation was particularly low in the first477
two years for the Italian ryegrass i.e. 19% in first year and 32% in478
second year. The low recovery of slurry nitrogen, and hence uti-479
lisation efficiency, is likely due to ammonia losses as a result of480
volatilisation, which may have been increased by the weather con-481
ditions at application. Nitrogen availability from sewage sludge and482
sludge compost is reported to range from 0% to 56% (Warman and483
Termeer, 2005). As mineral N fertiliser was applied after emergence484
of hemp and sunflower, i.e. at the rapid period of growth the N from485
mineral fertiliser was available to plants as well as the N from the486
sewage sludge. Because of the lack of N during the rapid growth487
period of plants the above ground biomasses of slurry treatment488
were comparable with the control treatment.489
It also revealed from the study that the above ground biomass490
yield depended on weather conditions. Weather conditions influ-491
enced the crops above ground biomass formation (especially of492
hemp) dramatically in 2011, because precipitation amount in rapid493
growth period was too small. Poisa et al. (2005) have said that494
above ground biomass amount of hemp depends very much on the495
amount of precipitation and its distribution during the vegetation496
period.497
Prade et al. (2012b) showed that energy output-to-input ratio of498
briquette production from hemp is strongly yield-dependent and499
±30% change in biomass yield had a substantial effect on the abso-500
lute value for net energy yield. Our trial showed that the above501
ground biomass yield below 8 Mg ha−1 was unprofitable if the price502
of hemp briquettes was the same as that of wood briquettes. In503
point of packaging the pellets are better option than briquette.504
However, pelleting requires higher energy input, especially for505
hemp grinding because of strong fibres. Sunflower pelleting is prob-506
ably less complicated and might be alternative to briquetting in507
small-scale boilers. In addition to the difference of energy con-508
sumption comparing pelleting with briquetting, factors influencing509
fuel characteristics of industrial hemp (Alaru et al., 2011; Prade510
et al., 2012a) as well as sunflower (Alaru et al., 2011) should be511
taken into account.512
The profitability is highly dependent on briquette prices and513
could therefore fluctuate according to the economic situation.514
Hartmann and Apaolaza-Ibánez (2012) suggested that the creation515
of green energy brands may be an alternative of increasing the516
selling price of renewable energy. This enables to increase pro-517
duction profitability of dedicated energy crops or to decrease the518
requirement of minimum above ground biomass. In addition to519
high yielding there is a possibility to reduce costs by harvesting520
energy crops in spring but the preliminary observation in our study521
indicated fibre hemp lodging during winter.522
In poor soil conditions the cultivation of hemp was not prof-523
itable with low nitrogen inputs. The N fertiliser amount up to524
100 kg N ha−1 was low and cattle slurry applied before sowing did525
not cover the need for N of hemp and sunflower for high above526
ground biomass formation. The cost of slurry application was too527
high and the effect on biomass formation too small.528
5. Conclusions529
Energy sunflower has high potential to produce vigorous above530
ground biomass in north European conditions. But, it is necessary531
to continue the field trials with this crop to clarify the biomass532
yield stability over many years. In point of profitability the sewage533
sludge could be used as an organic fertiliser for fibre hemp and534
energy sunflower as an energy crop production because of high535
NUE and nitrogen recovery. In most years 100 kg N ha−1 did not536
guarantee profitable above ground biomass production of hemp 537
in low fertility soil. Cattle slurry for energy crops with slow initial 538
development is not a promising organic fertiliser. 539
Uncited references Q2540
European Commission (2009), Food and Agriculture 541
Organization of the United Nations (2011), ICRISAT (2013). 542
Acknowledgements 543
We thank Prof. Ingrid Williams for her linguistic help with this 544
manuscript. This study was financially supported by Estonian Agri- 545
cultural Ministry’ project “The agricultural crops utilisation for 546
burning and biogas production; assortment and agrotechnology.” 547
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