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AIR2-CT92-1089
Cynara cardunculus L. as New Crop for Marginal and Set-Aside Lands |
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Proposal No: | AIR2-CT92-1089 |
| Date Prepared: | September 1999 | |
| Source: | Final technical report |
Summary
Introduction The cardoon (Cynara cardunculus L.) is a species originally from the Mediterranean area which belongs to the Asteraceae Family (Compositae). It is a perennial species which during its natural cycle sprouts in autumn, passes the winter in a rosette stage and in spring develops a floral stalk that dries in summer while the roots stay alive. At the beginning of autumn, the buds in the upper part of the roots develop a new rosette in order to continue the cycle for several years.
The development cycle of C. cardunculus is perfectly adapted to the South European climate conditions. Because of its deep root system, it is able to extract water and nutrients from very deep soil zones and due to this, in non-watering conditions, using the rainwater accumulated during autumn, winter and spring, it is able to produce a very high amount of biomass in comparison with other herbaceous species which grow in the same environmentally limiting conditions.
According to previous studies, this crop can produce from 15 to 25 t/ha of biomass (dry weight) which may be used mainly for energetic purposes, for paper pulp or animal feeding. This crop produces about 1.5 - 2.5 t/ha of seeds, which have a high content of oil (22-25 %) and protein (almost 20%). These figures are very promising but they must be confirmed for different pedo-climatic situations. Agronomic practices and transformation techniques must be developed in order to establish a new agro-industry based on C. cardunculus biomass crop, suitable for growth on set-aside land.
Objectives The general objective of the project is to evaluate the potential of C. cardunculus as a new crop for Mediterranean climatic conditions and the application of the produced biomass as ruminant feed as well as for the paper pulp industry and energy use. The specific objectives are:
Activities
The following work was were carried out, divided into a number of topic-related activities.
1. Productivity network This determined the relationships between plant density (from 8000 to 57,000 plants/ha) on final biomass yield, carried out green forage harvesting (during autumn or winter) and looked at its influence on final dry biomass as well as investigating the effect of N top fertilisation on final dry biomass productivity. For these experiments the sowing was done during 1994 and a study of the climatic conditions of the different experimentation locations during 1994-95 and 1995-96 growing period was done in plots of 8 x 8 m each with 3 repetitions for each treatment. During summer, dry matter production was measured and the distribution among the different parts (leaves, stems, branches and capitula) was evaluated.
2. Water use efficiency studies These studies covered plant water status and stress, net photosynthetic activity and transpiration rate as well as evaporative demand. Leaf gas exchange parameters, specific leaf area, concentration of leaf chlorophyll pigments and nitrogen (N) were determined at different times of the year under field conditions.
3. Genotype collection and characterisation A total of 41 C. cardunculus populations were studied in terms of anatomical measurements, dry biomass productivity, seed oil content, seed oil characterisation (fatty acids content), total protein electrophoresis profile and specific isoenzymes profile.
4. Mechanisation Various alternatives were considered for both green forage harvesting for feed and dry biomass harvesting for industrial uses. For green forage winter harvesting, both a Mengele four-row self-propelled maize cutter-loader, type SF4000/2, and a Fiat DT 1300 Super tractor with Carraro trailer were investigated. For dry biomass a Taarup mower-conditioner, type 306R followed by a Mengele Law 345 Quadro self- loading trailer drawn by a Fiat DT 80-90 tractor was used. These machines were less costly but still of high operating capacity. For summer dry biomass harvesting two different machines were used; a M 132 Laverda combine-harvester with sunflower head and a mower-conditioner Laverda Mod. FTC2 and a trailed baler Gallignani Mod. 6000 were tested. The performance of the machinery and the possibilities of adaptation to the new crop was evaluated. Harvesting cost analysis was carried out.
5. Productivity of cardoon biomass Average productivity of cardoon dry biomass, obtained at the end of the growing cycle was 15.2 t d.m./ha in 1994-95 (445 mm of average rainfall) and 18.0 t d.m./ha in 1995/96 (646 mm of average rainfall). Average maximum productivities for both growing cycles were obtained in Thebes (Greece), where 28.6 t d.m./ha in 1994-95 (rainfall 490 mm) and 27.9 t d.m./ha in 1995-96 (rainfall 324 mm) were reported.
6. Ruminant nutrition The nutritive values of cardoon green forage (basal leaves), leaves silage, straw and seeds were determined using the A.O.A.C. (1984) techniques for dry matter (DM), organic matter (OM), ether extract (EE), crude fibre (CF), crude protein (CP) and enzymatic digestibility in green and dry forage. The fibrous fraction and the aminoacid composition in the whole seed and its kernel were determined. On the silage effluent obtained by pressing, the following determinations were made: soluble sugars, soluble nitrogen, ammonia nitrogen and acetic, propionic, butyric, isovaleric and lactic acids. Using adult wethers (sheep) the following were investigated: voluntary intake, raw matter digestibility, gross and digestible energy, the concentration in metabolisable energy, lactation net energy, maintenance and fattening net energy, ruminal degradability, and digestive kinetics.
7. Paper pulp production In order to characterise the raw material, the anatomical and chemical composition of the C. cardunculus stalk was done. Optical microscopy was used with fixed, stained microtomed sections. The chemical composition of the whole stalks as well as of the depithed material was determined using standard methods in relation to content of ash, silica, solvents, lignin, holocellulose as well as the monosaccharide composition of holocellulose. Kraft pulping process was studied in the laboratory on whole and unpithed stalks The fibre length distribution and the fibre length averages were determined for the different pulp fractions.
The ASAM pulping process was studied in the laboratory on whole and unpithed stalks and branches. The depithing was done after chipping by passing the dry material through a disc refiner with 2 mm disc clearance. A reference soda pulping was made with 20% total alkali, 0.05% anthraquinone, 60 min pulping time at 165'C and 170'C. Normal pulp bleaching was carried out using a chlorine-free bleaching sequence with hydrogen peroxide and oxygen. Another bleaching trial was made using whole plant material stored for three years under room conditions. ASAM I as well as ASAM 2 cooking, where sodium carbonate was used instead of sodium hydroxide was also investigated.
A soda and in situ generated soda process were also used with a liquid:solid ratio of 3.5 with impregnation at 95°C in presence of Na2CO3 followed by cooking with NAOH and Ca(OH)2 respectively, which generates NAOH and CaCO3. The following pulp properties were measured using AFNOR standards: tensile, burst, tear, double folding, bulk, stretch, air permeability, brightness. Refining behaviour was studied with a Lampen refiner only for the soda-AQ unbleached pulp. Bleaching of the pulps was done with ozone.
8. Energy applications In order to characterise the cardoon biomass for energy applications the ash, volatile matter, fixed carbon, elemental analysis, heating values, fusibility of ashes, thermogravimetric analysis and mayor and trace elements were determined. The biomass combustion tests were done in a pilot one MW BAFB (bubbling atmospheric fluidised bed) installation with a series of experiments under different conditions. The following parameters were measured on line:
Mass and energy balances of the combustion process were recorded from the experimental test data, which allowed a determining of the yields of both energy and carbon conversion.
9. Mineral nutrient extraction by the crop Aerial biomass production and that of the different parts: basal leaves, stem leaves, stem + branches, and capitula, were determined at the end of each growth cycle. The content in total nitrogen, phosphorus and potassium was determined separately for each plant part. Soil samples were also analysed.
10. Carbon balance of the crop Inorganic and organic soil carbon variation after two years cardoon growing was determined. Before sowing and after biomass harvesting, some soil representative samples for soil organic and inorganic carbon content determination were taken. Carbon content of the remaining root systems and stumps were also determined by elemental analysis. The amount of fixed carbon per hectare and year was established.
11. Energy input-output The various standard cultivation tasks were considered and the respective work rates (h/ha) and energy consumption rates (Mcal/h) were calculated. Assuming that production continues over 10 years, 1/10 of the energy inputs associated with establishment of the crop was added to the energy inputs for each production year. The final results were in terms of inputs per year and hectare. The heat values of the different components of aerial biomass were determined on dry matter basis, as higher and lower heating values.
12. Biomass production cost These were considered in terms of establishment costs for the first year and production costs for the following years. The implantation cost was calculated assuming the productive life of the crop at 10 years, with an interest rate of 5%. The working rates and materials used were the same as used for the energy balance estimation. Two different fertilisation systems were considered: the first based on using commercial fertilisers (N, P and K) and the second one taking into account only nitrogen fertilisation from commercial source, since the P and K would be supplied from the ashes of the combustion plant.
Results and Conclusions
In most experimental fields, the plantations with the highest plant densities (50,000- 57,000) yielded the highest productivities. Under limiting conditions (low yearly rainfall), there were no clear differences in productivity among the different plant densities. Winter harvesting had a negative effect on final biomass production. The later the forage harvesting was done, the more the productivity decreased. Winter harvesting decreased the final biomass production with respect to the control plot production in a percentage between 79.3% and 52.1% for the first growing cycle and between 89.1% and 56.7% for the second one.
The water use efficiency ranged between 2.89 and 3.27 in Madrid, between 1.82 and 4.35 in Catania and between 0.29 and 2.55 in Lisbon. It was not possible to correlate the figures with the total irrigation received by the crop. No differences could be found between the results of the N fertilised plants and those of the unfertilised plants.
In well developed plants, the average pattern of biomass distribution is: 20% basal leaves, 10% stem leaves, 40% stem and branches and 30% capitula. The average weight of the well developed capitula was 35.6 g, varying among populations from 21.6 to 59.0. The average seed proportion in the capitula was 33.4 % varying among populations from 15.6% to 40.2 %.
The average seed oil content was 27.2% plus/minus 2.5%, high enough to consider the possible cultivation for oil production. The composition of the oil was 10% palmitic, 3% stearic, 25% oleic and 60% linoleic, similar to sunflower oil. Three of the genotypes studied showed high oleic acid content (around 80%) and low linoleic acid content (around 4%).
The cost of forage harvesting was estimated at 93 ECU/ha for the self- propelled cutter-loader and trailer towed by tractor and 80 ECU/ha for the towed mower-conditioner and self-loading trailer). The system based on the mower conditioner had an effective work capacity of 0.82 ha/h and an operating work capacity of 0.65 ha/h. On the 26.2 t/ha harvested production basis, the hourly production of the mower conditioner system worked out at 17.04 t/h. The effective work capacity of the baler press was 0.28 ha/h and its operating work capacity 0.23 ha/h. On the 26.2 t/ha harvested production basis, the hourly production worked out at 6.03 t/h. Thus, the working time needed for the baler press is almost three times that of the mower conditioner.
The useful crop harvesting period could be approximately 300 hours/year taking into consideration week-ends and possible rainy days. This useful period in relation to the operative capacity of the machines would guarantee the possibility of harvesting a maximum area of approximately 195 ha/year for the mower- conditioner and 70 ha/year for the baler press. Under Spanish conditions, the estimated cost of the summer harvesting and baling of the dry biomass is 152.8 ECU/ha on the basis of 20 t (d.m.)/ha productivity.
The crude protein (CP) concentration in the green forage, as well as the low proportion of cell walls and their low level of lignification, are indicative of a very high quality forage, which was confirmed with its high digestibility (CP apparent digestibility coefficient of 77.63% and ruminal degradability of 79.7%).
The green forage from C. cardunculus is suitable for ensiling, as demonstrated by the high concentrations of lactic acid obtained and the nutritive quality of the product, with an absence of butyric acid and high digestibility (enzymatic digestibility -neutral detergent cellulase- of the organic matter ranging between 84.8 and 89.7%,0 as well as a high concentration of remaining soluble sugars (approximately 15% on average).
The seeds of Cynara cardunculus have a relatively high content of crude protein (CP) and ether extract (EE) concentrated in the kernel, which possesses a minimum level of fibre. In contrast the hull presents a high degree of lignification and a very high proportion of its protein linked to the fibre. Crude protein of Cynara cardunculus seeds is very degradable, with a normal amino-acid composition and an essential amino acid content of 46.9%. Methionine content is low, while lysine content is medium. The optimum use level for seeds in the diet for feed is 10%, however, it can be used up to 30% without important problems. The content in gross energy of this seed was of 5555 kcal/kg DM. The concentrations in digestible energy (DE) and metabolisable energy (ME) were calculated from the digestibility coefficient of energy obtained at a 30% substitution level, representing (per kg of dry matter) 3291 kcal and 2652 kcal, respectively. The lactation net energy expressed as UFL (Unites de fourrageres lait) and the maintenance and fattening net energy expressed as UFV (Unites de fourrageres viande") were 0.90 and 0.79 respectively.
The anatomy of the total cross-sectional area of the stalk shows that 18% corresponds to the area occupied by vascular bundles and fibres and 82% to parenchyma. Fibres are long, thin elements with a comparatively thicker cell wall. The external part of the stalk has on average longer fibres than the internal part. The following parameters were calculated for the Cynara fibres: souplesse coefficient 0.48, L:D ratio 93.4, and Runkel coefficient 0.50. The chemical composition of the raw material differs remarkably from wood. Hot water solubility is high, but lignin content as well as the amount of carbohydrates are lower.. The ash content is relatively moderate for annual plants, but it is high compared to wood. The hemicellulose content of this material is normal scale. The chemical composition of stalks and branches are very similar.
Kraft pulps show different strength properties between depithed and undepithed stalks. The pulp produced from depithed stalks had a much higher tensile index than the pulp from whole stalks. The Kappa number of pulps from the depithed material (manually or mechanically) was the same. However the pulp produced by using the mechanically depithed stem was obtained with 0.5 h shorter cooking time. The unbleached pulps were very easily refined and attained beating values of above 40°'SR with 1000 rotations. The pulp obtained with mechanically depithed stems showed values slightly lower than the other two pulps, but a much better drainage time. However, the increase in fines for beating rates above 2000 rotations led to very high drainage times. For all pulps their strength is adequate for use in general purpose papers, i.e. they show a tensile index near or above 70 N.ni/g. The pulp from the manually depithed stems shows higher tensile, tear and burst values.
The pulp from the mechanically depithed stems shows higher values. Tensile and tear values were higher for pulps from the manually depithed stems compared to pulp from the whole stalks and are always lower for pulp from the mechanically depithed stems.
For the ASAM pulping system variations in the total chemical charge showed that 20% total inorganic chemicals calculated as sodium hydroxide are required. In terms of yield and residual lignin content in the pulp are acceptable and the resulting pulp has good properties. The ASAM pulping of Cynara requires the addition of some anthraquinone and methanol. Pulping without methanol gives a higher residual lignin content of pulp and an insufficient fibre separation, which means that the reject content is extremely high. Increasing the methanol content of the liquor improves and benefits pulp viscosity as well as brightness.
The strength potential of the bleached Cynara pulps was satisfying, with tensile strength at a level which makes the pulp suitable for different fine paper products. The pulp properties from soda, soda-Anthraquinone and in-situ soda generating processes were similar to those of Kraft pulps. The in-situ soda generating process had no advantage over the soda process, while tensile strength and burst resistance increased with refining up to a beating degree of approximately 40°C, while tear resistance slightly decreased with refining. Bleaching of the Cynara pulp with ozone was possible, despite the initial brightness of the unbleached pulp being low. The results were better with a previous acidification. A two-step ozonization gave better results in relation to a single step treatment. A final treatment with hydrogen peroxide also allowed an increase of brightness.
In relation to the combustion applications of cardoon biomass, the most important characteristics are the following:
The combustion reactivity of C. cardunculus biomass is similar to that of other herbaceous biomass (e.g. cereal straw) but lower than that for woody biomass. For use in the experimental BAFB combustor the cardoon biomass had to be mixed with pine chips, with the best conditions found when a fuel ratio of 27/73 (pine chip/cardoon biomass) was used. The bed used was a mix of silica/limestone (70/30). The combustion efficiency of the most representative tests was evaluated, being well above 99% in all cases. A better boiler design and the optimisation of process conditions are required to reduce the CO emissions. The formation of CO is closely related to the presence of PAH's in gas emissions, thus indicating that the presence of these components is in relation to an incomplete combustion of the biomass. The PAH's number and concentration decreased substantially as the CO concentration decreased. The nitrogen oxides (expressed as NO) were maintained at levels between 150-300 ppm (at 6% 02 excess in dry gases) in all cases. These levels are, in general, below those permitted in the present legislation for 10-50 MWe thermal plants. In all cases, the values of sulphur oxides emissions were below 50 ppm, which is the lowest level detected by the gas analyser used.
Considering the whole aerial part of the crop, the average extraction of macronutrients per t of aerial biomass produced are: 13.21 kg of N, 1.60 kg of P (3.69 kg of P205) and 19.09 kg of K (22.9 kg of K20). It was concluded that cardoon cultivation can be used to clean soils contaminated with nitrates from previous excess use of agricultural fertilisers. A large amount of the potassium and phosphorous needed for the crop could be restored by adding the ashes obtained from cardoon combustion, if the biomass were used for energy purposes.
The global immobilised carbon per hectare of a cardoon standard crop (yield of 20t d.m./ha . year) could be estimated at 17.22 t/ha, that is equivalent to an annual C02 fixation of 63.14 t/ha.
The energy balance of the cardoon biomass production is extremely positive, because it represents an annual net production of 7.28 ton oil equivalent per hectare of plantation (300 GJ), with an energy ratio of 11 units produced as biomass per conventional energy unit consumed.
The cost of a standard cardoon production of 20 t (d.m.)/ha, equivalent to 8.0 t.o.e./ha, and depending on the fertilisation source, per t of dry biomass is 31 ECU. Cost production per GJ is 1.85 ECU and per toe is 77.53 ECU if full commercial fertilisers are used. These costs fall if ashes are used to provide P and K.
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