Environmental Engineering Reference
In-Depth Information
Figure 1.1. Pineapple at the Azores - a CAM crop.
means that increased CO 2 concentration will be beneficial for C4 plants, but may be inhibiting C3
plants. The third enzyme system for photosynthesis is called the CAM system, or crasulacean acid
metabolism. CAM crops produce 4-carbon organic acids like the C4 system, but they also can
capture light during the day and later fix the CO 2 during the night. Two crops are of agricultural
interest from this group - pineapple (Fig. 1.1) and sisal (a kind of agave that gives strong fibers).
Well-known C4 crops are sorghum, sugarcane, maize, miscanthus and cord grass. Some more
are seen in the Table 1.6. Most species still have the C3 system.
There are many different potential energy crops. Some interesting crops are as follows.
1.3.1 Switch grass
Switch grass (Fig. 1.3) is seen as a potential important energy crop. Yield has been 5.2-
11.1 tonnes/ha/y in test fields in the US. The net energy yield (NEY) has been 60 GJ/ha/y. Switch
grass has been used as a feedstock for bio-ethanol production and then has gained 5-40 times
more renewable energy as ethanol than fossil energy consumed for the production. This means a
reduction of green- house gases (GHG) by 94% compared to gasoline when used as a fuel. It can
also be pelletized or bricquetized as seen in Figure 1.2.
1.3.2 Giant Kings Grass
Giant Kings Grass has been able to produce up to 100 tonnes DS/ha per y at a farm in China by
Viaspace Company (Kukkonen, 2011). It can grow with high yields also on marginal land if there
is enough water through rain or irrigation. There may be 2-3 harvests per year and the need for
fertilizers is relatively low. With crops available today the crop is sensitive to frost, but it might
be that frost resistant genes could be transferred to it, to make it feasible also at higher altitudes
sometime in the future.
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