Energy crop cultivation yield

The assessment of the sustainability of the cultivation of energy crops includes the input and recycling of nutrients, the application of pesticides, the water-use efficiency, the consumption of fossil fuels and the balance of soil carbon. The aim is to recycle the nutrients, which is simple in the case of anaerobic digestion by applying the digestate to the field. If crops are combusted many of the minerals can be returned via the ash. In the case of liquid biofuels, exported nutrients are lost and have to be replaced. The application of pesticides, mainly herbicides, can often be reduced in comparison to food production, but the energy yield per hectare might be reduced if the share of weeds exceeds certain thresholds. Water use efficiency,... 

Keywords Carbon Cultivation Energy crops Energy yield Fertiliser Greenhouse gases Heavy metals Nutrients Sustainability Yield... 

The yields of non-conventional crops such as Miscanthus sinensis, poplar and willow are little known. With the exception of willows in Sweden, these new energy crop species are mostly cultivated on small plots and are often at the research stage. Consequently, these yield data have to be examined critically. The published yields of M. sinensis, for instance, range between 8 and 22 t )M ha 1 year-1 and were mainly measured under special conditions (Friihwirth et al. 2006 Scholz et al. 2007 Stolzenburg 2008). The denoted average yields of poplar and willow are a result of an expert census in Germany (KTBL 2006). 

In this article, this new energy crop has been introduced and its benefits extolled, in particular, the yield data of Table 1. However, the specifics were done within the economic and time constraints of the grant and are left open for more detailed scrutiny. In particular, the botany and plant physiology of the SSPs need clarification by experts, as do the physical characteristics of Table 1. Further studies are needed to establish heating values for the SSPs and to determine combustion characteristics. Knowledge of the cultivation and harvest of these plants must be expanded. The hope is, however, that the set of plants discussed here makes direct burnable biomass an economically feasible alternative on a broad scale. 

However, the area-related energy yield is not the sole criteria for evaluating the energy efficiency of a crop species and/or a fuel type. The energy inputs (CED) of cultivation and conversion processes (see Table 5.7), the DM losses, the energetic use of by-products and the further ways of utilisation must also be considered. 

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