Why diversify annual biomass production for energy – exemplified by green house gas emissions from the Danish IBUS bioethanol production concept

Summary

There is a need for integrating the biomass starting point into the energy manufacturing steps. It will secure that bioenergy is produced with limited use of non-renewable fossil fuel to secure that in the application of biomass a net emission reduction of green house gasses take place along the whole chain.
Intercropping, defined as the cultivation of two or more species simultaneously on the same area of land, is an traditional practice still widespread in the tropics and common in developed countries before the ‘fossilization’ of agriculture. This cropping strategy is based on the manipulation of plant interactions in time and space to optimize resource use and productivity. It is regarded as the practical application of basic ecological principles such as diversity, competition and facilitation (Hauggaard-Nielsen et al., 2007).
Cereal-legume annual intercropping show the possibility to increase input of leguminous symbiotic nitrogen (N) fixation into cropping systems reducing the need for fertilizer N applications (Jensen, 1996). Moreover, less need for pesticides are obtained due to improved competition towards weeds (Hauggaard-Nielsen et al., 2001) and less general damages on intercropped species by pest and disease organisms (Hauggaard-Nielsen et al., 2007). Intercropping is a more adaptive management practice as compared to the present arable crop rotations consisting mainly of sole crops.
Perennials like clover-grass intercrops or mixtures are obviously more diversified than traditional annual crops. Clover-grass leys are important in many agroecosystems today due to quality as feed for livestock, a high dry matter production (10 t ha-1 yr-1 unfertilized, where 95% of the N accumulation is N2 fixed by clover (Jørgensen et al., 1999) providing a nitrogen-rich residue, which may significantly reduce fertilizer requirements for the succeeding crop when mineralized (Hauggaard-Nielsen et al., 1998). Furthermore, clover-grass lays can be harvested several times a year and processed to ethanol throughout the year.
It is very much questioned whether bioethanol is a sustainable energy resource that can offer environmental and long-term economic advantages over fossil fuels, like gasoline or diesel. The aim of the present presentation is to debate the substitution of fossil fuels by crop biomass requiring the right selection of plant species according not only to chemical quality for efficient conversion but also to secure the development of ecologically benign farming system including biomass for energy.