Integrated Environmental Biotechnology 247ideal candidates for use in this role. It is clear that the benefits of weed suppression
as a means of maximising the harvested energy yield will also apply to many
other biomass crops.
Agricultural benefits of compost
In general terms, it is possible to summarise the agricultural benefits of compost
as the addition of humus material and nutrients, which improve soil structure and
fertility, respectively. Compost brings with it a readymade microbial community
which can significantly augment the complement already present in naturally
impoverished soils. With better physical structure, aeration is improved and root
growth facilitated. The ability of biowaste-derived material to contribute to a
soil-nutrient replacement programme, and thereby lead to a reduction in propri-
etary chemical fertiliser use, has been a consistent finding in numerous studies.
This also represents a further prospective contribution on two relevant sides of
the intervention triangle. Firstly, in reducing nitrogenous inputs, it may play a
useful part in reducing the farm’s pollution potential. Secondly, it becomes an
example of cleaner production, since by biocycling nutrients back into the chain
of biomass utility, it forms a closed loop system in respect of both minerals and
energy. There may still be further ‘clean’ benefits to come, since research at the
University of Kassel on a range of plants, including cabbage, carrots, potatoes
and tomatoes has found that the use of compost was associated with an improved
nitrate to vitamin C ratio in the final product. Moreover, in structurally deficient
soils especially, compost appears to produce better results than it is possible for
artificial fertilisers alone to achieve. Even so, most investigations have concluded
that while high application rates generally tend to give relatively big increases
in crop yield, at lower levels the effect is less significant, being very largely
attributable to the compost’s humus enhancing effect.
Biodiesel
Returning to the central consideration of bioenergy, it would be wrong to dis-
cuss this topic without at least some passing reference to biodiesel, even though,
since it revolves around a chemical refining process, it is not strictly produced
by biotechnology. Like the increasing number of mineral oil substitutes currently
available or under development, biodiesel is derived from vegetable oils. Modern
diesel engines demand a clean-burning fuel of uniform quality which can function
under all expected operating conditions. One of the main advantages of biodiesel
is that it can be used directly, in unmodified engines, with the additional bonus
that it can perform as a single, pure fuel, or as part of a mix with its traditional
counterpart, in any ratio desired. While there remains some disagreement as to the
scale of the environmental benefits to be gained, especially in respect of carbon
dioxide discharges, there is good evidence that particulate emissions are signifi-
cantly reduced. In addition, biodiesel is claimed to have better lubricant properties