Biomedical Engineering Reference
In-Depth Information
Nutrient requirements
To return to the issue of minerals, one of the chief potential bulk end uses of
biowaste-derived compost is as a horticultural amendment and fertiliser replace-
ment. There is no clear consensus between those working in the field as to how
much nutrient is removed from the system when SRC wood is harvested, esti-
mates for nitrogen loss ranging between 30 and 150 kg/ha. A study by the UK's
Forestry Commission produced figures of 135 kg/ha for nitrogen and 16 kg of
phosphate, which is around one-fifth the demands made by a cereal crop. On this
basis, it seems unlikely that nutrient removal would be a limit on fertile sites and
certainly not for the first few harvest cycles. In the case of soils with naturally
low fertility, or those which have been used for coppice cropping for some years,
supplementary mineral input may well be required. Clearly, if biowaste-derived
material is used for its water-holding properties, the concomitant humus and min-
eral donation would represent what might be described as a gratuitous benefit.
Process integration in this fashion brings evident economic advantages to any
commercial coppicing operation.
There is another way in which composts can help SRC. Direct competition
from other plants is one of the largest factors in poor coppice crop growth and
may even lead to outright failure in some cases. Uncontrolled grass or weed
growth around the trees in their first season can reduce the dry matter yield by a
fifth and halve their overall growth. Even after they have become properly estab-
lished, weed control remains an important part of optimising the energy crop's
performance, particularly where a soil's intrinsic water holding and/or nutrient
levels are less than ideal. Heavy mulching has been used very successfully in
many operations and, as is obvious from the previous discussions, biowaste soil
amendments are ideal 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 ready made microbial community
which can significantly augment the compliment 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 proprietary
chemical fertilisers 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
Search WWH ::
Custom Search