250 Environmental Biotechnology
obvious, and follow on logically from much of the preceding discussion, there is
a natural fit between agricultural and environmental biotechnologies and hence,
a significant potential for integration both between and within them.
Some of the ways in which this can take place in respect of biowaste-derived
soil amendment products have already been described and, clearly, the advan-
tages they convey are not limited to the particular energy crop examples cited.
Before leaving this particular topic, there is another aspect of their application
which is worthy of note, not least since it illustrates both integrated production
and a potential means of obviating current dependence on a significant environ-
mental pollutant.
Plant disease suppression
Intensively reared crops can suffer extensive and expensive losses resulting from
plant disease infection. Until the early 1930s, crop rotation and the use of animal
manures and green mulches provided the traditional protection regime; after this
time, chemical fumigation became the favoured method to deal with soil-borne
pathogens, which can accumulate heavily in intensive monocultures. Methyl bro-
mide has been the main agent used, its popularity largely attributable to its ability
also to destroy weeds and resident insect pests. It is, however, an indiscriminate
tool, and though it has contributed directly to the commercial viability of many
growers’ operations, it has been implicated in ozone depletion. Accordingly,
under the terms of the Montreal Protocol, it is due to be phased out by 2005.
This, coupled with other fears regarding residual bromine in food and ground-
water, has led to bans in Germany, Switzerland and the Netherlands, the latter
being, at one time, Europe’s largest user of methyl bromide soil fumigation.
A number of alternative options are being explored, including soil pasteurisa-
tion using steam, ultraviolet treatment and the development of resistant cultivars
using both selective breeding and genetic modification. The use of compost
extracts – so-called ‘compost teas’ – is also receiving serious consideration as a
means of crop-specific disease control. Their action appears to be two-fold, firstly
as a protection against foliar diseases and secondly as a inoculant to restoring or
enhancing suboptimal soil microbial communities.
Research projects in Germany, Israel, Japan, the UK, the USA and elsewhere
have found that these extracts are very effective natural methods to suppress or
control a number of plant diseases thus reducing the demand for artificial agro-
chemical intervention (Table 10.1). Direct competition with the relevant pathogen
itself is one of a variety of mechanisms believed to play a part in the overall
disease suppression, along with induced disease resistance, and the inhibited ger-
mination of spores. This is thought to be brought about by means of the extract’s
action on the surface of the leaves themselves and stimulatory effect on the asso-
ciated circum-phyllospheric micro-organisms. Bacteria, yeasts and fungi present
in the extracts have been shown to be active agents, while evidence points to a
number of organic chemicals, including phenols and various amino acids, also