Abstract:
"The application of bio-solids to established arable crops, using shallow injection techniques developed during this study, is feasible in environmental, economic,agronomic and engineering terms."
Novel approaches to bio-solids disposal and recycling are required to compensate for
expected increases in production, and to alleviate the extemal pressures exerted on the water company through legislation and increased public awareness of environmental
issues. A review of previous work has identied bio-solids application to arable
cropping as a promising benecial outlet for increased volumes of waste.
From this doctoral study, in collaboration with a parallel fast track project, a
improved, shallow injection system has been developed, based on soil mechanics
theory and extensive laboratory and field testing. Environmental pollution, in terms of
odour and ammonia emissions, may be signicantly reduced through the use of this
system, when compared to other shallow injection or surface application methods.
Nitrate leaching was found to be unaffected by the increased retention of valuable
nutrients under field conditions prevailing during the study period, and no detrimental
effect on agronomic performance has been identied following application to crops
up to three months prior to harvest.
Economically, a market exists for this technology, through the enhanced nutrient
value of the bio-solids product. However, product quality, consistency and other
enviromnental issues require solutions before the full economic benefits and market
acceptance can be realised. Theoretically, the increased application "window of
opportunity" has the potential to increase producers operating profits substantially
(1.7%/yr, Anglian Water Services Region) through reduced inventory, storage and
distribution costs.
Maximisation of enviromnental benefits has been addressed in terms of implement
control, by maintaining constant tine attitude to the soil, through a parallel linkage system. A analysis of the force system associated with the parallel lirkage system, in conjunction with the development of a model to predict tine depth, was used to
examine ways of optimising the dynamic performance of the system. This work
demonstrated that geometric changes to the parallel linkage are unlikely to affect
dynamic performance. However, the use of frictionless linkage joints in conjunction
with depth control skids was shown to improve dynamic performance signicantly
and a novel multiple curve fitting technique was developed to improve the accuracy
of the depth prediction model.