The UK Government has taken steps to increase the production and use of biofuels. The benefits of biofuels include greenhouse gas reductions, contributing to domestic and international targets, potential air quality benefits, the diversification of the fuel sector and an additional market for agricultural products. Oilseed rape (OSR) is currently the most widely grown crop used for biodiesel production. The future of oilseed rape and other biofuel crops such as Miscanthus will depend on improved agricultural practices, as currently, OSR crops only achieve predicted yields when grown on land not previously used to grow the crop. When rotations involve OSR following OSR, yields are always reduced by approximately 30%.With increased pressure to produce OSR for biofuel use, rotation intervals are likely to shorten and the loss of productive capacity will increase.
Reduction in yield with continuous cropping has been recorded for numerous crops in addition to OSR including sugar cane, wheat, maize, rice, barley, tobacco and potato. These yield declines have been related to a build-up of organisms deleterious to the crop including plant pathogenic fungi and nematodes, as well as changes in the microbial population in general. Quantification and characterisation of soil microbial biodiversity in relation to rotation intervals is required to determine the likely cause of yield decline in OSR. Although it is possible that a plant pathogen may be associated with yield decline, it is highly likely that the cause of OSR yield decline will be complex and a combination of biotic and abiotic factors. This is particularly so for OSR as metabolites released from roots are known to influence the microbial population in soil and residues of many brassicas have been used for disease control as ¡§biofumigants¡¨. A further concern is the long-term effects that such monocultures may have on soil quality and biodiversity in general and whether break crops can restore both soil biodiversity and allow a return in subsequent OSR yields.
The objective of this project will be to examine the impact of shortened rotations on rhizosphere biodiversity in biofuel crops, in particular OSR. The aim will be to determine the effects of a range of rotations of OSR and wheat on the diversity of soil fungi (including pathogens and mycorrhiza), soil bacteria and nematodes.
„« An established OSR field trial based in East Anglia funded by HGCA, planted by TAG and managed by Velcourt Ltd will be used to provide samples for this project.
„« DNA-based techniques will be used to examine populations of soil fungi (including pathogens, saprophytes and mycorrhiza), bacteria and nematodes. Attempts will be made to correlate diversity and abundance of indicator species with rotation history.
„« Classical isolation, identification and re-inoculation methods (Koch¡¦s postulates) will be applied as required.
„« Pot experiments will be used to establish a model system in the glasshouse to replicate and quantify the OSR decline and dissect the mechanisms involved. Two procedures will be used:
A) Determine the effect on plant biomass yield and the diversity of soil organism communities of oilseed rape roots (collected from continuous oilseed rape field plants) added to soil prior to planting of oilseed rape plants.
B) Determine the effect of repeated plantings of OSR seeds in the same soil.
A time course will be used to determine the period required to establish decline and to provide further samples for population characterisation. Experiment A will determine the role of residues and dead roots and Experiment B the role of living roots and exudates on the decline process.
Information from this research could be used to inform production of other biofuel species, such as Miscanthus, likely to be grown in monoculture with no, or short rotation breaks. Overall this project addresses Defra policy on the effect of sustainable farming systems and land management on biodiversity and soil protection, and policy on climate change through studies of alternative energy crops.