Using organic fertilisers to manipulate soil microbiology for improved nutrient bioavailability

Soils are essential to food production through the delivery of bioavailable nutrients required for crop growth. Depleted nutrients are routinely replenished as mineral fertilizers at specific times of the crop growing season to promote productivity. However, this approach means that fertiliser application rarely matches crop demand, resulting in costly and often environmentally damaging over-application of mineral fertilizers. In addition, soil organic matter (the natural reserve of nutrients) becomes depleted with a resultant reduction in biodiversity. This reduced organic matter and biodiversity has essentially reduced the soils natural ability to deliver crop available forms of nutrients, increasing the reliance of food production on agrochemicals. We will investigate novel ways to bioengineer soil organic matter through manipulating the microbiology using anaerobically derived digestates co-amended with other forms of organic materials. The intention is that this manipulation will increase the provision of nutrients to the crop throughout the year. Strategies will be investigated as to how to feed the soil microbiology directly, to improve nutrient delivery through the crop season. This is particularly novel as current fertilizer strategies focus on feeding the crop rather than soil microorganisms. Thus the intention is to increase soil organic matter reserves through increasing microbial biomass and biodiversity, and so re-connect the soils natural processes within the rhizosphere to improve nutrient availability. Hence the aim of this PhD is to understand the mechanisms associated with utilizing anaerobic digestate as a rich source of labile nutrients, combined with recalcitrant organic residues with high C/N ratio, towards improving crop nutrients. Digestate is particularly interesting as it has been subjected to anaerobic decomposition and so its fibre component may represent stable organic matter. An understanding of how these materials interact with rhizosphere microorganisms, and thereby instigate the release of organically bound nutrients for crop development throughout the year, will enable nutrient strategies to be developed that will reduce reliance on mineral fertilizers.