Abstract
Human-managed grasslands receive large amounts of organic and inorganic nutrient fertilisers which contribute to increasing biomass yields, but also profoundly influence key belowground processes and plant-soil-microbial interactions. This study addresses how longterm additions of nutrient fertilisers either in inorganic or organic forms might affect biogeochemical interactions in a permanent grassland subject to intensive management.I found for example, that after a 10-month incubation period under field conditions, highest root mass loss (~43%) was associated with highest additions of organic animal slurries, whereas lowest root mass loss (~29%) occurred in inorganically N-fertilised and unfertilised- control soils. Root mass loss was mainly driven by N-induced decreases in both root C:N ratios and Fungal-to-Bacterial (F:B) ratios. The study also demonstrates how 47 years of high organic p applications (through liquid manures) caused a 1,600% increase in soil P availability and > 400% increase in total soil P stocks (0-15 cm depth) when compared to control-unfertilised soils. Soils' ability to retain added P was quite remarkable whereby up to 62% of organic P and 48% of inorganic P annually applied since 1970 was retained in soils. The colonisation of arbuscular mycorrhizal fungi (AMF) in soils was still relatively high (50-75%) after ~50 years of 'normal' agronomic P inputs (e.g. ~30 kg P ha'1 yr1) and was strongly positively related to Plant P Use Efficiency (PUE). Finally, soil CO2 fluxes were not significantly affected by fertiliser type or rates of fertiliser application, but soil respiration was highest in plots receiving inorganic NPK applications. Cumulative annual CO2 emissions were not statistically significant among nutrient treatments. This study suggests that the delivery of multiple ecosystem services is constrained by unavoidable trade-offs between different biogeochemical Processes. However, grassland management can be modified to sustain some of these services in the long-term under agricultural intensification.
| Date of Award | Dec 2019 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Department of Agriculture, Environment and Rural Affairs |
| Supervisor | Dario Fornara (Supervisor) & Tancredi Caruso (Supervisor) |