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Title: Soil tests for predicting nitrogen supply in Irish soils
Author: McDonald, Noeleen Theresa
ISNI:       0000 0004 5371 6168
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2014
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Existing nitrogen (N) fertilizer recommendations for Irish grassland do not account for the potential variability in soil N supply through N mineralization. Research carried out within this thesis aims to identify a suitable N test that can estimate the potential range of N supplied in temperate soils and to increase the knowledge of soil metabolites linked with soil N mineralization. To fulfill these aims a series of interlinking studies were conducted. Initially laboratory studies investigating various soil N pools and N tests were undertaken, then a more in depth analysis of the carbon (C) and N metabolites in these soils was conducted using proton nuclear magnetic resonance spectroscopy (1H NMR). Following this a microcosm study was conducted to validate the laboratory findings and finally, field studies to investigate the temporal variability of soil N pools and their relationship with grass production. The laboratory studies found that there was large differences in mineralizable N (MN) capacity between Irish grassland soil types and that the Illinois soil N test (ISNT-N) was the best rapid predictor of MN across these soil types. The 1 H NMR analysis of these soils identified 7 metabolites, most as labile sources of C linked as regulators of N mineralization. The microcosm experiment, showed that a model combining ISNT-N, total oxidized N (TON), C:N and the interaction of ISNT-N X C:N best predicted grass OM production and N uptake. In the field study, soil mineral N was found to be highly transient, over the 15 month sampling period, while MN was less variable. Daily grass OM production was mainly explained by climatic variables and further evaluation across multiple seasons is therefore warranted. Overall this study highlights the real opportunity to improve N use efficiency with soil N testing, hence reducing costs to the farmer and losses to the environment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available