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Title: Nitrogen dynamics of an arable soil under different agronomic practices
Author: Redman, Mark H.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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It has become evident that the benefits of increased fertiliser N use in the UK may be offset by problems, such as nitrate leaching to surface and groundwaters. The broad objectives of this work were to investigate how the N dynamics of a 'typical' arable soil in south-east Scotland receiving recommended fertiliser N applications were modified by: 1) reducing fertiliser N application; 2) replacing the fertiliser N with a leguminous source of N (forage peas grown as a green manure crop); 3) growing a winter cover crop. All experimentation was field-based, with the main emphasis upon the direct measurement of NO3-N leaching losses from eight 300 m2 hydrologically isolated field plots, complemented by routine measurements of crop N uptake, soil mineral N, atmospheric N deposition and N2O flux. N2 fixation in the leguminous green manure was also measured, plus the mineralisation of the incorporated legume material. The efficacy of hydrological plot isolation in local soil types was first investigated using a small pilot plot. The main experimental period began with incorporation of the green manure in September 1987 and ended in April 1989. Crop yields were low and the utilisation of applied N very poor. There was no apparent financial incentive to reduce fertiliser N application or replace it with a leguminous green manure. Variable drainflow recovery from the plots hampered accurate estimation of NO3-N leaching losses, but results suggested that: leaching losses from arable soils in south-east Scotland are generally less than in southern Britain; reducing fertiliser N application had little effect upon leaching losses; autumn incorporation of the green manure increased leaching during the following winter; autumn cultivation increased leaching compared with no cultivation; spring-applied fertiliser N was susceptible to leaching loss; growth of a winter cover crop may have reduced winter leaching. Denitrification was likely to have been a very important N loss process, but was very difficult to measure directly in the heavy, poorly structured soil type.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available