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dc.contributor.authorStockdale, Elizabeth Anneen
dc.date.accessioned2018-01-31T11:38:20Z
dc.date.available2018-01-31T11:38:20Z
dc.date.issued1993en
dc.identifier.urihttp://hdl.handle.net/1842/27478
dc.description.abstracten
dc.description.abstractAn integrated series of field, laboratory and pot experiments was carried out between 1990 and 1993 to study the release of nitrogen from organic manures and its subsequent recovery by crops. The aim was to increase understanding of the soil processes controlling N release from manures and therefore enable N supply to be more closely matched to crop demand in organic cropping systems.en
dc.description.abstractThe study of N release from manures is handicapped by the lack of appropriate methods to measure rates of mineralisation (both net and gross) in the field. The use of isotope dilution techniques under field conditions was found to be difficult due to the slow diffusion of ammonium ions in soils. The release of N from manures was therefore studied indirectly by monitoring plant uptake and changes in the soil mineral N pool. Indices, used to predict N release, w ere not found to be applicable where additions of manure had been made.en
dc.description.abstractVarious management strategies aimed at maximising N supply for organic crops were studied. The N released from manures in the first year was shown to be derived mainly from the pool of mineral N added in the manure. The availability of this pool was controlled by the supply of soluble carbon also added in manures, which stimulates the growth of the microbial biomass and therefore leads to immobilisation of the mineral N. The availability of any immobilised N for crop growth is not clear, though some evidence suggested that it was completely recovered by a spring barley crop. The organic N pool of the manure did not seem to be important in supplying N for crop growth in the first year.en
dc.description.abstractThe use of 15N-labelled manures enabled the separation of the N taken up by plants into that derived from the soil and that derived from the manure. Manures were labelled non-uniformly by incubation with 15 N salts for a short period before application. W here the assumption could not be made that the manure was uniformly labelled, a simple model was developed based on isotope dilution theory, to calculate the percentage of plant N uptake from the manure. 15N was also used to determine the source of the N extracted by a number of methods, used to assess potential N availability.en
dc.description.abstractThe structure of a simple model was described, which could be used to select a manurial strategy, which maximised crop yields and estimated the potential N losses for an organic farm. It was suggested that this could be constructed using an expert system approach, which was able to refer to databases and simple models to provide the final output. The full development of such a model is not yet possible, as the availability of the N applied in organic manures is only partly understood. However, our understanding of the complex processes controlling the release of N from manures has been increased as a result of the work described.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2017 Block 16en
dc.relation.isreferencedbyen
dc.titleNitrogen supply for organic cropsen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelen
dc.type.qualificationnamePhD Doctor of Philosophyen


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