Thesis (Ph.D.)--University of Adelaide, Dept. of Agronomy & Farming Systems, 1997? / Bibliography: leaves 155-169.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 102-105). Also available via the Internet.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains iv, 64 p. : ill. Includes abstract. Includes bibliographical references.

Thesis (M.S.)--University of Wyoming, 2007. / Title from PDF title page (viewed on June 17, 2008). Includes bibliographical references (p. 56-60).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains vi, 63 p. : ill. (some col.), maps. Vita. Includes abstract. Includes bibliographical references (p. 40-46).

Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliography.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (MTech (Agriculture))--Cape Peninsula University of Technology, 2014. / Plants require nitrogen (N) to support desired production levels. Nitrogen fertilization strategy is a major consideration in field management with regard to achieving both economic and environmental objectives. For instance, in potato, insufficient N supply reduces tuber size and overall yield while excessive N supply can reduce tuber quality and increase environmental risk through nitrate (NO3-) leaching and nitrous oxide emission. Selection of an adequate N fertilizer application rate for crops is difficult, due to marked variations in soil N supply and crop N demand in both the field and over time. This research was conducted to characterise the ammonium transporter gene (AMT1) of Bambara groundnut and potato using molecular biology and bioinformatics methods. Nucleotide database sequences were used to design AMT1-specific primers which were used to amplify and sequence the core-region of the gene from Bambara groundnut and potato. Bioinformatics techniques were used to predict the structure and infer properties of the proteins. Nucleotide sequence alignment and phylogenetic analysis indicate that BgAMT1 and PoAMT1 are indeed from the AMT1 family, due to the clade and high similarity they respectively shared with other plant AMT1 genes. Amino acid sequence alignment showed that BgAMT1 is 92%, 89% and 87% similar to PvAMT1.1, GlycineAMT1 and LjAMT1.1 respectively, while PoAMT1 is 92%, 83% and 76% similar to LeAMT1.1, LjAMT1.1 and LeAMT1.2 respectively. BgAMT1 and PoAMT1 fragments were shown to correspond to the 5th - 10th transmembrane spanning-domains. Mutation of Bg W1A-L and S28A (for BgAMT1) and Po S70A (for PoAMT1) is predicted to enhance ammonium (NH4+) transport activity. Residues Bg D23 (for BgAMT1) and Po D16 (for PoAMT1) must be preserved otherwise NH4+ transport activity is inhibited. In all, BgAMT1 and PoAMT1 play a role in N uptake from the root while BgAMT1 may contribute more in different steps of rhizobia interaction. In an investigation of the correlation between AMT1 gene expression levels and leaf chlorophyll content index (CCI) with plant N status, potato plants were grown in a hydroponic greenhouse with 0.75 or 7.5 mM NO3- and 0.75 or 7.5 mM NH4+ as forms of N supply in a completely randomized design. Leaf CCI as measured by chlorophyll content meter, showed that an increase in N supply results in increased leaf CCI in response to both forms of N. Total RNA was isolated from leaf sampled at 28 days after treatment and expression level of the AMT1 gene was determined by reverse transcription-qPCR using a second set of primers designed for qPCR. The results showed that expression levels of AMT1 increased from 8.731 ± 2.606 when NO3- supply was high to 24.655 ± 2.93 when NO3- supply was low. However, there was no significant response in AMT1 expression levels to changes in NH4+. This result suggested that AMT1 transports NO3- less efficiently than NH4+, and thus more transport channels are required in the cell membrane when NO3- levels are low. Such variation in AMT1 expression levels are not necessary for NH4+ transport since the transport mechanism for NH4+ is efficient even at low NH4+ levels.

A two year field study located in Delta Municipality, British Columbia, was conducted to investigate the possible improvement of nitrogen (N) fertilizer recommendations for arable crops in the Lower Fraser Valley (LFV). After reviewing current N fertilizer recommendation systems in other humid regions, the approach taken in the study was to determine the applicability of a spring soil test and/or a N Index system for the LFV region. The project, which used sweet corn (Zea Mays saccharata) as the trial crop, consisted of two interconnected parts: 1) A 'Replicated Fertilizer Response Trial' which aimed to; a) Monitor soil N0₃-N and NH₄-N during spring to a depth of 80cm, using intervals of 0-20, 20-50, and 50-80cm. b) Investigate yield response and N uptake efficiency at four different rates of sidedress applied urea, 0, 50, 100 and 200 kg ha⁻¹ N. c) Compare the effectiveness of urea applied broadcast preplant, and applied by sidedressing, when the crop was approximately 30cm tall. 2) A 'Multifarm Survey' at 28 locations, comparing plots sidedressed with 135 kg ha⁻¹ N, to control plots containing only starter N. The aim of this survey vas to establish the range of N supplying capacities in some LFV soils and relate these capacities to other soil properties and site history. Monitoring mineral N in the soil demonstrated that soil N0₃-N increased during the spring, reaching a peak 5-6 weeks after planting. Maximum N0₃-N levels in the 0-80cm profile were 90 and 135 kg ha⁻¹ in 1984 and 1985 respectively. NH₄-N levels tended to be low compared to NO₃-N. As a proportion of total mineral N, NH₄-N decreased from approximately 25% at the beginning of May, to between 10 and 15% by mid June. Large amounts of spatial and temporal variability in both N0₃-N and NH₄-N were observed on the two sites studied. The difference in magnitude of mineral N between the years was due to a large number of site and weather factors which could not be separated. No significant differences in corn yield or crop N content were found between any of the four fertilizer treatments in the Replicated Response Trial. Similarly, no significant differences were found in the comparison of urea N applied by broadcasting before planting and urea N applied by sidedressing. Two reasons for this lack of response were suggested, one, that the soil plus starter N provided sufficient N for the crop's needs, and two, that the fertilizing techniques were inefficient considering the soil and weather conditions. The Multifarm Survey provided the greatest amount of information relevant to the project's objectives. It showed that the range of soil types and cropping regimes on corn fields in Delta Municipality was too narrow to have a direct influence on N supplied by the soil. Soil N supplying capacity was shown to be weakly related to organic matter, the study results suggested that a knowledge of site history was necessary before this relationship could be assumed to be positive. Such findings favoured the implementation of a spring soil test rather than a N Index system. Various approaches to estimating N fertilizer requirements using a spring soil sample were examined. In conclusion, the project showed that substantial amounts of N vere made available by the soil and that these should be taken into consideration when fertilizer recommendations are made. The study suggested that in a small agricultural region such as Delta Municipality, spring soil N0₃-N appeared to be sufficiently well correlated with total soil plus crop nitrogen to warrant the further investigation of a soil test for N. This test, for corn, should be as close as possible to sidedress time and the ideal sampling depth would be to 80cm. Anomalous sites with adverse soil conditions, such as poor drainage, marine influences, low pH or compaction should not be included in the test. / Land and Food Systems, Faculty of / Graduate

Nitrogen fertilizers are extensively used to enhance the growth of biomass crops. This study was conducted to determine the effect of N rates on the biomass yield and quality, and N uptake of several crops. The experiment was conducted at Fargo and Prosper, ND, in 2010 and 2011. The crops studied were forage sweet sorghum [Sorghum bicolor L. Moench], sorghum x sudangrass [Sorghum bicolor var. sudanense (Piper) Stapf.], kenaf [Hibiscus cannabinus L.], and reed canarygrass [Phalaris arundinacea L.]. The different crops constituted the main plots and the nitrogen rates were regarded as subplots. The five N rates were 0, 75, 100, 150, and 200 kg N ha-1. Forage sweet sorghum and sorghum x sudangrass had the greatest dry matter biomass yield. Nitrogen fertilization increased biomass yield for each of the crops. The results indicate that forage sorghum and sorghum x sudangrass have the greatest potential as a feedstock.