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 Title: Evaluation of nitrogen availability indices Author(s): Brown, Howard Martin Doctoral Committee Chair(s): Hoeft, Robert G. Department / Program: Crop Sciences Discipline: Agronomy Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Agriculture, Agronomy Chemistry, Agricultural Abstract: Both economic and environmental concerns dictate that N fertilizer be applied to optimize crop production and minimize potential for movement of N into surface and/or ground water resources. Field and laboratory studies were conducted to evaluate factors affecting the reliability of recommendations from three N availability indices and four laboratory methods to measure extractable organic N (EON), and the accuracy and repeatability of the Horiba Cardy Nitrate meter in determining NO$\sb3$-N content in soils and solution.Factors influencing the reliability of three N availability indices, Proven Yield Nitrogen (PYN), Presidedress Nitrate Test (PSNT), and Preplant Nitrate Test (PPNT), were evaluated at 76 sites from 1990-1992. Only 43 of the 76 sites responded to N fertilizer. Of the remaining 33 nonresponding sites, 15 could not be explained by previous crop, manure applications, or environmental conditions. The PYN system provided an adequate N recommendation compared to the PSNT and PPNT for the N-responsive sites. The use of the PSNT or PPNT improved N recommendations over that from the PYN on soils with a history of manure application or residual N.Reports of near optimal yields with little or no additional N fertilizer provides reason to find a laboratory method to predict a soil's responsiveness to N fertilizer. Four laboratory methods were evaluated for their ability to measure the fraction of soil organic N that is readily available to the growing crop. Soil samples collected from N-rate study sites were used in the evaluation (responding and nonresponding sites).The heated KCl method best predicted N responsiveness of the soils evaluated. Twelve of 16 nonresponsive soils were correctly characterized using this method.A quick, reliable way for "on-site" determination of soil NO$\sb3$-N would assist adoption of availability indices that allow credit for the concentration of NO$\sb3$-N in the soil profile before a N fertilizer application. A hand-held NO$\sb3$-meter was evaluated for analytical accuracy and precision through N recovery tests using 12 surface soils and through comparison to conventional NO$\sb3$-N determinations involving KC1 extractions and steam distillation. Meter response to interfering ions was also evaluated.Analyses of 12 surface soils for NO$\sb3$-N using the Horiba Cardy NO, meter were in close agreement with results obtained using KC1 extraction-steam distillation. Interference by C1, NO$\sb2$, and HCO$\sb3$ were observed at low NO$\sb3$-N concentrations, but were minimized with the use of an extraction solution containing 20 mg L$\sp{-1}$ of NO$\sb3$-N. The Horiba Cardy NO$\sb3$-meter is thus a reliable tool for rapid estimation of soil and solution NO$\sb3$-N concentrations. Issue Date: 1996 Type: Text Language: English URI: http://hdl.handle.net/2142/19552 ISBN: 9780591197471 Rights Information: Copyright 1996 Brown, Howard Martin Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9712206 OCLC Identifier: (UMI)AAI9712206
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