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https://hdl.handle.net/2142/19552
Description
Title
Evaluation of nitrogen availability indices
Author(s)
Brown, Howard Martin
Issue Date
1996
Doctoral Committee Chair(s)
Hoeft, Robert G.
Department of Study
Crop Sciences
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Chemistry, Agricultural
Language
eng
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.
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