Degree Type

Dissertation

Date of Award

1989

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

Richard M. Cruse

Abstract

Ridge conservation tillage systems are receiving increased attention as an alternative to flat no-till systems for row crop production. A recently-developed fertilizer applicator, the spoke-wheel injector has potential to improve fertilizer-use efficiency in ridge-till systems, but little work has been done to identify efficient N placements for ridges. A field study to investigate corn (Zea mays L.) response to ridge-till N placement methods and to examine the inorganic N distribution resulting from point-injected N fertilizer was conducted within a corn-soybean (Glycine max (L) Merr.) rotation at two central Iowa locations on poorly-drained till-derived soils. Urea-ammonium nitrate solution (UAN) treatments consisted of combinations of three placements (surface broadcast spray, point injection between rows, or point injection in rows) and five rates from 0 to 157 kg N ha[superscript]-1. To determine fertilizer-N recovery, [superscript]15N-depleted NH[subscript]4NO[subscript]3 (99.99% [superscript]14N) was substituted for UAN on one-row microplots from within the main plots of the 67- and 157-kg N ha[superscript]-1 treatments. Nitrogen recovery was estimated from plant samples taken at four growth stages from [superscript]15N-depleted microplots. Nitrate- and NH[subscript]4-N were determined on soil samples taken late in the growing season at five positions perpendicular to the plant row and at several depth intervals from 0-, 67-, and 157-kg N ha[superscript]-1 injection treatments;Generally, 157 kg N ha[superscript]-1 treatments resulted in soil NO[subscript]3-N and NH[subscript]4-N levels greater than other rates. The greatest N accumulations were measured around the injection point and in the ridge surface soil. Injected N resulted in significantly greater corn yields, percentage N derived from fertilizer, and percentage of fertilizer N recovered than broadcast, but differences between injection positions were generally not significant;A portion of the study area was used to compare the sufficiency of one- and three-row microplots for studying N uptake from in-row N applications. Nitrogen recoveries did not differ significantly between the two microplot types. One-row microplots seem to have potential to decrease the amount of labeled-N required under some experimental conditions.

DOI

https://doi.org/10.31274/rtd-180813-12387

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Alan Dean Blaylock

Language

en

Proquest ID

AAI9014881

File Format

application/pdf

File Size

80 pages

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