Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Richard M. Cruse


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.



Digital Repository @ Iowa State University,

Copyright Owner

Alan Dean Blaylock



Proquest ID


File Format


File Size

80 pages