Date of Award

January 2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Agronomy

First Advisor

Tony J Vyn

Committee Member 1

James Camberato

Committee Member 2

Tristan Coram

Committee Member 3

Timothy Filley

Abstract

The ability of modern maize (Zea mays L.) hybrids to accumulate more biomass and nitrogen (N) after the flowering period with extended photosynthesis capacity has been associated with improvements in grain yield (GY) and nitrogen use efficiency (NUE). The overall objectives of this research are to improve knowledge on N dynamics and physiological traits that are correlated with NUE using the “pulse-labeled” 15N application as a novel phenotyping strategy to characterize maize hybrids varying in yield stability and responsiveness to N under limited N environments. Three field experiments were established at Purdue University’s research farms during the 2013 and 2014 growing seasons; in each experiment five hybrids, including pairs of two modern “high yielding” commercial hybrids and two “high N responsive” hybrids (or potentially superior in NUE) and one old era hybrid from the 70’s were compared under zero N fertilizer application (0N) and a moderate rate of 112 kg of N per ha (112N). The “pulse-labeled” application of 15N at low N rates (2.1 to 3.2 kg 15N ha-1) in the root zones on both sides of consecutive plants enabled precise estimation of N uptake efficiency and allocation of the recent 15N uptake (15Nu) to plant components at six development stages per location/year between V14 and R6. Plant recovery of 15N was determined in above-ground maize plant components sampled 4 to 6 days after pulse labeling. Before flowering, plants recovered about 45% of the 15N fertilizer applied and 15Nu was more evenly distributed in plant components with about 50% of the total 15Nu found in the leaves and ~ 40% in the stems; a small amount of 15Nu was found in the husks at late vegetative stage. After the flowering period, 15Nu decreased in the vegetative organs and increased in the ears and/or kernels as the season progressed. Even at the late R5 stage plants recovered about 20% (at 0N) or 30% (at 112N) of the new 15N applied, and approximately 70% of the total 15Nu was allocated to kernels. NUE hybrids allocated up to ~20% of 15Nu to the leaves even at this late stage.

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