Agronomy and Horticulture, Department of


First Advisor

James C. Schnable

Date of this Version

Spring 4-23-2021

Document Type



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of James C. Schnable. Lincoln, Nebraska: May, 2021

Copyright © 2021 Mackenzie Zwiener


The movement of nutrients from old vegetative tissue to young leaves and reproductive organs is known as senescence. Senescence can be influenced by the environment of a plant, such as, drought, heat, and nutrient stress. These environmental stressors can also influence canopy architecture. Crop canopy consists of several traits including: leaf number, angle, length and width. Past research in crops like maize and rice have shown significant influences of more erect leaves, including, the ability for increased planting density, which optimizes light interception and increases yield. In a field trial of a sorghum association panel including 345 different sorghum varieties grown in a replicated design under nitrogen sufficient and nitrogen deficit conditions, we have found that sorghum leaf angle is plastic in response to nitrogen deficit stress. While the response of individual varieties varied, an overall statistically significant trend was observed towards smaller leaf angles (e.g. more erect leaves) under deficient nitrogen conditions. In parallel with field experiments, greenhouse experiments utilizing sorghum plants grown under different levels of nitrogen availability were also conducted. These confirmed the increased erectness of sorghum leaves under nitrogen deficient conditions. In addition, RGB and hyperspectral images collected from this experiment were used to train machine learning models to classify individual pixels into six classes: nonplant pixels, panicles, stems, green leaves, senescing leaves, and dead leaves. With this new method, we were able to track the progression of senescence through the life cycle of individual sorghum plants grown under different nitrogen treatments.

Adviser: James C. Schnable