Graduate Studies, UNL

 

Dissertations and Doctoral Documents from University of Nebraska-Lincoln, 2023–

First Advisor

Deepak Keshwani

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Catelyn Bridges, Daniel Uden, Jennifer Keshwani, Xueheng Shi

Department

Agricultural & Biological Systems Engineering

Date of this Version

2025

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy (Ph.D.)

Major: Agricultural and Biological Systems Engineering

Under the supervision of Professor

Lincoln, Nebraska, December 2025

Comments

Copyright 2025, the author. Used by permission

Abstract

This dissertation examines the transition from conventional linear agricultural and food bioenergy systems toward more circular, resilient, and resource-efficient configurations. Prior research indicates that spatial and temporal variability in soil, weather, animal biological responses, and management decisions strongly influences productivity, nutrient-use efficiency, and profitability. Studies have also shown that a diversified circular system can buffer these sources of variability, improving stability and adaptive capacity. Building on these insights, the central focus of this work is to develop an integrated modeling framework to evaluate circularity within the Corn-Water-Ethanol-Beef (CWEB) nexus and explore how climate variability and management choices shape system-wide performance.

Chapter 1 reviews the sources of variability and uncertainty across Food-Energy-Water (FEW) systems, emphasizing how environmental heterogeneity, climate fluctuations, biological processes, and management interactions shape outcomes in interconnected agricultural and bioenergy contexts. The chapter evaluates existing modeling approaches to study FEW systems and identifies the limitations of relying exclusively on agent-based or system dynamics methods. These insights underscore the need for a hybrid simulation approach that can model cross-sector flows, nonlinear responses, and feedback mechanisms within the CWEB network.

Chapter 2 presents a hybrid Agent-Based and System Dynamics model built in AnyLogic® that links crop production, ethanol processing, cattle feeding, coproduct utilization, and manure nutrient recycling. The model incorporates seasonal dynamics, lifecycle processes, and key sustainability indicators, including circularity indices, water footprint, and greenhouse gas emissions. Scenario experiments demonstrate how herd size, diet composition, and manure application rates influence circularity metrics, resource efficiency, and system stability, illustrating the value of hybrid modeling for evaluating bioeconomy pathways.

Chapter 3 integrates climate-driven yield variability by estimating an Autoregressive Distributed Lag (ARDL) model using historical climate records for Nebraska. The resulting coefficients are embedded in AnyLogic® to update annual crop yields under nine climate shock scenarios representing warming trends, drought and moisture extremes, and precipitation changes. The combined ABM-SD-ARDL framework captures how climate induced yield shifts propagate through feedstock availability, ethanol output, DDGS supply, manure nutrient recovery, and system idle periods over a three-year horizon, offering insights into short-term resilience within food-bioenergy systems. The appendix includes technical supplementary material detailing feed calculations, manure assumptions, and model parameters.

Advisor: Deepak Keshwani

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