Graduate Studies, UNL

 

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

First Advisor

Cody Creech

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

Amanda Easterly, John Westra, Nicolas Cafaro La Menza

Department

Agronomy

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: Agronomy

Under the supervision of Professor

Lincoln, Nebraska, December 2025

Comments

Copyright 2025, the author. Used by permission

Abstract

Sustainable crop production in the semi-arid High Plains of Nebraska faces challenges from limited precipitation, high interannual variability, and economic risk. This dissertation investigates the long-term productivity, water use, soil health, and economic sustainability of dryland crop rotations, with emphasis on the role of pulses as alternatives to fallow.

Chapter 1 analyzes nearly three decades (1995–2023) of on-farm data from the High Plains Agricultural Laboratory (Sidney, Nebraska) to compare seven crop rotations, including wheat, corn, millet, sunflower, and field peas. Results showed that wheat–corn–fallow (W–C–F) consistently outperformed traditional wheat–fallow (W–F) and more intensified four-year rotations, providing the highest grain yields, net returns, and precipitation-use efficiency.

Chapter 2 expands this analysis to additional long-term sites (North Platte and Brule, Nebraska), confirming that C-C-F and W–C–F remains a resilient rotation, while continuous wheat and heavily intensified rotations suffered yield penalties and economic losses, suggesting a threshold at cropping intensity at 0.67 CI.

Chapter 3 applied principal component analysis to soil chemical, microbial, enzymatic, and agronomic variables on a set of six crop rotations. Results demonstrated that water availability was the dominant driver of variability across systems but also revealed that crop rotations shape distinct microbial and soil fertility associations. Sustainable outcomes were linked to higher organic matter, enzyme activity, and balanced microbial communities.

Chapter 4 examined the replacement of fallow or cover crops with field peas and chickpeas. Results underscore the complexity of soil–crop–climate interactions and highlight the need for rotation designs that optimize yield and soil health. Integrating pulse crops seems promising for enhancing SOM benefits, whereas other certain crop sequences may require complementary nutrient or residue management to avoid trade-offs.

These findings demonstrate that sustainable intensification in west Nebraska is constrained by water availability. Moderate-intensity rotations such as W–C–F strike the most favorable balance between productivity, profitability, and ecological stability in the semiarid High Plains. Pulse crops like chickpeas and fields peas not only bring cash income but also ecosystem services like nitrogen credits and reduced erosion, suggesting more benefits than those obtained from oats cover crops.

Advisor: Cody Creech

Download

Share

COinS