Evaluating the Effects of Row Spacing, Legume Intercropping, Fertilizer Source, and Fertilizer Timing on Intermediate Wheatgrass in Eastern Nebraska

Authors

Madeline M. Johnston, University of Nebraska-LincolnFollow

First Advisor

Andrea D. Basche

Committee Members

Cody Creech, Nicolas Cafaro La Menza

Date of this Version

7-2025

Document Type

Thesis

Citation

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 Professor Andrea D. Basche

Lincoln, Nebraska, July 2025

Comments

Copyright 2025, Madeline M. Johnston. Used by permission

Abstract

Kernza^® is the trademarked name of the perennial crop intermediate wheatgrass (Thinopyrum intermedium). In addition to its potential for dual-use as a grain and forage crop, Kernza is marketed to provide needed environmental services by increasing crop biodiversity, sequestering soil carbon, and reducing nitrate leaching. However, more work is needed in cultivar selection and crop management to increase total grain yields and prevent long-term grain yield decline. Furthermore, research in quantifying and understanding Kernza’s ability to affect soil properties and water dynamics is limited.

Two field experiments were conducted at the Eastern Nebraska Research Extension and Education Center in randomized complete block designs over multiple harvest years (2022-2024) with varying severity of drought. One trial evaluated five of the latest Kernza cultivars in combination with factors of row spacing (38 cm, 76 cm), cropping system (monoculture, legume intercropping), and legume species (alfalfa, red clover) to determine effective combinations of genetics and management for yields and biomass. Results largely showed no differences between cultivars. Overall, monoculture stands in narrower rows produced the highest total yields and biomass with the lowest weed pressure, while legume-intercropped treatments produced the most consistent yields.

The second experiment evaluated a single cultivar grown using a single N rate (180 kg/ha N) under different fertilizer sources (urea, poultry manure) and timings (spring, fall) in comparison to a corn-soybean rotation (180 kg/ha urea) to primarily evaluate effects on soil and water dynamics. The results of this experiment suggest that observed changes in soil properties, such as pH, Ca, and Mg were a result of fertilizer source differences, whereas changes in SOM and P were only affected by year and were most likely a result of drought. Furthermore, Kernza tended to have less soil moisture than the corn-soybean rotation, suggesting the potential for reduced water losses and nitrate leaching under Kernza.

Together, these experiments demonstrate the potential to maintain grain yields with legume intercropping or poultry manure, and to increase grain yields with narrower rows. Furthermore, fertilizer source impacts the crop’s potential to enhance soil properties without yield penalties. Finally, Kernza has potential for reduced water or nitrate loss.

Advisor: Andrea D. Basche