Evaluating the Effects of Integrating Irrigation and Nitrogen Management with Cover Crops on Crop Growth, Yields, Resource Use Efficiency, and Nitrate Leaching in Irrigated Corn Systems

Authors

• Martha Nabaggala, University of Nebraska-LincolnFollow

First Advisor

Abia Katimbo

Committee Members

Sahila Beegum, Nicolas Cafaro La Menza, Derek Heeren, Saleh Taghvaeian

Date of this Version

4-2026

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: Agricultural and Biological Systems Engineering

Under the supervision of Professor Abia Katimbo

Lincoln, Nebraska, April 2026

Comments

Copyright 2026, Martha Nabaggala. Used by permission

Abstract

Water and nitrogen (N) are essential inputs in corn production and must be properly managed to maximize yield while minimizing nitrate leaching. Cover crops (CCs) are increasingly adopted to reduce nitrate leaching. However, limited research has evaluated the effectiveness of integrating CCs with optimized irrigation and N management on yield, resource use efficiency, and nitrate leaching. The overall goal of this research is to evaluate whether integrating cereal rye (Secale cereale L.) CCs with optimal irrigation and N management strategies could improve or reduce corn growth and yield while improving resource use efficiency with nitrate loss reduction. A systematic review synthesized literature on CCs, N, and irrigation strategies for reducing nitrate leaching. Although many studies examined individual and two-way practices, few evaluated the three-way integration on soil water dynamics, nitrate losses, and agronomic performance.

Based on the review findings, an experiment evaluated the combined effects of CCs, irrigation, and N management on soil water dynamics, nitrate leaching, and residual soil nitrate during dry (2024) and wet (2025) seasons. Field experiments were conducted in CC and no CC (NCC) systems at the West Central Research, Extension and Education Center. Treatments included: RFN (rainfed-full N (FN)), FIFN (full irrigation (FI)-FN), D_HIFN (50% FI-FN), D_MIFN (75% FI-FN), EIFN (125% FI-FN), FID_HN (FI-50% FN), and FIEN (FI-125% FN). Irrigation levels were applied using a variable‑rate irrigation system, with N applied at planting, side‑dress, and via fertigation. Soil water status was monitored pre- and post-CC termination using Watermark sensors (soil matric potential) and in-season using neutron moisture meters (volumetric water content). Nitrate measurements were obtained from in-season lysimeter samples and end-of-season soil cores.

The third study evaluated whether in-season corn growth, yields and resource use efficiency can all be further improved with addition of CCs under best irrigation and N management practices while mitigating nitrate leaching. Measurements included plant height, vegetation indices, biomass, N uptake, yield, actual evapotranspiration and water and N efficiency indices across treatments in CC and NCC strips.

This research shows that integrating CCs with optimized irrigation and N management can reduce nitrate leaching while maintaining yields and improving resource use efficiency.

Advisor: Abia Katimbo