Response of Soybean to Variable Irrigation Levels in Eastern Nebraska Using the AquaCrop Model

Authors

Anmol Singh, University of Nebraska-LincolnFollow

First Advisor

Saleh Taghvaeian

Second Advisor

Yufeng Ge

Committee Members

Frank Bai, Derek Heeren

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: Agricultural and Biological Systems Engineering

Under the supervision of Professors Saleh Taghvaeian and Yufeng Ge

Lincoln, Nebraska, July, 2025

Comments

Copyright 2025, Anmol Singh. Used by permission

Abstract

AquaCrop was calibrated and validated for soybean [Glycine max (L.) Merr.] using 19 irrigation treatments from five years using data from field experiments. The model accurately simulated canopy cover (CC), soil water content (SWC), and grain yield, with overall validation nRMSE values of 12%, 7%, and 7%, respectively. The overall validation nRMSE for SWC in individual 30-cm soil layers was comparatively higher, at 19%. The model was subsequently applied for long-term simulations (2010–2024) to estimate soybean yield and water requirements for two dominant soil types, Yutan silty clay loam and Tomek silt loam under three irrigation levels - rainfed, deficit irrigation, and full irrigation. Full and deficit irrigation were triggered when 140% and 100% of Readily Available Water (RAW) were depleted, respectively. The highest average simulated yields were obtained under full irrigation, and had similar range from 3.93 to 4.51 Mg ha^⁻¹ for both soils. Rainfed treatments produced the lowest average simulated yields, ranging from 1.11 to 4.39 Mg ha^⁻¹ for Yutan soils and 0.85 to 4.39 Mg ha^⁻¹ for Tomek soils. Across all years, the yield difference between full and deficit irrigation was less than 11%. Average irrigation requirements under full irrigation were 136 mm for Yutan soils and 159 mm for Tomek soils, while deficit irrigation reduced these amounts to 70 mm and 74 mm, respectively. Overall, AquaCrop showed good performance and can be valuable tool for evaluating irrigation strategies in Eastern Nebraska. Model results indicate that deficit irrigation has the potential to conserve water without significantly reducing soybean yield.

Advisors: Saleh Taghvaeian and Yufeng Ge