Intra- and inter-annual variability in the effects of nitrogen and irrigation rates on nitrate leaching and maize yield in the Bazile Groundwater Management Area of Nebraska

Authors: SINGH, ARSHDEEP - University Of Nebraska; RUDNICK, DARAN - Kansas State University; SNOW, DANIEL - University Of Nebraska; MISAR, CHRISTOPHER - University Of Nebraska; Birru, Girma; PROCTOR, CHRISTOPHER - University Of Nebraska; PUNTEL, LAILA - University Of Nebraska; IQBAL, JAVED - University Of Nebraska

Submitted to: Agriculture, Ecosystems & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2024
Publication Date: 1/7/2025
Citation: Singh, A., Rudnick, D., Snow, D., Misar, C., Birru, G.A., Proctor, C., Puntel, L., Iqbal, J. 2025. Intra- and inter-annual variability in the effects of nitrogen and irrigation rates on nitrate leaching and maize yield in the Bazile Groundwater Management Area of Nebraska. Agriculture, Ecosystems & Environment. 381. Article 109463. https://doi.org/10.1016/j.agee.2024.109463.
DOI: https://doi.org/10.1016/j.agee.2024.109463

Interpretive Summary: Groundwater NO3-N contamination has raised environmental and health concerns in the Midwestern United States. Particularly, High groundwater NO3-N contamination in sandy soils poses a significant threat to the sustainability of row crop production in vulnerable areas such as the Bazile Groundwater Management Area. To ensure sustainable crop production while protecting soil and water resources, it is essential to evaluate and adopt efficient nutrient and water management practices. This study demonstrated that applying nitrogen in multiple splits at either optimum or reduced rates can significantly lower NO3-N leaching in sandy soils. While reducing N fertilizer by 25% and 50% led to yield reductions of 8% and 11%, respectively, these reductions resulted in substantial decreases in NO3-N leaching by 24% and 51%, without significantly impacting RTNEnv. These findings highlight the tradeoff between lower maize yields, reduced NO3-N leaching, and societal economic returns in areas with groundwater NO3-N contamination. Moreover, the higher grain yield, greater RTN, and relatively lower NO3-N leaching observed with the 80% FIT treatment indicate that reducing irrigation can minimize NO3-N leaching without compromising maize yields or economic returns. Interestingly, annual variability in irrigation and grain yield had a greater influence on NO3-N leaching and economic returns than within-season N and irrigation management. For instance, despite lower irrigation and total water inputs in 2021, it yielded higher grain production, lower NO3-N leaching, less residual NO3-N and NH4-N, and higher RTN than 2022. Overall, the study shows that reducing nitrogen application rates is more effective in minimizing nitrate leaching and improving nitrogen use efficiency than reducing irrigation rates under the current sprinkler irrigation practices. Furthermore, inter-annual variability in NO3-N leaching should be factored into strategies for improving nitrogen management in groundwater management areas. Future research should focus on developing optimized irrigation scheduling and nitrogen rate models to further reduce NO3-N leaching while maintaining or improving crop productivity and economic returns.

Technical Abstract: Increasing groundwater NO3-N contamination has raised environmental and health concerns in irrigated sandy soils of Nebraska. This study aimed to evaluate the impact of suboptimum nitrogen (N) and deficit irrigation rates on NO3-N leaching, crop yield, and economic returns to nitrogen, both with (RTNEnv) and without (RTN) accounting for environmental costs. The two-year on-farm study utilized a two-factor factorial design with three N rates (optimum, suboptimum, and low) and three irrigation rates (farmer’s full irrigation [FIT], 80% of FIT, and 60% of FIT) in continuous maize grown on irrigated sandy soils in the Bazile Groundwater Management Area, Nebraska. The results indicated that nitrogen rates had a greater impact on seasonal NO3-N leaching than irrigation rates. Compared to the optimum (270 kg N ha'¹), the suboptimum (202 kg N ha'¹) and low N rates (135 kg N ha'¹) reduced NO3-N leaching by 24% (7 kg NO3- N ha'¹) and 51% (15 kg NO3-N ha'¹), respectively. Maize yield decreased by 8% (14.5 Mg ha'¹) and 11% (14.0 Mg ha'¹), while RTN dropped by $215 ha'¹ and $298 ha'¹, respectively. However, reduced N rates did not affect RTNEnv. The 80% FIT treatment produced significantly higher grain yield and RTN but did not affect NO3-N leaching compared to both the 60% FIT and FIT treatments. Additionally, inter-annual variability had a more pronounced effect on nitrate leaching than the treatments themselves. In 2021, NO3-N leaching was 64% lower due to 38% less irrigation, 37% higher grain N uptake, and 74% lower residual N—resulting in $214 more in RTN and $587 more in RTNEnv compared to 2022. In conclusion, findings suggest that reducing nitrogen rates is more effective in minimizing nitrate leaching than reducing irrigation rates under current sprinkler irrigation practices. Additionally, inter-annual variability in NO3- N leaching should be considered when developing strategies to improve nitrogen management.