Recent research from Iowa State University reveals a gradual increase in the demand for nitrogen fertilizer in Midwestern corn production, rising at a rate of approximately 1.2% annually over the past thirty years. This uptrend is closely tied to enhanced crop yields and wetter spring conditions, as detailed in a study published in Nature Communications.
The study examined historical data from both long- and short-term studies conducted by Iowa State University and the University of Illinois. The findings indicate that the optimal nitrogen rates required for corn in the Corn Belt have been increasing, contrary to previous assumptions of static rates over time. Researchers associate this trend with the nutrient demands of higher yields and increased nitrogen loss due to wetter springs.
Michael Castellano, a study co-author and agronomy professor, likened the situation to financial management, stating, “It’s like a bank account. If you pull money out, you need to deposit more money to keep the account going.”
Surveys among Iowa farmers corroborate these findings, showing a self-reported increase in nitrogen fertilizer application on corn over recent decades. Sotirios Archontoulis, another study co-author, noted, “Seeing this study come out, I’m sure some of them will say, ‘I knew it!’”
Efficiency Improving
The study underscores the necessity of enhancing fertilizer use efficiency to mitigate environmental impacts such as water quality degradation and greenhouse gas emissions. Matthew Helmers, a professor of agricultural and biosystems engineering and study co-author, emphasized the importance of aligning scientific recommendations with farmers’ experiences to improve nitrogen management.
Helmers stated, “Farmers hear information from lots of different sources. There’s some uncertainty there. But the more they can fine-tune their nitrogen management, the greater return they’ll see on their investment in the field and the more we will reduce environmental losses.”
Farmers have indeed become more efficient with nitrogen use over the years. For instance, while it was common to use 1 to 1.2 pounds of nitrogen per bushel of corn 20 to 30 years ago, many Iowa farmers now aim for 0.7 pounds or less. Enhanced efficiency practices include crop rotation, improved drainage, and spring fertilizer application, as highlighted in an ISU Extension and Outreach tipsheet.
Moreover, resources like the Iowa Nitrogen Initiative and the N-FACT tool offer tailored nitrogen rate recommendations, taking into account factors such as location, weather, and soil conditions.
Trend Likely to Continue
Mitchell Baum, the study’s lead author, indicated that efficiency improvements are crucial for environmental sustainability, especially as optimum nitrogen rates are projected to keep rising. “As long as yields are going to increase, unless there are massive increases in efficiency, we don’t see any signs of this slowing down,” Baum explained.
The research analyzed three types of optimum nitrogen rates: economic, agronomic, and environmental. These rates vary, with the economic optimum focusing on profit maximization, the agronomic optimum on yield maximization, and the environmental optimum considering the ecological costs. Notably, the disparity between the economic and agronomic optima has decreased over the last 30 years, whereas the gap between economic and environmental optima has expanded.
Archontoulis pointed out the trade-offs involved, stating, “If you want to cut nitrogen fertilizer rates below the required optimum and also maintain yields, well, we can’t have everything. If you reduce the nitrogen, you reduce yield.”
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