MANHATTAN, Kan. — Understanding how much nitrate is present in irrigation water is important not only for farm management decisions, but also for protecting the quality of drinking water, according to research from Kansas State University
Micah Cameron-Harp, K-State assistant professor in the Department of Agricultural Economics, and Matt Kirk, professor of geology, said recognizing nitrate contributions from irrigation water helps improve nutrient efficiency in crop production while also reducing the risk of excess nitrogen reaching water used by consumers.
“Many producers are not considering the amount of nitrate already being applied through their irrigation water,” Cameron-Harp said. “When you measure what’s there, you may be able to reduce fertilizer applications, which saves money and helps limit excess nitrate from moving into groundwater.”
Nitrate is highly soluble and moves easily with water through the soil profile. When more nitrogen is applied than crops can use, the excess can leach into aquifers — a primary source of drinking water for many rural communities.
The U.S. Environmental Protection Agency has established a maximum contaminant level of 10 milligrams per liter (mg/L) of nitrate-nitrogen in public drinking water systems to protect human health. At levels about 10 mg/L, nitrate can cause a condition known as methemoglobinemia, which prevents blood from carrying enough oxygen, causing bluish skin, headache, fatigue and difficulty breathing.
Kirk noted that groundwater monitoring across Kansas, shows variability in nitrate levels, making local testing essential.
“Every well and every water source is different,” Kirk said. “The only way to know how much nitrate is present in your irrigation water is to test it. Once you have that information, you can incorporate it into your nutrient management plan.”
Researchers emphasized that some neighboring states, including Nebraska, have more widely adopted irrigation water testing as part of routine nutrient management. In contrast, many Kansas producers have historically focused on soil testing without accounting for nitrate contributions from irrigation water.
According to Cameron-Harp, this overlooked input can represent a significant amount of applied nitrogen over the course of a growing season.
“If irrigation water contains measurable nitrate, that nitrogen still counts,” Cameron-Harp said. “Recognizing it allows producers to credit that amount toward their total crop needs, improving efficiency while advancing water quality goals.”
Producers interested in determining nitrate levels in their irrigation water can submit samples to commercial laboratories across the state or through Kansas State University testing services. Results can then be used alongside soil test data to fine-tune fertilizer recommendations.
Researchers highlight that proactive nutrient management benefits both farm profitability and community health.
“Protecting water quality doesn’t have to come at the expense of productivity,” Kirk said. “With good data and informed decision-making, we can support agricultural production while safeguarding drinking water for future generations.”
For more information on nitrate testing and nutrient management strategies, contact your local K-State Extension office.
