Carney: Iowa is leaking nutrients better left in its soil

Carney: Iowa is leaking nutrients better left in its soil

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The 2019 North Iowa crop year is history. Machinery is in the shed, the lids are on the grain bins, yields have been calculated, and some inputs for next year have been purchased. In a few fields, cover crops are growing and sending roots down to capture nutrients that this year’s crop did not use and storing them for next year. In far too many instances, land has been tilled, thus reducing its ability to absorb water and exposing it to potential erosion this winter and next spring.

The grain grown by area farmers finds its way into fuels for vehicles, food and meat products that are exported all over the world, and myriad consumer products. Unfortunately, as a result of how commodity grains are currently grown, Iowa also exports a large amount of agricultural nutrients downstream to the Gulf of Mexico. These expensive nutrients are lost through our waterways due to soil erosion, over-application, bad timing, and a lack of understanding of how soils work. The primary nutrient lost from Iowa soils is soluble nitrogen, or nitrate (majority of nitrogen used by plants is absorbed in nitrate form. Nitrate is highly leachable and readily moves with water through the soil).

Chris Jones, a research engineer in the Hydroscience and Engineering Department at the University of Iowa, has studied statistics of this loss using stream nitrate sensors across the state, rainfall information, and stream flows. His results for 2019 were released earlier this month and are sobering.

Dennis Carney


Results show a loss of 30 pounds of nitrate per acre in the Cedar River Watershed (Mason City and surrounding counties). This translates to a 2019 total Iowa stream load of 980 million pounds of nitrate leaving the state for the Gulf of Mexico. Of this total loss, 61% was carried by the Mississippi River and 39% by the Missouri River.

This huge amount of lost nitrogen was purchased by Iowa farmers for well over $300 million. In addition, the nitrogen loss causes dangerous problems for water supplies downstream and contributes to the dead zone in the Gulf of Mexico.

The scale of this environmental and economic issue is disturbing. Since 2003, Iowa stream nitrate loads have increased 100.4%, as measured by a five-year Running Annual Average. In 2013, Iowa implemented its Nutrient Reduction Strategy as the result of a directive from the Gulf of Mexico Hypoxia Task Force. Iowa’s goal from the beginning was a 45% reduction in the amount of nitrogen and phosphorus entering the state’s waterways. The strategy has emphasized voluntary cost-shared practices such as cover crops, nutrient reducing wetlands, and edge-of-field bioreactors to reach its goal.

After six years, in 2018, the amount of Iowa acres with cover crops has grown to nearly 900,000. Unfortunately, to meet the 45% reduction goal Iowa needs 12 million acres of cover crops in the state. Since the introduction of this voluntary strategy the total annual amount of nitrates leaving our state has increased by 46%. With the knowledge that Iowa’s nitrate loss has almost doubled in the span of 16 years, it is time to reassess our priorities.

Everyone in Iowa has an economic and environmental stake in the quality of our water. Changing the way things are done on our farms is difficult and takes time. But we have known for decades that unneeded tillage and the application of crop fertilizers months before they are needed by a crop result in soil and nutrient losses. Farm operators, landowners, agricultural groups, and the general public need to get involved now to solve this issue.

Dennis Carney is a Cerro Gordo Soil and Water District commissioner. The local office can be found at 1415 S. Monroe, Mason City. Online:


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