2026 January Stewardship Advocate

Nutrient Management on Iowa Corn Farms

The Iowa Nutrient Reduction Strategy (INRS) was unveiled in 2013 as a roadmap to assess and reduce nutrients transported to Iowa waterways and the Gulf of Mexico. Developed by experts from Iowa State University, the Iowa Department of Natural Resources and the Iowa Department of Agriculture and Land Stewardship, the INRS focuses on reducing nitrogen and phosphorus in Iowa’s water bodies. The strategy outlines efforts to reduce nutrients from point sources, such as municipal and industrial wastewater treatment plants, and nonpoint sources, including farm fields, golf courses, lawns and urban landscapes, in a scientific, reasonable and cost-effective manner. Iowa farmers play a key role in the success of this strategy.

Nutrient management is essential for farmers aiming to maximize crop yields. When producing high corn yields in Iowa, the key macronutrients required are nitrogen, potassium, phosphorus, and sulfur, along with micronutrients such as zinc, boron, and manganese. Fertilizers typically rank among the top two or three annual expenses for Iowa corn farmers. Using too much fertilizer not only incurs extra costs but can also result in nutrient runoff from the field. Conversely, insufficient fertilizer application can lead to reduced yields and lower revenue. Striking the right balance in fertilizer use is challenging due to varying factors such as weather conditions, soil types, soil fertility levels, and more.

Fortunately for corn growers, there are some methods and new technologies available to help them manage their fertility programs. A few of these methods are described below:

Grid Soil Sampling Combined with Variable Rate Applications

Grid soil sampling and variable rate application are techniques used to improve the efficiency of fertilizer use and soil management. Grid sampling involves dividing a field into smaller areas and collecting soil samples from each grid to determine how nutrients are dispersed across the field. The collected data is called a soil map and is used to create a “prescription” for a variable rate applicator that applies more fertilizer in areas where the soil tests read “low” and less fertilizer in areas where the soil tests read “high.” Using grid sampling and variable rate technology increases the probability that all corn plants in the field have adequate nutrients while reducing the likelihood of over or under-applying fertilizer.