Best Management Practices for Sidedressing Corn with Nitrogen

Nitrogen (N) is likely the most talked about nutrient in crop production, especially corn production, and for good reason as it takes N to help maximize yield potential. Applying N in the spring sounds like an easy decision to make since a corn crop needs it for so many key plant processes, but it should get the most scrutiny prior to making the sidedress application. Let’s review the 5R’s of N management:

  • Right Understanding

  • Right Source

  • Right Rate

  • Right Time

  • Right Place

Right Understanding – Nitrogen is needed by all crops to grow. It utilizes sunlight for many functions that are key to a plant’s ability to function, but its biggest influence is on yield potential.1 Optimum N levels increase the plant’s abilities to absorb phosphorus, potassium, and sulfur. The amount of available N and duration of its uptake contribute to the potential for superior grain yield.  

Right Source – Sidedress nitrogen options include:

  • Injection of ammonia (NH3) or urea-ammonium nitrate (UAN) (Figure 1)

  • Broadcasting ammonium nitrate, ammonium sulfate, or coated urea

  • Surface dribbling UAN

  • Broadcasting UAN or urea.

Nitrogen fertilizer comes in many forms, each with a varying amount of N. The source to apply depends on the application equipment, soil type, drainage, tillage practice, and how much is needed to appropriately “feed” the crop. Each source has benefits and drawbacks; therefore, the best source for your crop should be selected.

Right Rate – Soils tests can provide guidance on how much N your soils can hold. If soil tests are available, look at the Cation Exchange Capacity (CEC) number listed. The approximate amount of N a soil can hold at a given time can be calculated by multiplying the CEC number X 10. As an example, if the CEC = 19, about 190 pounds of N can be held in the soil at a given time.                                                             

Consider using the Iowa State University Regional Corn Nitrogen Rate Calculator to help determine the maximum return to N (MRTN) at selected N prices for each field.2 The calculator can be accessed at:

Figure 1. Sidedressing corn. Figure 1. Sidedressing corn.

Right Time – Application timing is a key! Adequate N availability is critical at V5 to V8 growth stages for ear development, with greatest uptake occurring between V8 to silking. Corn gets 25% of its annual N uptake between V6 to V12 and 40% of its uptake between V12 to VT, with the largest N uptake happening between V10 to V14, where corn can take up to 7 to 8 pounds of N/day. 

Right Placement – Nitrogen is very mobile in the soil. It can move with water to plant the roots, but can be lost through processes like leaching, denitrification, volatilization, and runoff. Nitrogen placement should be based on corn growth stage. Nitrogen fertilizer placed too close to the roots can burn them and can injure or even kill seedlings. If the N is placed too far away, it may be unavailable for plant use.  


1Ciampitti, I.A., Camberato, J.J., Murrell, S.T., and Vyn, T.J. 2013. Maize nutrient accumulation and partitioning in response to plant density and nitrogen rate: I. Macronutrients. Agronomy Journal 105:783-795. American Society of Agronomy.

2Corn nitrogen rate calculator. (In association with Iowa State University, Purdue University, University of Minnesota, Michigan State University, University of Illinois, University of Wisconsin, and The Ohio State University). Iowa State University Agronomy Extension and Outreach. Iowa State University.

Ciampitti, I.A. and Vyn, T.J. 2013. Grain nitrogen source changes over time in maize: A review. Crop Sci. 53:366-377. Crop Science Society of America.

Jeremy Miner

Technical Agronomist

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