In Season Phosphorus and Potassium Applications for Corn Nutrient Management

Nitrogen (N) and sulfur (S) are often considered for in-season nutrient applications because corn is highly responsive to both nutrients. Additionally, the nutrients are mobile in the soil. The odds of plants utilizing available nutrients increase when fertilizer applications occur close to the needs of the plants. Conversely, phosphorus (P) and potassium (K) are immobile in the soil, so adding P and K in-season provides positional challenges to get the nutrient into the plant through the roots.  

Many articles have been written about sidedressing N as it is an effective management practice.  We hear much less about the addition of P and K in-season as an alternative from the normal spring or fall broadcast or banding options. Phosphorus usage starts early, in fact most starter fertilizers are P based due to positive effects P can have on early-season growth in particular environments. Phosphorus uptake is relatively consistent through the corn plant’s life, whereas K resembles N and is needed during earlier growth stages. Phosphorus has 80% of its total uptake by the time it reaches the early reproductive stages.1  

Two other important facts are the relative amounts of P and K needed by a corn plant and soil test levels. Research at the University of Illinois in 2010 showed the total nutrient uptake for N, P, and K by a 230 bu/acre corn crop was 256, 101, and 180 lbs/acre, respectively.1 When compared to several of the micronutrients, N, P, and K are required at 4 to 200 times higher levels.1 This is important because the consequences can be dramatic if a soil is short on macronutrients. Soil test levels give insight to potential yield responses, and yield responses are unlikely if soil tests for P and K are in the high or very high range. Yield response from an in-season application is more likely when soil tests are low to very low.

What are the options for applying P and K fertilizers on your crop in-season (after planting)? 

In-season applications of P and K are not common; however, broadcasting P and K and incorporating them with cultivation is an option. Phosphorus and K incorporation is not required to prevent volatilization; however, cultivation is the best way to get fertilizer in the root zone.  

There are also liquid forms of P and K that can be applied to the plant foliage. Since P and K are taken up through the roots, research has shown foliar feeding has very limited success. The quantities of P and K needed by the plant and trying to bypass their usual way of uptake is not a cost-effective recommendation. 

Recently, there has been some limited work on banding dry P and K fertilizers in-season. This requires specialized equipment to drop a band of dry fertilizer alongside the emerged corn row. Liquid fertilizers are also applied this way but is considerably more expensive pound for pound of nutrient. This process can help with workload management. Assuming it works, it provides an ability to apply the nutrient closer to the time when it is needed.2  

In summary, P and K are immobile in the soil. The most common and best ways to get P and K into your corn plant is to have the nutrients where the roots grow, either in a band below the root system or broadcast and incorporated in the top 3 to 4 inches. In-season broadcasts can help your soil test levels longer term but may not improve the current crop. Foliar feeding has generally had few positive responses and depending on nutrients applied can cause crop injury. Banding dry P and K fertilizers alongside the emerged corn plants has shown a response in some studies, but at this point has not been well researched across the Corn Belt.  

With the launch of the Preceon™ Smart Corn System, the ability to do mid- and late-season fertilizer applications just became easier. Preceon™ is powered by short stature corn and may provide producers a longer window for standard toolbar applications.3 Additionally, with target plant heights of 5 to 7 feet, short stature corn can provide increased flexibility to access the crop all season and make fertility applications less of a risk for crop damage with standard ground equipment.

Tony Weis


1Corn Nutrient Uptake and Partitioning. Department of Crop Sciences, Crop Physiology, University of Illinois at Urbana-Champaign.

2Below, F. and Foxhoven, S. 2022. Banded fertility: Music for high yields. Commodity Classic Presentation. University of Illinois. Sponsored by Calmer Corn Heads.

3Based on a 2018 Huxley, Iowa breeding trial, The Smart Corn System shows potential to extend the window for toolbar applications (+5 to 7 days). Bayer Crop Science.

Websites verified 3/15/23.

Legal Statements

Preceon™ Smart Corn System including short stature corn developed through traditional breeding is expected to be available, subject to final commercialization decisions, for planting in the 2024 growing season. Short stature corn developed through biotechnology is not currently available for commercial sale or commercial planting. Commercialization is dependent on multiple factors, including successful conclusion of the regulatory process. The information presented herein is provided for educational purposes only, and is not and shall not be construed as an offer to sell.

ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

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