Tall green corn plant in soil. Top view. Fertilizer granules surrounding base of plant.

Crop Nutrition

In-Season Nitrogen Applications – Prevention Or Correction

Alan Blaylock, Ph.D.

Alan Blaylock, Ph.D.


Senior Agronomist

Dr. Alan Blaylock brings extensive North American and international experience in nutrient management to the agronomy team. University studies and service as a university extension soils specialist prepared him for a long career in the fertilizer industry. Having managed both domestic and global research and education programs, Dr. Blaylock has a wealth of experience in applying science-based nutrient management principles and products to solving practical questions. Dr. Blaylock earned Bachelor of Science and Master of Science degrees in agronomy and horticulture from Brigham Young University and a Ph.D. in soil science from Iowa State University. He has been in agriculture his entire life — from his childhood on an irrigated farm in eastern Oregon to teaching soil science at Iowa State University to his current role as an agronomist at Nutrien. These diverse experiences helped Dr. Blaylock develop the skills to excel in translating complex scientific principles into practical solutions. Although early in his university studies he explored computer science as a profession, deep family roots in agriculture brought him back to the people and values of his heritage. His career satisfaction comes from helping others improve the performance of nutrients and cropping systems.

Share This:

Spring is upon us. Fertilizer has been applied. Your crop has been planted. Your plan for the season is in place – now you’ve started to execute that plan. Are in-season nitrogen applications part of that plan? What if what you have planned isn’t enough or is disrupted by unpredictable weather events?

Nitrogen is perhaps the nutrient most influenced by weather events during the growing season, and applying a portion of the nitrogen in-season is commonly recommended as a best management practice (BMP) to reduce the risk of nitrogen loss, yield loss, and environmental impact. Whether in-season nitrogen applications are already in your plan or so-called “rescue” applications become necessary later because of nitrogen-loss events, some basic tools can help manage your decisions around these applications.

We can classify in-season nutrient applications – whether for nitrogen or other nutrients – into two basic strategies. The first we can call preventative, an application planned in advance as part of the nutrient management program. The second strategy is corrective, or what some call “rescue” applications, an application made in response to a need that develops during the growing season. Each strategy has advantages and disadvantages and carries certain risks. Keep in mind that nitrogen deficiencies during and after key yield-determining growth stages are likely to reduce yields. Applications after a deficiency has occurred may recover some yield but usually do not produce the full yield that would have been obtained if the deficiency had not occurred. For example, if corn is nitrogen deficient at tasseling, some yield can be recovered by applications as late as tasseling. However, nitrogen application at tasseling seldom recovers the full yield potential. Nitrogen deficiency at that growth stage has already reduced yield potential.

Preventative applications
Preventative applications are planned in advance and are usually made as a component of or supplement to the nutrient management plan. Below are some of the potential risks and advantages of the preventative strategy and knowledge that is needed for optimum results.


  • Weather conditions may delay the planned applications beyond the optimum time, and the crop suffers yield reduction because of a temporary deficiency.
  • If yield potential is reduced by some factor other than the target nutrient, you may unknowingly apply nutrients exceeding what is needed because you don’t wait for deficiencies to appear.
  • Nitrogen may not be moved into the root zone if rainfall is insufficient.


  • Preventative application potentially avoids temporary nitrogen deficiencies by planning and making applications before deficiencies appear.

Knowledge or tools needed

  • You must know how much nitrogen is needed during the different growth stages. For example, if planning to side-dress nitrogen on corn at the V8 growth stage, sufficient nitrogen must be applied earlier (preplant or at planting) to avoid deficiencies up to the growth stage of the intended side-dress application or a bit beyond. Some crop models are available to help estimate how much and when additional nitrogen is needed.
  • You must understand the behavior of available nitrogen sources to anticipate which nitrogen source(s) will be best suited for the planned application and the types of equipment that will be needed.

Corrective applications
Corrective applications, often called “rescue” applications, can be made if nitrogen deficiencies appear during the growing season. Nitrogen loss is frequently a risk in many cropping systems. If loss occurs, remaining nitrogen may not be sufficient and later additions may be necessary to avoid yield loss. Below are some of the potential risks and advantages of the corrective strategy and knowledge that is needed for optimum results.


  • By the time a deficiency appears, yield potential may have already been reduced.
  • Inability to detect, diagnose, and make the application in time to achieve the desired benefit.
  • May correct symptoms without a yield increase or other economic crop response.


  • Corrective applications are based on an actual observed need instead of an anticipated need.
  • Corrective applications may be less likely to apply nitrogen that is not needed.
  • Nitrogen can be applied after a loss event has occurred.

Knowledge or tools needed

  • Reliable diagnostic measures are needed to detect problems in a timely manner. Crop imaging technologies are growing in popularity. Plant sampling can detect deficiencies before they become visible symptoms.
  • Regular crop scouting for early deficiency detection.
  • Though difficult to estimate reliably, the amount of nitrogen lost can help determine how much additional nitrogen to apply. Some crop models have been developed to estimate lost nitrogen.
  • Appropriate fertilizers and equipment should be immediately available and ready to apply to avoid application delays.

In-season nitrogen application can improve nitrogen-use efficiency in many situations when properly used. Both preventative and corrective strategies can enhance a sound nutrient management plan if properly used. Each has its own advantages and risks that can influence the grower’s choice of strategy for specific fields or crops. While preventative applications are part of the advance planning, corrective applications can also benefit from experience and anticipation of nitrogen-loss events based on soils and typical weather events that may lead to in-season nitrogen needs. Both strategies rely on timely applications and knowledge of what the crop needs and when. Consider each situation and site-specific requirements to make the most of the investment in these applications.

For more information, contact your local agronomist or crop advisor. You may also find the following resources helpful.

Tools Available for In-season Nitrogen Management Decision Making. Penn State Univ. 2019. https://extension.psu.edu/tools-available-for-in-season-nitrogen-management-decision-making

Tips for In-season Nitrogen Management in Corn. J. Iqbal, C. Wortman, B. Maharjan, and L. Puntel. Univ of Nebraska. 2020. https://cropwatch.unl.edu/2020/tips-season-nitrogen-management-corn

Late-season nitrogen application: Is it worth it? F. Fernandez. Univ of Minnesota. 2020. https://blog-crop-news.extension.umn.edu/2020/07/late-season-nitrogen-application-is-it.html

In-season Adaptive Nitrogen Management Tools for Corn. USDA-NRCS. http://www.forestrywebinars.net/webinars/in-season-adaptive-nitrogen-management-tools-for-corn/

Evaluation of In‐Season Nitrogen Management Strategies for Corn Production. D. Ruiz-Dias. 2008. Agron. J. 100: 1711-1719. https://doi.org/10.2134/agronj2008.0175

PFR Report: In-Season Nitrogen Management. Beck’s Blog. June 2019. https://www.beckshybrids.com/Blog/ArtMID/841/ArticleID/2224/PFR-Report-In-Season-Nitrogen-Management#:~:text=Top%207%20Tips%20for%20In%2DSeason%20Nitrogen%20Management&text=Make%20sure%20an%20adequate%20supply,and%2For%20test%20nitrogen%20levels.