Sidedress Nitrogen for Decreased Nutrient Deficiency in Corn

Due to being highly mobile in the soil, nitrogen (N) deficiencies are common in corn plants. Heavy rains and flooding put corn crops at risk for nitrogen loss. In fact, the fields at the most risk for nitrogen loss following wet conditions are the ones where nitrogen was fall applied, followed by fields that had an early spring nitrogen application. If managed properly, appropriate nitrogen levels can result in substantial economic returns for farmers.

Nitrogen deficiency symptoms in corn

If your cornfield turns yellow, this is a sign of nitrogen loss. Nitrogen deficiency symptoms typically first appear on the older leaves, then turn into a V-shaped yellowing that runs down the midrib of the leaf toward the stalk.

Severe nitrogen deficiency symptoms include:

• Pale yellowish-green color
• Stunted growth
• Spindly stalks

Nitrogen application timing and use

Nitrogen mineralization from organic matter and prior season soybean residue can easily cover nitrogen demand during early growth stages. Prior to V8, corn takes up less than 25 lbs. of nitrogen, but plants begin to rapidly uptake nitrogen by V6 growth stage. By silking, plants have absorbed near 70% of the total nitrogen they need. Yield potential can decline if nitrogen isn’t available during this critical window. Timely nitrogen applications in the form of sidedressing can help to manage any crop needs in larger corn.

Grass plants, such as corn, need maximum nitrogen availability prior to tassel and continue to use large amounts through seed fill. To accomplish this, apply nitrogen ahead of tassel to reduce the risk from earlier applications. Multiple application timings and good management practices are the best approaches for success. Several universities provide nitrogen application timing research. The University of Illinois shows the impact of application types and timings across multiple years. Generally, it's best to split nitrogen applications between pre-plant and an in-season sidedress if a fall application wasn't possible. While sidedressing nitrogen is better than doing nothing, the University of Minnesota suggests sidedressing by V8 growth stage due to the role early nitrogen uptake has on yield potential. To maximize yield and enhance plant nutrient use efficiency, time application prior to peak uptake. 

Criteria to evaluate the need for nitrogen application:

• Assess your fields: By getting a look at your field from a bird’s-eye view, you’ll be able to better assess the need for additional nitrogen. This method also allows you to review many fields in a short amount of time. To do so, consider observing aerial digital images or using a drone to survey your crop.
• Perform soil tests: Soil sampling will provide a good representation of the nitrogen availability in soils. Make sure your soil sample depth is 12 inches or more. A late-spring test for soil nitrates can help you determine if nitrogen needs to be applied before the rapid growth begins. When corn plants are 6 to 12 inches tall, soil samples should be taken and analyzed, assessing the plant’s available nitrogen.
• Work the numbers: Consider your crop insurance plan, and discuss whether a nitrogen application will be worthwhile based on your coverage.

Sidedress nitrogen application options

A typical nitrogen application consists of 40 to 50 units of anhydrous ammonia, liquid or urea with a urease inhibitor, unless a test is used to determine the precise amount of nitrogen needed. If possible, apply nitrogen when there’s a chance of rain in the forecast, because occurrence shortly after application helps uptake in the root zone.

1. Anhydrous ammonia: A sidedress option that often requires larger field equipment for soil injections. Try to avoid leaf burn, especially on row ends when the toolbar picks up. The use of a nitrogen stabilizer is recommended when applying anhydrous ammonia.
2. Urea (dry): Can be broadcast across top of emerged corn with a high clearance applicator at higher speeds to cover more acres per day. Consider using a nitrogen stabilizer with urea to minimize volatilization losses since it will typically not be incorporated into the soil. Timing applications prior to rain events or row cultivation after application can also help minimize nitrogen loss with urea. Anticipate minor leaf burn from urea trapped with whorl of emerged corn.
3. UAN (liquid): Can be broadcast sprayed, injected into the soil or dribbled between rows. If dribbling, use a nitrogen stabilizer since it requires rain to move into the soil. Broadcast applications can cause leaf burn, necrosis and stunting. Broadcasting corn prior to V4 and applying at rates less than 60 lbs. of nitrogen per acre can help minimize crop injury. Visible damage should disappear quickly with good growing conditions. Anticipate more severe injury at higher broadcast application rates and with bigger corn. Broadcast application to V7 or larger corn is not recommended, and sidedressing should be considered.

Consider adding another nitrogen application where plant loss has occurred. Yellowing fields with uneven growth that still have a chance to reach maturity and make grain are most likely worth investing in an additional application. To get the most benefit, agronomists recommend applying nitrogen to such areas as soon as possible, ideally before pollination.

Evaluating nitrogen loss

Each season, farmers wonder about how much nitrogen they may have lost. But answering this question requires more questions to answer. Ask yourself what nitrogen sources you applied, when you made the applications, how was it applied, and what the weather (temperature and rainfall) conditions were since application.

Multiple methods can be used for assessing your current nitrogen status.

Commonly used methods to evaluate nitrogen soil loss:

1. Soil sample method
2. Crop sensors:
   1. Trimble^® GreenSeeker^® system
   2. OptRx^® system
   3. CropSpec^® system
3. Nitrogen models

In summary, nitrogen and nitrogen stabilizers are greatly influenced by the environment, and there isn’t a magical formula to outline nutrient loss.

Contact your Golden Harvest Seed Advisor with questions or for additional agronomic insights.