Nitrogen is the mineral nutrient required in the largest quantity for successful corn production. Its availability directly impacts plant health and the final yield harvested. Determining the precise amount of nitrogen fertilizer needed is complex because environmental factors, such as rainfall, soil type, and temperature, heavily influence how much nitrogen the plant can access naturally. Effective nutrient management requires understanding the plant’s needs and balancing them against potential losses.
Nitrogen’s Role in Corn Development
The primary function of nitrogen in corn is its role as a fundamental component of the chlorophyll molecule. Chlorophyll captures sunlight energy during photosynthesis. Without sufficient nitrogen, the plant cannot produce enough pigment, limiting its ability to create the sugars necessary for growth and grain development. Nitrogen is also an indispensable building block for amino acids, which form all plant proteins necessary for enzymatic processes and cell structure. Adequate nitrogen supports robust stalk structure, helping the plant resist breakage and lodging as heavy kernels develop.
Calculating Specific Nitrogen Needs
Determining the exact amount of nitrogen required begins with establishing a realistic yield goal for the specific field. The plant’s total nitrogen uptake is directly proportional to the amount of grain it produces. Corn generally requires approximately 1.0 to 1.2 pounds of nitrogen for every bushel of grain expected to be harvested. The actual fertilizer recommendation is derived by subtracting nitrogen credits already present in the soil from the total expected plant uptake requirement.
Soil Testing and Economic Models
The “Soil N Credit” is determined through various soil testing methods designed to measure plant-available nitrogen. The Pre-Sidedress Nitrate Test (PSNT) measures nitrate levels in the top foot of soil around the V5 or V6 growth stage, helping adjust the final application rate. Another accepted method is the Maximum Return to Nitrogen (MRTN) approach, which uses economic principles rather than a fixed yield goal. The MRTN system uses field trial data to recommend nitrogen rates that provide the greatest net return based on current corn and fertilizer prices.
Utilizing Nitrogen Credits
Previous crop history provides a significant credit to reduce fertilizer needs. A soybean crop typically leaves behind a nitrogen credit of 40 to 50 pounds per acre due to nitrogen fixation. Fields that have received manure applications also possess a substantial “Manure Credit” that must be factored into the overall nitrogen budget to prevent over-application.
Strategic Timing and Methods of Application
Timing and Split Application
Timing the application must coincide with the corn plant’s peak demand period. Corn uptake is slow early on, but demand accelerates dramatically starting around the V6 stage. The majority of the plant’s total nitrogen (60% to 70%) is absorbed between the V6 stage and the VT (tasseling) stage. Applying all nitrogen before planting risks significant losses through leaching or denitrification. Therefore, many growers adopt a split-application strategy, applying a small portion pre-plant followed by a larger side-dress application around the V6 to V8 stage.
Application Methods
The method of application influences efficiency and environmental loss. Injecting liquid nitrogen or banding granular fertilizers places the nutrient directly into the root zone. This localized placement minimizes surface exposure, reducing volatility and runoff potential compared to broadcasting. Fertigation involves dissolving fertilizer in irrigation water, allowing for precise, small-dose applications. Placing the nitrogen near active root growth is paramount for maximizing plant uptake.
Signs of Nitrogen Deficiency or Excess
Visual symptoms provide a clear way to diagnose whether the applied nitrogen rate was adequate. The classic sign of nitrogen deficiency is chlorosis, a distinct yellowing of the leaf tissue. This yellowing begins on the tips of the oldest, lowest leaves and progresses down the midrib in a characteristic V-shaped pattern. Since nitrogen is mobile, the plant moves it from older tissues to supply new growth. Persistent deficiency results in pale green, stunted plants, poor ear development, and reduced kernel fill. Stalk cannibalization, where the plant pulls nitrogen from its own stalk to fill the grain, leads to weakened stalks and increased lodging risk.
Conversely, applying too much nitrogen promotes overly lush, vegetative growth, increasing the likelihood of lodging and potentially delaying maturity. From an environmental perspective, surplus nitrogen is prone to being lost from the field. This excess can leach into groundwater or run off into surface waters, contributing to water quality issues.