N Deficiency

BY Dairyland Seed Agronomy Team

As we race towards a safe fall harvest season and the anticipation of running the chopper or combine to harvest a crop that we have sweated and worried about is, in some instances, almost akin to that of Christmas arriving or your first kiss. One of the questions that is always on the minds of farmers and agronomists is “did my corn crop have enough Nitrogen?”.

The photograph below shows a typical Nitrogen (N) deficiency symptom. We start to see a yellowing and necrosis at the leaf tip. This yellowing and necrosis moves its way down the center of the leaf.

As we move closer to R6 (physiological maturity or black layer), we are more apt to see a few leaves that look like this. The fewer of these type of leaves we see, and the later in the growing season we see them, is usually a good thing for having enough N in the plant.

Potential factors that influence N deficiency are:

Soil Texture: Course or low organic matter soils have less points of attachment for nutrients which allow a mobile nutrient like N to move throught the soil profile. A one-inch rainfall can move Nitrogen twelve inches down in the soil profile or leach away.
Leaching: Loss of nitrate (NO3-) nitrogen that is moved downward by soil water below crop root zone.
Denitrification/Volatization: Loss of surface-applied Nitrogen forms as a gas, which normally occurs when plant N uptake is low.
Time and Frequency of N application: The longer the time frame from planting N is applied the more likely it is to not be available.
Soil Temperature: As soil temperatures increase above 40°F, you are more prone to N leaching.
Rainfall or Ponding: As soils become waterlogged, oxygen deficient Nitrogen can start to move down through the soil profile.
Compaction and/or Sins of Planting: Tillage layers, tire tracks or/and actions that limit or stop root growth can reduce the roots’ ability to grow to the N source. Once a corn plant silks and tassels, the roots have reached their maximum width and depth.
Sulfur (S) and Potassium (K) Deficiencies: If plants are low on S or K, it limits the movement of Nitrogen in the plant in the case of S and accessing and bringing N into the plant into the case of K.

These factors as well as others can have an influence on both manufactured N sources as well as manure.

Nitrogen deficiency, in most instances, leads to yield loss, but the plant takes many actions to prevent it. As shown in the photo above, the plant is “pulling” N from the lower leaves of the plant. The plant pulls nutrients from the lower leaves and stalk to fill or continue to fill the kernels with starch. Once a plant starts to pull nutrients to fill kernels and becomes deficient, it never stops. It will sacrifice leaves and stalks to fill that kernel to have a viable seed.

The earlier a plant starts pulling nutrients away from the stalk, the more likely you are to have standability issues at harvest time. Standability and stalk degradation is further compounded the longer you wait to harvest that crop.

By scouting and scheduling field harvest, you will limit the yield robbing factors of stalk degradation and standability caused by Nitrogen and other nutrient deficiencies.

As always if you have question regarding this or other agronomic concerns contact your local Dairyland representative.