Avoid Anhydrous Injury in Corn
March 14, 2012 by Michael Goedeken
Avoid Anhydrous Injury in Corn
Each year many corn growers that use spring applied, preplant ammonia find some degree of anhydrous ammonia injury within their corn fields. Severe injury can cause significant germination problems or root pruning, which leads to stand loss or uneven stands, which can ultimately lead to significant yield losses. As the spring of 2012 begins, much of the corn belt has found itself putting on a lot of ammonia and considering planting very soon. This means that the time between anhydrous ammonia applications and planting will most likely be very minimal in many cases. Injury from anhydrous ammonia can be easy to diagnose but somewhat difficult to prevent. Below are some precautions and preventative measures to take to avoid anhydrous injury in corn.
Movement in The Soil
The first step in preventing anhydrous ammonia injury in corn is to understand how anhydrous moves in the soil. When anhydrous ammonia is applied to the soil, it can disperse approximately 3 to 4 inches away from the injection point. Most of this dispersal takes place within the first 24 hours. This means that a solid band of ammonia, 6-8 inches in diameter, may exist every 30 inches, or whatever the knife spacing may be. This band can very harmful to a germinating seed or a seedling root system that is trying to establish. Some factors that affect the travel distance away from the injection point include, soil moisture, amount of N being applied, and the tillage practices used after application. Since anhydrous ammonia has such great affinity for moisture, the wetter the soil, the less distance ammonia will travel. The drier the soil means it may travel further in search of moisture. Obviously, the more ammonia being applied the more concentrated the application band from injection point.
Diagnosing Injury in Corn
Generally, there are 3 signs that give the injury away. The first sign of anhydrous injury is a burnt radicle and burnt nodal root tips. The first root of a corn plant called the radicle should be 2-3 inches in length with many lateral roots extending outwards, resembling a "furry foxtail". (See Fig A) When exposed to high amounts of anhydrous ammonia, the tip of the radicle root is burnt, sometimes clear back to the seed in which it began. (See Fig B)
The second way to notice the injury is when the corn plants reach the rapid growth stage of approximately V5-V6. At this stage, plants that may have been injured by ammonia tend to get set back compared to other neighboring plants. The pattern resembles the same direction and pattern that the ammonia was applied, usually at an angle. This is due to heavy root burning just above the knife tracks or injection points, plants that were not injured away from the knife tracks go on to outgrow the other and pick up steam through the rapid growth stage, taking on a dark green color and getting much taller. (See Fig C)
The third sign then, is when the field is observed from a perpendicular view and the same knife crossing the row pattern shows a consistent wave pattern that many times gets mistaken for a bad starter pump on the planter. (See Fig D)
Preventing Anhydrous Injury in Corn
1. If at all possible, placement of anhydrous ammonia should reach 8-10 inches deep, particularly spring applications.
2. There is no magic number of days to delay planting after ammonia applications, the longer the waiting period the better. Although a good rule of thumb for planting time is 7-14 days after application.
3. Avoid spring applications in strip tillage systems. Try to make strips, plant and side dress.
4. Avoid spring applications in no till. Try to plant and side dress.
5. Tillage after application certainly stirs anhydrous ammonia up within the soil and makes it much less concentrated and less harmful to the small seed or seedling.
6. Be extremely cautious on coarse textured soils.
Special Notes: Many times during the heat of the season, getting the ammonia applied and planting corn run so close together. If time is of the essence and you are willing to take the risk, make sure application is deep. If N rates are 180#N plus, consider limiting the amount of N applied with ammonia to 150# of actual N, then making up the difference with surface applied liquid UAN (28% or 32%). This will lower the concentration of the injected band below the seed.