The wet fall and spring will cause anhydrous ammonia application and corn planting date to be close. This will lead to the oft asked question, "How long do I have to wait to plant corn after ammonia application?" If there is a soil separation between the ammonia zone and the seed, planting can be done the same day the ammonia is applied. If the seed is to be placed in the ammonia zone, the longer the waiting period the less potential for root injury. There is no magic number of days to wait.
Most of the diffusion of ammonia from the point of injection takes place the first 24 hours. Typically, ammonia will diffuse 2 1/2 to 3 inches from the point of injection causing a 5- to 6-inch diameter cylinder of ammonia. If soil conditions are wet, the injection knife will seal the sides of the injection slit, which will limit the diffusion and cause a very high concentration of ammonia below the soil covering or seal.
The depth of ammonia application is extremely important. The depth should be checked in the field. Use a spade to dig down through the injection zone to check depth. Ammonia should be injected 7 to 8 inches deep to minimize potential injury. Where possible, ammonia application at a slight angle to row direction will reduce the number of plants affected.
Ammonia injury causes desiccation of roots and die-back from the root tips. Injury is first noted in the field by uneven emergence, slow growth of some plants, and wilting of plants in dry weather. Root injury is noted by browning of the roots and in severe cases roots will be completely killed and turned black back to the seed. Ammonia injury is detected more frequently in dry weather because roots are slow to develop and destruction of a portion of the root systems limits water uptake.