Issue No. 7, Article 9/May 8, 2009
Some Nitrogen Placements Can Cause Plant Injury
While we all recognize the need to apply nitrogen (N) to increase crop production, it must be applied correctly to avoid or minimize plant injury. The most important point to remember is to keep anhydrous ammonia and urea-containing fertilizers away from the seed and the immediate rooting zone of the seedling. While it is possible to apply fertilizers directly below the seed zone when using strip-tillage or auto-guiding systems, anhydrous ammonia and urea should not be applied in this way. These fertilizers have or produce ammonia that can inhibit germination or severely damage young roots. While some people do this without a problem, it is a high-risk practice, and luck is the only reason those producers have not experienced difficulties.
Applying urea or UAN in contact with the seed not only is risky because of the potential for ammonia injury (urea transforms to ammonia when applied in the soil), the free ammonia will inhibit phosphorus uptake, and the impurity biuret in urea is toxic to seedlings. Safe ways to apply urea-containing fertilizers are to broadcast and incorporate or to apply at planting if you have a starter attachment that puts the fertilizer at least 2 inches to the side of the seed. At this time in the season, it is more important to plant and then worry about applying any needed N. However, if you must apply anhydrous ammonia before planting I recommend applying it at an angle to the row and waiting three to five days before planting. If you have auto-steering, then you can apply between the positions of the future crop rows and plant immediately after. Finally, do not apply if soils are wet; this can cause N loss, or escaping ammonia can injure plants as the soil cracks along the knife track when drying. If the corn has emerged, make sure liquid N fertilizers are not sprayed on the emerging seedling.--Fabián G. Fernández