A very efficient placement method for rates of nitrogen that can’t be placed at seeding is the preplant band. Despite the popularity of direct or one-pass seeding this is still used in crops where some pre-plant tillage is done – like for corn.
The past few years, more often in dry springs, I have seen stand thinning using this practice. When the corn row falls directly over the N band (be it ammonia or urea), seedlings are injured, stunted and sometimes killed. This leaves a repeating pattern in an angle across the field.
There are some standard guidelines if using this practice:
- Stand thinning may occur where the seed row intersects the N band. Band N on an angle so that it intersects just a short length of row. OR if the injection placement can be controlled with accurate GPS guidance positioning technology, split with the future corn row. Six inch separation should be sufficient.
- Place the nitrogen deep. Banding at 3” depth may be sufficient for slot closure and N retention in the soil – but this will only be an inch or so below the seed. The original guideline calls for 4” vertical separation of injection point and seed.
- The toxicity will be worse under dry conditions and on sandier soils.
- Waiting a certain period of time offers only a slight increase in safety. Injury can still occur even if planting is delayed for a considerable period of time.
- Increasing plant populations to account for such thinning will not eliminate the appearance of gaps in the row.
Figure 1 is of corn thinning over a preplant urea band.
Figure 1: Corn thinning over a preplant urea band (Photo by John Heard, Manitoba Agriculture)
Figure 2 is of corn seedling based on their proximity in intersecting the shallow placed preplant ammonia band.
Figure 2: Impact of shallow placed preplant ammonia band on corn seedlings (Photo by John Heard, Manitoba Agriculture)
Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture
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