Toxicity of Seed-Placed Urea Increases Dramatically Under Dry Seedbed Conditions
Placement of fertilizer with the seed may damage seedling emergence depending on:
- Crop species
- Seedbed moisture conditions
- Soil texture
- Soil pH (more ammonia toxicity under high pH)
- Seedbed utilization — amount of seedbed over which fertilizer is spread
- Fertilizer source
Tables are available in several publications (Table 7 of Manitoba Soil Fertility Guide) that indicate the safe rates of urea that can be applied with canola or cereal seed UNDER GOOD TO EXCELLENT MOISTURE CONDITIONS. In areas experiencing warm temperatures and drying winds, it is recommended to reduce safe rates of seed-placed urea by 50%. Using Agrotain treated urea may increase safety for cereals. For canola, the ammonium component of ammonium sulphate are as damaging as urea.
Seedbed moisture after seeding is actually more important than moisture at seeding. To help prevent drying of seedbeds, farmers should try to maintain surface residue and do a good job of on-row packing.
There are a number of alternative methods to apply N to spring sown crops in Manitoba without harming the seed. Such as:
- Side banding with double shoot openers
- Mid-row banding
- Preplant banding
- Preplant broadcasting
- Post-seeding surface broadcast prior to crop emergence
- Top-dressing after crop emergence
- Post-seeding surface banded
- Post-seeding nested or spoke wheeled
For further information, contact your MB Ag Office.