A reminder that if seedbeds turn dry, the safety margin shrinks when applying seed placed fertilizer. Seedburn can result from ammonia toxicity and/or salt content of fertilizers.
For nitrogen, our Soil Fertility Guide provided safe guidelines for seed placed urea on cereals and canola across a range of soil types and seed-fertilizer configurations. With the increased popularity of narrow seed and fertilizer spreads with disk drills, the safe rates are reduced. For example, safe urea rates for cereals vary from 10 to 25 lb N/ac going from sand to clay soil using disk openers on 6” row spacing. These guidelines are for moist soil and should be reduced by 50% if seedbed moisture is lower when weather is hot and windy.
The safe rates of seed placed phosphorus depends on the crop, with cereals being quite tolerant compared to soybeans, dry beans and canola. With a disk drill as described above, cereals can tolerate 50 to 60 lb P2O5/ac as mono ammonium phosphate while rates would be 20 lbs/ac for canola and less for beans. If there greater seedbed utilization (i.e. narrower rows or a wider seedrow with less fertilizer concentration) rates could be more liberal.
More on these safe rates of fertilizer is posted on Manitoba Agriculture’s website at: http://www.gov.mb.ca/agriculture/crops/soil-fertility/print,safe-rates-of-seed-placed-phosphorus-for-manitoba–narrow-row-and-row-crops.html
Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture