Quick test for safe rates of seed-placed fertilizer

May 2, 2018 - Issue 5

At what rate does seed-placed fertilizer start to reduce canola stands? A quick test for the safety of seed-placed fertilizer is to turn off the fertilizer feed for about 100 feet, mark the spot, and go back and compare stand establishment in treated and untreated areas. You may want to try this at a few sites in a field: hill tops, side slopes, an easy-to-view area near the road.

While this quick test will not help with planning for this year, it can influence decisions in following years. Take good notes on moisture, soil type, past herbicide use and other factors that can impact stand establishment across a field and from year to year. Multiple years of testing may be required to find your balance, particularly because results can be so different for moist versus dry years.

The safe approach. The safest recommendation for seed-placed fertilizer for canola is to put up to 20 lb./ac. of phosphate in the seed row and all other fertilizer, including the balance of phosphate, in a band outside the seed row. This split approach to phosphate in particular will be necessary on many fields, given that phosphorus (P) removal has far exceeded P fertilizer rates on many fields, and more soil tests are coming back “low” for P.

So many variables at play. In some situations, farmers can apply somewhat higher rates of seed-placed fertilizer without a major loss of plant stand or reduced profitability. Good moisture, for example, can greatly reduce risk. Drier soil conditions will increase the risk. Opener design, seed-bed utilization (SBU) and true separation between seed and fertilizer can also influence seed survival. From John Heard, Crop Nutrition Specialist with Manitoba Agriculture: “Many new openers have “close-to-seed” side-banding which could be considered as seed-placed.” Liquid versus dry phosphorus is probably a minor safety factor compared to placement distance from the actual seed. Results from Laryssa Grenkow’s M.Sc. thesis (University of Manitoba, 2013) found liquid more damaging to canola establishment than dry forms; in contrast, the South Dakota seed-placed fertilizer decision aid says liquid P “tends to be the least damaging to plant stands”.

Further reading:

Seed-placed fertilizer cautions for canola_John Heard
Why is it important to get anhydrous ammonia into moisture?
Anhydrous ammonia: Safety and the farmer

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