While the benefits of seed-placed fertilizer are certain, it is important to ensure proper amounts are being placed with the seed, says provincial crop specialist Mark Cutts.
“Applying too much fertilizer with the seed can reduce or delay crop emergence,” said Cutts. “To ensure seed-placed fertilizers are being managed properly, an understanding of the factors that influence their use is required.”
The fertilizer product most commonly evaluated for seed-placed safety is urea (46-0-0), which can reduce crop emergence through ammonia toxicity. A number of factors impact the amount of urea that can be seed placed: seedbed utilization (calculated as the spread of seed and fertilizer divided by the row spacing); soil conditions (soil texture, soil moisture); and seed size. There’s an interaction between these factors and, as a result, the amount of urea that can be seed placed varies considerably. Higher seedbed utilization (e.g. 50 per cent versus 10 per cent), finer-textured soils (clay versus sand), and a larger seed size (cereal versus canola) allow more urea to be placed with the seed.
Moisture received shortly after seeding (up to seven days post-seeding) can minimize the toxic effects, but the amount to be seed placed should reflect moisture conditions present at the time of seeding.
Many producers seed place phosphate fertilizers in order to ensure seedlings have early access to this nutrient. The main phosphate fertilizer used in Alberta, monoammonium phosphate (11-52-0, 12-51-0), generally has low seedling toxicity. However, there is a distinct difference in maximum amounts of seed-placed phosphate based on crop type.
“In general, cereal crops can tolerate the amount of phosphate that is typically seed placed, while crops such as oilseeds and pulses are more sensitive,” said Cutts.
In Alberta, at 10 per cent seedbed utilization, the maximum recommended rates of seed-placed phosphate for cereal, pea, and canola are 50, 25, and 15 pounds per acre respectively.
A third fertilizer product that can be seed placed is potassium chloride (0-0-60), and it can impact crop stand establishment through a salt effect. A safe level depends on crop type.
“Typically, tolerance is higher for cereal crops as compared to a smaller-seeded crop such as canola,” said Cutts. “Pulse crops are sensitive to seed-placed potassium fertilizer, and producers may need to consider alternative fertilizer placement approaches such as banding.”
For more information on seed placing fertilizers, go to www.agriculture.alberta.ca or call 310-FARM.