While applying fertilizer at the time of seeding has many benefits, it is important to use the right amount. Mark Cutts, crop specialist at the Alberta Ag-Info Centre, evaluates placement, impact, and types of fertilizer.
“Applying too much fertilizer with the seed can impact crop emergence,” says Cutts. “To ensure seed-placed fertilizers are being managed properly, producers need to understand the factors that influence their impact.”
The fertilizer product most commonly evaluated for seed-placed safety is urea (46-0-0). Seed placed urea can reduce crop emergence through ammonia toxicity. Factors that impact the amount of urea that can be seed-placed include seedbed utilization (calculated as the spread of seed and fertilizer divided by the row spacing), soil conditions, and seed size.
“As an interaction exists among these factors, the amount of urea that can be seed-placed varies considerably,” says Cutts. “Higher seedbed utilization (for example, 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.”
For seed-placed urea, moisture conditions at the time of seeding, and moisture received shortly after seeding up to seven days post-seeding, can minimize the toxic effects of urea in the seed-row. However, says Cutts, “To minimize the risk associated with urea, the amount that is seed-placed should reflect moisture conditions present at the time of seeding.”
“Many producers place phosphate fertilizers with the seed to ensure seedling plants 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’s typically seed placed, while crops such as oilseeds and pulses are more sensitive. In Alberta, at ten per cent seed bed 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). “Seed-placed potassium fertilizer can impact crop stand establishment through a salt effect,” says Cutts. “The safe level of potassium that can be applied with the seed depends on crop type. In general, tolerance is higher in cereal crops than in smaller seeded crop such as canola. Pulse crops are sensitive to seed-placed potassium fertilizer and producers may need to consider alternative fertilizer placement approaches such as banding.”
Source : Alberta Ag and Forestry