| | The importance of fertilizers for sustaining crop production is well recognized. To ensure fertilizers are used efficiently, proper amounts must be applied.
"One way producers can improve fertilizer efficiency is to ensure proper amounts are being placed with the seed," says Mark Cutts, crop specialist at Alberta Agriculture and Rural Development's Ag-Info Centre, Stettler. "Applying too much fertilizer with the seed can reduce or delay crop emergence and result in inefficient fertilizer use. In order 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). Seed-placed urea can reduce crop emergence through ammonia toxicity. A number of factors impact the amount of urea that can be seed-placed. Factors to consider include: seedbed utilization (calculated as the spread of seed and fertilizer divided by the row spacing), soil conditions (soil texture, organic matter content and soil moisture), and seed characteristics (seed size). It is important to recognize that an interaction exists between these factors and as a result the amount of urea that can be seed-placed varies considerably. Higher seedbed utilization (50 per cent versus 5 per cent), finer textured soils (clay verses sand) and a larger seed size (cereal versus canola) allow more urea to be placed with the seed.
It should be noted, that 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, to minimize the risk associated with urea, 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 seedling plants have early access to this nutrient," says Cutts. "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. For example, under good to excellent moisture conditions, maximum rates of seed-placed phosphate for cereal, canola and pea are 50, 25 and 15 pounds per acre, respectively. This is equivalent to approximately 100, 50 and 30 lbs of 12-51-0 fertilizer per acre."
A third fertilizer product that is commonly seed-placed is potassium chloride (0-0-60). Seed-placed potassium fertilizer can impact crop stand establishment through a salt effect. The safe level of potassium that can be applied with the seed depends on crop type. In general, tolerance is higher for cereal crops as compared to a 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.
"To ensure efficient fertilizer use and proper stand establishment, several factors must be considered when seed-placement of fertilizer occurs," says Cutts. "An understanding of these factors and how they interact will allow the maximum benefit of these fertilizers to be achieved."
For more information on seed-placing fertilizers, please refer to the Alberta Fertilizer Guide which is available on Alberta Agriculture and Rural Development's website, Ropin' the Web or contact the Ag Info Centre at 310-FARM (3276).
Contact: Mark Cutts 310-FARM (3276) |
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