Source: Government of Saskatchewan, Ken Panchuk, PAg, Provincial Specialist Soils
Adding phosphate with the seed or very near the seed-row at a safe rate is always the right decision for a rapid start. Every day counts when seeding progresses into June, so that flowering and maturity are not unnecessarily delayed.
Access to phosphorus is critical for early, healthy root development, nitrogen fixation process in pulses and legumes, early flowering, early and uniform ripening and seed production. The key is to apply the recommended rate (according to your soil test results) with the seed or very near the seed-row. At the same time, it is important to not exceed the maximum safe rate of phosphate applied with the seed. Guidelines for safe rates of seed placed phosphorus are available in the Phosphorus in Crop Production fact sheet.
If rates higher than the maximum rate for placed phosphate are required, apply some with the seed and the rest in a side or mid-row band with the nitrogen and other nutrients. With the high-yielding crops over the past few years, the soil phosphorus bank has been drawn down, so soil phosphorus levels need to be replenished.