• Soybeans
• Soil Health

Objective

To improve phosphorus management recommendations for soybeans in Saskatchewan by investigating crop response to monoammonium phosphate rates and placement methods.

Outcome

Field trials were initiated in 2015 and conducted over three seasons at four Saskatchewan locations (Indian Head, Outlook, Melfort and Scott) to improve provincial phosphorus management recommendations for soybeans. The results suggest the current recommendation of no more than 10-20 kg seed-placed P2O5/ha may be too conservative but side-banding is a preferable method for applying phosphorus to soybeans, especially at high rates. Positive yield responses to phosphorus fertilization were infrequent and modest but detected 25% of the time. Such responses occurred only when soil test phosphorus values were below 15 parts per million and there were no other major yield limiting factors. In the cases where positive responses occurred, they were similar across placement methods with the exception of one site the strongest response was to broadcast phosphorus. The response to broadcast phosphorus was better than expected; however, this is still not a recommended practice due to higher potential for movement in runoff and, over time, conversion into less soluble phosphorus forms. While the results varied amongst sites, on average seed yields were 6% higher when at least 40 kg P2O5/ha was applied; however, with 90 kg P2O5/ha placed in the seed row, yields did not significantly differ from the control. For the three responsive sites specifically, the yield benefit was 11-22% or 415-876 kg/ha (6-13 bu/ac).

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