Potential Phosphorus Export in Snowmelt as Influenced by Fertilizer Placement Method in the Canadian Prairies

Placement strategies for P fertilizer can affect P availability to crops and influence the amounts and forms of P removed from soil in runoff, contributing to eutrophication. On the Canadian prairies, most runoff occurs during snowmelt. Two adjacent farm fields in Saskatchewan, Canada, were used to assess the effects of spring P fertilizer placement on crop P uptake, residual soil P, and potential P export in simulated snowmelt. One was in conventional tillage (CT) with no history of P fertilization, and the other was in a no-till (NT) system with multiyear P fertilization at recommended rates. Fertilization (monoammonium phosphate) treatments were no P fertilizer (control); seed placed, deep banded, and broadcast and incorporated at 20 kg PO ha; and broadcast treatments at 20, 40, and 80 kg PO ha. Yield and P uptake were not affected by placement method. Water-extractable P at the soil surface after harvest was unaffected by placement or rate at either site but increased below the 5-cm depth at the NT site in 2016. Broadcast treatments increased P in runoff relative to in-soil P placement for the 20- and 80-kg PO ha treatments at the CT site and for the 80-kg PO ha treatment at the NT site. Thus, in-soil application of P fertilizer appears to be an effective strategy to reduce the risk of P export in snowmelt runoff.