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.

Solid-liquid separation method governs the in vitro bioaccessibility of metals in contaminated soil-like test materials.

An in vitro gastrointestinal model was used to explore the role of solid-liquid separation method on the bioaccessibility of trace elements in a smelter-impacted soil (NIST-2711) from Helena, MT and a mine overburden from an open-pit gold and silver mine in Mount Nansen, YK (YK-OVB). Separation methods studied included centrifugation (5,000 g, 12,000 g), syringe microfiltration (0.45 µm), and ultrafiltration (1,000 kDa, 50 kDa, 30 kDa, 10 kDa, 3 kDa). Results indicated that the use of syringe microfiltration generally yields the same bioaccessibility as the use of centrifugation and that the speed of centrifugation does not typically affect metal bioaccessibility. However, ultrafiltration consistently yields a significantly lower bioaccessibility than the use of centrifugation and syringe microfiltration. There are rarely any differences between bioaccessibility estimates generated using a low-resistance (1,000 kDa) and a high-resistance (3 kDa) ultrafiltration membrane; therefore, under the in vitro gastrointestinal conditions modeled herein, negligible quantities of trace elements are complexed to small molecules between 3 and 1,000 kDa. The primary exceptions to these trends were observed for Pb in NIST-2711 (5,000 g>12,000 g>0.45 µm>ultrafiltration) and for Tl in NIST-2711 and YK-OVB (5000 g∼12,000 g>0.45 µm>ultrafiltration). These results provide valuable information to researchers attempting to expand the use of in vitro bioaccessibility beyond soil Pb and As.