Runoff phosphorus retention in vegetated field margins on flat landscapes

Vegetated buffer strips (VBS) are often recommended as a management practice that farmers can use to help mitigate the environmental effects of runoff from agricultural fields. Previous research has shown that VBS can be effective at trapping phosphorus (P) and other farm-sourced environmental contaminants. This project measured the effectiveness of established vegetated strips at decreasing P in runoff from agricultural fields in Manitoba. Paired samples of runoff, taken at the field edge and in the vegetated strip, indicated that in I I of the 22 cases sampled (50%), P concentrations in the runoff decreased (on average 30%) as the flow passed through the vegetated strip. In 7 of the 22 case (32%) there was no difference; however, in four of the 22 cases (18%), runoff P concentrations increased, indicating the vegetated strip had become a source of runoff P. Soil samples from the VBS showed high available P concentrations at positions within the vegetated strip along the runoff flow path, and in 7 of 10 cases these concentrations were higher (33% on average) than in the field soil. Although the observations and numerical results suggest that VBS can be effective at removing P in runoff, perhaps the major limitation in this flat-land region is that runoff tends to flow through rather small portions of the VBS, and these may not have sufficient capacity to retain the runoff P in the longer term.