Rees, H. W., Chow, T. L., Zebarth, B. J., Xing, Z., Toner, P., Lavoie, J. and Daigle, J.-L. 2011. Effects of supplemental poultry manure applications on soil erosion and runoff water quality from a loam soil under potato production in northwestern New Brunswick. Can. J. Soil Sci. 91: 595-613. Soil erosion is a major threat to the economic viability of potato production in northwestern New Brunswick. One option for growers to increase soil organic matter and improve soil quality in potato fields is through poultry manure application. While poultry manure may be beneficial for soil quality, there are also potential risks to surface water quality associated with manure application. This study evaluated the effects of time of poultry manure application on potato fields in northwestern New Brunswick on soil erosion and runoff water quality. Seven permanent Wischmeier-like erosion plots, established in 1982, were used. Treatments consisted of a control (Ctrl) with no manure applied, and applications of 4 Mg ha^-1 of fresh poultry broiler manure in late fall (F), pre-planting (PP) and pre-hilling (PH) on 11% slope plots and a Ctrl, F and PH treatments on 8% slope plots. All poultry manured treatments increased potato total yield with a general trend of Ctrl<F<PH<PP, but only the 8% PH increase was significant (P<0.10). Potato yield of fall-applied poultry manure did not result in a significant reduction in yield compared with other treatments. May to October runoff was significantly reduced on the 11% PH, but increased on the 8% F treatment. May to October soil loss was significantly reduced on the 11% PH and 11% PP. The soil loss:runoff ratio was reduced by up to 15% with PP and PP<PH<F<Ctrl. Fall applications generally resulted in the greatest mean annual flow-weighted nutrient runoff concentrations and runoff nutrient loadings whereas PH resulted in some of the lowest nutrient concentrations and loadings. While high background concentrations of Escherichia coli were found in runoff, E. coli concentrations in runoff were increased 20-230% by manure application. Escherichia coli colonies survived the winters in northwestern New Brunswick and populations were cyclical being highest in summer and lowest in winter. Escherichia coli concentrations in runoff were significantly (P<0.10) correlated with air and soil temperature and soil loss. The PH appeared to provide the best balance between crop production and surface water protection. Further replicated research is required to support these results.