Jokela, W. E and Casler, M. D. 2011. Transport of phosphorus and nitrogen in surface runoff in a corn silage system: Paired watershed methodology and calibration period results. Can. J. Soil Sci. 91: 479-491. Transport of P, N, and sediment via runoff from crop fields, especially where manure has been applied, can contribute to eutrophication and degradation of surface waters. We established a paired-watershed field site to evaluate surface runoff losses of nutrients and sediment from different manure/crop/tillage management systems for silage corn production. During the 2-yr calibration period the four 1.6-ha watersheds, or fields, were treated identically with fall dairy manure application and chisel plowing, and runoff was monitored, sampled, and analyzed for suspended sediment (SS) and total and dissolved forms of P and N. That management was maintained as a control in one watershed, while alternative management systems were initiated on the three treatment fields. During the calibration period both concentrations and loads of SS and total and dissolved P and N varied by field and over 50% of runoff and dissolved P and N was from snowmelt runoff. Linear regressions of treatment fields against the control field were highly significant for runoff and concentrations and loads of all constituents. The estimated minimum detectable change (difference between means) was 10 to 30% for most parameters, suggesting a reasonable probability of success in detecting change in the treatment period.