Bruulsema, T. W., Mullen, R. W., O'Halloran, I. P. and Warncke, D. D. 2011. Agricultural phosphorus balance trends in Ontario, Michigan and Ohio. Can. J. Soil Sci. 91: 437-442. Agriculture is one of the sources of phosphorus (P) that feeds into Lake Erie, impacting water quality. A substantial proportion of the agriculture in Ontario, Michigan and Ohio falls in the Lake Erie drainage basin. We examine trends in the balance of the major inputs and outputs of P to the soils of this region. Only a few decades ago, recommended rates of P application for optimum crop nutrition amounted to considerably more P than crops removed. In recent years, actual P applications have come much closer to balancing removals, while crop yields have increased. This trend has positive implications for both crop productivity and water quality. The P balance serves as an appropriate performance indicator for P management reflecting both economic and environmental aspects of sustainability. Depending on assumptions regarding the recoverability of manure and the current implementation of reduced-P feeding strategies in the livestock industry, estimates of the P balance for the region in 2008 range from a surplus equivalent to 1% of crop removal to a deficit amounting to 23% of the amount of P removed by crops.