Ketterings, Q. M., Czymmek, K. J. and Swink, S. N. 2011. Evaluation methods for a combined research and extension program used to address starter phosphorus fertilizer use for corn in New York. Can. J. Soil Sci. 91: 467-477. Since there is no substitute for phosphorus (P), judicious use of P fertilizer is needed to protect water quality, world P reserves and farm economics. In 2001-2003, 78 on-farm corn (Zea mays L.) P trials were conducted on New York State (NY) dairy farms as part of a statewide, integrated (research and extension), outcome-focused project. The data showed fertilizer P could be eliminated or reduced to less than 28 kg P₂O₅ ha^-1 for fields very high or high in soil test P, respectively. We conducted: (1) case study P fertilizer management evaluations using 30 NY, and (2) a producer survey using a postcard evaluation tool, to determine project outcome potential and farmer intent to change P management. The two impact evaluations showed (1) P use could be reduced to 17 kg of P₂O₅ ha^-1 or less with soil-test based decision making, and (2) 81% of producers were likely to change P use in future years. Statewide P fertilizer sales decreased from 12 603 Mg (8.6 kg ha^-1) in 2000 to 10 092 tons (6.8 kg ha^-1) in 2007, a 20% reduction in P use. These results reflect the effectiveness of the impact evaluation tools and of outcome-based projects where extension and research are integrated and farmers and farm advisors are key participants in the design and implementation of the project.