Agricultural conservation programs aim to improve environmental quality by using payments to support voluntary adoption of environmentally sound practices. Supported practices, however, yield additional environmental gain only if they would not have been adopted without payment. We estimate additionality for selected practices using propensity score matching to analyze data from the Agricultural Resource Management Survey (ARMS). We find that greater than 95% of off-field structural practices (filter strips, riparian buffers) supported by payments are additional but that less than 50% of conservation tillage payments yield additional adoption. The effect of nutrient management payments varies across nutrient management practices and crops.