These are actually qualitative and quantitative measurements. For example, you can measure whether or not a farmer soil-tests. You can document whether or not a farmer is matching his nitrogen recommendations, or balance for fertilizer recommendations, to those soil tests and recommendations. You can determine, very quickly, whether or not he's using slow-release nitrogens. You can document whether or not he's using precision agriculture.
All of those features and technologies lend themselves to a higher level of fertilizer-use efficiency. That fertilizer-use efficiency increases crop yield while simultaneously decreasing the environmental footprint. Those are the things we should be measuring. Those are the things we should be rewarding farmers for.