The EU’s provisional agreement last week on changes to the Common Agricultural Policy envisions farmers setting aside 3 percent of their arable land for biodiversity efforts. While the share of agricultural land used for crops in the U.S. is about 39 percent less than in Europe, the number of acres sown to row crops has already been in decline. Market analysts were shocked last week when USDA found farmers planting fewer acres than crop prices would otherwise indicate. Some say declining acreage use is due to higher input costs and land values. It does not appear that paid land set-asides are a cause.  A key difference between Europe and the U.S. is land use as range or pastureland. Thirty-nine percent (173 million hectares) of...