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美国的土壤侵蚀是个严重的问题,然而作物生产力的长期损失还没有得到适当的估价。美国的1.68亿公顷耕地,有大约
Soil erosion in the United States is a serious problem, yet the long-term loss of crop productivity has not been properly valued. There are about 168 million hectares of arable land in the United States