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连续长期性的土壤侵蚀影响了美国的粮食生产。然而,能够说明土壤侵蚀影响作物产量的资料却很少。收集这些资料需
Continuous long-term soil erosion has affected the United States food production. However, there is little information that can explain the impact of soil erosion on crop yields. Collect this information