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美国衣阿华州自1968—1975年间实行保持土壤的最少耕作法的面积增加了十倍。全州约有1/3的耕地面积采用了这
The area of Iowa in the United States has increased tenfold since 1968-1975 with the least farming practices of soil conservation. About a third of the country’s arable land uses this