Não informado. (1935). Soil conservation. U.S. Department of Agriculture, Soil Conservation Service.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Soil Conservation. Washington: U.S. Department of Agriculture, Soil Conservation Service, 1935.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Soil Conservation. U.S. Department of Agriculture, Soil Conservation Service, 1935.
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