Não informado. (1935). Soil conservation. U.S. Department of Agriculture, Soil Conservation Service.
Citação do estilo Chicago (17ª ed.)Não informado. Soil Conservation. Washington: U.S. Department of Agriculture, Soil Conservation Service, 1935.
Citação MLA (8ª ed.)Não informado. Soil Conservation. U.S. Department of Agriculture, Soil Conservation Service, 1935.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.