Não informado. (1935). Soil conservation. U.S. Department of Agriculture, Soil Conservation Service.
Lua i Stíl Chicago (17ú heag.)Não informado. Soil Conservation. Washington: U.S. Department of Agriculture, Soil Conservation Service, 1935.
Lua MLA (8ú heag.)Não informado. Soil Conservation. U.S. Department of Agriculture, Soil Conservation Service, 1935.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.