Lewis, R. O. (1958). Soil conservation in the Philippines: Terminal report, February 15, 1956-February 1, 1958. United States Operations Mission to the Philippines.
Lua i Stíl Chicago (17ú heag.)Lewis, Ralph O. Soil Conservation in the Philippines: Terminal Report, February 15, 1956-February 1, 1958. [Manila]: United States Operations Mission to the Philippines, 1958.
Lua MLA (9ú heag.)Lewis, Ralph O. Soil Conservation in the Philippines: Terminal Report, February 15, 1956-February 1, 1958. United States Operations Mission to the Philippines, 1958.
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