Weir, W. W., & Gregory, R. W. (1938). Productive soils: The fundamentals of successful soil management and profitable crop production. J.B. Lippincott company.
Chicago-viite (17. p.)Weir, Wilbert Walter, ja R. W. Gregory. Productive Soils: The Fundamentals of Successful Soil Management and Profitable Crop Production. Chicago, Philadelphia [etc.]: J.B. Lippincott company, 1938.
MLA-viite (8. p.)Weir, Wilbert Walter, ja R. W. Gregory. Productive Soils: The Fundamentals of Successful Soil Management and Profitable Crop Production. J.B. Lippincott company, 1938.
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