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3. MACGILLIVRAY, J.H. 1953. Vegetable Production. McGraw-Hill Book Co., New York.
4. USDA Misc. Pub. No. 316;R Magruder,1938
5. ZINK, F.W. 1965. Growth and nutrient absorption in spring spinach. Proc. Am. Soc. Hort. Sci. 87, 380–386.