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2. Poultry manure; its nature, care and use;Papanos;Connecticut (Storrs) Agr. Exp. Sta. Bul.,1950
3. Soil and plant analysis;Piper,1947
4. The determination of the readily available phosphorus of soils;Truog;J. Amer. Soc. Agron.,1930
5. Fertilizers and Crop Production;Van Slyke,1932