Availability of Tennessee Raw Rock Phosphate in Relation to Fineness and other Factors 1

made separations of raw ground Florida rock by means of sieves and bolting cloth and reported that the fineness of division had an important influence upon the availability of the raw phosphate. DeTurk and Sears4 report results of tests of raw phosphates of three degrees of fineness, showing negative results on the first two crops. This investigation was started in ~92 ~ for the purpose of obtaining more information on the effect of degree of fineness upon the availability of raw rock phosphate. The experiment was conducted in galvanized iron pots painted on the inside with acid-resisting black asphalt paint. Duplicate series of pots were filled with Bedford silt loam, a slightly.acid, light-colored soil from the Bedford experiment field. 5 This soil had been found to be notably deficient in phosphorus in a long series of field tests. Another series of duplicate pots were filled with a phosphorus-deficient Carrington silt loam, a slightly acid, dark soil from Benton County. One application of phosphates was made and the pots were. cropped with small red forcing radishes, black bearded winter barley, Burr Learning corn, and winter wheat. Each pot contained about ~5 kilos of soil, kept at about 50% water-holding capacity with tap water. Lime was applied only in pot No. ~ ~ in each series; however, the tap water used for watering contained some lime. The ~.4 grams of P205 applied to each pot was equivalent to approximately ~,4oo pounds of ~6% acid phosphate or 800 pounds per acre of 28% raw rock phosphate.