The Use of Standard Soils with the Potassium Thiocyanate Test for Estimating Lime‐Requirement of Soils 1

During the past year, the writer has been using what may be termed "standard" or "known" soils in connection with the potassium thiocyanate test (3, 4)a for estimating the quantity of lime needed per acre by red clover and alfalfa, or sweet clover, to enable them to make good growth. These standard soils are soils whose lime-requirement has been estimated by several of the common methods and on which the field response of clover and alfalfa to liming is known. By studying a large number of soils in the field, where the growth and condition of crop was noted and where information was secured as to when the soil was limed and the kind and quantity of lime applied to the acre, it was possible to work out a dependable correlation between the lime-requirement of red clover, or alfalfa, on a given soil and the color developed on testing representative samples of that soilwith the "richorpoor"4 or other potassium thiocyanate solution. In attempting to determine the lime-requirement of clover, it is well to consider several factors. (a) The length of the rotation, is important; a larger application of lime will be needed for clover in a long rotation of seven or eight years than in a short one of three of four years. (b) The quantity of manure used per acre and where in the rotation it is applied with respect to clover, whether for corn one year preceding it, on the new clover seeding or for cropsfollowing it, should be considered. (c) The quantity of acid phosphate or other fertilizer used on the small grain crop in which the clover is seeded needs its share of attention. (d) The fineness of limestone, when this form is being used, must have due consideration. Liinestone, or other liming material, corrects the soil condition which for the present