Nitrogen Leaching in Soil on the Experiment Station Farm at Lexington

Maury silt loam is the main soil type on the Agricultural Experiment Station farm at Lexington. This is the highly phosphatic soil of the Central Bluegrass region of the State. It also occurs in the Bluegrass region of Tennessee south of Nashville. The surface soil is eight to twelve inches of mellow reddish-brown silt loam. Underneath, it grades into a clay loam to clay reaching rock usually at six to ten feet. In the main, no doubt because of the high calcium content, the under soil is quite granular, very friable, and drainage is good. The high phosphorus content of 3,000 to 16,000 pounds or even more in the acre plow layer, practically precludes any need for application of phosphates. A fair supply of potassium is also present, averaging about 25,000 pounds in the acre plow layer. Field tests on the Experiment Station farm of ground limestone, phosphate and potash materials showed practically no response of any of the crops in a rotation of corn, soybeans, wheat, and red claver in the period 1912-1930 when the cornstalks, wheat straw, and soybean straw were returned to the soil CDNitrogen ranges from £,500 to 4,000 pounds, occasionally more, in the acre plow layer, depending mainly on the way the soil has been farmed. Economically, this nutrient is the most important one in this soil,' and because of climatic conditions leaching is an important factor in its maintenance. Average rainfall at Lexington is about fortyfour inches during the year and about fifteen inches during the period December to March, inclusive. The soil also is not frozen enough in most winters to prevent percolation. Several studies have been made on the production and disposition of nitrate in soil on the Experiment Station farm. For a time nitrate was determined in the fall in soil seeded to wheat. In some years the amount was large before being reduced by the wheat. In one year, seventy-five pounds of nitrate-nitrogen was present in September in an acre plow layer after Burley tobacco (2). In another year, barley after tobacco on land plowed out-of an old bluegrass sod, contained in the tops and roots 156 pounds of nitrogen per acre the last of November. It also was found that wheat seeded much after the first of October in some years did not take up all the nitrate in the soil. In a test (3) in one year, barley and wheat were seeded at different times after tobacco. Nitrogen in the crop and nitrate-nitrogen in the soil in December, expressed as pounds per acre, were: