This organic or vegetable matter consists of the partly decomposed residues of plants, including the roots and fallen leaves which may accumulate naturally, and the green manure crops, crop residues and farm manure which may be supplied in farm practice. Thus the nitrogen of a soil is measured approximately by its content of organic matter; and, vice versa, the percentage of nitrogen is an approximate measure of the organic matter, because nitrogen is a regular constituent of the organic matter normally contained in soils. Consequently if the organic matter of a soil is reduced the supply of nitrogen is also reduced. In the most depleted soils nitrogen is usually the most deficient element, although it may not be the only deficiency. Thus in the depleted "Leonardtown loam," which occupies such extensive areas of land in Southern Maryland, near the District of Columbia, and which has been to a large extent agriculturally abandoned after one or two centuries of farming, only 900 pounds of nitrogen are found in the plowed soil of an acre--that is, in 2,000,000 pounds of surface soil, corresponding to about 6-2/3 inches an acre. This total amount if made available would be sufficient for only six such crops of corn as are actually produced on our best land in good seasons, and yet it is four times as much as is contained in an equal weight of the subsoil. The average prairie land of the Corn Belt contains only 5000 pounds of nitrogen in the plowed soil of an acre 6-2/3 inches deep, whereas a 100-bushel crop of corn removes 150 pounds of nitrogen from the soil. A simple computation shows the supply in the plowed soil to be sufficient for only 33 such crops. Even the 100-bushel crop of corn per acre is known to have been produced in many places on exceptionally rich land, and yet the ten-year average yield in the United States is only 25 bushels to the acre. 200 Per Cent for Nitrogen On Broadbalk Field at Rothamsted, England, wheat has been grown on the same land every year for about two-thirds of a century. As an average of the sixty years, 1852 to 1911 the yield was 12.6 bushels an acre on unfertilized land, 14.6 where mineral plant food was annually applied, 20.3 where nitrogen salts alone were used, and 37 where both nitrogen and mineral plant food were applied. During the thirty years, 1882 to 1911 the average yields were 11.7 bushels an acre on the unfertilized land, 14 with minerals, 18.7 where only nitrogen salts were used, and 38 where both nitrogen and minerals were regularly supplied. These absolute data from the oldest agricultural experiment station in the world should help us to understand why the ten-year average yield of wheat is 33 bushels an acre for all of Great Britain, 37-1/2 for England alone, and only 14 for the United States.