Relations of Higher Plants to the Formation of Nitrates 75 



the crops received an application of quicklime at the rate of 2000 pounds 

 per acre. Alfalfa roots on both limed and unlimed soil possessed tubercles. 

 In the spring of 1910 strips of land through both the limed and the unlimed 

 parts of the alfalfa and the timothy plats were hoed bare of vegetation, and 

 these strips were kept free from plants of all kinds during 1910 and 1911. 



The nitrate-producing power of alfalfa soil and of timothy soil 



The rate at which nitrate formation takes place in soil is well known to 

 be influenced by a number of conditions, such as the basicity of the soil, 

 the degree of aeration, and the like. That it may be influenced by the 

 nature of the vegetation growing on the soil appears to be true of the soil 

 used in these experiments. The method adopted for measuring nitrate pro- 

 duction was as follows : The soil was sampled by means of a soil auger to a 

 depth of eight inches. The borings from the plat or section of plat to be 

 tested were mixed, quartered, and placed in an air-tight jar while still 

 moist. When the jar was brought to the laboratory, moisture and nitrates 

 were determined within twelve hours after sampling. Nitrates were deter- 

 mined in 100 grams of moist soil by means of the disulfonic-acid method. 

 Another 100 grams of moist soil was placed in a bottle having a capacity 

 of 250 cubic centimeters, and sufficient water was added to bring the mois- 

 ture content to 25 per cent of the dry weight of the soil. A loose cotton 

 plug was inserted into the mouth of the bottle, which was then placed in 

 an incubator and kept at a temperature of 30° C. for the number of days 

 stated in the following tables. In some of the earlier tests, 500 milligrams 

 of ammonium sulfate was added to each 100 grams of soil; this practice 

 was afterwards abandoned, however, and does not apply to results obtained 

 after 1910. Tests were made also by adding 100 milligrams of dried blood 

 to 100 grams of soil and incubating as above. The soil for the test without 

 dried blood and the soil for the test with dried blood were weighed out at 

 the same time; so that the nitrification of the soil with only its normal 

 supply of organic nitrogen was tested, as well as its nitrifying power when 

 an abundant supply of organic nitrogen was present. 



In 1909 the rate of nitrification of soil from the alfalfa plats and from the 

 timothy plats was tested by using ammonium sulfate as described above. 

 The samples were taken to a depth of eight inches on October 6. 



In Table 25, which contains the results of these tests, the quantity of 

 nitrates produced in ten days represents the difference between the quan- 



