WATER SOILS. 25 



"In 8 of those cases samples were taken in 1 ft. sections to a depth of 4 ft., at the 

 other intervals at a depth of 2 ft. By doing this we have secured a detailed record 

 of the changes in the amount and distribution of nitric acid through an entire grow- 

 ing season for 3 plats of corn, 2 plats of potatoes, 2 plats of clover, 1 plat of alfalfa, 

 and 1 ])lat of oats. . . . 



"Side by side with the nitric acid determinations we have made a study of the 

 total soluble salts as indicated by the electrical resistance, the two sets of determina- 

 tions being usually made on each set of samples. 



"The amounts of water present in the field soil have been recorded at each interval 

 and for each depth, and the total amount of dry matter produced on each plat has 

 also been recorded; so that we are now in possession of a fairly accurate set of data 

 showing the amount of nitric acid and the amount of water present in the soil, 

 throughout the season, upon which known amounts of nine crops have been grown." 



The experiments on tillage were made in the i)lant house with cylinders 52 in. 

 deep and 18 in. and 3 ft. in diameter in 3 series, as follows: (1) Not cultivated, (2) 

 cultivated 3 in. deep once a week, and (3) cultivated 3 in. deep once in 2 weeks. 

 The soil used was a clay loam and had in different cases previously borne crops of 

 corn, clover, oats, potatoes, and timothy and beets following beans. No water was 

 applied and there was no drainage from the cylinders during the experiment. The 

 gains and losses of nitric nitrogen and soluble salts during the 93 days of the 

 experiment are recorded. 



"The general conclusions suggested by this study may be stated as follows: 



" ( 1 ) Nitrification has taken place at all depths down to 3 ft. below the surface, 

 and hence that in these cases it is not a process limited to the surface few inches. 



"(2) As a general rule there has been the highest increase of nitric nitrogen in the 

 surface foot and the increase in the third foot has generally exceeded that in the 

 sei'ond foot. 



"(3) Tlie increase of nitric nitrogen has been greater at all depths, as a rule, where 

 the soils have not ])een cultivated than where they have. 



"(4) In two groups of cylinders there has been a tendency for the nitric nitrogen 

 to decrease rather than increase. 



" (5) There has been 22 per cent more nitric nitrogen developed from the soil after 

 clover than from the .soil after corn, and 13 per cent more than from that after oats 

 during the 93 days. 



"(()) But the soil after growing corn the same number of years that the other had 

 grown clover Ijegan the experinient with nearly three times as much nitric nitrogen 

 in it as the soil after clover did and it closed the cultivation i)eriod with 17 per cent 

 more nitric nitrogen. 



"(7) The soil, after oats, Ijegan the experiment with 2.6 times as much nitric 

 nitrogen as the clover soil did and it closed the cultivation period with 13.8 per cent 

 more nitric nitrogen. 



"(8) The fertilizing power of clover appears to depend more upon the amount of 

 nitrogenous material left in the soil which is ca|)able of rapid nitrification than upon 

 nitric nitrogen accumulated by it. 



"(9) With the marsh soil yielding poor crops there was in both cases a heavy gain 

 of nitric nitrogen in the first foot, but in the soil giving l^etter yields there was only 

 a small gain in the not cultivated ground and a loss in the surface foot of cultivated 

 ground. Indeed there was a total mean gain in the poorer soil of 37.47 parts per 

 million but one of only 2.97 parts per million in the l^etter soil for all three feet, 

 while in the case of the clay loam the total mean gain was 8.77 parts i)er million of 

 nitric nitrogen." 



Similar observations on cylinders filled with sand or pine barrens soil on which 

 clover and alfalfa had been grown and turned under as green manure confirmed the 

 above conclusion that "the clovers leave a soil in such a condition that the rate of 



23194— No. 1—01 3 



