280 EXPERIMENT STATION RECORD. 



than the total salts imlicated. This may he due to the destructiou of l)icarl)onate3 

 by the nitric aeid when it is forming. 



"(5) The amount of nitrates and soluble salts under growing crops and in fallow 

 ground at the same time is very different. Our observations show a relation for 

 nitrates of 10.88 lbs. in the surface foot per acre as a mean, to 47.3.65 lbs. for imme- 

 diately adjacent fallow ground at the same time. 



"(6) It was found that stirring the soil once per week, as compared with the stir- 

 ring of it once in two weeks, left the soil after 91 days with 98.16 as compared with 

 53.01 lbs. of nitric nitrogen per million of dry soil. In the second series of experi- 

 ments, which covered 258 days, the soil stirred once per week had acquired a mean 

 of 225.41 parts, and that once in two weeks 158.79 parts per million of dry soil, show- 

 ing the largest gains with the more frequent cultivation. 



"(7) It was found that stirring the soil to depths of 1 in., 2 in., 3 in., and 4 in. 

 during an interval of 258 days resulted in an increasing amount of nitric nitrogen 

 until the 3 in. depth was passed, but that cultivation 4 in. deep gave a smaller 

 nitrification than the 3 in. depth did. 



"(8) In the plant house cylinders nitrification api)ears to have taken place to a 

 depth of 3 ft., but was most rapid in the surface foot. 



"(9) There was 22 per cent more nitric nitrogen developed in soil ujjon which 

 clover had grown than from that after corn, and 13 per cent more than from that 

 after oats, during the same time, under like conditions. 



"(10) Virgin soil which had grown corn continuously the same number of years 

 that like soil had grown clover contained, at the ])eginning of the cultivation experi- 

 ment, nearly three times as much nitric nitrogen as that upon which the clover had 

 grown, and it closed the cultivation period with 17 per cent more. 



"(11) Virgin soil growing oats began the cultivation experiment, after the same 

 number of years of cropping as the soil hearing clover, with 2.6 times as much nitric 

 nitrogen, and closed the 91 days with 13.8 per cent more. 



"(12) Clover and alfalfa appear to hold the nitric nitrogen in the soil down to a 

 lower limit than corn, oats, and potatoes do, but when the crop is removed from the 

 ground nitrification appears to go on faster in the clover and alfalfa soil. 



"(13) The amcjunt of nitric nitrogen left in the surface foot of soil before crops begin 

 to turn yellow for lack of available nitrogen becomes very small, the amount found 

 being 0.213 parts per million where oats were yet green, and 0.025 parts per million 

 where they were turning yellow. In corn it was found as low as 0.95 parts where 

 corn was green, and 0.10 parts per million where it was strongly yellow. 



"(14) The amounts of nitric nitrogen and of soluble salts were found greatest 

 between the rows of corn, as they were coming into tassel, and least, directly beneath 

 hills, except in the surface 6 in., and in the fourth foot where the relations were 

 slightly reversed. 



" ( 15) The amounts of nitric nitrogen and of total soluble salts are less in the deeper 

 ground water of wells of this vicinity than in the soil moisture of the fourth foot, the 

 nitric nitrogen being Only about one-third of the amount. 



"(16) Observations indicate that when the textural equilibrium of soils is destroyed 

 in the presence of salts in solution the reflocculation and regranulation of the soil 

 may take out of solution a portion of the salts, leaving a smaller percentage present 

 after establishing the new equilibrium." 



The soil solution for tlie determination of nitric nitrogen was prepared by kneading 

 for 2 or 3 minutes in a mortar 50 gm. of the soil in a close muslin sack with 250 cc. of 

 a 0.1 per cent solution of formaldehyde containing 5.36 cc. of a saturated solution of 

 potash alum. The solution was then wrung from the sack and allowed to settle. Fifty 

 cubic centimeters of the clear solution was evaporated to dryiiess on a water bath, 

 12 to 20 drops of disulphonic acid were added, and after standing at least 10 minutes 

 with thorough stirring 20 cc. of distilled water and enough ammonia to make the 

 solution alkaline were added. The nitric nitrogen was determined by the colorimetric 



