WATER SOILS. 931 



In view of tht large amount.^ of iiitriites found in the erops exuniinetl (ais high as 

 12,317 parts per million of dry matter in potato stems), the authors tested the 

 accuracy of the ordinary Kjeldahl method as applied to such materials and found a 

 considerable error due to incomplete recovery of the nitrates by this method. 



There was an average gain of 79.27 lbs. of nitrates in the surface foot of the soils 

 during winter. 



A study of the intluence of temperature on nitrification was made by the following 

 method: "From a large (juantity of the field soil, thoroughly mixed in a tray out of 

 doors, when the temperature was near 82°, about 2,000 gm. were taken and put into 

 a 4-qt. tin pail, to be placed in another receptacle surrounded by water at the 

 desired temperature." The temperatures maintained in different cases were about 

 35, 48, 68, and 90° F. "The soil was kept under conditions which permitted nor- 

 mal aeration, and the moisture content of the soil was maintained nearly constant by 

 tlie addition of water at the time the samples were taken, to restore that lost by 

 evaporation during the interval." The observations extended over 27 days, April 

 11 to May 8. Determinations of nitric nitrogen were made at the beginning and at 

 about 2-day intervals in duplicate 50 gm. samples of each soil, care being taken "not 

 to have the soil samples exjiosed to the temperature of the lal)oratory more than a 

 few moments before the nitrates were washed out in the formalin solution to ai-rest 

 both nitrification and denitrification." 



The soil used "was in fairly good condition of fertility, but had received no manure 

 or other fertilizers for more than 5 years. At the lowest temperature the mean daily 

 rate of nitrification was 0.1594 part of nitric nitrogen per million of dry soil; or, 

 expressed as calcium and magnesium nitrates, this is equivalent to 0.876 lb. per 

 million pounds of dry soil. The surface 6 in. of an acre of this soil weighs about 

 1,370,000 lbs., and the above rate of increase would mean a production of 1.2 lbs. per 

 day per acre and 120 lbs. in 100 dftj'S. The rate of nitrification at the highest tem- 

 perature was 6.232 times more rapid than at the lowest temperature, the mean daily 

 rates for the 4 temperatures being, in parts per million of dry soil, as follows: At 

 35° F. 0.1593, at 48° F. 0.1999, at 68° F. 0.4376, at 90° F. 0.9927." 



These observations indicate that considerable nitrification may go on at as low a 

 temperature as 35° F. 



The results of observations on the influence of fall plowing on nitrification show 

 that "if the total nitrates found in the jjlowed ground of August 19 and September 30 

 are (-(.mpared, it will be seen that there has been a gain of 148.56 lbs. per acre during 

 the 42 days. In the same way, comparing the total nitrates in the 4 ft. of the 

 unplowed ground of the same dates, it will be seen that there has been a gain of 

 113.92 lbs. per acre, so that the effect of the plowing has been to increase the nitrates 

 34.64 lbs. per acre, or about 0.8 of a pound per day." 



The total nitrates in soil which had been plowed in the fall just as the ground was 

 freezing and again April 12 the succeeding spring ' ' was 183.53 lbs. per acre, while that 

 in the uni)lowed ground was 160.71 lbs. per acre, a difference of 22.82 lbs. in favor of 

 the plowing; but on April 29 the nitrates on the unplowed ground had incTeased to 

 355.52 U)s. per acre, while that on the plowed ground contained only 327.97 lbs. or 

 27.55 lbs. per acre less. Accepting the figures as representing the facts, it appears 

 that the ground not plowed has increased in its nitrate content faster tiian the i)lowed 

 ground did, and at the rate of some 50.37 lbs. per acre. This is what should be 

 expected if (1) nitrates are brought toward the surface by ca[)illarity; (2) if there 

 was greater evaporation from the ground not plowed than from that jdowed, and (3) 

 if the rate of nitrification was the same in both cases." 



Studies on black marsh soils, V. II. Kivc and A. R. Wiirrsox ( WiHcunsin Sta. 

 Rpt. 1901, pp. 2S2-2.S6, Jif/i^. J). — Fxi)eriments in continuation of tliose of previous 

 years (E. S. R., 13, p. 27) were made in cylinders to determine the effect of turning 



27718— No. 1(1—02 3 



