334 



Journal of Agricultural Research 



Vol. XII, No. 6 



EFFECT OF TEMPERATURE AND CARBON DIOXID 



The next point to be investigated was the possible effect of compara- 

 tively rapid changes of temperature. This was an important consider- 

 ation in studying fluctuations in soluble nutrients within a short period 

 of time. Such fluctuations were found to occur. It was extremely 

 desirable to know whether the change in solubility was due merely to the 

 physical effect of the increased temperature or was a secondary influence 

 due to increased activity of the bacterial flora. Such activity would 

 result in the production of appreciable quantities of carbon dioxid and a 

 possible increase in soluble soil compounds. 



A series of studies were undertaken to investigate these various 

 effects. A silty day loam soil of excellent productivity was used. One 

 container of this soil had been kept fallow all season; the other had 

 grown a crop of barley. Both samples contained practically identical 

 quantities of moisture, slightly below the optimum for this soil. 



One portion of each soil was placed in a bacteriological incubator at 

 29° C. A second was kept in a refrigerator at 6° for two hours, a third 

 was treated with carbon dioxid for 24 hours, a fourth was air dried at 

 20° for 48 hours, and a control portion was kept for 24 hours untreated. 

 The results are given in Table VI. 



Table VI. — Effect of loiv temperature, increased temperature, air-drying, and carbon' 

 dioxid on water-soluble nutrients 



[Results expressed as parts per milUon of dry soil] 



The data in Table VI must first be considered by applying the mean 

 factor of error for the several determinations. This correction shows 

 that the effect of the temperature treatments in the incubator and re- 

 frigerator has been negligible. It is therefore probable that sudden wide 

 changes of concentration of water-soluble nutrients are due to other 

 factors than changes in the solubility of plant food caused by tempera- 

 ture alone. 



The air-drying to which the two samples were subjected was carried 

 out at 20° C. without exposure to sunlight. It was consequently less 



