EXPERIMENT STATION BULT.ETINS, 583 



EFFECT OF ORGANIC AfATTER ON THE TEMPERATURE OF 



SOILS. 



OBJECT AND METHOD OF EXPERIMENTATION. 



Organic matter possesses two physical properties wliich have a re- 

 markable influence npon the soil temperature. These are color and 

 water holding capacity. The soils ^Wth the largest amount of organic 

 matter will have the darkest color. Dark or black colored soils, possess- 

 ing the highest absorbing capacity for heat, would tend to be much 

 warmer than the light colored or white soils, which have less heat ab- 

 sorbing power. On the other hand, the soils with the greatest organic 

 content carry also the largest amount of water, and water possessing 

 such great specific heat and other properties, would tend to keep the 

 temperature of tliese soils low. It was in order to ascertain to what 

 extent these two physical properties of the organic matter would op- 

 pose each other, that the following experiment was undertaken. It 

 consisted of studying the daily temperature of a sandy soil which con- 

 tained organic matter in the proportions of 1.81, 2.01, 3.32, 5.47, 6.95% 

 and 100% peat. It was prepared by excavating a trench over 3 feet 

 deep and 3 feet wide, placed in it wooden boxes 3x3x3 feet without 

 bottom or top and filled them with a sandy soil. The soil of the upper 

 21 inches w^as then taken from each box, added to it the proper amount 

 of organic matter (peat), thoroughly mixed, and then placed back into 

 the box. The percentages of organic matter shown above represent the 

 percentage amounts found by the ignition method, after the respective 

 proportions of peat Avere added. To the soil showing 1.81% organic 

 matter no peat was added. This is, therefore, the original organic con- 

 tent of the soil as determined by the above method. These various 

 amounts of organic matter imparted to the soil different shades of 

 color, ranging from very light to very dark. The soil with the 1.81% 

 organic matter was covered with a very thin layer of very white quartz 

 sand, thus giving to it a very white color. 



The experiment was prepared and was ready for the intended study 

 by October, 1911, but because of an accident to the thermometers, the 

 temperature records were not commenced till the middle of February, 

 1912. 



The temperatures were taken by the electrical resistance thermom- 

 eters already described, at two different depths, 5 and 18 inches, daily 

 throughout the vear, except on Sundavs, three times a day at, 7 A. M., 

 12 M., and 6 P. M. 



The tables to follow show the daily, montlily, seasonal, and yearly 

 maximum, minimum and average temperatures, for all the soils at both 

 depths. All the tables with few exceptions are accompanied by dia- 

 grams to show their salient facts graphically. On the daily tempera- 

 ture charts are also plotted the meteorological data in order to show 

 more readily any influence that they might have on the soil temperature. 



