792 STATE BOARD OF AGRICULTURE. 



Tlic ]>i'iii(ii)al facts rcvoaled by tlic preceding tables may be suniniarizcd 

 as follows: (1) Tlc highest seasonal amplitude occurred in the summer, 

 the smallest in the winter and an intermediate between these two in the 

 spring and autumn. The magnitude of the spring and fall fluctuation 

 was about equal and only about half as great as that of the summer; 

 while, the yearly average amplitude was equal in magnitude to that of 

 the spring or fall. (2) The amplitude of the air was far greater than 

 that of any soil at any depth. 



ADDITIONAL I<]XPERIMENTAL DATA ON THE TEMPERATURE 

 OF SAND WITH DIFFERENT AMOUNTS OF ORGANIC MAT- 

 TER, AT VARIOUS DEPTHS FOR 1913, 1914, AND 1915. 



PLAN OF THE EXPERIMENT. 



Organic matter possesses two physical properties which exert a very 

 marked influence upon soil temperature. These are color and water- 

 holding capacity. The soils with the largest amount of organic matter 

 will have the darkest color. Since dark color possesses the highest ab- 

 sorbing capacity for heat these soils will tend to be much warmer, dur- 

 ing the insolation, than the light colored soils, which reflect a large 

 amount of the solar rays. On the other hand, the soils with the greatest 

 organic matter content will carry also the highest amount of water and 

 water possessing such great specific heat, latent het^t of evaporation, and 

 other properties, will tend to keep the temperatu/-e of these soils low. 



It was in order to ascertain to what extent these two physical proper- 

 ties of the organic matter would oppose each other and which one would 

 predominate, that the following experiment was undertaken. It con- 

 sisted of measuring the temperature of a soil to which was added dif- 

 ferent amounts of organic matter (peat). It was prepared by making 

 a long trench over 3 feet deep and 3 feet wide, placing in it, about a 

 foot apart, wooden boxes 3x3x3 feet without bottom and top and filling 

 them with a sandy soil. The soils of the upper 24 inches were then taken 

 out from all the boxes, except one, each soil was thoroughly mixed with 

 the proper amount of peat, and then placed back into its respective box. 

 There w'ere six boxes, one containing soil to which was added no peat, 

 another contained only peat, and the other four had soil with various 

 proportions of peat. The percentage of total organic matter of the 

 various soils, except peat, as deteinnined bv the ignition method is shown 

 by the following figures: 1.81, 2.01, 3.32,' 5.47, and 6.95%. To the soil 

 showing 1.81% organic matter no peat w^as added. This amount of or- 

 ganic matter, therefore, was originally present in the soil. This untreat- 

 ed soil was covered with a thin layer of white quartz sand so as to give 

 it a distinct w'hite color. The color of the various soils, therefore, ranged 

 from very white to very black. 



The temperature was measured in all the soils at two different depths 

 every day except Sunday for almost four years. It was recorded by 

 means of the electric thermometers already described. During the years 



