EXPERIMENT STATION BULLETINS. 641 



TEMPERATURE OF CULTIVATED, UNCULTIVATED, AND SOD 



LANI^. 



OBJECT AND METHOD OF EXPERIMENTATION. 



The object of this research was' to study the temperature of land un- 

 der cultivated, uncultivated, and sod conditions. A few workers have 

 alreadv made casual observations on this line of studv but no one has 

 conducted a very thorough and extensive investigation. It was to sup- 

 ply the latter need that this experiment was undertaken. 



The experiment was commenced in November, 1911, and the tempera- 

 ture of the soil under the above treatments was measured at two dif- 

 ferent depths, 7 and 20 inches respectively, by means of soil thermo- 

 graphs which were procured from Friez, Baltimore. Maryland. There 

 were four thermographs, two of which were double and two single. 

 The former were made by special order and had two soil bulbs instead 

 of one. One of the single soil thermographs registered the air tem- 

 perature also. 



The ideal way to study soil temperature, in order to get the absolute 

 maximum and minimum, would be by means of such instruments as 

 these if they were accurate and dependable. Unfortunately, they do 

 not always possess these qualities. On account of the large mass of 

 liquid in the bulbs, they are slow to respond to variations of tempera- 

 ture; the pen is too thick, and hence, the line is too heavy for accurate 

 readings. Again, the setting of the recording sheets around the clock 

 is not always exactly the same for the different times. The most seri- 

 ous defect, however, is that the standardization is only relative, not 

 absolute, and if a small change takes place, the experimenter may not 

 detect it. Furthermore, the bulbs may leak and in such a case the 

 records are worthless. This unfortunate occurrence happened twice in 

 the present work, and hence, has broken the continuous records. The 

 bulbs at the depth of 20 inches of the uncultivated and sod plots 

 began to leak in January and the records of this depth of both plots 

 were lost from this time on till May when the defective bulbs were 

 repaired. Since the thermographs of both plots were double, the bulbs 

 of the upper 7 inches also had to be removed in order to repair those 

 at the lower depth, and hence, the records of the upper depths were 

 also lost during the month of April, after the thawing had taken place. 

 On the whole, however, these instruments gave quite satisfactory results. 



In order not to disturb the natural condition of the ground the bulbs 

 were placed in the following manner : Small trenches were dug in the 

 ground 20 inches deep, 6 inches wide and 20 inches long. At one end 

 of these trenches wooden rods of the same diameter as the bulbs were 

 bored into the soil horizontally at the proper depths. The rods were 

 then taken out, the bulbs put in their place and the trench filled up 

 with the excavated soil. In this manner the bulbs were kept under 

 undisturbed ground and the records, therefore, may be considered to 

 be of soils under natural conditions right from the start. 



The ground on which the plots were situated was very smooth and 

 SI 



