492 STATE BOARD OF AGRICULTURE. 



Both these obstnrles. hoM-ever. oould he eliminated or obviated to 

 a very larire extent by havinc; thermometers made to order with the 

 same lenjjth of bulbs and with the ])roper length of stems. But there 

 are still other disadvantag;es connected with snch instruments such as 

 (1) their franibility and consequently their unsuitability for lonj; dura- 

 tion or permanent experiments; (2) their inconvenience for reading; 

 and consequently 1lie errors that may arise due to parallax; and 

 (3) the adherins: at the mercury column to the stem thus giving low 

 or high readings. 



Perhaps on account of these difficulties, and also because of the many 

 other complex obstacles involved, the general subject of soil tempera- 

 ture has heretofore recei\Ted comparatively little investigation. In fact, 

 there is on record no extensive, thoro, and systematic investigation on 

 the subject. Considerable work has been done on certain individual 

 phases of the problem. The first and best scientific study of the sub- 

 ject has been done in Germany by Wollny and his associates. In no 

 other country has the subject received much attention. In America the 

 only important studies are the few practical observations made by 

 Kinir. and the recent work of Patten on heat transference in soils. 



While the greater part of the past work is good so far as it goes, 

 there is considerable which is rather inferior, the results of which have 

 led to many erroneous and faulty conclusions. Many of these unsound 

 conclusions have been deducted from short duration experiments; from 

 only one phase of the subject; and from results which were obtained 

 under too artificial conditions. The subject of soil temperature is a 

 most complex problem, and in order to arrive at proper, definite and 

 valid conclusions, it must be investigated from all standpoints, and as 

 far as possible, under both natural and controlled conditions. That 

 the subject demands a broad study for arriving at definite and sound 

 conclusions, is evidenced by the great number of factors which affect 

 or influence it. These factors may be divided into two general group;*, 

 intrinsic and external. The intrinsic factors are those contained in the 

 soil, such as specific heat, specific gravity, heat conductivity, radiation, 

 absorption, moisture content, organic matter content, concentration of 

 solution, evaporation, nature of surface, topographic position, etc. 

 Tho external factors consist of the meteorological elements, chief of 

 which are the air temperature, sunshine, barometric pressure, wind 

 velocity, dew point, humidity, precipitation, etc. Each one of these gen- 

 eral groups may be subdivided into two parts, one part tending to im- 

 part heat to the soil and thereby raise its temperature, and the other 

 part tending to take away heat from the soil and thereby lower its 

 temperature. These opposincr factors are in operation all the time, 

 but some predominate over the others at different seasons of the year. 

 A temperature record, therefore, taken at any time under field condi- 

 tions may be considered to be the resultant or summation of the effects 

 or forces of these opposing or contesting factors. 



In view of the paramount importance of the subject, of our limited 

 knowledge, and fhc uncertainty of many conclusions concerning it. 

 it has seemed essential and justifiable to undertake an investigation 

 of the probleiji. Such an investigation, however, to lip o^ the greatest 

 value should be conducted more thoroughly, extensfvely. and system- 

 atically than it has been heretofore. Accordingly the policy followed 



