618 EXPERIMENT STATION RECORD. 



SOILS— FEETILIZERS. 



An investigation of soil temperature and some of the most important fac- 

 tors influencing it, G. J. Bouyoucos (Michigan Sia. Tech. Bui. 17, pp. 196, 

 figs. 5Jf). — This is the first report on a systematic study undertaken "to inves- 

 tigate, individually or in combination, many of the chief soil factors affect- 

 ing tht boll temperature ; second, to study the effects of these various factors on 

 the temperature of the soil under field conditions; and, third, to ascertain the 

 relationship between soil temperature and the different meteorological elements." 

 It is confined to " the results of the completed laboratory experiments and 

 the results of only one year of the field experiments." The methods employed, 

 many of them original, are described and the results obtained in the study of 

 specific heat and heat conductivity of soUs; effect of color on radiation and the 

 radiating power of soils under different conditions or tretitments; temperature 

 of different types of soil; effect of organic matter on soil temperature; tempei-a- 

 ture of cultivated, uncultivated, and sod land; effect of soluble salts on the rise 

 and fall of temperature of soils; and effect of decomposition of manure on soil 

 temperature are presented in detail. 



The method employed in the study of specific heat " was devised in tlie course 

 of the investigation and was adopted Lq preference to a large number of others 

 that were tried. This method consists in wrapping a definite weight of soil in 

 a known weight of filter paper, tying the latter with a very fine thread, then 

 suspending it in a heater at a temperature of about 97° C. After the soU had 

 remained in the heater for 2 or more hours and had attained a constant tem- 

 perature it was dropped at once into the calorimeter and stirred vigorously 

 until the maximum temperature was indicated on the thermometer. This tem- 

 perature was usually obtained in about one minute. . . . Both the free soil and 

 the filter paper upon becoming wet increased the temperature, but this increase 

 was deducted from the final calculation by ascertaining it in a separate experi- 

 ment wherein was used the same amount of soil, filter paper, and water as in 

 the regular determinations and having them at about the same temperature 

 (25°)." The heat conductivity was measured under controlled laboratory con- 

 ditions in cores of soil cut at different seasons of the year. The special appara- 

 tus devised for the purpose is described in detail. 



Radiation was measured by means of a Beckmann thermometer in preference 

 to a thermopile, the complete apparatus used (which was in part the same as 

 that employed for measuring heat conductivity) being described in full. 



It was found in general that " the specific heat of different types of soil, 

 gravel, sand, loam, clay, and peat, in dry condition, did not differ very mate- 

 rially. This was true both by equal weights as well as by equal volumes. The 

 specific heat of peat was about half as great as that given to it by other inves- 

 tigators. The moisture content of these different soils in their natural condition 

 varied very greatly, and since water has such high specific heat it made a tre- 

 mendous difference in their final specific heat. 



"The heat transference in the different soils was measured (1) in their dry 

 condition, (2) in their natural state under laboratory conditions, and (3) under 

 field conditions. It was found in all these three states that the order of heat con- 

 ductivity was the same. Gravel possessed the highest heat-transmitting power, 

 followed in order by sand, clay, loam, and peat, respectively. Convectional cur- 

 rents, molecular diffusion, and distillation influenced very greatly the rate of 

 flow of heat, and consequently the values obtained do not represent the true 

 heat-conducting power of these different types of soil. 



" In field conditions the solar radiation tended to travel with greater rapidity 

 and facility vertically than horizontally. 



