302 SOILS: PROPERTIES AND MANAGEMENT 



color, the white soils radiating more heat than the black 

 ones. The following data from Bouyoucos, 1 substantiating 

 those of Lang, 2 are a conclusive negative answer to such 

 a query : — 



Radiation of Different-colored Sands, White being 

 taken as 1.00 



White 1.000 



Black 991 



Blue 981 



Green 981 



Red 991 



Yellow 989 



The addition of organic matter, provided its decay has 

 been of the proper sort, will consequently always raise 

 the soil temperature, other factors of course being equal. 

 Wollny, 3 in experimentation with soils covered with thin 

 layers of different-colored material, found marked dif- 

 ferences under field conditions. The black soil not only 

 exhibited the highest temperature, but also showed a 

 greater amount of fluctuation. The minimum tempera- 

 tures of the different-colored soils were almost the same. 

 The temperature differences of course decreased with 

 depth. Some typical data obtained on a clear day, as 

 quoted from Wollny's work, are as follows : — 



1 Bouyoucos, G. J. An Investigation of Soil Temperature. 

 Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 30. 1913. 



2 Lang, C. Uber Warme-absorption und Emission des 

 Boden. Forsch. a. d. Gebiete d. Agri.-Physik, Band 1, Seite 

 379-407. 1878. 



3 Wollny, E. Untersuchungen uber den Einfluss der Farbe 

 des Bodens auf dessen Erwarmung. Forsch. a. d. Geb. d. 

 Agri.-Physik, Band I, Seite 43-69. 1878. Also, Untersuch- 

 ungen uber den Einfluss der Farbe des Bodens auf dessen Erwar- 

 mung. Forsch. a. d. Geb. d. Agri.-Physik, Band IV, Seite 

 327-365. 1881. 



