Importance of Soil Warmth 425 



shows the observed difference in temperature of a 

 drained and an undrained soil : 



Temperature 



Condition of Temp, of of drained of undrained Differ- 

 Date Time weather air soil soil ence 



April 24 |p east wind 60.5 F. 66.5 54.00 12.50 



April 25 3 3 Q to m C1 U easrwind riSk 64 ' F- 70<0 58 - 00 12 - 00 



April 26 2 L3 J C1 U fo 7 re r nooif 11 th6 45 - F- 50 - 44 ' 00 6 - 00 



A _:! 07 1-30 to Cloudy and sunshine, n o -a ^ ft o r n 7 ro A 9r ,o 



April 27 2pm W i n d S. W. brisk 53 ' F ' 



AI 9s 7 to Cloudy and sunshine, .- n o v 47 n o 4d = n o 9 = ft o 



April 28 g 3Q a m wind N w brisk 45.0 F. 



The difference in the rate of evaporation from 

 clayey soil and sandy soil, when both are well 

 drained, will often be enough to leave the clay 

 soil 7 F. colder in the surface foot and 5 colder 

 in the second and third feet below the surface. 



IMPORTANCE OF SOIL WARMTH 



Ebermayer concluded from his observations that 

 relatively little growth can take place with most cul- 

 tivated crops until after the soil temperature has 

 been carried above 45 to 48 F., and the maximum 

 results are reached only after a temperature of 68 

 to 70 has been attained. 



Sachs showed that both pumpkin and tobacco 

 plants wilted, even at night and with an abundance 

 of moisture in the soil, when its temperature fell 

 much below 55 F., the osmotic pressure being then 

 too feeble to maintain a sufficient movement of soil 

 moisture to keep the plant cells turgid. Phenomena 



