174 



SCIENCE 



[N. S. Vol. XL VII. No. 1207 



alike on all plots, there being very little injury 

 to this cereal. Directly contrary results were 

 obtained the second season, the temperature 

 being lowest and the survival least on the wet 

 plots. 



This apparent anomaly seems to have been 

 due to the character of the seasons and the 

 changes in specific heat and thermal conduc- 

 tivity that takes place when water changes to 

 ice. The first winter was comparatively mild 

 and snow covered the plots during the coldest 

 weather to a depth of several inches. As a 

 result the soil was never frozen more than a 

 few inches deep or for more than a few days at 

 a time. Consequently, the changes in temper- 

 ature were much less rapid on the wet than on 

 the dry plot because of the specific heat and 

 the latent heat of fusion of the water. The 

 temperature of the wet plot was therefore more 

 uniform, the highest daily maxima and minima 

 being recorded for the dry plot. 



The second winter was colder, and since the 

 plots were not protected with snow they were 

 frozen most of the time. The relationship 

 between the wet and dry soil that was main- 

 tained during the first season was directly re- 

 versed, the lowest daily minima and the least 

 survival being recorded on the wet soil. This 

 reversal was apparently due to the difference 

 in specific heat and the thermal conductivity 

 of ice and water. When water freezes the 

 specific heat is reduced approximately one 

 half while the thermal conductivity is in- 

 creased more than three times.^ Consequently 

 the difference in apparent specific heat of a 

 wet and a dry soil is much less when it is 

 frozen than when unfrozen, while the differ- 

 ence in thermal conductivity is greatly in- 

 creased. The increase in the latter is suffi- 

 cient to overbalance the difference in apparent 

 specific heat permitting the temperature fluc- 

 tations of the air to be more quickly recorded 

 in the soil. 



The wet and dry clay plots exhibited the 

 same relation between moisture content, tem- 

 perature and winter-killing that was found for 

 the silt loam, only in greater degree. For ex- 

 ample, 81.Y per cent, of the wheat and ll.V 



1 Eeed and Guthe, Macmillan Co., 1914. 



per cent, of the barley survived on the dry silt 

 loam as compared with 52.5 per cent, and 7.2 

 per cent, for the wheat and barley, respectively, 

 on the wet silt loam, or a difference in favor 

 of the dry soil of 29.5 per cent, for the wheat 

 and 4.5 per cent, for the barley. On the clay, 

 89.4 per cent, of the wheat and 58.8 per cent, 

 of the barley survived on the dry plot as com- 

 pared with 20.4 per cent, and 2.1 per cent, for 

 the wheat and barleyj^espectively, on the wet 

 plot, or a difference of 69.0 per cent, for the 

 wheat and 18.3 per cent, for the barley. The 

 difference in temperature between wet and dry 

 plots was also greater on the clay than on the 

 silt loam. 



On the sandy plots the effect of moistiire on 

 temperature and winter-killing was contrary 

 to its effect on clay or silt loam when the soil 

 was frozen, but corresponded qualitatively 

 with the latter types when they were not 

 frozen. The temperature of the dry sand was 

 lower during the winter and the survival less 

 than for the wet sand, freezing apparently 

 having little influence. This was probably 

 due to the fact that sand is a much better con- 

 ductor of heat than other soils and hence there 

 is less difference in the thermal conductivity 

 of wet and dry sand than for soils of the 

 heavier types. Also the water capacity of sand 

 is much less than that of other soils, and there 

 is consequently less change in the thermal 

 conductivity when it is frozen. 



Further data may permit prediction on the 

 relative survival of grain crops on soils of dif- 

 ferent type and moisture content. The prelim- 

 inary work indicates that a sandy soil is colder 

 and the survival of plants growing upon it less 

 than on a dry clay or loam soil, and also colder 

 than a wet clay or a wet loam during those 

 seasons when the ground remains unfrozen 

 much of the time. It appears probable that 

 dry sand is colder during the winter than a 

 wet sand regardless of the character of the 

 season, but a dry clay or silt loam is colder 

 than a wet soil of the same kind, only when 

 the ground remains unfrozen. 



S. C. Salmon 



Kansas State Agricultural College, 

 Manhattan, Kans. 



