Chapter III. 



THE TEMPEEATURE OF THE SOIL. 



OBSERVATIONS AT HOUGHTON FARM AND GENEVA, N. Y., BY 

 D. P. PENHALLOW. 



Ill reference to the value of soil temperatures, Penhallow states 

 (Agr. Sci.. Vol. I, p. 78) : 



A jsroper knowledo-e of the temperature of the soil must serve to 

 o-uide us in reference to the time of planting particular seeds and the 

 depth at which they should be planted, as determined by the condition 

 and character of the soil. When the farmer gently packs the earth 

 over the planted seed he derives a measure of benefit in the higher 

 temperature of the soil at that place, whereby germination is accel- 

 erated. Similarly, we can understand that cultivation during periods 

 of excessive heat must tend to avert some of the evil results otherwise 

 following from an excess of temperature. Moreover, in seasons of 

 great or even of ordinary dryness a judicious system of irrigation 

 must be of the greatest advantage, not only as supph'ing needed fluids 

 for the general functions of gTowth, but as reducing the otherwise 

 high tem})erature of the soil to a degree that is well within the danger 

 limit and consistent with normal growth. 



Penhallow also shows from observations at Houghton Farm and at 

 Geneva, X. Y., that all layers of the soil within 8 inches of the surface 

 have temperatures that depend not merely upon absorption of solar 

 heat but also upon the cooling due to radiation and evaporation. 

 The depression due to evaporation amounts to about 8° C. on the 

 average of the warmer half of the year and is even more than this 

 when hot days and strong dry winds produce an excessive evaporation. 



OBSERVATIONS BY E. S. GOFF. 



E. S. Goff adduces observations to show that the temperature of the 

 water at the time when it enters into the roots from the soil has some 

 relation to the temperature of the stem of the plant for a short 

 distance above the surface soil, and that the distance up the stem to 

 which this temperature is felt depends upon the rajiidity of the flow 

 of the sap, and therefore ultimately on the rapidity of transpiration 

 from the leaves. (Agr, 8ci., Vol. I, p. 134.) 



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