224 NATURE AND PROPERTIES OF SOILS 



from Haberlandt 1 show the need of careful temperature con- 

 trol in the propagation of plants: 



Table XL VI 



GERMINATION TEMPERATURES 



Other desirable biological activities, especially those due to 

 bacteria, are impeded if not brought entirely to a standstill by 

 a temperature of 32° F. Such changes as decomposition of 

 organic matter, the production of ammonia from nitrogenous 

 organic matter, the formation of nitrate nitrogen from am- 

 monia and the fixation of atmospheric nitrogen depend on 

 heat conditions which, fortunately, are optimum for the de- 

 velopment of higher plants. 



Desirable chemical reactions in the soil are much retarded 

 by low temperatures, heat greatly accelerating such phe- 

 nomena. This is especially noticeable in the tropics where 

 weathering is much more rapid and intense than in temperate 

 regions. Much of the hydration, oxidation, carbonation and 

 solution in a temperate climate occurs in the summer when 

 high temperature lends its aid to such desirable reactions. 



1 Haberlandt, F., Die Oberen und Unteren Temperaturgrenze fur die 

 Keimung der Wichtigeren Landwirthschaftlichen Samereien; Landw. 

 Versuchs. Stat., Band 17, Seite 104-106, 1874. 



