CHARACTERISTICS OF SOILS 11 



Every one acquainted with crops will recall how rigid 

 even to tender crispness are the leaves of a corn plant 

 in the early morning, when growing in warm moist soil. 

 The leaves would not be so crisp, and might even appear 

 wilted, if the soil were too cold. 



16. Root development. As the part of the plant 

 above ground develops from the seedling to the mature 

 plant, its demands for food and anchorage increase; 

 since the part of the plant underground must furnish 

 both, there must be adequate development underground 

 also. Few realize how great this development is. King, 

 in what seems to be a conservative estimate, 1 has shown 

 that the roots of a single healthy corn plant, placed end 

 to end, would amount in length to not less than one- 

 fourth mile, and probably would often much exceed this. 

 It is only when the soil temperature is correct that this 

 great development can be most satisfactorily made. 



17. Best temperature for root action. The tempera- 

 tures best suited to food preparation and for germination 

 are also good for root activity as regards both growth 

 and feeding. Hall gives 83.6 F. as the optimum soil 

 temperature for growth of barley and wheat, and 92.6 F. 

 as the optimum for maize and kidney beans. He gives 

 93 F. as the temperature at which maize roots made 

 their maximum growth 55 millimeters in 24 hours. 2 

 These temperatures, with a single exception, are higher 

 than the highest averages of observed temperatures shown 

 in Table IV. The exception is for 1 inch deep in Ne- 

 braska soil. 



18. Temperature and the rest-period. The period 

 elapsing between the harvesting of one crop and the plant- 



1 King, The Soil, p. 210. 2 Hall, The Soil, p. 114. 



