156 



THE PRINCIPLES OF SOIL MANAGEMENT 



legumes at 52.87 per cent of moisture. Warington 

 concludes, from the results of Hellriegel and Wollny, 

 that "when the soil contains 80 per cent of the water 

 required to saturate it, the proportion was too high; 

 and that when the water amounted to only 30 per cent 

 of saturation,, the proportion was too low for the pro- 

 duction of a maximum crop. The largest crops were 

 obtained when the proportion of water lay between 

 40 and 60 per cent of that required for full saturation." 



^ t~ CO 



^ o i 



<= RAINFALL IN INCHES ^ d 



Fig. 49. Curve showing moisture content of a light sandy loam early- 

 truck soil, Union Springs, Alabama, June, 1896. 



Cameron and Gallagher have shown that the maxi- 

 mum and minimum points are marked by distinct 

 changes in: (1) The cohesion of the soil. (2) Its volume 

 weight. (3) The freedom with which the soil gives up 

 moisture. The first of these facts is of especial import- 

 ance in the tillage of soil. Between the maximum and 

 the minimum points the soil "works" at its best. It 

 does not puddle, and it is sufficiently moist to give that 

 desirable state of granulation which is expressed by 

 good tilth. The clods of the clay soil are not hard, and 



