172 SOILS 



depends upon quick germination, we can afford, 

 on some soils and in some seasons, to sacrifice 

 a good deal of water for the sake of gaining this 

 important result. 



The soil at the bottom of the hoof -mark or foot- 

 print is more moist than the surrounding soil be- 

 cause it is more compact and losing more water by 

 evaporation, having no mulch above it. The soil 

 in a field that has been rolled is more moist on top 

 than if it had not been rolled, but the soil below the 

 compacted portion, from five to twenty inches 

 deep, is much dryer than it would have been had 

 the surface been left loose. In other words, the 

 upper five or more inches of soil have been made 

 more moist, by rolling, at the expense of the soil 

 beneath. Within twenty-four hours after rolling this 

 difference can be noticed. Part of the loss of mois- 

 ture from rolled soil is due to the fact that the surface 

 is left very level and smooth, so that it offers less 

 obstruction to the wind. The velocity at which the 

 wind passes over rolled ground may be nearly 

 twice as great as on rough, unrolled ground. This 

 means that much more moisture is sucked from the 

 soil by the wind. 



When Rolling to Assist Germination is Practicable. 

 -The farmer must decide whether the gain from 

 rolling, in better germination, is greater than 

 the loss, in the reduction of the total amount 

 of water available for the growth of the crop. 

 That depends upon the rainfall and upon the 

 moisture-holding capacity of the soil. Rolling 

 for the purpose of assisting germination is of 

 greatest value on the lighter, looser and coarse- 

 grained soils, especially the sands and sandy 

 loams. These are so open that the air may circu- 

 late through the surface soil quite freely, drying it 



