166 Irrigation and Drainage 



Throwing a eld into ridges with deep furrows between, as is 

 done with some of the wide -shovel cultivators, and as used to 

 be done generally in laying corn by, has little to recommend it 

 except on flat fields of stiff, heavy soil, in wet climates or seasons. 

 The chief objection to the ridges and furrows is that they greatly 

 increase the evaporating surface and the amount of soil which is 

 thrown out of use. In the case of potatoes, however, especially 

 on the heavy soils, the last cultivation should be to hill them in 

 order to form a loose, deep, mellow soil, in which the tubers may 

 form and expand without meeting with excessive resistance. 

 Indeed, it is quite doubtful whether there are many soils in which 

 potatoes will not do better if hilled to some extent the last thing 

 before the vines spread to cover the ground. The earlier 

 cultivation should by all means be flat. 



10. Rolling in Relation to Soil Moisture 



The roller has an extensive use in many localities 

 in fitting land for crops in the spring or fall. It 

 shonld be understood, however, that when the surface 

 of a field is finished with a heavy roller, it is left in 

 a condition in which its moisture will be rapidly lost, 

 and for several reasons : 



1. Firming the surface reestablishes the capillary 

 connection with the soil below, and the moisture is 

 brought to the surface quickly from depths as great 

 as four feet. The appearance to the eye is that the 

 ground is made more moist, and so it is at the sur- 

 face, as a matter of fact, but it must never be for- 

 gotten that this is at the expense of moisture stored 

 deep in the ground. 



2. Rolling leaves the surface smooth and even, 

 so that it absorbs heat rapidly from the sun on a 



