166 



TILTH AND TILLAGE 



kill obnoxious weeds in the third manner by summer following, 

 quack grass and Canada thistles especially. 



Cultivation to conserve moisture should be done before the 

 land is allowed to dry out. A good mulch should be prepared 

 at the beginning of a dry period. 



Fio. 110. Two other types of walking cultivators. A, four-shovel; B, two-shovel cultiva- 

 tor, or double shovel plow. B is a cultivator commonly used in the South. 



Crops on heavy soils are best cultivated, especially for the first 

 time, when the moisture conditions are right. When this is done 

 subsequent cultivations are made much easier because a layer of 

 well-loosened soil prevents baking. 



Some soils, particularly the black lowland silt and clay loams, 

 shrink considerably when they dry out causing big cracks to form. 

 Such lands should be cultivated frequently to prevent as much 

 as possible the formation of these cracks, and to fill them when they 

 do occur (Fig. 111). 



