190 Physics of the Soft. 



of soil on the coolest nights. To destroy these roots will, 

 in most cases, cause a greater loss by root pruning than 

 can be gained by saying moisture. It is possible also, by 

 too frequent tillage, to make the texture of the mulch so 

 fine that its effectiveness is decreased. 



220. Cultivations Should Be Most Frequent in the Spring. 

 In the early part of the season when the aeration of the 

 soil, the warming of it and the killing of weeds are other 

 important objects to be attained it is more important to 

 cultivate frequently. This is the season of the year when 

 the effectiveness of mulches decreases most rapidly, it is 

 the season when there is least danger of destroying the 

 roots of the crop, and it is the time when cultivation is 

 needed to help develop plant food. 



221. Cultivation After Heavy Rains. Whenever a rain 

 has occurred which has thoroughly united the soil crumbs 

 to one another, and with the soil below, it is time to cul- 

 tivate again if this can possibly be done without too heavy 

 root pruning, and the cultivation should be done just as 

 quickly as the soil will permit. In the early part of the 

 season there is little danger of root pruning if the culti- 

 vator teeth do not go too close to the plants and not more 

 than 3 inches deep. 



A rain which does not wet down more than 3 inches 

 cannot be saved by cultivation; all that can be done in 

 this case is to permit the surface roots to get as much 

 of it as possible and to stir, if it appears expedient, when 

 the wetting is likely to strengthen the upward movement 

 too much. It must be remembered in this connection, 

 however, that if, late in the season, the roots of the crop 

 have spread horizontally through the whole soil, anything 

 which strengthens the rise of the deeper water, causing 

 it to come nearer the surface, at the same time brings it 

 to the roots where it is needed, and hence it will seldom 

 happen that a crop like corn or potatoes can be helped by 



