256 Bacteria in Relation to Country Life 



It appears thus that the benefits accruing from the 

 turning under of green crops may not be as great on 

 heavier soils. None the less, even with these it may bring 

 rich rewards. Numerous facts show that the phosphoric 

 acid and potash of many heavy soils are practically 

 inaccessible to the crops without and abundance of 

 easily decomposable organic matter. They show, 

 likewise, that shale, slate and clay soils are maintained 

 in better tilth, conserve their moisture better, and 

 allow a more uniform crop development when abundantly 

 provided with humus. Hence, an intelligent use of 

 cover-crops may prove highly profitable on heavier 

 soils. However, greater care is required in the selection 

 of the green-manuring crop, and in the nianner and 

 time of seeding. 



It has been fotind that crops like field-peas, horse- 

 beans and vetches are most suitable among the legumes 

 for green-manuring purposes for heavy soils. Impover- 

 ished soils in northwestern United States and Canada 

 have been improved by the growing of winter rye, fol- 

 lowed by field-peas &s a green-manuring crop. The latter 

 may therefore be said to do the same work here as that 

 performed by the cowpea in the southern states. In 

 some of the European countries, notably. England, 

 horse-beans and sainfoin have been employed widely 

 as soil-renovators, while on the Continent, seradella 

 and various clovers have been used in a similar capacity. 



In comparing the development and utilization of 

 green-manuring crops on light and heavy soils, account 

 must be taken ,of the activities of the various bacteria 

 concerned in the fixation of atmospheric nitrogen, as 



