14 FOB AGE CROPS 



tent of the valuable element nitrogen. The prin- 

 cipal reasons for the rotation of crops are based on 

 these facts. The purpose of a rotation is to pro- 

 long the period during which profitable grain and 

 other crops may be produced with the natural 

 supplies of plant -food. 



Under present conditions in this country, the 

 area that is devoted to the growing of hay is rela- 

 tively large, although the average yield per acre is 

 comparatively small. It is probable that the main- 

 tenance of fertility by means of rotations is not so 

 greatly influenced by the growth of leguminous hay 

 crops as would be the case if, aside from their 

 value as forage, there were a better understanding 

 of their usefulness in soil improvement. The low 

 average yield per acre of hay may be ascribed to 

 several causes, chief among which are: 



1. Too extensive systems of practice, which do 

 not provide for sufficient available plant-food. * 



2. Lack of general information concerning the 

 habits of growth, usefulness and composition of 

 many grasses and legumes, which are well adapted 

 to special conditions, including lack of knowledge 

 of the best combinations of these plants. 



3. Defective systems of rotation, which do not 

 provide for a proper succession of cereals and le- 

 gumes, or which leave the land bare for long periods. 



4. Too little care in the preparing and manuring 

 of the land for seeding. 



