MANURING AND WORN-OUT SOILS 341 



unusual value in improving the soil. Seeding is at the 

 rate of twenty to thirty pounds per acre, and after 

 spring frosts in the North; fall seeding is preferred 

 in the South. The sod is cut for three to eight 

 years; hence alfalfa can be used only in a long 

 rotation. 



Other Leguminous Green Manures. The four 

 plants mentioned above are the great soil-improvers 

 of America. Other crops are often or occasionally 

 grown. Canadian field peas are frequently grown 

 in the North, especially on rough soils, and either 

 alone or sown with grains to support the vines. 

 The seeding is one and a half to two bushels per 

 acre. Market gardeners often grow garden peas, 

 pick the pods and then plow under the vines, thus 

 getting double value from the crop. Vetches of 

 various kinds, particularly the smooth vetch and 

 the hairy vetch, are often used, especially in the 

 Pacific Northwest. Vetches are used extensively 

 for orchard cover crops in the East. The seeding 

 is about one bushel per acre. Hairy vetch may 

 become a bad weed unless looked after sharply. 



The soy bean, also called "soja bean" and "Jap- 

 anese pea," is very serviceable in many sections. It 

 is hardier than the cowpea and can be grown 

 farther north. When grown for soil improvment 

 the whole crop should be plowed under, as the 

 roots and stubble do not contain such a large pro- 

 portion of the pl^nt foods as clover and cowpea 

 stubble. White sweet clover and lupines are 

 sometimes grown for green-manuring. 



NON-LEGUMININOUS CROPS FOR GREEN-MANURING 



Rye is the most useful of plants that improve the 

 soil when plowed under, but do not enrich it in 



