Rotations, Manuring and Fertilizing 55 



culture and on high-priced land, as in trucking and 

 market-gardening, an amount of fertilizer can be used 

 profitably that would be impracticable in general field 

 culture. For these reasons, general advice concerning 

 the use of fertilizers is of little value. It is a local and 

 personal problem. 



GREEN-MANURING 



Green-manuring is beneficial chiefly because it improves 

 the physical condition of the soil through the addition 

 of decaying vegetable matter, which becomes humus. 

 Leguminous green-manuring crops, such as the clovers 

 and cowpeas, also may enrich the soil with nitrogen, 

 accumulated through the nodules on their roots. No 

 green-manuring crop adds to the soil any more potash or 

 phosphoric acid than it took out. If the soil is deficient 

 in these plant-foods, therefore, it is necessary to supple- 

 ment green-manuring with applications of the mineral 

 plant-foods. Heavy applications of nitrogenous manures 

 and fertilizers tend to make soft berries. This difficulty 

 is largely overcome by the free use of leguminous green- 

 manuring crops in the rotation. Except when large 

 quantities of barn manures are available at a low price, 

 green-manuring is the most practicable method of keep- 

 ing the soil in good heart. The use of green-manuring 

 crops in strawberry rotations is considered on pages 45 

 to 49. 



FARM MANURES 



For many years, farm manures, especially horse ma- 

 nure, were used in North America almost to the exclusion 

 of other fertilizing materials. Nearly all the unfavorable 



