ABSORPTION OF NUTRITIVE SALTS 415 



able during the summer, when armnonification and nitri- 

 fication are active. Phosphorus is the substance usually 

 most needed by maize. 



332. The feeding of grass crops. Grasses, when in 

 meadow or in pasture, are greatly benefited by manures. 

 They are less vigorous " feeders " than the cereals, have 

 shorter roots, and, when left down for more than one 

 year, the lack of aeration in the soil causes decomposition 

 to decrease. There is usually a more active fixation of 

 nitrogen in grass lands than in cultivated lands, but this 

 becomes available very slowly. 



Different soils and different climatic conditions neces- 

 sitate different methods of manuring for grass. Farm 

 manures may well be applied to meadows in all situations, 

 while the use of nitrogen is generally profitable. 



333. Leguminous crops. Most of the leguminous 

 crops are deep-rooted and are vigorous " feeders." Their 

 ability to take nitrogen from the air makes the use of that 

 fertilizer constituent unnecessary except in a few in- 

 stances, such as young alfalfa on poor soil, where a small 

 application of nitrate of soda is usually beneficial. Lime 

 and potassium are the substances most beneficial to leg- 

 umes on the majority of soils. 



334. Root crops. Many root crops will utilize very 

 large quantities of plant-food if it is in a form in which 

 they can use it. Phosphates and nitrogen are the sub- 

 stances generally required, the latter especially by beets 

 and carrots. 



335. Vegetables. In growing vegetables, the object 

 is to produce a rapid growth of leaves and stalks rather 

 than seeds, and often this growth is made very early in 

 the season. As a consequence, a soluble form of nitrogen 

 is very desirable. Farm manure should also have a promi- 



