ABSORPTION OF NUTRITIVE SALTS 415 



able during the summer, when ammonification 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- 



