V ERTICAL FARMING 



21 



using the last named form, care must be exercised to prevent a 

 heavy application from burning the organic matter or humus 

 out of the soil. Ground or burned sea shells are also extensively 

 used and make an excellent form of agricultural lime. Gypsum 

 is used under certain conditions. Lime also has a material 

 effect on the structure of the soil, especially when it has a 

 tendency to be sour, by causing it to granulate better, thereby 

 increasing its power to absorb and hold water. Especially in 

 the east and southeast the use of lime is imperative for the best 

 success .in growing alfalfa and certain other legumes. The 

 cow pea seems to resist a sour condition in the soil remarkably 

 well. Lime also helps somewhat to liberate potash from resist- 

 ant minerals. Salt is sometimes used for the same purpose. 

 The growth of nitrogen fixing bacteria is greatly stimulated 

 when lime is added to make up any deficiency that may exist in 

 the natural soil. 



Potash is a highly essential plant food. It exists naturally in 

 most soils and in some of them is found in large amounts. In 

 some soils, notably coastal plains sands, it is present in but 



SHIP DISCHARGING CARGO OF EXPENSIVE FERTILIZERS 



