114 Fertilizers 



Cocoa shells. 



Sometimes cocoa shells are ground and sold for fertilizer. 

 They contain on the average 2.5 per cent of nitrogen, 

 .75 per cent of phosphoric acid and 2.5 per cent of potash. 

 They are not considered a highly valuable source of 

 plant-food. 



Green sand marl. 



Marl may contain one or more of the constituents, 

 phosphoric acid, potash and lime. Shell marls are usually 

 very rich in lime, but contain only traces of phosphoric 

 acid and potash. The green sand marls of New Jersey 

 often contain very considerable amounts of phosphoric 

 acid and potash, though they vary widely in composition. 

 They contain, on the average, 2.20 per cent of phosphoric 

 acid, 4.70 per cent of potash, and 2.90 per cent of lime. 

 These constituents, particularly the potash, are, as a rule, 

 slowly available. 



Marl, however, is an important amendment to soils, 

 not only because of its content of mineral constituents, 

 but because these constituents are associated with prod- 

 ucts that exert a very favorable mechanical effect upon 

 soils. Large areas of land in the state of New Jersey, 

 formerly unproductive, chiefly because of physical im- 

 perfections, have been made very productive mainly 

 through the application of marl. 



The use of marl is now less general than when the fer- 

 tilizing constituents from artificial sources were dearer, 

 and when the labor of the farm was more abundant and 

 cheaper. The quicker effect of more soluble fertilizer 

 constituents has had an influence in reducing the use of 

 marl where quick returns are desirable. Where farmers 



