606 Transactions of the American Institute. 



the surface that comes in tlie. decay of old blades, and the tongh mat 

 of roots holds the little granules to the surface, \vhcre the elements 

 can act on them. For this reason green sand is generally found to act 

 most promptly on grass lands. When applied to sandy soils, where 

 there is not much vegetable matter to act upon it, marl is partly 

 losit by being mixed with the deep sand, where it finds nothing to dis- 

 solve it. By numerous inquiries among the observant farmers of 

 middle Jersey, I have found that experience on this point proves the 

 conclusions to which microscopical study had led me. It acts quick- 

 est on sod, especially a moist sod. In fertilizing sand, it is not used 

 as the first application, for it would find no profitable company, but 

 after such lands have been limed or dressed with muck, or had a lush 

 growth of rye or clover turned under, green sand comes in as a very 

 useful agent to heighten fertility. 



There is one crop that is an exception to this general rule, and that 

 is the potato. There is more profit in using marl on potatoes than on 

 any other crop. I have sometimes been asked to explain this, and 

 the answer is that the potato wants two or three things that other 

 plants do not want, and wliich green sand furnishes. Green sand yields 

 some magnesia, a little sulphuric acid, and plenty of oxyd of iron ; 

 all these, and especially the latter, are beneficial to the potato. So 

 important is iron, that some months ago I remember a thoughtful 

 farmer sent the club a long communication showing that iron would 

 stop the rot. Certain it is that potatoes grown with green sand are 

 smoother, fairer, and healthier than others, and the marl-using farmers 

 have been very little troubled with the rot. May I not then earnestly 

 recommend to all farmers living within 100 miles of the marl-beds to 

 buy green sand enough to j)ut some in the hill witli those choice new 

 varieties of the potato that have not as yet become diseased. For 

 its potash, green sand is worth as much as leached ashes ; the 

 phosphoric acid makes it useful for grain and the protoxyd of iron 

 gives it peculiar value as a preventive of rot in the potato. 



On lands that are already ricli marl will not prove so potent as 

 Bome concentrated ammonial, that is, rank smelling stufi'. For instance, 

 a sagacious old farmer in Salem county told me that some believed 

 twenty years ago, when they first began to cart marl, that it would 

 enable them to get 100 bushels of shelled corn from an acre. " I 

 told them," said he, " it would never get uj) higher than seventy-five, 

 and it hasn't and it won't." But for lifting up worn land from pro- 

 ducing a power of twenty-five bushels to a power of sixty and seventy 



