492 Journal of Agricultural Research voi. xv. No. 9 



While the growth made in cultures in which the potassium demand is 

 satisfied by greensand deposits (the poisonous Courtland greensand ex- 

 ceptea; ^s iiiarkedly superior to that contained in cultures containing the 

 commoner potassium salts (potassium nitrate excepted), it must be 

 remembered that in the case of the salts a majority of the cultures con- 

 tain an excess of salts, whereas in the marl and greensand cultures the 

 concentration rarely exceeds the optimum and probably still less often 

 attains it. 



Concerning Courtland greensand, so often excepted in the above dis- 

 cussion, it may be said that this deposit has been found to belong to the 

 unusual class of so-called "poisonous marls." Since this is a very 

 unusual cisz and one not likely to be often encountered, it is sufficient 

 to say that ground limestone added at the rate of a ton or more to the 

 acre seems likely to render this greensand a useful fertilizer when applied 

 at the rate of i to 5 tons per acre. 



CONCLUSIONS 



It has been shown by pot experiments carried out with crushed quartz 

 and Shive's culture solution as a basis that greensands and greensand 

 marls from Virginia and New Jersey are able to supply sufficient potas- 

 sium to satisfy the demand of Turkey Red wheat and red clover during 

 the first two months of their growth. This enables them to make a greater 

 dry weight of tops than was seen in similar cultures in which the potassium 

 demand was supplied by potassium chlorid, potassium sulphate, and 

 potassium phosphate. The prompt availability of sufficient potassium to 

 meet the needs of many, perhaps most, farm crops seems to be indicated. 



