240 Journal of Agricultural Research voi.xix.no. 6 



have been known to destroy all vegetation and advises that the use of 

 such marls should be confined to well-limed land or that they should be 

 composted with lime before being applied. In 1906 Patterson (12) 

 published the results of the examination of 95 samples of Maryland marl. 

 In summing up the results of his experimental work covering a period 

 of 1 1 years this writer concludes that the shell marls of Maryland have 

 very little commercial value because of the great bulk of worthless 

 material contained in them but that they should have considerable local 

 agricultural value, both as a source of lime and also for the potassium 

 which they contain. He concludes that while much of the potassium 

 in marls will become slowly available to plants through weathering, the 

 change necessary to liberate the potassium could readily be brought 

 about by burning the calcarious marls and slaking the product. 



In a popular discussion of the agricultural value of greensand marl 

 Blair (j) concludes that since potassium is of especial value to grass and 

 to potatoes, the striking benefits derived from the use of marl on these 

 crops would lead to the belief that such crops can use the potassium 

 of the marl to a considerable extent. 



From pot experiments carried out with crushed quartz and Shive's 

 cultural solution as a basis, True and Geise {13, p. 492) conclude that — 



greensands and greensand marls from Virginia and New Jersey are able to supply 

 sufficient potassium to satisfy the demands of Turkey Red wheat and red clover 

 during the first two months of their growth. 



They secured a greater dry weight of tops from cultures containing green- 

 sand marl than from those in which the potassium demand was supplied 

 by potassium chlorid, potassium sulphate, or potassium phosphate. 

 These results are in harmony with those reported by Lipman and Blair 

 {8) who found that soybean plants fertilized with greensand produced 

 as great a yield of hay as those receiving an application of soluble potas- 

 sium salts, although the former failed to produce seed. These last- 

 mentioned authors hold that their results seem to furnish proof of the 

 ease with which the soybean gets its potash from slowly available sources 

 up to the time the beans are forming and maturing. In the same report 

 these writers describe another experiment in which Canada field peas 

 and soybeans growing in sand cultures were given a general fertilizer 

 treatment to which was added marl containing 6.5 per cent of potash. 

 Two pots in this series received 20 gm. of marl, while two additional pots 

 received in addition to the 20 gm. of marl, 3 gm. of sulphur each, with 

 the thought that the oxidation of the sulphur might result in making 

 more of the potash of the marl available. The Canada field peas were 

 grown as the first crop, followed by the soybeans as a second crop. Both 

 pots receiving the sulphur treatment gave very much decreased yields 

 of field peas, and in one of the duplicates the soybeans that followed the 

 peas failed completely. The other duplicate, however, gave a yield of 

 soybeans slightly in excess of that produced by any of the other treat- 



