Dec. 2, 1918 



Greensand as a Source of Potassium 



485 



Table I. — Analyses of greensand deposits used in experiments 



Material. 



Greensand, Courtland, Hanover 

 County, Va 



Greensand, Red Bank, Monmouth 

 County, N. J 



Greensand marl. Red Bank, Mon- 

 mouth Cotmty, N. J 



Greensand marl, Hanover County, 

 Va 



Greensand marl, near Tunstall, New 

 Kent County, Va 



Greensand marl, mixture of equal 

 parts of No. 4 and 5 



Calcium 

 oxid. 



Per cent. 



0-33 

 1-75 

 7-45 



12.50 

 9. 20 



10.85 



Phospho- 

 rus 

 pentoxid. 



Per cent. 

 O. 16 



•95 

 1.25 



•17 

 •25 



Sulphur 

 trioxid. 



Per cent. 

 O. 27 



Trace. 



Absent. 



•50 

 .26 



•38 



Potassium oxid. 



Soluble 

 in dilute 

 hydro- 

 chloric 

 acid. 



Per cent. 

 2.65 



6.80 



6. 10 



1.8s 



1-35 

 I. 60 



Total 

 potas- 

 siiun 

 oxid 

 present. 



Per cent. 

 5-76 



7-63 



6.77 



2. 16 



1.52 



1.84 



EXPERIMENTAL METHODS 



The purpose of the experimental work reported here was to ascertain 

 whether these deposits are capable of serving as a useful source of potas- 

 sium for growing plants, and if so, how promptly the potassium becomes 

 available. It is shown clearly in the above analyses and in scores of 

 others to be found in the extensive literature that potassium is present 

 in greensands in considerable quantity, but earlier investigations tended 

 to show that it is present'in the form of a rather stable silicate the avail- 

 ability of which for plant uses has been called in question.^ 



In order to gain time and the better to control conditions of work, pot 

 experiments were carried out in the greenhouses of the department dur- 

 ing the past winter (191 7-1 8). Glazed earthen pots of the ordinary 6- 

 inch type were first used, but it was found that the glazing was usually 

 checked by many fine cracks which reached through the surface of the 

 glaze. The pots themselves were found to furnish soluble impurities^ 

 among them potassium compounds, in such quantities as led to the aban- 

 donment of this type of container. Common porous pots, well soaked 

 in hot paraffin, the surplus of which was quickly drained off while still 

 hot, gave satisfactory results. The saucers were treated in the same way. 



The purest obtainable sand was used as a solid medium. A grade 

 known as "crushed quartz" was found to be satisfactory when submitted 

 to rather searching tests. 



The best chemicals were used in making up the culture solutions. 



In view of the fact that the problem was expected to give results of 

 practical value, wheat (Triticuni aestivum) and red clover {Trifolium 

 pratense) were chosen as suitable test plants. 



'It should always be borne in mind in considering problems of this nature that the plant's operations are 

 not bounded by the limits which prevail in chemical-laboratory tests, and reactions that are difficult in the 

 test tube are sometimes easily performed by the living plant. 



