242 Journal of Agricultural Research voi. xix, no. 6 



PURPOSE AND PLAN OF THE INVESTIGATION 



With the foregoing results in mind the present investigation was 

 undertaken for the purpose of determining the effect of different composts 

 upon the availability of the potassium of greensand. The investiga- 

 tion consisted of composting greensand with sulphur, soil, and manure 

 in varying proportions, taking samples from time to time, extracting 

 these samples with distilled water and analyzing the water extracts for 

 the acidity, sulphate, and potassium contained. 



Two series of composts were conducted, one series containing a green- 

 sand from Sewell, N. J., having a relatively high percentage of potas- 

 sium, and the other a greensand from Crownsville, Md., having a rather 

 low percentage of potassium. Each compost contained as a basis 1 ,500 

 gm. of greensand. The materials added were the same for each series 

 and were as follows : 



COMPOST NO. MATERIALS ADDED TO GREENSAND. 



1 and 8 Nothing. 



2 and 9 500 gm. sulphur. 



3 and 10 500 gm. sulphur; 500 gm. manure. 



4 and II 500 gm. sulphur; 250 gm. manure; 250 gm. soil. 



5 and 12 500 gm. sulphiu-; 500 gm. soil. 



6 and 13 500 gm. sulphtu-; 500 gm. soil; 0.02 per cent aluminum sulphate 



(Al2(S04)3) 0.18 HjO; 0.02 per cent ferrous sulphate (FeS04) 

 0.7 H2O. 



7 and 14 500 gm. sulphur; 250 gm. soil; 250 gm. manure; 10 gm. calcium 



carbonate (CaCOa). 



Commercial flowers of sulphur, partially rotted yard manure air-dried 

 and ground fine, Collington sandy loam, and precipitated calcium 

 carbonate were used. The aluminum and ferrous sulphates were added 

 to composts 5 and 12 in order to determine whether these salts would 

 exert a stimulating effect upon the rate and amount of sulphofication. 

 McLean (u) found that, under certain conditions, these salts in com- 

 bination exerted a marked stimulating action on sulphur oxidation 

 processes when present in small amounts. He advocated the use of 

 0.4 pound per ton, or 0.02 per cent, of each for sulphur-floats composts. 

 It was thought desirable to ascertain whether this effect would be 

 obtained with sulphur-greensand composts. 



METHODS OF PROCEDURE 



The air-dry materials for each compost were weighed and thoroughly 

 mixed. Similar smaller amounts of the same materials were mixed in 

 the same proportions, from which the moisture-holding capacity of each 

 compost was determined according to the Hilgard method (7, p. 209). 



After being mixed, each compost was placed in a glazed pot, and water 

 was added to one-half the determined water-holding capacity. The 

 samples for the first analyses, showing the amounts of water-soluble 



