Dec. IS, 1919 



Oxidation of Sulphur in Soils 



331 



EXPERIMENTAL WORK 



EXPERIMENTS WITH COMPOSTS OF ROCK PHOSPHATE, SULPHUR, SOIL, 



AND MANURE 



The materials used were as follows : The rock phosphate was Tennessee 

 brown rock containing 14.2 per cent of phosphorus and guaranteed 95 

 per cent to pass a 100 mesh sieve. The sulphur was ground brimstone 

 or crude sulphur. The soil was a fertile bluegrass soil obtained from the 

 Station farm and had a high phosphorus content. The manure was 

 partly rotted horse manure, fairly free from straw. The sulphofying 

 soil or starter was obtained from Dr. H. C. McLean, of the New Jersey 

 Agricultural Experiment Station. This starter was simply a mixture of 

 soil, rock phosphate, and sulphur, in which the sulphofying organisms 

 were numerous and active. 



Composts No. I to 4 were prepared on May 4, 191 7, as follows: 



Table I. — Composition of composts i to 4 {in pounds) 



The ingredients in each compost were thoroughly mixed, but no 

 starter was added. On November 20, 1917, however, ^ pound of starter 

 was thoroughly mixed with each compost heap. 



The determinations include acidity, water-soluble phosphorus, ammo- 

 nium-citrate-soluble phosphorus, total phosphorus, sulphates, nitrites, 

 nitrates, total nitrogen, and moisture. 



The methods used for acidity, sulphates, and water-soluble and am- 

 monium-citrate-soluble phosphorus were practically the same as those 

 given by Lipman, McLean, and Lint {10), with the following exceptions: 

 In the water-soluble phosphorus determinations, 20 gm. of compost were 

 used and phosphorus was determined at first on 16 gm. and later on smaller 

 aliquots. In the ammonium-citrate-soluble phosphorus determinations, 

 20 gm. of compost were digested with 100 cc. of ammonium citrate 

 solution, and 2-gm. aliquots were used. In the last two determinations, 

 however, in all cases the amount was reduced to 2 gm. in the digestion 

 and i-gm. aliquots in the determination. 



In all citrate-soluble phosphorus determinations made on and after 



June 19, 191 8, the procedure recommended by Dr. J. W. Ames, of the 



Ohio Agricultural Experiment Station, was used as follows : The aliquot 



solutions were evaporated with 5 cc. of 50 per cent magnesium nitrate 



134796"— 19 3 



