Dec. 15,1919 



Oxidation of Sulphur in Soils 



335 



EXPERIMENTS WITH COMPOSTS OF ROCK PHOSPHATE, SULPHUR, AND SOIE 



Composts 5 to 10 were prepared on December 20, 191 7, from the same 

 materials as were used in the experiments just described. The formula 

 is given in Table VI. 



Table VI. — Composition of composts 5 to 10 {in pounds) 



Ingredients. 



No. s, 7, 

 and 9. 



No. 6. 8. 

 and 10. 



Soil 



Rock phosphates. 



Sulphur 



Starter 



66^ 

 100 



Total. 



167 



33K 

 100 



167 



The proportions of the various ingredients were the same as those 

 recommended by the Agricultural Committee of the National Research 

 Council for cooperative study, except that the amounts were reduced 

 for these experiments. Otherwise No. 5 and 6 were carried on according 

 to the Committee's directions. 



The starter was first mixed with 10 pounds of soil, the whole moistened 

 and stirred every day for 3 days, then added to the remainder of the soil. 

 The rock phosphate and sulphur were mixed separately, and finally all 

 were thoroughly mixed together. These composts were maintained at 

 15 to 20 per cent moisture content with distilled water and were stirred 

 every 7 to 10 days. All except No. 9 and 10 were kept in the heated 

 part of the greenhouse during the winter. 



Since the writer thought it might prove of some interest to study the 

 behavior of these composts under different conditions. No. 7 and 8 were 

 prepared at the same time and kept at the same temperature and moisture 

 content but not stirred throughout the experiments. Composts in a 

 duplicate set, No. 9 and 10, were treated in the same manner as No. 5 and 

 6, except that they were kept in the unheated part of the greenhouse during 

 the winter. During the first four months No. 9 and 10, while kept at a 

 temperature somewhat above that on the outside, were subjected to a 

 very much lower temperature than the remainder. Especially was this 

 true during the winter, which was the coldest on record. Since May, 

 1 91 8, however, all have been at the same temperature. 



The same determinations were made and the same methods used as in 

 the other experiments except that the total nitrogen was not estimated. 

 The results obtained are given in Tables VH to X. 



