June 15, 1920 Effect of Manure-Sulphur Composts on Greensand 247 



compared with that of the Maryland greensand. As was previously 

 mentioned, the lime requirement of the New Jersey material is 4,200 

 pounds of calcium carbonate, while for the Maryland greensand the 

 requirement is only 3,400 pounds. The results recorded in Table III 

 would appear to justify the conclusion that an initial acidity correspond- 

 ing to a lime requirement of 3,400 pounds of calcium carbonate exerts 

 a slightly depressing effect upon sulphofication, and that an acidity 

 corresponding to a lime requirement of 4,200 pounds of calcium car- 

 bonate is less favorable. Ames and Boltz (/) found that calcium 

 carbonate when added in excess of the lime requirements exercised a de- 

 pressing effect upon the oxidation of sulphur in their soil-sulphur compost. 

 When they reduced the application to half, the oxidation of sulphur 

 increased but was less than when no carbonates were added. 



SOLUBLE SULPHATES 



A comparison of the results recorded in Table IV with those given in 

 Table III shows that the accumulation of water-soluble sulphates parallels 

 very closely the development of acidity. 



It will be observed that the sulphur trioxid determinations fluctuate 

 somewhat after having attained a maximum at the end of about 12 

 weeks. These fluctuations are probably due to variations in the mois- 

 ture content and the temperature of the composts, since such variations 

 are known to have an effect upon colloidal silicates, which in turn might 

 exercise, through adsorption, an appreciable effect upon the soluble sul- 

 phur trioxid obtained in the water extraction. A calculation shows that 

 at the end of our 23-week period, approximately 15 per cent of the total 

 sulphur used in composts 3 and 10 had been oxidized, while for the 

 composts in which one-half of the manure had been replaced by soil 

 about 1 1 per cent of the total sulphur had been oxidized. These figures 

 show that the amount of sulphur used was in excess of the amount 

 necessary to secure the most economical results. 



SOLUBLE POTASSIUM 



The amount of water-soluble potassium in each compost at stated 

 intervals is given in Table V. 



A comparison of these figures with those given in Tables III and IV 

 brings out the fact that with the increase in acidity and the accumulation 

 of sulphur trioxid there is a corresponding increase in the amount of 

 potassium in the water extract. The potassium, however, continues 

 to increase for some weeks after the acidity and sulphur trioxid have 

 reached a maximum. It seems necessary for a certain degree of acidity 

 to be developed before any appreciable amount of potassium is made 

 water soluble, the larger amounts of acidity and soluble sulphate break- 

 ing down the greensand more rapidly. 



