juneis, I920 Effect of Manure-Sulph2ir Composts on Greensand 253 



former were softer than those of the latter and seemed to be more soluble, 

 as is shown by composts i and 8 in Table V. These figures show that 

 although the New Jersey greensand contains more than four times as 

 much potassium as the Maryland greensand, the amount of water-soluble 

 potassium is the same. 



In considering Table VII it is pertinent to ask to what extent the 

 manure has contributed to the total amount of potassium recovered in 

 the water extract. To answer this question Table VIII has been pre- 

 pared upon the assumption that all the potassium in the manure was 

 made soluble and was recovered in the water extract. 



Table VIII. — Relation of potassium content of the manure to the water-soluble potas- 



siutn obtained 



a The percentages in this colvmin are based on the assimiption that all the potassium in the 

 iflHp Tvater-«;nhihli» 



made water-soluble 



manure waso 



From the last column of Table VIII it will be seen that even on this 

 basis it is possible in only one case to account for more than 17 per cent 

 of the potassium as coming from the manure. It is evident, therefore, 

 that from 80 to 90 per cent of the potassium found in the water extract 

 must have come from the greensand or from the soil and greensand. 



Referring again to the manure composts in Table VII, it will be seen 

 that the total amount of potassium recovered by water extracts from 

 these composts varies from 9.1 per cent to as much as 41.3 per cent of 

 the total initial amount present. 



It is important to consider the relation between the oxidation of sul- 

 phur and the liberation of potassium. This relation is a converging 

 ratio, which was rather wide during the period of greatest oxidation of 

 sulphur and diminished rapidly as the potassium was released. While it 

 was not expected that this ratio would be resolved to a constant figure 

 for all of the composts, because of the different materials used, in each 

 series the composts containing manure do show a rather uniform relation be- 

 tween these processes. On the basis of the initial weights of the composts. 

 Table IX shows the maximum number of grams of sulphur oxi- 

 dized and of water-soluble potassium obtained, and their ratio, as deter- 

 mined from the water extracts. 



