1905.] 



On the Retention of Bases by the Soil. 



29 



down of the finest particles set free by the defioeculation into the subsoil or 

 the drains. The bad texture of the soil following on the use of sodium nitrate 

 is particularly to be seen on the mangel field, where it reaches its maximum 

 on the plots receiving sodium nitrate and other neutral alkali salts like 

 potassium sulphate and sodium chloride : it has been repeatedly observed to 

 be at its worst in the winter and spring after a large crop has been grown on 

 the sodium nitrate plots. As the soil of this field contains but little calcium 

 carbonate, some of the base left behind in the soil by the growth of the crop 

 would consist of bicarbonate of sodium or potassium, especially where the 

 other alkali salts are applied in the manure, and there would be quite enough 

 i'ree alkaline carbonate thus formed to cause a thorough defioeculation of the 

 soil. This explanation would agree with the observed fact that the defioecu- 

 lation is much diminished where superphosphate only, an acid manure, is used 

 in conjunction with the sodium nitrate. 



III. — Effect of Organic Manures on the Eeaction of the Soil. 



Although the evidence is not so trustworthy as in the case of sodium 

 nitrate, yet the use of farmyard manure and of rape cake seems also to result 

 in a diminished race of loss of calcium carbonate to the soil. Some of this 

 may be due to the lessened percolation consequent on the greater water- 

 retaining power of the soil enriched in humus, but another cause may be 

 sought in the bacterial decomposition of calcium salts in the organic ddiris. 

 Farmyard manure contains various calcium salts derived from the vegetable 

 matter out of which it has been formed, sometimes in their original form, but 

 partly broken down into the undefined carbon compounds known as 

 " humates." Calcium humate, Wollny* has already shown, can be converted 

 into calcium carbonate by bacteria present in the soil, while the following 

 experiments show that the commonest of all calcium salts in the plant, the 

 widely distributed calcium oxalate, is readily fermented to carbonate. 

 100 c.c. of a nutrient solution containing — 



Ammonium sulphate 0"2 gramme. 



Sodium chloride - 2 „ 



Potassium hydrogen phosphate ... - l „ 



Magnesium sulphate 0-05 „ 



Ferrous sulphate - 04 „ 



were placed in an Erlenmeyer flask plugged with cotton -wool in the usual 

 way ; to this 1 gramme of calcium oxalate was added, together with, in some 

 cases, a small quantity of other organic nutrient, and the flask and its 

 * 'Zersetzung der organischen Stoffe,' 1897, p. 217. 



