MANURES FOR SPECIAL SOILS 209 



the soil as to render it infertile. By the addition of extra 

 lime the fertility is recovered. There is little doubt that the 

 acidity of such soils resulting from sulphate of ammonia 

 is produced largely by the growth of moulds ; the use of 

 lime discourages these, and promotes more healthy bacterial 

 life. Nitrate of soda, when used on light soils, has been 

 found at Woburn to produce similar results, although the 

 causes are certainly not identical. One of the reasons, 

 apparently, why nitrate of soda has been unsatisfactory on 

 these light soils is that when the nitrogen has been used by 

 the plant, the soda is left behind. In the presence of soda 

 clay becomes colloidal, and in a soil of open structure such 

 colloidal solutions of clay readily drain away deep down into 

 the subsoil ; consequently the clay particles are carried 

 away from the surface and deposited deep down in the soil. 

 If the total amount of clay particles is small, the whole stock 

 of clay may be removed from the surface, which becomes 

 absolutely dry within a few hours of the cessation of rain, 

 and the germination of seeds becomes almost impossible. 

 The behaviour of calcium cyanamide in sandy soils may 

 follow more than one method of procedure. Calcium 

 cyanamide readily breaks down, yielding ammonia, when it 

 nitrifies in the usual way. Experimental results at Rotham- 

 sted point to an almost quantitative conversion of cyanamide 

 into nitrates. Calcium cyanamide, however, may contain 

 a certain amount of dicyanodiamide, which checks nitrifica- 

 tion in the soil. 



Superphosphate is a favourite fertilizer for the lighter 

 soils. These light soils are easily worked, and a readily 

 soluble fertilizer like superphosphate need not be applied 

 early. The ready solubility of superphosphate enables it 

 to be used even as a top dressing. When labour is short, 

 it is a great advantage to be able to leave fertilizing with 

 superphosphate until a late date. Superphosphate is not a 

 suitable fertilizer unless the soil contains a moderate amount 

 of lime. Alternations in the use of basic slag and super- 

 phosphate are therefore a satisfactory solution of this 

 difficulty. Basic slag has often given excellent results on 

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