DAIRY AND SEED IMPROVEMENT MEETINGS. 4OI 



"As a manure, nitrate of soda is, of course, treated as a source 

 of nitrogen. It is not sufficiently realized how valuable the soda 

 base may be. This is not because the soda is in any way neces- 

 sary to the nutrition of the plant, but because of the action of 

 any soluble salt upon the insoluble potash compounds in the 

 soil. The potash in the soil is due to the partial weathering of 

 double silicates Hke feldspar into clay which is to be regarded as 

 pure kaolinite but as containing a certain proportion of zealitic 

 bodies intermediate between feldspar and kaolinite — hydrated 

 double silicates containing potash, soda, magnesia, and lime com- 

 bined with alumina and silica. Any soluble salt, and particularly 

 a soluble soda salt, will react with these zeolites and exchange 

 bases to an extent depending upon the relative masses of the 

 two bodies, hence nitrate of soda acts on the clay in the soil, and 

 brings a little potash into solution. To such an extent does 

 this action take place that in practice a dressing of nitrate oi 

 soda on any but the lightest soils, will dispense with the necessity 

 of a specific potash manuring even for potash loving crops." 



Writing of the effect of nitrate of soda in Rothamsted experi- 

 ments with mangolds over a series of 25 years, Mr. Hall states : — ' 

 "The plots receiving potash all give about the same yield what- 

 ever the source of nitrogen, but on plots without potash the 

 yield is only maintained on the nitrate of soda plot; on the 

 other two the plant is neither supplied with potash by the 

 manure, nor is the soil forced to yield some of its stored up 

 potash as it is by the nitrate of soda, whereupon the yield 

 decHnes by one-half or more. For 25 years, then, the use of 

 nitrate of soda alone has enabled the soil to supply a mangold 

 crop with the large amount of potash it wants, though the store 

 of potash in the soil apparently soon becomes exhausted when 

 a manure is used which cannot bring it into solution. With 

 other crops the same results are obtained, though the lack of 

 potash does not become manifest so quickly as in the case of 

 mangolds." 



Mr. Hall further quotes the results of a ten-year series of 

 experiments with barley to show that nitrate of soda "has dis- 

 pensed with the necessity of a potash dressing, which after a 

 time becomes necessary when sulphate of ammonia is the nitro- 

 genous manure." 



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