54 FERTILISERS CONTAINING NITROGEN [chap. 



of a potash dressing, which after a time becomes 

 necessary when sulphate of ammonia is the nitrogenous 

 manure. 



One of the most characteristic effects of the use 

 of nitrate of soda as a manure, either repeatedly or in 

 any quantity, is its deleterious action upon the texture 

 of a heavy soil ; farmers have repeatedly observed 

 that where nitrate of soda has been applied the 

 land remains very wet and poaches badly if it is at 

 all disturbed before it has dried. Market gardeners 

 in particular, who manure heavily with nitrate of 

 soda, have found this destruction of the tilth a 

 serious drawback to its use. The cause has usually 

 been put down to the hygroscopic character of nitrate 

 of soda ; since the salt itself readily attracts moisture 

 from the air and will even liquefy spontaneously, it 

 is considered that it keeps the land moist for the 

 same reason. But the extra amount of moisture that 

 could be held in the soil by a few hundredweights of 

 nitrate of soda would be wholly imperceptible when 

 distributed through the hundred tons or more which 

 the top inch of soil weighs per acre, even if the 

 application of nitrate of soda persisted near the 

 surface and were not quickly washed down in the 

 soil. Some of the Rothamsted plots in the mangold 

 field, where very large amounts of nitrate of soda 

 have been applied year after year for the last fifty 

 years, show this deterioration of tilth in very marked 

 fashion, the land being intolerably sticky after rain 

 and drying into hard intractable clods, so much so 

 that it is very difficult to secure a plant of roots unless 

 the season is favourable. Determinations, however, 

 of moisture in the surface soil do not show any sensible 

 difference between these plots of bad texture and those 

 v/orking more kindly, so that we must put aside the 



