IX.] FERTILISERS DESTROYING THE TEXTURE 291 



but evaporated every day. An efflorescence practically 

 identical with white alkali is sometimes seen on green- 

 house borders, which are constantly watered, but never in 

 sufficient quantities to cause percolation ; and gardeners 

 again are familiar with the check of growth which 

 sometimes occurs in the case of plants long in one pot 

 and constantly watered with hard water. The remedy 

 is to water from time to time so heavily as to cause 

 abundant percolation and thus wash all the salts out. 



Closely related to some of the phenomena presented 

 by alkali soils are certain secondary effects upon the 

 texture of the soil which are produced by the action of 

 some of the salts used as artificial manures. A good 

 friable texture in a heavy soil depends upon the clay 

 particles being generally flocculated and gathered 

 together into little aggregates, which give the soil a 

 coarser grain until they are resolved into their ultimate 

 particles by incautious working when the clay is in a wet 

 state. It has already been shown that acids and most 

 soluble salts, particularly those of calcium, possess a 

 strong flocculating power, whereas the soluble alkalis 

 the carbonates and hydrates of sodium, potassium, 

 and ammonium are active deflocculators, causing the 

 clay particles to separate into their most fine-grained 

 condition. 



It has long been recognised that large or frequent 

 dressings of nitrate of soda had an injurious action upon 

 the tilth of the soil, causing it to remain very wet, and 

 then to dry into hard, unkind clods. Since nitrate of 

 soda is very hygroscopic, the wetness induced in the 

 land was attributed to the absorption of moisture from 

 the atmosphere by the nitrate of soda, but when it is 

 considered what a very small proportion the water 

 absorbed by as much as 5 cwt. of nitrate of soda would 

 bear to the hundred tons which is the approximate 



