120 L. COHEN. 



with similar proportions of manure in the field. The culture 

 pot is under complete control — we see to it that it contains 

 never less than about 20°/° of moisture, that is that our soil 

 water is not more than a *15 + a/4°f solution, hut what 

 happens on the farm ? On many occasions during the pro- 

 gress of a field experiment the moisture goes down to 5°/°, 

 (causing the concentration to reach #), and here we have 

 a theoretical instance where the development of a crop 

 may be seriously retarded by the application of the same 

 proportion of the very material that under optimum con- 

 ditions of moisture might produce a threefold return. 



As a practical example: — Nobbe, Wolff, and other con- 

 tinental experimenters, have proved that the growth of 

 many farm crops are seriously hindered when the water in 

 which their roots are suspended contains more than '2f of 

 soluble ash ingredients; this being the case, and supposing 

 that we find a soil to contain '02°/° of soluble salts, and we 

 wish to add as a manure for the crop nitrate of soda say 

 at the rate of 2 cwt. per acre, or *02/°. Then we increase 

 the concentration in the following way: — when the un- 

 manured soil contains 20°/° of moisture the latter holds 'If 

 of salts, a very favourable medium for assimilation, but by 

 the addition of the manure this figure is doubled and reaches 

 the danger mark quoted above, and it thus becomes evident 

 that in order to get favourable results from this addition, 

 it will be necessary to keep always at least 20°/° of moisture 

 in the soil, a condition seldom practicable in dry countries. 

 It is possible that in many cases farmers and others have 

 developed an insuperable prejudice against the use of 

 chemical fertilisers, because these had been tried on their 

 land under conditions similar to above. 



In his book " The Soil," p. 91, A. D. Hall tells us that 

 Dr. Sachs came to the conclusion, as the results of experi- 

 ments with plants in pots, that different soils can yield up 



