144 Farmyard Manure. 



As regards tlie practical effect which salts of soda and 

 potash are capable of displaying with reference to the nutrition 

 of plants, the former are not to be compared to the latter in 

 point of efficacy. It was believed at one time that soda was 

 capable of replacing potash in the ashes of our crops, but this 

 opinion was not based on trustworthy evidence. On the con- 

 trary, the best and most extensive series of ash analyses of our 

 crops show that whilst the amount of potash, within certain 

 limits, is constant in the ashes of plants, that of soda, especially 

 of chloride of sodium, is liable to great fluctuations, arising, no 

 doubt, from local conditions of the soil. 



The fact that soils are capable of absorbing potash from 

 soluble manuring matters, whilst no special care is manifested 

 by them to retain the equally soluble soda salts, appears to me to 

 account, to some extent at least, for the comparative constancy of 

 the amount of potash in the ashes of our crops, as well as for 

 the fluctuation of the amount of soda in the same. 



The power of soils to retain potash in large proportions must 

 have the effect of converting the salts of potash in the manure 

 applied to the land into compounds which, though not altogether 

 insoluble in water, are yet sufficiently difficult of solution to 

 permit only a limited and fixed quantity to enter into the vege- 

 table organism in a given period. The case is different with 

 salts of soda ; for as soils do not appear to retain them in any 

 high degree, and plants have no selecting power, but absorb by 

 endosmosis whatever is presented to the spongioles of their 

 roots in a state of perfect solution, it is evident that more soda 

 Avill enter into the plants when grown on a soil naturally abound- 

 ing in this alkali or heavily dressed with common salt, than 

 when grown upon a soil poorer in soda. 



We have here, at the same time, an interesting illustration of 

 the fact that the soil is the great workshop in which food is pre- 

 pared for plants, and that we can only then hope to attain unto 

 a more perfect knowledge of the nutrition of plants and the best 

 means of administering to their special wants when we shall have 

 studied, in all their details, the remarkable changes wliich we 

 know, through the investigations of Mr. Thompson and Professor 

 Way, take place in soils when manuring substances are brought 

 into contact with them. The subject is full of practical interest, 

 but also surrounded by great difficulties, which, it appears to me, 

 can only l)e overcome when the investigation is taken up in a 

 truly scientific spirit, without reference to the direct application 

 which, in due course, no doubt, well-established chemical prin- 

 ciples will receive in agriculture. It is the undue anxiety to 

 obtain at once what is popularly called a practical result, the 

 grasping after results which at once may be translated into so 



