362 MIXTURE OF NITRATE WITH SULPHATE OF SODA. 



is to be explained by the absence of sulphuric acid, which appears to 

 aid especially in the development of the latter class of plants. 



On this subject, however, experiments are too limited in number, in 

 general too inaccurately made, and our information in consequence too 

 scanty, to enable us as yet to arrive at satisfactory conclusions. 



12°. Mixed Saline Manures. — The principle already so frequently 

 illustrated, that plants require for their rapid and perfect development 

 a sufficient supply of a considerable number of different inorganic sub- 

 stances, will naturally suggest to yon that in our endeavours to render 

 a soil productive, or to increase its fertility, we are more likely to suc- 

 ceed if we add to it a mixture of several of those substances, than if we 

 dress it or mix it up with one of them only. This theoretical conclu- 

 sion is confirmed b^' universal experience. 



Nearly all the natural manures, whether animal or vegetable, which 

 are applied to the land, contain a mixture of saline substances, each of 

 which exercises its special effect upon the after-crop — so that the final 

 increase of produce obtained by the aid of these manures, must be as- 

 cribed not to the single action of one of their constituents, but to the 

 joint action of all. An important practical problem, therefore, pro- 

 pounded by scientific agriculture in its present state, is — what mixtures 

 of saline substances are most likely to be generally useful, what others 

 specially useful, to this or to that crop ? The complete solution of this 

 problem will require the joint aid of chemical theory and of agricultu- 

 ral experiment, — of experiments often varied and probably long con- 

 tinued. But that we may finally expect to solve it, will appear from 

 what has already been accurately observed in regard to the effect of 

 certain artificial mixtures upon some of our cultivated crops. Thus — 



a. Mixture of Nitrate with Sulphate of Soda. — If, instead of dressing 

 young potatoes with nitrate or with sulphate of, soda alone (page 331|, 

 we employ a mixture of the two, the growth of the plant is much more 

 promoted and the crop of potatoes much more largely increased. Thus 

 Mr. Fleming (in 1841) applied to his potatoe crop a mixture of equal 

 weights of nitrate and of dry sulphate of soda, in the proportion of 200 

 lbs. of the mixture to the imperial acre, with the following remarkable 

 result : — 



Undressed, . . . 66 bolls, each 5 cwt., per acre. 

 Dressed, .... 107 bolls. 



Increase, ... 41 bolls,* or 10 tons per acre ! 



The stems also were six and seven feet high. The addition of nitrate 

 of soda to a portion of the same field gave a produce of only 80 bolls. 

 Similar effects, of which, however, I have not yet obtained the numeri- 

 cal results, have been observed on the same crop in various localities 

 during the present season (1842). 



The effect of this one artificial mixture holds out the promise of 

 much good hereafter to be ob^ined by the judicious trial of other mix- 

 tures — probably of a greater number of substances — upon all the crops 

 we are in the habit of raising for food. 



b. Wood ashes. — This opinion is strengthened by the effects which 



' See Appendix, p. 20. 



