Soda-Salts in Agriculture. 301 



when attention should be prominently directed to the dis- 

 tinction between essential and non-essential ash-constituents 

 which I have been in the habit of drawing; for more than eig-ht 

 years. The development of the doctrine of vegetable nutrition 

 demands that such a distinction should be made, both in a 

 qualitative and quantitative sense — that is to say, it is desirable 

 that we should know positively not only what soil-constituents 

 are absolutely necessary for the growth of our cultivated crops, 

 but also what is the amount of each ash-constituent that has 

 to be regarded as indispensable for bringing our various crops to 

 maturity, and what is the amount which may be considered as 

 superfluous or accidental. 



Although I do not look upon chloride of sodium and soda- 

 salts in general as essential ash-constituents of plants, I am far 

 from denying the beneficial effect which salt is capable of pro- 

 ducing in particular cases. Indeed, my own experience leads 

 me to admit that salt is a useful and cheap manure, which, 

 judiciously applied, frequently yields a large increase of corn, 

 roots, or hay, and seldom does any harm. 



On porous sandy soils, roots, especially when the season 

 happens to be dry, are apt to pass so rapidly through all the 

 stages of growth that their leaves begin to drop before they have 

 had time enough on the one hand to collect atmospheric food, 

 and on the other to accumulate mineral matter from the soil in 

 sufficient quantity for the development of an abundant crop of 

 bulbs. On such soils the application of 3 or 4 cwt. has given 

 me a large increase in roots, and 7, 8, or even 9 cwt,, so far from 

 doing any harm, increased the produce of mangolds by 2|- to 4 

 tons per acre. On the other hand, it does mischief when it is 

 applied in excessive doses (and such I consider all quantities 

 exceeding 5 cwts. per acre), to stiff, wet, clay soils, and soils gene- 

 rally which are cold, and which bring their grain, root, and 

 grass crops slowly to maturity, for salt has a remarkable tendency 

 to prolong the period of vegetation, and delay the arrival of 

 maturity, and consequently, when it is misapplied, the crude 

 juices circulating in the unripe leaves are not sufficiently elabo- 

 rated or ripened, within the period during which the roots can 

 be left in the field, for the production of a large and heavy crop. 



As common salt certainly has the power of prolonging the 

 period during which our cultivated crops can be kept growing in 

 the field, much advantage can be derived from its use by the 

 intelligent agriculturist, who, bearing in mind the circumstances 

 under which it is desirable to prolong the life of plants, will 

 chiefly employ it as a top-dressing or otherwise when he has to 

 do with light, porous, and naturally dry soils. 



This useful property of common salt is probably common to 



