166 THE PRINCIPLES OF 



In the extensive experiments at Rothamsted we find in- 

 vestigations upon barley, wheat, oats, turnips, swedes, mangel 

 wurzel, and permanent pasture, covering, in fact, the whole 

 ground that is of direct interest to the bulk of our farmers. 

 In the corn experiments it is interesting to notice the pertin- 

 acious manner in which unmanured land keeps throwing up fair 

 crops year after year. It has been pointed out by Dr. Gilbert, 

 that plots of wheat and of barley which have been continu- 

 ously unmanured for some thirty-five to forty years, are still 

 yielding crops averaging thirteen and fourteen bushels per 

 acre per annum a yield superior to that of the United 

 States of America, or even of such an old cultivated country 

 as France. If we examine the agricultural statistics of the 

 United States we shall find some States only producing eight 

 bushels per acre of wheat. It is therefore remarkable that 

 these corn-yielding fields at Rothamsted continue for a long 

 period to give such a satisfactory amount as fourteen bushels 

 per acre. But it is not so with root crops. These crops 

 when unmanured give, as you will readily see by examination 

 of the Rothamsted papers, a miserable result. On unmanured 

 plots, that is on plots in which it is attempted to grow roots 

 year after year without any aid, the result is simply nil. 



Passing in the next place to the effect which is produced 

 by additions of certain of the lesser important substances, 

 I take as examples the application of considerable quantities 

 per acre of sulphate of potash, sulphate of soda, and sulphate 

 of magnesia. The yield is very slightly increased by 

 such applications. In the case of barley it has risen from 

 seventeen and a half bushels upon the continuously un- 

 manured plots to nineteen and a quarter bushels. That is 

 a very small and inadequate increase, and not such as would 

 induce the farmer to incur the expense of supplying such 

 substances. 



Superphosphate is, we know, of vast importance, and in 



