30 



On Subsoil- Ploughing. 



that subsoiling is of no use on their land. The quality of land is 

 the same in all ; consisting of a level and uniform tract of that 

 peculiarly tenacious soil, the lias clay, containing, as we see by 

 the analysis furnished by Mr. Black (made at Edinburgh)^ no 

 less than 43 per cent, of alumina or pure clay. The next evi- 

 dence I shall adduce is that of Mr. Stevenson, of Rainton, near 

 Boroughbridge, a very enterprising and judicious tenant-farmer ; 

 whose farm chiefly consists of a stiff red clay, on the red sandstone 

 formation. He began by subsoiling 17 acres in the winter of 

 1 835-6 : the summer following, these 1 7 acres grew a remarkable 

 crop of turnips, though the year was in general a failing one for 

 that crop. The turnips were followed by barley, seeds, wheat, 

 — all good crops. When ploughed deep again for turnips, at the 

 end of the course, it was found to work much lighter than the 

 land not subsoiled. The man who held the plough in both 

 instances found a great difference in the mellowness of the soil 

 turned up, and consequently in the labour of the horses. The 

 subsoil, on analysis, showed 24 per cent, of alumina. The exact 

 analysis is as follows : — 



Specific Gravity, 2-070. 

 100 Parts contain — 

 Of water of absorption . 



Silica 



Alumina 



Oxide iron 



Soluble matter 



Loss 



100 



7 

 ,55 

 24 



4* 



Mr. Stevenson found so much benefit from the operation, that 

 he has since subsoiled 27 acres, and means to continue it on a 

 large scale. A glance at the experiments above described en- 

 ables us to make a first approximation to the solution of this 

 much debated question. It appears probable that a soil contain- 

 ing not more than 24 per cent, of alumina may be subsoiled with 

 advantage, but that when it exceeds 40 per cent, no permanent 

 improvement is derived from the operation. Many more experi- 

 ments must be made before this approximation can be so modified 

 as to make it of general application : and I would beg to suggest 

 to those gentlemen who may feel disposed to assist in the inquiry, 

 that any account of the use of the subsoil-plough on land con- 

 taining more than 24 and less than 40 per cent, of alumina 

 would be particularly valuable, as the first point to ascertain is, 

 the maximum quantity of alumina which may exist in land with- 

 out making it unfit for subsoiling. From what has been stated 



