LECTURE XIV. 



The physical qualities and chemical constitution of a soil may be changed by art.— Nature 

 of the' plants dependent upon that of the soil on which they grow.— Mechanical methods 

 of improving the soil.— Effects produced by draining.— Theory of springs.— Effect of 

 ploughing, subsoiling, deep ploughing and trenching.-^Artificial improvement by mixing 

 with clay, sand, or marl. 



The facts detailed in the preceding lecture may be considered as af- 

 fording sufficient proof that the abiUty of the farmer to grow this or that 

 crop upon his land, is very much restrained by its natural character and 

 constitution. Each soil establishes upon itself — so to speak — a vegeta- 

 tion suited to its own nature, one that requires most abundantly those 

 substances which actually abound in the soil — and the art of man can- 

 not long change this natural connection between the living plant and the 

 kind of land in which it delights to grow. 



But he can change the character of the land itself. He can alter 

 both its physical qualities and its chemical constitution, and thus can fit 

 it for growing other races of plants than those it naturally bears — or, if he 

 choose, the same races in greater abundance, and with increased luxuri- 

 ance. It is, in fact, in the production of such changes, that nearly all the 

 labour and practical skill of the husbandman — apart from local peculiari- 

 ties of climate, &c. — is constantly expended. For the attainment of 

 this end he drains, ploughs, subsoil- ploughs, and otherwise works his 

 land. For this end he clays, sands, marls, and manures it. By these 

 and similar operations the land is so changed as to become both able and 

 willing to nourish and ripen those peculiar plants which the agriculturist 

 wishes to raise. On this practical department of the art of culture, 

 the principles explained and illustrated in the preceding parts of these 

 lectures, throw much light. They not only explain the reason why cer- 

 tain practices always succeed in the hands of the intelligent farmer, but 

 why others also occasionally and inevitably fail — they tell him which 

 practices of his neighbours he ought to adopt, and which of them he had 

 better modify or wholly reject, — and they direct him to such new modes 

 of improving his land as are likely to add the most to its permanent 

 productive value. 



The operations of the husbandman in producing changes upon the 

 land, are either mechanical or chemical. When he drains, ploughs, 

 and subsoils, he alters chiefly the physical characters of his soil — when 

 he limes and manures it, he alters its chemical constitution. These two 

 classes of operations, therefore, are perfectly distinct. Where a soil con- 

 tains all that the crops we desire to grow are likely to require, mere me- 

 chanical operations may suffice to render it fertile — but where one or 

 more of the inorganic constituents of plants are wanting, draining may 

 prepare the land to benefit by further operations, but it will not be alone 

 sufficient to remove its comparative sterility. I shall, therefore, con- 

 sider in succession these two classes of practical operations : — 



1°. Mechanical methods of improving the soil, including draining, 

 ploughing, mixing with clay, sand, &c. 



