108 EFFECTS ON " FREE LIGHT LAND." 



however, would make it profitable in these, as well as other cases, 

 to adopt a mild and meliorating course of tillage. 



Less improvement will be obtained by marling worn soils of the 

 kind called " free light land/' than other acid soils which originally 

 produced much more sparingly. The early productiveness of this 

 kind of soil, and its rapid exhaustion by cultivation,, at first view 

 seem to contradict the opinion that durability and the case of im- 

 proving by putrescent manures are proportioned to the natural 

 fertility of the soil. But a full consideration of the circumstances 

 will show that no such contradiction exists. 



In defining the term natural fertility, it was stated that it should 

 not be measured by the earliest products of new land, which might 

 be either much reduced, or increased, by temporary causes. The 

 early fertility of free light land is so rapidly destroyed, as to take 

 away all ground for considering it as fixed in, and belonging to the 

 soil. It is like the effect of dung on the same land afterwards, 

 which throws out all its benefit in the course of one or at most two 

 years, and leaves the land as poor as before. But still it needs 

 explanation why so much productiveness can at first be exerted by 

 any acid soil, as in those described in the 14th experiment. The 

 causes may be found in the following statement. These soils, and 

 also their sub-soils, are principally composed of coarse sand, which 

 makes them of more open texture than best suits pine, and (when 

 rich enough) more favourable to other trees, the leaves of which 

 have no natural acid, and therefore decompose more readily. As 

 fast as the fallen leaves rot, they are of course exposed to waste ; 

 but the rains convey much of their finer pa^ts down into the open 

 soil, where the less degree of heat retards their final decomposition. 

 Still this enriching matter is liable to be further decomposed, and 

 to final waste ; but though continually wasting, it is also continu- 

 ally added to by the rotting leaves above. The shelter of the 

 upper coat of unrotted leaves, and the shade of the trees, cause 

 the first as well as the last stages of decomposition to proceed 

 slowly, and to favour the mechanical process of the products being 

 mixed with the soil. But there is no chemical union of the vege- 

 table matter with the soil. When the land is cleared, and opened 

 by the plough, the decomposition of all the accumulated vegetable 

 matter is hastened by the increased action of sun and air, and in 

 a short time everything is converted to food for plants. This 

 abundant supply suffices to produce two or three fine crops. But 

 now, the most fruitful source of vegetable matter has been cut off; 

 and the soil is kept so heated (by its open texture) as to be unable 

 to hold enriching matters, even if they were furnished. The land 

 soon becomes poor, and must remain so, as long as these causes 

 operate, even though cultivated under the mildest rotation. When 

 the transient fertility of such a soil is gone, its acid qualities 



