SOIL EXHAUSTION AND ROTATION IN CROPS. 81 



pare them for the crop ; so that, although these fertilizers may 

 in some cases do nothing towards feeding the crop directly, 

 they help to feed it by this indirect action in dissolving and 

 bringing into an active form the materials which the soil con- 

 tains in abundant quantity but in an inert state. 



To go back and review, in a couple of statements : Ex- 

 haustion is tlie reduction of the producing capacity of the soil 

 below the point of profitable cultivation, and depends either 

 upon the absolute removal of certain materials, or their re- 

 moval to such a point that the supply is below the demand of 

 the crop, and such removal of materials must be compensated 

 either by suitable fertilizing applications or by making the 

 unavailable materials still present in the soil available by 

 fallow, tillage, «fec. 



Mr. Lawes, of England, a gentleman who has devoted a 

 great deal of attention to agriculture, and spent a great deal 

 of money in its study, and who has arranged the most beauti- 

 ful and elaborate field experiments that have ever been made 

 in any country, has brought out in a recent publication the 

 distinction between the "natural strength" of the soil and 

 what he designates its " condition ;" and as this distinction is 

 an extremely important one, I will devote a few moments to 

 its consideration. The natural strength of a soil is its feeding 

 power and adaptedness to crops in all those respects which 

 belong to the soir by its original nature. This standard fer- 

 tility or productive power is something characteristic of the 

 soil, something you cannot separate from it, something be- 

 longing to its entire mass and dependent upon its original 

 composition, texture, and properties. It is a thing which lasts 

 a long time, and perhaps has scarcely any limit in the matter 

 of duration, whatever may be its limit in the quantity of crop 

 which the soil will produce. Every soil has its natural 

 strength, greater or less, the degrees covering a very wide 

 range. You have all heard of soils which are remarkable for 

 their productiveness, or for their want of productiveness. The 

 valley of the Nile, for instance, is a region which has been 

 cultivated for a period longer than history can define with any 

 accuracy, and produces large crops annually of the most ex- 

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