142 



Power of Soils to absorb Manure. 



crops ; and in a third will be found the per centage of each which 

 a soil must contain to furnish this last quantity. 







1 Crop. 



20 

 Crops. 



'• Per Centage 

 of the soil 

 removed 

 by 20 crops. 







Phosphoric Acid . 

 Sulphuric Acid . 



Magnesia 



lbs. 

 170 



30 

 8 

 16 

 10 

 40 

 3 



lbs. 



3400 

 600 

 160 

 320 

 200 

 800 

 60 



0-152 

 0-027 

 0-007 

 0-014 

 0-009 

 0-036 

 0-003 









277 



5540 



0-248 





Now it is common and usual to find from one-tenth to two-tenths 

 per cent, of potash in ordinary soils, a quantity several times greater 

 than is here shown to be necessary for twenty crops of wheat ; and 

 I would ask any chemist acquainted Yv^ith the analysis of soils, 

 whether he has ever met with a soil which repays cultivation, 

 which had not very much more of all these mineral ingredients 

 than that given in the last column. The fact is, that there is an 

 almost unlimited supply of the mineral requisites of plants in 

 soils, but that the great agricultural problem is to get at them — 

 to render them available ; and here again it seems reasonable to 

 suppose that abundant cultivation, which lets in carbonic acid 

 and ammonia to the soil, may by that very act be providing the 

 potash and phosphate of lime which the former, and the silica 

 which the latter, are endowed with the power of dissolving, and 

 presenting to the roots of plants. 



But it is plain that there is a limit to all this ; and whilst I 

 cannot see why a considerable number of successive crops of 

 wheat might not, by virtue of the manure-collecting and manure- 

 preparing process of abundant cultivation, be raised from land 

 without the direct application of manure, I am decidedly opposed 

 to the principle of continuing this system on the same land for 

 an unlimited number of years. The capabilities of the soil, great 

 as they might be, must in that case gradually be diminished, and 

 ultimately fail altogether ; besides, such a plan Avould be unne- 

 cessarily hazardous. What is to prevent land that has been 

 cropped successively with wheat on this plan for 10 or 15 years, 

 supposing it has been found to answer for that period, from being 

 changed for other land Vv^hich has not been exposed to that drain ? 



With one or two more remarks, I will take leave of this subject 



* Calculated on a soil 10 inches in depth, and weighing 1000 tons to the acre. 



