19 



have no knowledge imparted of what substances. It is not enough to say of manure, for this is a 

 compost of all the bodies necessary for plants. If we still further advance the speculations of prac- 

 tical men and assert that the exhaustion is of organic matter or humus, the position is denied by the 

 second precept, for seed crops such as beans are exhausting whilst they require little humus 

 — whilst on the other hand, many forage plants as cabbages, turnips, beets, are not seeds crops, but 

 exhausting. We do not deny that excellent rotations devised by practical men do exist, but we do 

 deny that every rotation based upon the foregoing indefinite precepts is necessarily good, and if they 

 be no guide without the assistance of experience gained at great cost and by separate observations in 

 the field, they are worse than useless. The defect of the precepts rests in this, that Ave are not 

 informed in what respect the food of different plants varies, nor in what particular seed crops exhaust 

 the soil. The apologists of the system may assert that these are remote facts not within the reach 

 of the propomiders, but this being the case the time has now arrived when a closer approximation to 

 truth may be made and the former precepts abandoned or improved by modern investigation. 



F. Of the Exhausting Qualities of Crops. 



The soil may be exhausted to such a degree that it will cease to produce certain forage plants 

 without the introduction of a single seed crop. If we enrich any field so that it produces tobacco 

 and follow this crop by cabbages, turnips, flax, taking no seed from either, we speedily reach a 

 period when none of these plants will yield a remunerating crop. This is one kind of exhaustion, 

 but it is not complete exhaustion, for corn, wheat, oats, beans and clover seed may be obtained in 

 good quantity from the same field. On the other hand, a few crops of hemp seed, linseed, corn, oil 

 grains, wheat, will lam down the land to barrenness ; but this exhaustion is altogether different from 

 the preceding ; it is, in truth, the specific exhaustion produced by seed crops, and it matters not 

 which are the seeds. Hence there are two distinct kinds of exhaustion well known to practical men 

 and it behoves us, who desire the advancement of agriculture, to make the line of demarkation 

 betw^n them bold and distinct. There are other kinds of exhaustion to which we shall refer 

 presently. 



In a paper I had the honor of reading before the Association last year, I made a thorough 

 examination into the nature of the exhaustion of lands by seed crops. The object of the commu- 

 nication was to prove the following points : 



1. That all seeds contain an excess of phosphoric acid, amounting usually to thirty-five or 

 forty per cent, of the entire ash, nearly the whole of the ash being in many cases phosphates ; 

 this was demonstrated in the case of corn, wheat, beans, hemp seed, flax, peas, cotton and other 



