RETARDATION OF THE PERIOD OF EXHAUSTION. 173 



nearly the same as in the preceding year, because the 

 conditions for tlie formation of straw have been but 

 slightly altered. 



Thus then, by taking away from the ground less than 

 formerly, we increase the number of remunerative crops, 

 or the sum total of grain produced in the whole series of 

 corn harvests. Some of the straw-constituents are con- 

 verted into corn-constituents, and are now removed from 

 the field in the latter form. Tlie period of final ex- 

 haustion, though sure to come in the end, will, under 

 these circumstances, occur later. The conditions for the 

 production of grain go on continually decreasing, because 

 the substances removed in the corn are not replaced. 



It would make no difference in this respect, if the 

 straw were cut and carted about the field, or used as 

 fitter for cattle, and then ploughed in ; the supply thus 

 bestowed upon the field, having been originally taken 

 from the field, cannot enrich it. 



Considering that the combustible elements of the 

 straw are not supplied by the soil, it is clear that in 

 leaving the straw in the ground we leave nothing more 

 than the ash- constituents of the straw. The field re- 

 mained somewhat more fruitful than before, because a 

 fittle less had been taken away. 



If the corn or its ash -constituents were ploughed 

 in with the straAV, or if, instead of it, a correspond- 

 ing quantity of some other seed containing the 

 same ash-constituents as wheat, e. g. ground rape-cake, 

 that is, rape-seed freed from the fatty oil, were given 

 in proper proportion to the ground, its composition 

 would remain the same as before : the next year's crop 

 would equal that of the preceding year. If after every 

 harvest the straw is always in this manner retiu-ned to 

 the field, the further consequence will be an inequality in 



