REMUNERATIVE OAT CROP AFTER RYE. 167 



cwts.) of grain, and 3800 kilogrammes ( = 74rJ cwts.) of 

 straw) takes away from the ground per hectare only 180 

 kilogrammes ( = 3^ cwt.) of ash-constituents. 



If the production of an average wheat crop requires 

 the presence in the soil of 25,000 kilogrammes of the 

 ash-constituents of wheat plants, a soil with only 18,000 

 kilogrammes of such constituents will prove sufficiently 

 rich to give an average and a succession of remunera- 

 tive crops of rye. 



By our reckoning, a field, though exhausted for the 

 cultivation of wheat, still contains 18,492 kilogrammes 

 of mineral constituents, the same in properties as those 

 which the rye plant requires. 



If it is asked after how many years continuous rye- 

 cultivation the average crop will sink down to a three- 

 quarter crop, assuming this to be no longer remunera- 

 tive, we find that the field will produce 28 remunerative 

 rye-crops, and after 28 years will be exhausted for its 

 cultivation. 



The nutritive substances yet remaining in the soil 

 will still amount to 13,869 kilogrammes of ash-con- 

 stituents. 



A field on which rye can no longer be cultivated 

 with profit is not on that account unfruitful for oats. 



An average crop of oats (2000 kilogrammes ( = 39 

 cwts.) of grain, and 3000 kilogrammes ( = 59 cwts.) of 

 straw) takes from the soil 310 kilogrammes ( = 6 cwts.) 

 of ash-constituents, being 60 kilogrammes ( = 1*2 cwt.) 

 more than is removed by a wheat crop, and 130 kilo- 

 grammes ( = 2|- cwts.) more than by a rye crop. If 

 the absorbent root-surface of the oat plant were the 

 same as that of rye, oats after rye would not yield a 

 remunerative harvest ; for a soil supplying, for the, 

 production of a crop of oats, 310 kilogrammes out of a 

 stock of 13,869 kilogrammes, loses thereby 2'23 per 

 cent, of its store of mineral constituents, whereas the 

 roots of rye extract only 1 per cent. 



To produce a remunerative crop of oats after rye is 

 only possible when the root-surface of the oat plant 

 exceeds that of the rye in the proportion of 2 -23 to 1. 



