REMUNERATIVE OAT CROP AFTER RYE. 169 



A field on wliicli rye can no longer be cultivated with 

 profit is not on that account unfruitful for oats. 



An average crop of oats (2000 kilogranunes (=39 

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

 straw) takes from the soil 310 kilogrammes ( = G 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 jdeld a remunerative 

 liarvest ; for a soil supplying, for the production of a 

 crop of oats, 310 kilogrammes out of a stock of 13,869 

 Idlogrammes, 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 Avhen the root-surface of the oat plant 

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



Oat crops will therefore exhaust the soil the most 

 speedily ; after 12| years the harvest will sink to three- 

 fourths of the original amount. 



None of the causes tending to diminish or increase the 

 crops have any influence on this law of exhaustion of the 

 soil by cultivation. Whenever the stock of nutriment has 

 been lowered to a certain point, the ground ceases to be 

 productive, in an agricultural sense, for cultivated plants. 



For eveiy cultivated plant such a law exists. This 

 state of exhaustion will inevitably take place, even though 

 only a single one of the various mineral constituents 

 required for the nutrition of the plants has been witli- 

 drawn from tlie soil by a succession of crops ; for the one 

 constituent which fails or is deficient renders all the rest 

 ineffective. Witli each crop, each plant, or portion of a 

 plant, taken away from a field, the soil loses part of the 



