Continuous Growth of Wheat Without Manure. 37 



irrespective of variations due to good or bad seasons is, 

 probably, up to a certain period, equivalent to about a 

 quarter of a bushel per acre per annum, representing a gross 

 produce in grain and straw of 401b. per acre. But, with 

 each decline, the reduction must obviously become less and 

 less ; atmospheric influences, and even the small amount of 

 ammonia brought down in the rain, will produce a great 

 effect upon a declining crop. Hence, the actual process of 

 the exhaustion of the soil differs considerably from all the 

 preconceived ideas on the subject. The soil, in fact, not 

 only contains more fertility, but also holds it with a much 

 firmer grasp, and parts with it less readily, than was 

 previously thought to be the case. 



The average annual amount of total produce (grain and 

 straw) removed has been 1 ton per acre, containing nearly 

 19001b. of absolutely dry matter; and there is strong 

 evidence, derived from other experiments in the field, to 

 prove that the carbon, indeed a large proportion of the 

 organic matter, is derived from the atmosphere, whilst the 

 nitrogen and the mineral matter are taken from the soil. 

 This would divide the products into from 94 to 95 per cent, 

 atmospheric constituents (including water), and from 5 to 6 

 per cent, soil constituents. The average amount of soil 

 constituents (minerals and nitrogen) annually removed by 

 this unmanured wheat crop is from lOOlb. to 1201b. per acre ; 

 and of the three most important constituents of plant 

 growth there have been removed about 171b. of potash, lOlb. 

 of phosphoric acid, and 201b. of nitrogen. 



It appears, then, that upon a field which has been under 

 arable cultivation certainly for two or three centuries and 

 possibly for a much longer period and which has consequently 

 lost a very considerable amount of its original fertility, there 

 is after the removal of forty unmanured crops a yield 

 which differs very little from the average of some of the 

 great wheat-growing countries of the world ; the yield of the 

 TJnited States, India, and China being, it is stated, from 



