VIII.] THEORIES OF MANURING i6i 



ever, high, being only 35 bushels of wheat and 34 

 bushels of barley, and though it might have been 

 increased had the straw and clover hay been made into 

 manure and returned to the soil, only a level of 

 production below the average can be maintained if the 

 land is left to natural recuperative actions. As soon as 

 larger crops are aimed at and the soil is brought into 

 higher condition to produce them, the wasteful actions 

 are increased in a higher ratio, as may be seen from the 

 example of the wheat plot dunged every year. Conse- 

 quently, to get the land up to the level of 5 qrs. of 

 wheat, not only the extra nitrogen contained in 5 qrs. 

 above 4 qrs. must be added, but a great deal more must 

 be brought in, in order to make up for the increased 

 rate of loss taking place in land in higher condition. 



We thus find it impossible to construct a balance- 

 sheet for the land that sets off the removal of plant food 

 in the crop against the original stock in the soil and the 

 additions in the manures, because any such summary is 

 upset by the unknown gains and losses suffered by the 

 nitrogen in the soil, nitrogen being the most important 

 element of plant food. As we began by dismissing the 

 idea that we could decide upon the manuring of a given 

 field by finding out by analysis some particular substance 

 lacking in the soil which could be supplied as manure, 

 so now we must dismiss in its turn the theory that for 

 the proper manure we have only to provide what the 

 crop will take away from the soil. The first theory 

 made too much of the soil, since it assumed that 

 different soils possess radical differences which do not 

 exist ; the second theory fails because it takes no account 

 of the soil at all, and neglects the enormous reserves of 

 plant food therein contained. In fact, no general theory 

 of manuring can be drawn up which will predict the 

 appropriate treatment for every plant beforehand — we 



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