8 The Rothamsted Experiments. 



cropping is to reduce the available supplies of such mineral 

 constituents in the soil below that which is requisite to 

 obtain the full benefit of the annual atmospheric supply of 

 carbon and nitrogen, or whether it is the supply in the soil 

 of the carbon or the nitrogen which is most exhausted. 



3. The use of ammonia-salts alone, which provide nitrogen 

 for the growth of the crop, shows whether or not the latent 

 mineral wealth of the soil is more than sufficient for the 

 annual atmospheric supply of available nitrogen. 



4. And the object of sowing one plot with ammonia-salts 

 in the autumn and another in the spring was to determine 

 whether it was practically advantageous to sow such soluble 

 manures in the autumn on so light a soil. 



5. The mixture of mineral manures and ammonia-salts 

 shows, when the results are compared with those of each of 

 these manures used separately first, whether the annually 

 available native mineral supply of the soil, taken together 

 with that in the manure, was not capable of producing a much 

 greater amount of growth than was the annual atmospheric 

 supply of nitrogen ; and, secondly, whether the amount of 

 nitrogen supplied to the soil, when such a quantity of 

 ammonia- salts was used alone, was not in excess in propor- 

 tion to the annually available supply of minerals from the 

 soil itself. 



6. Bape-cake contains a large proportion of carbonaceous 

 and nitrogenous organic substances, and some mineral 

 matter ; and the nitrogen supplied in the quantity of it used 

 was nearly identically the same as, or, perhaps, rather 

 greater in amount than, that in the ammonia-salts of the 

 other experiments. 



7. The farmyard manure was the product of yards in 

 which bullocks were fed on turnips with a moderate quantity 

 of oil cake. In this manure there would be added to the soil 

 every year a larger supply of every constituent than was 

 contained in the increased wheat crop grown. 



The results are summarised in a series of tables, in 



