22 



THE ROTHAMSTED EXPERIMENTS. 



Artificial 

 manures. 



Produce 

 with artifi- 

 cial man- 

 ure and 

 iirithout 

 manure. 



crop. It shows the average yield over four consecutive 

 seasons, 1845-48, of roots, of leaves, and of total produce, of 

 Norfolk white turnips, grown without manure, and with a 

 variety of artificial manures. The upper division shows the 

 produce without mineral manure, and the lower division the 

 mean produce of different mineral manures — namely (1), 

 superphosphate of lime (plot 5) ; (2) superphosphate and 

 potash salt (plot 6) ; (3) superphosphate, and potash, soda, 

 and magnesia salts (plot 4). 



The first point to notice is, that on some of the manured 

 plots there is an average of about 11 tons of roots, and more 

 than 4^ tons of leaves, giving of total produce per acre more 

 than 15£ tons. "Without manure," on the other hand, this 

 assumed "restorative crop" yields an average of only 1 ton 

 4 cwt. of roots, 17 cwt. of leaves, and a total produce of only 

 2 tons 1 cwt. The character of the unmanured root was, 

 moreover, totally different. It had more the shape of a carrot 

 than of a turnip. Its composition was also totally different 

 from that of the cultivated root, as is strikingly illustrated 

 by the following figures, which relate to the crops of the third 

 season of the experiments, 1845. 



Composi- 

 tion of roots 

 grown with 

 and with- 

 out man- 

 ures. 



Without manure 

 Farmyard manure . 

 Superphosphate of lime 



Roots 

 per acre. 



tons. cwt. 

 13| 



17 

 11 



Nitrogen 



per cent 



in dry matter. 



per cent. 

 3.31 

 1.56 

 1.52 



Effect of 



nitrogenous 



manure. 



Thus, under the influence of manure there is a very large 

 amount of non-nitrogenous substance accumulated, diluting, 

 so to speak, the high percentage of nitrogen of the natural, 

 uncultivated root. There is indeed also much more nitrogen 

 taken up by the cultivated plant ; but in it there is, in pro- 

 portion to the nitrogen, a large amount of other matters 

 formed, the accumulation of which converts the plant into an 

 important food-crop. Even mineral manures alone, especially 

 those which contain phosphates, have a very marked effect 

 in inducing such accumulation ; and it is pre-eminently by 

 the action of such manures that a great amount of fibrous 

 root is developed in the surface-soil, under the influence of 

 which more nitrogen, and at the same time more mineral 

 matters, are taken up. 



The results in the other columns of Table 3 (p. 21) show 

 that the addition of nitrogenous manure, whether as ammo- 



