120 The Control of the Soil [pt. ii 



manures. Experiments on the best way of preparing the 

 bed are badly needed : there is great diversity of opinion 

 among good practical men on the subject. Numerous 

 manurial experiments have been made, however, and 

 have demonstrated the need of adding lime wherever 

 finger and toe {Plasmodiophora brassica) is common, of 

 supplying nitrogen compounds, phosphates, and on 

 light soils potash as well. 



The efifect of the clover or seeds mixture on the soil is 

 that it adds nitrogenous organic matter to the soil (p. 45). 

 Experiments have shown that crop residues of this sort 

 not only increase the soil fertility by the additional 

 nitrogen thus introduced, but they are particularly 

 valuable in reducing the harmful effects of bad weather 

 on the soil, and steadying the fluctuations of soil pro- 

 ductiveness produced by bad weather. This is well 

 illustrated by a comparison of the wheat crop taken 

 after clover (supplemented by artificial fertilisers) on 

 the Agdell Field at Rothamsted, with that on the 

 Broadbalk Field where no green crop is ever ploughed 

 in but where a liberal dressing of artificials is given. On 

 an average the Agdell plot gives a yield of 34| bushels 

 against 29| on Broadbalk, and it is a much steadier crop. 

 It has only twice fallen below 25 bushels, once in 1867 

 and again in that notorious year of disaster 1879, when 

 it fell as far down as 13| bushels. But the Broadbalk 

 plot which has never been green manured fluctuates to a 

 much greater extent; the yield has frequently dropped 

 below 25 bushels (Table TV). 



American experiments have led to substantially the 

 same results^. 



^ See Minnesota Bull. No. 125, 1912 : Ohio Circular, No. 131 : and experi- 

 ments in Iowa and Illinois quoted in Hosier and Gustafson, Soil Physics. 



