CONCLUSIONS 215 



crops fall off more slowly, and the cereals, especially the wheat, 

 maintain a fair production for a long period. 



2. The unmanured wheat and barley grown in rotation 

 continue to give much greater produce than they do on land 

 similarly unmanured but growing the same crops year after 

 year. This is, however, chiefly in virtue of the two fallowings 

 the land receives during the four-years' course, the unmanured 

 land losing about the same amount of plant food in the one 

 case as in the other. 



3. On the manured plots the yield of Swedes is determined 

 by both phosphatic and nitrogenous manure, chiefly by the 

 former; the yield of cereals is determined by the available 

 nitrogen in the soil. 



Leguminous crops like clover and beans are dependent on 

 the supply of minerals, particularly of potash, and are even 

 somewhat decreased by the presence of much nitrogen in the 

 soil. 



4. The inclusion of a clover crop in the rotation, besides 

 providing a crop of hay, leaves the land so much richer in 

 nitrogen that the succeeding wheat crop is greatly increased. 

 The good effect of the clover persists and may be traced through 

 all the crops of the rotation. With beans in place of the 

 clover, no beneficial effect is produced on the succeeding 

 crops. 



5. The effect of such residues as are left by an organic 

 manure like rape cake applied to the Swedes, or those left on 

 restoring the Swedes to the land, or the residues left by a 

 clover crop, is to be traced in the three following crops at 

 least. In the third crop they are, however, becoming small, 

 and even in the second year after the application of the 

 manure the effect of the residues becomes masked by any 

 new addition of nitrogenous manure, although they may still 

 remain and go to build up the " condition " of the soil. 



6. The losses of nitrogen to strong land farmed on the four- 

 course system are almost made up by the growth of a crop of 

 clover, and will be more than repaired by a dressing of 15 tons 



