126 Tlie Control of the Soil [pt. ii, ch. vi 



simply to be ploughed in. The supply of plant nutrients 

 is kept up by the addition of appropriate artificial 

 manures and by suppljdng imported foods to sheep on 

 the land and to cattle in the yards, when much of the 

 fertiUsing constituents are excreted and thus get on to 

 the land. 



Wherever the soil is not too wet or sticky the rotation 

 is so arranged as always to provide a crop that sheep can 

 eat. Part of the land is kept in permanent pasture and 

 thus becomes richer in nitrogenous organic matter. The 

 necessary mineral food is added in the form of phos- 

 phates and potassium salts. 



