IX.] CATCH CROPS 275 



than to plough them in, and though the greater part of 

 the humus is thus lost to the land, there is still a con- 

 siderable gain, while the essential manurial substances — 

 nitrogen, phosphoric acid, and potash — are almost 

 wholly returned to the soil. Where the land is light 

 enough to be improved by the treading of sheep and 

 the rainfall admits of catch-cropping, there is no better 

 way of building up a fertile soil than by folding ; the 

 actual enrichment of the soil can be effected either by 

 manuring for the catch crops with inorganic fertilisers 

 like superphosphate and nitrate of soda or by consuming 

 cake and corn with them. The losses inherent in making 

 dung are thus obviated, for when the urine falls directly 

 on the land, no evaporation of ammonia is allowed to 

 take place ; no labour is required ; the tilth of the land 

 is improved by the humus and the trampling of the 

 sheep ; no more effective nor cheaper system of growing 

 corn can be devised than to alternate it with green crops 

 consumed on the land, as is practised with so much 

 success on the brick earths of West Sussex and the 

 chalky loams of Wiltshire. 



