114 The Control of the Sod [pt. ii 



In both cases the organic matter added to the soil 

 comes largely from the air, being built up by the crop 

 under the influence of sunshine : in passing through the 

 animal some is used up but much is excreted. 



(3) A third method of adding organic matter to the 

 soil consists in ploughing in a leafy crop : this is known 

 as green manuring and may be adopted wherever live 

 stock are not available. It is a very old method, but has 

 come into considerable prominence since Schultz in 1880 

 enormously improved his estate of barren sand at Lupitz 

 at very small cost by growing lupins fertihsed with 

 potash, phosphates and lime and then ploughing them 

 in. The lupins, being leguminous plants, fixed nitrogen 

 from the air and thus increased the stock of nitrogenous 

 organic matter in the soil: indeed they acted like a 

 dressing of farmyard manure. Various modifications 

 have come into use: in this country mustard is some- 

 times used for the purpose and is found on the sandy 

 soil at Woburn to give better results than vetches, 

 although it is a non-leguminous crop: on the heavier 

 soil at Rothamsted, however, it gives poorer results: 



Yield of wheat, bushels per acre 



Green manuring has not been extensively adopted in 

 this country because farmers prefer to feed their crops 

 to stock and so get fat animals as well as manure. But 



1 J. A. Voelcker's experiments, Four years: 1906, 1908, 1910, 1912. 



2 Three years: 1907, 1910, 1912 



