188 PLOUGHING IN GREEN CROPS. 



Prof. Sprengel, of Germany, published in the year 

 1842 a number of valuable papers in the Garden- 

 ers' Chronicle upon green manuring, from which 

 we glean the following : 



" It is the operation of growing certain plants 

 merely for the purpose of ploughing them in as soon 

 as they have reached a certain maturity (namely, 

 are in blossom), which may be done either on the 

 spot or by conveying them to another field. This 

 is no modern discovery, for it was used even by the 

 E-omans, especially with the lupine. Although 

 this sort of manuring has been extolled by some 

 authors beyond all measure, it cannot be doubted 

 that it is a very advantageous operation, especially 

 on light land with a pervious subsoil. Its advan- 

 tages are that most of the plants grown for green 

 manuring obtain from the subsoil, by means of 

 their deep roots, those substances which are required 

 as food by shallow-rooted plants, and which are 

 thus brought back to the surface whence they were 

 previously removed by rain ; at the same time they 

 convey substances to the surface which it never 

 before possessed. These are the chief advantages 

 derived from ploughing in green crops, which, how- 

 ever, have not been hitherto properly appreciated. 

 Among the more useful substances thus brought 

 up from the subsoil are potash, soda, chlorine, sul- 

 phuric and phosphoric acids, magnesia, and lime. 

 The green crop, when ploughed in, enriches the 



