THE PEIKCIPLES OF MANUKING 197 



tution, and there is a general consensus of opinion that 

 this can be done most suitably and economically when 

 preparing the land for green crops. It sometimes hap- 

 pens, however, that the supply of farmyard manure is 

 too limited to allow of a dressing sufficient for all pur- 

 poses, and the deficiency has to be made up by the use 

 of artificial manures. In that case a certain quantity 

 of all three constituents should be given, but the pre- 

 dominant ingredient should be, for swedes and turnips, 

 phosphates, for mangolds, nitrate of soda, and for pota- 

 toes, potash manure. 



Leguminous Crops. The assimilative capacity of the 

 leguminous crops is greater than that of the roots, but 

 not so great as that of the cereals and grass. They con- 

 tain larger quantities of the fertilising ingredients than 

 the latter and stand more in need of special phosphatic 

 and potash manures, but they do not require the direct 

 application of the heavy dressings of farmyard manure 

 that are necessary for the green crops. Like turnips 

 and swedes, they contain a large quantity of nitrogen 

 and, also like them, they do not require very large 

 quantities of nitrogenous manures, but for a very differ- 

 ent reason. When the soil is in a suitable condition and 

 contains the necessary bacteria, the leguminous crops can 

 utilise the free nitrogen of the air (p. 143), and are, to that 

 extent, independent of nitrogenous compounds in the 

 soil either naturally present or applied in the form of 

 manures. They have, however, the power of absorbing 

 nitrogenous compounds like other crops, and if the soil 

 be not well supplied with available nitrogen, the appli- 

 cation of a small quantity of nitrogenous manure often 

 has a good effect. 



Garden Crops. The same general principles apply to 

 the manuring of garden as of farm crops, but there are 

 one or two points that deserve special consideration. 



