THE LIFE AND GROWTH OF SEEDLINGS 25 



certain plants for certain soils is the fact underlying the rotation 

 of crops. In Norfolk, turnips are followed by barley, barley by 

 clover, and that by wheat. Clover requires a great deal of potash, 

 wheat very little ; on the other hand, clover requires a great deal 

 of lime, wheat hardly any. In some parts of Gloucestershire, the 

 regular rotation is wheat, oats, seed grass and clover, roots ; 

 in other parts of the same county it is slightly different, wheat 

 is followed by roots, these by barley or oats, and lastly comes 

 clover and seed grass. 



It has long been known, in fact since the time of Vergil, that 

 leguminous crops were good for the ground, but it is only of 

 late years that the reason of this has been ascertained. Experi- 

 ments have shown conclusively not only that the soil is richer 

 in nitrogen after a leguminous crop has been grown on it, 

 but that the effect is felt even the second year when a cereal is 

 planted. In his book The Soil, Mr. Hall gives the following 

 account of some striking results : " A piece of land which had 

 been cropped for five years by cereals, without any nitrogenous 

 manure, was divided into two portions in 1872, one being sown 

 with barley alone and the other with clover in the barley. In 

 1873, barley was again grown on the one portion, but clover in the 

 other, three cuttings of clover being obtained. Finally, on 1874, 

 barley was grown on both portions. The quantities of nitrogen 

 removed in the crops of 1873 and 1874 are shown in the table : 



" Nitrogen in crop Ibs. per acre. 



1873. Barley . . 37-3 

 Clover . . 151-3 



1874. Barley . . 39*1 

 Barley . . 69-4 



"Thus, the barley which followed the clover obtained 30-3 Ib. 

 more nitrogen than the barley following barley, though the 

 previous clover crop had removed 114 Ib. more nitrogen than the 

 first barley crop. An analysis of the soil was made in 1873, after 

 the clover and barley had been removed ; this showed down to 

 the depth of 9 inches an excess of nitrogen in the clover land, 

 despite the larger amount which had been removed/ ' 



It is clear from these experiments that leguminous plants 

 enrich the soil, owing to their being able to use the free nitrogen 

 of the air. During the last twenty years, this property of 



