1 6 4 



SOIL CONDITIONS AND PLANT GROWTH 



this advantage of position stand in great need of lime even when cri 

 per cent, is present. As the amount of clay increases, the need for lime 

 becomes greater because flocculation is now wanted ; soils with 20 per 

 cent, or more of clay need two or three times as much lime as sandy 

 soils. It is impossible to fix limits that shall hold universally. Before 

 an analyst recommends lime or chalk on a sandy soil he should satisfy 

 himself that acid indicators like finger-and-toe, spurry, etc., are present, 

 and before he states that lime is not necessary on a clay he should be 

 quite sure that further additions would have no beneficial flocculating 

 effect. The following soils were known to respond to lime : 



Alumina. In general the alumina is approximately equal in amount 

 to one-third of the clay fraction, indicating that the acid treatment 

 breaks down some definite group of silicates associated mainly with 

 the clay fraction in the soil. The following examples may be quoted : 



Exceptions to the rule occur when much fine silt is present, the 

 alumina then being markedly less than one-third of the clay : 



1 The numbers are those used in Soils and Agriculture of Kent, Surrey, and Sussex 

 (Hall and Russell), 



