324 SOIL CONDITIONS AND PLANT GROWTH 



and vegetation relationships of the soil. Very full inquiries 

 must be made on the spot as to the agricultural value of the 

 land, the crops and manures most suitable, its behaviour 

 during drought and wet weather, and any special points to be 

 observed during cultivation. Information is also wanted 

 about the most troublesome weeds, the native vegetation, 

 hedgerow and other timber, etc., and note must be taken of 

 the position of the soil in regard to water supply, the nature 

 of the strata down to the permanent water table, etc. The 

 most reliable information is obtained only by properly con- 

 ducted manurial trials. 



It is usual to take the sample to a depth of 9 inches and 

 a lower sample to a depth of 18 inches, but if any marked 

 change occurs in the soil the sample should only be taken to 

 the point where it sets in. The subsoil sample does not char- 

 acterise the formation any better than the surface sample, but 

 it affords a useful check and helps in detecting abnormalities. 



The vegetation areas correspond with the geological forma- 

 tions only so long as the lithological characters remain con- 

 stant. Some formations are very uniform, e.g. the Folkestone 

 beds of the Lower Greensand, but, in general, certain changes 

 are observed. Where the formation has been laid down in an 

 estuary of no very great size, the coarser particles are deposited 

 near the old shore and the finer particles farther out, so that 

 a gradual change from finer to coarser soil is observed in 

 travelling along the formation, necessitating a soil division 

 into two or three vegetation areas ; the Hythe beds of the 

 Lower Greensand and the London clay afford illustrations. 

 Considerable trouble often arises when the formation consists 

 of a number of strata of sands and clays, and the outcrops are 

 so narrow that no one type persists over any large area. The 

 simplest method of procedure is to map out any uniform areas 

 that possess sufficient agricultural importance, and then group 

 the remaining less important soils simply into gravels, sands, 

 loams, and clays. In dealing with drift soils, it is well first to 

 map the uniform areas and then look out for lines of uniformity 

 and make up regions within which the agricultural character- 



