THE SOIL IN RELATION TO PLANT GROWTH 147 



Lupitz estate, Germany (255) and Dr. Edwards' experiments at Capel 

 St. Andrews, Suffolk. On such land an industrious cultivator may 

 make a living but not a fortune. 



Under favourable conditions recourse may be had to dressings of 

 clay (as in Lincolnshire) or to warping (in the Fens). 



Barren conditions also result when, by reason of a thin parting of 

 clay or its low situation, water cannot run away but accumulates and 

 forms a marsh. Reclamation in such cases is possible as soon as a 

 way out has been found for the water. 



Loams. As the proportion of fine material in the soil increases and 

 that of coarse material falls off, a gradual change in the character of 

 the soil sets in, till finally, but without any sharp transition, a new type 

 is reached known as a loam. The increase of fine material somewhat 

 retards the movements both of air and of water, so that loams are char- 

 acterised by a more uniform water content throughout the mass than 

 sands. On the other hand loams show less tendency to become water- 

 logged or to allow plants to become parched in very dry weather than 

 clays. The soil decompositions proceed normally, rapidly producing 

 plant food, with little tendency to "sour" 1 or other abnormal con- 

 ditions so long as sufficient calcium carbonate is present. In con- 

 sequence most plants will grow on loams, even some of those supposed 

 to be specially associated with some other soil type. Thus, where a 

 chalk and a loam soil meet, it is not uncommon to find the chalk plants, 

 e.g. traveller's joy (Clematis Vitalbd] y guelder rose, etc., wandering on 

 to the loam and it is much more difficult to find the line of separation 

 of the soils than where the chalk abuts on to a sand or a clay. For 

 the same reason loams allow of very wide choice in the systems of 

 husbandry, and, as they become very fertile under good management, 

 they are usually in this country all cultivated. Closer observation 

 over a limited area shows, however, that a given class of loam is 

 more suited to one crop than to another; the ecologist recognises 

 differences in the sub-associations or facies, and the practical man 

 will distinguish between a potato soil, ,a barley soil, a wheat soil, 

 etc. ; distinctions due no doubt to water and air relationships, and 

 arising from differences in the compound particles. Unfortunately no 

 method of investigating the compound particles has yet been devised, 

 and a study of the ultimate particles by a mechanical analysis is alone 

 possible. But even though the differences are thus attenuated they 

 can still be traced, as shown by the analyses in Table LIX. of soils in 

 Kent, Surrey, and Sussex, known to be well suited to the parti- 

 cular crops. 



1 See p. 63 



