126 SOIL CONDITIONS AND PLANT GROWTH 



phosphates are not usually needed because the soil conditions already 

 tend to promote good root development. Only small quantities of 

 manure must be added at the time, as the soil has little retentive 

 power. Above all, no very costly scheme of manuring should be 

 recommended till preliminary trials have shown its profitableness. 



A soil underlain at a short distance below the surface by a bed of 

 gravel, a layer of rock, or a "pan," is liable to be either parched or 

 waterlogged, and its water supply is usually so unsatisfactory that cul- 

 tivation is unprofitable. Under low rainfall the land becomes a steppe, 

 under rather higher rainfall a heath, but the vegetation is always xero- 

 phytic, consisting of heather, ragwort, broom, etc., the trees being birch 

 and conifers — the latter often planted in recent times. No method of 

 cultivating these soils has ever been devised, and most of them still 

 remain barren wastes, defying all attempts at reclamation. Two 

 special cases have, however, yielded to treatment: — 



1. When the layer of rock or the pan is only thin and is, in 

 turn, underlain by a rather fine-grained sand, its removal brings about 

 continuity in the soil mass and thus effects a great improvement in 

 the water supply. The soil now resembles the fertile sands, and should 

 be treated in the same way. A good example is afforded by Cox 

 Heath, Maidstone (p. 140). 



2. Where the gravel or rock is not too near the surface, systematic 

 green manuring with lupines and other crops fertilised by potassium 

 salts and calcium carbonate will often effect sufficient improvement to 

 make cultivation profitable. Examples are afforded by the Schultz- 

 Lupitz estate, Germany (255) and Dr. Edward's 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- 



