146 SOIL CONDITIONS AND PLANT GROWTH 



winter feeding of sheep on the land is a common way of fertilising, but 

 crops must be sown early, or the fertilising material is washed out 

 unused, and the young roots have no time to strike into the subsoil 

 before the surface layer dries out. High farming is the only profitable 

 way of dealing with these soils ; any carelessness in cultivation lets in 

 hosts of weeds, such as poppies, knot-weed (Polygonum aviculare), spur- 

 rey (Spergula arvensis), sorrel, horsetail, convolvulus, creeping butter- 

 cup, and others. Crops should follow each other in rapid succession, 

 any interval being a period of loss ; under good management two or 

 even three market-garden crops can be secured in the year, while 

 in purely farming districts catch crops should always be taken. 

 Organic manures are very necessary to increase the water-holding 

 capacity : sheep-folding or green-manuring are, therefore, very desirable. 

 Calcium carbonate is often needed and is better applied as ground 

 chalk or limestone than as lime. Potassium salts are beneficial and 

 may be added as kainit ; nitrates often give remarkable results, but 

 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. 161). 



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- 



