SOIL CONDITIONS AFFECTING PLANT GROWTH 45 



by von Seelhorst (2 57*^), and by Pfeiffer, Blanck, and Friske 

 (2244 



In soil, other and indirect factors come into play ; too much 

 water causes the exclusion of air ; certain reduction products 

 are then formed by bacteria which have a direct toxic effect 

 on the plant. 



These relationships are constantly recurring in field obser- 

 vations. On moist soils — clays and loams — the plants usually 

 have large wide leaves and grow to a considerable size, whilst 

 on the drier sands the vegetation is narrow leaved and more 

 stunted, but the root system is well developed.^ A copious 

 water supply leads to a more protracted growth and to a re- 

 tardation of the ripening processes ; indeed, in very wet dis- 

 tricts, wheat and barley are grown only with difficulty, if at all, 

 because ripening may be so long delayed that frosts supervene 

 and damage the crop. Oats are less affected, as they are 

 usually cut before they are ripe. 



Water supply and temperature are the two chief factors 

 determining the distribution of crops. In the warm, dry, 

 eastern counties of Great Britain crops are grown for seed ; 

 great quantities of wheat and barley are grown in Norfolk, 

 Suffolk, and the Isle of Thanet ; mangold seed and turnip 

 seed is produced in East Kent. Wetter districts are more 

 favourable for swedes and oats ; very wet districts for grass. 

 The warm, moist, south-west of Cornwall is very favourable 

 for early vegetables, cabbage, cauliflower, etc., whilst the cooler 

 Lincolnshire and Cheshire are well suited to potatoes. It is 

 possible by suitable operations to modify somewhat both the 

 temperature and the water content of the soil, and so to make 



Footnote continued from opposite page — 



Irrigation. Protein per cent. 



25 ins. 16*23 



15 „ I2'92 



No irrigation. 13 "62 



For the small effect of soil conditions see Washington Ag. Expt. Sta. Bull., 

 Ill, and A. D. Hall, Journ. Bd. Agric, 1904, 2, 321. Sodium hydrate and 

 magnesium oxide affect the composition (pp. 73, 75). 



1 See p. 310 et seq. 



