4o6 



SOIL CONDITIONS AND PLANT GROWTH 



Water supply in soil, available for 

 • plants, 221 et seq. 



effect on bacterial activity, 



272, 276. 



numbers, 272, 



276, 286. 



movement of, 218 et seq. 



utilisation of food, 38. 



— the " principle " of vegetation, 3. 



— vapour, absorption by soil, 170. 

 Waxlike constituents of soil, 144. 

 Weathering of soil, 93, 99. 

 Weeds, checked by heavy crop, 55. 



Weeds, control by metallic salts, 85. 

 Wilting coefficient, 221. 



— phenomena of, 221. 



— point, 168, 221. 

 Woodland soils, nitrates in, 146. 



nitrification in, 146. 



nitrogen content, 55. 



Zeolites, reactions of, io5. 



— supposed presence in soil, 109. 

 Zinc salts, beneficial in small quantities, 



56, 85.. 

 harmful in larger amounts, 85. 



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