396 



SOIL CONDITIONS AND PLANT GROWTH 



Artificial manures, 18, 19, 20. 



Ash constituents of plants ; composi- 

 tion of, 10. 



essential to growth, 10, 



14. 



functions of, 10. 



importance as manure (see 



also Mineral constitu- 

 ents), 2, 15, 16. 



Asparagine as plant nutrient, 57. 



Aspartic acid as plant nutrient, 57. 



Assimilation, effects of temperature on, 



35- 



Auximones, 236. 

 Availability of mineral nutrients, 234, 



245. 353- 

 Azotobacter. See Nitrogen fixation. 



activity in natural conditions, 200. 



effect of humus on, 199. 



test for soil acidity, 242. 



and clostridium, relative distribution 

 of, 204. 



BACTERIA as makers of plant food, 26, 

 175, 216. 



Bacterial activity and nitrate produc- 

 tion, 270 et seq. 



soil productiveness, 176, 216, 



260 et seq. 



numbers in soil, effect of external 



conditions on, 272, 275 et seq., 

 286. 



in field soils, 275 et seq., 292. 



in soil, 217, 262, 264 et seq., 276, 



292. 

 not clearly related to 



plant growth, 266. 



rapid fluctuations in, 270, 292. 



under different crops, 297. 



Bacteriotoxins in soils, supposed, 249. 



" Bake " land, 241. 



Barium salts, effect on plant growth, 



74- 

 Basicity in soils, harmful effect of lack 



of, 117. 



Black soils, properties of, 307, 310. 

 Bleisand, 163. 



Bones, fermentation of, 211. 

 Boron, harmful in large amounts, 78. 



helpful in small quantities, 56, 78. 

 Brownian movement of clay particles, 



105. 

 Buffer action, 115. 



CAESIUM salts and plant growth, 74. 

 Calcareous soils, 94, 303. 



characteristics of plant growth 



on, 304. 

 Calcicolous plants, 74, 304 et seq. 



Calcifuges, 74, 304 et seq. 



Calcium in plants : association with 



nitrogen, 74. 

 more in leaf than in seed, 74. 



carbonate, amount desirable in soil, 



119. 



effect in soil, flocculation, 117. 



neutralisation of acid, 



117. 

 other effects, 117, 119, 



329. 



on soil organisms, 273. 



plant, small quantities, 



239- 



excess, 86, 304. 



not always essential to fertility, 



118. 



production in soil, 296. 



rate of removal from soil, 119. 



compounds in soil, 121. 



oxide. See Lime. 



salts, effects on plant growth, 74, 



78. 

 soil organisms, 274. 



sulphate. See Gypsum. 

 Carbohydrates, absorbed and utilised 



by plants, 57. 



effect on ammonia production, 186. 



denitrification, 202, 209 et seq. 



nitrogen fixation, 198. 



soils, 201. * 



elaboration in plants affected by 



potassium salts, 70. 



transformation in plants affected by 



phosphates, 67. 

 Carbonates, amount in soil, 337. 



determination in soil, 335, 350. 

 Carbon cycle in soil, 175. 



nitrogen ratio in plant residues, 



.75. ^ 

 soil, 175, 273. 



dioxide, effects of variation on 



plant growth, 57. 



evolution in soil, 175, 177 ; rela- 

 tion to ammonia production, 

 185. 



inhibiting effects on germina- 

 tion, 85. 



in soil air, variations in, 227, 



277. 



necessary for plant growth, 10. 



percentage in soil atmosphere, 



227. 



toxic effect on root, 51. 



variations in atmosphere, 57. 

 source of, for plants, 10, 12, 56. 



Cardiganshire, damage done by lead 



mines, 85. 

 Carr, 134. 



