INDEX 



Absolute specific gravity, of soil Air of soil, oxygen in, 146 



particles, 35. 



and "heavy" soil, 35. 



and "light" soil, 35. 

 Absorbed fertilizers, 100. 

 Absorption, of lime by soils, 188. 



of gases, test for, 111. 



selective, 99. 



selective, test for, 111. 

 Absorptive power of different crops, 



107. 

 Absorptive properties of soils, 99. 

 Acid phosphate, absorption by soil, 

 173. 



manufacture and composition, 172. 



vs. rock phosphate, 174. 

 Acid soils, described, 112. 



causes of, 113. 



crops adapted to, 116. 



crops injured by, 116. 



effect of drainage on, 113. 



effect of fertilizers on, 114. 



effect of green manures on, 115. 



effect of plant growth on, 114. 



litmus paper test for, 117. 



relation to bacteria, 129. 



tests for, 122, 123. 



Truog test, 118. 



weeds that nourish on, 115. 

 Adobe, composition of, 27. 



distribution of, 27. 

 iSColian soils, described, 26. 



adobe, 27. 



loess, 27. 

 Air of soil, composition, 145. 



control of movement, 148. 



control of volume, 148. 



demonstration of movement, 152. 



in relation to drainage, 79. 



movements, 144. 



nitrogen in, 147. 



quantities present, 143. 



relation to pore space, 143. 



relation to water, 144. 



usefulness of, 146. 

 Alkali and irrigation, 120. 



control of, 121. 



effect of crops on, 119. 



movements of, 118. 



removal of, 120. 



tolerance of different plants to, 

 119. 

 Alkali soils, nature of, 118. 

 Alluvial soils, character of, 23. 



described, 22. 



distribution of, 23. 



formation of, 22. 

 Ammonia, absorption by plants, 156. 



test for, in soil, 141. 

 Ammonification, 132. 

 Animals, effect on structure, 41. 

 Apatite, plant-food materials in, 7. 

 Apparent specific gravity, and 

 "heavy" soil, 38. 



and "light" soil, 38. 



of soil particles, 38. 

 Auger for sampling soil, 29. 

 Available plant-food materials, 94. 

 Availability, conditions that in- 

 fluence, 95. 



of nitrogenous fertilizers, 166. 



Bacteria, action on mineral matter, 



129. 

 ammonification caused by, 132. 

 conditions affecting growth, 128. 

 decomposition of nitrogenous 



organic matter, 131. 

 decomposition of non-nitrogenous 



organic matter, 130. 

 examination of nodules for, 142. 



249 



