280 SOILS AND FERTILIZERS 



as plant food? What function does it take in plant economy? 

 205. How much phosphoric acid is removed in ordinary farm 

 crops ? 206. To what extent is phosphoric acid present in soils ? 

 207. What are the sources of the soil's phosphoric acid? 208 What 

 are the commercial sources of phosphate fertilizers ? 209. Give 

 the four calcium phosphates and their relative fertilizer values. 

 210. Define reverted phosphoric acid. 211. Define available phos- 

 phoric acid. 212. In what forms do phosphate deposits occur? 

 213. State the general composition of phosphate rock. 214. Ex- 

 plain the process by which acid phosphates are made. Give re- 

 actions. 215. How is the commercial value of phosphoric acid de- 

 termined? 216. What is basic phosphate slag and what is its value 

 as a fertilizer? 217. What is guano? 218. How do raw bone 

 and steamed bone compare as to field value ? As to composition ? 

 219. What is dissolved bone? 220. How is bone-black obtained, 

 and what is its value as a fertilizer? 221. How are phosphate fer- 

 tilizers applied to soils? In what amounts? 222. How may the 

 phosphoric acid of the soil be kept in available condition ? 



CHAPTER VIII. 



223. What is the function in plant nutrition of potassium ? 224. 

 To what extent is potash removed in farm crops? 225. To what 

 extent is potash present in soils? 226. What are the sources of 

 the soil's potash? 227. What are the various sources of the potash 

 used for fertilizers ? 228. What are the Stassfurt salts, and how 

 are they supposed to have been formed ? 229. What is kainit ? 

 230. How much potash is there in hard-wood ashes? 231. In 

 what ways do ashes act on soils? 232. How do unleached ashes 

 differ from leached ashes? 233. What is meant by the alkalimetry 

 of an ash ? 234. Of what value, as fertilizer, are hard- and soft- 

 coal ashes? 235. What is the fertilizer value of the ashes from 

 tobacco stems? 236. Cottonseed hulls? 237. Peat-bog ashes? 

 238. Saw-mill ashes ? 239. Lime-kiln ashes? 240. How is the 

 commercial value of potash determined? 241. How are potash 

 fertilizers used? 242. Why is it sometimes necessary to use a lime 

 fertilizer in connection with a potash fertilizer? 



CHAPTER IX. 



243. What can be said regarding the importance of lime as a 

 plant food? 244. To what extent is lime removed in crops? 245. 

 To what extent do soils contain lime ? 246. What are the lime fer- 

 tilizers? 247. Explain the physical action of lime fertilizers. 248. 

 Explain the action of lime on heavy clays. 249. On sandy soils. 

 250. In what ways, chemically, do lime fertilizers act? 251. How 

 may lime aid in liberating potash? 252. What is marl? 253. How 



