334 SOILS AND FERTILIZERS 



pasture land ? 197. Is it economical to make a number of small 

 manure piles in a field ? Give reason. 198. At what rate per 

 acre may manure be used ? 199. To what crops is it not advisable 

 to add stable manure ? 200. How do a crop and the manure pro- 

 duced from that crop compare in manurial value ? 201. Why do 

 manures have such a lasting effect upon soils ? 202. Why does 

 manure from different farms vary so much in value and composi- 

 tion ? 203. In what ways may stable manures be beneficial ? 



CHAPTER VII 



204. What may be said regarding the importance of phosphorus 

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

 205. What is phosphoric acid and how much is removed in ordi- 

 nary 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. Name the four calcium phosphates and give their relative fer- 

 tilizer values. 210. Define reverted phosphoric acid. 211. Define 

 available phosphoric acid. 212. In what forms do phosphate 

 deposits occur ? 213. State the general composition of phosphate 

 rock. 214. Explain the process by which acid phosphates are made. 

 Give reactions. 215. How is the commercial value of phosphoric 

 acid determined ? 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 composi- 

 tion ? 219. What is dissolved bone ? 220. How is bone black 

 obtained, and what is its value as a fertilizer ? 221. How are 

 phosphate fertilizers 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. 

 What is potash and to what extent is it removed in farm crops ? 

 225. To what extent is potash present in soils ? 226. What are 



