336 SOILS AND FERTILIZERS 



analysis and inspection of fertilizers necessary? 264. What are 

 the usual forms of nitrogen in commercial fertilizers? 265. Of 

 phosphoric acid and potash? 266. How is the value of a commer- 

 cial fertilizer determined? 267. What is gained by home mixing 

 of fertilizers? 268. What can be said about the importance of 

 tillage when fertilizers are used? 269. How are commercial fer- 

 tilizers sometimes injudiciously used? 270. How may field tests 

 be conducted to determine a deficiency in available nitrogen, phos- 

 phoric acid, or potash? 271. To determine a deficiency of two 

 elements? 272. How are the preliminary results verified? 273. 

 Why is it essential that field tests with fertilizers be made? 274. 

 Under what conditions does it pay to use commercial fertilizers? 

 275. What is the result when commercial fertilizers are used in 

 excessive amounts? 276. Under ordinary conditions, what special 

 help do the following crops require : wheat, barley, corn, potatoes, 

 mangels, turnips, clover, and timothy? 277. In what ways do 

 commercial fertilizers and farm manures differ? How do they com- 

 pare in crop-producing value ? 



CHAPTER XI 



278. Does the amount of fertility removed by crops indicate the 

 nature of the fertilizer required? In what ways are plant-ash 

 analyses valuable? 279. Explain the action of plants in rendering 

 their own food soluble. To what extent does the soil solution sup- 

 ply plant food ? 280. Why do crops differ as to their power of pro- 

 curing food? 281. Why is wheat grown on a clay soil less liable 

 to need potash than nitrogen? 282. What position should wheat 

 occupy in a rotation? 283. In what ways do wheat and barley 

 differ in feeding habits ? 284. What can be said regarding the food 

 requirements of oats? 285. Corn removes from the soil twice as 

 much nitrogen as a wheat crop, yet wheat usually thrives after 

 corn. Why? What help is corn most liable to need in the way 

 of food? 286. What is flax wilt? 287. What position should flax 

 occupy in a rotation? 288. On what soils does flax thrive best? 



