168 SOILS AND FERTILIZERS 



rily hold for every soil. It will be noticed that there is con- 

 siderable discrepancy in these results, but that is always to 

 be expected. A fertilizer may have a more rapid rate of am- 

 monification or nitrification than another fertilizer in one 

 soil and less rapid in another soil. 



219. Relative values of organic and inorganic nitrogenous 

 fertilizers. — In the experiments cited the organic fertilizers 

 were, in every case, less effective than the inorganic ones. 

 However, the cost of a pound of nitrogen is generally more in 

 the better class of organic fertilizers, like dried blood, than it 

 is in the inorganic fertilizers, like nitrate of soda and sulfate 

 of ammonia. This may be because of the demand of fer- 

 tilizer manufacturers for a dry material for their goods, but 

 the beneficial effect of the organic matter it contains may 

 also be a factor in creating the demand for dried blood. 



QUESTIONS 



1. Name the forms in which nitrogen occurs in soils. 



2. State what forms of nitrogen are absorbed by crops, and what 

 differences exist between plants in this respect. 



3. Name the fertilizer materials that contain nitrogen, and spec- 

 ify the form in which nitrogen occurs in each. 



4. What crops are particularly benefited by nitrate fertilizers ? 



5. How is the nitrogen of nitrate and ammonia fertilizers likely 

 to be lost from soils, especially if no crop is on the land ? 



6. How may danger arising from formation of poisonous products 

 in the decomposition of cyanamid be avoided ? 



7. Describe the effects of nitrogen on plant growth. 



8. State the order of availability of nitrogen in nitrate of soda, 

 sulfate of ammonia and dried blood. 



LABORATORY EXERCISES 



Exercise I. — In Exercise V, Chapter I, an experiment designed 

 to show the importance of the plant-food materials to plant growth 

 was described. If this test has been properly conducted the influ- 

 ence of nitrogen upon plant growth will be clearly shown. 



