PREFACE 



There is at present need for a text on general agricultural 

 chemistry which will cover the field briefly, in a Logical 



manner, giving only the facts, and not consisting of a dis- 

 connected series of quotations and tables from the very 

 extended literature of the subject. The need for such a 

 text has been particularly marked in teaching large classes 

 of students at The Pennsylvania State College. As a con- 

 sequence the present book has been written. While it is 

 intended primarily for students who have had previous 

 training in Botany, Chemistry, Geology and Physics, it is 

 sufficiently elementary to make it of value to any intelligent 

 person. 



Concerning some of the statements made in the text it 

 is well known that a difference of opinion exists among 

 authorities, but it is deemed better to present them as facts 

 rather than to give the various arguments or to omit them 

 altogether. 



Since the raising of crop plants is the fundamental business 

 of agriculture, and since on them depend the life and growth 

 of animals, there is discussed first the plant, its .germination, 

 growth, and products. Then are taken up the various 

 conditions necessary for plant growth, such as the atmos- 

 phere, soil, fertilizers, and spray materials. A short chapter 

 on the gas engine is inserted at this point, since the increasing 

 use of power on the farm in the raising and marketing of 



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