INTRODUCTION TO FIELD EXPERIMENTS WITH 



FERTILIZERS. 



A difficult problem. — Some of the questions most frequently 

 asked by farmers are these : What fertilizer shall 1 use on my 

 land ? How can I tell just what combination or mixture of plant- 

 foods is best adapted to my soils ? What is the best all round fer- 

 tilizer ? Such questions are among the hardest that can be asked 

 in the whole field of agriculture. They cannot be answered off- 

 hand in a day or a week ; it may take months and in some cases 

 years to answer them. Many a farmer spends his whole life on the 

 farm without even trying to solve these problems, or without getting 

 correct answers if he does try to solve them. 



What regrulates crop production. — A farmer grows an acre of 

 corn and harvests a modest crop of 10 bushels. What is the cause 

 of this very poor yield ? Something must be wrong and it is for 

 him to try and find out wherein the trouble lies. The poor yield 

 may be due to one or more of several conditions. It may be lack 

 of moisture, or too much moisture ; the soil may be too acid ; it 

 may be deficient in either nitrogen, phosphoric acid or potash ; it 

 may be too cold and heavy ; it may not contain enough nitrifying 

 organisms to maintain a good supply of nitrates, or it may contain 

 too many denitrifying organisms which destroy nitrates ; it may be 

 too compact and therefore may not leave enough air spaces between 

 the soil particles ; capillary action may be imperfect ; there may be 

 lack of humus ; the texture may not be suitable to the crop grown ; 

 and so on. 



The law of the minimum. — This is most important with refer- 

 ence to plant growth. It means that the one essential condition which 

 is at a minimum, or is at the lowest grade, during the growth of a crop, 

 is the one condition that regulates the amount of crop grown. 



For example, a field may have all the essential conditions favor- 

 able for producing a large crop, except one. Let that one be a lack 



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