Emil Truog 53 



better soil tests and more satisfactory interpretation of the results thus 

 obtained. Today, soil testing is carried forth on a vast scale in many 

 states and countries. In Wisconsin during the present year, several 

 hundred thousand soil samples will be tested for pH, readily available 

 phosphorus and potassium, and in some cases for available boron and 

 other nutrient elements. 



The determination of the pH of soils is now both simple and ac- 

 curate. The result tells immediately whether or not it is advisable to 

 add lime for the most satisfactory growth of various crops. It also tells 

 when a soil is so highly alkaline that special treatment is needed to 

 counteract the condition. 



Recognition that three categories of availability of each plant nutrient 

 should be considered and that transformation from one category to 

 another takes place is of tremendous help in the interpretation of re- 

 sults of soil tests for potassium. For example, in the case of this ele- 

 ment, it is now quite generally recognized that for the satisfactory 

 production of general farm crops, a minimum level of 200 pounds per 

 acre-plow-layer of readily available (category A) potassium should be 

 present. However, if this drops, say to 100 pounds through cropping, 

 it is a much more serious matter in a strongly podzolized soil of north- 

 ern Wisconsin than in a mildly podzolized soil of similar texture in 

 southern Wisconsin, because in the former there will be much less 

 category B potassium present which will change to the A category 

 with crop feeding. Also, if it is desired to raise the level of category A 

 potassium to 200 pounds in both cases, it will take considerably more 

 potash fertilizer in the strongly podzolized soil because of more rapid 

 and greater transformation to the naturally depleted B category. 



Although interpretation of results of soil tests for the other nutrient 

 elements may vary considerably from that for potassium, nevertheless, 

 as it now appears, the general pattern should be quite similar. To be 

 sure, much more research is needed in connection with methods of 

 determining the amounts and forms of the various nutrient elements 

 present in soils in the three availability categories. With the knowledge 

 and special analytical instruments now at hand and being developed, 

 further progress in this field is certain to be rapid. Thus, soil fertiliza- 

 tion and management to the end that soils be made still better mediums 



