FERTILIZERS. 37 



apply potassium for hay crops, root crops and potatoes, as 

 these crops use very large amounts of this element. The 

 most common kinds of potassium fertilizers sold commer- 

 cially are some of the mineral potassium salts, such as kainit, 

 muriate of potash, which is a product refined from the mineral 

 potassium salts; and wood ashes. 



Calcium is generally quite abundant, but some soils have 

 very little in the form of carbonate, usually called lime. 

 The lack of sufficient lime is usually suspected, if clover and 

 alfalfa fail to grow well. Where there is insufficient lime 

 the soil is said to be sour or acid. This condition can not 

 be corrected by applying manure. Lime in some form must 

 be supplied. Quicklime (the form used for plastering), 

 finely ground limestone, slaked lime, or marl will accomplish 

 the desired result; that is, neutralize the acid in the soil. 



Testing for Acidity 



The most reliable test is the field plot test. If a shortage of lime 

 is suspected, alfalfa may be sown in a field. Divide it into three plots, 

 apply no lime on one plot, 1 ton of lime per acre to another plot, and 

 2 tons of lime per acre on a third. If the alfalfa does well on all three 

 plots, no lime is needed. If it does poorly on the no-lime plot, but 

 well on the other two, 1 ton of lime per acre is sufficient. If the crop 

 is better on the plot receiving the heavier treatment, the soil is quite 

 sour and needs the heavy application of lime. Men familiar with 

 soils and soil needs may test soil quite accurately in the field or labora- 

 tory and tell whether or not lime is needed. Blue litmus paper, if 

 placed in moist soil, will turn pink if acid is present. Some test, such 

 as the litmus paper test and muriatic acid test, are recommended, even 

 for those not experienced in soil testing. They give at best only an 

 indication and should be followed by field tests before much expense 

 is incurred in buying lime or in sowing alfalfa without applying lime. 



Acid prevents the growth of nitrogen-forming bacteria. 



When in doubt as to whether or not your soil needs lime it is best 

 to ask your county agent to test it or send a one-pound sample to your 

 Experiment Station. Such tests are made free of charge. 



Complete Fertilizers. — Many companies prepare fertil- 

 izers ready for use. These fertilizers usually contain cal- 

 cium, nitrogen, phosphorus, and potassium, also a consider- 

 able amount of other material called filler to make up the 

 bulk and weight. Such fertilizers are called complete fertil- 

 izers. It is seldom economical to use them, because it is 

 seldom necessary to apply them all, as the elements not 

 needed, if appUed, are wasted. The cheapest and most 



