Lime and Calcium Compounds 147 



Do soils need lime? 



There are a number of ways to determine whether a 

 soil needs lime. It is known that lime leaches out of soils, 

 that crop production and decomposition of organic matter 

 increase acidity, and therefore the application of lime 

 becomes necessary in the course of time. For these reasons 

 the history of any field is an important guide. There is 

 a common weed sheep sorrel which in the absence 

 of cultivation and crowding thrives in acid soils, and it is 

 one of the best natural indications of the need of lime. 

 An attempt to raise red clover a crop decidedly respon- 

 sive to lime is a reliable method to determine the char- 

 acter of soil so far as lime is concerned if there is no serious 

 lack of potash which may have a similar effect. 



There are a number of chemical tests which are very 

 accurate but are not entirely satisfactory for the farmer's 

 use. The litmus paper test serves its purpose in the 

 laboratory, but it is not always reliable in the field. It 

 is based on the fact that blue litmus paper turns red 

 when placed in contact with acid, and red turns blue 

 when in contact with basic compounds such as lime. 

 Hence an acid soil will turn blue litmus red, and if such 

 is the case, the need of lime is indicated. When a 

 little finely pulverized soil fails to show any visible 

 effervescence when it is covered with dilute hydrochloric 

 acid, it is a good indication that the proportion of 

 carbonate of lime must be below what is desirable for the 

 healthy growth of vegetation, but this is not an infallible 

 rule nor a positive sign that the soil contained excessive 

 amounts of acid. Chemical tests of absolute depend- 

 ability may be made in properly equipped laboratories, 

 and it is well for farmers to obtain such tests. But the 



