94 Effective Farming 



surface of a part of each one, and replace the parts of the ball. 

 Leave the paper in contact with the soil in the first ball for 

 five minutes, the second for ten minutes, the third for thirty 

 minutes, and the fourth for an hour. If the papers on 

 examination have turned red, the soil is acid and in need of 

 lime. Differences in the color of the papers will give an idea 

 of the extent of the acidity of the soil. 



Rendering plant-food available. Compounds of phosphorus 

 in the soil are rendered available as plant-food by the action 

 of lime. When soluble salts of phosphorus are applied to the 

 soil, they react chemically and form either dicalcium phosphate 

 or some such compound as phosphate of iron or phosphate of 

 aluminum. In the soils in which lime is plentiful, the first- 

 named compound is formed, and in soils lacking lime the other 

 compounds result. The dicalcium phosphate is more readily 

 soluble in the soil- water than the others ; consequently in a 

 soil not in need of lime, the phosphorus is more readily avail- 

 able than in one deficient in lime. 



Lime has a somewhat similar action on potash ; certain 

 reactions take place in soils in which lime is abundant and set 

 potassium free from compounds that remain unavailable as 

 plant-food in a soil deficient in lime. 



Nitrification is not active in sour soils, but it is so in neutral 

 soils. Thus when the acidity is reduced by an application of 

 lime, nitrification can take place, which means more available 

 nitrogen in the soil. 



Improving the physical condition of soil. Clay soils espe- 

 cially are improved. They become more crumbly and can be 

 made into good tilth more readily. Such soils often are hard 

 and full of cracks, causing loss of moisture, but when they are 

 plentifully supplied with lime, these conditions are not so likely 

 to arise. 



Lime as an aid for legumes. Alfalfa and red clover do not 

 make a good growth on sour soils. In fact it is usually impos- 

 sible to secure a stand if the soil is very acid. Many soils that 



