254 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



an excess of lime water has been used. If it does not become 

 pink, the soil is still acid. A number of tests are made, so as to 

 ascertain two quantities of lime water, with one of which the soil 

 is acid, by the other, made alkaline. This appears to be a good 

 method. 



Other Effects of Lime. We have already seen that lime is 

 necessary to plant life. Cereal grasses require from about Y\ to 

 YZ as much lime as potash, while leguminous plants take up as 

 much lime as potash, if not more. Lime is usually considered as 

 present in abundance in the soil, but it is quite possible that some 

 soils, especially sandy soils do not supply a sufficient quantity of 

 active lime for the use of certain leguminous plants. 



The following is a brief summary of the part which lime 

 (chiefly in the form of carbonate) plays in the soil 1 : 



1. It flocculates clay particles, making the soil more crumbly 

 and, with better tilth, more retentive of water and more easily 

 penetrated by rain. 



2. It aids growth of bacteria which convert organic nitrogen 

 to nitrates, those which assimilate nitrogen and other bacteria. 



3. It neutralizes acids and maintains the soil in an alkaline 

 condition, which is the condition most favorable to the majority 

 of cultivated plants. 



4. It makes a soil productive which contains relatively small 

 quantities of plant food. 



5. It counteracts the deleterious effect of an excess of magnesia 

 in the. soil. 



6. It liberates potash in the soil. 



7. It unites with phosphoric acid, preventing it from forming 

 less valuable phosphates of iron and alumina. 



An excess of carbonate of lime may prove injurious to some 

 plants, notably grape vines and citrus plants. From eight to 

 twenty per cent, of lime may have this effect. 



Carbonates of magnesia may, to a certain extent, act in the 

 same way as lime. We have already seen that it is well for lime 

 1 See Kellner, Landw. Versuchs-stat., 1896, p. 210. 



