loOcT.. 191-3] Rcliitioii of Lime to Soil Fertility. 621 



Mechanical Effect of Lime. 



When a clay deficient in lime is wetted it becomes sticky and swells 

 up somewhat after the manner of starch paste or glue. On drying it 

 becomes very hard. If lime, however, is added, the cla\ will not juiddle 

 well, and or. drying it crumbles. Fig. i shows an ordinary clay from 

 the Western Plains rubbed up with water. The photograph was taken 

 20 hours after the cylinders were .set up. No. i had nothing added to the 

 ■clay; the clay remains swollen up in the water, which is still muddy. 

 In No. 2 the addition of lime has caused coagulation (sometimes referred to 

 as flocculation) of the clay, which has then settled down as a fine powder. 

 No. 3 got neutral carbonate of lime, which is practically insoluble, and 

 'hence had no immediate action. Xo. 4 got gypsum, which, like lime, is 

 sufficiently soluble to act. Soluble lime compounds produce this coagulat- 

 ing effect on clay soils which then become more friable and porous, suffer 



1. Control blank. 2. With liuif. 3. Carbonate of lime. 4. With suliihate of lime. 

 FIG. I. COAGULATING EFFECT OF VARIOUS FORMS OF LIME. 



less from working wet, and shrink and cake less on drying. Gypsum has 

 not the other effects of lime in soils, but it has that of coagulating heavy 

 clay. Hot lime will generally be preferred on stiff clay to all others — ■ 

 to gypsum because it has basic character and can correct sourness, and 

 to ground limestone (carbonate) because the latter is slow to effect coagula- 

 tion. In time, however, carbonate will also coagulate clay, as it gradually 

 passes into solution as bicarbonate in the soil water. 



Where gypsum can be obtained cheaply, it will form a useful applica- 

 tion to heavy clay soils. 



When the drainage waters from a district, and the water puddles in 

 the fields remain long muddv. we have an indication of want of lime. 

 Clear puddles in a clay district show sufficient solnfc'.e lime compounds 

 to be present. The waters of the Lower Goulburn, for example, have 

 obviously drained from an area deficient in lime. 



