56 Elementary Principles of Agriculture 



dust may have as much as 10 per cent of water. When 

 wet, clays become sticky and impervious to water and 

 air, and, of course, root growth cannot take place when 

 the soil is in this condition. If kneaded or puddled by 

 working at this time, it does not crumble on drying. 

 Clay particles have a tendency to cling together in small 

 lumps, or floccules, especially if lime is present. This 

 makes them more open and porous, and lightens the 

 draft in plowing. Water evaporates slowly from clay 

 soils.* 



90. Calcareous, or Limy Soils. Many fertile soils 

 contain large quantities of crumbled limestone (car- 

 bonate of calcium). The presence of lime in a soil may 

 be easily detected by the effervescence (giving off of 

 gas) when treated with acids. Strong vinegar will 

 answer. Try it on some lumps of soil. Finely pul- 

 verized limestone has physical properties similar to 

 clay. Lime tends to improve clay soils by making 

 them more granular and porous. Lime also acts bene- 

 ficially on sandy soils by increasing their water-hold- 

 ing power. The fertile black lands of Texas contain 

 from 5 to 40 per cent of carbonate of lime. Soils low 

 in lime often become sour or acid, (^ 141). 



90a. Effect of Lime on Clay Soils. Take about three pounds of 

 stiff clay soil and work into a soft plastic mass by wetting and 

 kneading. Divide into three equal parts. Round one into a ball 

 and put on a board. Work the second up with an equal volume of 

 air-slaked lime, and the third with half as much air-slaked lime. 

 Put all three on a board and let dry. Describe the results. What 

 is the effect of the lime on clay soils? 



90b. Effect of Lime on Clay Particles. Clay settles slowly in water. 

 The particles are so fine that they float in water like dust in the air. 

 Rub up some clay in water until the water is turbid. Pour a little 



*Are the clay soils of your community classed as drought-resistant soils? 



