Tilth and Tillage of the Soil 



1759 



diagrams in Fig. 91. In the following table is given the proportion of 

 pore space in some common classes 'of soil : 



TABLE 2. Pore Space in Soil 



Kind of soil 



Proportion of pore space 



Percentage 



Parts by- 

 volume 



Clean beach sand 



Sandy loam. Good tilth. . 

 Sandy loam. Puddled. . . . 



Silt. Good tilth 



Clay. Good granular tilth 

 Clay. Puddled 



35 to 40 

 40 to 50 

 20 to 40 

 45 to 55 

 50 to 65 

 25 to 45 



1/3 to 2/5 

 2/5 to 1/2 

 i/5 to 2/5 

 3/7 to 5/9 

 1/2 to 2/3 

 1/4 to 2/5 



The average size of the pores is much more important than their total 

 volume, although the latter is important. In general it may be remembered 

 that one half of the volume of soil is pore space. 



SAND 



LOAM 



r CL^y ^ 



GRANULATED PUDDLED 



20Z 



30Z 



50% 



A/8 v 



'--.--WATER. 



L/fVAW/LABl F 



: --/so/l W& 





Fig. 91. — Diagrams representing the proportion of space occupied by soil material, 

 water, and air in a section of different soils. The availability of the soil water and 

 the presence of sufficient air are dependent on the right physical condition of the soil 



The soils of the extremes of texture, as clay, sand, and gravel, and con- 

 sequently of the extremes in sizes of pores, arc adapted to special crops. 

 The soils of intermediate fineness, and therefore of intermediate size of 

 pores, are suited to a wide variety of crops and types of farming. They 

 are used for mixed farming and usually command the highest prices as 

 farm lands. These types include silt, loam, and the different grades of 

 medium and heavy sandy loam. A certain amount of granular structure 

 should be maintained in these latter soils, for they may develop a bad 



