200 POWER AND THE PLOWi 



sticky, plastic quality when wet. The soil particles may 

 occur in a finely divided state, as in silt or clay soils, or in the 

 coarse state found in sandy or gravelly soils. Usually, and 

 especially in case of cultivated soils composed of finer particles, 

 the soil grains occur in clusters, or kernels. The varying sizes 

 of these kernels largely determine the physical characteristics, 

 or texture, of the soil. The larger the grains and kernels, the 

 more open and permeable the soil to the action of water and 

 air through the air spaces within it, and the lower the moisture- 

 holding capacity becomes, owing to the reduction of the total 

 surface. The optimum condition for plowing depends largely 

 on local conditions, including the nature of the soil. 



Where the soil particles are extremely minute, the soil 

 may contain a large percentage of water, yet yield a limited 

 amount for the use of plants, owing to the tenacity with which 

 the moisture clings to the soil grains. It is practically impos- 

 sible, except under extreme heat, to dry a soil entirely. In 

 fine-grained soils it is desirable that the soil kernels be of fair 

 size, both to increase the ease with which plants can secure 

 water and to render the soil more porous. If plowing is done 

 while the soil is too wet, these kernels are easily broken down, 

 and the soil grains will assume the closest possible arrangement, 

 making the movement of air, water and plant roots extremely 

 slow and difficult. A high content of lime in such a soil tends 

 to flocculate it i. e., collect it into kernels hence soils 

 naturally or artificially limed may be handled safely when 

 containing a fair amount of moisture. If such a soil is plowed 

 when too dry, the plow will shear it into thicker layers, and 

 coarser kernels will be formed. If very dry, the soil has prac- 

 tically no elasticity, and is merely broken into clods. In sandy 

 soils the tendency of soil grains to form clusters is very slight, 

 hence under any conditions there is little shearing action. 

 Sandy soils may be plowed at any convenient time, provided, 

 as sometimes occurs in the South, heavy rains do not follow 

 shortly afterward to cause the soil to run together and destroy 



