SOIL SESSION, 159 



soil. When the organic matter is deeply and abundantly distributed 

 throughout the root zone, it acts as parting planes between the soil par- 

 ticles which prevent them from running together during times when 

 the soil is long over-saturated with water. At the same time, when 

 shrinkage comes in times of drought, the finely divided and well dis- 

 tributed organic matter greatly favors the action of the surface films of 

 water in drawing the small particles of soil together into bunches. (Due 

 of the most important advantages of growing the grasses like bluegrass, 

 timothy and redtop in the rotation, is that, through their immense num- 

 ber of roots closely threaded in among the soil particles, they greatly 

 facilitate the bunching of the soil particles together. Such crops are 

 nruch more helpful in this way than are the clovers, whose great ser- 

 vice lies in their power to increase the nitrogen content of the soil. 

 The two types together, or in alteration, give the best and most enduring 

 effects. 



Winter weathering, naked summer following, fall plowing and 

 liming are other treatments which greatly influence soil structure. 



