82 SOIL IMPROVEMENT 



from the soil particles. It therefore follows that as the 

 supply of organic matter becomes less the number of 

 beneficial bacteria decreases and less plant food is made 

 available. Soils deficient in organic matter hold less 

 moisture than those well supplied with humus. Humus, 

 or organic matter, is spongy in nature and when incor- 

 porated in the earth holds the soil grains apart, giving 

 large openings into the soil for water to enter, and at the 

 same time the spongy nature of the organic matter holds 

 the water within the soil after it has entered. It is esti- 

 mated that ioo pounds of sand will hold approximately 

 22 pounds of water, and ioo pounds of clay about 55 

 pounds of water, but 100 pounds of humus will hold 143 

 pounds of water. It is therefore evident that the more 

 humus a soil contains the greater its water holding 

 capacity. 



The organic matter or humus must be supplied either 

 by plowing under leguminous crops and straw and corn- 

 stalks or by using for feed and bedding all the crops 

 grown on the farm and returning the manure to the land 

 with the least loss possible. 



A rotation suggested is corn with one-half the field 

 seeded to a legume such as sweet clover or alfalfa, fol- 

 lowed the second season with barley or oats, with one- 

 half the land in cowpeas or soy beans where the winter 

 catch crop has been plowed under; third year, wheat or 

 rye, in which clover or meadow grass has been sown; 

 fourth year, clover, or clover and timothy; fifth year, 

 wheat and clover, or timothy and clover; sixth year, 

 clover or mixed grass crop. In succeeding chapters 

 other combinations suitable to mixed farming are set 

 forth. 



In grain farming most of the coarse products should be 

 returned to the soil and occasionally a crop of clover 

 clipped and left on the ground. To avoid clover sickness 

 it may sometimes be necessary to sow red clover or alsike 



