TILLAGE 231 



or the subsurface packer. The use of these implements closes any 

 large air spaces that exist in the soil that would tend to increase 

 either evaporation or percolation and hence renders the soil much 

 more retentive of moisture than it would he otherwise. 



(c) Organic Matter. The water holding capacity of the soil 

 may he largely increased through the addition of organic matter. 

 This constituent acts as a sponge, absorbing large quantities of 

 water which are held against the force of gravity. Capillary 

 movement is retarded, thus decreasing surface evaporation. 



(d) Deep Rooting Crops. The effect of deep rooting crops 

 is somewhat similar to deep plowing or subsoiling except that the 

 openings made by the roots become partly filled with organic 

 matter, which in itself is beneficial. The openings furnish a 

 passageway for water and air to greater depths than any practical 

 tillage could do, thus enlarging the water reservoir. The decay of 

 the organic matter produces a somewhat granular condition in the 

 deeper subsoil that aids in the absorption and retention of moisture. 

 Often the subsurface and subsoil become so compact that the water 

 is prevented from percolating through them to any great extent, 

 and this permits the surface stratum to become saturated and then 

 a large amount of run-off and evaporation must necessarily occur. 



Removing the Excess of Moisture by Tillage. The re- 

 moval of water by tillage is not often practiced and its applica- 

 tion is very limited. Yet if a few inches of surface soil con- 

 tains too much water this may be removed to some extent by 

 tillage, which encourages evaporation from the stirred soil, but 

 the greatest care is necessary. The soil may be plowed or culti- 

 vated and left somewhat rough, thus giving it a chance to dry 

 out. This may purmit seeding earlier than if left in its orig- 

 inal compact condition. In certain soils rolling may be of benefit 

 because of the effect it has in compacting the soil and facilitating 

 capillary movement of moisture to the surface where it is evapo- 

 rated. Frequent cultivation may also have a similar effect in 

 drying out the cultivated soil, since every cultivation will bring to 

 the surface moist soil that will become dry. and better conditions 

 for seeding may be produced in this way. This should not be 

 practiced with soils that are easily puddled, but may be advisable 

 for sandy soils or those having an abundance of organic matter. 



Decreasing Losses from Soils. Water is lost from soils 

 by percolation to depths below fhe capillary limit by drainage or 



