DRY-LAND AGRICULTURE 247 



the first week after a rain (>0 per cent occurred during the first 

 three days, hence the necessity for cultivation as soon as possible. 



(d) Subsurface Packing. Newly plowed soil contains many 

 large air spaces and is too open for retaining water against evapora- 

 tion. Subsurface packing is resorted to for closing these air spaces 

 and preventing excessive loss of water by evaporation. This is 

 accomplished in a variety of ways. Figure 107 shows the subsur- 

 face packer which is used for this purpose. The wedge-like wheels, 

 five inches apart, crowd the soil to both sides, thus compacting the 

 subsurface, but leaving a mulch on the surface. This implement 

 was invented by Mr. H. YV. Campbell, of Lincoln, Nebraska, one 

 of the pioneers in dry farming. 



Other methods are resorted to for compacting the subsurface, 



FlO. 107. Cuinpbi-11 Subsurface Packer. 



such as using the disk set straight. The ordinary smooth roller 

 would not be desirable for this purpose, because the compact ion 

 that it produces renews capillarity at the surface and would cause 

 a loss of moisture unless a mulch were again produced on the sur- 

 face. In fact, the smooth roller should never be used on a dry farm, 

 as the flat surface produced encourages the soil to blow. The cor- 

 rugated roller leaves the soil rough and this prevents or at least 

 greatly lessens blowing. The rolling should not be done parallel 

 to the direction of the prevailing winds, but at right angles to it. 



(e) Storing of Rainfall. A very important factor in dry farm- 

 ing is the storing of the rainfall of one year in the soil for the 

 use of the crop the coming season. The major part of the /.one 

 in which the water is stored should be sufficiently deep so that it is 

 beyond the depth of ready capillary movement to the surface and 



