32 DRY FARMING IN THE GREAT BASIN. 



the binder and where a large amount of straw is plowed under and 

 incorporated with the soil, there is probably no reduction of the 

 humus content ; in fact, there might even be an increase of the humus 

 imder this practice, for the soils in their native condition bear but 

 scanty vegetation, which probably adds organic matter to the soil 

 very slowh^ 



With this large amount of wheat straw plowed under in the autumn 

 and allowed to lie over the next winter, followed by continued surface 

 tillage, conditions appear to be xerj favorable to the growth of any 

 bacteria that might aid the conversion of this straw into available 

 plant food. In fact, the conditions under which this surface mulch 

 is maintained seem to be particularly favorable for the activities of 

 nitrifying and other soil-enriching bacteria. It is well known that 

 there are bacteria that under favorable conditions work on the com- 

 plex proteids in the organic matter of the soil and change them into 

 available plant food in the form of nitrates. In addition to these so- 

 called nitrifj'ing organisms, there are known to be other forms of 

 bacteria that while living chiefly on the decaying nonnitrogenous 

 organic matter of the soil are able to utilize and fix atmospheric 

 nitrogren in much the same wav as do .those bacteria that live and 

 develop nodules on the roots of some leguminous plants. 



THE HEAVT SOILS NOT LEACHED.' 



The heavier soils such as have 'been found best suited to dry farm- 

 ing in the Great Basin have such a high water-holding capacity that 

 with the ordinary light rainfall of the region there is no cumulative 

 downward movement of water through them. In other words, the 

 rain water that enters these soils is held by caj)illary force against the 

 force of gravity, and instead of moving downward to join an under- 

 ground water table, it is returned to the air either by direct evapora- 

 tion from the soil surface or by transpiration processes through plants. 

 This is, of course, not true for any but the deeper and heavier soils. 

 Soils that occur as thin layers over impervious material, or those with 

 so coarse a texture as to have a very low water-holding capacity, can 

 not act as effective storage reservoirs. This fact again indicates the 

 desirability of heavy soils for dry farming. 



The importance of the fact that some of these dry-farmed soils are 

 not leached by the rain water becomes apparent when it is realized 

 that the soluble salts that result from the ordinary processes of soil 

 weathering and from the activity of various organisms are not 

 washed out of the soil, but remain to be used by plants. The prover- 

 bial richness of so-called arid soils, as well as the occurrence of 

 alkali in soils of dry regions, is due to the fact that such soils are not 

 leached bv the rain. 



103 



