34 DRY FARMIISTG IN THE GREAT BASIN. 



reckoned as produce over the whole area, half in crop and half fallow, the whole 

 acre grows much less both of grain and straw than where the crop is grown 

 year after year on the same land. 



An analysis of the results from alternately fallowed plats, how- 

 ever, shows the real benefits of fallowing. Both the seasonal rain- 

 fall and the amount of leaching from the land were measured for a 

 series of years, and when the years of light rainfall and consequent^ 

 diminished leaching are grouped together and contrasted with the 

 years of heav}^ rainfall and increased leaching, it is seen that the 

 yields following the drier season were high as compared with the 

 others. Thus, for the years when the rainfall for the four months, 

 September to December, inclusive, averaged 8.88 inches and the per- 

 colation was only 4 inches, the yield after the fallow was 2,743 pounds, 

 as against 1,810 pounds on the continuous wheat plat, a gain of 933 

 pounds, or 52 per cent. For the group of years when the rainfall 

 averaged 13.66 inches during the same four months and the percola- 

 tion was 8.92 inches, the wheat after fallow yielded 1,757 pounds, 

 against 1,627 on the continuous wheat plat, a gain of 130 pounds, or 

 only 8 per cent. In other words, as a result of the decreased percola- 

 tion more of the nitrates were left in the soil. 



It seems probable from these results that with conditions such as 

 exist on the dry lands of the Great Basin, where there is practically 

 no loss by percolation, the products of nitrification during a fallow 

 year would be quite sufficient to overcome any tendency toward the 

 exhaustion of these soils. 



THE FIXATION OF NITROGEN. 



The bacterial action by which the complex proteids of the organic 

 matter in the soil are converted into nitrates or other forms of nitro- 

 gen is but one of the several sources of the nitrate supply of soils. 

 It is well known that bacteria living in the roots of some leguminous 

 plants are able to combine atmospheric nitrogen into available forms, 

 and it has been discovered more recently that practically all culti- 

 vated soils contain bacteria which are able to combine atmospheric 

 nitrogen and make it available to plants, drawing their energy mean- 

 while from the carbohydrate material of the soil humus." 



There are many indications that the sustained productiveness of 

 the dry-farmed soils of the Great Basin is due, in part at least, to 

 the activities of this latter group of nitrogen-fixing bacteria. The 

 same conditions that favor the action of the nitrifying or humus- 

 reducing organisms also favor the action of the nitrogen-fixing bac- 

 teria, viz, a supply of carbohydrate material as furnished by disin- 



o Hall, A. D. Science, N. S., 22 : 453, 1905. 

 103 



