26 SOILS OF THE TRUCKEE-CARSON IRRIGATION PROJECT. 
to produce toxic effects, and a lack of mineral plant food in the virgin 
soils is almost out of the question. 
Both soils are low in organic matter, as are all arid soils. Good 
soil management in other somewhat similar regions would indicate 
that the addition of organic matter to these soils in the form of barn- 
yard manure or green manure should produce beneficial physico- 
chemical effects, and such treatments have been applied somewhat 
extensively as a matter of experiment during the last two or three 
years. The poor soil apparently has not been benefited to a noticea- 
ble degree. The good soil has been somewhat improved, although 
even here the improvement has not been striking. A minute field 
examination of these good and poor spots a year or more after they 
had received applications of organic matter revealed a remarkable 
difference; all traces of the organic material had disappeared from 
the fertile spots, while the larger part of the manure added to the 
infertile spots was in an almost perfect state of preservation. Another 
peculiar difference was that in the poor spots, at depths of 6 to 28 
inches, an irregularly distributed, dark-colored, foul-smelling layer 
was found, undoubtedly due to the presence of a peculiar organic 
decomposition product, while such a layer was never found associated 
with good soil. It should not be inferred from this description that 
this black layer was found only where organic matter has been added 
as a treatment; it was quite generally distributed through these 
infertile soils and is presumably due to the decay of such material as 
was turned into the soil when it was first reclaimed, such as sagebrush, 
oreasewood, rabbit brush, and other desert plants, together with the 
roots of these plants which have been accumulating for long periods 
of time. Laboratory samples showed that this black substance was 
easily oxidized, for when a sample was taken to the laboratory, dried, 
and subsequently moistened for physiological experiments, all traces 
of the black color and peculiar odor disappeared. 
These unusual conditions of the decay of organic matter are neces- 
sarily somewhat closely associated with improper bacteriological 
conditions; that is, the improper utilization of organic fertilizers is 
due either to an improperly balanced or incomplete bacterial flora 
or to physical or chemical conditions preventing the performance of 
the normal activities of the bacteria present. 
Titrations of some of the aqueous extracts indicated that sodium 
carbonate (black alkali) was present in the poor soils but not in the 
good soils. It was also apparent that calcium sulphate and gypsum, 
when applied in large quantities, produced a decided effect in floc- 
culating the finely divided or colloidal clays. Samples were collected 
with a sterile spatula from the sides of freshly dug holes and placed 
in sterile containers.- Portions of these samples were inoculated into 
211 7 
