Maintain the Fertility oe Our Soils. 
5 
felspar must be altered and the potash brought into another form, 
or, in other words, it must be prepared for the use of the plant. In 
our virgin soils, this preparation had, to a certain extent, taken 
place, but this supply of prepared, available potash was quickly 
used up, and the magnificent crops of the first few years gave place 
to poor and unremunerative ones. 
The phosphoric acid in our soils is also furnished, certainly in 
a large measure, by the felspars. A sample of this mineral, just as 
it was broken from the granite of which it formed a part, con¬ 
tained more phosphoric acid than some of our soils. The amount 
was below the minimum considered necessary to a fertile soil, but 
was equal to or greater than the amount found to be present in six¬ 
teen out of fifty-five samples of soils representing the different 
counties of this state. 
The same facts pertain to this substance, regarding the extent 
to which it is prepared to be taken up by the plant, or, as it is gen¬ 
erally expressed, its availability, as to the potash. 
« 
OUR SOILS NOT RICH IN POTASH AND PHOSPHORIC ACID. 
The average Colorado soils, as represented by a considerable 
number of samples from almost as many portions of the state, are 
not very rich in these elements of plant food, potash and phosphoric 
acid; that is, the amount of potash taken up by dilute acids is very 
moderate indeed, while the total amount of phosphoric acid is com¬ 
paratively small, only about one-tenth of the samples analyzed show¬ 
ing two-tenths of one per cent, or more, and about one-third of 
them as much as one-tenth per cent, or more. This statement, un¬ 
like the one relative to potash, has reference to the total amount of 
phosphoric acid present, because dilute acids extract the whole of 
it from the soil. 
THE NITROGEN IN OUR SOILS. 
This element may be considered as having been furnished 
wholly by the agency of animals or plants. It is the most variable 
plant food in soils in general, depending, also, to a considerable de¬ 
gree, on conditions of climate, which are of less effect in the cases 
of potash and phosphoric acid. There are the same questions of 
availability regarding the nitrogen as regarding the other two 
plant foods mentioned. But assuming that a fairly productive soil 
contains about one-tenth per cent, of nitrogen, nearly all of our 
soils would measure up to this standard, but only a comparatively 
small number of them would have a considerable excess above this, 
less than one-third of the samples analyzed showing as much as 
two-tenths per cent, of nitrogen. 
The statements made in the preceding paragraphs pertain al¬ 
most exclusively to virgin soils. 
