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Collection: Directories and Documents > Pamphlets
Report on the Agriculture Experiment Stations of the University of California (PH 4-16)(1890) (211 pages)
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Page: of 211
164 UNIVERSITY OF CALIFORNIA.
of gardeners. In nature it is emphasized by the effects of the washingdown of the poor sandy soils of pine and “black-jack ” ridges upon the
heavy black prairie soils of the Southwestern States, where the “mahogany” soils so formed are in the highest repute for both productiveness,
‘“safeness,” and durability, and are invariably preferred to the black, heavy
prairie soils.
eee
Of course there must be a limit to the favorable effects of such dilution,
even if effected by means of sand, which renders the soil more readily
penetrable by roots. So soon as, instead, the dilution is brought about by
inert clay, the production of the soils falls pari passu with the dilution; a
fact of which, again, abundant natural evidence may be found in the Southwest, especially on tertiary territory.
But even in the case of dilution with sand, not only is there a necessary
limit beyond which plants cannot make up by greater spread of root for
the diminished amount of available plant food existing within a given
space; but it is also obvious, and abundantly exemplified in nature, that
this limit is materially influenced by the nature of the plant’s root system,
and especially by its ability to develop abundant root-hair cells. The
better provided it is in this latter regard, the greater will be its ability to
utilize plant food spread through an extended space in a diluted form.
Quantitative experiments on the limit of dilution for wheat will be made
at te station this season, with rich, heavy adobe of part of the station
grounds.
A material limiting cause in the premises is the nearness to the surface
of either the water table, or of hardpan difficult or impossible to penetrate
by the roots. It has repeatedly occurred in California that sandy soils of
low plant-food percentages that yielded heavy crops while the water was
at the depth of ten or twelve feet, ceased to produce so soon as, by increase
of irrigation in the neighborhood, the water rose within five feet or less of
the surface. Examination showed that the active root system has thus
been confined to less than half of the bulk of soil previously occupied by it
in these pervious soils. In clay soils, five feet would have been more than
sufficient depth for the same crops, as their roots would not go deeper in
any case. In the same region, calcareous hardpan lying at the same depth
has, like the water, caused production to languish after a few years; ut
when it was broken through, after the lapse of a year, vigor was restored.
It is then absolutely indispensable that both the physical character—as to
penetrability, absorptive power, ete.—of a soil should be known, as well as
its depths above bedrock, hardpan, or water, before a judgment of its quality,
productiveness, and durability can be formed from its chemical conor
But it is equally obvious that without a knowledge of the chemical composition, it is not possible to form such a judgment with “ connaissance de
cause.” Definite information on both classes of properties must be before
the agricultural expert; and it will be his own fault if from such data he
cannot “beat” the old farmerin judging of soils.
High and Low Percentages ; Adequacy and Inadequacy.—It need hardly
be reiterated that any estimate of what are high or low, adequate or inadequate amounts, as indicated by analysis, can be based only upon actual
comparative observation or expervment of plant growth in virgin soils.
may be objected even to this, that as we are unable to appreciate by the
balance small additions of effective fertilizers to an acre of soil (as ¢ J
that of a hundred pounds of sodic nitrate), the errors of observation will
obscure or obliterate differences actually occurring in natural soils. This
objection would be tenable if these errors bore alone upon the available por
tion of the important soil ingredients. As they bear upon the total amounts,