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Title: Report on the Agriculture Experiment Stations of the University of California (PH 4-16)(1890) Collection Type: Directories and Documents Collection Name: Pamphlets Catalog #: PH 4-16 Author: E.W. Hillgard Published: 1890 # of Pages: 211 Download PDF: User Login Required Download OCR Text: User Login Required

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Original Held At: Searls Historical Library Location: 161 Nevada City Hwy, Nevada City, CA 95959

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170 UNIVERSITY OF CALIFORNIA. and severely from lack of drainage than similar soils of low iron percentage. Ean par —This item in the analysis conveys little information as to the character of a soil, because only asmall partof the clay present is usually dissolved by the digestion as practiced in this laboratory. Together with the “soluble silica,” however, the figure for alumina often shows very strikingly the degree of decomposition to which the soil has been subject, especially (as noted above) in the presence of much lime. It also serves, sometimes, to indicate the copious presence of aluminic hydrate in some form, when its proportion to the soluble silica admits of no other combination. In such cases, moreover, the loss by ignition is always unusually heavy. When the figure for alumina is very small (2 per cent or less), the indication is that the soil is a very sandy one, of very low hygroscopic power. ; Phosphoric Acid—The conviction that has gradually established itself that the practical values of the several calcic phosphates are not nearly as different as was at first assumed, has materially increased the interest of phosphoric acid determinations in soils, particularly when these are strongly calcareous, and, therefore, according to the well known play of affinities, most of the phosphoric acid present will be in the form of tri-calcic phosphate. There is a good reason why less phosphoric acid in a soil will suffice in soils rich in lime, than in those in which there is no base ready to dispute the possession of the acid with ferric oxide and alumina, which render it relatively insoluble and'inert. The very minute amount of phosphates present in the best of soils will render the search of the roots for them very laborious, unless it can be conveyed to them in solution, independently of the acids the roots may exude. From the discussion of the upland loam soils of the Southwestern States, I have been led to consider 03. per cent of P,O, as the least amount that can be considered adequate for profitable production in their case, and that the percentage should rise to .10 per cent to be satisfactory. Butin calcareous, and also in very sandy soils of great depth, less seems a good supply even there, and in California (where nearly all soils are calcareous) the percentage does not very often exceed .10 per cent, even in soils of great present productiveness and durability. The same is true of a good many productive bottom soils of the Southwest, which, however, are always of the calcareous class. Phosphoric acid percentages above .20 occur more rarely in California than in the Southwest; but in the arid region of Texas, and in the basaltic soils of Oregon, Washington, and Montana, .30 per cent and over is not uncommon. In the latter cases the occurrence of apatite crystals in the mother rocks is easily observable, and while such crystals scattered in the soil may be somewhat refractory in dissolution, yet the mechanical and chemical processes of soil formation must have supplied an abundance of finely pulverized mineral (“floats”) available for the use of vegetation. These basaltic soils produce extraordinary crops of grain within a very short growing season. It will be interesting to observe how soon their productiveness will decline, and what fertilizer will produce the best effect. I predict that phosphates will not be wanted first, but either nitrogen or potash, when the latter is not present in great abundance. The determination of phosphoric acid soluble in connection with the humus extracted by Grandeau’s method is highly interesting; for whether or not that portion may be considered fully available, it is certainly very much more so than that whichis left undissolved in the same process. The determination has, therefore, been made in all soils analyzed for the past ten years, and has proved very instructive in showing why some soils, with