Chapter 9, P. 146); More Especially Those of Nitrification, Thus

supplying the readily assimilable form of nitrogen. Also in favoring the development and activity of the root bacteria of legumes, and of the other nitrogen-gathering bacteria, such as Azotobacter (ibid. p. 156).

3. The rendering available, directly or indirectly, of relatively small percentages of plant-food, notably phosphoric acid and potash; as shown in the preceding pages.

4. The prompt conversion of vegetable matter into black, neutral humus, and (as shown in the case of the soils of the arid region) the concentration of the nitrogen in the same; while accelerating the oxidation of the carbon and hydrogen, as shown by S. W. Johnson and others.

6. It counteracts the deleterious influence of an excess of magnesia in the soil, as first shown by Loew, and verified by his pupils in Japan.

7. In alkali soils, according to Cameron and May, it counteracts the injurious action of the soluble salts upon the growth of plants, not only in the form of carbonate, but also in those of sulfate and chlorid.

Bull. No. 1, Div. Veget. Physiol, and Plant Pathol. U. S. Dept. Agr.; et al.

Loeb, Publications of the Spreckel’s Physiological Laboratory of the University of California, has shown a similar protective influence of the lime salts in sea-water, against the other salts, in the case of the lower marine organisms.

8. As a matter of experience, both in the case of grapes and orchard as well as wild fruits, an adequate but not excessive supply of lime in the soil will produce sweeter fruit than when lime is in small supply.

9. An excess of carbonate of lime in soils (from eight to twenty per cent and more), constituting “marliness,” tends to seriously disturb the nutrition and general functions of many plants (calcifuge), and to produce a suppression or diminution of the formation of chlorophyll and starch; as in the case of grape vines, citrus fruits and others, which nevertheless flourish best in lands moderately calcareous.

Among the points thus enumerated the third and fourth require some comment. Without pretending to define exactly how lime acts in rendering other ingredients more available to plant assimilation, attention may be called to the fact that lime carbonate may be considered as acting similarly to, albeit more mildly than, caustic lime, in the displacement of other bases from their compounds. It doubtless acts thus in liberating potash from its zeolitic compounds. As to phosphoric acid, the connection of the effect of lime carbonate with the remarkable availability of that substance when present in the form of tetra-basic salt, in the case of phosphate slag, is at least possible.

As to the action of lime carbonate in forming humus, no one who has observed the characteristic dark black tint of our calcareous “prairie soils” can question the fact; which moreover is perfectly explicable upon the analogy already alluded to, with caustic lime, which, together with caustic alkalies (potash and soda), is known to act powerfully in the conversion of vegetable matter into humus. That instead of liberating the nitrogen in the form of ammonia, as do the caustic hydrates, the milder carbonate should only cause the formation of humic amides, is quite intelligible. That such is really the case, has been conclusively proved by the investigations of the writer made conjointly with M. E. Jaffa (Rep. Sta. Cal. Agr. Expt. 1892-4); the general result being that while in the humid region the average nitrogen-content of soil-humus is less than 5%, in the upland soils of the arid region (where all soils are calcareous) that percentage rises as high as 22.0%, with a general average of between 15 and 16%. That such highly nitrogenous material can be more readily attacked by the nitrifying bacteria than when a large excess of other oxidable matter is present, is at least a legitimate presumption, especially in view of the very active nitrification known to take place in the arid regions everywhere. So long as a large excess of carbohydrates is present, the oxidation of these will naturally take precedence over that of the relatively inert nitrogen. The accumulation of the latter in the humus-substance of the arid region, where oxidation of the organic matter of the soil is very active, points strongly to this view of the case.

“Black Soils;” Agric. Science, January, 1892.

Magnesia.—While the differences in respect to the proportions of lime are the most prominent and decided, yet the related substance, magnesia, shows also a very marked and constant difference as between the soils of the humid and arid regions. It will be observed that the general average for magnesia in the soils of the Atlantic Slope is about double that of lime; Florida and Rhode Island being the only states in which the average is lower for magnesia than for lime. In the arid region, on the contrary, magnesia on the general average is nearly the same as lime; in the average by states, somewhat less; thus bringing the ratio for the two regions for magnesia up to one to six or seven. This also is so decisive a showing that no accident could bring it about. We must conclude that climatic influences have dealt with magnesia similarly as with lime; which from the standpoint of the chemist is just what might be expected, since magnesia carbonate behaves very much like that of lime toward carbonated waters.

That magnesia is a very important plant-food ingredient is apparent from its invariable and rather abundant presence in the seeds of plants, where it takes precedence of lime. Its functions in plant nutrition have been specially investigated by O. Loew, particularly with respect to its relations to lime. As already stated in connection with the soil-forming properties of magnesian minerals (see chapter 2), soils containing large proportions of magnesia generally are found to be unthrifty, the lands so constituted being frequently designated as “barrens.” Loew finds that certain proportions of lime to magnesia must be preserved if production is to be satisfactory, the proportion varying with different plants, some of which (e. g. oats) will do well when the proportion of lime to magnesia is as 1:1, while others require, that that ratio should be as 2 or 3 is to 1, to secure the best results. In general it is best that lime should exceed magnesia in amount.

Bull. No. 18, Div. Vegetable Physiology and Plant Pathology; Bull. No. 1, Bureau of Plant Industry, U. S. Dept. of Agr.; Bull. College of Agriculture, Tokyo, Vol. 4, No. 5.

Loew explains the injurious action of magnesium salts thus: The calcium nucleo-proteids of the organic structures are transformed in presence of soluble salts of magnesium into magnesium compounds, while the calcium of the former enters into combination with the acid of the magnesium salt. By this transformation the capacity for imbibition will change, which must result in a fatal disturbance of functions. The presence of soluble lime salts will prevent that interchange. Thus certain algæ perished in a solution containing 1 per 1000 of magnesium nitrate, but remained alive when .3 per 1000 of calcium nitrate was added.

Magnesia seems to be specially concerned in the transfer of phosphoric acid through the plant tissues, in the form of dimagnesic-hydric phosphate, which is rather soluble in the acid juices of plants. It is probable that, apart from the relations just referred to, such excess of lime as is known to produce chlorosis in plants interferes with the transfer of the magnesic phosphate. Some plants, as already stated, dispose of an excess of lime by depositing it in the form of oxalate, while others (such as the stone crops) excrete it on the surface of leaves and stems in the form of carbonate. But others seem to possess this power to a limited extent only.

In the case of soils containing much magnesia the proper proportion between it and lime may easily be disturbed by the greater ease with which lime carbonate is carried away by carbonated water into the subsoil, thus leaving the magnesia in undesirable excess in the surface soil. Hence the great advantage of having in a soil, from the outset, an ample proportion of lime. From this point of view alone, then, the analytical determination of lime and magnesia in soils is of high practical value.

Aso, Furuta and Katayama (Bull. Coll. Agr. Tokyo, Vol. 4 No. 5; Ibid. Vol. 6), have by direct experiment determined the most advantageous ratio of lime to magnesia in several crop plants. They find for rice and oats 1:1, for cabbage 2:1, for buckwheat 3:1; there being apparently a connection between the extent of leaf-surface and lime requirement, since leaves contain predominantly lime, while in the fruit, magnesia predominates.

Manganese.—A decided difference in the manganese content of the arid as against the humid soils appears in the table, the ratio being about 11:13 in favor of the humid soils. Manganese has not been regarded as being of special importance to plant growth in general, although, as already stated, some plants contain a relatively large proportion of manganese in their ashes; thus, e. g., the leaves of the long-leaved pine of the cotton states. But no definite data showing the importance of this element to crops were available until Loew and his co-workers at Tokyo established its stimulating action in a number of cases, in which crop production was materially increased by the use of protoxid salts of manganese. Aso applied manganous chlorid to an experimental plot of thirty square meters, at the rate of twenty-five kilos of Mn₃O₄ per acre, and thus obtained a yield of rice one-third greater than on the control plot, at a cost of about $2.00, while the value of the increase of the product was nearly $68.00. More experimental evidence on this subject is required to establish the general value of the large-scale use of the salts of manganese; which are obtained in large quantities as a comparatively valueless by-product of the bleaching industries.

Rep. Agr. and Geology of Mississippi, 1860, p. 360.

Bull. Agr. Coll. Tokyo, Vol. V., Nos. 2 and 4.

Ibid. Vol. 6.

The “Insoluble Residue.”

Remembering, in discussing the facts shown by the table, that the fundamental difference between the regime of the humid and arid regions is the presence in the latter of an almost continuous leaching process, in which the carbonated water of the soil is the solvent; remembering, also, that the least soluble portion of rocks and soils is quartz or silica (sand, as usually understood), it would be predicable that this ingredient should in the humid region be found to be more abundant in soils than in the arid. This portion is represented by the “insoluble residue” of the table.

Inspection shows that both in the averages of the single states, and in both of the general averages, this difference between the soils of the humid and the arid regions of the United States is strongly pronounced; the ratio being substantially as 69% in the arid region to 84% in the humid.

We must then conclude that the leaching process must have influenced materially other soil ingredients than lime, which have remained behind in such amounts as to depress the percentage of insoluble residue in the soils. It remains to be shown what are the substances so retained.

Insoluble and Soluble Silica and Alumina.

The ingredient most nearly correlated with the insoluble residue is the free silica which remains behind with it when the acid with which the soil has been treated is evaporated to dryness. The silica is separated from the practically insoluble, undecomposed minerals by boiling with a strong solution of sodic carbonate. The amount of this “soluble silica” is obviously the measure of the extent to which the soil-silicates have been decomposed in the treatment with acid.

The most prominent of these is usually supposed to be clay—the hydrous silicate of alumina that in its purest condition forms kaolinite or porcelain earth. Any alumina found in the usual course of soil analysis is generally referred to this mineral, which contains silica and alumina nearly in the proportion of 46% to 40%.

In very many cases, however, the reference of these two ingredients to clay is manifestly unjustified. This is clearly so when (as not unfrequently happens) the amount of alumina found exceeds that which would form clay with the ascertained percentage of soluble silica; it is almost as certainly so when, in addition to the alumina, other bases (notably potash, lime and magnesia), are found in proportions which preclude their being in combination with any other acidic compounds present. The only possible inference in such cases is that these bases, together with at least a portion of the alumina, are present in the form of hydrated, and therefore easily decomposable silicates or zeolites.

The subjoined analysis by R. H. Loughridge, of a clay obtained in the usual process of mechanical soil analysis (by precipitating with common salt the turbid water remaining after 24 hours subsidence in a column of 200 millimeters) from a very generalized soil of northern Mississippi, shows one of the many cases in which the numerical ratios of the several ingredients are incompatible with the assumption that silica and alumina are present in combination as clay (kaolinite) only:

ANALYSIS OF COLLOIDAL CLAY.

Insoluble matter 15.96 Soluble silica 33.10 Potash (K₂O) 1.47 Soda (Na₂O) 1.70 Lime (CaO) .09 Magnesia (MgO) 1.33 Br. ox. of Manganese (Mn₃O₄) .30 Peroxid of iron (Fe₂O₃) 18.76 Alumina (Al₂O₃) 18.19 Phosphoric acid (P₂O₅) .18 Sulfuric acid (SO₃) .06 Carbonic acid (CO₂) .00 Water and organic matter 9.00 ------ Total 100.14

If in this case we assign all alumina to silica, as required for the composition of kaolinite or pure clay, there yet remains a trifle over twelve (12.17) per cent of silica to be allotted to the other bases present. Deducting from this the ascertained amount of silica soluble in sodic carbonate, pre-existing in the raw material (.38 per cent), we come to 11.79 per cent as the amount of silica which must have been in combinations other than kaolinite, viz., hydrous silicates, or soil zeolites, formed either with the bases other than alumina shown in the analysis or, more probably, containing some of the alumina itself in essential combination.

We are thus enabled to obtain from the determination of the soluble silica an estimate of the extent to which these soil zeolites, that form so important a portion of the soil in being the repositories of the reserve of more or less available mineral plant-food, are present in the soils of the several regions. A glance at the table shows that the general average of soluble silica is very much greater in the soils of the arid regions than in those of the humid, approximating one to two in favor of the arid division.

Looking at the details of the several states, we find that on the arid side Washington has a relatively low figure for soluble silica, which in the average, however, is overborne by the high figures for California and Montana. The explanation of this fact probably lies in the derivation of the majority of the Washington soils examined, from lake deposits brought down gradually from the humid region at the heads of the Columbia drainage, where sandy beds are very prevalent; while the country rock—the basaltic eruptives—are very basic, and moreover slow to disintegrate. In California and Montana the rocks are infinitely varied, and the general outcome of their weathering is plainly a predominance of complex hydrous silicates in the soils, as compared with humid regions.

Differences in the Sands of the Arid and Humid Regions.—In chapter 5 mention has been made of the fact that while in the humid regions, “sand” as a rule means quartz grains, mostly with a clean surface and very frequently rounded and polished, in the arid regions even the coarse sand grains consist of, or are covered with, a great variety of minerals in a partially decomposed condition. This is owing to the absence of the abundant rainfall which in humid climates continually washes down the finely divided, half-decomposed mineral matter into the subsoil; while in arid climates the light rains cannot produce any such washing effect and hence the sand grains remain incrusted with the products of either their own decomposition, or of that of neighboring particles; it being therefore not concentrated in the finer portion only, viz., the clay and finest silts. This fundamental difference, which is illustrated in the analytical table below, at once explains why in the arid regions generally, sandy soils are found so highly productive that, owing to their easy cultivation they are preferred to the clayey lands, in which tillage and irrigation are more difficult. It is a well-known fact that on the “sands of the desert” when either irrigated, or wetted by rain, vegetation at once springs up with remarkable luxuriance, even on sand drifts; and this productiveness appears to be quite as lasting as that of “strong” clay soils of the humid regions.

This difference is curiously illustrated on the southern edge of the “black adobe” or prairie soil area which surrounds Stockton, Cal. Here we find on the opposite sides of a small stream (French Camp slough) the two extremes, of heavy clay and the sandy soils which for many years made Stanislaus county the “banner” county for wheat. The grain product of both banks ranked alike in quantity and quality in average years; but in extreme seasons sometimes one, sometimes the other failed, according to the weather conditions which favored one or the other soil. No one would think of sowing wheat on so sandy a soil in the humid States.

Table Illustrating Difference in Sands of the Humid and Arid Regions.

===============================+========+=======+=====+========= |Per cent|Potash.|Lime.|Magnesia. Clay. |in Soil.| | | -------------------------------+--------+-------+-----+--------- Mississippi | 21.64 | .32 | .03 | .29 California 1281 Chino | 7.60 | .16 | .14 | .17 “ Jackson | 16.43 | .13 | .12 | .08 Silt .06-.016 mm. diam. | | | | Mississippi | 35.10 | .41 | .15 | .36 California (Chino) | 18.53 | .24 | .53 | .29 “ Jackson | 34.90 | .10 | .04 | .08 Silt .016-.025 mm. diam. | | | | Mississippi | 13.67 | .12 | .09 | .10 California, Chino | 5.49 | .05 | .11 | .02 “ Jackson | 9.96 | .08 | .04 | .10 Silt .025-.036 mm. diam. | | | | Mississippi | | | | California, Chino | 3.92 | | | “ Jackson | 7.68 | .06 | .02 | Silt .036-.047 mm. diam. | | | | Mississippi | | | | California, Chino | 6.40 | .05 | .18 | “ Jackson | 8.21 | .04 | .01 | Coarse Silt .047-.072 mm. diam.| | | | California, Chino | 7.92 | .06 | .23 | “ Jackson | 5.91 | .01 | .01 | Fine sand .072-.12 mm. diam. | | | | California, Chino | 11.87 | .06 | .26 | “ Jackson | 4.03 | .01 | .01 | Sand .12-.50 mm diam. | | | | California, Chino | 36.11 | .11 | .69 | “ Jackson | 10.10 | | | -------------------------------+--------+-------+-----+---------

===============================+==========+=======+================= |Phosphoric|Soluble|Alumina.| Summ- Clay. | Acid. |Silica.| | ation. -------------------------------+----------+-------+--------+-------- Mississippi | .04 | 7.17 | 3.97 | 11.82 California 1281 Chino | .04 | 1.70 | 1.35 | 3.56 “ Jackson | .05 | 2.83 | 2.13 | 5.34 -------------------------------+----------+-------+--------+-------- Silt .06-.016 mm. diam. | | | | Mississippi | .07 | 2.87 | 1.36 | 5.22 California (Chino) | .06 | 4.96 | 1.76 | 7.84 “ Jackson | .02 | 2.50 | 2.44 | 5.18 -------------------------------+----------+-------+--------+-------- Silt .016-.025 mm. diam. | | | | Mississippi | .02 | .32 | .17 | .82 California, Chino | .01 | .80 | .51 | 1.50 “ Jackson | .007 | 1.01 | 1.01 | 2.25 -------------------------------+----------+-------+--------+-------- Silt .025-.036 mm. diam. | | | | Mississippi | | | | .36 California, Chino | | | | lost “ Jackson | .006 | 0.82 | .74 | 1.70 -------------------------------+----------+-------+--------+-------- Silt .036-.047 mm. diam. | | | | Mississippi | | | .55 | trace California, Chino | .01 | .80 | .64 | 1.66 “ Jackson | .001 | .43 | | 1.12 -------------------------------+----------+-------+--------+-------- Coarse Silt .047-.072 mm. diam.| | | | California, Chino | .02 | .89 | .59 | 1.79 “ Jackson | .003 | .42 | .30 | .77 -------------------------------+----------+-------+--------+-------- Fine sand .072-.12 mm. diam. | | | | California, Chino | .03 | .98 | | 1.43 “ Jackson | .003 | .28 | .09 | .40 -------------------------------+----------+-------+--------+-------- Sand .12-.50 mm diam. | | | | California, Chino | .04 | 2.43 | 1.59 | 4.98 “ Jackson | | | |Not detd -------------------------------+----------+-------+--------+--------

Analyses by R. H. Loughridge.

Analyses by L. M. Tolman.

Analyses by E. H. Lea.

Analyses by R. H. Loughridge.

Analyses by L. M. Tolman.

Analyses by E. H. Lea.

It thus appears that while in the Mississippi soil, solubility of plant-food practically ceased at grain-diameter of .036 mm, in the arid California soils, as large an amount was found in the sand-grain sizes between .12 and .50 millimeters as in the fine silt .016 to .025 mm. in Mississippi.

Hydrous Silicates are More Abundant in Arid than Humid Soils.—This predominance of hydrous silicates in the soils of the arid regions should not be a matter of surprise when we consider the agencies which are brought to bear upon these soils with so much greater intensity than can be the case where the solutions resulting from the weathering process are continually removed as fast as formed, by the continuous leaching effect of atmospheric waters. In the soils of regions where summer rains are insignificant or wanting, these solutions not only remain, but are concentrated by evaporation to a point that, in the nature of the case, can never be reached in humid climates. Prominent among these soluble ingredients are the silicates and carbonates of the two alkalies, potash and soda. The former, when filtered through a soil containing the carbonates of lime and magnesia, will soon be transformed into complex silicates, in which potash takes precedence of soda, and which, existing in a very finely divided (at the outset in a gelatinous) condition, serve as an ever-ready reservoir to catch and store the lingering alkalies as they are set free from the rocks, whether in the form of soluble silicates or carbonates. The latter have another important effect: in the concentrated form at least, they, themselves, are effective in decomposing silicate minerals refractory to milder agencies, such as calcic carbonate solution; and thus the more decomposed state in which we find the soil minerals of the arid regions is intelligible on that ground alone.

It must not be forgotten that lime carbonate, though less effective than the corresponding alkali solutions, nevertheless is also known to produce, by long-continued action, chemical effects similar to those that are more quickly and energetically brought about by the action of caustic lime. In fact, the agricultural effects of “liming” are only in degree different from those produced by marling with finely pulverized carbonate; and in nature the same relation is strikingly exemplified in the peculiarly black humus that is characteristic of calcareous lands, but which can be much more quickly formed under the influence of caustic lime on peaty soils.

In the analysis of silicates we employ caustic lime for the setting-free of the alkalies and the formation of easily decomposable silicates, by igniting the mixture; but the carbonate will slowly produce a similar change, both in the laboratory and in the soils in which it is constantly present. This is strikingly seen when we contrast the analyses of calcareous clay soils of the humid region with the corresponding non-calcareous ones of the same. In the former the proportions of dissolved silica and alumina are almost invariably much greater than in the latter, so far as such comparisons are practicable without assured absolute identity of materials. That is, calcareous clays or clay soils are so sure to yield to the analyst large precipitates of alumina, that experience teaches him to employ smaller amounts for analysis than he would of non-calcareous materials, in order to avoid unmanageably large bulks of aluminic hydrate. It is but rarely that even the heaviest non-calcareous soils yield to the acid usually used in soil analysis more than 10 per cent of alumina; while heavy calcareous clay (prairie) soils commonly yield between 13 and 20 per cent. It would be interesting to verify this relation by artificial digestions of one and the same clays with calcic carbonate at high temperatures, as it must always be extremely difficult to insure absolute identity of all other conditions in natural materials.

In most of these cases, what is true of alumina is also true of the soluble silica. But since the latter is constantly liable to be dissolved out by solutions of carbonated alkalies, it is not surprising that this relation is not always shown.

Report of the Tenth Census, Vols. 5 & 6; see especially the analyses of soils from Mississippi and Alabama. Also the Reports of the California Experiment Station.

Aluminic Hydrate.—In numerous cases, the amount of alumina dissolved in analysis is greatly in excess of the soluble silica, so as to force the conclusion that a portion of the latter must be present in a different form from that of clay (kaolinite); the only choice being between that of complex hydrous silicates (none of which, however, could contain as large a percentage of alumina as clay itself) and aluminic hydrate. The latter is alone capable of explaining the presence of more alumina than silica in easily soluble form; and the visible occurrence of “gibbsite” and “bauxite” in modern formaations renders this a perfectly simple and acceptable explanation. Since these minerals are known to be incapable of crystallization, we are moreover led to the presumption that it will as a rule be found in the finest portions of the soil, viz., in the “clay” of mechanical analysis.

Excepting the relatively rare minerals of the Allophane, Kollyrite, and Miloshite group.

Some illustrations of these conditions are given below, for soils from Mississippi and California. The soluble silica being all assigned to kaolinite, the rest of the alumina must be assumed to be present as hydrate, since no other compound could fulfil the stoichiometrical requirements. The table therefore shows the differences between the amounts of alumina found by analysis, and those assignable to kaolinite, calculated to the mineral bauxite—the most abundant, as well as the one containing the medium proportion of water, among the three naturally occurring aluminic hydrates.

TABLE SHOWING EXCESS OF ALUMINA OVER SILICA IN SOILS; CALCULATED AS BAUXITE.

(A) = Total soluble in HCl. (B) = Corresponding to Bauxite. (C) = Other Soluble Matters. Miss. = Mississippi. Cal. = California. -------+---------------+--------+------+-----+----+-----+-----+----- Number.| Name of Soil. |County. |State.| (A) |SiO₂|Al₂O₃| (B) | (C) -------+---------------+--------+------+-----+----+-----+-----+----- 195 |Prairie |Alcorn | Miss.|28.57| 3.6| 14.4|14.12| 2.92 346 |Dark Loam |Chicasaw| “ |10.32| 6.6| 11.2| 6.91| .86 288 |Flatwoods Clay |Pontotoc| “ |26.94| 5.0| 11.3| 8.75| 3.48 676 |Red Volcanic |Lake | Cal.|41.00| 5.9| 22.6|21.90| 2.00 332 |Mojave Desert |Kern | “ |24.82| 5.0| 9.2| 6.10| 5.13 191 |Red Foothill |Merced | “ |23.32| 4.5| 8.8| 6.20| 3.05 -------+---------------+--------+------+-----+----+-----+-----+----- 705 |Red Chaparral |Shasta | “ |28.75| 5.5| 14.4|12.10| 1.12 706 | “ “ | | | | | | | | Subsoil | “ | “ |28.40| 4.7| 17.4|16.70| 1.32 -------+---------------+--------+------+-----+----+-----+-----+----- 573 |Tulare Plains |Tulare | “ |29.27| 3.4| 8.7| 7.20|11.16 701 |Dry Bog | “ | “ |27.29| 4.3| 12.4|10.90| 5.04 1004 |“Slickens“ Sed.|Butte | “ |30.80| 8.0| 14.2| 9.20| 1.95 656 | “ “ |Yuba | “ |22.23| 3.0| 10.4| 9.80| 2.19 517 |Brownish Loam |Butte | “ |29.80| 4.8| 12.0| 9.80| 4.42 561 |Black Loam | “ | “ |30.21| 3.2| 13.0|12.80| 4.67 -------+---------------+--------+------+-----+----+-----+-----+----- 563 |Sacramento | | | | | | | | Alluvium | “ | “ |23.46| 2.7| 10.4|10.90| 4.58 -------+---------------+--------+------+-----+----+-----+-----+----- 863 |Red Foothill |Nevada | “ |56.80|11.0| 36.4|33.60| 1.22 861 | “ “ | “ | “ |45.46|11.5| 22.0|14.10| 3.97 -------+---------------+--------+------+-----+----+-----+-----+-----

It is apparent from this table that if, as is probable, the aluminic hydrate accumulates in the “clay” of the analysis, it will in some cases form a very considerable percentage of the same, and detract to that extent from its plastic, adhesive and other properties. But it must be remembered that the assumption upon which this table is calculated, leaves out of consideration the zeolitic portion, which as the 6th column shows, is frequently quite large as measured by the bases found, to which no other form of combination can be assigned. Since some of the alumina undoubtedly takes part in the formation of such zeolites, the silica must to that extent be withdrawn from the estimate made for kaolinite. While it is impossible to make any definite numerical allowance for this fact, it clearly will tend in many cases to increase materially the amount of alumina that must be assigned to the hydrate condition. It will be noted that in most cases given, the alumina per cent is rather large.

Since any complex zeolite would contain less alumina than kaolinite, this assumption more than covers the possible zeolitic alumina.

The relatively large number of such cases shown in the table for California soils is not a matter of accident; for even a cursory glance at the columns of analyses of California (and Washington and Montana) soils, shows that the cases in which the alumina exceeds the silica in amount are rather predominant, while the reverse is the case in the humid region. But it must not be inferred that the reverse relation is not also frequently observed even in the arid region; it occurs in fact in close proximity to the localities where some of the most striking instances of excess of alumina over soluble silica have been found.

See for comparison the data given in vols. 5 and 6 of the report of the Tenth Census of the United States.

Thus Nos. 861 and 863 from the neighborhood of Grass Valley, which show this excess most strikingly, occur within 15 miles of localities which show almost the reversal of the numbers given for the two former, and at a level of about a thousand feet lower. It would seem, on the whole, that the excess of alumina occurs most frequently in connection with soils formed from eruptive rocks; in the case referred to, from volcanic ash. It will require more detailed study to detect the causes of these marked differences.

Retention of Soluble Silica in Alkali Soils.—It is somewhat surprising that, contrary to the expectation one would naturally entertain, the alkali lands, so frequently rich in the carbonates of the alkalies that would dissolve free silica, on the contrary, show most frequently an excess of soluble silica over alumina. This is probably to be explained from the very liberal opportunities afforded in the alkali soils for the formation of complex zeolitic masses by the retention in soil of the soluble alkali salts, and the abundance of lime always present in them. As already stated, we usually find in alkali soils a very large proportion of both alkaline and earthy bases in acid-soluble silicate combinations. But much farther research is needed to explain fully the marked discrepancies observed in this respect between soils not only occurring in closely contiguous localities, but also showing marked similarities in their general composition.

Ferric Hydrate.—There is no obvious reason, from the chemical standpoint, why iron, that is, ferric hydrate or iron rust, should be more abundant in the soils of the arid regions, as the averages given in the table suggest; moreover, the fact does not impress itself upon the eye, since the orange or reddish tints are by far more common in the humid than in the arid regions of the United States at least. The California average is considerably influenced by the very highly ferruginous soils from the foothills of the Sierra Nevada, and by the black (magnetite) sand so commonly present; that of Oregon by the black, highly ferruginous country rock (basalts), from which they are partly derived. The average for Montana is not higher than that of three states of the humid region, and less than that of Kentucky. We might imagine a cause for depletion of iron in the soils of the humid areas in the frequency with which humid moisture and high temperature will during the summers concur toward the bringing about of a reducing process in the soil, which by getting the iron into proto-carbonate solution would make it liable to be leached into the subsoil, as is frequently the case; yet the resulting “black gravel” or bog ore, in its various forms, is of not infrequent occurrence in the arid regions also. A constant quantitative difference due to climatic conditions does not appear to be shown by the data thus far at command, but the finer distribution of the ferric hydrate in the humid temperate as well tropical regions is obvious to the observer, from the frequent redness of humid and tropical soils.

Manganese.—An unexpected and apparently well-defined contrary relation appears to be shown as regards the related metal manganese; the average percentage of which is in all cases less in the arid than in the humid region. The cause of this relation is altogether obscure; it is too frequent to be accidental.

Phosphoric Acid.—As regards that highly important soil ingredient, phosphoric acid, the indication in the table that there is no characteristic difference in the average contents in soils of the arid and humid regions, respectively, is doubtless correct. This substance is so tenaciously retained by all soils that there is no obvious reason why there should be any material influence exerted upon its quantity by leaching, or by any of the differences in the process of weathering that are known to exist between the two climatic regions. Moreover, it is apparent that the average for the arid region is made up out of very widely divergent figures; that of California exceptionally low (lower than any of those for the states of the humid regions), while those for Washington and Montana are exceptionally high. The latter is due to country rocks (“basalts”) showing abundance of microscopic crystals of apatite, which in some cases raise the contents of the soils in phosphoric acid to nearly twice the average given for the states.

The forecast that for most California soils, fertilization with phosphates is of exceptional importance, has already been abundantly confirmed by cultural experience. Few definite data are as yet available from other arid states, where fertilization is thus far sporadic and unsystematic. But it is predictable that in view of the presence of an excess of lime carbonate in the arid soils, and the unfavorable effect of this compound on the rapid solubility of tri-calcic phosphate demonstrated by Schloesing, Jr., by Böttcher and Kellner and Nagaoka, fertilization with readily available phosphate fertilizers will be found necessary among the first, all over the arid region, especially in view of the scarcity of humus in arid soils. Ann. Sci. Agronomique, tome 1, 1899.

Landw. Presse, 1900, No. 52; ibid. 1901, Nos. 23 and 24.

Bull. Univ. Tokyo, Vol. 6, No. 3. Production was diminished to less than one half when lime was used with bone meal, and actual assimilation of phosphoric acid to one fifth.

A curious instance of the effects of continued warm maceration in rock decomposition is afforded by the highly ferruginous soils derived from the black basaltic lavas of the Hawaii Islands. These lavas, like the basalt sheet of the Pacific Northwest, contain a large amount of crystallized phosphate minerals, notably apatite and vivianite. A correspondingly large proportion of phosphoric acid is found in the soils derived from these rocks, up to nearly two per cent. But almost the entirety of this substance is present in the form of an insoluble, basic iron compound, difficultly soluble even in acids, and rendering it wholly unavailable to vegetation. So that actually the most pressing need of most of these soils is phosphate fertilization. The same is probably true of some of the highly ferruginous soils of California and of the Cotton States.

See table, chapter 19, p. 256.

Sulfuric Acid.—From the absence of the leaching process in the soils of the arid region, we should expect that sulfates would be more abundant in them than in the soils of the humid. This is certainly true in the case of the alkali soils, which are characteristic of the regions of deficient rainfall. See below, chapter 22.

Hence the showing made in the general table, indicating that sulfates are equally abundant in the soils of the humid than in those of the arid regions, is surprising in view of the efflorescences of alkali sulfates so frequently observed in the latter. This is obviously due to the fact that the majority of such alkali soils has, on account of their local nature and usually heavy lime content, been excluded from the comparison; which otherwise would have made a very different showing.

Potash and Soda.—The compounds of the alkali metals potassium and sodium, being on the whole much more soluble in water, even without the concurrence of carbonic acid, than those of calcium and magnesium, the leaching process that creates such pronounced differences in the case of the two earths must affect the alkali compounds very materially. Comparison of the soils of the two regions in this respect shows, indeed, very great differences in the average contents of potash and soda. For potash the ratio is .216 to .670 per cent on the general average, and .187 to .670 per cent, in the average by states; for soda, .140 per cent to .350 per cent on the general average, and .110 per cent to .420 per cent in the average by states. For both, therefore, the general average ratio is as one to between three and four for the humid as against the arid region.

It is curious that an approximation to the ratio of one to two, or somewhat less, is maintained in the average proportion of soda to potash in both regions; but this does not by any means hold good in detail, very high potash-percentages being often accompanied by figures for soda very much below the above ratio. This is the result of an important difference in the chemical behavior of the two alkalies, which has already been alluded to in connection with the discussion of the zeolites. (See chapter 3, p. 38).

The process of “kaolinization,” being that by which clays are formed out of feldspathic minerals and rocks such as granite, syenite, trachyte, etc., results in the simultaneous formation of solutions of carbonates and silicates of potash and soda. These coming in contact with the corresponding compounds of lime and magnesia, also common products of rock decomposition, are partly taken up by the latter, forming complex, insoluble, hydrous silicates (zeolites). In these, however, potash whenever present takes precedence of soda; so that when a solution of a potash compound is brought in contact with a zeolite containing much soda, the latter is partially or wholly displaced and, being soluble, tends to be washed away by the rainfall into the country drainage. Hence potash, fortunately for agriculture, is tenaciously held by soils, while soda accumulates only where the rainfall or drainage is insufficient to effect proper leaching, and in that case manifests itself in the formation of what is popularly known as “alkali soils;” namely those in which a notable amount of soluble salts exists, and is kept in circulation by the alternation of rainfall and evaporation, the latter causing the salts to accumulate at the surface and to manifest themselves in the form of saline crusts or efflorescenses. Alkali lands are a characteristic feature of all regions of scanty rainfall, and are found more or less on all the continents. The substances composing the alkali salts are retained not only in their soluble form, but by their continued presence influence profoundly, in several ways, the processes of soil formation. A more detailed discussion of this important subject is given in chapters 22 and 23.

Arid Soils are Rich in Potash.—One of the most important practical conclusions flowing from the comparison of the potash contents of the humid and arid soils respectively is that while in the former, potash is usually among the first substances to be supplied by fertilization when production languishes, in the arid regions it will as rule come last in order among the three ingredients commonly so furnished. Aside from the water-soluble potash salts always forming part of the salts of the alkali lands proper, which in many cases will alone hold out for many years under the demands of cultivation, they rarely contain much less than one per cent of acid-soluble potash; occasionally rising as high as 1.8 per cent. That in such lands potash-fertilization is uncalled-for and ineffective, hardly requires discussion; while on the other hand, phosphates are commonly required for full production after ten or fifteen years of cultivation without returns. Nitrogen usually comes next in order, but sometimes is the first need.

In the light alkali lands of the southern California Experiment Substation at Chino, the average content of water-soluble potash in ten acres amounts to the equivalent of 1,200 pounds of potash sulphate per acre. Outside of this the acid-soluble potash of the soil is .95%., equal to 38,000 pounds per acre-foot.

The constant indiscriminate purchase and use of all three ingredients, so urgently recommended by fertilizer manufacturers because of their success in the humid Eastern States, is therefore very poor economy for the farmers of the arid region. Excepting cases of very intense culture, e.g. of vegetables or berries, the use of potash salts is but rarely remunerative, and therefore uncalled-for, in arid soils for a number of years.

Humus.—The figures shown in the table for the average humus-percentages in the soils of the two regions do not adequately represent the very important differences actually existing; partly because of the inadequate number of determinations made by the same method (Grandeau’s), partly because of the differences in the composition, and especially in the nitrogen-content of this substance, which render direct comparison delusive. A detailed discussion of the marked differences existing between the humus of arid and humid soils in this respect has already been given (chapter 8, p. 135); showing that the high nitrogen-percentage in the arid humus probably compensates largely the lower humus-percentage, while rendering nitrification more rapid, because the oxygen is not consumed by overwhelming amounts of carbon and hydrogen; which, as is already known, take precedence of nitrogen in the oxidation of humus substances. Nitrates are almost always more abundant in the soils of the arid region than in those of the humid, sometimes to the extent of influencing injuriously the quality of certain crops, such as tobacco and sugar beets. Nevertheless, nitrogen is ordinarily, in the arid region, the substance requiring replacement next to phosphoric acid. And when considered in connection with the small humus-content, so liable to burning-out, this places green-manuring with leguminous plants among the first and most vital improvements to be employed there.

The Transition (semi-humid or semi-arid) Region.—The sloping plains country lying between the Rocky Mountains and the Mississippi, quite arid at the foot of the mountains, but with rainfall increasing more or less regularly to eastward, form a transition-belt between the arid and humid region of which but a small portion has been systematically studied in respect to its soil formations. The analyses made of soils of the two adjacent states of Minnesota and North Dakota, have been placed in the general table (p. 377) to show how far in their general relations their soils correspond to the generalizations deduced from the comparison of the decidedly arid and humid soil areas chiefly represented in the table. Although it has not been possible, for lack of detailed data, to eliminate the soils originating from calcareous formations, it will be seen that those of semi-arid Dakota differ from those of more humid Minnesota, almost throughout, as would be anticipated from the studies of the extremes, given in this chapter.