Chapter XX

SOILS OF THE ARID AND HUMID[125] REGIONS.

_Composition of Good Medium Soils._—In the preceding tables examples have been given of rather extreme types of soils, both rich and poor throughout, and also of such as are deficient in one or several of the important ingredients. In the table below are given the analyses of some of the good average farming lands; uplands of several states, both of the humid and arid regions. In the former, the representative timber trees of such lands are the black, red, white and (less characteristically) the post, black-jack, Spanish, overcup and locally some other oaks; grading higher in proportion to the presence of more or less hickory, and lower as the latter is replaced by pine. In the states south of Ohio, the “oak and hickory uplands” are what the farmer usually looks for, outside of the valleys or bottoms.

[125] In the discussion in this chapter the “humid region” referred to is always that of the temperate zones, unless expressly otherwise stated. The most humid region of all—the tropics—is treated under a special head.

_Criteria of Lands of the Two Regions._—In the country west of the Rocky Mountains, the timber, while locally very characteristic, cannot be as broadly used as a criterion, partly on account of its scarcity, partly because the dominant factor in the growth of trees is _moisture_, which is measurably independent of chemical soil-composition. The latter, moreover, on account of climatic conditions, already alluded to (chapter 16), does not vary as materially in the arid as the humid region, on account of the almost universal presence of larger proportions of lime carbonate; the variations of which in the humid region govern largely the vegetative changes. For we there find _the timber growth of the lowlands ascending into the uplands so soon as the latter becomes decidedly calcareous_; as is abundantly exemplified in the loess or “bluff” formations bordering the Mississippi, Ohio, and Missouri rivers, where the black walnut, tulip tree, ash, honey-locust, together with the lowland oaks, hickories and cane usually characterizing the stream bottoms, grow abundantly and with luxuriant development on the adjoining steep hill country as well (see below, chapters 24, 25).

UPLAND SOILS OF HUMID REGION.
====================================================================
OAK UPLANDS WITH HICKORY AND WALNUT.
-----------------------+----------+---------------+--------+--------
State. |Tennessee.| Mississippi. |Alabama.|Georgia.
| | | |
-----------------------+----------+--------+------+--------+--------
County. |Rutherford|Pontotoc|Benton|Cherokee| Polk
-----------------------+----------+--------+------+--------+--------
Number of Sample. | 7 | 226 | 216 | 110 | 502
-----------------------+----------+--------+------+--------+--------
ANALYSIS OF FINE EARTH.| | | | |
| | | | |
Insoluble matter |75.35 |83.27 | |78.73 |72.32
| 82.66 | 88.83|83.35 | 84.77| 76.55
Soluble silica | 7.31 | 5.56 | | 6.04 | 4.23
Potash (K₂O) | .26 | .37 | .55| .26 | .73
Soda (Na₂O) | .26 | .22 | .08| .12 | .17
Lime (CaO) | .34 | .28 | .25| .33 | .29
Magnesia (MgO) | .30 | .23 | .48| .40 | .26
-----------------------+----------+--------+------+--------+--------
Bro. ox. of Manganese | | | | |
(Mn₃O₄) | .04 | .28 | .76| .22 | .18
-----------------------+----------+--------+------+--------+--------
Peroxid of Iron (Fe₂O₃)| 5.18 | 2.39 | 4.80| 3.71 | 6.29
Alumina (Al₂O₃) | 5.57 | 4.51 | 6.28| 5.08 | 7.10
Phosphoric acid (P₂O₅) | .08 | .08 | .07| .09 | .26
Sulfuric acid (SO₃) | .08 | .02 | .06| .10 | .11
Carbonic acid (CO₂) | | | | |
-----------------------+----------+--------+------+--------+--------
Water and organic | | | | |
matter | 5.50 | 3.11 | 4.20| 5.15 | 6.60
-----------------------+----------+--------+------+--------+--------
Total |99.77 |100.32 |100.88|100.23 |99.54
-----------------------+----------+--------+------+--------+--------
Humus | | | | |
“ Ash | | | | |
| | | | |
Hygroscopic Moisture | 7.29 | 4.08 | 6.84| 4.50 | 8.71
absorbed at °C | 22°C | | | | 18°C
-----------------------+----------+--------+------+--------+--------
SHORT-LEAVED PINE.
-----------------------+--------+---------+-----------------+---------
State. | North | South | Mississippi |Louisiana
|Carolina|Carolina | |
-----------------------+--------+---------+--------+--------+---------
County. |Cabarrus|Spartan- | Sumner |Franklin|Morehouse
| | burgh | | |
-----------------------+--------+---------+--------+--------+---------
Number of Sample. | 9 | 5 | 142 | 71 | 232
-----------------------+--------+---------+--------+--------+---------
ANALYSIS OF FINE EARTH.| | | | |
| | | | |
Insoluble matter |78.79 | 43.74 |90.23 |88.75 |81.70
| 86.19| 49.61| 92.55| 90.56| 87.45
Soluble silica | 7.40 | 5.87 | 2.32 | 1.81 | 5.75
Potash (K₂O) | .13 | .21 | .24 | .14 | .44
Soda (Na₂O) | .01 | .09 | .09 | .09 | .27
Lime (CaO) | .34 | .03 | .09 | .07 | .10
Magnesia (MgO) | .31 | .21 | .20 | .19 | .24
-----------------------+--------+---------+--------+--------+--------
Bro. ox. of Manganese | | | | |
(Mn₃O₄) | .05 | .01 | .07 | .08 | .39
-----------------------+--------+---------+--------+--------+--------
Peroxid of Iron (Fe₂O₃)| 4.99 | 11.70 | 1.84 | 2.41 | 3.55
Alumina (Al₂O₃) | 4.02 | 26.54 | 1.86 | 2.20 | 4.87
Phosphoric acid (P₂O₅) | .14 | .13 | .09 | .08 | .10
Sulfuric acid (SO₃) | .08 | .01 | .01 | .01 | .08
Carbonic acid (CO₂) | | | | |
-----------------------+--------+---------+--------+--------+--------
Water and organic | | | | |
matter | 3.88 | 11.60 | 2.83 | 4.31 | 2.54
-----------------------+--------+---------+--------+--------+--------
Total | 100.14 |100.22 | 99.87 | 100.14 |100.03
-----------------------+--------+---------+--------+--------+--------
Humus | | | | |
“ Ash | | | | |
| | | | |
Hygroscopic Moisture | 3.65 | 11.21 | 3.57 | 4.4 | 5.47
absorbed at °C | 21.8°C | 21.8°C | 21.8°C | |
-----------------------+--------+---------+--------+--------+--------

UPLAND SOILS OF ARID REGION.

======================+============================================
| CALIFORNIA.
+----------+---------+------------+----------
|Placer Co.|San Diego| Ventura Co.|Riverside
| Auburn. | Co. | | Co.
| |National | |Arlington.
| | City. | |
----------------------+----------+---------+------------+----------
Number of Sample. | 51 | 47 | 182 | 1406
----------------------+----------+---------+------------+----------
ANALYSIS OF FINE EARTH.| | | |
----------------------+----------+---------+------------+----------
Insoluble matter | | | 74.91 | 76.41
| 69.52 | 86.21 | 82.84 | 84.61
Soluble silica | | | 7.93 | 8.20
----------------------+----------+---------+------------+----------
Potash (K₂O) | .38 | .48 | .62 | .87
Soda (Na₂O) | .07 | .14 | .16 | .29
Lime (CaO) | .96 | .36 | .95 | 1.57
Magnesia (MgO) | 1.09 | .54 | .96 | 1.33
----------------------+----------+---------+------------+----------
Br. ox. of Manganese | | | |
(Mn₃O₄) | .39 | .10 | .04 | .04
----------------------+----------+---------+------------+----------
Peroxid of Iron(Fe₂O₃)| 12.42 | 3.69 | 5.07 | 4.20
Alumina (Al₂O₃) | 10.97 | 5.12 | 5.94 | 5.30
Phosphoric acid (P₂O₅)| .16 | .23 | .13 | .14
Sulfuric acid (SO₃) | .01 | .03 | .04 | .01
Carbonic acid (CO₂) | | | |
----------------------+----------+---------+------------+----------
Water and organic | 5.14 | 2.60 | 2.67 | 1.60
matter | | | |
----------------------+----------+---------+------------+----------
Total | 101.10 | 99.50 | 99.41 | 100.05
----------------------+----------+---------+------------+----------
Humus | 1.14 | .56 | 1.06 | .20
“ Ash | 1.12 | 1.04 | 1.00 | .64
Hygroscopic Moisture | | 2.30 | 6.59 | 1.77
absorbed at °C | | 15 | 15 | 15
----------------------+----------+---------+------------+----------
======================+=======================++==================
| WASHINGTON. || MONTANA.
+---------+-------------++---------+--------
| Bunch | Bunch grass || Judith | Near
| grass |Selah Valley,|| Gap. | Bozeman
|Ritzville| Rolling || | Allen’s
| Ridge. | Upland. || | Ranch.
----------------------+---------+-------------++---------+--------
Number of Sample. | 46 | 37 || 371 | 387
----------------------+---------+-------------++---------+--------
ANALYSIS OF FINE EARTH.| | || |
----------------------+---------+-------------++---------+--------
Insoluble matter |76.71 | 77.18 || 74.17 |67.28
| 82.00 | 81.69 || 78.80| 73.83
Soluble silica | 5.28 | 4.59 || 4.61 | 6.54
----------------------+---------+-------------++---------+--------
Potash (K₂O) | .72 | .62 || 1.07 |1.20
Soda (Na₂O) | .09 | .24 || .16 | .21
Lime (CaO) | 1.04 | 1.32 || .71 | 2.92
Magnesia (MgO) | .94 | .92 || 1.16 | 1.44
----------------------+---------+-------------++---------+--------
Br. ox. of Manganese | | || |
(Mn₃O₄) | .05 | .05 || .97 | .62
----------------------+---------+-------------++---------+--------
Peroxid of Iron(Fe₂O₃)| 5.14 | 5.62 || 4.20 | 4.63
Alumina (Al₂O₃) | 5.74 | 5.24 || 7.08 | 8.09
Phosphoric acid (P₂O₅)| .16 | .13 || .12 | .18
Sulfuric acid (SO₃) | .01 | .05 || .02 | .01
Carbonic acid (CO₂) | | || 1.76 |
----------------------+---------+-------------++---------+--------
Water and organic | | || |
matter | 4.58 | 3.52 || 6.54 | 5.37
----------------------+---------+-------------++---------+--------
Total |100.48 | 99.37 || 99.94 | 99.69
----------------------+---------+-------------++---------+--------
Humus | .90 | .48 || |
“ Ash | .42 | .32 || |
Hygroscopic Moisture | 5.60 | 4.84 || 9.77 |10.37
absorbed at °C | 15 | 15 || 15 | 15
----------------------+---------+-------------++---------+--------

_Soils of the Humid Region._—Taking a view, first, of the table showing the soils of the _humid_ region, it appears that the change of vegetation from walnut and hickory to the short-leaved pine bears no visible relation to the increase or decrease of potash or phosphoric acid, but is plainly governed mainly by the amount of lime present. Where the short-leaved pine prevails the soil is almost always either neutral or shows the alkaline reaction in the course of half an hour; but where the long-leaved pine predominates the soil has almost always an acid reaction. The latter is also usually found in bottoms in which the loblolly pine (_P. taeda_) prevails, and where, although the soil may show a fair proportion of lime in the analysis, it does not exist in the form of carbonate.

_The examples here given are from lands not derived from, or underlaid by, limestone formations._ Where the latter exist the percentage of lime is usually materially increased; as it is also in the lowlands or bottoms when compared with adjacent uplands (see above, chapter 10, p. 162; chapter 18, p. 331); as well as in the delta lands of rivers.

_Soils of the Arid Region._—Even a cursory comparison of the soils of the arid regions of the Pacific slope with those of the humid, as given in the above tables, shows some striking points of difference. The most obvious is the uniformly high percentage of lime, and usually also of magnesia, in the arid soils, and that quite independently of underlying formations, calcareous or otherwise. This occurs despite the fact that while limestone formations are very prevalent east of the Rocky Mountains, they are quite scarce west of the same. The red (Laramie) sandstones of Wyoming, the slates of the foothills of the Sierra Nevada, the clay shales, granites and eruptives of the Coast Ranges of California, Oregon and Washington, and the varied black rocks of the great lava sheet of the Pacific Northwest, all alike produce soils of high _lime_ content as compared with Eastern soils not derived from calcareous formations. This fact has already been referred to, but is more fully illustrated in the table below.

Aside from the lime-content, however, it will be noted in the preceding table that the _potash_-content of the arid soils is on the average considerably higher than in those of the humid region. In fact it is hard to find west of the Rocky Mountains (except where high elevation causes a humid climate) any soils as poor in potash as are many of the commonly cultivated lands of the Eastern United States.

Other ingredients do not show such marked differences from the purely chemical standpoint: yet, as will be shown below, the forms in which silica and alumina occur are also not inconsiderably modified.

GENERAL COMPARISON OF SOILS FROM THE ARID AND HUMID REGIONS OF THE UNITED STATES.[126]—In order to verify the conclusions just mentioned upon the broadest basis possible, the following table has been compiled from all available sources; partly published, partly in manuscript only, having remained in the writer’s hands since the cessation of the Northern Transcontinental Survey, prosecuted from 1880 to 1883, under the auspices of the Northern Pacific Railroad, in Washington and Montana. The published data are derived partly from the records of State surveys, partly from the soil work connected with the Tenth Census; partly also from those of Experiment Stations. In most cases it has of course been necessary to restrict the comparison to such analyses as have been made by substantially identical methods, for reasons already given; but in the cases of some states from which numerous analyses made by the Kedzie method, adopted by the Association of Official Chemists, were available, the average has been given but the name of the state starred, to indicate that the percentages, excepting phosphoric acid, are lower than they would be if made by the method adopted by the writer, particularly as regards potash. The adoption of the one-millimeter mesh for the fine-earth sieve instead of the half-millimeter size also creates an unfortunate and ineliminable discrepancy.

[126] Abstracted and revised from Bulletin No. 3, U. S. Weather Bureau, 1893.

In order to exhibit clearly the influence of climate as distinct from other local conditions, it was also necessary to eliminate, in both the arid and humid regions, the soils directly derived from, or connected with calcareous formations; such as the prairies of the Southwestern States, the Bluegrass region of Kentucky, etc. This rule having been applied impartially to the soils of both climatic regions, it can hardly be questioned that the conclusions flowing from a discussion of the results of the comparison are entitled to as much weight as are those of any comparison based on large numbers of observations made, not with reference to the special point under consideration, but with a practical object of which the governing conditions were more or less uncertain, and required to be ascertained by a process of elimination.

The table gives, first, the averages for each ingredient for
each of the states represented, the number of analyses from
which the averages are derived being given in each case.
These averages are given separately for the states of the
humid and the arid regions respectively; and at the base
of each group the grand average is shown in two forms. The
first gives the figures as derived from the aggregate number
of soil analyses in each great group, being 696 for the
humid, 178 for the transition region and 573 for the arid,
divided into the totals resulting from the summation of each
ingredient for the whole 696, 178 and 573, respectively.

The second form is that in which the soils of each state
are considered as representative of the general character
of such state, as the result of intentional selection; such
as actually occurred in the cases of those included in the
census work of 1880. The figures given here are therefore
the result of a summation of the _state averages_
as such, and of their division by the number of states
represented.

It will be noted that while these two modes of presentation
do change the figures a little, yet in either form the
same general result is outlined with striking accuracy.
It is also notable that notwithstanding the less complete
extraction of soil-ingredients in the starred (★)states,
the general ratios between arid and humid soils remain
substantially the same. For Western Oregon, local calcareous
formations compel omission of three lime figures from the
averages.

AVERAGE COMPARISON OF SOILS IN THE HUMID AND ARID REGIONS
OF THE UNITED STATES.
(A) = Number analyzed.
(B) = Insoluble Residue.
(C) = Soluble Silica.
(D) = Sum of Insoluble Residue and Soluble Silica.
(E) = Potash
(F) = Soda.
(G) = Lime.
(H) = Magnesia.
===========================+===+=====+=====+=====+===+====+====+====
| | | | | | | |
|(A)| (B) | (C) | (D) |(E)| (F)| (G)| (H)
| | | | | | | |
---------------------------+---+-----+-----+-----+---+----+----+----
| | | | | | | |
HUMID REGION. | | | | | | | |
| | | | | | | |
Rhode Island ★ | 7|82.41| 1.69|84.10|.15| .09| .43| .27
North Carolina | 20|81.63| 3.50|85.13|.15| .06| .09| .08
South Carolina | 30|85.54| 3.39|88.93|.12| .07| .07| .12
Georgia | 40|86.07| 2.89|88.96|.15| .07| .08| .10
Florida | 10|85.33| 1.33|86.66|.07| .03| .09| .03
Alabama | 50|81.58| 4.89|86.47|.23| .07| .17| .21
Mississippi | 97|85.87| 4.39|90.26|.28| .11| .15| .31
Louisiana | 35|81.12| 3.54|84.66|.19| .09| .16| .23
Arkansas | 38| | |88.54|.17| .06| .08| .43
Kentucky |185| | |86.72|.20| .10| .08| .19
Ohio ★ |140| | |87.00|.26| .35| .28| .44
| | | | | | | |
Oregon (W. of Cascades) | 44|64.82| 5.38|70.20|.23| .19| .83| .73
Average for Humid Region |696|84.17| 4.04|88.21|.21| .14| .13| .29
“ by States | |81.59| 3.45|85.04|.18| .11| .11| .26
| | | | | | | |
TRANSITION REGION. | | | | | | | |
| | | | | | | |
Minnesota. ★--Semi-humid |144|76.60| 8.74|85.34|.30| .23| .65| .43
North Dakota. ★--Semi-arid| 34|68.44| 7.28|75.72|.42| .73| .91| .64
Average for region |178|75.04| 8.46|83.50|.33| .32| .70| .47
| | | | | | | |
ARID REGION. | | | | | | | |
| | | | | | | |
Montana | 59|70.98| 4.17|75.15|.87| .27|1.03|1.36
Idaho | 17|75.34| 5.22|80.56|.56| .26| .85|1.11
Wyoming ★ | 23|76.86| 2.25|79.11|.64| .41|1.91|1.31
Colorado ★ | 16|77.70| 7.10|84.80|.44| .44|1.43| .81
Utah ★ | 38| | |81.04|.98| .53|1.77| .73
Arizona | 20|64.58|13.78|78.36|.82| .43|2.37|1.89
Nevada ★ | 22|71.77| 5.95|77.72|.54| .93|2.04| .96
California |262|66.28| 9.79|76.07|.61| .29|1.25|1.50
---------------------------+---+-----+-----+-----+---+----+----+----
Oregon East of | 7|72.10| 9.68|81.78|.54| .26|1.23| .73
Washington Cascades |109|71.60| 6.09|77.69|.65| .36|1.25| .96
---------------------------+---+-----+-----+-----+---+----+----+----
Averages for Arid Region |573|69.16| 6.71|75.87|.67| .35|1.43|1.27
“ by States | |71.91| 7.11|79.02|.67| .42|1.61|1.14
---------------------------+---+-----+-----+-----+---+----+----+----

(I) = Br. oxide Manganese.
(J) = Peroxid of Iron.
(K) = Alumina.
(L) = Phosphoric Acid.
(M) = Sulfuric Acid.
(N) = Water and Organic Matter.
(O) = Hygroscopic Moisture.
(P) = Humus.
(Q) = Nitrogen in Humus.
(R) = Nitrogen in Soil.
===========================+===+====+====+===+===+=====+====+====+=====+===
| | | | | | | | | |
|(I)| (J)| (K)|(L)|(M)| (N) | (O)|(P )| (Q) |(R)
| | | | | | | | | |
---------------------------+---+----+----+---+---+-----+----+----+-----+---
| | | | | | | | | |
HUMID REGION. | | | | | | | | | |
| | | | | | | | | |
Rhode Island ★ |.04|3.59|3.66|.09|.10| 7.43|5.23|2.59| |
North Carolina |.07|4.72|5.71|.12|.06| 3.98|4.18| | |
South Carolina |.05|2.47|4.59|.11|.06| 3.39|4.22| .42| |
Georgia |.09|2.75|4.02|.11|.10| 3.62|3.54| | |
Florida |.08| .60|1.17|.08|.05| 1.89|1.72| | |
Alabama |.12|3.81|2.70|.13|.05| 4.04|7.07| | |
Mississippi |.14|2.64|4.07|.09|.03| 3.33|5.41| | |
Louisiana |.02|3.12|4.24|.10|.05| 4.26|6.66| | |
Arkansas |.21|3.10|3.51|.15|.05| 3.70|2.47| | |
Kentucky |.20|6.01|3.52|.11|.04| 3.69|1.85| | |
Ohio ★ | |3.11|3.36|.11|.04| 5.04| | | |
Oregon (W. of Cascades) |.09| 11.64 |.23|.16| 3.20| |1.55| |
Average for Humid Region |.13|3.88|3.66|.12|.05| 4.40| |1.22| |
“ by States |.10|3.26|3.68|.12|.06| 3.96| |1.52| |
| | | | | | | | | |
TRANSITION REGION. | | | | | | | | | |
| | | | | | | | | |
Minnesota. ★--Semi-humid | |2.83|4.43|.22|.01| 7.30| |2.91| 6.53|.19
North Dakota. ★--Semi-arid| |3.62|5.17|.19|.05|13.85| |4.67| 7.28|.34
Average for region | |2.08|4.57|.21|.02| 8.55| |3.24| 6.67|.22
| | | | | | | | | |
ARID REGION. | | | | | | | | | |
| | | | | | | | | |
Montana |.37|4.28|6.81|.22|.06| |7.14| | |
Idaho |.02|3.85|6.38|.16| | 5.01|2.00|1.68| 5.95|.10
Wyoming ★ | |3.05|6.61|.18|.11| 5.48| | | |
Colorado ★ | |3.82|4.98|.23|.03| 3.57|2.31| | |.03
Utah ★ |.03|3.08|5.50|.22| | 6.27|2.37| | |
Arizona |.06|4.92|6.43|.13|.06| 3.57| |1.65| |
Nevada ★ |.32|5.67|5.00|.32|.14| 5.93| | | |.12
California |.06|6.61|8.44|.10|.06| 4.74|6.09|0.91|15.23|.14
Oregon } East of |.08| 10.75 |.11|tr.| 4.40| | .67| |
Washington } Cascades | |5.37|6.31|.21|.03| 5.77|5.14| | |
Averages for Arid Region |.11|5.48|7.21|.16|.06| 5.15|5.46|1.13|12.50|.13
“ by States |.13|4.74|6.27|.19|.07| 4.71|5.34|1.03|10.59|.10
---------------------------+---+----+----+---+---+-----+----+----+-----+---

_New Mexico._—Few analyses of New Mexico soils have been made, but the average results of six partial determinations made by Goss, and one full analysis made by Hare according to the method of the writer, and given below, show substantial accord with the averages of the above table. The averages of Goss’ determinations are: Potash .780, Phosphoric acid .221, Nitrogen .108 per cent.

CHEMICAL ANALYSIS OF RIO GRANDE SILT
(_by Prof. R. F. Hare._)

Deposited on land by irrigation.

Insoluble matter 63.70
Potash (K₂O) 1.06
Soda (Na₂O) .22
Lime (CaO) 4.97
Magnesia (MgO) 2.43
Br. ox. of Manganese (Mn₃O₄) .14
Peroxid of Iron (Fe₂O₃) 5.80
Alumina (Al₂O₃) 6.86
Phosphoric acid (P₃O₅) .16
Sulfuric acid (SO₃) .13
Carbonic acid (CO₂) 7.45
Water and organic matter 9.98

Humus 1.17
“ Nitrogen 11.11
“ “ per cent. in soil .13

Hygroscopic Moisture absorbed at °C 2.63

DISCUSSION OF THE TABLE.

_Lime._—Considering in this table, first, _lime_, a glance at the columns for the two regions shows a surprising and evidently intrinsic and material difference, approximating in the average by totals to the proportion of 1 to 11; in the average by states, 1 to 14½. This difference is so great that no accidental errors in the selection or analysis of the soils can to any material degree weaken the overwhelming proof of the correctness of the inference drawn upon theoretical grounds, viz., that the soils of the arid regions must be richer in lime than those of the humid countries. For the differences in derivation would, in view of the wide prevalence of limestone formations in the humid regions concerned, produce exactly the reverse condition of things from that which is actually found to exist; and if further proof were needed it can readily be found in the detailed discussion of the analyses of the soils of the arid areas forming the contrast. This shows that for instance, in Washington highly calcareous soils are directly derived from the black basaltic rocks; while similarly, calcareous lands are found in California to be the outcome of the decomposition of granites, diorites, lavas, clay-shales and sandstones.

It is not easy to overrate the importance of this feature of the soils of the arid region, as it is intimately connected with other theoretically and practically important facts, in part already mentioned.

_Summary of Effects of Lime Carbonate in Soils._—It is best to summarize, briefly, at this point, the advantages (and possible disadvantages), resulting from the presence of a proper amount of lime carbonate in soils, so far as these are at present understood.

_Physically_, even a small amount of lime carbonate, by its solubility in the carbonated soil-water, will act most beneficially in causing the flocculation of clay and in the subsequent conservation of the flocculent or tilth condition, by acting as a light cement holding the soil-crumbs together when the capillary water has evaporated; thus favoring the penetration of both water and air, and of the roots themselves. It should be added that according to the experience of the writer, amounts of lime carbonate in excess of 2% do not add to the favorable effects, except as would so much sand.

As to chemical effects, among the most important are:—

1. The maintenance of the neutrality of the soil, by the neutralization of acids formed by the decay of organic matter, or otherwise.

2. The maintenance, in connection with the proper degrees of moisture and warmth, of the conditions of abundant bacterial life (see above, 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,[127] 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.[128]

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

[128] 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,[129] 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.

[129] “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,[130] 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.

[130] 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.[131] But no definite data showing the importance of this element to crops were available until Loew and his co-workers at Tokyo[132] 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[133] 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.

[131] Rep. Agr. and Geology of Mississippi, 1860, p. 360.

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

[133] 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.[134]

[134] 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[135] | 21.64 | .32 | .03 | .29
California 1281 Chino[136] | 7.60 | .16 | .14 | .17
“ Jackson[137] | 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[138] | .04 | 7.17 | 3.97 | 11.82
California 1281 Chino[139] | .04 | 1.70 | 1.35 | 3.56
“ Jackson[140] | .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
-------------------------------+----------+-------+--------+--------

[135] Analyses by R. H. Loughridge.

[136] Analyses by L. M. Tolman.

[137] Analyses by E. H. Lea.

[138] Analyses by R. H. Loughridge.

[139] Analyses by L. M. Tolman.

[140] 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.[141] 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.

[141] 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;[142] 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.

[142] 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.[143]
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.

[143] 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.[144] 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.

[144] 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.,[145] by Böttcher and Kellner[146] and Nagaoka,[147] 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. [145] Ann. Sci. Agronomique, tome 1, 1899.

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

[147] 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.[148] 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.

[148] 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,[149] 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.

[149] 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.