The total amount of these salts ordinarily found in alkali lands (i. e. in such as in the dry season show saline efflorescences on the surface) is from about one tenth of one per cent to as much as three per cent of the weight of the soil, taken to the depth of four feet. The percentage of salts having been determined in samples representing a tract, it becomes easy to calculate, approximately, the total amounts of each salt present per acre, on the basis of the weight of the soil per acre foot. For the soils of the arid region, such weight will usually range from three million five hundred thousand to four million pounds per acre-foot; the latter being the most usual figure, of which it may be conveniently remembered, that forty thousand pounds represent 1 per cent. We are thus enabled to estimate e. g. the amount of gypsum required to neutralize the carbonate of soda in the salts, or the amounts of valuable nutritive ingredients—potash, phosphoric acid and nitrates—present in the land in the water-soluble form.
As has been shown in the preceding discussion, the analysis at the surface foot alone, which has frequently been alone made, gives no definite clew whatever to the total amounts of salts to be controlled. A full estimate is of special importance in enabling us to forecast what culture plants are likely to succeed on a given tract, by reference to the table of “tolerances” given below ([chapter 23, page 467]).
Composition of Alkali Soils as a Whole.—As may be imagined, the presence of the alkali salts finds expression in the analytical statement of their composition, although not to the extent usually anticipated from their superficial aspect. The table annexed gives the composition of fourteen alkali soils, taken to the depth of one foot, at times when there was no visible accumulation of salts on the surface. The averages of the several ingredients determined are given in the fifteenth column, and a comparison of its figures with those of the general table on [page 377 of chapter 20] will show some marked characteristics. We find the average potash-content to be but little less than twice as great as in the general average for the state of California; in the case of lime the ratio is nearly as one to three, in the case of magnesia nearly one to two; in that of phosphoric acid, one to two and a half, of which in the presence of carbonate of soda an unusually large proportion is in a readily soluble, often in the water-soluble, condition (see preceding table).
The usual proportion of soda, of one-fourth to one-half of the amount of potash, is changed to one-half or three-fourths; in the case of the strongest alkali lands soda may equal or even exceed the potash content. As the latter, however, is invariably high to very high, it does not happen as frequently as might be supposed that the soda content exceeds that of potash as shown by the usual method of soil-extraction with water.
That the potash percentage should always be high in alkali lands, is hardly surprising when it is considered that the continued presence of the salts resulting from rock decomposition affords opportunity for the full exercise of the preference with which potash is known to be retained in soils by the formation of complex zeolitic silicates. In most cases the potash-percentage exceeds .75%, and rises as high as 2.0%; as is shown in the table.
COMPOSITION OF ALKALI SOILS
AS A WHOLE.
- (A) = White Ash, Fresno.
- (B) = Wire Grass, Visalia.
- (C) = Plains, Cross Creek, Tulare
- (D) = Salt Grass, B. V. Slough.
| Collection Number. | (A) | (B) | (C) | (D) | Tulare Lake Alluvium, Tulare County | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| —704— | —585— | —573— | —700— | —891— | —893— | —77— | |||||||
| Coarse Materials. > 0.55ᵐᵐ | 14.29 | 1.50 | 4.10 | ||||||||||
| Fine Earth | 85.71 | 98.50 | all | all | 95.90 | ||||||||
| CHEMICAL ANALYSIS OF FINE EARTH. | |||||||||||||
| Insoluble matter | 85.87 | 88.58 | 66.47 | 71.42 | 66.08 | 69.46 | 87.06 | 89.04 | 54.71 | 64.55 | 56.92 | 67.15 | 67.34 |
| Soluble silica | 2.71 | 4.95 | 3.38 | 1.98 | 9.84 | 10.13 | |||||||
| Potash (K₂O) | .34 | 1.22 | 1.82 | .49 | 2.02 | 1.65 | 1.05 | ||||||
| Soda (Na₂O) | .25 | .68 | .44 | .35 | 2.73 | .54 | .84 | ||||||
| Lime (CaO) | 1.16 | 3.04 | 4.31 | 1.20 | 2.46 | 2.96 | 6.51 | ||||||
| Magnesia (MgO) | .50 | .09 | 1.59 | 1.07 | 2.93 | 3.12 | 3.69 | ||||||
| Bro. ox. of Manganese (Mn₃O₄) | .03 | .03 | .08 | .03 | .03 | .04 | .04 | ||||||
| Peroxid of Iron (Fe₂O₃) | 3.28 | 5.82 | 6.04 | 5.82 | 7.46 | 6.73 | 5.05 | ||||||
| Alumina (Al₂O₃) | 3.22 | 7.14 | 8.69 | .17 | 11.50 | 10.35 | 7.97 | ||||||
| Phosphoric acid (P₂O₅) | .10 | .24 | .74 | .08 | .11 | .16 | .32 | ||||||
| Sulfuric acid (SO₃) | .12 | .66 | .26 | .13 | .01 | .01 | .08 | ||||||
| Carbonic acid (CO₂) | 2.55 | 2.53 | 1.81 | .93 | 4.42 | ||||||||
| Water and organic matter | 1.79 | 7.09 | 4.15 | 1.13 | 4.34 | 5.77 | 3.71 | ||||||
| Total | 99.37 | 99.97 | 99.51 | 99.51 | 99.95 | 99.92 | 101.29 | ||||||
| Chlorin, per cent. | |||||||||||||
| Humus | .60 | 1.00 | 1.00 | .17 | .88 | .47 | |||||||
| “ Ash | .35 | .84 | .74 | .20 | 1.03 | 2.18 | |||||||
| “ Nitrogen, per cent. in Humus | 18.66 | 14.10 | 9.37 | ||||||||||
| ““per cent. in soil | .11 | .15 | .05 | ||||||||||
| Hygroscopic Moisture | 2.22 | 8.53 | 8.74 | 2.16 | 10.50 | 8.6 | |||||||
| absorbed at°C | 14° | 15° | 10° | 10° | |||||||||
COMPOSITION OF ALKALI SOILS
AS A WHOLE.
| Collection Number. | Tulare Substation | Ten-acre tract. Chino. S.B. Co. | Carisa Plain S.L. Obispo | Perris Valley, Jacinto river, Jacinto Plain, Riverside Co. | Sand, Coachella, Riverside Co. | Silt, Imperial, S. Diego Co. | Average of soils. | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| —1159— | —1284— | —1423— | —1758— | —1760— | —2471— | —2325— | ||||||||||
| Coarse Materials > 0.55mm. | 1.96 | 1.00 | 9.00 | 7.50 | 3.50 | |||||||||||
| Fine Earth. | 98.04 | 99.00 | 91.00 | 92.50 | 96.50 | all | all | |||||||||
| CHEMICAL ANALYSIS OF FINE EARTH. | ||||||||||||||||
| Insoluble matter | 72.98 | 73.58 | 62.62 | 70.92 | 57.33 | 69.48 | 41.59 | 63.13 | 35.20 | 58.95 | 58.95 | 77.54 | 62.67 | 73.60 | 63.08 | 72.19 |
| Soluble silica | 6.60 | 18.30 | 12.15 | 21.54 | 23.75 | 11.37 | 10.93 | 9.11 | ||||||||
| Potash (K₂O) | 1.20 | .95 | 1.23 | 1.37 | 1.16 | 1.26 | .74 | 1.17 | ||||||||
| Soda (Na₂O) | .52 | .50 | .77 | 1.97 | .96 | .37 | .29 | .78 | ||||||||
| Lime (CaO) | 1.86 | 5.07 | 4.46 | 4.23 | 8.00 | 2.71 | 3.75 | 3.71 | ||||||||
| Magnesia (MgO) | 1.81 | .84 | 3.12 | 3.80 | 5.69 | 2.20 | 1.68 | 2.29 | ||||||||
| Br. ox. of Manganese (Mn₃O₄) | .08 | .06 | .01 | .03 | .04 | .05 | .01 | .04 | ||||||||
| Peroxid of Iron (Fe₂O₃) | 6.86 | 6.43 | 7.65 | 9.65 | 7.33 | 6.43 | 3.71 | 6.30 | ||||||||
| Alumina (Al₂O₃) | 5.66 | 4.88 | 6.16 | 7.26 | 6.29 | 5.53 | 4.26 | 6.65 | ||||||||
| Phosphoric acid (P₂O₅) | .10 | .21 | .43 | .23 | .28 | .21 | .22 | .20 | ||||||||
| Sulfuric acid (SO₃) | .03 | .06 | .06 | .34 | .21 | .08 | .36 | .17 | ||||||||
| Carbonic acid (CO₂) | 3.76 | 4.19 | 6.49 | 1.05 | 2.32 | 2.14 | ||||||||||
| Water and organic matter | 2.54 | 1.02 | 2.63 | 2.89 | 4.71 | 2.55 | 8.93 | 4.19 | ||||||||
| Total | 100.24 | 99.70 | 99.99 | 99.81 | 99.84 | 99.98 | 99.87 | |||||||||
| Chlorin, per cent | .12 | Trace. | ||||||||||||||
| Humus, per cent | .37 | 1.99 | 1.39 | .60 | .91 | .46 | .69 | .82 | ||||||||
| “ Ash, per cent | .32 | 1.13 | .95 | .92 | 1.75 | .42 | .69 | .82 | ||||||||
| “ Nitrogen, per cent. in Humus | 16.75 | 10.20 | 14.36 | 6.66 | 7.70 | 10.90 | ||||||||||
| ““, per cent. in soil | .06 | .20 | 06 | .04 | .07 | .07 | ||||||||||
| Hygroscopic Moisture | 5.81 | 8.46 | 9.43 | 8.85 | 2.64 | 2.98 | 5.63 | |||||||||
| absorbed at°C | 15° | 15° | 15° | 15° | 15° | 15° | 15° | |||||||||