Soils, their formation, properties, composition, and relations to climate and plant growth in the humid and arid regions

by Eugene W. Hilgard

All soils bearing such vegetation show with red litmus paper, when wetted, a neutral reaction at first, which after the lapse of twenty or thirty minutes turns to a blue alkaline one; such as is given under the same conditions by the carbonates of lime and magnesia.

But the reverse is not necessarily true; for we occasionally find soils containing considerable amounts of lime carbonate that yet fail to bear lime vegetation. This is the case of extremely heavy clay soils, as exemplified in the table below in the case of the last three soils; while the first, No. 220, exemplifies a case where although potash is exceptionally high, only scrubby oak growth is produced in presence of an amount of lime that in sandy lands would show profuse lime growth.

TABLE ILLUSTRATING THE NEED OF HIGH
LIME-PERCENTAGES IN HEAVY CLAY SOILS.

	Mississippi.			California.
	Flatwoods Pontotoc Co.	Hogwallow Jasper Co.	Ridge Prairie, Smith Co.	Yellowridge, Alameda Co.
No. Sample.	230	242	203	4
CHEMICAL ANALYSIS OF FINE EARTH.
Insoluble matter	77.85	76.76	51.75	86.00
Soluble silica
Potash (K₂O)	.75	.53	.53	.19
Soda (Na₂O)	.11	.19	.22	.15
Lime (CaO)	.18	.42	.48	.48
Magnesia (MgO)	.83	.67	1.01	.45
Br. ox. of Manganese (Mn₃O₄)	.17	.56	.10	.04
Peroxid of Iron (Fe₂O₃)	5.90	4.12	23.79	4.01
Alumina (Al₂O₃)	10.30	10.06	10.85	5.53
Phosphoric acid (P₂O₅)	.05	.06	.15	.06
Sulfuric acid (SO₃)	.03	.06	.02	.02
Carbonic acid (CO₂)
Water and organic matter	3.69	5.73	11.39	4.05
Total	99.86	99.17	100.29	100.99
Hygroscopic Moisture	9.3	6.8	19.7
absorbed at°C	22.0	air-dry	17.0

All of the soils in this table are heavy clays, very difficult to till; in all, the lime-percentage falls below .5%; and none bear any lime vegetation, the Mississippi soils having a stunted growth of black jack and post oaks, such as is universally known to indicate soils too poor for profitable cultivation. The California soil bears stunted live-oak (Q. agrifolia); but not being as heavy as its brethren from Mississippi, though unthrifty, is more readily improved.

Comparison with the two first sandy soils in the table on [p. 352] shows, that with plant-food percentages equal to, or even much below those here shown, not only was vigorous lime growth present, but crop-production was good and even high.

We are thus led to the conclusion that the greater the clay percentage in a soil, the more lime carbonate it must contain in order to possess the advantages of a calcareous soil; and that while in sandy lands lime growth may follow the presence of only .10% of lime, in heavy clay soils not less than about .6% should be present to bring about the same result. This is apparent to the eye in that the dark-tinted humus characteristic of truly calcareous lands, does not appear in clay soils until the lime-percentages rise to nearly 1%; while in sandy lands a much smaller amount (say .2%) will produce this effect.

European Standards.—It is of interest to consider, in connection with preceding discussions, the estimates given by Maercker of Halle, of the practical value of soils corresponding to chemical composition as ascertained by analysis with strong acids, substantially in accordance with the methods adopted by the writer.

PRACTICAL RATING OF SOILS BY PLANT-FOOD PERCENTAGES
ACCORDING TO PROF. MAERCKER,
HALLE STATION, GERMANY.

Grade of Soil.	Potash.	Phosphoric Acid.	Lime.		Total Nitrogen.	Humus Nitrogen.
			Clay Soil.	Sandy Soil.
Poor	Below 0.05	Below 0.05	Below .10	Below .05	Below .05
Medium	0.05 - 0.15	.05 - .10	.10 - .25	.10 - .15	.05 -.10
Normal	0.15 - 0.25	.10 - .15	.25 - .50	.15 - .20	.10 - .15
Good	0.25 - 0.40	.15 - .25	.50 - 1.00	.20 - .30	.15 - .25
Rich	Above 0.40	Above .25	Above 1.00	Above .30	Above .25
Av’age for California	0.70	0.08	1.08			.102
““ Arid Reg.	.73	.12	1.36		.11	(?)
““ Humid Reg.	.22	.11	.11		.12	.166