“Putty Soils” is the name popularly given in the Cotton States, and probably elsewhere, to soils usually occurring in low ground and also known as “cray-fishy.” They consist of very uniform, powdery sediment, with little or no coarse sand and still less of clay to render them coherent. When wet these soils behave precisely as would glazier’s putty, adhering to the surface of even the best-polished plowshare, so that no furrow-slice can be turned and the plow is soon dragged out of the ground. At a very closely limited condition of moisture such lands may plow fairly well; but when this limit is passed in the least (as sometimes happens in the course of a single day), it turns up only hard clods, which in a few hours of sunshine become so hard that no instrument of tillage short of a sledgehammer will make any impression upon them. The physical analysis of these usually gray soils shows that they contain only a trifling amount of clay; perhaps 1 or 2%, playing the part of linseed oil in making putty out of whiting. Even the addition of lime does not help such soils much, because there is little or no clay to flocculate. They are, as a matter of fact, among the most refractory lands the farmer has to deal with. A soil showing similar behavior, though not quite as extreme as in the case of the Gulf or Cotton States’ soils in question, occurs at the culture substation at Paso Robles, California, and is probably closely correlated to the physical hardpan referred to above. The physical analysis of this soil yielded the following result:
| MECHANICAL ANALYSIS OF SOIL. | |||
|---|---|---|---|
| Designation. | Diameter. | Percentage. | |
| Sand | .50 | mm. | 14.24 |
| .30 | “ | 15.17 | |
| .16 | “ | 8.88 | |
| .12 | “ | 5.60 | |
| Silt | .072 | “ | 6.75 |
| .047 | “ | 8.35 | |
| .036 | “ | 8.55 | |
| .025 | “ | 6.03 | |
| .016 | “ | 17.77 | |
| “Clay” | ? | 7.50 | |
It would seem the best and almost only remedy to be applied to such soils as these is the introduction of vegetable matter or green-manuring, by which their texture is loosened: for the hauling of mere clay upon the land would hardly accomplish the purpose intended, within the limits of farm economy.
Dust Soils, which during the dry season are even in their natural condition so loose as to rise in clouds and render travel very uncomfortable, are not uncommon in arid countries, e. g., in Washington and adjacent parts of Oregon, on the uplands bordering the Columbia, Yakima and Snake rivers. The physical analyses of three of such soils, given in the table below, will convey some idea of their peculiarities in this respect.
| PHYSICAL ANALYSIS OF DUST SOILS. | |||||
|---|---|---|---|---|---|
| Hydr. Value. | Diameter. | No 17. | No. 37. | No. 79. | |
| Clay | <.0023. mm. | <.10—? | .93 | 3.59 | 1.27 |
| Silt | <.25 mm. | .010 | 30.93 | 13.06 | 32.29 |
| .25 to .5 | .016 | 3.20 | 5.82 | 12.75 | |
| .5 to 2.0 | .025-.047 | 7.18 | 27.37 | 37.51 | |
| 2.0 to 8.0 | .047-.120 | 21.88 | 43.78 | 10.92 | |
| Sand | 8.0 to 64.0 | .12- .50 | 32.39 | 49.57 | 3.97 |
| Total | 96.57 | 98.18 | 98.72 | ||
Slow penetration of Water.—Soils of this class are wetted with extreme slowness by irrigation water; so that when first taken under cultivation it sometimes takes twenty-four hours to soak the land for twelve inches in each direction. Irrigation furrows must be placed very close together and in large numbers, in order to ensure the wetting of the soil so that the crop shall not suffer from lack of moisture at a distance of two or not more than three feet. Where the irrigation furrows are drawn farther apart a fine stand of grain may be seen within eighteen inches of the same, while farther away the crops may be dying from lack of moisture. This difficulty is by no means infrequent in the arid region, and is difficult to overcome except by frequent and thorough tillage, which gradually increases the rapidity of water-penetration; as has been shown in the soils of the alluvial prairies of the Yakima country in the State of Washington. It is necessary, however, to take care that they shall always contain an adequate amount of humus or vegetable matter, in order to prevent re-consolidation by the burning-out of the humus during the warm, rainless season.
There is an unmistakable resemblance between these dust soils of the Northwest and the “putty” soils mentioned above; both showing a very low percentage of clay with a relatively large amount of the finest sediments, with a sudden downward break of the curve before the coarser grain-sizes are reached. It would seem as though the absence of these intermediate grains favors the close packing of the fine sediments in the interstices of the coarse ones, thus bringing about the imperviousness, which is the chief obstacle to their cultivation.
Effects of coarse Sand.—Coarse sand intermingled with heavy clay soils has but little effect in improving the tilling qualities, unless carried to such excess as renders it financiallyimpracticable. In actual practice it is frequently possible to improve such soils by properly distributing upon them the washings of the adjacent hills, which will always carry sands of many grades; and when it is intended to improve garden land by hauling sand it is important to choose the latter so as to complement the deficient grain-sizes of the soil. The sand of wind drifts or dunes is generally well adapted to such improvement, being, as Udden[28] has shown, of a fairly definite composition of sufficiently wide range of grain-sizes for the purpose.
The effects of humus in modifying soil texture are discussed farther on.