Fig. 58.—Soil-dilution Experiment:
Photograph showing Mature Plants.
The following table shows the percentage composition of the original as well as the diluted soils, while the photographs show the development of the plants in their successive stages, so far as these could be observed; the continued attacks of mildew and plant lice preventing full maturity being attained.
COMPOSITION OF BLACK ADOBE
AND SAND DILUTIONS.
| Chemical analysis of fine earth. | Original soil. 1:0 | Dilutions. | |||
|---|---|---|---|---|---|
| 1:1 | 1:3 | 1:4 | 1:5 | ||
| Insoluble matter | 54.50 | 77.25 | 88.62 | 90.00 | 92.42 |
| Soluble silica | 19.60 | 9.50 | 4.75 | 3.80 | 3.17 |
| Potash (K₂O) | .73 | .36 | .18 | .15 | .12 |
| Soda (Na₂O) | .20 | .10 | .05 | .04 | .03 |
| Lime (CaO) | 1.15 | .57 | .29 | .23 | .19 |
| Magnesia (MgO) | 1.08 | .54 | .27 | .22 | .18 |
| Br. ox. of Manganese (Mn₃O₄) | .04 | .02 | .01 | .01 | .01 |
| Peroxid of Iron (Fe₂O₃) | 8.43 | 4.22 | 2.11 | 1.68 | 1.40 |
| Alumina (Al₂O₃) | 7.92 | 3.96 | 1.98 | 1.58 | 1.32 |
| Phosphoric acid (P₂O₅) | .19 | .10 | .05 | .04 | .03 |
| Sulfuric acid (SO₃) | .04 | .02 | .01 | .01 | .01 |
| Carbonic acid (CO₂) | |||||
| Water and organic matter | 6.54 | 3.27 | 1.64 | 1.31 | 1.09 |
| Loss in analysis | 1.18 | .09 | .04 | .03 | .03 |
| Total | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
| Humus | 1.21 | .60 | .30 | .24 | .20 |
| “ Ash | .94 | .47 | .23 | .19 | .16 |
| “ Nitrogen, p. cent in Humus | 18.58 | 18.58 | 18.50 | 18.58 | 18.58 |
| ““p. cent in soil. | .203 | .10 | .05 | .04 | .034 |
The restricted volume of soil occupied by the roots in the undiluted adobe soil, together with the very abundant development of root-hairs, is very striking. A marked change in these respects is manifest in the first dilution, and increasingly so as dilution increases; the paucity of root-hairs is very marked in the last (greatest) dilution, in which, as the photograph of the plants shows, the development was decidedly behind that in the pot containing dilution 1:4. The latter in fact showed the best development not only in this case, but in two other series of tests conducted at the same and subsequent times; and strangely enough, also in the pulverulent, “sandy loam” soil of the southern California substation tract. In the latter series, which for lack of space cannot be figured here, the main difference was that in the undiluted soil the roots filled the entire soil mass, instead of remaining near the surface, as in the pure adobe. It is possible that the latter was too wet when given the full half of its water-capacity, although, as the figures show, the water was slowly introduced from below by means of glass tubes, ending within a shield to prevent puddling.
Limitation of Root Action.—These results, representing five soils of different percentage-composition and physical character, but identical chemical composition and ratios between the several ingredients, and similarly acted upon by the atmospheric agencies in the past, illustrate strikingly the impossibility of judging correctly of a soil’s productiveness from percentages of chemical ingredients alone. It is clear that the physical characters of the land as well as its depth, must be essentially taken into account. But there is obviously a certain limit beyond which greater perviousness and root-penetration cannot make up for deficiency in the absolute amounts of plant-food within possible reach of the plant; for in the case of excessive dilution these are rendered partially inaccessible within the time-limits of a season’s growth.
It is hardly necessary to say that these experiments require repetition with the aid of the experience acquired in these first trials, not only in the laboratory but also in the field. It will be especially interesting to compare with the results obtained in these strongly calcareous soils, the effects of dilution in such soils as those of Florida, mentioned below; the probability being that where lime is naturally deficient, the effects of dilution will be much more pronounced in diminishing production, because of the absence of the previous favorable action of lime upon the availability of the soil-ingredients.
Lowest Limit of Plant-food Percentages and Productiveness found in Virgin Soils.—The subjoined table shows some of the very low plant-food percentages found in natural soils, all being of a sandy character:
| Mississippi Soils. | Florida Soils. | ||||||
|---|---|---|---|---|---|---|---|
| Homochitto Bottom. | Shell Hammock. | Pine Woods. | Pine Flats. | Pine Lands. | |||
| First Class. | Second Class. | ||||||
| Number of Sample. | 68 | 83 | 206 | 214 | 6 | 7 | |
| CHEMICAL ANALYSIS OF FINE EARTH. | |||||||
| Insoluble matter | 92.16 | 96.08 | 93.23 | 95.59 | 94.46 | 95.63 | 96.51 |
| Soluble silica | 1.67 | .88 | |||||
| Potash (K₂O) | .15 | .05 | .26 | .06 | .19 | .12 | |
| Soda (Na₂O) | .04 | .06 | .07 | .05 | .04 | .06 | |
| Lime (CaO) | .12 | .10 | .12 | .02 | .07 | .06 | |
| Magnesia (MgO) | .21 | .12 | .18 | .07 | .04 | .04 | |
| Br. ox. of Manganese (Mn₃O₄) | .28 | .05 | .15 | .05 | .06 | .05 | |
| Peroxid of Iron (Fe₂O₃) | 1.18 | .52 | 1.25 | .46 | .32 | .22 | |
| Alumina (Al₂O₃) | 3.22 | .46 | 2.36 | .85 | .92 | .47 | |
| Phosphoric acid (P₂O₅) | .08 | .10 | .03 | .02 | .11 | .09 | |
| Sulfuric acid (SO₃) | .05 | Trace | .02 | Trace | .09 | .06 | |
| Carbonic acid (CO₂) | |||||||
| Water and organic matter | 2.70 | 3.02 | 2.33 | 2.28 | 1.88 | 1.81 | |
| Total | 100.19 | 100.56 | 100.00 | 99.45 | 99.85 | 99.49 | |
The average of plant-food percentages in all these soils is quite low, and at first sight there seems to be little choice between them. Yet two of them—Nos. 68 and 88, from Mississippi—are not only quite productive at the outset, but also fairly durable. This becomes measurably intelligible when it is known that both are of great depth, and so well drained that roots can descend for many feet; while the composition of the soil-material is almost identical for three or four feet. On the other hand, both Nos. 206 and 214 are quite shallow, being underlaid by sand almost devoid of plant-food at about two feet. In addition, both have extremely low percentages of phosphoric acid; while the rest show near .10% of that ingredient, an amount which, as will be seen hereafter, is considerably above the recognized limit of deficiency. The two Florida soils however bear only pine; they are underlaid by almost clean sand at two or three feet, and are therefore quickly exhausted. It will also be noted that their lime-percentage is only about half of that of the two first-named Mississippi soils, both of which bear a strong growth of deciduous timber trees, grape vines, and other vegetation indicating the presence of lime carbonate.