No. 29, the sugar-cane land from Maui, was still in fair production, but beginning to weaken as against its first production. No. 27, the guava land from Hawaii, originally bore a luxuriant cover of wild guava, but after bearing one fair crop of seed-cane and one of ratoons, the cane planted on it “spindled up” and died so soon as the seed-cane planted was exhausted. Both the island soils, originally derived from the weathering of the black basaltic lavas of the region, were well supplied with mineral plant-food (see above, page 356), and the humus-content in both was exceptionally high; and neither was in an acid condition. The difference in their nitrogen-content, both in the totals and in the humus itself, suggested that notwithstanding the relatively high total of nitrogen in No. 27, it might be nitrogen-hungry, in view of the low percentage of the nitrogen in the humus.
Fig. 59.—Growth of Wheat on Guava Soil from Hawaii Island.
Confirmatory Experiment.—A pot-culture with wheat, the results of which are shown in the [figure below], fully confirm this suspicion. One kilogram of soil was used in each of two pots, one being fertilized with half a gram of Chile saltpeter. The experiment could not be carried to full completion on account of the overwhelming invasion of mildew; but the figures speak for themselves. Moreover, a field trial made on the island with saltpeter, in pursuance of the writer’s recommendation, resulted in a luxuriant growth of the cane.
Data for Nitrogen-adequacy.—It appears from the facts shown above, that for the growth of grasses a nitrogen-percentage in the humus of 1.7 is wholly inadequate, no matter how much humus may be present. A percentage of 3.15 in the Maui soil, No. 29, containing nearly 11% of humus, gave only a fair crop of sugar-cane; on the Berkeley grass plot, with 3.40% and only 1.65 of total humus, the ray grass was barely maintaining life. The ramie, with 4.17% of nitrogen in the soil-humus, was still doing fairly well.
It is doubtless impossible to give one and the same absolute figure for nitrogen-deficiency for all plants and soils. Where the conditions of nitrification are favorable, as in the presence of much of the earth carbonates, a smaller percentage may suffice for the same plants that elsewhere suffer; and it is highly probable that different minima will be found for plants of different relationship and root-habits. But there is every reason to believe that in the nitrogen-percentage of soil-humus, considered in connection with other chemical and physical conditions and soil derivations, we have a means of ascertaining the needs of plants with respect to nitrogen-fertilization, if proper study be given to the subject. Broadly speaking, it appears to be necessary to keep the nitrogen-percentage of soil-humus near 4% to insure satisfactory production.
It having been suggested that the frequent and disastrous crop failures on the noted tchernozem or black-earth soils of Russia might be due in part at least to nitrogen-depletion of the humus, the writer obtained through the courtesy of Prof. P. Kossovitch of St. Petersburg soil samples from the center of the Black-earth region, both cultivated and uncultivated. These samples are in appearance exactly like some of the dark alluvial soils of Louisiana and California, and approach them very nearly in the essentials of composition, as will be seen from the table below:
ANALYSES OF BLACK SOILS,
| Tchernozem (Russia.) | Alluvial Black clay lands. | |||
|---|---|---|---|---|
| Virgin | Cultivated | Louisiana No. 240. | California No. 1167. | |
| Black-land Houma. | Black-land Tulare. | |||
| CHEMICAL ANALYSIS OF FINE EARTH. (No coarse material in soils.) | ||||
| Insoluble matter | 48.38 | 55.09 | 35.48 | 62.43 |
| Soluble silica | 13.21 | 12.28 | 20.76 | 16.99 |
| Potash (K₂O) | .72 | .52 | 1.03 | 1.09 |
| Soda (Na₂O) | .20 | .13 | .13 | .77 |
| Lime (CaO) | 1.51 | 1.31 | .72 | 1.46 |
| Magnesia (MgO) | .73 | .75 | .88 | 1.44 |
| Br. ox. of Manganese (Mn₃O₄) | .05 | .03 | .01 | .06 |
| Peroxid of Iron (Fe₂O₃) | 7.12 | 4.80 | 7.10 | 4.98 |
| Alumina (Al₂O₃) | 5.22 | 4.73 | 15.45 | 6.87 |
| Phosphoric acid (P₂O₅) | .14 | .13 | .15 | .12 |
| Sulfuric acid (SO₂) | .07 | .08 | .25 | .02 |
| Carbonic acid (CO₂) | ||||
| Water and organic matter | 22.78 | 19.94 | 18.52 | |
| Total | 100.13 | 99.79 | 100.48 | 100.59 |
| Humus | 5.11 | 5.54 | 5.07 | 1.33 |
| “ Ash | 1.80 | 1.40 | .91 | .36 |
| “ Nitrogen, p.c. in Humus | 4.63 | 4.22 | ||
| ““ , p.c. in soil | .27 | .24 | ||
| Available Potash (citric acid method) | .014 | .010 | ||
| Available Phosph. acid (citric acid method) | .011 | .008 | .08 | .01 |
| Hygroscopic moisture absorbed at | 12.07 17°C | 18.82 13°C | 5.38 15°C | |
It will be seen that the Russian soil is of high fertility according to the standards given above, and that the nitrogen-content of the abundant humus is amply within the limits of adequacy suggested by the experience in California and Hawaii. The humus-content of the arid California soils is characteristically low as compared with the Russian tchernozem as well as with the Houma backland of humid Louisiana; but its nitrogen-content is doubtless at least three times that of the latter, as is that of the humus of similar lands in which it has been determined.