Chapter 20, Page 379). for in General, We Find That _lower Percentages

of potash, phosphoric acid and nitrogen are adequate, when a large proportion of lime carbonate is present_.—This has already been referred to in connection with the table of soils of low percentages, given above. In the interpretation of results obtained by analysis this point must always be kept in view; and in the numerical statements made below, it must be understood that they refer to virgin soils sufficiently supplied with lime to assure a constant excess of lime carbonate, maintaining the conditions of nitrification and insuring the absence of acidity. (See chapter 9, page 146).

Potash.—In respect to potash, the writer was led by his early investigations in the State of Mississippi to conclude that less than one-fourth of one per cent (.25) of potash constituted a deficiency likely to call for early fertilization with potash salts; while as much as .45% of the same seemed to cause the land to respond but feebly to such fertilization. He has not found it necessary to revise materially that early conclusion, whether from his own work or from that of others. Within the last decade, Prof. Liebscher of Göttingen has arrived at this identical figure from analyses made of soils upon which he had conducted a seven-year series of fertilizer tests; he having found that potash fertilization produced no sensible, or at least no paying results on land giving that figure, and otherwise well provided with plant-food. The different (lower) figures given by Schloesing, Risler and other French chemists in discussing the soils of France are doubtless due to the weak acid and short period of digestion employed in the analysis; an unfortunate discrepancy of methods which precludes any direct comparison of results.

Untersuchungen über die Bestimmung des Düngerbedürfnisses der Ackerböden und Kulturpflanzen, von G. Liebscher; Journal für Landwirtschaft 43 (1895), Nos. 1 & 2, pp. 48-216.

These figures apply both to the arid and the humid regions in the temperate zones. In the tropics we find very much lower percentages quoted as adequate; thus in the laterite soils of India and Samoa, according to Wohltmann, in the soils of Jamaica according to Fawcett, and in those of Madagascar according to Müntz and Rousseaux. There, potash-percentages over .10% seem to be high, and in Madagascar some lands in fair production range as low as .01%. The soil-extractions have however in these cases been made with a weaker acid than above specified, so that some increase of the figures (perhaps 33 to 50%) have to be allowed for. But even then there can be no question that a far less amount of potash, as determined by acid-extraction, is found sufficient for crop production in the tropics; doubtless because of the very intense decomposing (“fallowing”) effect of the continuous heat and moisture, tending also to a rapid decomposition of organic matter and a proportionally rapid formation of carbonic and nitric acids. Such soils are of course constantly kept in a leached condition, as a result of the heavy and continuous rainfall.

La Valeur Agricole des Terres de Madagascar. Ann. de la Science Agronomique, 2’me série, tome 1, 1901.

Phosphoric Acid.—As regards the lower limit of adequacy of phosphoric acid, there is a remarkable agreement in the investigations made everywhere. It was placed at .05% by the writer as long ago as 1860, as the result of investigations made in the State of Mississippi; and the same figure has since been arrived at independently by agricultural chemists in France, Russia, Germany and England. The cause of this remarkable agreement is undoubtedly the readiness with which the phosphates that come under consideration at all for the nutrition of plants, are dissolved by almost any acid treatment likely to be used in soil analysis. Almost the same agreement exists in regard to the “adequacy” of .1% of P₂O₅; while all soils showing percentages between .1 and .05% are considered weak on this side, and liable to need phosphate fertilization soon. One-fourth of one per cent is an unusually high percentage in most countries; .30% and over is exceptional in non-ferruginous soils. But as stated on a previous page, a high percentage of lime carbonate may offset a smaller percentage of phosphoric acid, apparently by bringing about greater availability; and a similar effect seems to result from the presence of a large supply of humus.

On the other hand, very large percentages of finely divided ferric hydrate may, especially in the absence of lime carbonate, render even large supplies of phosphoric acid inert and useless, by the formation of the totally insoluble ferric phosphate. Aluminic hydrate probably acts in a similar manner. The following table gives examples in point, as regards ferric hydrate.

HAWAIIAN SOILS SHOWING HIGH CONTENTS OF FERRIC OXID. (Rept. Cal. Exp. Sta. 1894-5, page 27.) =============================+===============+======================= | Oahu. | Hawaii. -----------------------------+-------+-------+-------+-------+------- NUMBER OF SAMPLE. |No. 21.|No. 22.|No. 24.|No. 26.|No. 27. -----------------------------+-------+-------+-------+-------+------- Coarse Materials. 0.55ᵐᵐ | 2.00 | 2.50 | 4.00 | 3.00 | 5.00 Fine Earth | 98.00 | 97.50 | 96.00 | 97.00 | 95.00 | | | | | CHEMICAL ANALYSIS OF | | | | | FINE EARTH. | | | | | Insoluble matter | 15.84 | 14.49 | 26.99 | 28.66 | 21.07 Soluble Silica | 14.07 | 30.37 | 10.26 | 7.35 | 2.68 Potash (K₂O) | .45 | .26 | .40 | .61 | .44 Soda (Na₂O) | .14 | .08 | .26 | .17 | .25 Lime (CaO) | .26 | 1.04 | .52 | .68 | .28 Magnesia (MgO) | .65 | .80 | .96 | 1.04 | .60 Br. ox. of Manganese (Mn₃O₄) | .05 | .03 | .21 | .20 | .07 Peroxid of Iron (Fe₂O₃) | 39.05 | 19.68 | 19.10 | 18.23 | 30.10 Alumina (Al₂O₃) | 14.61 | 18.29 | 21.41 | 20.18 | 14.38 Phosphoric acid (P₂O₅) | .19 | .32 | .64 | .70 | .97 Sulfuric acid (SO₃) | .03 | .09 | .32 | .21 | .29 Carbonic acid (CO₂) | | | | | Water and organic matter | 14.18 | 14.59 | 18.60 | 21.65 | 28.60 +-------+-------+-------+-------+------- Total | 99.52 |100.04 | 99.67 | 99.61 | 99.73 | | | | | Humus | 3.35 | 3.24 | 4.84 | 5.43 | 9.95 “ Ash | 3.12 | 2.22 | 2.76 | 3.56 | 6.70 “ Nitrogen, p.c. in Humus | 3.30 | 9.800| 2.800| 3.100| 1.71 “ “ , p.c. in soil | .112| .314| .134| .168| .17 Phosph. acid in humus ash | .110| .166| .580| .500| Soluble in 2% Citric acid | .004| .020| .035| .037| .025 in Nitric acid, 1.20 sp. g.| .190| .320| .640| .700| .970 in Chlorhydric acid | | | | | (1.115 sp.g.) | .430| .350| 1.600| 1.280| Hygroscopic moisture 15°C. | 18.50 | 21.25 | 23.07 | 23.14| 23.81 -----------------------------+-------+-------+-------+-------+-------

Unavailability of Ferric Phosphate.—It will be noted that in the soils from Oahu with an overwhelming amount of ferric oxid (mostly in the form of hydrate or rust) the citric acid has taken up only an insignificant amount of phosphoric acid; nitric acid took up 40 to 50 times as much, and chlorhydric doubled even this. In the much less ferruginous Hawaiian soils, though containing more alumina, the citric acid extracted nearly ten times as much; proving that it is chiefly ferric oxid, and not the alumina as has been supposed, that causes the insolubility of phosphoric acid in soils and doubtless also in fertilizers. The very unusually high content of phosphoric acid in the Hawaiian soils, exceeding all others on record, so far as known to the writer, emphasize the effects of ferric hydrate upon soluble phosphates; while the fact that these very soils are greatly benefited by the use of phosphate fertilizers, proves that the Dyer (citric acid) method for the determination of available phosphoric acid which in soils Nos. 21 to 26 yielded results largely in excess of the established limit in European soils, cannot be successfully applied to these highly ferruginous soils. It should also be noted that the amounts of phosphoric acid found in the humus extracted by the Grandeau method is in the first two Hawaiian soils over ten times the amount extracted by citric acid, but that while they rise and fall together, no definite quantitative ratio exists between the two.

It is obvious that in such soils, fertilization with water-soluble phosphates would be likely to result in the quick partial withdrawal of the same from useful action, and that any excess not promptly taken up by the crop, is likely to become inert and useless. It will evidently be desirable to use the phosphates in the form of bone meal or basic slag (Thomas Phosphate), which because of their difficult solubility will be acted upon but very slowly, if at all, by the ferric and aluminic hydrates.

Nitrogen.—In determining the nitrogen-content of the soil, a great variety of methods has been followed. Some include all that can be obtained by the combustion of the organic matters of soil and from the nitrates present in the same; while others, the writer among the number, believe that the mainly important source of nitrogen to the plant being the nitrification of the humus-nitrogen, the determination of the humus by the method of Grandeau, and of the nitrogen contained in it, should be the standard; the unhumified vegetable matter being of no definitely ascertainable value, and the nitrates varying from day to day and being liable to be lost by leaching at any time; therefore forming no permanent feature of the soil. Considering the variety of methods, the unanimity with which about one-tenth of one per cent (.10) has been assumed as the ordinarily adequate percentage is remarkable. In view of the extremely variable amount of nitrogen in the humus (ranging from 1.7 to nearly 22%), the amount of the latter cannot, of course, afford even an approximation to the nitrogen-content; except that as in the humid region, the nitrogen-percentage is not known to exceed about 5 or 5.5%, an approximate estimate can be made on that basis. In the arid region, according to location, the nitrogen-percentage may be from three to six times greater for a similar amount of humus. (See chap. 8. p. 135). In the writer’s experience, a nitrogen-percentage of .1% in the arid region is a very satisfactory figure, indicating that the need of nitrogen-fertilization is not likely to arise for a number of years.

Nitrification of the Organic Matter of the Soil.—In order to test the question whether or not the nitrogen of the unhumified debris existing in surface soils is directly nitrifiable, the writer selected a soil which in its natural condition sustains intense nitrification, so that at some points it contains as much as 1200 pounds of sodic nitrate per acre. The composition of this soil, representing the land of the “ten-acre tract” of the southern California substation, is as follows:

SOIL FROM “TEN-ACRE TRACT,” SOUTHERN CALIFORNIA SUB-STATION, NO. 1284.

Coarse Materials > 0.55ᵐᵐ 1.00 Fine Earth 99.00 ------ 100.00 CHEMICAL ANALYSIS OF FINE EARTH.

Insoluble matter 62.62} 70.92 Soluble silica 8.30} Potash (K₂O) .95 Soda (Na₂O) .50 Lime (CaO) 5.07 Magnesia (MgO) .84 Br. ox. of Manganese (Mn₂O₄) .06 Peroxid of Iron (Fe₂O₃) 6.43 Alumina (Al₂O₃) 3.88 Phosphoric acid (P₂O₅) .21 Sulfuric acid (SO₃) .06 Carbonic acid (CO₂) 3.66 Water and organic matter 6.02 ----- Total 99.70

Water-soluble matter, per cent. .137 Sodic nitrate, per cent. .020

Humus 1.99 “ Ash 1.13 “ Nitrogen, per cent. in Humus 10.30 “ “ , per cent. in soil .203 Total Nitrogen in soil .330 “ “ in unhumified matter .127 Available Potash {citric} .03 Available Phosphoric acid {method} Hygroscopic Moisture absorbed at 15° C. 5.81

It will be noticed that this is a rather strongly calcareous soil, (nearly 9% of calcic carbonate), slightly impregnated with alkali, of which about one-ninth is saltpeter. One portion of this soil was thoroughly leached with distilled water until not a trace of nitrates could be detected in the leachings. Another portion was treated for the removal of humus according to the Grandeau method (see chapter 8, page 132); the extracted soil showed under the microscope an abundance of vegetable debris, some slightly browned as from incipient humification.

The calcic and magnesic carbonates withdrawn in the humus-extraction were then restored to the soil in the form of finely divided precipitates and thoroughly mixed in, first in the dry and then in the wet condition; the extracted soil being repeatedly wetted with turbid water from the leached soil, in order to replace and reinfect it with the nitrifying bacteria. Both soils were then spread out in flat glass dishes and placed in a wooden box containing also a similar flat dish with distilled water, upon which played the draught from the inlet pipe opening into the outer air, with outlet-holes in the cover at the opposite end; thus keeping the air within fairly moist. In addition, the soils themselves were moistened with distilled water every three days and restored to a loose condition by stirring. The whole was placed so as to maintain, during the greater part of the 24 hours, a temperature of from 30 to 35 degrees C. At intervals the samples of both soils were leached and color-titrated for their nitrate content by the picric-acid test. The results, calculated as sodic nitrate, during two years were as follows:

=====================+============+==============+========== Nitrate formed during|Four months.|Twelve months.|Two years. ---------------------+------------+--------------+---------- Leached natural soil | .012 | .0420 | .061 Extracted soil | None. | .0030 | .0042 ---------------------+------------+--------------+----------

It will be noted that in the course of four months, nitrification had not sensibly set in the extracted soil; while in the leached natural soil the nitrate-content had reached to three-fifths the amount originally present, and in the course of a year the nitrate-content of the latter was more than double that of the original (unleached) soil; while that in the extracted soil had only reached one-seventh of the same. At the end of two years we find a still farther increase of nitric nitrogen in both, the ratio between the two remaining about the same (1:14). At the same time the ratio of increase attained at first had materially diminished in the water-leached soil, probably on account of the accumulation of the niter itself.

It thus appears that although the nitrogen of the unhumified organic matter constituted about 40% of the total in the original soil, it would during the entire year have contributed only to an insignificant extent to the available nitrate-supply; while the fully humified “matière noire” contributed fourteen times as much. During the ordinary growing-season of four or five months the unhumified organic matter would have yielded practically nothing to the crop.

Functions of the unhumified Vegetable Matter.—The chief utility of the unhumified matter in the soil consists of course in its gradual conversion into true humus, in the course of which it evolves carbonic gas to act on the soil minerals; while at the same time it helps to render the soil more porous and thus facilitates the action of the aerobic bacteria, for which it serves as food. Hence the addition of vegetable matter to soils not already too “light” is always advantageous, so long as it does not introduce injurious, non-humifiable ingredients, like turpentine in the sawdust of resinous pines. But it is always advisable to first use such matter as litter for stock, in order to better prepare it for the processes of humification, under the influence of ammoniacal fermentation, such as occurs in the decay of green plants or animal matter. A portion of the ash ingredients also is quickly utilized by solution in the soil-water.

Matière Noire the Only Guide.—According to these results it is clear that in order to gain any tangible indications with respect to crop-bearing, it is the nitrogen in the humus proper, the matière noire only, that should serve as the basis; and that as a current source of nitrogen to the plant, the unhumified matter is hardly entitled to more consideration than the “insoluble silicates.” For, the favorable conditions for nitrification under which the above experiment was conducted, will very rarely be even approached under field conditions.

What are the Adequate Nitrogen Percentages in the Humus?—The nitrification of the matière noire being, apparently, the main source of plant-nutrition with that element under ordinary conditions, the question naturally arises as to what may be considered an adequate nitrogen-content of that substance, so as to permit a full supply of nitrates to the crop.

The data extant on this subject are rather scanty, and thus far have all been obtained at the California Experiment Station. But they seem to be very cogent in proving that the growth of crops removed from the soil causes a rapid depletion of the nitrogen in the humus-substance, and that so soon as the nitrogen-percentage in the same falls below a certain point, the soil becomes “nitrogen-hungry;” so that the application of nitrogenous fertilizers is needed and is very effective. The data in the table below, as well as the figure of a culture experiment (No. 52 below), illustrate this point.

ADEQUACY AND INADEQUACY OF NITROGEN CONTENTS OF HUMUS. =========+=======+==================+=========+=========+=========== Collection|Kind of| Locality. |Per cent.|Per cent.| Per cent. Number. | Soil. | |Humus in |Nitrogen | Nitrogen | | | Soil. |in Humus.|in Soil. | | | | | ---------+-------+------------------+---------+---------+----------- 6 | Black |Near Stockton, San| | | | Adobe.| Joaquin Co., Cal.| 1.05 | 18.66 | .196 ---------+-------+------------------+---------+---------+----------- 1679 | “ |Virgin Soil, | | | | | University | | | | | Grounds, Berkeley| 1.20 | 18.58 | .203 ---------+-------+------------------+---------+---------+----------- 1842 | “ |Ramie plot, Univ. | | | | | Grounds, 10 years| | | | | cultivated | 1.80 | 4.17 | .075 ---------+-------+------------------+---------+---------+----------- 1841 | “ |Grass plot, Univ. | | | | | Grounds, 10 years| | | | | cultivated | 1.65 | 3.40 | .056 ---------+-------+------------------+---------+---------+----------- 29 | Dark |Sugar-cane land, | | | | loam. | Maui, H. T. | 10.90 | 3.15 | .347 ---------+-------+------------------+---------+---------+----------- 27 | Dark |Guava-land hills, | | | | loam. | near Hilo, Hawaii| 9.95 | 1.71 | .170 | | Island | | | ---------+-------+------------------+---------+---------+-----------

The Supply of Soil Nitrogen, Rep. Cal. Expt. Station, 1892-93, page 68; ibid., 1894-95, page 28; The Recognition of Nitrogen Hungriness in Soils, in Bull. 47, Div. of Chemistry, U.S. Department of Agriculture, 1895; Landw. Presse, No. 53, July 1885. See also for detailed data chapter 8, page 135.

Calculated upon the true humus substance (matière noire), not by determining total (incl. unhumified) nitrogen in the soil.

Nos. 6 and 1679 show the usual humus-and nitrogen-percentages in the “black adobe” or “prairie” soils of California. Nos. 1842 and 1841 represent the same soil as 1679, upon which, however, ramie and ray grass had respectively been growing, without fertilization, for about ten years; showing that while the humus-content of the soil has increased, the nitrogen-content of the humus has decreased in the case of ramie by 72.78%, in that of the grass by 76.78%; reducing the land to figures commonly found in the humid region. In the case of the ramie, the partial return through the leaves has resulted in a higher humus-content, together with higher nitrogen-percentage, than in the case of the grass, which in the several cuttings annually made, caused a greater depletion in nitrogen and a smaller accession of humus. The grass was very weak in its growth and partially dying out.

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.

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 | Alluvial | (Russia.) | Black clay lands. +------+----------+---------+---------- | | |Louisiana|California | | | No. 240.| No. 1167. |Virgin|Cultivated+---------+---------- | | |Back-land|Black-land | | | Houma. | 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, per cent. | | | | in Humus | 4.63| 4.22 | | “ “ per cent. | | | | in soil | .27| .24 | | Available Potash | | | | (citric acid method) | .014| .010 | | Available Phosph. acid | .011| .008 | .08 | .01 (citric acid method) | | | | Hygroscopic Moisture | | 12.07 | 18.82 | 5.38 absorbed at | | 17°C | 13°C | 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.

INFLUENCE OF LIME UPON SOIL FERTILITY.

Assuming as substantially correct the numerical data given above in respect to the three leading ingredients of plant-food—phosphoric acid, potash and nitrogen,—the dominant role of lime in soil fertility, already mentioned, requires some farther illustration and discussion.

“A Lime Country is a Rich Country.”—The instant change of vegetation when we pass from a non-calcareous region to one having calcareous soils, has already been alluded to. (See this chapter, p. 354). But it is not necessary to be a botanist to see the change in the prosperity of the farming population as one enters a lime district. The single log-cabin with, probably, a wooden barrel terminating the mud-plastered chimney, is replaced, first by double log-houses, then by frame, and farther on by brick buildings, with the other unmistakable evidences of prosperity. Thus this is seen in passing from the mountain region of Kentucky into the “blue-grass” country, which is throughout underlaid by calcareous formations; and thus, likewise, in crossing the strike of the formations of Alabama, Mississippi and Louisiana, or any other region where underlying calcareous formations have contributed to the formation of the soils, as compared with some adjacent district where this is not the case. The calcareous loess areas bordering on the Mississippi river and some of its chief tributaries, are conspicuous cases in point, as are also the prairies of Illinois and Indiana.

Effects of High Lime-content in Soils.—The table below illustrates the fact that in the presence of high lime-percentages, relatively low percentages of phosphoric acid and potash may nevertheless prove adequate; while the same, or even higher amounts, in the absence of satisfactory lime-percentages prove insufficient for good production.

This statement appears contradictory of the observations of Schloesing upon the solubility of phosphoric acid in presence of lime carbonate (Am. Sci. Agron., tome 1, 1899), but the natural conditions seem to justify fully the above conclusion.

SOILS SHOWING LOW PHOSPHORIC ACID PERCENTAGE. ============================+====================================== | HIGH LIME. +-----------+---------+---------------- |Mississippi|Louisiana| California +-----------+---------+------+--------- | Kemper | Vernon | Yuba | Amador | County | County |County| County ----------------------------+-----------+---------+------+--------- Number of Sample. | 139 | 171 | 499 | 1113 ----------------------------+-----------+---------+------+--------- Chemical Analysis of | | | | Slate Fine Earth. | | | | Soil ----------------------------+-----------+---------+------+--------- Insoluble matter | | 53.19 | 78.79| 49.96 | 67.08 | 74.29| | 64.92 Soluble silica | | 21.10 | 3.80| 14.96 ----------------------------+-----------+---------+------+--------- Potash (K₂O) | .70 | .33 | .25| 1.48 Soda (Na₂O) | .14 | .06 | .04| .43 Lime (CaO) | 1.37 | 1.40 | 1.02| .60 Magnesia (MgO) | 1.00 | .74 | .40| 2.21 Br. ox. of Manganese (Mn₃O₄)| .25 | .15 | .02| .05 Peroxid of Iron (Fe₂O₃) | 6.75 | 4.52 | 5.81| 11.52 Alumina (Al₂O₃) | 13.07 | 11.36 | 6.28| 12.31 Phosphoric acid (P₂O₅) | .03 | .05 | .04| .05 Sulfuric acid (SO₃) | .08 | .12 | .02| .02 Carbonic acid (CO₂) | | | | Water and organic matter | 9.45 | 7.27 | 3.64| 6.63 +-----------+---------+------+--------- Total | 99.91 |100.29 |100.19|100.22 +-----------+---------+------+--------- Hygroscopic Moisture | 11.45 | 18.11 | 4.80 | 5.74 absorbed at °C | 8.0 | 25.5 | 15.0 | 15.0 ----------------------------+-----------+---------+------+---------

============================+======================================= | LOW LIME. +-----------------+--------------------- | Mississippi | California +---------+-------+-----------+--------- |Chickasaw|Carroll| Shasta |Humboldt | County |County | County | County ----------------------------+---------+-------+-----------+--------- Number of Sample. | 164 | 48 | 559 | 207 ----------------------------+---------+-------+-----------+--------- Chemical Analysis of | | | | Fine Earth. | | | | ----------------------------+---------+-------+-----------+--------- Insoluble matter |93.62 | | 76.27 | 65.35 | 94.98| 89.39 | 80.38| 72.24 Soluble silica | 1.36 | | 4.10 | 6.90 ----------------------------+---------+-------+-----------+--------- Potash (K₂O) | .09 | .19 | .50 | 1.13 Soda (Na₂O) | .07 | .08 | .04 | .28 Lime (CaO) | .07 | .08 | .10 | .11 Magnesia (MgO) | .13 | .07 | .40 | 3.33 Br. ox. of Manganese (Mn₃O₄)| .02 | .12 | .01 | .12 Peroxid of Iron (Fe₂O₃) | 1.09 | 1.21 | 6.67 | 6.99 Alumina (Al₂O₃) | 1.47 | 4.37 | 8.48 | 10.24 Phosphoric acid (P₂O₅) | .03 | .05 | .04 | .17 Sulfuric acid (SO₃) | .01 | .05 | .01 | .02 Carbonic acid (CO₂) | | | | Water and organic matter | 2.00 | 4.09 | 3.97 | 5.63 +---------+-------+-----------+--------- Total |99.94 | 99.70 |100.62 | 100.24 +---------+-------+-----------+--------- Hygroscopic Moisture | 1.80 | 4.66 | 5.05 | 7.87 absorbed at °C |11.0 | 11.0 | 17.0 | 13.0 ----------------------------+---------+-------+-----------+---------

Nos. 139 and 171 are heavy black prairie soils of high productive capacity, whose production had, at the time of sampling, lasted almost undiminished for over twenty years. Nearly the same is true of the two California soils, Nos. 499 and 1113; which, however, are ferruginous loams of only moderate clay-content. In all, the percentage of phosphoric acid shown by the analysis is at or below the recognized limit of deficiency, while the lime-content of all is as high as is required for the welfare of any soil, however constituted. The potash-percentage also is low in all except the “red foothill soil,” No. 1113.

Passing to the soils of low lime-content, we find the two Mississippi soils, poor in both potash, lime and phosphoric acid, so low in production as to be wholly unprofitable in cultivation without previous fertilization; No. 559, from California, produced two fair crops of barley and then no more. No. 207, is the soil of Eel river bottom, California; profusely productive at first, by virtue of its high content of both potash and phosphoric acid; but “giving out” under a few years’ culture of clover or alfalfa (which draw heavily upon lime), and quickly restored to productiveness under the influence of dressings of quicklime. In this case the soil had become acid, a condition which always militates against the success of culture plants, and more especially against those of the leguminous relationship.

What are Adequate Lime Percentages?—We have in the presence or absence of the natural vegetation peculiar to calcareous soils (“calciphile”) an excellent index of the presence or absence of such amounts of lime carbonate as fulfil the conditions of its beneficial effects. Lists of such plants for the United States are given farther on; they agree almost throughout with such plants as are everywhere recognized by American farmers as indicating productive soils.

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| Hog- | Ridge | Yellow | Pontotoc| wallow| Prairie,| ridge, | Co. | Jasper|Smith Co.|Alameda Co. | | 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. =====================+==========+==========+==================== | | | Lime. Grade of Soil. | Potash. |Phosphoric+----------+--------- | | Acid. | Clay | Sandy | | | Soil. | Soil. ---------------------+----------+----------+----------+--------- Poor |Below 0.05|Below 0.05|Below .10|Below .05 Medium | 0.05-0.15| .05 - .10| .10- .25| .10-.15 Normal | 0.15-0.25| .10 - .15| .25- .50| .15-.20 Good | 0.25-0.40| .15 - .25| .50-1.00| .20-.30 Rich |Above 0.40| Above .25|Above 1.00|Above .30 =====================+==========+==========+==========+========= Av’age for California| 0.70 | 0.08 | 1.08 “ “ Arid Reg. | .73 | .12 | 1.36 “ “ Humid Reg.| .22 | .11 | .11 ---------------------+----------+----------+-------------------- | | Grade of Soil. | Total | Humus | Nitrogen.| Nitrogen. | | ---------------------+----------+---------- Poor | Below .05| Medium | .05-.10| Normal | .10-.15| Good | .15-.25| Rich | Above .25| =====================+==========+ Av’age for California| | .102 “ “ Arid Reg. | .11 | (?) “ “ Humid Reg.| .12 | .166 ---------------------+----------+----------

It will be observed that according to Maercker’s valuation, the average California soil is “rich” in potash and lime, but only “medium” as regards its contents of phosphoric acid and nitrogen. In this respect, and almost throughout, Maercker’s ratings are in remarkable agreement with those made by the writer as far back as 1860. It also appears that Maercker’s figures for “normal” soils correspond to those of the American humid regions; the “arid” figures for potash and lime being “abnormally” high.

See discussions of analyses of Mississippi soils in the Report on the Agriculture and Geology of Mississippi, 1860; same in Rep. On Cotton Production, Tenth Census, 1880, Vol. 5; also Appendix to the Report on the Experiment Stations of the University of California, 1890, p. 163.

Unfortunately neither Maercker’s method of preparing the soil extract, nor his ratings as given in the table, are accepted by all soil chemists even in Germany. As will be seen by reference to Wohltmann’s work on the soils of Samoa and Kamerun (chap. 21, p. 404), his methods and numerical estimates differ widely from those given by Maercker, and also from those adopted by the Prussian soil surveys. Reference to the analyses of the soils of Madagascar by Müntz and Rousseaux, given in the same chapter, page 406, shows still another different method, although as it happens their numerical estimates do not differ very widely from those of Wohltmann. In both cases, a special, more incisive extraction is made for the determination of potash. Why the same more energetic action is not used for the other ingredients also, is not stated, and is obscure. Fortunately, in all cases the action is at least sufficiently strong to secure the dissolution of all the lime existing in the form of carbonate, and of all, or nearly all, the phosphoric acid not securely locked up as ferric phosphate; the latter being inert, is of no special interest (see Analyses of Hawaiian Soils, this chapter, page 256).