Jan.,
1913
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
THE SIGNIFICANCE OF T H E LIME-MAGNESIA RATIO I N SOIL ANALYSES
lends it plausibility, since there are so many physical, chemical, and biological factors involved in fertility.
B y P. L. GILE AND C. N. AGETON Received Sept. 13, 1912
LIME-MAGNESIA RATIO I N SOILS OF P O R T 0 RICO
Somc twelve years ago Loew announced the hypothesis t h a t plants make their maximum growth, other factors of course being favorable, only when the available lime and magnesia are present in a certain ratio. All the details of this hypothesis do not require repetition here. Briefly, it is held t h a t a n excess of either lime or magnesia in the soil is injurious, and that by increasing the deficient element until a ratio of CaO to MgO of I/I t o 4 / 1 obtains (the optimum ratio varying for different crops), a more favorable condition for growth is secured. Investigators in different countries have tested Loew’s hypothesis in water and pot culture experiments. Without reviewing all these experiments,I the results in some cases have been confirmatory and in others contradictory. I t is evident that if this hypothesis holds true under soil conditions, the lime-magnesia ratio is of the utmost significance in soil analysis2 -determining one of the TABLEI.--kNALYSES Soil Number of sample.. . . . . . . . . . . . . . . Insoluble residue. . . . . . . . . . . . . . . . . . . . Volatile matter.. ..................... Alumina, Also3
39 1 33.59 29.14
Lime. CaO.. . . . . . . . . . . . . . . . . . . . . . . . . . Magnesia, MgO.. .. Potash, K20. . . . . . Phosphoric acid, P2
26.11. 0.22 0.57 0.16
33
In a survey of the soils planted t o pineapples1 it was found that the soils producing vigorous plants and good yields of fruit contained lime and magnesia in the following ratios: 1/5, 13/1, 3/1, 3/1, 6/1, I O / I , 2 5 / I , 4 O / I , 73/19 I / 2 , 2 7 / I , 1/13! 7/19 S / I , 7 / 1 , 1 4 / 1 1 1/3.” Four soils analyzed from the Florida 12/1, Keys had the ratios of CaOjMgO of 38/1, 30/1, IOO/I and ~ O O / I . I n some of the soils where the ratio is very wide there is less than I per cent. of CaO and only a trace of MgO. Where both the bases are present in such small quantities i t might very well be that a n unfavorable ratio would not affect the fertility t o such a n extent as though they were present in greater quantities. However, a particularly fertile soil, producing some of the finest pineapple plants on the Island and supporting a luxuriant citrus grove, contained 4 . 2 5 per cent. of CaO, 0 . 1 7 per cent. of MgO, and 0 . 2 4 per cent. of CO,. The lime-magnesia ratio
HACIENDAS “&fERCEDITA”
AND “FLORIDA”
Soil
Sub-soil
Soil
392 32.56 28.76 5.98 4.05 27.21
400 28.39 31.48 5.08 3.75 29.23
trace
trace
401 19.53 35.52 3.85 2.56 36.79 0.91 0.25 0.13
O F SOILS PROM
Sub-soil
0.63 0.05
0.16 0.14
422 23.73 34.53 4.59 3.40 32.19 1.32 0.05 0.19
Soil
Sub-soil
423 21.45 34.40 4.42 3.82 34.21 1.56 0.04 0.10
452 21.81 32.27 8.54 4.34 25.78 0.69 0.42 0.19
453 9.48 39.16 4.07 1.06 435.53 0 59 0.33 0.10
Sub-soil
-
-
-
-
__
-
Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
98.53
99.24
98.23
99.54
100.00
100.00
100.04
100.32
Nitrogen, N ....................... Carbon dioxide, COz. . . . . . . . . . . . . . . . . Calcium carbonate, CaC03.. . . . . . . . . . Reaction to litmus. .
.22 19.72 44.86
.01 20.20 45.94
.20 21.69 49.34
.14 27.91 63.49
.33 26.81 60.99
.23 24.85 56.54
.09 21.99 50.27
.03 35.70 81.22
alk.
alk.
alk.
alk.
alk.
alk.
alk.
nlk.
fertility factors, and showing the need of a n application of either lime or magnesia. Soil investigations carried on in Porto Rico during the last five years afford data t h a t bear upon this subject. Also a series of experiments have been conducted which show t h a t the lime-magnesia ratio affects the growth of plants under some conditions but not under others. Analyses made of the typical soils planted t o pineapples and sugar cane show t h a t the content of lime and magnesia varies greatly. If the hypothesis of Loew holds true for soil conditions and the ratio of lime t o magnesia is one of the controlling factors in fertility, then those soils with a very unfavorable ratio should be of low productivity. If the soils with unfavorable ratios are not of low productivity it would seem t o show t h a t the hypothesis is not tenable, at least not for all soil conditions. On the other hand, the fact t h a t some soils with favorable ratios are fertile and other soils with unfavorable ratios are unfertile does not prove the hypothesis, but merely References to the different experiments are given in Circ. 10 and Bull. 12 of the P. R. Agr. Expt. Station. For determining the lime and magnesia available to, or affecting the plants, Loew prescribes digestion of the fine earth with 10 per cent. hydrochloric acid-practically the method of the A. 0. A. C. 1
in this soil, then, was 2 5 / 1 and the absolute quantity of lime was high. The soils from the Florida Keys which have the lime-magnesia ratios of 3 8 / 1 , 30/1, IOO/I, and ~ O O / I contain, respectively, 21.13 per cent. CaO and 0.56 per cent. MgO, 2 0 . 3 4 per cent. CaO and 0.69 per cent. MgO, 1 7 . 0 1 per cent. CaO and 0 . 1 7 per cent. MgO, 10.96 per cent. CaO and trace of MgO. The analyses show that the lime is present partly as carbonate and partly combined with organic matter. These soils are reported as bearing a good crop of pineapples. They are exceptional in containing a tremendous amount of organic matter. Because of the high content of organic matter pineapples grow well in these soils although they will not succeed in ordinary soils containing 2 per cent. of carbonate of lime.3 These soil analyses show t h a t the good pineapple soils of Porto Rico have, on a n average, wide limemagnesia ratios, that an exceptionally fertile soil has Bull. 11, P. R . Agr. Expt. Station. In some of the analyses reported in Bull. 11 the magnesia is present only a s a trace. In calculating the ratios for these sods it is assumed that 0 . 0 2 per cent of MgO is present, although the amount is probably nearer 0.01 per cent or less. 3 P. L. Gile, Bull. 11, P. R. Agr. Expt. Station. 1
2
34
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
a ratio of 2 5 / 1 , .and that some soils having ratios of 30/1 t o ~ O O / I are a t least ordinarily productive. A partial survey has also been made of the soils planted t o sugar cane. Most of the clay lands carry from 0.2 per cent. t o 1.50 per cent. of lime and from 0.5.per cent. to 2 . 0 0 per cent. of magnesia and no carbonate, most of the lime and magnesia probably being present as silicates, as the soils are low in organic matter. I n these clay soils the ratio of lime to magnesia runs I/I, 1/4, 4/5, 1 / 2 , 2 / s , 3/2, 1/3, 1 / 2 , 1 / 3 , 3 / 2 , or generally with the magnesia slightly in excess of the lime. Some of these soils are quite productive and others very unproductive. There is no correlation between the fertility and the lime-magnesia ratio, as was to be expected. Certain of the loamy soils, however, show great variations in the content of lime and magnesia. I n Table I are given the acid analyses of four samples of surface soil with the sub-soil. Samples 391, 400, 422, and 452 represent the surface foot of soil, and samples 392, 401, 432, and 453 are the respective sub-soils taken from the first t o second foot. Each sample is a composite of three borings. Samples 391, 400 and 4 2 2 are all taken from different areas in a field belonging t o Central “Mercedita” near Ponce, P. R. This field is planted to sugar cane and is one of the most productive cane soils on the Island. Last year the average return from this field for plant cane was over sixty tons of sugar cane (variety Cristalina) per acre. This is a n exceptional yield for Porto Rico and a very good yield for any country. Samples 452 and 453 are the soil and sub-soil respectively of a field in Hacienda, “Florida,” Yauco, P. R. This field is on a rather steep side hill and, while it does not produce so much as the valleys below, it is, with irrigation, a fairly productive soil. The analysis would seem t o show the crops were limited more by the nitrogen supply than anything else. The above analyses show that in different parts of the “Mercedita” field the first foot of soil contains lime and magnesia in various ratios of I I ~ / I ,1461/1 and 24/1 and the respective sub-soils have ratiosof 1360/1, 40/1 and 2 2 / 1 . I n the “Florida” field the top soil contains lime and magnesia in the ratio of 42/1 and in the sub-soil the ratio is 7 7 / 1 . The areas where the different samples were taken were selected as representatively fertile areas. As each sample is a composite of three separated borings it is evident that the fields were fairly sampled. The determination of carbon dioxide in these soils shows t h a t the lime, a t least, is present as carbonate, thus in a n easily available form. The above analyses show that sugar cane cangrow luxuriantly in soils containing a tremendous excess of lime over magnesia, providing the other fertility factors are in proper condition. It is, of course, not impossible that still larger crops might be obtained from the “Mercedita” field if the lime-magnesia ratio were nearer I , but in view of the exceptional yield this is very improbable. We are then confronted with the facts: t h a t some
Jan., I913
soils with lime-magnesia ratios of 30/1 t o ~ O O / I are productive pineapple soils ; t h a t one soil with the ratio of 2 j / I is a n exceptionally productive soil for citrus fruits and pineapples ; that another soil where the ratio varies from 2 2 / 1 to 1461/1 is a n exceptionally productive soil for sugar cane. Thus the observations of Porto Rican soils would seem t o show that in soil analyses the ratio of lime to magnesia is of no signjficance and that cases where the ratio parallels the fertility are due t o chance. The many pot experiments of other investigators which have failed to show any influence of the lime-magnesia ratio‘ make it clear t h a t the above observations are not exceptional. CONDITIONS UXDER W H I C H T H E RATIO MAY I N F L U E N C E GROWTH
The above analyses do not show, however, that there is no physiological basis for Loew’s hypothesis. I n act, from the work of Loew and numerous investigators it is apparent that under certain artificial conditions the ratio of lime to magnesia may markedly influence growth. The results obtained by Osterhout,z Kearney and Cameron,~ Lipman,4 and Hansteenj show that in certain solutions (containing few salts) not only the ratio of lime to magnesia affects growth, but also the ratio of other bases. From the work of the above investigators and also of Benecke,6 it is apparent that solutions of various single nutritive salts are toxic to plant and lower animal life. A mixture of two salts is less toxic than either alone and, in a more complex mixture, all the salts which are toxic alone may lose their toxicity. Lime salts exert the strongest antagonism in overcoming the toxicity of magnesium salts although lime is not specific in this antagonism. These facts furnish a physiological basis for such a n hypothesis as t h a t of Loew. The hypothesis of the lime-magnesia ratio, however, does not explain the generality of these facts but merely the special case of the antagonism between lime and magnesia. This work on the antagonism of various salts in solution does not necessarily show t h a t the ratio of lime to magnesia affects growth under all conditions. I n a series of experiments made by one of us,’ where rice was grown in a comple e nutrient solution containing lime and magnesia in excess, i t was found that the concentration influenced the effect produced by the ratio of lime t o magnesia. When the lime and magnesia were present in concentrated solutions, the ratio of these bases markedly influenced the growth. As the concentration of the lime and magnesia was diminished, however, the influence of the ratio diminished. I n dilute solutions. ratios of lime to magnesia between I O / I and 1 / 1 0 had no effect on the growth. This work mentioned above, on the toxicity of va1 D. Jleyer, Landw. Yakrb., 1904, p. 371. D. Meyer, Landw. Yahrb., 1910, Euianszungband 111.. p. 254. 0. Lemmermann, et al., Laddw. Yahrb., 40, Xos. 1-2. 2 W. J . V. Osterhout, Bot. Gaz., 44, 2 5 9 . 3 Kearney and Cameron, U. S. Dept. Agr., K e p o r f 7 1 (1902). 4 Chas. B. Lipman, Bot. Gaz., 48, 105. j B. Hansteen, Yahrb. f. z’iss. Botanik, 47, 289. W. Benecke. Ber. d . D . Bot. Gesell., 26, 3 2 2 . P. L. Gile, Bull. 13, P. R.Agr. Expt. Sta.
’
Jan., 1913
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
rious single salts and the antagonistic action of other salts in overcoming the toxicity, applies to conditions obtaining in solutions. Because the addition of ime exerts a strong antagonism in overcoming the toxicity of a solution of magnesia and vice uemu, it does not necessarily follow that such a n antagonistic action is exerted in ordinary soils. In ordinary soils it is probable that the ratio of the bases has no bearing on the fertility in the respect noted above, for the following reasons : I . The soil particles exert a physical effect in diminishing the toxicity of any salt solution. Jensen found that in quartz sand much higher concentrations of toxic salts were required to produce death than in water cultures.= 2 . The soil solution is a more or less balanced solution, containing a great variety of ions, and undissociated molecules.2 3. The soil solution, so far as we can determine, is a dilute solution. These acts, of course, do not apply to soils impregnated with alkali salts. In alkali soils we might expect to find the productivity influenced by the ratio of lime t o magnesia, as well as by the ratios of other bases,^ since in such soils we have relatively concentrated solutions of soluble salts. The experiments with soils in pot cultures to test the hypothesis have thus far given conflicting results. The method of these experiments has been to add the carbonates, sulphates, and chlorides of lime and magnesia to different soils to alter the lime-magnesia ratios. The pot experiments of Loew and his coworkers in Japan have apparently confirmed the theory.4 These experiments have been criticized on the ground that they were not always carried out in duplicate, that too few plants were grown, and t h a t the conclusions mere not always based on the relative weights of the plants but sometimes on the relative heights and number of branches.5 The pot experiments of Meyer6 and of Lemmermann, Einecke and Fischer,7 which are by far the most exhaustive on the subject, have given negative results. These have been criticized on the ground that too many plants were grown per pot and that insufficient fertilizer was supplied, 8 It should be borne in mind in judging these experiments that when large doses of the carbonates or oxides of lime and magnesia are added t o the soil, not only the ratio of lime t o magnesia is altered, but also the reaction of the soil. Since ground marble, ground magnesite, precipitated calcium carbonate and precipitated magnesium carbonate vary in the intensity S. H. Jensen, Bot. Gaz., 43, 11. How successive additions of various ions diminish the toxicity of a solution is shown IIY W. J . V. Osterhout, Bot. Gaz.. 44, 259. 3 Kearney and Cameron, LOC. cit. Vd. Reports in Vol. I., Nos. 1 and 2, of Agr. E x p t . Sta., Tokyo; also Vols. IV., V., VI., VII., of Col. of Agr., Tokyo Imp. Univ. 0. Lemmermann, et al., Landw. Yahrb., 11, Xos. 1-2. p. 177. D. Meyer, Land& Yahrb.. 1904, 3 7 1 : 39, 254 (1910) (Enganzungsband 111). 0 . Lemrnermann, A . Einecke, H. Fischer, Lartds. Yahrb., 4 0 , N o s .
'
1-2.
Loew, I b l d . , 42, 181 (1912).
35
of their action,' a mixture of ground marble and ground magnesite will induce a reaction different from that induced by either alone. It has been amply shown t h a t the reaction of a soil is one of the strongest factors in determining the growth of certain plants. Hence in the experiments where large amounts of lime and magnesium carbonates were applied to the soil the results in many cases may be attributed as well t o variations in the soil reaction as to variations in the lime-magnesia ratio. SUMMARY
The soil experiments to test directly the effect of the lime-magnesia ratio on the growth of plants have given conflicting results. This lack of' agreement may be due to the fact that some of the experiments were not properly carried o u t ; or it may be that the apparently confirmatory results arrived a t by some investigators are to be attributed rather to alterations in the soil reaction than to the lime-magnesia ratio. From the effect of salts on plants grown in water cultures we should not expect plants to be influenced by the ratio of the bases under the conditions obtaining in any but alkali soils. From field observations i t is certain that soils with an exceedingly wide ratio of lime to magnesia may be exceptionally fertile. Hence it would appear that in analyses of ordinary soils the ratio of lime to magnesia is of no significance, but in analyses of the soluble salts of alkali soils the ratio of lime to magnesia may be exceedingly important. PORT0
RICO.%GRICULTURAL
EXPERIM.IENT S T A T I O Y
>fAYAGUBZ
A PROPOSED MODIFICATION OF T H E OFFICIAL METHOD O F DETERMINING HUMUS B y 0. C. SMITH Received August 24, 1912
The determination of the humus content of soils
has always presented difficulties because of the inability to obtain a clear solution for evaporation. There have been several methods proposed but none of them have given very good satisfaction on all soils. By adding ammonium carbonate solution, a clear filtrate is obtained. By evaporating to dryness and again extracting with 4 per cent. ammonium hydroxide a clear solution is obtained, but this process is long and tedious and some of the humus is a p t to be occluded by the precipitate of clay. Other methods for obtaining clear solutions are by the use of a Pasteur filter, a centrifuge and a modified clay filter. The official method states that the 4 per cent. ammonium hydroxide solution should be shaken for the first twenty-four hours and then allowed to stand twelve hours and settle. The clearest part is then drawn off,filtered, and the determination made without any further treatment. This filtering does practically no good, and it is only very rarely that enough clear solution can be obtained in this way to make the determination satisfactorily. Our experience shows, however, that if the sediment is not allowed to settle, but is shaken well, and all of the soil possible is poured 1 D. Meyer, Landw. I'ahrb., 1904, 371 : also Kossovich and Althausen. E x p . Sta. Record, 23, 226.
