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Vol. 15, No. 6
Manganese, Aluminium, and Iron Ratio as Related t o Soil Toxicity’ By R. H. Carr and P. H. Brewer PURDUE UNIVERSITY,LAFAYETTE, IND.
Manganese, aluminium, and iron are present in many soils in easily soluble form and in quantities suficient to be toxic. They are quite soluble in a 5 per cent solution of potassium thiocyanate, giving a red color when iron (together with aluminium) is present, and a green color when manganese is present in manganic form after being ma+ basic enough ( p H 5.5) to remove the red color of ferric thiocyanate. Aluminium, ferric and ferrous iron, manganese, cakium bicarbonate as calcium carbonate, and magnesium precipitate as hydroxides in the order named and range in reaction from p H 4.0 to p H 10.0. It is believed that different amounts of limestone added to the soil precipitate some of these elements in the same order, depending on the amounts added and the p H attained. But little evidence of green color or manganese toxicity was evident when 0.006 to 0.008 per cent of manganese was present in the potassium thiocyanate extract of a soil sample, but 0.015 to 0.03 per cent was accompanied by a very pronounced toxicity.
W h e n a solution of manganese in the form of potassium permanganate combines with the iron o j ~ferric chloride in the presence of potassium thiocyanate, a brown precipitate continues to form and a colorless solution is produced until the two metals are present in equal weights. If the iron solution is added in excess, the color reddens in proportion to the iron added. T h i s would seem to explain the action of certain acid soils which give no red color when a water solution of potassium thiocyanate (or a n alcoholic solution diluted with water) is added to the soil, as noted by Comber. W h e n considerable manganese is found in a soil in soluble form, as indicated by the formation of a green color in the potassium thiocyanate solution, it will require 40 to 50 cc. of 0.1 N base per 50 g. of soil (equivalent to 4 to 5 tons of limestone per acre in addition to that necessary to remove the red color) to precipitate the manganese as hydroxide. The addition of this amount of limestone would be very expensive and in some instances would cost more than the original price of the land.
URING a recent investigation by one of the writers* on the development of a method for the determination of soil acidity by the use of potassium thiocyanate solution, it was noted that certain soils would cause the development of a green color of varying degrees of intensity, after the red color of ferric thiocyanate had been made to disappear by the addition of a base. The significance of this color reaction was not appreciated a t the time, but it has been associated with soils of poor crop production and seems to be worthy of further investigation. The green color is caused by the presence of some soluble manganic compound in the soil uniting with the potassium thiocyanate solution. The combination produces a compound Bimilar in color to that obtain,ed when potassium permanganate is added to a solution of potassium thiocyanate and the solution made basic (to methyl red) with sodium or potassium hydroxide. No color develops when made basic with ammonium hydroxide or when manganese sulfate or chloride is used in place of potassium permanganate. I n the application of this method, some exceptions were noted with certain nonproducing soils, in that only a few hundred pounds or less per acre of limestone would be required to remove the red color, while the soils continued to be about as toxic to plants as before. However, the appearance of varying shades of green color in the potassium thiocyanate solutions upon the removal of the red color gave a clue, and indicated that there was present in considerable quantity a substance which analysis proved to be manganese and which had not been precipitated by the amount of limestone added.
toxicity has been reviewed by Hartwell and Pernloe~%,~ Mirasol14and others, and need not be repeated here. The toxicity of soluble iron is not so well understood, as it nearly always occurs associated with soluble aluminium in an acid soil, but it is not thought to be harmful when present in amounts reported in Table I. The role of small amounts of manganese as an essential plant food element has been presented by McHargue16and the toxicity of excess of soIuble manganese has been reported by Morsel6 Skinner and Reid,’ Kelley18 and others, and there is little doubt but that the presence of soluble manganese compounds (75 lbs. or more per acre) will have a toxic influence on plants in an acid soil. The writers have had rather limited experience in determining manganese toxicity in pot work, but what they have had is in harmony with that reported by others. Considerable experimental work has been done, however, in injecting solutions of these s d t s into cornstalks in concentrations from 0.1 to 0.01 N , and the evidence indicates that aluminium toxicity is quite different in its effect on the plant than that of manganese, as the former causes the stalk and leaves to deaden in 24 hrs. when only 1cc. of 0.1 N aluminium sulfate is added, while a t least 50 cc. of manganese sulfate of the same concentration will be required to effect appreciable injury. Aluminium seems to combine with the protein material located just beneath each node of the cornstalk, thereby interfering with the sap movement and finally resulting in the death of the plant. The work of Asog leads him to conclude that manganese compounds interfere with plant growth by retarding the growth of the roots and causing the development of marginal firing and brown spots on the leaves of the plant. “Microscopic examination of these spots indicated that no disease was present, but that the cells in the affected spots were dead and brown though they retained their shape.”
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NATUREOF ALUMINIUM AND MANGANESE TOXICITY That soluble aluminium and manganese compounds of the soil are toxic to plant growth when present in the soil solution has been known for some time. The literature on aluminium 1 Presented before the Division of Agricultural and Food Chemistry at the 84th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 to 8, 1922. * THISJOURNAL, 13 (1921),931.
Soil Science, 6 (1918),259. I b i d . , 10 (1920),153. J . A m . Chem. Soc., 44 (1922),1592. 6 Mass. Agr. Expt. Sta., Bull. 204 (1921) Bur. Plant Industry, Bull. 4 4 1 (1916). * Hawaii Expt. Sta., Bull. 28 (1912). 9 Bull. Coll. Agr. Tokyo, 2 (1902),177 8
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TABLE I-MANGANESE, ALUMINIUM, AND IRON RATIOAS R B ~ A T ETDO So14 TOXICITY Lime Manganese Required 70 SOIL Lbs./Acre 0.0193 Owensville clay loam 600 Waverly clay 920 0,0035 Crosby clay 1920 0.00176 0.0219 Huntinzton silt loam 1400 0,0035 Tyler d a y 860 0.0017 Subsoil t o No. 103 2600 0.0009 Portsmouth sandy loam 8000 0.0018 Waverly silt 2800 0,0307 Miami clay loam 5600 0.0098 Hagerstown loam (N. C .) 2000 Sioux silt loam 0.0168 4000 Marshall silt loam 0.007 3020 xoo Clarksville silt loam 0.0045 .~~ 1000 0.018 Fox silt loam Marshall silt loam (Present) 2000 0.007 Crosby clay 720 0.031 0,025 Wabash silt loam (Ill.) 1800 1300 Crosby clay 0.026 0.013 Decalb silt loam (Ohio) 1700 2600 0.017 Miami clay 3200 0,002 Subsoil t o No. 120 2400 0.015 Miami clay Hawaii 0 0.09 Crosby clay (limed) 0.008 0 1600 Miami clay (Pa.) 0.028
Soil
T Y P E OF
hT0.
101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 126
Color of Solution Green
...
0.041 0.074 0.045 0.059 0.033 0.0134 0.077 0.068 0.056 0.051 0 0.035 0,080 0,043 0.051 0.056 0.080 0.021 0.112 0.062 0.06
Green Pale green Green
...
G;&
Gr&
Green Green Green Green
..
Green Very green
..
pea green
Trace Trace 0.0045
CROPYIELD TREATMENT Very poor limed Good limed Good limed Very poor Good limed
....
Good response t o phosphate and lime Yield in proportion t o lime added No response t o phosphate No record Fair, little response t o lime Good. fair resvonse t o lime Good: resvonse to lime poor iimed Grind
Fiocyield Plant diseases prevalent Plant diseases prevalent Corn-root rot Poor corn Pia;{ diseases Drevalent Pineapple trouble Good limed Rose bush trouble
The form in which these elements exist in the soil is not well understood. It has been noted, however, that they are not very soluble in distilled water, but are soluble to a considerable extent in a 5 per cent solution of potassium thiocyanate when the soil is in air-dry condition, but not after being burned a t about 700” C. De Sornay13 showed that while 2 per cent nitric acid would dissolve a considerable amount of manganese from the soil, he could not get more than a trace dissolved by water, using the same methods of extraction in each case. It has been shown by Morse6 that the sulfuric acid produced by the application to certain soil of ammonium sulfate, produced highly unproductive soil, and the evidence indicates that it was partly due to the production of soluble manganese. In view of the large amount of mineral extracted from the soil by the potassium thiocyanate solution, as well as the color changes the solution undergoes, it was thought best to make a study of what elements are in the soil solution when the acidity is lessened to any extent by the addition of different amounts of calcium carbonate.
PRECIPITATION OF SOILELEMENTS AS HYDROXIDES In order to do this it was necessary first to secure data as to the pH a t which different elements in the soil solution are precipitated as hydroxides when a base is added. From the work of B1um,14as well as that of Greenfield and BusweLl,15 it was noted that aluminium precipitation is nearly completed a t p H 5.5, especially in the presence of phosphates, and the precipitate starts to redissolve a t about p H 8.6. It has been shown by Conner16 that aluminium was more completely precipitated as a phosphate a t pH 3.9 than it was a t pH 6 as a hydroxide. The writers, using the colorimetric method, found that ferric iron was also precipitated as a hydroxide a t a pH of about 5.5, and ferrous-iron precipitation started a t about pH 6 and was completed a t about p H 7.9, while manganese did not begin precipitation as a hydroxide until a pH of about 7.2 was reached, and was completed a t about pH 7.9, or nearly to the point of red color formation with phenolphthalein. The application of these data to soil-acidity determinations is possible when it is known that the aluminium and ferric iron is about all precipitated when sufficient base has been Bull. Z’association d e s chim. d e sucr. et d e disl , S O (1912), 96. J . A m . Chem. Soc., 38 (1916), 1280. 16 I b i d . , 44 (1922), 1435. 18 J . A m . SOC.Agyon., 1s (1921), 113. 18
Mahin, “Quantitative Analysis,” p. 461. 11 Assoc. Official Agr. Chem., Methods, 1920, p. 315. 11 T ~ I IJOURNAL, S 13 (1921). 931.
%
SOLUBILITY OF SOILMANGANESE
METHODOF OBTAININGSOILEXTRACT
10
0.0008 0.0045 0.0136 0.0068 0.0023 0.0045 0.0135 0.0045 0,0180 0.0045 0.0135 0.0046 0.0045 0.0135 0 0,009 0.013 0.009 0.0036 0.011 0.0036 0.0036
0.051
... ... ...
The soils represented in the table were secured from five states. One, No. 123, came from Hawaii, where soils containing much soluble manganese are quite common. This soil is exceptional in that it contains much soluble aluminium and manganese and no iron. No. 104 contains high manganese as well as aluminium, and has not responded well in crop yield to any fertilizer treatment in 5 yrs., but is improved somewhat where 2000 lbr. of limestone have been added. Tests were made with potassium thiocyanate on the limed soil from the same field, and no red color was produced. In fact, the solution was as green as in the unlimed part, showing that the iron and aluminium had been precipitated, but the continued occurrence of poor crops on limed soil indicated the presence of soluble manganese in amounts sufficient to be toxic. The same conditions were found in Nos. 101, 109, 111. No. 106 is a subsoil to No. 103 and both contain about the same amount of soluble manganese, but the surface soil contains over three times as much soluble iron and is red in water solution, whereas the other is colorless. (The soluble manganese-iron ratio, however, was probably changed when water was added to soil.) No. 107 is a black, sandy soil, and contains very little manganese, but considerable soluble aluminium and iron. This soil is very toxic without liming, but responded remarkably to liming and requires about 8 tons of limestone per acre to change the reaction of the soil to pH 5.5, a t which point these two elements are precipitated as hydroxides or phosphates. Nos. 123 and 124 are very low in phosphates and the aluminium is not all precipitated at pH 5.5. This is shown by the malysis of the extract as well as by the blue-black color produced when an alcoholic logwood extract is added to the colorless solution. Soil No. 107 remains red in a water solution of potassium thiocyanate, as was to be expected from the high iron and low manganese content.
Iron
0.0133 0.060 0.064
%
Green
I n order to secure data as to the amount and prevalence of soluble manganese as well as aluminium and iron in acid soils, an analysis was made of the potassium thiocyanate extract of a large number of soils. In most cases the soil treatment and crop yield were known. In making the analysis 50 g. of 20-mesh1 air-dried soil were used and 100 cc. of a 5 per cent solution of potassium thiocyanate in methyl or ethyl alcohol added and shaken for 1 hr. Fifty cubic centimeters of the filtered solution were used for the determination of manganese, aluminium, and iron. The sodium bismuthate methodlo was used for manganese determination, while the iron and aluminium were precipitated as hydroxides and determined.ll The lime requirement was determined by the potassium thiocyanate method.12 The data for twenty-five of the soil samples thus analyzed are given in Table I.
Aluminium
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added to remove the red color of ferric thiocyanate (pH 5.59, and at this point a green color will develop on standing if the soil contains appreciable amounts of soluble manganese, and a large amount of base will be required to change the solution to a pH of about 7.9, where precipitation of manganese is complete. Hence, the potassium thiocyanate method would not check the Veitch method on soils containing much soluble manganese. The titration curves of these elements, as well as those of magnesium and calcium, are given in the graph. It will be noted from the graph that aluminium starts precipitating as a hydroxide while still quite acid, pH 3.8, and is largely precipitated a t an acidity of pH 5.5, especially where phosphates are present in solution. The same is true with ferric iron, except that precipitation does not begin until nearly pH 5.5, and consequently has a short titration range, as indicated by the curve for this element. It will be noted also that the changing of calcium bicarbonate to calcium carbonate, according to Greenfield and Buswell, follows a curve of precipitation similar to that of manganese, while that of magnesium precipitation as a hydroxide does not become appreciable until a pH of nearly 10.0 is reached. This may be the reason for the supposed efficiency of dolomitic limestone in correcting toxicity when applied to certain soils. kIANGANESE-IROS
TABLE11-MANGANESE-IRON COLORRELATIONSHIP IN POTASSIUM THIOCYANATE
4 5
6 7 8
9
Wt. of Wt. of Manganese Iron G. G. 0,001079 0,0007.57 0.001079 0.000826 0.001079 0,000892 0.001079 0.000963 0.001079 0.001032 0.001079 0.001101 0.001078 *0.001171 0.001079 0.001238 0.001079 0.001397
SOLUTIONS
Excess of Manganese or Iron G. 0,000322 0.000253 0.000187 Manganese excess 0.000116 0.000047 I 0,000022 0.000092 0.000139 0.000318
I
COLOR Colorless
Pink Red
This relationship will be evident from the figures given in Table 11, which were obtained by adding 10 cc. of a 5 per cent potassium thiocyanate solution to 1 cc. of a 0.1 N 17
J . Agr. Sci., 10 (1920), 420.
solution of potassium permanganate in test tubes. T o these solutions were added increasing amounts of iron in the form of ferric chloride. As a result no color developed when manganese was in excess of iron, but when iron was in excess a red color appeared which was proportional to the excess of iron present. OF ALUMINUM, FERRIC AND FERROUS IRON, M A N q A N t J t ; AND MACNLJIUM Ai3 HYDROXIDE3 ,$ AND CALCIUM BICARBONATE A3 CALCIUM CARBONATE PRECIPITATION
COLOR RELATIONSHIP
Another color test for the presence of manganese besides the green color just mentioned was suggested to the writers through a statement made by Comber,17who started the use of potassium thiocyanate in water solution in testing qualitatively for “sour” soils. He noted especially two soils which were known to be acid, having a lime requirement of 0.03 and 0.06 per cent calcium carbonate, but when these soils were tested with a water solution of potassium thiocyanate no pink color developed, as he was accustomed to find in other acid soils tested. This led him to the use of 95 per cent ethyl alcohol as the solvent instead of water, and the two unruly soils gave a red color as was first expected. Comber explains this by saying, “It was expected, on both physical and chemical grounds, that the concentration of the ferric thiocyanate in the liquid phase would be increased by making this alteration.” The physical reason seems apparent enough, but the chemical one became more remote as the writers theorized on the matter, and finally several of the high-manganese acid soils were tested as explained by Comber, with a similar experience. They were tested also by adding an alcoholic solution of potassium thiocyanate, thus securing the red color; then, by adding water, the color disappeared in some high manganese soils and not in others. It was later found that where the color did not disappear there was a preponderance of soluble iron over that of manganese.
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0.1 N NaOH PFR 100 Cc. OF SOLUTION
However, the red color of the ferric thiocyanate can be made to disappear by adding additional manganese. The nature of this reaction, as well as that producing the green color, is being further investigated.
INTERPRETATION OF COMBER’S “SOUR”SOILTEST This color test of Comber’s is being exploited in certain places, and the significance of the test has misled some through their attempts to give it a quantitative interpretation. The writers believe the development of red color when an alcoholic solution of potassium thiocyanate is added to a dry, acid soil means that the soil is more acid than pH 5.5, and that iron, and usually aluminium, compounds are in solution, the depth of red produced being proportional to the soluble ferric iron present, according to the standard colorimetric method of determining iron in this form. However, if a water solution of the thiocyanate is used on the same soil, or if an alcoholic solution of the salt is added to a wet or damp soil, it may be still more acid than pH 5.5, but no color will develop if there is excess of soluble manganese over iron, as previously explained; but in case the iron is in excess over manganese, in presence of just enough water to permit ionization to take place, the red color of ferric thiocyanate will develop even where manganese is present in large amounts. Hence, considerable care must be exercised in the interpretation of the qualitative test.
June, 1923
1ND USTRIAL AND ENGINEERING CHEJfISTRY
DISCUSSION A large amount of investigation has been done along soilacidity lines, and it would seem that the time is ripe for more definite expressions in describing soil conditions than have been commonly applied in the past. The term “neutral” as applied to soil should include to what indicator it is neutral or what p H it has-as neutral to methyl red would leave ferrous iron and manganese and sometimes aluminium in soil solution. “Thoroughly limed” is another term frequently used, and the reader asks, “Thoroughly limed to accomplish what?”-as the limestone required to precipitate ferric iron and aluminium at p H 5.5 will usually be all that is required, unless manganese is present, and there is no use in adding two tons to precipitate the manganese when four or five tons are required to do it. This condition may be determined by the potassium thiocyanate method for soil acidity. It would seem, from the data gathered by numerous investigators, that the most desirable reaction of the soil for
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most crops ranges between p H 5.5 and 6.5. In view of this fact it would not seem feasible to add limestone enough to precipitate the manganese as a hydrate, not only because of the expense involved, but also because the soil reaction is changed from its most productive phase, owing possibly to iron being thrown out of solution and aluminium coming back into solution, as shown by the graph. No suggestions are offered as to best treatment for the manganese soils described to make them productive, except that it was noted that some of these responded best to applications of manure. This may have been due to the organic matter changing the form in which manganese was present. It is not the intention of the writers to convey the idea that all nonproductive soils are due to the presence of these elements in excess, as this is not the case, but it is believed that manganese is the chief cause of toxicity in some soils and aluminium in other soils, and that the potassium thiocyanate method for soil acidity is useful in detecting soil trouble from these sources.
Qualitative Scheme for Detection of Cyanamide and Related Corn poun ds‘ By G. H. Buchanan AMERICANCYANAMID Co., 611 FIFTH AvE., N E W YORK,N. Y.
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In the experimental laboratory of the American Cyanamid are closely related to cyanT HAS been said of cyanamide that, like benCompany the examination of nitrogenous mixtures is a matter amide in a structural or of daily routine, and a standardized procedure which is applicable generical sense, but rather ~ 0 1and ethyl alcohol, it is a fundamental raw to the mixtures most commonly encountered has been deoised. This because of their commerprocedure, worked out in a form similar to that used in ordinary cial relationship. In alphamaterial of organic chemistry. The justice of the qualitative schemes of inorganic chemistry and suficiently explicit betical sequence, the ten characterization will be to be followed by anyone familiar with their technic, has proved SO forms, which are the ones useful that we feel warranted in making it public. most commonly encoungranted when it is recalled that cyanamideis the starttered in the work of this ing material for the comlaboratory, are as follows: merciitl production of such important compounds as urea, Ammonia and its sa,ts Guanylurea and its salts thiourea, dicyandiamide, and guanidine, and that these are Cyanamide Nitric acid and its salts Hydrocyanic acid and its salts Thiocyanic acid and its salts intermediates for a host of other organic compounds. MoreThiourea over, the place of cyanamide in the preparation of the inor~ f its salts ~ ~ ~ ~ Urea ganic compounds of nitrogen is well established-ammonia, nitric acid, and their salts are produced from it, and the It is assumed that the mixtures under examination contain development in this country of a highly successful process no nitrogenous compounds other than those listed. Profor its transformation into cyanide is one of the distinctive vision is made for the interference of the inorganic radicals achievements of recent chemical technology. most commonly found in commercial mixtures. The scheme This increase in the technical applications of cyanamide has consists essentially of three parts. been remarkably rapid, so that the analytical chemist may be PRELIMINARY TESTSFOR THE MOST COMMONINTERcalled upon a t any time to examine a mixture which either FERING RADICALS-sulfide, although rarely present in large contains cyanamide or has been prepared from it. When he amount, is a common constituent of commercial mixtures, attempts to inform himself concerning the analytical char- and must be completely removed on account of its interacteristics of this group of nitrogenous compounds he is more ference in all the tests in which silver nitrate is used. Phosthan likely to meet with difficulty, either because he may not phate, a common ingredient of the mixtures to which this qualifind in the published literature methods of testing which are tative scheme is most often applied, must also be removed. applicable to the commercial mixtures under examination, or PREPARATION OF SOLUTION FOR AxALYsIs-The sulfides because he may be in doubt as to the behavior of nitrogenous and phosphates are removed and a solution suitable for the forms other than those for which the tests have been specif- application of the subsequent tests is obtained. Since it ically chosen. is impossible to draw the analytical directions so closely as to cover all possible contingencies, many details are left to the THESCHEME The scheme here given provides for the identification of judgment Of the lDENTIFICAT1oN OF NITRoGENoUs FoRMS-TestS and ten nitrogenous forms when present in practically any combination. These forms were selected, not because they all comments as seem necessary for their intelligent application are given. The formal procedures are confined to the 1 Presented before the Division of Fertilizer Chemistry a t the 64th analytical operations, and remarks being given Meeting of the American Chemical Society, Pittsburgh, P a , September 4 in the notes. to 8, 1922.
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