Feb., 1917
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
DIFFERENT CLASSES OF C A S S E D FOODS
Wrong conclusions have often been reached by confusing different kinds of canned foods and assuming - that a certain condition in one class of foods was due t o the same cause as an apparently similar condition in another class. For instance, acid fruits dissolve an appreciable amount of tin and iron, owing to the solvent action of the fruit acids. Errors have sometimes been made by assuming that tin dissolved in some other types of foods, such as canned pumpkin or shrimp, was also due to acidity, when, as a matter of fact, i t is apparently due to the presence of certain amino bodies. The solution of tin in foods of this class is not accompanied by the generation of hydrogen’and does not form springers Attention has already been called to the fact that springers (cans under very slight pressure) are often caused in acid fruits by the hydrogen liberated by the action of the fruit acids on the metal of the container. It sometimes happens that cans of other products (such as corn) which do not dissolve tin and iron, are found under slight pressure and are apparently springers. Erroneous conclusions have sometimes been reached by assuming that the pressure in these cans is due to the same cause as that in cans of acid fruits that appear t o be in the same condition. This is not merely an academic question. Responsibility for spoilage involving many thousands of dollars is sometimes a t stake. It is often of the utmost importance to determine whether the responsibility rests with the can manufacturer, the canner, or the conditions under which the finished product is stored. VARIATIONS I N CAUSES O F SPOILAGE
In the enforcement of municipal food laws and regulations and, to a certain extent, in the enforcement of state laws, there is sometimes a failure t o discriminate between canned foods which have spoiled by reason of improper sterilization or leaky cans, and those which have become more or less swelled by reason of the hydrogen generated by the action of the fruit acids on the metal of the container. Foods of the latter class, though neither decomposed nor injurious to health, are undoubtedly not merchantable and their sale or use should not be permitted. The condition of springers, and even of what appear to be hard swells in acid fruits, is usually due to the character of storage after the product was canned and, when the goods are criticized, responsibility should be placed where it belongs. The designation of such a product as decomposed is unscientific, because it is not true. It is unjust t o the manufacturer, for the product was merchantable when it left his hands and would have remained so with proper subsequent treatment. A chemist who makes a decision of this kind works injury to the chemical profession in the minds of business men who are conversant with the situation,
It should not be understood that chemists are more prone than others to inaccurate statements regarding the manufacture of foods. Magazine writers give vivid descriptions of processes they have not seen and even prominent authorities on dietary diseases and in the practice of medicine not infrequently make statements which show a complete lack of information of the technology of foods of a generation ago, much less the practice of the present day.
It not infrequently falls to the lot of a chemist in the canning industry to explain to b siness men, as well as he can, how it is possible that a man who makes definite and positive statements regarding a subject of which he has no knowledge is not necessarily equally erroneous in his views on other matters. S 4 T I O N A L C.4h.NBRS’ h S ~ O C I A T l O N
WASHINGTON, D. C.
SOME OBSERVATIONS O N . THE PRESENT STATUS OF THE SUBJECT OF THE AVAILABILITY OF NITROGEN IN FERTILIZERS’ BY
CHAS.B. LIPMAN
In order to gain a clear comprehension of our present-day views on soil fertility it is necessary t o divest one’s self largely of traditional theories, formulas and fancies of the vintage of 1850. If this is so of soil fertility in general, and no progressive scholar in soil science will deny that i t is, it must of necessity be true of that one phase thereof which concerns itself with the availability of some of the plant food elements. These statements are not intended as destructive criticism as the following discussion will indicate. They are meant only for the purpose of arousing from their lethargy those who are either too conservative or too indolent to keep abreast of the scouting parties in soil fertility studies. No one rises with greater alacrity than the writer to render homage to the last two generations of investigators for their splendid contributions to our knowledge of plants and soils. No one appreciates more deeply the value of the gigantic work in chemical analyses of plants, soils, and fertilizers which the investigators mentioned have achieved. We could not very well have done without these numerous analyses. They constitute the growing pains of our adolescent period and as such are presumably ineluctable and necessary accompaniments of normal development. But once we have successfully weathered them, once they have contributed their quota to the creation of our modern views, they have served their purpose and the bona fide scientist must move on t o a sounder and fact-fortified science and a saner philosophy with respect to crop production. Everything which I have to say to you to-day takes its origin on such a basis of thought and action as I have just described &nd is an attempt to make as nearly lucid as my humble powers will permit the answer to the question, “Where do we stand on the problem of the availability of fertilizer nitrogen today?” Let us first understand clearly the meaning of the term “available nitrogen.” In the case of phosphorus and potassium, availability means but one thing, and namely, that some mineral compound containing the element in question is soluble in the soil moisture. So far as we can a t present determine it makes but little difference to the welfare of the plant if the latter assimilates potassium from the sulfate, nitrate, phosphate, or any other mineral salt. Likewise, it seems to be a matter of indifference to the plant, as it were, if phosphorus is presented to it in the form of calcium, potassium, magnesium, or other phosphate. The only condition upon which availability depends, therefore, in the case of all the other essential chemical elements than nitrogen to plant growth, is that they must be in some compound which is soluble in soil moisture. This is not necessarily the case, however, with nitrogen. In fact, the situation with respect to the latter element is very complicated. Some plants appear to assimilate nitrogen with benefit in a large number of water-soluble forms whereas others may assimilate these same forms but be injured by all except the nitrate form. Still others may use nitrogen in the form of ammonia without apparent injury, but are much more wasteful of nitrogen under those circumstances and need much more of i t in the form of ammonia than in the form of nitrate to produce one pound of dry matter. Availability of nitrogen, therefore, if I may repeat again, is by no means so simple a consideration as the availability of the other essential chemical elements. Fortunately, however, we know that the nitrate form of nitrogen is the only one which can be used advantageously and economically by terrestrial plants (rice and similar semi-aquatic plants are of course excepted). Time will not permit fuller consideraPresented at the 53rd Meeting of the American Chemical Society, New York City, September 25 t o 30, 1916.
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tion of the points brought before you in this paragraph, but you can find a detailed discussion of the theoretical considerations involved therewith in Russell’s “Soil Conditions and Plant Growth,” and in the papers by Schreiner and his associates, and in that of Miller and Hutchinson on the general subject of the forms of nitrogen assimilated by plants. METHODS EMPLOYED FOR THE DETERMINATION OF “AVAILABLE” NITROGEN I N FERTILIZERS
The methods thus far emplayed for the determination of availability of nitrogen in fertilizers have been of two classes, v i z , vegetation and laboratory tests. The former class of methods is the most reliable since it permits our obtaining an answer to our question directly from the plant, which is of course the organism affected. On the other hand, it is obvious that the method of vegetation tests is expensive, onerous, and extremely tedious. Besides, no determination of availability of nitrogen fertilizers for a series of crops on one soil may be regarded as pertinent to another group of soils even if the same crops be under consideration. All of this means that a logical consequence of the vegetation test method for the availability of nitrogen in fertilizers would be empirici3m run riot. Even if it were possible t o consummate the huge task involved in such procedure, and it is very doubtful if it would be, the results would always be open to the suspicion of incompleteness. The second class of methods must in the nature of the case be arbitrary for some time t o come. The latter circumstance does not preclude, however, the possibility of their thorough correlation with vegetation tests so that they may become firmly established as specific criteria. The laboratory methods are based on the general principle, or more correctly speaking, on the general assumption that the $ate of oxidation of organic nitrogen is an index of the rate a t which it may be rendered available t o the plant. This is strictly so only in the case of the neutral and alkaline permanganate methods which are described in Bulletin 107 (Rev.) of the Bureau of Chemistry, United States Department of Agriculture. I n the case of the other partially accepted laboratory method, namely, the determination of ammonifiaBility of the organic nitrogen of the fertilizer, this is only partly true since the process of ammonification in soils partakes of the nature both of oxidation and reduction reactions. I n other words ammonia formation in soils represents the algebraic sum of the reduction and oxidation reactions with respect to nitrogen of soil microorganisms. I n the first class of laboratory methods purely chemical reactions are involved while in the second class bacterio-chemical reactions obtain. It will be seen, therefore, that to be valid the first class of laboratory methods must be correlated with the actual supply in vegetation experiments of available nitrogen from any given nitrogenous fertilizer. I n the case of the second class of methods it must be demonstrated that a more or less definite relation obtains between the capability of fertilizer nitrogen to ammonify and the usableness of such ammonia or substances produced therefrom in a similar ratio for plants. In the case of the purely chemical methods the correlation has sometimes been made satisfactorily and sometimes very unsatisfactorily. I n the case of the bacterio-chemical method under analysis, similar though on the whole better, results have been obtained. For these reasons it occurred to the writer that in many soils the oxidation or anlmonification of organic fertilizer nitrogen might not indicate the actual rate of transformation of organic nitrogen through all stages into the final nitrate form which in all probability is the form a t the disposal of all terrestrial plants in the soil. THE NITRIFICATION METHOD AND THE COMPARISON THEREWITH
OF OTHER METHODS
With the foregoing idea in mind the writer proposed the use
Vol. 9, No.
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of the nitrification method as a standard test for the availability of fertilizer nitrogen. This test has of course been used by many investigators in connection with various researches on soil microorganisms, but the proposition has never been made t o employ it as a standard method for the purpose above mentioned as was the case with the ammonification method. The proposition in question is based on the idea that nitrates constitute the end product of nitrogen transformation in normal soils, that they are always found in more or less considerable quantities in soils, whereas ammonia is usually found only in traces, and because all experimental data now a t hand point to nitrates as the form of nitrogen which plants generally will absorb from soils by preference over any other form. I had also suspected for some time that, a t least in certain groups of soils, there might be no parallelism between the ammonifiability and the nitrifiability of organic nitrogen. It should be added before proceeding with the discussion farther, that the strongest support which I possessed for the idea of using the nitrification method as a standard method for nitrogen availability lay in the experiments of Vogel a t Bromberg and others in Germany, England, and in this country which pointed to a fairly accurate correlation between a soil’s nitrifying power, other things being equal, and its crop-producing power. With these ideas as a basis, the writer, with the assistance of Prof. P. S. Burgess, carried out a series of investigations with a large variety of California soils and a considerable number and variety of nitrogenous fertilizers. I n these investigations the ammonifying as well as the nitrifying powers of the soils in question for the fertilizers tested were determined. The nitrification studies have been reported in Bulletin 260 of the California Agricultural Experiment Station and the comparison between the ammonification and nitrification data will soon appear in Soil Science. The method employed for the nitrification studies was an adaptation of the wellknown ammonification method proposed by J. G. Lipman and consisted chiefly in mixing I g. of the organic nitrogenous fertilizer t o be tested with IOO g. of soil, making up to optimum moisture content and incubating for I mo. a t 28 t o 30’ C. At the end of the incubation period nitrates were determined by the colorimetric method. I n brief, the results of these studies seemed t o show the following: I-That the nitrogen in a n organic nitrogenous fertilizer like dried blood, high-grade tankage or fish guano may be readily ammonified, but not necessarily readily nitrified by soils. 2-That the nitrogen in low-grade nitrogenous organic fertilizers like steamed bone meal, cottonseed meal, sewage sludge, and garbage tankage, while ammonifying slowly, might be readily nitrified by the soils in question under the conditions described. 3-That most truly arid soils nitrify the organic nitrogen of low-grade nitrogenous fertilizers well, but that the converse is true with respect t o the high-grade nitrogenous materials. q-The opposite is true of soils with plenty of organic matter and large internal surface which resemble the humid soils. 5-That the excess of ammonia elaborated from the highgrade nitrogenous fertilizers by arid soils is toxic to the nitrifying bacteria and that therefore no nitrates are formed. 6-That sulfate of ammonia is readily nitrified by the truly arid soils but only relatively feebly by the soils of a more humid nature. 7-That relatively speaking, the low-grade organic nitrogenous fertilizers and sulfate of ammonia are better suited for application to arid soils than the high-grade materials. The foregoing conclusions were further strengthened by another series of investigations carried out by the writer and Prof. Burgess
Feb., 1917
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERIiVG C H E M I S T R Y
and Dr. Klein which is soon to be reported in the Journal of Agricultural Research. In these investigations about 50 Eastern soils representing the different states in the Union were compared with about 1 5 0 California soils representing four soil survey areas, in regard t o nitrifying powers. The results of these investigations indicate that in general, and contrary to the teachings of Hilgard and others, the arid soils, so far from possessing more intense nitrifying powers than the humid soils, are actually more feeble than the latter in that respect. This is true whether the soil's nitrifying powers be determined by means of the soil nitrogen alone or by means of added fertilizer nitrogen. I t appears moreover that nearly all humid soils nitrify dried blood nitrogen satisfactorily and sulfate of ammonia nitrogen relatively feebly and that the obverse is true of arid soils. The results of the investigations above described have been called in question by Kelley on the basis 'that our methods of determining the nitrifying powers of soils by admixing with soils such large proportions of fertilizers as I per cent, were not valid, because the concentration of nitrogen in the soil was made too high and therefore abnormal as compared with field practice. Kelley claims that by using very small quantities of dried blood (approximately such as are used in field applications) with soils he was able to obtain good nitrification in cases in which large quantities of dried blood would give no nitrification a t all. That this is beyond question true we have no desire to deny. Our only claim has been and is that the relative ratings we have accorded to soils in the direction of nitrifying powers for different fertilizers would still hold true by whatever arbitrary method was adopted for their determination. In other words, I believe that soils are correspondingly strong or weak in nitrifying power, according as they behave in tests such as we made, so long as any one method is used consistently throughout This seems to me to be true still by further confirmatory experiments of the vegetation order which will be described below, and despite the fact that I believe in all probability we shall have to adopt nitrification methods in general like those proposed by Kelley. I desire t o repeat again, however, that I cannot as yet see how the method which we employed militates against the validity of our conclusions. If it does so a t all it operates in the direction of the degree of accuracy in our results, and not against their character and kind. Many of the theoretical considerations concerned with the results briefly discussed above cannot for lack of time be given here, and my hearers are referred to the papers above mentioned and to others soon to appear for a full discussion of our views and those of others. CONFIRMATORY VEGETATION EXPERIMENTS
On learning of the objections t o our methods and conclusions, which are discussed above, the writer and Prof. Gericke determined to choose a n arid soil which by our method showed no power to nitrify dried blood nitrogen and which was known to be in need of available nitrogen, and by vegetation tests to establish the availability of various fertilizers therein. Accordingly, we chose an arid blow sand from near Oakley, Cal., for the experiments. Pot cultures were employed in the greenhouse and all treatments were run in triplicate. Barley was the crop tested. Moreover, in order t o meet the objections in question, the fertilizers were applied on a field basis in one part of the experiment and on our laboratory basis on the other. Where the fertilizers were employed on the field basis an equivalent of all fertilizers to an 800 lb. per acre application of dried blood was applied, the equivalent being calculated t o equal quantities of nitrogen in all pots. The fertilizers were thoroughly mixed with the soil before the planting was done and the following materials were used: dried blood, steamed bone meal, cottonseed meal, sulfate of ammonia, nitrate of soda and nitrate
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of calcium. The nitrifying powers of the soils in question were determined for all non-nitrate fertilizers used by our regular laboratory method above referred to. According to this it was found that dried blood yielded no nitrates and that sulfate of ammonia, cottonseed meal and steamed bone meal were about equal in nitrifying power. From the very start the growth of the plants in the different pots indicated clear differences in availability of the nitrogen. At first the steamed bone meal was slightly superior to the cottonseed meal and sulfate of ammonia nitrogen, but the latter two forms soon manifested as high an availability as the former and toward the end of the growing season slightly surpassed it. The dried blood showed itself from start to finish t o be distinctly inferior to all the other materials as did also the sodium and calcium nitrates The sodium nitrate, however, was considerably better than the calcium nitrate. When the total weights of dry matter were considered, it was found that the sulfate of ammonia stood first, the cottonseed meal was a close second, and the steamed bone meal a good third. The others were all considerably inferior, but the dried blood nitrogen and nitrate of soda gave similar results and the calcium nitrate was the lowest on the list. So far as the yield of grain alone is concerned, the sulfate of ammonia again stands first and the cottonseed, meal and steamed bone meal are about equal and close seconds. The other fertilizers are about equal as regards grain production and distinctly in the third class. These results will all be presented in full in a forthcoming publication, but enough has been stated above to show that a distinct correlation exists between the nitrifiability of fertilizers in the Oakley soil and their availability to barley plants in that soil. Whether or not the correlation could be drawn more closely by another method is beside the point. Our main thesis is that the nitrifiability of fertilizers as determined by some laboratory method is a reliable guide to the determination of their availability; that soils of different climatic regions differ markedly in that respect; and that the standards on the availability of nitrogen in different fertilizers as previously established under humid soil conditions will probably have to be revised, for arid soils a t least. Without any intention to introduce anti-climactic considerations I cannot refrain from emphasizing again, t o obviate possible misunderstandings, the position taken by me in regard to the subject in hand. I do not claim the nitrification method to be much less arbitrary than the ammonification method. But I do claim that it can be correlated more closely with field effects of nitrogenous fertilizers than the ammonification method and much more so than either of the permanganate methods. This is especially so in the case of arid soils in which ammonifiability seems to fall far short of the nitrification method in usefulness. Again, in saying all this, I am not unaware of the satisfactory correlations drawn by Brown a t Iowa, by J. G. Lipman a t New Jersey, and by others between ammonifying powers of soils and their crop-producing powers. I am merely pointing out that such correlations do not hold for soils in general as do those based on the nitrification method. It should be added, moreover, that none of the laboratory methods can be expected to furnish absolute results, but only relative ones, but if they indicate the latter, they serve their purpose admirably
In view of the foregoing, I would urge the adoption by the fertilizer and soil chemists of the method of nitrifiability of nitrogen fertilizers for the determination of their availability. Whether the nitrification methods be adopted in one form or another is a secondary question that can probably be agreed on without difficulty. UNIVERSITY OF CALIFORNIA
BERKELEY
