April, 1924
I,YDCSTRIAL A N D ENGTNEERING CHEMISTRY
371
Available Nitrogen in Fertilizers’ Need of a New Method for Its Determination By James W. Kellogg B U R E A UOF CHEMISTRY. PENNSYLVANIADEPARTMBNT OF AGRICULTURE, HARRISBURG, PA.
HE subject of available nitrogen in fertilizers and studies of methods for its estimation have occupied the active interest of agricultural chemists ever since commercial fertilizers were first produced and used for supplying plant food to the soil. For several years the agronomist engaged in soil investigations and the fertilizer control officials, as well as the manufacturers, have been vitally interested in this problem, and have hoped for a simple, accurate, and dependable method that would show what proportion of the total nitrogen of a fertilizer was available, in the same fashion and with a t least the same degree of accuracy that available phosphoric acid and water-soluble potash can be estimated.
T
OFFICIALMETHODS rlbout twelve years ago two well-known methods were brought to the chemists’ attention, which have been adopted as official by the Association of Official Agricultural Chemists -namely, the alkaline and neutral permanganate methods. These methods show approximately the proportion of waterinsoluble organic nitrogen that is “active” or rendered soluble by the solutions used, thus indicating the quality or character of the materials used to supply organic nitrogen. They do, no doubt, give some idea of the quality of that portion of the nitrogen insoluble in water, for which purpose they were developed, but they do not tell how much of the total nitrogen is “available,” as this word is understood by the average agriculturist. The results obtained by one method are greatly variable and unlike those obtained by the other. Experience has shown that consistent results are not obtainable by either of them on the same sample. This point has been well illustrated by Magruder,2 who has shown that of twelve rrsults on the same sample, secured by several analysts using the alkaline permanganate method, the water-insoluble nitrogen varied from 0.22 to 0.62 per cent, the “active” from 0.12 to 0.31 per cent, resulting in conclusions that from 42 to 64.3 per cent of the water-insoluble organic nitrogen was “active” or that the character of the materials supplying the organic nitrogen was either “good” or “poor.” As is.well known, criteria by which the sources of organic nitrogen should be classed as “good,” “passed,” or “poor” have not yet been agreed upon, thus causing confusion in the interpretation of the results obtained by these methods. These points, as well aB the facts that the expression “activity of the waterinsoluble nitrogen” is difficult for the average layman to comprehend and that these two methods do not give credit to the proportion of nitrogen soluble in water, make it highly desirable to find a new method which will show directly the amount of available nitrogen in a fertilizer. This view is also expressed by Robinson and Winterj3as follows: The authors’ experiences lead t o two conclusions regarding the future development of methods for determining t h e availability of organic nitrogen: ( 1 ) t h a t any new methods must be built upon a n entirely new foundation, for which more fundamental 1 Presented under t h e tiLle “A New Method Needed for Available Nitrogen in Fertilizers” before t h e Division of r’ertllizer Chemistry at the 6 6 t h Meeting of t h e American Chemical Society, Milwaukee, Wis , September LO to 14, 1923. 2 J rlssoc. Oficaal Agr. Chem., 6 , 464 (1922). 8 Ibid., S, 446 (1922).
chemical knowledge of the factors involved in availability is necessary; and ( 2 ) t h a t it is highly desirable t h a t more systematic vegetation experiments be carried on, thus giving more reliable standards upon which t o base conclusions regarding t h e value of any methods proposed.
The originators of these methods, and others who have followed them closely, never considered that they should be used to show the total available nitrogen in a fertilizer, but only that they should indicate the quality of that portion of the nitrogen insoluble in water. A few, however, have interpreted the results as “available” nitrogen, even considering the “active” as “available,” thus lending additional confusion to a proper understanding of the quality of nitrogen under examination. It is not intended to discredit the value of the present tFo methods, nor the great amount of research work thus far accomplished; but from the point of view of the control official and the sellers and users of commercial fertilizers, it is held that a new method, which can be simply, accurately, and inexpensively used, is highly desirable and urgently needed. If it has been possible to find a method for the determination of citrate-insoluble phosphoric acid and from this to estimate the L‘available,’’it ought to be possible to develop a new method which, in a similar way, would show what proportion of the total nitrogen in a fertilizer was available. At the 1921 New York meeting of this division this subject was discussed, and it was the opinion of many that some action should be taken toward reporting available nitrogen in fertilizers. A statement was made that the present permanganate methods were not adaptable for fertilizer control work, and that the publication in fertilizer reports of the results of official analyses so obtained was misleading and confusing to the average person. Therefore, realizing the need for some new method or else a modification of the present ones, such spare time as could be found was given to a study of this problem, and the following main points were considered:
REQUISITES OF NEWMETHOD Any new method should require but one weighing of a portion of a sample and one determination for nitrogen in addition to that for total nitrogen, thus reducing the time and cost of operation. Such a method should give accurate check results in the hands of the average analyst. A medium should be used which would, after previously extracting the water-soluble nitrogen, attack, reduce, and dissolve that portion of the nitrogen in organic materials which is believed to be used, a t least to a large extent, by growing crops, and which, from experience and as determined by pot or field tests, would be considered as available. In other words, the medium so employed should measure the greater portion of the nitrogen in those ammoniated materials that are known to be highly available, and should attack only a relatively small proportion of the nitrogen in such materials as are considered low in available nitrogen as well as in commercial value. Finally, it ought to be possible to determine the unavailable nitrogen and, by deducting this from the total, to show
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
the difference as “available,” which should consist of that soluble in water and that reacting to the medium used. SELECTION O F MEDIUM Since it was the organic matter of the fertilizer that was to be treated or reduced, it followed that some medium was desired, which, acting as a reducing agent, would attack and dissolve the partly disintegrated, or what might perhaps be termed “available,” organic nitrogen and not act upon the nitrogen considered as unavailable, and which had not undergone a natural or processed reduction. Because of the properties of oxalic acid this reducing agent was used as a medium in the development of a tentative method for determining the amount of available nitrogen. It is realized that this method is far from being ideal or telling the true story, and also that the results obtained are by no means complete enough to draw conclusions as to the efficacy of the method or to base much dependence on the figures secured. The results thus far secured by this method, however, have proved interesting, and it is at the suggestion of those who have given encouragement to this work that the method and the results are presentgd at this time. The main object of this paper, therefore, is only to show the need for a new method and to stimulate interest and activity to such an extent that in the near future some new method will be brought forth and adopted, which can be used by all analysts throughout the country. STRENGTH OF MEDIUM AND TIMEOF TREATMENT Having decided upon the medium and the use of a 1-gram sample and 100 cc. of solution, as suggested by the permanganate methods, the next step was to determine the proper strength of medium and the time of treatment. A sample of mixed goods, showing 40 per cent activity and dried blood high in activity by the alkaline permanganate method, was tried out with strengths of from 2 to 20 per cent, boiling from 15 to 30 minutes. The 2 per cent solution gave over 80 per cent available nitrogen in the mixed goodsqand over 50 per cent in the dried blood. Eight special mixtures were then prepared, consisting of varying proportions of nitrate of soda, dried blood, mixed goods high and low in alkaline permanganate activity, acid phosphate, and pulverized leather, and tests were made by digestion with 0.5, 5, and 10 per cent solutions of oxalic acid. In the samples estimated as high and in those low in available nitrogen, the 15-minute boiling in 100 cc. of 0.5 per cent acid gave correspondingly high and low results, the leather showing 63 per cent available nitrogen. As these figures proved more promising than the greater strengths, a few trials were made with 0.05 N , 0.02 N , 0.01 N , and 0.005N solutions, which indicated that the 0.01 N acid might give more interesting results. DETERMINATION OF NITROGEN AVAILABILITY Samples were then obtained from experiment stations and manufacturers, representing goods that had been used for activity tests by the alkaline permanganate method and a few that represented pot tests-in all about thirty different samples, which were employed for further studies. Most of them were then analyzed for activity by the alkaline permanganate method, and treated for availability by the 0.01N oxalic acid method, the analytical work being performed by G. J. Kuhlman, Jr., of this bureau. The results, together with the few pot test figures obtainable, are presented in the table, and represent the last work performed with the tentative method as finally used, which is as follows: TENTATIVE METHOD-A 1-gram sample of fertilizer is weighed out and transferred to a No. 40, 12.5-cm. Whatman
Vol. 16, No. 4
filter paper and washed with distilled water (room temperature) until the filtrate amounts to 250 cc. The filter paper and residue are then transferred to a 300-cc. Pyrex beaker (tall form 76 X 114 mm.), 100 cc. of 0.01Noxalic acid solution (room temperature) are added, and the whole is digested by heating to the boiling point and boiling continuously for 15 minutes. (Total heating and boiling should require approximately one-half hour.) Immediately after digestion is completed, 50 cc. of cold distilled water are added and the solution is decanted, filtered, and washed with cold water through a No. 40, 12.5-cm. Whatman filter paper until the filtrate from washings asounts to 250 cc. The filter paper and residue, which includes the insoluble or inactive nitrogen, are then transferred without drying to a Kjeldahl flask and the nitrogen determined (Gunning method preferred). The nitrogen thus obtained deducted from the total nitrogen previously determined is estimated as available nitrogen. Note.-Blanks for nitrogen in filter paper and reagents should be determined and deducted.
DISCUSSION OF RESULTS-It will be noted that in many instances-as, for example, in Nos. 10,11,17, and 19-there were many inconsistencies, but on the other hand some of the results appear to give proper credit to materials considered high in availability, such as dried blood and some of the base goods-as, for example, Nos. 23, 24, 27, and 31. Compared with the nine pot tests, the oxalic acid method checks fairly well in No. 18, blood, and Nos. 13, 14, and 15, but does not check well in the remaining cases. On the other hand, the alkaline permanganate activity results, compared with the pot tests, do not show concordant results, as noted in Nos. 10, 11, 14, 15, and 16. It is regretted that a larger number of samples, representing actual pot tests, could not have been secured for these studies. NITROGEN AVAILABILITY STUDIES-OXALICACIDMETHOD Activity Alkaline Perman- “Available” R. 1. Pot Waterganate lnsoluble Method (Pa.) Tests
-NITROGENTotal MATERIALS USED % B Blood 13.99 18 Blood 13.69 20 Blood 13.41 9 Leather H b g ) 5 83 32 Leather {Mich.) 3 : 86 1 M i x 4 lhirrh \__”__ ava il.) 3.61 2 Mia:ed (low ava it.) 3.00 4 Mix:ed (low ava il.) 2.90 5 Mix:ed (high 1.37 avaiii.) 7 Mix:ed (high 1.37 avaiil.) 10 Mix.ed (R. I., 1.75 was hed) 11 Mix.ed (R.I., was hed) 3.04 12 Mixed (R. I., 2.51 washed) 1.77 13 Mixed (R. I.) 14 MixmA ( D 1.72 was i&‘- -’’ 15 Mix ed (R.I., 1.17 was1bed) 16 Kanona tank(R. I., age washed) 8.34 17 Castor pomace (R.I., washed) 4.94 19 Rase goods (R.I.) 1.80 21 Castor pomace 4.71 23 Nitrogenous meal 6.91 24 Nitrolene tankage 7.45 25 Omega tankage 8.09 26 Kanona tankage 7.67 27 Wet base goods (YtJ 1.64 28 Digester tankaEe 8.48 29 Base goods 8.06 30 Base goods 8.14 31 Nitrolene tankage 8.31
%
%
13.50 13.20 13.15 5.82 3.85
64.2 61.2 63.8 26.8 41.0
%
..
“Available” Oxalic Acid Method
0.01 N
%
80
.. .. ..
9i:7 93.2 47.3 28.6
1.72
45.4
..
67.0
2.79
42.9
..
34.3
2.83
44.3
..
..
0.66
43.9
.. ..
.. ..
0.58
33.2
1.70
43.7
25
62.9
2.94
47.5
100
22.4
2.45 0.80
43.4 51.0
50
17.5 60.5
1.59
61.0
49
29.1
1.08
56.0
21
18.8
7.70
55.2
39
42.1
4.31
..
100
18.6
0.59 4.58 4.5s
36.8
24
7s.3
3.28 6.6s
..
..
..
.. .. .. ..
71.9 48.8 99.9
42.5 61.2
6.87
.. .. ..
0.40
76.4
.. ..
7.30 6.69 6.52
51.0. 52.8 50.8
... .
..
24.8 43.4 41.7
2.54
40.0
..
62.7
36.4
