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Group Title: Department of Soils mimeo report
Title: A rapid method for the determination of nitrogen in soil
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Permanent Link: http://ufdc.ufl.edu/UF00091540/00001
 Material Information
Title: A rapid method for the determination of nitrogen in soil
Alternate Title: Department of Soils mimeo report 60-2 ; University of Florida
Physical Description: 7, 5 leaves : ; 28 cm.
Language: English
Creator: Moskovic, Armin
University of Florida -- Dept. of Soils
University of Florida -- Agricultural Experiment Station
Publisher: Department of Soils, Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla.
Publication Date: October 26, 1959
 Subjects
Subject: Soils -- Nitrogen content -- Florida   ( lcsh )
Soils -- Analysis -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Armin Moskovic.
Bibliography: Includes bibliographical references (leaf 7).
General Note: Cover title.
General Note: "October 26, 1959."
 Record Information
Bibliographic ID: UF00091540
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 79301344

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Full Text













DEPARTMENT OF SOILS MIMEO REPORT NO.60-2


A RAPID METHOD FOR THE DETERMINATION OF NITROGEN IN SOIL
by

Armin Moskovic


Department of Soils
Florida Agricultural Experiment Stations
Gainesville, Florida


October 26, 190










Department of Soils
Agricultural Experiment Station
University of Florida

A RAPID METHOD FOR THE DETERMINATION OF NITROGEN IN SOIL*

Armin Moskovic**


Introduction

The total nitrogen method as described by Kjeldahl (6), although

accurate, is long and tedious. The whole operation, from weighing to

titration, takes about 5 hours of continuous work. One way of making

it faster would be to shorten the digestion time and eliminate the

distillation.

A study of the literature suggested the use of perchloric acid as

a means of digestion. Mears and Hussey (3) found that the use of small

quantities of 6c% perchloric acid in the Kjeldahl determination consider-

ably shortened the time of digestion without appreciably affecting the

accuracy of the results. They worked with different substances, such

as milk, urine, albumin, cattle manure; but not with soil. Mears and

Hussey believed explosion of the sulphuric acid-perchloric acid-organic

matter mixture to be quite improbable; they made over 500 determinations

without accident. The author's experience confirms their opinion.

Elimination of the distillation was accomplished by Chiles (1), who

developed the direct titration of the digested solution with Nesslert s

reagent, Chiles found that the use of a protective to prevent precipi-

tation of color in the nesslerized solutions made it possible to nessler-

ize any of the commonly used Kjeldahl digestion mixtures. He had best


* This work was supported in part by a grant-in-aid from the Phillips
Petroleum Company which is gratefully acknowledged. .

** Formerly Laboratory Assistant, Department of Soils, Agricultural
Experiment Station, Gainesville, Florida.


I







-2-

results with an especially prepared Eum arabic solution as a protective

colloid. However, he did not work with soil but with such materials

as bllod, urine, milk and tankage.

Peech and English (4) later introduced these methods for the micro-

chemical determination of ammonia in soil. The objective of the present

work was to adapt them for macrochemical soil test for total nitrogen.

Method of Procedure

The air-dry soil is thoroughly ground in a mortar, and appropriate

sample, packed in filterpaper, is placed in a Kjeldahl flask, previously

calibrated to 500 ml. The following additions are made: 50 ml. concentrated

sulphuric acid with 40 g. salicylic acid added per 4 kg. sulphuric acid;

.3 g. cupric sulphate; ca. 5.0 g. (teaspoonful) potassium sulphate, (1).

The solution is mixed well, heated to boiling, then cooled. One ml. 70%

perchloric acid is added, mixed well, then digested until all organic matter

is oxidized. During the digestion the flasks are shaken 2 to 3 times. Towards

the end of the digestion an additional 0.1 ml. perchloric acid is added out

of a micropipette to complete the digestion. It is not necessary to completely

cool the flask. The entire digestion usually takes between 7 and 15 minutes,

The colorless samples are left boiling for an additional 15 minutes. After

cooling, distilled water is added; the solution becomes hot but it may be

cooled in running water. The digest is then filled to the 500 ml. mark on the

Kjeldahl flask with distilled water, thoroughly mixed and filtered through a

Whatman No. 40, 11 cm, folded filterpaper. The first droplets of the filtrate

are discarded. Ten ml. of filtrate from sandy loams and loams, or 15 ml. from

fine sand are pipetted into 350 ml. Erlenmeyers. Two drops of Nessler's

reagent are added, mixed well and a quantity of gum solution equal to 10%

of the used filtrate is added. The filtrate preparation is made alka-












line with a 60% sodium hydroxide-tartrate solution, which is added

down the side of the flask, taking care not to add too much because it

sometimes results in turbidity. The solution is alkaline when the 2 drops

of Nessler's reagent, previously added, give it a faint yellow tint.

Usually 10-15% as much sodium hydroxide-tartrate solution is used as

the quantity of filtrate. The sodium tartrate tends to prevent preci-

pitation of color in the nesslerized solutions (4). The mixture is

then shaken and made to 95 ml. with distilled water, 5 ml. of Nessler's

reagent are added, mixed well for one-half minute, left to stand for 15

minutes for the development of color, then the percentage transmission

is read. A Cenco photolometer (blue filter) was found satisfactory for

determining percent transmission.

The nitrogen content of soil is
5a-2
N = be

where a = ppm. N on the standard curve

b = ml. of the digest used

c = weight of the soil sample.

The digested solution is usually almost colorless. Sometimes, when a

soil contains considerable iron, as for example Red Bay fine sandy

loam, the digested liquid has a greenish tint, which may alter the

results. In such cases better results have been achieved with the

addition of 15-20% gum, instead of the usual 10%. However, the addi-

tional gum solution influences the light transmission, The percentage

of blanks containing 0.5, 1.0, 1.5 and 2.0 ml. of gum solution, diluted

to 100 ml. with distilled water, should be determined and the blank

transmission of the additional gum solution added to the percentage trans-

mission of the samples. All determinations probably should be made'in









-4-

duplicate, although the present investigations were made with single

samples only.

It was found that quantities of soil resulting in 20-100 ug. N per

ml. of the digest gave the best results. For most mineral soils of Florida

5.0 g. are appropriate. However, for mucks and peats 0,25 0.50 g. is
sufficient.

Preparation of the Standard Curve

Ammonium sulphate mixed with soils of a low nitrogen content (4)

was used to obtain values for a standard curve. A 20 ppm. nitrogen

solution was prepared by dissolving 040942 g. ammonium sulphate in dis-

tilled water and diluting it to 1000 ml. The nitrogen content of a Lake-

land fine sand was determined with the conventional Kjeldahl method to

be 0.011%. Five g. of this soil were digested by the perchloric method.

One hundred ml. of the ammonium sulphate solution were added to the di-

gest and diluted to 500 ml. with distilled water and filtered. This

solution contains 2550 micrograms N (2000 ug. derived from the ammonium

sulphate and 55/Oug. from the soil). The standard curve was determined
as shown in the table below:


Aliquot N Transmission
(mi.) &',.) ()W
2 10.2 66.0
I 20.4 62.5
6 30.6 58.0
8 40.8 53.5
10 51.0 o0.0
12 61.2 46.0
14 71.t4 3.0
16 81.6 39.0
18 91.8 35.0
20 102.0 32.5


The N content was plotted against percent transmission and the standard

curve drawn. A new standard curve should be prepared for every new batch

of reagents.









-5..-

Preparation of the Reagents

Sulphuric-salicylic acid.

40 g. salicylic acid are dissolved in 4.0 kg. concentrated sulphuric

acid.

Nessler's Reagent (5).

Transfer 70 g. potassium iodide and 55 g. iodine to a 500 ml. Erlen-

meyer flask and dissolve in 50 ml. distilled water. Add 70 to 75 g.

mercury, shake continuously and vigorously for 7 to 15 minutes, or until

the iodine has nearly disappeared. The solution becomes hot; as soon

as the red iodine solution has become visibly pale, though still red,

cool in running water and continue shaking until the reddish color has

been replaced by the greenish color of the double iodide. The whole op-

eration does not take more than 15 minutes. Separate the solution by

decantation and repeated washing of the mercury precipitate with distilled

water. Add a cooled solution of 224 g. potassium hydroxide in 280 ml.

of distilled water and fill to 1000 ml. with distilled water. Leave stand-

ing until clear and then decant into a brown flask or bottle. Immediately

before use add 5 ml. of gum solution for every 100 ml. of Nessler's reagent

(2). This solution is twice as concentrated as that prepared by Folin

and Wu (2), in accord with a suggestion by Peech and English (4).

Protective gum solution (1).

10.0 g. acacia gum are dissolved in 190 ml. distilled water. This

is done by initially stirring the gum powder with a little water until

sticky, then gradually adding more water until dissolved. Add 4 g. per-

mutit, shake repeatedly, decant, repeat the treatment with permutit, de-

cant. After decanting, add about 10% of Nessler's reagent, mix thoroughly

and repeatedly and leave standing for two days to settle. Decant into a

brown bottle or ft~s Acacia Gum U.S.P. Select No. 1 Powdered, produced









-6-

by S. B. Pennick and Co. resulted in the best gum solution.
Sodium Hydroxide-tartrate solution (i).

Dissolve 25 lb.. of technical sodium hydroxide in 18 liters of dis-

tilled waters. This corresponds to 61 g. sodium hydroxide in 100 ml.

water. Dissolve 80 g. sodium tartrate in every 100 ml. of the sodium

hydroxide solution.

Results and Discussion.
The Perchloric Acid Method considerably shortens the time necessary

to determine nitrogen in soil. For example, the following time was

found to be sufficient for tests with South Florida soils:

No, Soil Type Quantity Digestion time
g Minutes

6 Leon f.s. 10.0 12
7 Leon f.s. 10.0 8
9 Bladen l.f.s. 5.0 8
2h Sunniland f.s. 2.5 8
28 Okechobee muck 0.5 8
31 Everglades peat 0.25 8
0h Perrine marl 2.0 10
$6 Inrokalee f.s. 10.0 10


Two hours were necessary to digest the same soils with the Kjeldahl

method and at least one additional hour is necessary for distillation
(distillation is not a part of the perchloric acid method).

The initially dark colored digest suddenly and very impressively

changes into almost colorless liquid.

The results with both methods are generally in good accord. Occa-

sionally, however, they may differ considerably, as shown here:

No, Soil Type Results (%N) Difference
Kjeld. Perchlor.
24 Red Bay f.s.. r 4.14S 6 0.60 34
48 ked Bay ..s.1. 0.43-44 0.55-60 25-37
$6 Norfolk f.s.l. 0.35-6 0.144-16 26-31








-7-

Ls mentioned earlier, this is caused in the case of Red Bay f.s.l, by

the high content of red ferric oxide and hydroxide, which gives to

the digest a faint yellow tint, thus altering the result. The yellow

tint disappears by increasing the gum solution to 20% of the digest used

for Nesslerization and the results agree within 7% with those obtained

by the Kjeldahl procedure (see Table 1, page 4, last item),

Often large unexplainable differences occur between duplicate

determinations made by the Kjeldahl procedure. Normally, these dif-

ferences are around 5% or less. Sometimes, however, they may be as

great as 35, 50 and even 100l, Replicate-determinations will give

usual results. The perchloric acid determination of nitrogen in soil

No. 56 could be such a difference, however not detectable, because

replicate determinations have not been made.

Best results are obtained by using aliquots which yield 40-80.ug.

nitrogen. Determinations with aliquots of digest between 10 and 15 ml.

give percentages most closely agreeing with those obtained by the

Kjeldahl procedure, as shown in Table 1.

LITERATURE CITED

1. Chiles, H. M. Direct nesslerisation of Kjeldahl digestions.
Jour. Amer. Chem. Soc. 50:217. 1940.

2. Folin, Otto and Wu, Hsien. A system of blood analysis. Jour.
Biol. Chem. 38:81. 1919.

3. Mears, B. and Hussey, R. E. The use of perchloric acid as an
aid in the Kjeldahl nitrogen determination, Jour. Ind. Eng. Chem.
13:105U. 1921.

4. Peech, M. and English, L. Rapid microchemical soil tests. Soil
Sci. 57:167. 1944.

5. Vanselow, A. P. Preparation of Nessler's reagent. Jour. Ind.
Eng. Chem., Analyt. Ed. 12:516, 1940,

6. Hillebrand, W. F. and Lundell, G. E. F. Applied Inorganic
Analysis, pp. 636-641. John Wiley & Sons. 1953.


100 copies.











Table 1

Percentage nitrogen in soil as determined by digestion with perchloric acid and by
the Kjeldahl procedure.



Soil No, Soil Type Kjeldahl Results Perchloric aoid Percentage
Results of
K3jeldahl
Total Difference ag N/ml aliquot N N Nitrogen
N Between De- of of iug %
I terminations digest digest
I. %in ml._____


18 Ruston f.s.l*


6.0


.059
.060


9.3


42 Irvington f.s.l. .094
.091


43 Red Bay f.s.l,


Carnegie f.s.l.


46 Norfolk ,AL.


6.3


.062
.o64


.051


.0o44
.oUU


20O
3.5
5.5
7,0
10.0
13.5
17.0

1.0
2.0
3.5
4.5
6,5
8.5
11.0
2.0
3.5
5.0
6.5
10.0
13.0
15.5

2.0
4.0
6.0
8.0
12,0
16,0
19,0
2.0
4.0
7.0
9.0
13.0
18.0
22,0


.6,5
16.5
29.0
40.0
57.0
7860
96.0

3.0
27.0
35.0
54.0
68.0
88,0

5.5
19.0
30.5
40.0
68.0
85.0
100.0
7,0
20.0
330O
45.5
62.0
83.5
100.0


3.0
15.0
28.0
44.0
65.0
85.0
99,0


a027
0o47
.053
.057
.057
.058
.056

*030
.070
,077
.078
.083
.080
.080
.027
.054
.060
.063
.068
.065
.064

.035
4050
.055
.057
.051
.052
s064

.030
.037
.040
.o49
.050
.o4,0
.045
0379

.OU9i'
0^0S


m-

90
97
97
98
95
MM-
--rn
84
84
90
87
87

-m
97
102
110
UO
105
103

-1-
108
112
100
102
125
m-

89
109
111
104
100












Table 1. (Page 2)


Soil No. Soil Type Kjeldahl Results Perchloric acid Percentage
Tota- Difference 'Ig N/ml Iquot N I Kjeldahl
N Between De- of of u g % Nitrogen
terminations digest digest
% in mi.


24 Red Bay fos.a,






47 Red Bay f.s.lo






48 Red Bay f.s.l*


4.6


.046
.045





.o59
.059





.0o43
.044


52 Faceville f.s.l. .073
.079





53 Faceville f.s.l. .079
.077


7.6






7.8


2,0
3.5
5.5
7.0
10.5
14.0o
17.0
2.0
3.5
5.0
7.0
10.0
14.0
17.0
2.0
5.0
7.0
9.0
14.0
18.0

1.5
3.0
4.0
5.5
8.5
11.0
14.0

1.5
3.0
4,o
5.5
8.0
10.0
12.5


11.0
23.0
33.0
41.0
64.0
83.0
96.0

14.0
23.0
34.0
47.0
64.0
85.0
97.0

15.0
32.0
40.0
54.o
77.0
96.0

5.0
17.0
25.0
38.0
58.0
80.0
96.0

8.0
17.0
25.0
38.0
52.0
72,5
88.0


.055
.066
.060
.058
.061
.060
,056

.070
.066
.068
.067
.064
.060
.057
.075
*064
.059
.060
.055
.053

.033
.057
.062
.069
.068
.073
.068

.0514
.057
.062
.069
.065
.072
.070


133
129
135
133
124


115
114
118
102
97


134
137
125
120


85
94
94
100
94
--a

79
88
83
92
90









Table 1. (Page 3)


Soil No. Soil Type Kjeldahl Results Perchloric acid Percentage
_..... -__Results of
Kjeldahl
Total Difference ug N/ml aliquot N N Nitrogen
N between De- of of ug %
% terminations digest digest
% in ml.


55 Americus l.s.






56 Norfolk f.s.1.





57 Tifton f.s.l.






58 Tifton f.s.l.






59 Tifton f.s.l.


.o47





.036
.035




.076
.077





.063
.066





.051
.049


3.6





7.7


2.0
4.0
6.0
8.5
12.5
16.5
20.5

3.0
6.0
9.0
11.0
17.0
23.0

1.5
2.5
4.0
5.0
8.0
10.5
13.0

1.5
3.0
5.0
6.5
9.5
12.5
15.5
2.0
4.0
6.0
8.0
12.0
16.0
20.0


10.0
23.0
35.0
50.0
70.0
88.0
99.0

10.0
25.0
40.0
51.0
77.0
99.0

8.0
21.0
28.0
51.0
70.0
85.0

4.0
15.0
30.5
37.5
57.0
79.0
96.0

5.5
15.0
25.5
35.0
57.0
77.0
92.0


.050
.059
.058
.056
.053
.048

.033
.041
.046
.045
.043

W-M-
.032
.052
.056
.064
.067
.065

.021
.050
.060
.058
.060
.063
.062

.027
.037
.042
.044
.047
.048
.016
.OU~6


--->

123
122
116
110
100


126
131
130
123

-a-
68
74
84
88
85
-a-

94
91
94
98
97
a---

84
88
94
96
92










Table 1. (Page 4)


Soil tet Soil Type Kjeldahl Results Perchloric acid Percentage
Results of
Kjeldahl
Total Difference ag N/ml aliquot N N Nitrogen
N between De- of of gug %
% terminations digest digest
% in ml.
1i


64 Tifton f.s.l.


60 Blanton f.s.


41 Irvington f.s.l.


(The following results obtained with a standard curve other than Fig. I.)


24 Red Bay f.s.1.


.045


20% gum solution added.


.064


.033
.033
.034


.065
.063


6.5


1.5
3.0
5.0
6.5
9.5
12.5
15.5

4.0
10.0
19.0
19.0
29.0

1.5
3.0
5.0
6.5
9.5
12.5
15.5

1.0
2.0
3.0
4.0
6.0
7.5
9.5


4.o
15.0
31.0
40.0
58.0
79.5
96.0


18.0
48.0
100.0


8.0
2)4.0
35.0
57.0
77.0
96.0

13.0
21.0
33.0
42.0
62.0
75.0
92.0


.027
.050
.062
.061
.061
.064
.062


.018
.027
.025
.034


.027
.048
.054
.060
.061
.062

.130
.105
.110
.105
.103
.100
.097


MM--
---
97
92
92
100
97


81
76
102

-M-
75
84
94
95
97
---

103
98
96
93
91


.109
.106


10.8


2.5
4.5
7.0
9.0


11.0
21,0
36.0
43.0


.045
.047
.051
.o48


100
104
lOl
113
107


61 Magnolia s.l.








Table 1. (Page 5)


Soil No. Soil Type Kjeldahl Results Perchloric acid Percentage
Results of
Kjeldahl
Total Difference g N/ml aliquot N N Nitrogen
N between De- of of /ug j
S terminations digest digest
%.


32 Norfolk s.1. .036
,035




36 Tifton s.l. .060
.057




38 Tifton s.l. .082
.088





37 Red Bay f.s.1. .063
.067





37 Red Bayf S l*' #063
.067


54 Magnolia f.s.l, .089
86
91


3.6


3.0
6.0
8.5
11.5
17.5
23,0

2.0
5.5
7.0
10.0
13.5
17.0

1.5
2.5
3.5
5.0
7.0
9.5
11.5
2.0
3.5
5.0
6.5
9.5
12.5
15.5

2.0
3.5
5.0
6.5
20.0
4.0
6.5
9.0
13,0
18.0
22.0


14.0
24.0
38.0
50.0
74.0
87.0

12.0
28.0
35.0
56.0
69.0
90.0

8.0
17.0
25,0
38.0
55.0
77.0
95.0

10.0
19.0
33.0
51.0
77.0
99.0

9.0
21.0
33.0
40.0

11.0
24.0
35.0
54.0
77.0
95.0


.040
.o43
,0o43
.013
.039

.060
.051
.050
.056
.051
.053
.054
.068
.078
.076
.080
.081
.082

.028
.038
.051
.o54
x054
.061
.064

.045
.060
.066
,061


.055
.074
.078
.082
.085
.086


l-a-
114
129
122
122
111
---
86
85
95
86
90

a---
92
89
94
95
96

aa -
a---
80
84
95
100


103
95


83
88
92
95
97


* 20% gum solution added.




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