one litre with distilled water and adjusted to pH 4.8) and about ¼ g of activated charcoal. The solution ... The stand- ard curve was prepared using 0, 1, 2, 3, 4, and 5-ml aliquots of 20 ppm NOs-N .... 11 Schuffelen, A. C., et al., Neth. J. Agr. Sci.
Plant and Soil 42, 305-308 (1975)
Ms. 2527
SHORT COMMUNICATION
A rapid m e t h o d for d e t e r m i n a t i o n of nitrate, nitrite, and a m m o n i a c a l nitrogen in soils* Summary A rapid procedure is proposed for simultaneous determination of NH4-, NO~-, and NO3-N in field moist samples. The procedure involves extraction, with Morgan's solution followed b y determination of NH4-N b y Nessler's reagent, NO2-N b y x-naphthylamine and sulphanilic acid and NOa-N b y phenol-disulphoric acid. The method will suit small laboratories and 50 to 75 samples can be analysed in a day. Due to low recoveries of nitrogen in tropical and sub-tropical areas of the world 9 the need for intensive field studies on nitrogen dynamics have been widely felt. A large number of field experiments are being conducted to study the efficiency of nitrogen applied to field crops in these countries and this permits an opportunity to study the fate of applied nitrogen. It is very well recognised that there would be considerable variability in soil samples even within the same plot and m a n y a times estimates considerably diifer between replicates. I n studies involving nitrogen dynamics, speed of analysis of the samples is also very important because the nitrogen transformations are dynamic in nature. Very few laboratoires will have required soil sample storage facilities and invariably the samples must be analysed while still moist. This point has also been emphasised b y B r e m n e r a. Many workers 1 2 4; have shown t h a t storage and handling of soils samples could largely influence the proportions of ammonium, nitrite, and nitrate nitrogen. Even simple field experiments would involve the handling of a m i n i m u m 40 to 50 samples at a time. P r a s a d 8 has proposed a procedure based upon the extraction methods used in the Netherlands by small laboratories 11 for quick simultaneous determination of nitrate, nitrite and ammonium nitrogen. This paper reports the data on recovery of added nitrate, nitrite and ammonium nitrogen to soil samples when estimated b y the procedure proposed.
Material and methods The laboratory experiments from which the data are reported in this paper were conducted on a sandy clay loam soil belonging to old alluvium series * Contribution No. 70. Division of Agricultural Chemicals, I.A.R.I, New Delhi 110012.
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SHORT COMMUNICATION TABLE 1 Characteristics of the soil used Characteristics
Value
Mechanical analysis (%) a) Sand 61.0 b) Silt 15.0 e) Clay 24.0 pH (1:2:5 soil to solution) 7.7 Total nitrogen (%) 0.07 Available nitrogen (Prasad v kg/ha) 24.4 Available (Olsen's) PzOs (kg/ha) 62.3 Available K~O (kg/ha) 353.0 Ammoniacal nitrogen (ppra) 4.4 Nitrate nitrogen (ppm) 9.0 Nitrite Nitrogen (ppm) Traces Cation exchange capacity (me/100 g soil) 11.6 Organic carbon (%) 0.6
and having important physical and chemical characteristics as given in Table I. E x t r a c t i o n of n i t r a t e , n i t r i t e a n d a m m o n i u m n i t r o g e n f r o m s o i l s a m p l e s . The procedure adopted was same as reported by S c h u f f e l e n et al. 11 and consists of mechanically shaking 10 g of soil with 50 ml of Morgan's Reagent (100 g of sodium acetate + 30 ml of glacial acetic acid, diluted to one litre with distilled water and adjusted to pH 4.8) and about ¼g of activated charcoal. The solution was filtered through W h a t m a n n No. 1 filter paper. If some turbidity is seen, the filtrate could be transferred to funnel and refiltered. Although in these laboratory experiments moisture estimation was not necessary, in field samples it is possible and advisable t o u s e moist samples immediately after taking them from the field. I n such cases about 50-g samples should be simultaneously kept for moisture determination for adjusting the results obtained to dry weight basis. D e t e r m i n a t i o n of N O s - N . This was done using a I0 ml aliquot of the above extract and following the procedure as described b y J a c k s o n 5 The colour developing reagent used was phenol-disulphonic acid. The standard curve was prepared using 0, 1, 2, 3, 4, and 5-ml aliquots of 20 ppm NOs-N solution (prepared with potassium nitrate). Determination of N O 2 - N . Nitrites were estimated by using 1- to 5-ml aliquots of the above extract and following the procedure described by P r i n c e 10 The reagents used for developing pink colour were: ~-naphthylamine and sulphanilic acid. ( P r a s a d has later obtained better results with (N-1-Napthyl) ethylenediamine hydrochloride in place of x-naphthylamine
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as p r o p o s e d b y M o n t o g o m e r y a n d D y m o c k 6). T h e s t a n d a r d c u r v e was p r e p a r e d using a 1-ppm N O 2 - N s o l u t i o n ( p r e p a r e d w i t h p o t a s s i u m nitrite). Determination of N H a - N . A m m o n i u m n i t r o g e n was d e t e r m i n e d using a 2 m l a l i q u o t of t h e a b o v e e x t r a c t a n d following t h e p r o c e d u r e d e s c r i b e d b y S c h u f f e l e n et al. 11. A t u r b i d i t y m a y be e n c o u n t e r e d w i t h some soils b u t using a n a p p r o p r i a t e d i l u t i o n one c a n easily o v e r c o m e t h i s p r o b l e m . Results and discussion T h e d a t a in T a b l e 2 s h o w t h e r e c o v e r y of 87 to 90 p e r c e n t of t h e a d d e d N O a - N , while in case of N O 2 - N t h e r e c o v e r y w a s 85 t o 90 p e r cent. T h e rec o v e r y of a d d e d N H 4 - N was a b o u t 80 p e r c e n t for t h e soil used in t h e studies. E s t i m a t i o n of N H 4 - N in t h e e x t r a c t s b y N e s s l e r i z a t i o n as p e r p r o c e d u r e desc r i b e d a b o v e a n d b y distillation m e t h o d were also c o m p a r e d . B o t h t h e proced u r e s gave s a m e r e s u l t s a n d t h e s e are g i v e n in T a b l e 3. The d a t a p r e s e n t e d in T a b l e 2 clearly s h o w t h a t t h e p r o p o s e d p r o c e d u r e is fairly reliable for s i m u l t a n e o u s e s t i m a t i o n of N O 3 - N , N O 2 - N a n d N H 4 - N in soil s a m p l e s . O n l y in case of N H a - N , t h e r e c o v e r y was s l i g h t l y low a n d t h i s w o u l d g e n e r a l l y be i n f l u e n c e d b y t h e a m m o n i u m fixing c a p a c i t y of t h e soils.
TABLE 2 Recovery of N0a-N, NOz-N and NH4-N added to soil N added (mg)
N recovered (mg)
Recovery (%)
5.0 10.0 20.0 30.0 40.0 50.0 I00.0
NOa-N 4.5 9.0 17.5 27.0 35.2 45.0 88.5
90.0 90.0 87.5 90.0 88.0 90.0 88.5
2.5 5.0 10.0 15.0
NOz-N 2.2 4.5 9.0 12.8
88.0 90.0 90.0 85.3
5.0 10.0 15.0 20.0 25.0 50.0 100.0
NH4-N 4.1 8.1 12.4 15.6 20.5 41.0 81.5
82.0 81.0 82.7 78.0 82.0 82.0 81.5
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Estimation of NH4-N (ppm) by Nesslerisation (as described above) and by distillation after extraction with Morgan's reagent By Nesslerisation
By distillation
12.6 31.8 45.0
12.1 30.9 44.5
T h e a u t h o r s ' e x p e r i e n c e is t h a t a l a b o r a t o r y t e c h n i c i a n c a n easily h a n d l e 50 t o 75 s a m p l e s i n a d a y a n d c o m p l e t e l y d e t e r m i n e t h e N O s - , N O 2 - a n d N H 4 - N . C o n s i d e r i n g t h e v a r i a b i l i t y e n c o u t e r e d i n t h e soil s a m p l e s a n d t h e e r r o r s w h i c h c r e e p i n d u e t o t h e p o o r s t o r a g e a n d care of t h e s a m p l e s , t h e rec o v e r y s h o w n a b o v e e v e n of a d d e d N H 4 - N s h o u l d b e c o n s i d e r e d s a t i s f a c t o r y . T h e p r o c e d u r e will also p e r m i t t h e collection of a l a r g e v o l u m e of d a t a f r o m various tropical and sub-tropical countries, which happen to be underdevelo p e d or d e v e l o p i n g n a t i o n s w i t h v e r y l i t t l e l a b o r a t o r y facilities.
Acknowledgment W e are g r a t e f u l t o Dr. S. K. M u k e r j e e , H e a d of t h e D i v i s i o n of Agricult u r a l C h e m i c a l for h e l p a n d e n c o u r a g e m e n t . K. L. S A H R A W A T and P~AJENDRA PRASAD Division of Agr. Chemicals, Indian Agr. Research Instt., New Delhi 110012. Received May 28, 1974
1 A l l e n , S. E. and G r i m s h a w , H. M., J. Sci. Food Agr. 13, 525-529 (1962). 2 B i r c h , H. F., Plant and Soil 10, 9-31 (1958). 3 B r e m n e r , J. M., I n Methods of Soil Analysis. Ed. C. A. B l a c k . p. 1179-1237. Am. Soc. Agron. Madison (1965). 4 Gasser, J. K. R., J. Sci. Food Agr. 12, 778-784 (1961). 5 J a c k s o n , M. L., Soil Chemical Analysis. Prentice-Hall, Inc., New Jersey, U.S.A. p. 199-201 (1958). 6 M o n t o g o m e r y , H. A. C. and D y m o c k , J. F., Analyst 86, 414-416 (1961). 7 P r a s a d , R., Plant and Soil 23, 261-264 (1965). 8 P r a s a d , R., A Practical Manual for Soil Fertility, Division of Agronomy, Indian Agr. Research Inst., New Delhi (Mimeographed) (1968). 9 P r a s a d , R. et ~., Advances in Agron. 23, 337-883 (1971). 10 P r i n c e , A. L., Soil Sci. 59, 47-52 (1945). 11 S c h u f f e l e n , A. C., et al., Neth. J. Agr. Sci. 9, 2-16 (1961).
