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Humic fertilizer effects on the rate of nitrification in soil tests
Bioresource Technology 39 (1992) 49-54
Humic Fertilizer Effects on the Rate of Nitrification in Soil Tests Francisco A. Riera, Ricardo Alvarez & Jos6 Coca* Department of Chemical Engineering, University of Oviedo, 33071 Oviedo, Spain (Received 20 October 1990; accepted 28 November 1990)
Abstract
The nitrification of standard soil samples, measured as the amount of NNO~ being formed at different periods of time, by oxiammoniated biomass waste fertilizers was investigated. Oxiammoniated olive pits and almond shells were mixed with the soil and nitrification rates were studied over a 14-week period. The infrared spectra of soluble and insoluble ammoniated fractions and the oxidized raw material, were used to draw con; clusions concerning the presence of functional groups in the fertilizer. Key words: Nitrification tests, humic fertilizer activity. INTRODUCTION The production of humate and nitrohumate derivatives from lignite, peat and agricultural wastes has attracted considerable attention as possible slow-release nitrogen fertilizers (Davis & Scholl, 1939; Kim et al., 1981). Practically all the processes reported involve oxiammoniafion reactions of the raw material in the gas or liquid phase. In some cases greenhouse and field tests were carfled out in order to study the agrobiological activity of the products (Lahiri et al., 1966; Berkowitz etal., 1970). Previous research has demonstrated the agrobiological inactivity of 'nitrogen enriched coal' (NEC), modified NEC and mixtures of NEC with urea and ammonium nitrate (Berkowitz et al., 1970). NEC was obtained by oxidative ammoniafion of coal with ammonia and air at 300°C, the resulting product contained about 17 wt% total *Main project researcher.
nitrogen. The low availability to the soil of nitrogen held by the NEC fertilizer can be explained in terms of reaction mechanisms suggested for the gas-oxiammoniation process (Schwartz et al., 1965). Nitrogen in heterocyclic compounds is not easily assimilated by microorganisms, at least over short time periods, and hence has little nutrient value. However, modifications of the NEC process by carrying out the oxiammoniation reaction in the liquid phase, indicate that significant amounts of water-soluble nitrogen are produced. In such products 38% of the total nitrogen was identified as a water-soluble fraction and 54% of the waterinsoluble nitrogen was active (Prasad et al., 1974). The oxiammoniation of lignites was also carried out in an ammonia medium, under oxygen pressure. The product contained 12% total nitrogen and, in some conditions, 64% of it was watersoluble and 99% of this fraction was active as fertilizer (Giiriiz, 1980). In the work mentioned above the determination of available nitrogen was carried out using neutral permanganate. The characterization of the fertilizer value as watersoluble and active nitrogen water-insoluble fractions is an indication of the fertilizer practical nutrient value, but is not a substitute for field trials, Nitrification tests give a good indication of nitrogen--, nitrate transformations, when large amounts of the fertilizer are not available. It is recognized that these kinds of test are only of indicative nature, but it is accepted that nitrogen compounds converted to nitrate are readily used by plants. In addition, nitrification tests enable comparative studies between the oxiammoniated product and conventional fertilizers, such as ammonium nitrate or urea.
49 Bioresource Technology 0960-8524/92/S03.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain
50
F. A. Riera, R. Alvarez, J. Coca
The objective of this study is to determine the nitrogen mineralization of a soft containing humic fertilizers or fractions obtained from agricultural wastes by means of a two-step oxiammoniation reaction (oxidation+ ammoniation), in the liquid phase. Results are compared to those obtained when ammonium nitrate was added to the soil.
METHODS
Hydrolyzed olive pits and almond shells were used as raw material. They are a waste product from furfural plants and contain significant amounts of lignin, that can be converted in humates and nitrohumate salts. The oxiammoniation process takes place in two steps: (a) treatment of the raw material with nitric acid in order to generate acidic groups such as --OH and --COOH (Coca et al., 1985); Table 1 shows the optimum conditions of the oxidation process and the oxidized product characteristics; (b) ammoniation of the previously oxidized product in the liquid phase. The influence of temperature, ammonium hydroxide concentration and the solid/liquid (S/L) ratio on the ammoniation reaction was studied. The process yielded two fractions, i.e. water-soluble and waterinsoluble, that were collected and analyzed separately. Several methods have been described to determine the availability of nitrogen in nitrogenous fertilizers and its influence on the nitrification capacity of softs (Hamence, 1950). In this work a percolation method has been used to determine the nitrification capacity of a soft and the nitrification rate (N--'NO~-) of the nitrogen contained in the humic fertilizer. All tests were carried out with the same soft, nitrate-free, 68 wt% organic matter content and
pH in the range 5.5-5.8. The initial treatment of the soil was similar to that reported in the literature (Hamence, 1950). Soft-fertilizer mixtures (20% humidity) were prepared. Addition of 0.05% of calcium carbonate is recommended. Amounts of fertilizer equivalent to 28 mg of nitrogen were added. The soil-fertilizer samples were then placed in glass cylindrical containers (22 x 3 cm) and supported by a glass perforated plate. Cotton was placed at the top and base of the container to prevent drying and perlite was homogeneously mixed with the soft-fertilizer samples to facilitate aeration. The containers were covered with dark paper to prevent algal growth and placed in a chamber at 26-30°C and at high humidity. Every week, for a period of 94 days, 50 ml of distilled, nitrate-free water was percolated through the containers and leached solutions were collected. Samples were analyzed for nitrates by a spectrophotometric method (AOAC, 1965). To remove the color of the percolated samples, nitrogen-free active carbon was added to the solutions and thoroughly mixed for a few minutes. Then the mixture was allowed to settle down and filtered. A colorless filtrate was obtained and then analyzed for nitrates. Nitrate analysis of active carbon after its filtration did not show any presence of nitrates. Infrared spectra were determined using a Perkin-Elmer model 1310 (PerkinElmer, New York, USA). The KBr pellets were carefully prepared in order to avoid moisture interference (Stevenson, 1982).
RESULTS AND DISCUSSION Incubation tests Figure 1 shows the nitrogen content analyzed during the incubation period; each point on the graph corresponds to the mean of two experiments. Line
Table 1. Optimum oxidation conditions for the treatment of the raw
material (olive pits and almond shells) with nitric acid, and product properties Oxidized olive pits
(°c) [HNO3] (% wt) t (min) (S/L) ratio (% wt) Acidity of the product (ml NaOH/g) Losses in weight (% wt) Total nitrogen (%)
20
Oxidized almond shells
30
42.3 240 0"163
45 60 0.29
42"0 34"4 2"6
45"1 43"6 2"9
Humic fertilizer effects on nitrification
o/O
50
N(ppm)
8
/o/°/j oO
40
/
o~O-
3O 0//oO,//74~..o .0......
1
~o! 10
1~
I
I
0
(a)
I
I
I
40
20
I
I
I
80
t
100
t (days)
N.,p,.j
SO7o/O 7 ,oo(/o/
40
30
/ ~/°/
10
!
o- . . . . . . . .
I
o
d" 0 (b)
I
60
I 20
I 40
l
I 60
I
I
I
80
I 100
t (days)
Fig. 1. Totalnitrogen content analyzed during the incubation test. (1) Control test (no fertilizer added); (2) oxidized olive pits; (3) oxidized almond shells; (4) oxiammoniated olive pits, water-insolublefraction; (5) oxiammoniatedolive pits, water-soluble fraction; (6) oxiammoniated almond shells, water-insoluble fraction; (7) oxiammoniated almond shells,water-solublefraction; (8) ammoniumnitrate.
1 or 'soil control' and line 8 refer, respectively, to unamended soil and NH4NO 3 (at 28 mg N per cylindrical container). Table 2 identifies the numbers which designate the different fertilizers and the process conditions at which they were obtained. Figure 2 shows the extent of N - , NOjtransformations of each sample with respect to the nitrification of the control test. Water-insoluble fractions (lines 4 and 6) have no practical influence on the nitrification rate of the soil and behave as inerts. Some anomalous results obtained for fractions 4 and 6 show that the nitrification is lower than for the control. This is probably due to a certain lack of precision of
51
the method, particularly when the material is highly hygroscopic and it is not easy to obtain a homogeneous mixture with soil. Consequently in spite of the nitrogen content of water-insoluble fractions (2.6% for ohve pits and 5"3% for almond shells), there is no effect on soil nitrification. It appears that the nitrogen in those samples is not readily available to the soil and microorganisms cannot transform it into nitrates, at least within the test period. Oxidized products (lines 2 and 3) have a noticeable influence on soil nitrification. After 94 days, 40% of the nitrogen above the control test was transformed into nitrate. Nitrogen in oxidized products can be in either nitro or nitroso forms (Charmbury, 1945). A n important part of it is in a highly oxidized state and can be easily released as nitrate upon permanganate oxidation. A smaller portion of this nitrogen is in a less oxidized state and can be released as ammonia by alkali boiling. Water-soluble fractions proved to be more efficient as fertilizer than ammonium nitrate, in the case of olive pits. These results are in good agreement with those reported by other researchers (Charmbury, 1945) in which nitrohumates obtained by treating with aqueous ammonia behaved similarly to commercial ammonium nitrate. Therefore, it seems that the ammoniation reaction has an influence on the percentage of nitrogen available to the soil and that the total amount of nitrogen fixed in the final product is highly dependent upon the oxidation reactions. Some authors (Chakrabartty & Berkowitz, 1969; Oka et al., 1980) suggested that heterocyclic stable nitrogen compounds are formed during oxiammoniation reactions at high temperatures in the gas phase, but it is apparent that different reactions take place during the aqueous phase ammoniation. Furthermore, ammoniacal nitrogen in final products represents 40% of the total nitrogen content. It can be observed in Fig. 2 that at the end of the test more than 80% of nitrogen for the water soluble fraction of the oxiammoniated olive pits had been transformed into nitrate (with respect to the control test) for olive pits and 60% for the same fraction of almond shells. Ammoniacal nitrogen is considered to be readily assimilated by plants and hence several explanations of this behavior are possible: (a) part of the nitrogen fixed in non-ammoniacal forms can be transformed into nitrate; (b) the water-soluble fraction enhances both the microorganism activity and the nitrifica-
F. A. Riera, R. Alvarez, J. Coca
52
Table 2. Identification of fertilizers added to the soil Line on Figs I and 2
Material
Process conditions
N~
NNH3b
T (°C)
[NH 40H]
(S/L)
WSF"
210
2"75
1"65
--
210
2.75
1.65
48.8
210
2.4
0"62
43-2
210
2.4
0-62
--
Soil without fertilizer added (control)
Oxidized olive pits Oxidized almond shells Oxiammoniated olive pits, water-insoluble fraction Oxiammoniated olive pits, water-soluble fraction Oxiammoniated almond shells, water-insoluble fraction Oxiammoniated almond shells, water-soluble fraction Ammonium nitrate
2.6 2.9 2.6 12.6
5-0
5'3 12.6
5"3
35"0
21"0
aTotal nitrogen in %. bNitrogen present in ammoniacal forms in %. 'Water-soluble fraction percentage. **Optimum conditions: (2) 20°C, 42.4 wt% (HNO3) , 240 rain. (3) 30°C, 45"0 wt% (HNO3), 60 min. tion rate, n o t only because of its nitrogen content, but also d u e to the high c o n t e n t of organic m a t t e r in the fertilizers. A c o m b i n a t i o n of the aforem e n t i o n e d processes could also occur. A d d i t i o n a l research is n e e d e d to d e t e r m i n e the availability of the remaining nitrogen and its release rate to the soil.
BO
6O
40
T
Infrared spectra
20
0L
-10
L 0
(a)
I
I 20
I
I 40
I
I 60
I
I 80
t (days)
I
7 100
5 80
8
.60
,m 0
40
~
20: 4 0 0
(b)
20
40
60
80
100
t (days)
Fig. 2. Nitrification tests in soil for oxidized and ammoniated products. (2) Oxidized olive pits; (3) oxidized almond shells; (4) oxiarnmoniated olive pits, water-insoluble fraction; (5) oxiammoniated olive pits, water-soluble fraction; (6) oxiammoniated almond shells, water-insoluble fraction; (7) oxiammoniated almond shells, water-soluble fraction; (8) ammonium nitrate.
Infrared spectra of h u m i c substances p r o v i d e useful i n f o r m a t i o n o n the nature a n d a r r a n g e m e n t of the functional groups in the molecules, in spite of their complexity (Stevenson, 1982; Schnitzer & Gupta, 1964). Figure 3 shows s o m e infrared spectra o b t a i n e d for oxidized olive pits (Fig. 3(a)) and the a m m o n i a t e d soluble (Fig. 3(c)) and insoluble (Fig. 3(b)) fractions, b u t they are representative of all the h u m i c fertilizers tested. T h e three spectra show a strong a b s o r p t i o n b a n d b e t w e e n 3 0 0 0 a n d 3 6 0 0 cm-1. T h e s e arise f r o m H - b o n d e d O H groups including C O O H and possible m o i s t u r e o n the samples, also in s o m e cases N - - H groups m a y contribute to a b s o r p t i o n in this wavelength region. T h e fiat b a n d s are representative of various functional groups vibrating over a wide range of energies a n d n o f i n n conclusions can be d r a w n as to their structure. A w e a k a b s o r p t i o n b a n d at 2 9 0 0 c m - 1 appears in the case of oxidized olive pits. T h i s b a n d is stronger for water-insoluble fractions (Fig. 3(b)) a n d does not exist for water-soluble fractions. T h i s a b s o r p t i o n is linked to aliphatic C - - H groups ( C - - H stretching) a n d indicates the pre-
Humic fertilizer effects on nitrification
80
a
40
20t [
: 3500
~ 3000
2500
1 2000
I 1800
I 1600
I" 1400
, 1200
'
Frequency (crn "~)
Fig. 3. Infrared spectra obtained for (a) oxidized olive pits; (b) ammoniated olive pits, insoluble fraction; (c) ammoniated olive pits, soluble fraction.
sence of CH 2 and C H 3 groups. Original lignin structures contain these chains and its presence in oxidized olive pits means that some of these structures remain unaffected after the oxidation reaction. For the water-insoluble fraction the presence of this band would support the hypothesis that this fraction is not too much affected by the ammoniation process. Both oxidized olive pits and the water-insoluble fraction show absorption bands in the 1100 c m -1 region which are commonly assigned to C - - O stretching of polysaccharide or polysaccharide-like substances and substituted quinones (Stevenson, 1982). Very weak bands appear between 1600 and 1800 cm -1 for oxidized olive pits. A band at approximately 1720 cm -1 (assigned to C O O H groups) does not exist in the case of waterinsoluble fractions and it is very weak in the water-soluble fractions, but in this latter case new bands appear at 1575 and 1390 cm -1, which are characteristics of the C O O - ion. These results agree with previous studies (Theng & Posner, 1967) on the COOH--" C O O N H 4 transformation in an alkali medium. A weak peak at 1720 cm -~ in the spectra of salt compounds (water-soluble fractions) indicates the presence of small amounts of ketonic and aldehydic groups. Precise assignments in the 1600-1660 cm -1 region cannot be easily made. Several authors have proposed many different vibrations in this region (Stevenson, 1982), but there is no agreement on this point.
CONCLUSIONS The nitrification tests show a high percentage of nitrogen available (approximately 80%) in the
53
water-soluble ammoniation fractions during the tested period (14 weeks). No conclusions can be drawn about the remaining fixed nitrogen and the nitrogen release rate for such a short period. However, N - N O 3 transformations in the case of water-soluble fractions are fast, as important amounts of ammonium salts have been detected and the behavior is similar to the ammonium nitrate used as control. Tests have also shown the inactivity of water-insoluble fractions (about 40% of final product). This fraction is practically unaffected by the ammoniation process. Its structure is very similar to the oxidized material and the acid groups content is very low. Oxidized products have an intermediate behavior and 40% of their nitrogen can be transformed into NO3. Investigations of the remaining nitrogen behavior are needed in order to assess the potential applications of these fertilizers. Structural analysis should be carried out in order to elucidate the organic nitrogen structures involved in the process.
REFERENCES AOAC (1965). Official Methods of Analysis, ed. William Horwitz. AOAC, Washington. Berkowitz, N., Chakrabartty, S. K., Cook E D. & Fujikawa, J. I. (1970). On the agrobiological activity of oxidatively ammoniated coal. Soil Sci., 110, 211-17. Chakrabartty, S. K. & Berkowitz, N. (1969). On the chemistry of coal-ammonia-oxygen reaction. Fuel, 48, 151-60. Charmbury, H. B., Eckerd, J. W., La Torre, J. S. & Kinney, C. R. (1945). The chemistry of nitrogen in humic acids from nitric acid treated coal. J. Am. Chem. Soc., 67, 625-8. Coca, J., Alvarez, R. & Fuertes, A. B. (1985). Oxi-ammoniation of pine bark particles. Can. J. Chem. Eng., 63, 835-9. Davis, R. O. E. & Scholl, W. (1939). Ammoniated peat... Effect of varying the conditions of ammonia treatment on nitrogen quality. Ind. Eng. Chem., 31,185-9. Gtiriiz, K. (1980). Oxi-ammoniation of Elbistan lignite to produce a nitrogenous fertilizer. Fuel, 59, 772-6. Hamence, H. (1950). A method for the determination of the relative availability of nitrogen in nitrogenous fertilizers. J. Sci. FoodAgr., 1, 92-6. Kim, Y. K., Wendell, M. P. & Hatfield, J. D. (1981). Fertilizer from the oxidative ammoniation of sawdust. Ind. Eng. Chem. Prod. Res. Dev., 20, 205-12. Lahiri, A., Mukherjee, P. N. & Banerjee, S. (1966). Fertilizers from coal. Planter's J. and Agriculturist, 5, 385-6. Oka, H., Inoue, S. & Sasaki, M. (1980). Reactions of peat humic acid with ammonia. Neryo Kyokoishi, 59, 241-9. Prasad, M., Chowdhury, S. B. & Roy, A. K. (1974). Further studies on the process of producing fertilizers from coal in slurry phase under pressure. Indian J. Technol., 12, 137-41.
54
F. A. Riera, R. Alvarez, J. Coca
Schnitzer, M. & Gupta, U. C. (1964). Some chemical characteristics of the organic matter extracted from the 0 and 32 horizons of a gray wooded soil. Soil Sci. Soc. Am. Proc., 28, 374-7. Schwartz, D., Asfeld, L. & Geen, R. (1965). The chemical nature of the carboxyl groups of humic acids and conver-
sion of humic acids to ammonium nitrohumates. Fuel, 44, 417-24. Stevenson, F. J. (1982). Humus Chemistry: Genesis, Composition, Reactions. John Wiley and Sons, New York. Theng, B. K. G. & Posner, A. M. (1967). Nature of the carbonyl groups in soil humic acid. Soil Sci., 104, 191-201.
Humic Fertilizer Effects on the Rate of Nitrification in Soil Tests Francisco A. Riera, Ricardo Alvarez & Jos6 Coca* Department of Chemical Engineering, University of Oviedo, 33071 Oviedo, Spain (Received 20 October 1990; accepted 28 November 1990)
Abstract
The nitrification of standard soil samples, measured as the amount of NNO~ being formed at different periods of time, by oxiammoniated biomass waste fertilizers was investigated. Oxiammoniated olive pits and almond shells were mixed with the soil and nitrification rates were studied over a 14-week period. The infrared spectra of soluble and insoluble ammoniated fractions and the oxidized raw material, were used to draw con; clusions concerning the presence of functional groups in the fertilizer. Key words: Nitrification tests, humic fertilizer activity. INTRODUCTION The production of humate and nitrohumate derivatives from lignite, peat and agricultural wastes has attracted considerable attention as possible slow-release nitrogen fertilizers (Davis & Scholl, 1939; Kim et al., 1981). Practically all the processes reported involve oxiammoniafion reactions of the raw material in the gas or liquid phase. In some cases greenhouse and field tests were carfled out in order to study the agrobiological activity of the products (Lahiri et al., 1966; Berkowitz etal., 1970). Previous research has demonstrated the agrobiological inactivity of 'nitrogen enriched coal' (NEC), modified NEC and mixtures of NEC with urea and ammonium nitrate (Berkowitz et al., 1970). NEC was obtained by oxidative ammoniafion of coal with ammonia and air at 300°C, the resulting product contained about 17 wt% total *Main project researcher.
nitrogen. The low availability to the soil of nitrogen held by the NEC fertilizer can be explained in terms of reaction mechanisms suggested for the gas-oxiammoniation process (Schwartz et al., 1965). Nitrogen in heterocyclic compounds is not easily assimilated by microorganisms, at least over short time periods, and hence has little nutrient value. However, modifications of the NEC process by carrying out the oxiammoniation reaction in the liquid phase, indicate that significant amounts of water-soluble nitrogen are produced. In such products 38% of the total nitrogen was identified as a water-soluble fraction and 54% of the waterinsoluble nitrogen was active (Prasad et al., 1974). The oxiammoniation of lignites was also carried out in an ammonia medium, under oxygen pressure. The product contained 12% total nitrogen and, in some conditions, 64% of it was watersoluble and 99% of this fraction was active as fertilizer (Giiriiz, 1980). In the work mentioned above the determination of available nitrogen was carried out using neutral permanganate. The characterization of the fertilizer value as watersoluble and active nitrogen water-insoluble fractions is an indication of the fertilizer practical nutrient value, but is not a substitute for field trials, Nitrification tests give a good indication of nitrogen--, nitrate transformations, when large amounts of the fertilizer are not available. It is recognized that these kinds of test are only of indicative nature, but it is accepted that nitrogen compounds converted to nitrate are readily used by plants. In addition, nitrification tests enable comparative studies between the oxiammoniated product and conventional fertilizers, such as ammonium nitrate or urea.
49 Bioresource Technology 0960-8524/92/S03.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain
50
F. A. Riera, R. Alvarez, J. Coca
The objective of this study is to determine the nitrogen mineralization of a soft containing humic fertilizers or fractions obtained from agricultural wastes by means of a two-step oxiammoniation reaction (oxidation+ ammoniation), in the liquid phase. Results are compared to those obtained when ammonium nitrate was added to the soil.
METHODS
Hydrolyzed olive pits and almond shells were used as raw material. They are a waste product from furfural plants and contain significant amounts of lignin, that can be converted in humates and nitrohumate salts. The oxiammoniation process takes place in two steps: (a) treatment of the raw material with nitric acid in order to generate acidic groups such as --OH and --COOH (Coca et al., 1985); Table 1 shows the optimum conditions of the oxidation process and the oxidized product characteristics; (b) ammoniation of the previously oxidized product in the liquid phase. The influence of temperature, ammonium hydroxide concentration and the solid/liquid (S/L) ratio on the ammoniation reaction was studied. The process yielded two fractions, i.e. water-soluble and waterinsoluble, that were collected and analyzed separately. Several methods have been described to determine the availability of nitrogen in nitrogenous fertilizers and its influence on the nitrification capacity of softs (Hamence, 1950). In this work a percolation method has been used to determine the nitrification capacity of a soft and the nitrification rate (N--'NO~-) of the nitrogen contained in the humic fertilizer. All tests were carried out with the same soft, nitrate-free, 68 wt% organic matter content and
pH in the range 5.5-5.8. The initial treatment of the soil was similar to that reported in the literature (Hamence, 1950). Soft-fertilizer mixtures (20% humidity) were prepared. Addition of 0.05% of calcium carbonate is recommended. Amounts of fertilizer equivalent to 28 mg of nitrogen were added. The soil-fertilizer samples were then placed in glass cylindrical containers (22 x 3 cm) and supported by a glass perforated plate. Cotton was placed at the top and base of the container to prevent drying and perlite was homogeneously mixed with the soft-fertilizer samples to facilitate aeration. The containers were covered with dark paper to prevent algal growth and placed in a chamber at 26-30°C and at high humidity. Every week, for a period of 94 days, 50 ml of distilled, nitrate-free water was percolated through the containers and leached solutions were collected. Samples were analyzed for nitrates by a spectrophotometric method (AOAC, 1965). To remove the color of the percolated samples, nitrogen-free active carbon was added to the solutions and thoroughly mixed for a few minutes. Then the mixture was allowed to settle down and filtered. A colorless filtrate was obtained and then analyzed for nitrates. Nitrate analysis of active carbon after its filtration did not show any presence of nitrates. Infrared spectra were determined using a Perkin-Elmer model 1310 (PerkinElmer, New York, USA). The KBr pellets were carefully prepared in order to avoid moisture interference (Stevenson, 1982).
RESULTS AND DISCUSSION Incubation tests Figure 1 shows the nitrogen content analyzed during the incubation period; each point on the graph corresponds to the mean of two experiments. Line
Table 1. Optimum oxidation conditions for the treatment of the raw
material (olive pits and almond shells) with nitric acid, and product properties Oxidized olive pits
(°c) [HNO3] (% wt) t (min) (S/L) ratio (% wt) Acidity of the product (ml NaOH/g) Losses in weight (% wt) Total nitrogen (%)
20
Oxidized almond shells
30
42.3 240 0"163
45 60 0.29
42"0 34"4 2"6
45"1 43"6 2"9
Humic fertilizer effects on nitrification
o/O
50
N(ppm)
8
/o/°/j oO
40
/
o~O-
3O 0//oO,//74~..o .0......
1
~o! 10
1~
I
I
0
(a)
I
I
I
40
20
I
I
I
80
t
100
t (days)
N.,p,.j
SO7o/O 7 ,oo(/o/
40
30
/ ~/°/
10
!
o- . . . . . . . .
I
o
d" 0 (b)
I
60
I 20
I 40
l
I 60
I
I
I
80
I 100
t (days)
Fig. 1. Totalnitrogen content analyzed during the incubation test. (1) Control test (no fertilizer added); (2) oxidized olive pits; (3) oxidized almond shells; (4) oxiammoniated olive pits, water-insolublefraction; (5) oxiammoniatedolive pits, water-soluble fraction; (6) oxiammoniated almond shells, water-insoluble fraction; (7) oxiammoniated almond shells,water-solublefraction; (8) ammoniumnitrate.
1 or 'soil control' and line 8 refer, respectively, to unamended soil and NH4NO 3 (at 28 mg N per cylindrical container). Table 2 identifies the numbers which designate the different fertilizers and the process conditions at which they were obtained. Figure 2 shows the extent of N - , NOjtransformations of each sample with respect to the nitrification of the control test. Water-insoluble fractions (lines 4 and 6) have no practical influence on the nitrification rate of the soil and behave as inerts. Some anomalous results obtained for fractions 4 and 6 show that the nitrification is lower than for the control. This is probably due to a certain lack of precision of
51
the method, particularly when the material is highly hygroscopic and it is not easy to obtain a homogeneous mixture with soil. Consequently in spite of the nitrogen content of water-insoluble fractions (2.6% for ohve pits and 5"3% for almond shells), there is no effect on soil nitrification. It appears that the nitrogen in those samples is not readily available to the soil and microorganisms cannot transform it into nitrates, at least within the test period. Oxidized products (lines 2 and 3) have a noticeable influence on soil nitrification. After 94 days, 40% of the nitrogen above the control test was transformed into nitrate. Nitrogen in oxidized products can be in either nitro or nitroso forms (Charmbury, 1945). A n important part of it is in a highly oxidized state and can be easily released as nitrate upon permanganate oxidation. A smaller portion of this nitrogen is in a less oxidized state and can be released as ammonia by alkali boiling. Water-soluble fractions proved to be more efficient as fertilizer than ammonium nitrate, in the case of olive pits. These results are in good agreement with those reported by other researchers (Charmbury, 1945) in which nitrohumates obtained by treating with aqueous ammonia behaved similarly to commercial ammonium nitrate. Therefore, it seems that the ammoniation reaction has an influence on the percentage of nitrogen available to the soil and that the total amount of nitrogen fixed in the final product is highly dependent upon the oxidation reactions. Some authors (Chakrabartty & Berkowitz, 1969; Oka et al., 1980) suggested that heterocyclic stable nitrogen compounds are formed during oxiammoniation reactions at high temperatures in the gas phase, but it is apparent that different reactions take place during the aqueous phase ammoniation. Furthermore, ammoniacal nitrogen in final products represents 40% of the total nitrogen content. It can be observed in Fig. 2 that at the end of the test more than 80% of nitrogen for the water soluble fraction of the oxiammoniated olive pits had been transformed into nitrate (with respect to the control test) for olive pits and 60% for the same fraction of almond shells. Ammoniacal nitrogen is considered to be readily assimilated by plants and hence several explanations of this behavior are possible: (a) part of the nitrogen fixed in non-ammoniacal forms can be transformed into nitrate; (b) the water-soluble fraction enhances both the microorganism activity and the nitrifica-
F. A. Riera, R. Alvarez, J. Coca
52
Table 2. Identification of fertilizers added to the soil Line on Figs I and 2
Material
Process conditions
N~
NNH3b
T (°C)
[NH 40H]
(S/L)
WSF"
210
2"75
1"65
--
210
2.75
1.65
48.8
210
2.4
0"62
43-2
210
2.4
0-62
--
Soil without fertilizer added (control)
Oxidized olive pits Oxidized almond shells Oxiammoniated olive pits, water-insoluble fraction Oxiammoniated olive pits, water-soluble fraction Oxiammoniated almond shells, water-insoluble fraction Oxiammoniated almond shells, water-soluble fraction Ammonium nitrate
2.6 2.9 2.6 12.6
5-0
5'3 12.6
5"3
35"0
21"0
aTotal nitrogen in %. bNitrogen present in ammoniacal forms in %. 'Water-soluble fraction percentage. **Optimum conditions: (2) 20°C, 42.4 wt% (HNO3) , 240 rain. (3) 30°C, 45"0 wt% (HNO3), 60 min. tion rate, n o t only because of its nitrogen content, but also d u e to the high c o n t e n t of organic m a t t e r in the fertilizers. A c o m b i n a t i o n of the aforem e n t i o n e d processes could also occur. A d d i t i o n a l research is n e e d e d to d e t e r m i n e the availability of the remaining nitrogen and its release rate to the soil.
BO
6O
40
T
Infrared spectra
20
0L
-10
L 0
(a)
I
I 20
I
I 40
I
I 60
I
I 80
t (days)
I
7 100
5 80
8
.60
,m 0
40
~
20: 4 0 0
(b)
20
40
60
80
100
t (days)
Fig. 2. Nitrification tests in soil for oxidized and ammoniated products. (2) Oxidized olive pits; (3) oxidized almond shells; (4) oxiarnmoniated olive pits, water-insoluble fraction; (5) oxiammoniated olive pits, water-soluble fraction; (6) oxiammoniated almond shells, water-insoluble fraction; (7) oxiammoniated almond shells, water-soluble fraction; (8) ammonium nitrate.
Infrared spectra of h u m i c substances p r o v i d e useful i n f o r m a t i o n o n the nature a n d a r r a n g e m e n t of the functional groups in the molecules, in spite of their complexity (Stevenson, 1982; Schnitzer & Gupta, 1964). Figure 3 shows s o m e infrared spectra o b t a i n e d for oxidized olive pits (Fig. 3(a)) and the a m m o n i a t e d soluble (Fig. 3(c)) and insoluble (Fig. 3(b)) fractions, b u t they are representative of all the h u m i c fertilizers tested. T h e three spectra show a strong a b s o r p t i o n b a n d b e t w e e n 3 0 0 0 a n d 3 6 0 0 cm-1. T h e s e arise f r o m H - b o n d e d O H groups including C O O H and possible m o i s t u r e o n the samples, also in s o m e cases N - - H groups m a y contribute to a b s o r p t i o n in this wavelength region. T h e fiat b a n d s are representative of various functional groups vibrating over a wide range of energies a n d n o f i n n conclusions can be d r a w n as to their structure. A w e a k a b s o r p t i o n b a n d at 2 9 0 0 c m - 1 appears in the case of oxidized olive pits. T h i s b a n d is stronger for water-insoluble fractions (Fig. 3(b)) a n d does not exist for water-soluble fractions. T h i s a b s o r p t i o n is linked to aliphatic C - - H groups ( C - - H stretching) a n d indicates the pre-
Humic fertilizer effects on nitrification
80
a
40
20t [
: 3500
~ 3000
2500
1 2000
I 1800
I 1600
I" 1400
, 1200
'
Frequency (crn "~)
Fig. 3. Infrared spectra obtained for (a) oxidized olive pits; (b) ammoniated olive pits, insoluble fraction; (c) ammoniated olive pits, soluble fraction.
sence of CH 2 and C H 3 groups. Original lignin structures contain these chains and its presence in oxidized olive pits means that some of these structures remain unaffected after the oxidation reaction. For the water-insoluble fraction the presence of this band would support the hypothesis that this fraction is not too much affected by the ammoniation process. Both oxidized olive pits and the water-insoluble fraction show absorption bands in the 1100 c m -1 region which are commonly assigned to C - - O stretching of polysaccharide or polysaccharide-like substances and substituted quinones (Stevenson, 1982). Very weak bands appear between 1600 and 1800 cm -1 for oxidized olive pits. A band at approximately 1720 cm -1 (assigned to C O O H groups) does not exist in the case of waterinsoluble fractions and it is very weak in the water-soluble fractions, but in this latter case new bands appear at 1575 and 1390 cm -1, which are characteristics of the C O O - ion. These results agree with previous studies (Theng & Posner, 1967) on the COOH--" C O O N H 4 transformation in an alkali medium. A weak peak at 1720 cm -~ in the spectra of salt compounds (water-soluble fractions) indicates the presence of small amounts of ketonic and aldehydic groups. Precise assignments in the 1600-1660 cm -1 region cannot be easily made. Several authors have proposed many different vibrations in this region (Stevenson, 1982), but there is no agreement on this point.
CONCLUSIONS The nitrification tests show a high percentage of nitrogen available (approximately 80%) in the
53
water-soluble ammoniation fractions during the tested period (14 weeks). No conclusions can be drawn about the remaining fixed nitrogen and the nitrogen release rate for such a short period. However, N - N O 3 transformations in the case of water-soluble fractions are fast, as important amounts of ammonium salts have been detected and the behavior is similar to the ammonium nitrate used as control. Tests have also shown the inactivity of water-insoluble fractions (about 40% of final product). This fraction is practically unaffected by the ammoniation process. Its structure is very similar to the oxidized material and the acid groups content is very low. Oxidized products have an intermediate behavior and 40% of their nitrogen can be transformed into NO3. Investigations of the remaining nitrogen behavior are needed in order to assess the potential applications of these fertilizers. Structural analysis should be carried out in order to elucidate the organic nitrogen structures involved in the process.
REFERENCES AOAC (1965). Official Methods of Analysis, ed. William Horwitz. AOAC, Washington. Berkowitz, N., Chakrabartty, S. K., Cook E D. & Fujikawa, J. I. (1970). On the agrobiological activity of oxidatively ammoniated coal. Soil Sci., 110, 211-17. Chakrabartty, S. K. & Berkowitz, N. (1969). On the chemistry of coal-ammonia-oxygen reaction. Fuel, 48, 151-60. Charmbury, H. B., Eckerd, J. W., La Torre, J. S. & Kinney, C. R. (1945). The chemistry of nitrogen in humic acids from nitric acid treated coal. J. Am. Chem. Soc., 67, 625-8. Coca, J., Alvarez, R. & Fuertes, A. B. (1985). Oxi-ammoniation of pine bark particles. Can. J. Chem. Eng., 63, 835-9. Davis, R. O. E. & Scholl, W. (1939). Ammoniated peat... Effect of varying the conditions of ammonia treatment on nitrogen quality. Ind. Eng. Chem., 31,185-9. Gtiriiz, K. (1980). Oxi-ammoniation of Elbistan lignite to produce a nitrogenous fertilizer. Fuel, 59, 772-6. Hamence, H. (1950). A method for the determination of the relative availability of nitrogen in nitrogenous fertilizers. J. Sci. FoodAgr., 1, 92-6. Kim, Y. K., Wendell, M. P. & Hatfield, J. D. (1981). Fertilizer from the oxidative ammoniation of sawdust. Ind. Eng. Chem. Prod. Res. Dev., 20, 205-12. Lahiri, A., Mukherjee, P. N. & Banerjee, S. (1966). Fertilizers from coal. Planter's J. and Agriculturist, 5, 385-6. Oka, H., Inoue, S. & Sasaki, M. (1980). Reactions of peat humic acid with ammonia. Neryo Kyokoishi, 59, 241-9. Prasad, M., Chowdhury, S. B. & Roy, A. K. (1974). Further studies on the process of producing fertilizers from coal in slurry phase under pressure. Indian J. Technol., 12, 137-41.
54
F. A. Riera, R. Alvarez, J. Coca
Schnitzer, M. & Gupta, U. C. (1964). Some chemical characteristics of the organic matter extracted from the 0 and 32 horizons of a gray wooded soil. Soil Sci. Soc. Am. Proc., 28, 374-7. Schwartz, D., Asfeld, L. & Geen, R. (1965). The chemical nature of the carboxyl groups of humic acids and conver-
sion of humic acids to ammonium nitrohumates. Fuel, 44, 417-24. Stevenson, F. J. (1982). Humus Chemistry: Genesis, Composition, Reactions. John Wiley and Sons, New York. Theng, B. K. G. & Posner, A. M. (1967). Nature of the carbonyl groups in soil humic acid. Soil Sci., 104, 191-201.