nitrogen mineralization of sludge-amended soil

Bioresource Technology 39 (1992) 285-290

Nitrogen Mineralization of Sludge-Amended Soil M. D. Serna & F. Pomares

Departamento de Ecolog/a, Instituto Valenciano de Investigaciones Agrarias, Apartado Oficial, 46113, Moncada, Valencia, Spain

(Received 27 September 1990; revised version received 5 November 1990; accepted 30 January 1991)

Abstract

Mineralization of organic N is one of the main factors governing the annual amount of sewage sludge applied to agricultural cropland. The purpose of this study was to determine N-mineralization of 12 sewage sludges in a given soil during a 16-week aerobic incubation by analysis of inorganic N produced by a nonleached procedure.

The amounts of N mineralized in a soil amended with sewage sludges ranged from 74 to 428 mg N kg -1 soil, Expressed as a percentage of total organic N added to soil, the N mineralized ranged from 13.8 to 45"6%. The aerobically treated sewage sludges gave higher mineralization rates than the anaerobically treated wastes. Values of potentially mineralizable N (No) varied from 71 to 394 mg N kg -1 soil, and mineralization rate constant (k) ranged from 0.089 to 0"883 week -~. The k values varied among sewage sludges sufficiently so that a single value could not be assumed. The parameter IV,, x k was a very good predictor of N availability.

Key words: N-mineralization, sewage sludges, first-order kinetics, potentially mineralizable N, mineralization rate.

INTRODUCTION

The application rate of sewage sludge to land must be determined on the basis of crop N requirement to avoid hazards associated with excessive NO 3 in soil. The crop N uptake depends on the available N in sludges. In order to determine available N it is necessary to know the mineralizable organic N of sludges. The literature suggests that mineralization of organic N in sewage sludge is a complex process which is dependent on several factors: soil type, soil pH, temperature, aeration, moisture, and rate or type

of waste. Laboratory analysis indicates that the type of stabilization process, anaerobic or aerobic, has a significant effect on the N mineralization rate (Sommers et al., 1976).

Studies with anaerobically digested sludge gave N mineralization rates of 4-48% in 16 weeks (Ryan et al., 1973), 14-25% in 13 weeks (Magdoff & Chromec, 1977) and 40-42% in 15 weeks (Epstein et al., 1978). For aerobically digested sludges, mineralization rates ranged from 36 to 41% during a 13 week laboratory incubation period (Magdoff & Chromec, 1977).

Based on data in the literature from Stevenson (1965) and Stanford and Smith (1972), it has been widely assumed that N mineralization reactions follow approximate first-order kinetics. Stanford and Smith (1972) calculated the first-order rate constant (k) and potentially mineralizable N (IV,,) using log transformed data. Smith et al. (1980) evaluated this method and found that a nonlinear least squares equation gave more accurate estima- tions of k and N o. Also, those parameters were calculated by a parabolic function by Molina et al. (1980) and Lindemann and Cardenas (1984). In these cases, two mineralization rate constants were estimated in order to distinguish between rapid and slow mineralization processes.

The objectives of this study were: (i) to determine the N mineralization patterns for a variety of sewage sludges obtained from several sewage treatment plants in Spain, and (ii) to estimate N o and k by the Smith et al. (1980) method.

METHODS

285

Soil and sludges Aerobic and anaerobically digested sewage sludges were obtained from different sewage treatment plants in Spain. The soil used was taken from surface layer (0-15 cm); this soil was clas-

Bioresource Technology 0960-8524/91/S03.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain

286 M. D. Serna, F. Pomares

sifted as Xerorthent (Soil Taxonomy, 1975). It had a sandy-loam texture, basic pH, and a low level of calcium carbonate. Soil and sewage-sludge samples were air-dried and ground to pass through a 2 mm sieve. Some properties of the soil and sludges are given in Table 1.

Incubation procedure Sludges were mixed with soil at the rate of 50 Mg ha- l (28 g kg- l soil). The samples were incubated aerobically under a nonleached procedure. The incubation period was 16 weeks at 25°C. The soil moisture content was adjusted weekly to about ] of field capacity. The samples were extracted with 2 M KCI at a soil to extractant ratio of 1 : 5.

Mineralized N (NH~- + NO;- + NO2) was determined after 2, 4, 6, 8, 12 and 16 weeks of incubation. In each period, three replications of each soil-sludge mixture and a nonamended control soil were analysed.

Statistical analysis The inorganic N data measured at each of the six incubation periods were statistically analysed using a nonlinear regression approach described by Smith et al. (1980). From this analysis, esti- mates for the amount of potentially mineralizable N (No) and the first-order rate constant (k) for the 16-week incubation period were obtained. In the present study, the Smith et al. (1980) method and a computer program were used to solve the fol- lowing equation:

Nm = No(1 - e -k')

where

N m = amount of N mineralized at a specific time, N o = potentially mineralizable N,

k = first-order rate constant, t = time of incubation.

Chemical analyses Organic N in soil and sludge samples was determined by a semi-micro Kjeldahl method (Bremner & Mulvaney, 1982). Determination of inorganic forms of N (NH 2- + NO 3 + NO2) was carried out by steam distillation with MgO and Devarda's alloy (Bremner, 1965a; Bremner & Keeney, 1966; Keeney & Bremner, 1966). Organic C was determined by a Walkley & Black modified procedure (Nelson & Sommers, 1982). Soil pH measurements were made in a 1:2 soil/ (sludge) :water paste.

RESULTS AND DISCUSSION

Mineralization of organic N Nitrogen mineralized during laboratory incubation is generally considered the most satisfactory method available for assessing the potential capacity of soils to mineralize organic N (Bremner, 1965b). Amounts of N mineralized during the incubation period are given in Table 2.

The cumulative amounts of N mineralized in aerobically digested sludges ranged from 95 mg N kg- l soil in sample AE 6 to 428 mg N kg- l soil in

Table 1. Properties of soil and sewage sludges

Designation Organic N Inorganic N Organic matter C/N pH (%) (ppm) (%)

Soil 0"072 0 1-44 11.6 7"6

Sewage sludges

Anaerobically digested Madrid 1 AN 1 0"86 3027 21-6 10-8 6"7 Casteil6n A N 2 2.01 32 47.0 13"5 6"8 Pinedo A N 3 1.82 3084 40.2 10.9 7"0 Alicante A N 4 3.32 831 72.7 12.4 6.8 Madrid 2 A N 5 1.71 3105 41"0 11"7 7"4 Butarque A N 6 2-28 2410 44.3 10" 1 6"4

Aerobically digested Burriana A E 1 2.94 1172 42.8 8.1 6"8 ViUarreal A E 2 2" 19 1823 34.5 8'4 6'9 Elda A E 3 2-28 102 35.4 8.9 7.1 Sagunto A E 4 3.48 2378 38.4 5.9 6.5 Oliva A E 5 4.67 452 55.8 6.8 6.4 Paterna A E 6 1.46 0 24"3 9"6 7.3

Nitrogen mineralization o f s ludge-amended soil

Table 2. N mineralization in sewage sludges by incubation procedure

287

Wastes N mineralized a Organic N b N o' k d N o k e rf mineralized

AN 1 105 45'6 87 0"883 77 0"955** AN 2 74 13'8 71 0"217 15 0'844* AN 3 97 19"8 85 0"454 38 0"907* AN 4 262 29"3 226 0"355 80 0"948** AN 5 78 17"0 71 0"802 57 0"912" AN 6 174 28"3 151 0"671 101 0"960** AE 1 251 31"7 210 0"449 94 0"926** AE 2 223 31"7 205 0"673 138 0"964** AE 3 247 40"2 206 0"462 95 0"908* AE 4 359 38"3 328 0"342 112 0"987*** AE 5 428 34"0 394 0"353 139 0"975*** AE 6 95 24"1 128 0"089 11 0"960**

~Quantified data from 16 weeks incubation at 25°C (Mineralized N - Control mineralized N), in mg N kg- J soil. b(N mineralized/organic N added) x 100. 'Potentially mineralizable N obtained from nonlinear least squares regression (mg N kg- l soil). '/First-order rate constant obtained from nonlinear least squares regression (week- J). "(mg N kg- l soil week- l). fCorrelation coefficients obtained as a result of application of the nonlinear least squares equation: *, **, ***, significant at the 0"05, 0"01 and 0.001 levels, respectively.

sample A E 5, with a mean value of 267 _ 115 mg N kg -1 soil (mean va lue_s t anda rd deviation). The highest values were obtained from A E 4 and A E 5 sewage sludge samples, which had the lowest C /N ratios (5.9 and 6.8, respectively). The correlation coefficient (r) value for N mineralized versus C /N was r = - 0"885; significant at the 0"05 level. These results agreed with those reported in the literature showing that N mineralization of sewage sludge decreases as its C /N ratio increases (Tester et al., 1977). The range of N mineralized found in this work was lower than those reported by Voos and Sabey (1987) and Yoneyama and Yoshida (1977), but higher than those reported by Parker and Sommers (1983) and Garau et al.

(1986). The correlation coefficient between mineralized N and organic N of aerobically digested sludges was significant at the 0-001 level (r--0"963). Expressed as percentages of organic N in sewage sludges, the cumulative amounts of N mineralized ranged from 24.1 to 40.2%, with a mean value of 33.3 _+ 5.7%. These results are similar to those reported by Garau et

al. (1986), Chaussod et al. (1978) and Hsieh e t al. (1981) but lower than those obtained by Magdoff and Chromec (1977). The correlation coefficient obtained from these data and the organic N percentage of aerobically digested sludges was nonsignificant ( r = 0"439).

In this study, the pat tern of N mineralization was a function of sludge type. Representative data are shown in Fig. 1 to illustrate the relationship

between inorganic N released and time of incubation. In control t reatment N was immobilized up to a 4 week incubation period, and then N started to be released for the rest of the incubation period. A n initial N immobilization in two sandy loam soils was also found by Haque and Walmsley (1972).

The aerobically digested sludges exhibited a rapid, initial release of inorganic N, followed by a relatively constant rate of mineralization from weeks 4 to 16. These wastes showed the same pat- tern of N mineralization when compared to those reported by Parker and Sommers (1983).

For anaerobically digested sludges, the amount of N mineralized ranged f rom 74 to 262 mg N kg -~ soil, with a mean value of 132___73 mg N kg -~ soil (Table 2); this range was lower than those reported by Lindeman and Cardenas (1984), Reddy et al. (1984) and King (1984). The correlation coefficient between these data and the organic N of anaerobically digested sludges was r--0"798; significant at the 0"05 level. When all the wastes were included, the r value coefficient was 0.912; significant at the 0-01 level. Expressed as a percentage of organic N in sewage sludges, the cumulative amounts of N mineralized ranged from 13.8 to 45.6%, with a mean value of 25.6 _+ 11.5%. These results were similar to those reported by Ryan et al. (1973), King and Morris (1972), Mitchell e t al. (1978) and Lindemann and Cardenas (1984). The correlation coefficient between these data and the organic N percentage


47O

370

70

0 4 8 12 16 0 4 8 12 16

INCUBA]ION TIME (week)

Fig. 1. Cumulative amounts of N mineralized in aerobically (A) and anaerobically (B) digested sludges during aerobic incubation in relation to incubation time.

of anaerobically digested sludges was nonsignificant (r= -0"296). In general, higher amounts of mineralizable N were present in aerobically digested sludges than in anaerobically digested sludges. Anaerobic digestion of sludge reduces the amount of N mineralization that occurs after the sludge is applied to soil (Parker & Sommers, 1983).

The anaerobically digested sludges showed a rapid, initial release of inorganic N during the initial 2 or 4 weeks, followed by a relatively constant rate of mineralization by weeks 4-8, and then it tended to increase slowly from 8 to 16 weeks; this increase was greater in sample AN 4 than in the other types of sewage sludges (Fig. 1 ).

At the beginning of the incubation, mineralized N exceeds the N needs of a microbial population resulting in a net increase of mineralized N. Sub- sequently, the mineralization curve becomes almost a plateau, and finally the bacterial growth decreases when mineralized N is not sufficient to maintain such a population. At this time, the decomposition of the organic matter and the mineralization of its N dominate. This would justify an increase in the N release observed over the last weeks of incubation.

For anaerobically digested sludges, the lowest amount of mineralized N was given by sample AN 2, which had the highest C/N ratio of this group. The correlation coefficient obtained from N mineralized versus C/N, with the exception of sample AN 4, was r = - 0 " 7 5 5 . Sample AN 4 showed anomalous behaviour with respect to the other sludges, having the highest amounts of N

mineralized and also a high C/N ratio. Overall, results of this study confirm that N mineralization in sewage sludges is inversely dependent on their C/N ratio, although this fact was more evident in the case of aerobically digested sludges.

As far as the suitability of these results to other soil is concerned, different authors (Miller, 1974; Sommers et al., 1976; Tester et al., 1977; Terry et al., 1979) concluded that the breakdown of municipal sludges was similar in soils having widely different textures and chemical characteristics. However, Chae and Tabatabai (1986) found that the total N mineralized in the sludge-treated soil varied markedly, depending on the type of soil used.

Kinetics of N mineralization The curvilinear relationship between N mineralized and time indicates that N mineralization can be approximated by first-order kinetics. This relationship was calculated by nonlinear least squares regression assuming first-order kinetics.

The N o values obtained for this procedure ranged from 71 to 394 mg N kg-~ soil, with a mean value of 180+103 ppm (Table 2). This value was similar to those reported by Griffin and Laine (1983) and Lindemann and Cardenas (1984). The mean values obtained in this work were different considering aerobically and anaerobically digested sewage sludges separately (245 + 97 ppm and 115 + 62 ppm, respectively). The results were similar to those obtained by Garau et al. (1986) who reported higher N O values for aerobically digested sludges than those for

Nitrogen mineralization of sludge-amended soil 289

anaerobically digested sludges. On the other hand, Harding et al. (1985) showed that N O was greater in anaerobically digested sludges compared to aerobically digested sludges. The calculated N values in this study agree very closely with the cumulative N mineralized during 16 weeks of incubation (r=0"988, significant at the 0.001 level). The correlation coefficient between total N and N O was r= 0"90; significant at the 0-001 level.

The k values obtained ranged from 0"089 to 0"883 week-~, with a mean value of 0.479 + 0.236 week -~ (Table 2); these values varied so much among sewage sludges that a single value could not be assumed. The mean values of k denote that the mineralizable N fraction is released at an average rate of 47.9% week -~, based on the quantity of mineralizable N remaining after each successive week of incubation. The k values obtained were similar to those reported by Voos and Sabey (1987) and Parker and Sommers (1983), although the mean value reported by the latter authors was slightly lower than those obtained in this study (0-286-0.626 week- t with a mean value of 0.452+0.092 week-~, and 0.137-0.633 week -l, with a mean value of 0.308 + 0.172 week-~, respectively). On the other hand, Chae and Tabatabai (1986), Griffin and Laine (1983) and Lindemann and Cardenas (1984) reported k values lower than those obtained in this study.

When No was multiplied by its respective rate constant (k), the product obtained could be used as an index of N availability. The product of N times k is the amount of N potentially mineralizable in 1 week under optimum soil temperature and moisture conditions (Mary & R6my, 1979; Stark & Clapp, 1980). The Nok values (i.e. N multiplied by k) obtained in this work ranged from 11.3 in sample AE 6 to 139 mg N kg -~ soil week-~ in sample AE 5 (Table 2). These results support the suitability of N o k as a reliable index of N availability, because the sewage sludges previously mentioned (AE 6 and AE 5) showed the highest and one of the lowest amounts of available N, respectively (Fig. 1). The correlation coefficient between N mineralized in 16 weeks and Nok was r = 0"799; significant at the 0"01 level.

As a result of the application of the nonlinear least squares equation of the data obtained during the incubation process, correlation coefficients have been reported (Table 2). Most of the coefficients were significant at high levels of prob- ability. From these results it is possible to conclude that, for most sludges, there was excel-

lent agreement between the actual data points and the predicted values. These results show that a single first-order kinetics equation can be used to describe sludge N mineralization in soils.

ACKNOWLEDGEMENTS

We are grateful to the Generalidad Valenciana and the Instituto Valenciano de Investigaciones Agrarias for financial support.

REFERENCES

Bremner, J. M. (1965a). Inorganic forms of nitrogen. In Methods of Soil Analysis, Part 2, Agronomy 9, ed. C. A. Black et al. American Society of Agronomy, Madison, Wisconsin, pp. 1179-237.

Bremner, J. M. (1965b). Nitrogen availability indexes. In Methods of Soil Analysis, Part 2, Agronomy 9, ed. C. A. Black et al. American Society of Agronomy, Madison, Wisconsin, pp. 1324-45.

Bremner, J. M. & Keeney, D. R. (1966). Determination and isotope-ratio analysis of different forms of nitrogen in soils: 3. Exchangeable ammonium, nitrate and nitrite by extraction-distillation methods. Soil Sci. Soc. Amer. Proc., 30,577-82.

Bremner, J. M. & Mulvaney, C. S. (1982). Nitrogen total. In Methods of Soil Analysis, Part 2, Agronomy 9, ed. C. A. Black et al. American Society of Agronomy, Madison, Wisconsin, pp. 595-624.

Chae, Y. M. & Tabatabai, M. A. (1986). Mineralization of nitrogen in soils amended with organic wastes. J. Environ. QuaL, 15, 193-8.

Chaussod, R., Germon, J. C. & Catroux, R. (1978). Deter- mination de la valeur fertilisante des boues residuaires. Aptitude a lib~re l'azote. Rapport Minist~re de I'Envi- ronnements, INRA, Dijon, France, 57 pp.

Epstein, E., Keane, D. B. & Meisinger, J. J. (1978). Minerali- zation of nitrogen from sewage sludge and sludge compost. J. Environ. Qual., 7, 217-21.

Garau, M. A., Felip6, M. T. & Villa, M. C. R. (1986). Nitrogen mineralization of sewage sludges in soils. J. Environ. Qual., 15, 225-8.

Griffin, G. F. & Laine, A. F. (1983). Nitrogen mineralization in soils previously amended with organic wastes. Agron. J., 75, 124-9.

Haque, 1. & Walmsley, D. (1972). Incubation studies on mineralization of organic sulphur and organic nitrogen. Plant Soil, 37,255-64.

Harding, S. A., Clapp, C. E. & Larson, W. E. (1985). Nitrogen availability and uptake from field soils five years after addition of sewage sludge. J. Environ. Qual., 15, 95-100.

Hsieh, Y. P., Douglas, L. A. & Motto, H. L. (1981 ). Modeling sewage sludge decomposition in soil. J. Environ. QuaL, 10, 59-64.

Keeney, D. R. & Bremner, J. M. (1966). Determination and isotope-ratio analysis of different forms of nitrogen in soils: 4. Exchangeable ammonium, nitrate and nitrite by direct- distillation methods. Soil Sci. Soc. Amer. Proc., 30, 583-7.

King, L. D. (1984). Availability of nitrogen in municipal, industrial and animal wastes. J. Environ. Qual., 13, 609-12.


King, L. D. & Morris, H. D. (1972). Land disposal of liquid sewage sludge: the effect on yield, in vitro digestibility and chemical composition of Coastal Bermudagrass (Cynodon dactylon L. Pers.). J. Environ. Qual., 1,325-9.

Lindemann, W. C. & Cardenas, M. (1984). Nitrogen mineralization potential and nitrogen transformation of sludge- amended soil. SoilSci. Soc. Amer. J., 48, 1072-7.

Magdoff, F. R. & Chromec, F. W. (1977). Nitrogen mineralization from sewage sludges. J. Environ. Sci. Health, AI2, 191-201.

Mary, B. & R6my, J. C. (1979). Essai d'appr6ciation de la capacit6 de min6ralisation de l'azote de grande culture. I. Signification des cin6tiques de min6ralisation de la mati~re organique humifi6e. Ann. Agron., 30, 513-27.

Miller, R. H. (1974). Factors affecting the decomposition of an anaerobically digested sewage sludge in soil. J. Environ. Qual., 3, 376-80.

Mitchell, M. J., Hartenstein, R., Swift, B. L., Neuhauser, E. F., Abrams, B. I., Mulligan, R. M., Brown, B. A., Craig, D. & Kaplan, D. (1978). Effects of different sewage sludges on some chemical and biological characteristics of soil. J. Environ. QuaL, 7, 551-9.

Molina, J. A. E., Clapp, C. E. & Larson, W. E. (1980). Poten- tially mineralizable nitrogen in soil: the simple exponential model does not apply for the first 12 weeks of incubation. Soil Sci. Soc. Amer. J., 44,442-3.

Nelson, D. W. & Sommers, L. E. (1982). Total carbon, organic carbon, and organic matter. In Methods of Soil Analysis, Part 2, Agronomy 9, ed. C. A. Black et al. American Society of Agronomy, Madison, Wisconsin, pp. 539-79.

Parker, C. E & Sommers, L. E. (1983). Mineralization of nitrogen in sewage sludges. J. Environ. Qual., 12, 150-6.

Reddy, G. B., Dunn, S. J. & Ross, S. M. (1984). Nitrogen transformations in sludge amended soils. Sci. Total Environ., 37, 163-9.

Ryan, J. A., Keeney, D. R. & Walsh, L. M. (1973). Nitrogen transformations and availability of an anaerobically digested sewage sludge in soil. J. Environ. Qual., 2, 489-92.

Smith, J. L., Schnabel, R. B., McNeal, B. L. & Campbell, G. S. (1980). Potential errors in the first-order model for estimating soil nitrogen mineralization potentials. Soil Sci. Soc. Amer. J., 44, 996-1000.

Soil Taxonomy (1975). A basic system of soil classification for making and interpreting soil surveys. Agricultural Handbook No. 436, Soil Conservation Service, USDA.

Sommers, L. E., Nelson, D. W. & Yost, K. J. (1976). Variable nature of chemical composition of sewage sludges. J. Environ. Qual., 5, 303-6.

Stanford, G. & Smith, S. J. (1972). Nitrogen mineralization potentials of soils. Soil Sci. Soc. Amer. Proc., 36,465-72.

Stark, S. A. & Clapp, C. E. (1980). Residual nitrogen availability from soils treated with sewage sludges in a field experiment. J. Environ. Qual., 9, 505-12.

Stevenson, F. J. (1965). Origin and distribution of nitrogen in soil. In Soil Nitrogen, Agronomy 10, American Society of Agronomy, Madison, Wisconsin, pp. 1-42.

Terry, R. E., Nelson, D. W. & Sommers, L. E. (1979). Decomposition of anaerobically digested sewage sludge as affected by soil environmental conditions. J. Environ. QuaL, 8, 342-7.

Tester, C. F., Sikora, L. J., Taylor, J. M. & Parr, J. F. (1977). Decomposition of sewage sludge compost in soil: I. Carbon and nitrogen transformation. J. Environ. Qual., 6, 459-63.

Voos, G. & Sabey, B. R. (1987). Nitrogen mineralization in sewage sludge-amended coal mine spoil and topsoil. J. Environ. Qual., 16, 231-7.

Yoneyama, T. & Yoshida, T. (1977). Nitrogen mineralization of sewage sludges in soil. SoilSci. Plant Nutr., 24, 139-44.

nitrogen mineralization of sludge-amended soil

Documents