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Nitrogen loss in chicken litter compost as affected by carbon to nitrogen ratio and turning frequency
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Bioresource Technology 99 (2008) 7495–7503
Nitrogen loss in chicken litter compost as affected by carbon to nitrogen ratio and turning frequency G.A. Ogunwande *, J.A. Osunade, K.O. Adekalu, L.A.O. Ogunjimi Department of Agricultural Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria Received 16 October 2007; received in revised form 10 February 2008; accepted 14 February 2008 Available online 25 March 2008
Abstract The study was undertaken to investigate the effects of carbon to nitrogen (C:N) ratio and turning frequency (TF) on the loss of total nitrogen (TN) during composting of chicken litter (a mixture of chicken manure, waste feed, feathers and sawdust) with a view to producing good quality compost. Carbon to nitrogen ratios of 20:1, 25:1 and 30:1 and TF of 2, 4 and 6 days were experimented. The initial physico-chemical properties of the litter were determined. During the composting process, moisture level in the piles was periodically replenished to 55% and the temperature, pH and TN of the chicken litter were periodically monitored. Also, the dry matter (DM), total carbon (TC), total phosphorus (P) and total potassium (K) were examined at the end of composting. The results showed that both C:N ratio and TF had significant (p 6 0.05) effect on pile temperature, pH changes, TN, TC, P and K losses while DM was only affected (p 6 0.05) by C:N ratio. All treatments reached maturation at about 87 days as indicated by the decline of pile temperatures to near ambient temperature. Losses of TN, which were largely attributed to volatilization of ammonia (NH3), were highest within the first 28 days when the pile temperatures and pH values were above 33 °C and 7.7, respectively. Moisture loss increased as C:N ratio and TF increased. In conclusion, the treatment with a combination of 4 days TF and C:N ratio 25:1 (T4R25) had the minimum TN loss (70.73% of the initial TN) and this indicated the most efficient combination. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Composting; C:N ratio; Turning frequency; Total nitrogen loss
1. Introduction Raw litter may be applied directly to farmland, but it has the potential to create human and animal health risks, and cause surface and ground water pollution. One method of litter treatment that will enhance raw litter quality and reduce the environmental impact of land application is composting. Composting manure has been recognized as an effective way to partially solve the growing concern of solid waste management. Composting is a biological process in which organic wastes are stabilized and converted, under controlled conditions, into a product to be used as a soil conditioner and organic fertilizer (Brake, 1992; Haga, 1999). The processes improves the storage and handling *
Corresponding author. Tel.: +234 803 4007128. E-mail address: [email protected] (G.A. Ogunwande).
0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.02.020
characteristics of the manure by reducing its volume and weight, kills pathogens and weed seeds, minimizes the production of phytotoxic substances, reduces unpleasant odours (Tiquia and Tam, 1998), and stabilizes the nutrients and organic matter (OM) in it (Michel et al., 1996). However, one of the most negative effects of composting animal manures is the loss of N through ammonia (NH3) volatilization which reduces the fertilizer value of the manure, and constitutes an important economic loss. Hence, composting changes the nature of the waste and can affect its usefulness as a soil amendment (Tiquia and Tam, 2000). Ammonia emissions result from aerobic or anaerobic bacteria activities in manure (Zhang et al., 1991). The emissions have been reported to consist of over 92% of all N losses during composting of beef feedlot (Eghball et al., 1997), and between 47% and 62% of the initial total N during composting of poultry layer manure (Kithome et al., 1999). Hansen et al.
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Nomenclature T2R20 T2R25 T2R30 T4R20 T4R25
treatment with C:N ratio 20:1 treatment with C:N ratio 25:1 treatment with C:N ratio 30:1 treatment with C:N ratio 20:1 treatment with C:N ratio 25:1
a combination of 2 days TF and
T4R30
a combination of 2 days TF and
T6R20
a combination of 2 days TF and
T6R25
a combination of 4 days TF and
T6R30
treatment with C:N ratio 30:1 treatment with C:N ratio 20:1 treatment with C:N ratio 25:1 treatment with C:N ratio 30:1
a combination of 4 days TF and a combination of 6 days TF and a combination of 6 days TF and a combination of 6 days TF and
a combination of 4 days TF and
(1989) reported N losses up to 33% of the initial N during composting of poultry manure while losses during composting of animal manure ranged from 21% upward to 77% (Martins and Dewes, 1992). Several studies have shown that NH3 volatilization increases with an increase of pH, moisture content (MC), aeration, NH3 concentration, or temperature (Bishop and Godfrey, 1983). The most widely used parameter for composting is the C:N ratio of the initial composting material; high initial C:N ratio will cause a slower beginning of the process and the required composting time to be longer than usual (Tuomela et al., 2000) while low initial C:N ratio results in high emission of NH3 (Tiquia and Tam, 2000). Eghball (1997) reported that the composting period may take longer if water content is not maintained at a proper level. Turning is often cited as the primary mechanism of aeration and temperature control during windrow composting (Michel et al., 1996; Tiquia, 1996), while turning frequency is commonly believed to be a factor which affects the rate of composting as well as compost quality (Tiquia, 1996). Near-neutral pH is preferred for most efficient microbial activity during composting. Moore et al. (1997) found that NH3 volatilization from poultry litter increases once pH rises above 7.0. Temperature is a simple and excellent indicator of how well the composting process is progressing and how much O2 is being used (Walker, 2004). Haga (1999) and Misra et al. (2003) reported that high temperatures during composting contribute to the killing of weed seeds and pathogenic organisms. Although N losses have been measured for different C:N ratios (Hansen et al., 1989; Eghball et al., 1997) and turning frequencies (Tiquia et al., 1997; Wong et al., 2001), the combined effects of these composting factors on the quality of poultry litter are not well understood. The nutrient that has received the most attention in composting systems is N since it is the most needed element for plant nutrition, and according to Stephenson et al. (1990), raw poultry manure contains higher concentrations of N, Ca and P than manure from other livestock. The present study therefore aims to: (1) investigate the effects of different C:N ratios and turning frequencies on the changes in TN during composting of chicken litter in windrow piles and (2) determine the optimum combination of turning frequency and carbon
to nitrogen ratio that will minimize nitrogen loss during composting. 2. Methods 2.1. Composting in turned windrow piles The experiment was conducted during the dry season on an open site at the back of Agricultural Engineering building, Obafemi Awolowo University, Ile-Ife, South-West of Nigeria, between the months of December, 2005 and March, 2006. The experimental set up was a 3 3 factorial design with C:N ratios at 20:1, 25:1 and 30:1, and with turning frequencies at every 2 days, every 4 days and every 6 days. Nine piles of chicken litter were built, each in a pit of size 1.2 m 1.2 m square base and a height of 0.3 m. Each pile had a pyramidal shape with a square base of 1.2 m 1.2 m and a height of about 0.76 m. Each pile was replicated three times and turned manually using a hand shovel. Fresh chicken manure was collected in batches from a poultry farm in Ile-Ife, South-West of Nigeria within 4 days prior to composting. The bulking material (sawdust) mixed with the manure was collected from a sawmill plant, also in Ile-Ife. Sawdust was used because of its low MC, porosity and high C:N ratio. The initial properties of the Table 1 Initial properties of the chicken manure and sawdust Parameter
Total N (%) Ash (%) Total C (%) C:N ratio Total K (ppm) Total P (ppm) pH MC (%)
Concentration (dry weight basis) Manure
Sawdust
2.10 ± 0.11 52.34 ± 1.20 26.47 ± 1.13 13:1 203.90 ± 4.10 2.70 ± 0.10 8.34 ± 0.04 54.0 ± 2.48a
nd 3 ± 0.17 53.89 ± 1.71 nd nd nd 7.60 ± 0.10 30.0 ± 1.10a
Mean and standard error are shown (n = 3). nd – not determined; ppm – parts per million. a Value on wet weight basis.
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chicken manure and sawdust are summarized in Table 1. The N, P and K contents of the sawdust were assumed to be negligible as various authors (Galler and Davey, 1971; Eghball, 1997) have reported these elements as traces in sawdust. The concentration of ash, TC, TN, C:N ratio, P, K and moisture content (MC) of the initial composting mixture was theoretically calculated based on the results of the initial analyses. The C:N ratio of the raw manure was raised to 20:1, 25:1 and 30:1 through the addition of sawdust (Brake, 1992), and in accordance with the recommendation of Rynk et al. (1992) on rapid composting. The MC of the litter was adjusted to 55% (wet basis) at the beginning of composting by the method given by Brake (1992). The MC was measured periodically (precisely a day to turning operation) and replenished to 55% (wet basis) during turning operation such that every part received moisture. 2.2. Sampling and analytical procedures Ambient temperature and temperatures within each pile were measured daily and before the turning operation using a digital dry bulb thermometer, at two locations (0.25 m from the top and 0.25 m from the bottom) within the pile. The temperature measurements were taken between the hours of 06:00 am and 08:00 am when the ambient temperature was fairly stable. Three samples each were collected fortnightly at three locations in a pile (0.25 m from the top, at the middle and 0.25 m from the bottom) and composited. Samples were analyzed for the following parameters: moisture content (105 °C for 24 h); ash content (expressed as a percentage of residues after ignition at 600 °C for 5 h); TN using regular-kjeldahl method (Bremner, 1996); total K (after acid digestion) using atomic absorption spectrophotometer (Alpha 4 model); total P (after acid digestion) using ultra-violet visible spectrophotometer (UNICAM UV1 model) of wavelength 660 nm; pH (1:10 w/v sample: water extract) using a pH meter with a glass electrode. The TC was estimated from the ash content according to the formula (Mercer and Rose, 1968): TC ð%Þ ¼ ½100 Ash ð%Þ=1:8
ð1Þ
Losses of DM, TC, TN, P and K from the pile during composting were calculated according to the equation (Sanchez-Monedero et al., 1996): X 1Y 2 Y loss ð%Þ ¼ 100 100 ð2Þ X 2Y 1 where X1 and X2 represent the initial and the final ash concentrations, Y represents DM, TC, TN, P and K and Y1 and Y2 represent the initial and final concentrations of Y. Samples were analyzed for TC, P and K at the beginning and at the end of the process while TN and pH were analyzed every 2 weeks. All mass measurements (except MC) were expressed on 105 °C dry weight basis.
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2.3. Statistical analysis In order to better understand the effects of the different treatments, data were subjected to statistical analyses, using Statistical Analysis System procedure (SAS, 2002). Two-way analysis of variance (ANOVA) was performed to compare variations in compost properties. Where significance was indicated, Least Significant Difference (LSD) test was used to establish which treatment was significantly different. 3. Results and discussion Composting duration was 87 days and within the range of 15 and 180 days reported by Rynk et al. (1992) and Michel et al. (1996) for converting manure into stabilized compost. Cumulative MC (wet basis) added to replenish the piles increased from 161.67% to 270.57% as TF increased from 6 to 2 days, and increased from 176.90% to 248.37% as C:N ratio increased from 20:1 to 30:1. This revealed that moisture loss increased as the TF and C:N ratio increased. Table 2 presents the gain and loss in compost elements by the end of composting. Increases were observed in the ash concentration of all the treatments and this revealed that effective OM degradation occurred during the composting process. Although the piles were built on the ground, losses in compost elements due to leaching were considered insignificant as the piles were not wet enough to drain water. C:N ratio and TF affected (p 6 0.05) TC, total P and K concentrations (Table 3). The LSD test showed the treatment(s) that was significantly different for each of the parameter (Table 4). By the end of composting, all the treatments, except for T4R25, had increased C:N ratios. The increase could be attributed to vigorous NH3 volatilization during composting. Increase in the C:N ratios have also been reported in previous composting (Eghball et al., 1997; Tiquia and Tam, 2000). 3.1. Temperature patterns The pile temperatures during composting ranged between 28 and 71 °C. The results of the t-test revealed that there was no significant (p > 0.05) difference between the mean temperatures at the upper and lower locations within the piles. Both the C:N ratio and TF had significant (p 6 0.05) effect on pile temperature (Table 4). There was also a significant (p 6 0.05) interaction between C:N ratio and TF (C:N TF) among the treatments with 6 days TF. Pile temperature had a significant (p 6 0.05) correlation with TN and pH. This confirms the findings by Tiquia et al. (1998) on the correlation of temperature with compost properties. All the composting treatments started with thermophilic temperatures in the range of 55 and 71 °C (Fig. 1a– c), an indication that the C:N ratios were ideal. The short thermophilic phase (ranging between 17 and 22 days) observed is associated with turned windrow method (Diaz et al., 2002), but also, likely related to small size of piles
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Table 2 Loss and gain in compost elements Treatment
Dry matter loss (%)
Total C loss (%)
Total N loss (%)
Total P loss (%)
Total K loss (%)
T2R20 T4R20 T6R20 T2R25 T4R25 T6R25 T2R30 T4R30 T6R30
16.10 ± 1.01 18.37 ± 1.71 15.18 ± 0.24 16.36 ± 1.50 7.72 ± 2.14 10.01 ± 0.80 17.95 ± 0.86 18.01 ± 2.15 22.86 ± 1.21
79.98 ± 0.71 72.20 ± 1.08 63.12 ± 0.92 80.45 ± 1.08 72.40 ± 1.44 69.28 ± 0.96 83.52 ± 0.13 81.94 ± 1.19 80.91 ± 1.18
88.17 ± 0.28 82.72 ± 0.45 86.80 ± 0.32 82.85 ± 0.42 70.73 ± 0.80 87.42 ± 0.67 87.12 ± 1.06 83.93 ± 2.44 81.34 ± 1.10
62.78 ± 1.51 4.60 ± 9.16a 53.96 ± 0.48 57.22 ± 1.48 1.77 ± 2.29a 50.97 ± 1.21 53.66 ± 0.11 55.65 ± 3.55 67.16 ± 0.49
85.78 ± 0.17 79.57 ± 0.28 82.10 ± 0.12 70.89 ± 0.54 57.17 ± 0.62 50.61 ± 0.46 85.60 ± 0.15 82.84 ± 0.16 76.14 ± 0.27
Mean and standard error are shown (n = 3). a Percent gain.
Table 3 ANOVA results showing effects of C:N ratio and TF on some compost parameters Effect
DF
SS
MS
F-value
Pr > F
(a) Total carbon C:N ratio 2 TF 2 Error 22
542.33 479.79 215.90
271.16 239.89 9.81
27.63 24.45
<.0001 <.0001
(b) Total phosphorus C:N ratio 2 TF 2 Error 22
3026.61 10184.82 5129.95
1513.30 5092.41 233.18
6.49 21.84
(c) Total potassium C:N ratio 2 TF 2 Error 22
3027.59 582.70 267.50
1513.79 291.35 12.16
124.50 23.96
0.006 <.0001
Table 4 Least significant difference (LSD) test on the main and interaction effects on compost parameters Factor level (a) Main effect C:N ratio 20:1 25:1 30:1 LSD TF
<.0001 <.0001
involved. However, in this study, TF affected (p 6 0.05) the short thermophilic phase. The fact that the temperatures rose to between 55 and 71 °C indicated that the pathogens and weed seeds would have been destroyed (Haga, 1999; Misra et al., 2003). There were slight increases in the pile temperatures immediately after each turning operation in the early days of the experiment. This was responsible for the rise and fall pattern of the temperature profile and has been reported as the re-activation of the composting process, which is explained by the incorporation of external material into the pile, providing degradable substrate for the microbial biomass (Gracia-Gomez et al., 2003).
2 days 4 days 6 days LSD
(b) Interaction effect C:N TF2 20:1 25:1 30:1 LSD
Temperature
pH
DM
TN
42.39b 52.49a 53.57a 2.57
8.75a 9.33a 5.14b 3.45
16.55a 11.36b 19.61a 2.44
85.90a 80.33b 84.13a 1.80
49.34a 53.14b 45.96c 2.57
9.69b 9.19b 4.35a 3.45
ns ns ns –
86.05a 79.13b 85.19a 1.80
ns ns ns –
ns ns ns –
ns ns ns –
88.17a 82.85b 87.12a 2.35
C:N TF4
20:1 25:1 30:1 LSD
ns ns ns –
ns ns ns –
18.37a 7.71b 18.00a 6.95
82.72a 70.73b 83.93a 5.21
C:N TF6
20:1 25:1 30:1 LSD
29.51c 54.93a 53.44b 1.02
ns ns ns –
15.18a 10.12b 22.86c 2.95
86.80a 87.42a 81.34b 2.67
Superscripts with the same letter are not statistically different at p 6 0.05, according to the least significant difference (LSD); ns – mean value not significant at p 6 0.05, according to the LSD.
3.2. Dry matter C:N ratio had a significant (p 6 0.05) effect on DM loss (Table 4) while the interaction between C:N ratio and TF (C:N TF) among treatments with 4 and 6 days TF also affected (p 6 0.05) the loss. Dry matter losses ranged from 7.72% to 22.86% (Table 2). This loss was lower than the range of 35–50% reported by Kithome et al. (1999). 3.3. pH In this study, both the C:N ratio and TF affected (p 6 0.05) pH change (Table 4). The decrease in pH values
associated with decrease in TF may have been caused by the production of short-chain organic acids as a result of reduced air supply to the composting piles. The initial pH values ranged between 8.13 and 8.63. High values (8.73–9.34) were observed during the second week in all the treatments (Fig. 2a–c) and this was probably due to the decomposition of OM in the piles due to high pile temperatures (>45 °C) and microbial activities. Increase in pH values was also reported by Baeta-Hall et al. (2005) as due to the decomposition of OM. The fact that the pH values rose to between 8.0 and 9.0 indicated that the composting
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a
7499
80 Ambient
70
T2R20 T4R20
Temperature (ºC)
T6R20
60
50
40
30
20 1
11
21
31
41
51
61
71
81
Composting time (days)
b
80
70 Ambient
Temperature (ºC)
T2R25 T4R25
60
T6R25
50
40
30
20 1
11
21
31
41
51
61
71
81
Composting time (days)
c
80
Ambient
70
T2R30
Temperature (ºC)
T4R30 T6R30
60
50
40
30
20 1
11
21
31
41
51
61
71
81
Composting time (days)
Fig. 1. Changes in air and pile temperatures of composting piles with (a) C:N 20:1, (b) C:N 25:1 and (c) C:N 30:1. Error bars show standard errors of means (n = 3).
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a
9.6 T2R20
9.2
T4R20 T6R20
pH
8.8
8.4
8
7.6
7.2 0
2
4
6
8
10
12
Composting time (weeks)
b
9.6 T2R25 9.2
T4R25 T6R25
pH
8.8
8.4
8
7.6
7.2 0
2
4
6
8
10
12
Composting time (weeks)
c
9 T2R30 9.2
T4R30 T6R30
pH
8.8
8.4
8
7.6
7.2 0
2
4
6
8
10
12
Composting time (weeks)
Fig. 2. Changes in pH of piles with (a) C:N 20:1, (b) C:N 25:1 and (c) C:N ratio 30:1 due to TF effect. Error bars show standard errors of means (n = 3).
process was successful and fully developed (Sundberg et al., 2004). The final pH values ranged between 7.53 and 7.83.
This was an indication of stabilized OM (Sesay et al., 1997).
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3.4. Total nitrogen The results of the ANOVA showed that C:N ratio, TF, and the interaction of C:N ratio and TF (C:N TF) had significant (p 6 0.05) effect on TN loss (Table 4). The results of the multiple regression analysis with stepwise selection of variables showed that temperature, pH, C, C:N ratio and DM were significantly (p 6 0.05) correlated with TN. The cumulative TN losses by the end of composting ranged between 70.73% and 88.17% of the initial TN concentration in all treatments (Table 2), with the least loss (70.73%) observed in treatment T4R25. Although temperature and pH were significantly (p 6 0.05) correlated with TN, an interesting finding is the fact that neither temperature nor pH was significantly (p > 0.05) correlated with TN in treatment T4R25. This implied that temperature and pH did not contribute significantly to TN loss in treatment T4R25. The TN losses were greater than losses reported by Hansen et al. (1989), Kirchmann and Witter (1989) during composting of poultry manure. The high losses may likely be related to the small size of piles used in this experiment. Between 43% and 91% of TN losses occurred within the first 28 days of composting in all the treatments (Fig. 3a–c) when the pile temperatures and pH were above 33 °C and 7.7, respectively. A significant part of the TN losses was probably by NH3 volatilization, which was favoured by the high temperature and pH values in this period, as reported by several authors (Bishop and Godfrey, 1983; Tiquia and Tam, 2000). Losses of TN may also have been due to mineralization of OM by micro-organisms (Laos et al., 2002; Grigatti et al., 2004), or to the exposure of the piles to direct sunlight which may have accelerated the decomposition and loss of valuable nutrients (Kwakye, 1977). The decrease in TN loss (as observed in treatments T6R20 and T4R25 during week 4, and treatments T4R30 and T6R30 during week 8) during composting may be attributed to increase in organic N due to a concentration effect as a consequence of strong degradation of organic C compounds (Tiquia and Tam, 2000). Except in treatments with C:N ratio 30:1, the least losses of TN were observed at 4 days TF (Fig. 4). The average values showed that treatments with 2 and 6 days TF had higher losses of TN (86.05% and 85.19%, respectively) than treatments with 4 days TF (79.13%); this could be attributed to aeration rate (turning frequency) of the piles. Treatments with 2 days TF had the highest air supply, while treatments with 6 days TF had the least. Losses of TN in the 2 days TF treatments may have been largely due to NH3 volatilization as a result of high air supply to the piles. Several studies have indicated that NH3 volatilization increased remarkably with the increase of air supply (Zhang et al., 1994; Beck et al., 1997). Losses of TN in the 6 days TF treatments may also have been largely due to NH3 volatilization as a result of possible insufficient air supply to the microorganisms thereby creating some state of anaerobic conditions in the piles. Products of such conditions have been reported as objectionable gases and odours such as hydro-
Fig. 3. Total N losses in piles with (a) C:N 20:1, (b) C:N 25:1 and (c) C:N 30:1 due to TF effect. Error bars show standard errors of means (n = 3).
gen sulphide (H2S) and NH3 (Zhang et al., 1991; Day and Funk, 1998). Treatments with C:N ratio 20:1 had the highest loss of TN (85.90%), followed by treatments with C:N ratio 30:1 (84.13%) while treatments with C:N 25:1 had the least (80.33%). This could be attributed to porosity (which is a function of the C:N ratio) of the piles. Treatments with C:N ratio 20:1 were the least porous, hence TN losses may have been largely due to NH3 volatilization as a result of possible insufficient air supply (due to fewer air pores in the piles) to the micro-organisms thereby creating some state of anaerobic conditions in the piles. On the
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Cumulative total N loss (%)
95
85
C:N 20:1
75
C:N 25:1 C:N 30:1 Average 65 2
4
6
Turning frequency (days)
Fig. 4. Relationship between C:N ratio and TF with respect to total N losses. Error bars show standard errors of means (n = 3).
other hand, treatments with C:N ratio 30:1 had the highest porosity, hence TN losses may have been largely due to NH3 volatilization as a result of possible high air supply (due to higher number of air pores) to the piles. In view of these facts, it could be said that, the least loss of TN occurred at a state when the composting process was averagely aerobic/anaerobic, at a combination of C:N ratio 25:1 and 4 days TF. 4. Conclusions The results showed that both C:N ratio and TF were significant on pile temperature, pH changes, TN, TC, P and K losses while DM was only affected by C:N ratio. The highest TN losses occurred during the period when the pile temperatures and pH values were above 33 °C and 7.7, respectively. Moisture loss was observed to increase as the C:N ratio and TF increased. Total N loss was least in treatment T4R25. References Baeta-Hall, L., Saagua, M.C., Bartolomeu, M.L., Anselmo, A.M., Rosa, M.F., 2005. Bio-degradation of olive oil husks in composting aerated piles. Bioresource Technology 96, 69–78. Beck, J., Kack, M., Hentschel, A., Csehi, K., Jungbluth, T., 1997. Ammonia emission from composting animal wastes in reactors and windrows. In: Voermans, J.A., Monteny, G.J. (Eds.), Proceedings of the International Symposium, Ammonia and Odour Control from Animal Production Facilities, Vinkeloord, The Netherlands, pp. 381– 388. Bishop, P.L., Godfrey, C., 1983. Nitrogen variations during sludge composting. BioCycle 24, 34–39. Brake, J.D., 1992. A Practical Guide for Composting Poultry Litter, MAFES Bulletin, p. 981. Bremner, J.M., 1996. Nitrogen-total. In: Sparks, D.L. (Ed.), Methods of Soil Analysis. Part 3 – Chemical Methods. SSSA Inc., ASA Inc., Madison, WI, USA, pp. 1085–1122. Day, D.L., Funk, T.L., 1998. Processing manure: physical, chemical and biological treatment. In: Animal Waste Utilization: Effective Use of Manure as a Soil Resource. Ann Arbor Press, Chelsea, Michigan.
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G.A. Ogunwande et al. / Bioresource Technology 99 (2008) 7495–7503 leaves to grass mix ratio and windrow vs pile configuration on the composting of yard trimmings. Compost Science and Utilization 4, 26– 43. Misra, R.V., Roy, R.N., Hiraoka, H., 2003. On-farm composting methods. FAO Corporate Document Repository.. Moore, P.A., Huff Jr., W.E., Daniel, T.C., Edward, D.R., Saucer, T.C., 1997. Effect of aluminum sulfate on ammonia fluxes from poultry litter in commercial broiler houses. In: Proceedings of Fifth International Symposium on Livestock Environment, Transactions of the ASAE 2, pp. 883–891. Rynk, R., van de Kamp, M., Wilson, G.B., Singley, M.E., Richard, T.L., Kolega, J.J., Gouin, F.R., Laliberty, L., Kay Jr., D., Murphy, D.W., Hoitink, H.A.J., Brinton, W.F., 1992. On-farm Composting. Northeast Regional Agricultural Engineering Services, Ithaca, New York. Sanchez-Monedero, M.A., Bernal, M.P., Roig, A., Cegarra, J., Garcia, D., 1996. The effectiveness of the Rutgers system and the addition of bulking agent in reducing N-losses during composting. In: Van Cleemput, O., Hofman, G., Vermoesen, A. (Eds.), Progress in Nitrogen Cycling Studies. Kluwer Academic, Dordretch, pp. 133–139. SAS, 2002. Statistical Analysis Software Guide for Personal Computers. Release 9.1. SAS Institute Inc., Cary, NC 27513, USA. Sesay, A.A., Lasaridi, K., Stentiford, E., Budd, T., 1997. Controlled composting of paper pulp sludge using aerated static pile method. Compost Science and Utilization 5, 82–96. Stephenson, A.H., McCaskey, T.A., Ruffin, B.G., 1990. A survey of broiler litter composition and potential value as a nutrient resource. Biological Wastes 34, 1–9. Sundberg, C., Smars, S., Jonsson, H., 2004. Low pH as an inhibiting factor in the transformation from mesophilic to thermophilic phase in composting. Bioresource Technology 95, 145–150.
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Tiquia, S.M., 1996. Further composting of pig manure disposed from the pig-on-litter (POL) system in Hong Kong. Ph.D. Thesis, The University of Hong Kong Pokfulam Road, Hong Kong. Tiquia, S.M., Tam, N.F.Y., 1998. Elimination of phytotoxitcity during cocomposting of spent pig manure, sawdust litter and sludge. Bioresource Technology 65, 43–49. Tiquia, S.M., Tam, N.F.Y., 2000. Fate of nitrogen during composting of chicken litter. Environmental Pollution 110, 535–541. Tiquia, S.M., Tam, N.F.Y., Hodgkiss, I.J., 1997. Effects of turning frequency on composting of spent pig-manure sawdust litter. Bioresource Technology 62, 37–42. Tiquia, S.M., Tam, N.F.Y., Hodgkiss, I.J., 1998. Changes in chemical properties during domposting of spent litter at different moisture contents. Agriculture, Ecosystems and Environment 67 (1), 79–89. Tuomela, M., Vikman, M., Hatakka, A., Itavaara, M., 2000. Biodegradation of lignin in a compost environment: a review. Bioresource Technology 72 (2), 169–183. Walker, F., 2004. On – farm composting of poultry litter. The Agricultural Extension Service, The University of Tennessee Institute of Agriculture. Wong, J.W.C., Mak, K.F., Chan, N.W., Lam, A., Fang, M., Zhou, L.X., Wu, Q.T., Liao, X.D., 2001. Co-composting of soybean residues and leaves in Hong Kong. Bioresource Technology 76 (2), 99–106. Zhang, R., Ishibashi, K., Day, D.L., 1991. Experimental study of microbial decomposition in liquid swine manure, and generation rates of ammonia. In: Proceedings of the Livestock Waste Management Conference, American Society of Agricultural Engineers, St. Joseph, Michigan. Zhang, R., Day, D.L., Christianson, L.L., Jepson, W.P., 1994. A computer model for predicting ammonia release rates from swine manure pits. Journal of Agricultural Engineering Research 58 (4), 223–229.
Bioresource Technology 99 (2008) 7495–7503
Nitrogen loss in chicken litter compost as affected by carbon to nitrogen ratio and turning frequency G.A. Ogunwande *, J.A. Osunade, K.O. Adekalu, L.A.O. Ogunjimi Department of Agricultural Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria Received 16 October 2007; received in revised form 10 February 2008; accepted 14 February 2008 Available online 25 March 2008
Abstract The study was undertaken to investigate the effects of carbon to nitrogen (C:N) ratio and turning frequency (TF) on the loss of total nitrogen (TN) during composting of chicken litter (a mixture of chicken manure, waste feed, feathers and sawdust) with a view to producing good quality compost. Carbon to nitrogen ratios of 20:1, 25:1 and 30:1 and TF of 2, 4 and 6 days were experimented. The initial physico-chemical properties of the litter were determined. During the composting process, moisture level in the piles was periodically replenished to 55% and the temperature, pH and TN of the chicken litter were periodically monitored. Also, the dry matter (DM), total carbon (TC), total phosphorus (P) and total potassium (K) were examined at the end of composting. The results showed that both C:N ratio and TF had significant (p 6 0.05) effect on pile temperature, pH changes, TN, TC, P and K losses while DM was only affected (p 6 0.05) by C:N ratio. All treatments reached maturation at about 87 days as indicated by the decline of pile temperatures to near ambient temperature. Losses of TN, which were largely attributed to volatilization of ammonia (NH3), were highest within the first 28 days when the pile temperatures and pH values were above 33 °C and 7.7, respectively. Moisture loss increased as C:N ratio and TF increased. In conclusion, the treatment with a combination of 4 days TF and C:N ratio 25:1 (T4R25) had the minimum TN loss (70.73% of the initial TN) and this indicated the most efficient combination. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Composting; C:N ratio; Turning frequency; Total nitrogen loss
1. Introduction Raw litter may be applied directly to farmland, but it has the potential to create human and animal health risks, and cause surface and ground water pollution. One method of litter treatment that will enhance raw litter quality and reduce the environmental impact of land application is composting. Composting manure has been recognized as an effective way to partially solve the growing concern of solid waste management. Composting is a biological process in which organic wastes are stabilized and converted, under controlled conditions, into a product to be used as a soil conditioner and organic fertilizer (Brake, 1992; Haga, 1999). The processes improves the storage and handling *
Corresponding author. Tel.: +234 803 4007128. E-mail address: [email protected] (G.A. Ogunwande).
0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.02.020
characteristics of the manure by reducing its volume and weight, kills pathogens and weed seeds, minimizes the production of phytotoxic substances, reduces unpleasant odours (Tiquia and Tam, 1998), and stabilizes the nutrients and organic matter (OM) in it (Michel et al., 1996). However, one of the most negative effects of composting animal manures is the loss of N through ammonia (NH3) volatilization which reduces the fertilizer value of the manure, and constitutes an important economic loss. Hence, composting changes the nature of the waste and can affect its usefulness as a soil amendment (Tiquia and Tam, 2000). Ammonia emissions result from aerobic or anaerobic bacteria activities in manure (Zhang et al., 1991). The emissions have been reported to consist of over 92% of all N losses during composting of beef feedlot (Eghball et al., 1997), and between 47% and 62% of the initial total N during composting of poultry layer manure (Kithome et al., 1999). Hansen et al.
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Nomenclature T2R20 T2R25 T2R30 T4R20 T4R25
treatment with C:N ratio 20:1 treatment with C:N ratio 25:1 treatment with C:N ratio 30:1 treatment with C:N ratio 20:1 treatment with C:N ratio 25:1
a combination of 2 days TF and
T4R30
a combination of 2 days TF and
T6R20
a combination of 2 days TF and
T6R25
a combination of 4 days TF and
T6R30
treatment with C:N ratio 30:1 treatment with C:N ratio 20:1 treatment with C:N ratio 25:1 treatment with C:N ratio 30:1
a combination of 4 days TF and a combination of 6 days TF and a combination of 6 days TF and a combination of 6 days TF and
a combination of 4 days TF and
(1989) reported N losses up to 33% of the initial N during composting of poultry manure while losses during composting of animal manure ranged from 21% upward to 77% (Martins and Dewes, 1992). Several studies have shown that NH3 volatilization increases with an increase of pH, moisture content (MC), aeration, NH3 concentration, or temperature (Bishop and Godfrey, 1983). The most widely used parameter for composting is the C:N ratio of the initial composting material; high initial C:N ratio will cause a slower beginning of the process and the required composting time to be longer than usual (Tuomela et al., 2000) while low initial C:N ratio results in high emission of NH3 (Tiquia and Tam, 2000). Eghball (1997) reported that the composting period may take longer if water content is not maintained at a proper level. Turning is often cited as the primary mechanism of aeration and temperature control during windrow composting (Michel et al., 1996; Tiquia, 1996), while turning frequency is commonly believed to be a factor which affects the rate of composting as well as compost quality (Tiquia, 1996). Near-neutral pH is preferred for most efficient microbial activity during composting. Moore et al. (1997) found that NH3 volatilization from poultry litter increases once pH rises above 7.0. Temperature is a simple and excellent indicator of how well the composting process is progressing and how much O2 is being used (Walker, 2004). Haga (1999) and Misra et al. (2003) reported that high temperatures during composting contribute to the killing of weed seeds and pathogenic organisms. Although N losses have been measured for different C:N ratios (Hansen et al., 1989; Eghball et al., 1997) and turning frequencies (Tiquia et al., 1997; Wong et al., 2001), the combined effects of these composting factors on the quality of poultry litter are not well understood. The nutrient that has received the most attention in composting systems is N since it is the most needed element for plant nutrition, and according to Stephenson et al. (1990), raw poultry manure contains higher concentrations of N, Ca and P than manure from other livestock. The present study therefore aims to: (1) investigate the effects of different C:N ratios and turning frequencies on the changes in TN during composting of chicken litter in windrow piles and (2) determine the optimum combination of turning frequency and carbon
to nitrogen ratio that will minimize nitrogen loss during composting. 2. Methods 2.1. Composting in turned windrow piles The experiment was conducted during the dry season on an open site at the back of Agricultural Engineering building, Obafemi Awolowo University, Ile-Ife, South-West of Nigeria, between the months of December, 2005 and March, 2006. The experimental set up was a 3 3 factorial design with C:N ratios at 20:1, 25:1 and 30:1, and with turning frequencies at every 2 days, every 4 days and every 6 days. Nine piles of chicken litter were built, each in a pit of size 1.2 m 1.2 m square base and a height of 0.3 m. Each pile had a pyramidal shape with a square base of 1.2 m 1.2 m and a height of about 0.76 m. Each pile was replicated three times and turned manually using a hand shovel. Fresh chicken manure was collected in batches from a poultry farm in Ile-Ife, South-West of Nigeria within 4 days prior to composting. The bulking material (sawdust) mixed with the manure was collected from a sawmill plant, also in Ile-Ife. Sawdust was used because of its low MC, porosity and high C:N ratio. The initial properties of the Table 1 Initial properties of the chicken manure and sawdust Parameter
Total N (%) Ash (%) Total C (%) C:N ratio Total K (ppm) Total P (ppm) pH MC (%)
Concentration (dry weight basis) Manure
Sawdust
2.10 ± 0.11 52.34 ± 1.20 26.47 ± 1.13 13:1 203.90 ± 4.10 2.70 ± 0.10 8.34 ± 0.04 54.0 ± 2.48a
nd 3 ± 0.17 53.89 ± 1.71 nd nd nd 7.60 ± 0.10 30.0 ± 1.10a
Mean and standard error are shown (n = 3). nd – not determined; ppm – parts per million. a Value on wet weight basis.
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chicken manure and sawdust are summarized in Table 1. The N, P and K contents of the sawdust were assumed to be negligible as various authors (Galler and Davey, 1971; Eghball, 1997) have reported these elements as traces in sawdust. The concentration of ash, TC, TN, C:N ratio, P, K and moisture content (MC) of the initial composting mixture was theoretically calculated based on the results of the initial analyses. The C:N ratio of the raw manure was raised to 20:1, 25:1 and 30:1 through the addition of sawdust (Brake, 1992), and in accordance with the recommendation of Rynk et al. (1992) on rapid composting. The MC of the litter was adjusted to 55% (wet basis) at the beginning of composting by the method given by Brake (1992). The MC was measured periodically (precisely a day to turning operation) and replenished to 55% (wet basis) during turning operation such that every part received moisture. 2.2. Sampling and analytical procedures Ambient temperature and temperatures within each pile were measured daily and before the turning operation using a digital dry bulb thermometer, at two locations (0.25 m from the top and 0.25 m from the bottom) within the pile. The temperature measurements were taken between the hours of 06:00 am and 08:00 am when the ambient temperature was fairly stable. Three samples each were collected fortnightly at three locations in a pile (0.25 m from the top, at the middle and 0.25 m from the bottom) and composited. Samples were analyzed for the following parameters: moisture content (105 °C for 24 h); ash content (expressed as a percentage of residues after ignition at 600 °C for 5 h); TN using regular-kjeldahl method (Bremner, 1996); total K (after acid digestion) using atomic absorption spectrophotometer (Alpha 4 model); total P (after acid digestion) using ultra-violet visible spectrophotometer (UNICAM UV1 model) of wavelength 660 nm; pH (1:10 w/v sample: water extract) using a pH meter with a glass electrode. The TC was estimated from the ash content according to the formula (Mercer and Rose, 1968): TC ð%Þ ¼ ½100 Ash ð%Þ=1:8
ð1Þ
Losses of DM, TC, TN, P and K from the pile during composting were calculated according to the equation (Sanchez-Monedero et al., 1996): X 1Y 2 Y loss ð%Þ ¼ 100 100 ð2Þ X 2Y 1 where X1 and X2 represent the initial and the final ash concentrations, Y represents DM, TC, TN, P and K and Y1 and Y2 represent the initial and final concentrations of Y. Samples were analyzed for TC, P and K at the beginning and at the end of the process while TN and pH were analyzed every 2 weeks. All mass measurements (except MC) were expressed on 105 °C dry weight basis.
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2.3. Statistical analysis In order to better understand the effects of the different treatments, data were subjected to statistical analyses, using Statistical Analysis System procedure (SAS, 2002). Two-way analysis of variance (ANOVA) was performed to compare variations in compost properties. Where significance was indicated, Least Significant Difference (LSD) test was used to establish which treatment was significantly different. 3. Results and discussion Composting duration was 87 days and within the range of 15 and 180 days reported by Rynk et al. (1992) and Michel et al. (1996) for converting manure into stabilized compost. Cumulative MC (wet basis) added to replenish the piles increased from 161.67% to 270.57% as TF increased from 6 to 2 days, and increased from 176.90% to 248.37% as C:N ratio increased from 20:1 to 30:1. This revealed that moisture loss increased as the TF and C:N ratio increased. Table 2 presents the gain and loss in compost elements by the end of composting. Increases were observed in the ash concentration of all the treatments and this revealed that effective OM degradation occurred during the composting process. Although the piles were built on the ground, losses in compost elements due to leaching were considered insignificant as the piles were not wet enough to drain water. C:N ratio and TF affected (p 6 0.05) TC, total P and K concentrations (Table 3). The LSD test showed the treatment(s) that was significantly different for each of the parameter (Table 4). By the end of composting, all the treatments, except for T4R25, had increased C:N ratios. The increase could be attributed to vigorous NH3 volatilization during composting. Increase in the C:N ratios have also been reported in previous composting (Eghball et al., 1997; Tiquia and Tam, 2000). 3.1. Temperature patterns The pile temperatures during composting ranged between 28 and 71 °C. The results of the t-test revealed that there was no significant (p > 0.05) difference between the mean temperatures at the upper and lower locations within the piles. Both the C:N ratio and TF had significant (p 6 0.05) effect on pile temperature (Table 4). There was also a significant (p 6 0.05) interaction between C:N ratio and TF (C:N TF) among the treatments with 6 days TF. Pile temperature had a significant (p 6 0.05) correlation with TN and pH. This confirms the findings by Tiquia et al. (1998) on the correlation of temperature with compost properties. All the composting treatments started with thermophilic temperatures in the range of 55 and 71 °C (Fig. 1a– c), an indication that the C:N ratios were ideal. The short thermophilic phase (ranging between 17 and 22 days) observed is associated with turned windrow method (Diaz et al., 2002), but also, likely related to small size of piles
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Table 2 Loss and gain in compost elements Treatment
Dry matter loss (%)
Total C loss (%)
Total N loss (%)
Total P loss (%)
Total K loss (%)
T2R20 T4R20 T6R20 T2R25 T4R25 T6R25 T2R30 T4R30 T6R30
16.10 ± 1.01 18.37 ± 1.71 15.18 ± 0.24 16.36 ± 1.50 7.72 ± 2.14 10.01 ± 0.80 17.95 ± 0.86 18.01 ± 2.15 22.86 ± 1.21
79.98 ± 0.71 72.20 ± 1.08 63.12 ± 0.92 80.45 ± 1.08 72.40 ± 1.44 69.28 ± 0.96 83.52 ± 0.13 81.94 ± 1.19 80.91 ± 1.18
88.17 ± 0.28 82.72 ± 0.45 86.80 ± 0.32 82.85 ± 0.42 70.73 ± 0.80 87.42 ± 0.67 87.12 ± 1.06 83.93 ± 2.44 81.34 ± 1.10
62.78 ± 1.51 4.60 ± 9.16a 53.96 ± 0.48 57.22 ± 1.48 1.77 ± 2.29a 50.97 ± 1.21 53.66 ± 0.11 55.65 ± 3.55 67.16 ± 0.49
85.78 ± 0.17 79.57 ± 0.28 82.10 ± 0.12 70.89 ± 0.54 57.17 ± 0.62 50.61 ± 0.46 85.60 ± 0.15 82.84 ± 0.16 76.14 ± 0.27
Mean and standard error are shown (n = 3). a Percent gain.
Table 3 ANOVA results showing effects of C:N ratio and TF on some compost parameters Effect
DF
SS
MS
F-value
Pr > F
(a) Total carbon C:N ratio 2 TF 2 Error 22
542.33 479.79 215.90
271.16 239.89 9.81
27.63 24.45
<.0001 <.0001
(b) Total phosphorus C:N ratio 2 TF 2 Error 22
3026.61 10184.82 5129.95
1513.30 5092.41 233.18
6.49 21.84
(c) Total potassium C:N ratio 2 TF 2 Error 22
3027.59 582.70 267.50
1513.79 291.35 12.16
124.50 23.96
0.006 <.0001
Table 4 Least significant difference (LSD) test on the main and interaction effects on compost parameters Factor level (a) Main effect C:N ratio 20:1 25:1 30:1 LSD TF
<.0001 <.0001
involved. However, in this study, TF affected (p 6 0.05) the short thermophilic phase. The fact that the temperatures rose to between 55 and 71 °C indicated that the pathogens and weed seeds would have been destroyed (Haga, 1999; Misra et al., 2003). There were slight increases in the pile temperatures immediately after each turning operation in the early days of the experiment. This was responsible for the rise and fall pattern of the temperature profile and has been reported as the re-activation of the composting process, which is explained by the incorporation of external material into the pile, providing degradable substrate for the microbial biomass (Gracia-Gomez et al., 2003).
2 days 4 days 6 days LSD
(b) Interaction effect C:N TF2 20:1 25:1 30:1 LSD
Temperature
pH
DM
TN
42.39b 52.49a 53.57a 2.57
8.75a 9.33a 5.14b 3.45
16.55a 11.36b 19.61a 2.44
85.90a 80.33b 84.13a 1.80
49.34a 53.14b 45.96c 2.57
9.69b 9.19b 4.35a 3.45
ns ns ns –
86.05a 79.13b 85.19a 1.80
ns ns ns –
ns ns ns –
ns ns ns –
88.17a 82.85b 87.12a 2.35
C:N TF4
20:1 25:1 30:1 LSD
ns ns ns –
ns ns ns –
18.37a 7.71b 18.00a 6.95
82.72a 70.73b 83.93a 5.21
C:N TF6
20:1 25:1 30:1 LSD
29.51c 54.93a 53.44b 1.02
ns ns ns –
15.18a 10.12b 22.86c 2.95
86.80a 87.42a 81.34b 2.67
Superscripts with the same letter are not statistically different at p 6 0.05, according to the least significant difference (LSD); ns – mean value not significant at p 6 0.05, according to the LSD.
3.2. Dry matter C:N ratio had a significant (p 6 0.05) effect on DM loss (Table 4) while the interaction between C:N ratio and TF (C:N TF) among treatments with 4 and 6 days TF also affected (p 6 0.05) the loss. Dry matter losses ranged from 7.72% to 22.86% (Table 2). This loss was lower than the range of 35–50% reported by Kithome et al. (1999). 3.3. pH In this study, both the C:N ratio and TF affected (p 6 0.05) pH change (Table 4). The decrease in pH values
associated with decrease in TF may have been caused by the production of short-chain organic acids as a result of reduced air supply to the composting piles. The initial pH values ranged between 8.13 and 8.63. High values (8.73–9.34) were observed during the second week in all the treatments (Fig. 2a–c) and this was probably due to the decomposition of OM in the piles due to high pile temperatures (>45 °C) and microbial activities. Increase in pH values was also reported by Baeta-Hall et al. (2005) as due to the decomposition of OM. The fact that the pH values rose to between 8.0 and 9.0 indicated that the composting
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a
7499
80 Ambient
70
T2R20 T4R20
Temperature (ºC)
T6R20
60
50
40
30
20 1
11
21
31
41
51
61
71
81
Composting time (days)
b
80
70 Ambient
Temperature (ºC)
T2R25 T4R25
60
T6R25
50
40
30
20 1
11
21
31
41
51
61
71
81
Composting time (days)
c
80
Ambient
70
T2R30
Temperature (ºC)
T4R30 T6R30
60
50
40
30
20 1
11
21
31
41
51
61
71
81
Composting time (days)
Fig. 1. Changes in air and pile temperatures of composting piles with (a) C:N 20:1, (b) C:N 25:1 and (c) C:N 30:1. Error bars show standard errors of means (n = 3).
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a
9.6 T2R20
9.2
T4R20 T6R20
pH
8.8
8.4
8
7.6
7.2 0
2
4
6
8
10
12
Composting time (weeks)
b
9.6 T2R25 9.2
T4R25 T6R25
pH
8.8
8.4
8
7.6
7.2 0
2
4
6
8
10
12
Composting time (weeks)
c
9 T2R30 9.2
T4R30 T6R30
pH
8.8
8.4
8
7.6
7.2 0
2
4
6
8
10
12
Composting time (weeks)
Fig. 2. Changes in pH of piles with (a) C:N 20:1, (b) C:N 25:1 and (c) C:N ratio 30:1 due to TF effect. Error bars show standard errors of means (n = 3).
process was successful and fully developed (Sundberg et al., 2004). The final pH values ranged between 7.53 and 7.83.
This was an indication of stabilized OM (Sesay et al., 1997).
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3.4. Total nitrogen The results of the ANOVA showed that C:N ratio, TF, and the interaction of C:N ratio and TF (C:N TF) had significant (p 6 0.05) effect on TN loss (Table 4). The results of the multiple regression analysis with stepwise selection of variables showed that temperature, pH, C, C:N ratio and DM were significantly (p 6 0.05) correlated with TN. The cumulative TN losses by the end of composting ranged between 70.73% and 88.17% of the initial TN concentration in all treatments (Table 2), with the least loss (70.73%) observed in treatment T4R25. Although temperature and pH were significantly (p 6 0.05) correlated with TN, an interesting finding is the fact that neither temperature nor pH was significantly (p > 0.05) correlated with TN in treatment T4R25. This implied that temperature and pH did not contribute significantly to TN loss in treatment T4R25. The TN losses were greater than losses reported by Hansen et al. (1989), Kirchmann and Witter (1989) during composting of poultry manure. The high losses may likely be related to the small size of piles used in this experiment. Between 43% and 91% of TN losses occurred within the first 28 days of composting in all the treatments (Fig. 3a–c) when the pile temperatures and pH were above 33 °C and 7.7, respectively. A significant part of the TN losses was probably by NH3 volatilization, which was favoured by the high temperature and pH values in this period, as reported by several authors (Bishop and Godfrey, 1983; Tiquia and Tam, 2000). Losses of TN may also have been due to mineralization of OM by micro-organisms (Laos et al., 2002; Grigatti et al., 2004), or to the exposure of the piles to direct sunlight which may have accelerated the decomposition and loss of valuable nutrients (Kwakye, 1977). The decrease in TN loss (as observed in treatments T6R20 and T4R25 during week 4, and treatments T4R30 and T6R30 during week 8) during composting may be attributed to increase in organic N due to a concentration effect as a consequence of strong degradation of organic C compounds (Tiquia and Tam, 2000). Except in treatments with C:N ratio 30:1, the least losses of TN were observed at 4 days TF (Fig. 4). The average values showed that treatments with 2 and 6 days TF had higher losses of TN (86.05% and 85.19%, respectively) than treatments with 4 days TF (79.13%); this could be attributed to aeration rate (turning frequency) of the piles. Treatments with 2 days TF had the highest air supply, while treatments with 6 days TF had the least. Losses of TN in the 2 days TF treatments may have been largely due to NH3 volatilization as a result of high air supply to the piles. Several studies have indicated that NH3 volatilization increased remarkably with the increase of air supply (Zhang et al., 1994; Beck et al., 1997). Losses of TN in the 6 days TF treatments may also have been largely due to NH3 volatilization as a result of possible insufficient air supply to the microorganisms thereby creating some state of anaerobic conditions in the piles. Products of such conditions have been reported as objectionable gases and odours such as hydro-
Fig. 3. Total N losses in piles with (a) C:N 20:1, (b) C:N 25:1 and (c) C:N 30:1 due to TF effect. Error bars show standard errors of means (n = 3).
gen sulphide (H2S) and NH3 (Zhang et al., 1991; Day and Funk, 1998). Treatments with C:N ratio 20:1 had the highest loss of TN (85.90%), followed by treatments with C:N ratio 30:1 (84.13%) while treatments with C:N 25:1 had the least (80.33%). This could be attributed to porosity (which is a function of the C:N ratio) of the piles. Treatments with C:N ratio 20:1 were the least porous, hence TN losses may have been largely due to NH3 volatilization as a result of possible insufficient air supply (due to fewer air pores in the piles) to the micro-organisms thereby creating some state of anaerobic conditions in the piles. On the
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Cumulative total N loss (%)
95
85
C:N 20:1
75
C:N 25:1 C:N 30:1 Average 65 2
4
6
Turning frequency (days)
Fig. 4. Relationship between C:N ratio and TF with respect to total N losses. Error bars show standard errors of means (n = 3).
other hand, treatments with C:N ratio 30:1 had the highest porosity, hence TN losses may have been largely due to NH3 volatilization as a result of possible high air supply (due to higher number of air pores) to the piles. In view of these facts, it could be said that, the least loss of TN occurred at a state when the composting process was averagely aerobic/anaerobic, at a combination of C:N ratio 25:1 and 4 days TF. 4. Conclusions The results showed that both C:N ratio and TF were significant on pile temperature, pH changes, TN, TC, P and K losses while DM was only affected by C:N ratio. The highest TN losses occurred during the period when the pile temperatures and pH values were above 33 °C and 7.7, respectively. Moisture loss was observed to increase as the C:N ratio and TF increased. Total N loss was least in treatment T4R25. References Baeta-Hall, L., Saagua, M.C., Bartolomeu, M.L., Anselmo, A.M., Rosa, M.F., 2005. Bio-degradation of olive oil husks in composting aerated piles. Bioresource Technology 96, 69–78. Beck, J., Kack, M., Hentschel, A., Csehi, K., Jungbluth, T., 1997. Ammonia emission from composting animal wastes in reactors and windrows. In: Voermans, J.A., Monteny, G.J. (Eds.), Proceedings of the International Symposium, Ammonia and Odour Control from Animal Production Facilities, Vinkeloord, The Netherlands, pp. 381– 388. Bishop, P.L., Godfrey, C., 1983. Nitrogen variations during sludge composting. BioCycle 24, 34–39. Brake, J.D., 1992. A Practical Guide for Composting Poultry Litter, MAFES Bulletin, p. 981. Bremner, J.M., 1996. Nitrogen-total. In: Sparks, D.L. (Ed.), Methods of Soil Analysis. Part 3 – Chemical Methods. SSSA Inc., ASA Inc., Madison, WI, USA, pp. 1085–1122. Day, D.L., Funk, T.L., 1998. Processing manure: physical, chemical and biological treatment. In: Animal Waste Utilization: Effective Use of Manure as a Soil Resource. Ann Arbor Press, Chelsea, Michigan.
Diaz, M.J., Madejon, E., Ariza, J., Lopez, R., Cabrera, F., 2002. Cocomposting of beet vinasse and grape marc in windrows and static pile system. Compost Science and Utilization 10 (3), 258–269. Eghball, B., 1997. Composting manure and other organic residues. Cooperative Extension, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln.
G.A. Ogunwande et al. / Bioresource Technology 99 (2008) 7495–7503 leaves to grass mix ratio and windrow vs pile configuration on the composting of yard trimmings. Compost Science and Utilization 4, 26– 43. Misra, R.V., Roy, R.N., Hiraoka, H., 2003. On-farm composting methods. FAO Corporate Document Repository.
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