Waste Management & Research31(2) 203 –211© The Author(s) 2013Reprints and permission: sagepub.co.uk/journalsPermissions.navDOI: 10.1177/0734242X12468195wmr.sagepub.com

Introduction

China is currently the largest pork and poultry producer in the world, with high growth rates of livestock and poultry produc-tion. Manure production was estimated at 270,000,000 t in 2008 (National Bureau of Statistics of China, 2009). Composting, as an environmentally friendly and economical alternative for treat-ing solid waste, has the advantages of improving soil structure, increasing soil organic matter (SOM), suppressing soil-borne plant pathogens and enhancing plant growth (Bustamante et al., 2008; Roca-Perez et al., 2009; Takakai et al., 2010).

Composting provides the energy for the degradation process and the heat for killing the pathogens, and transforms highly het-erogeneous organic matter (OM) into stable solid form known as humus (Kabore et al., 2010). The decomposition extent-how much of the original OM is transformed into humus-can be used as indicator of compost maturity (Hsu and Lo, 1999; Zmora-Nahum et al., 2005). Humus produces dissolved organic carbon (DOC) when dissolved in water, which affects the chemical behavior of pollutants by absorption, complexation and chelation (Guthrie et al., 2005). Fluorescence excitation-emission matrix (EEM) spectroscopy is utilized extensively to determine the components of DOC. The excitation/emission (Ex/Em) maxi-mum peaks in EEM contours have been associated with protein-like, fulvic acid-like and humic acid-like substances (Coble, 1996). The fluorescence intensity was proportional to these mate-rials at low concentrations (Moral et al., 2009). The peak and intensity of fluorescence was applied to assess compost maturity, but these techniques lack the ability to capture the heterogeneity

of samples (Yu et al., 2011). Fluorescence regional integration is then recommended in order to analyze quantitatively all the wavelength-dependent fluorescence intensity data from the EEM spectra (Marhuenda-Egea et al., 2007).

Microorganisms use carbon (C) for both energy and growth, whereas nitrogen (N) is essential for protein and reproduction. The optimum carbon/nitrogen ratio (C/N) for compost varies with the raw material, but should generally be between 20 and 30. When the C/N is low, the available carbon is fully utilized; excess nitrogen is then lost, mainly in the form of ammonia (Li et al., 2008). Usually, to obtain the ideal composting condi-tions, large amounts of organic amendments had to be added. Use of reduced amount of bulking agents in low C/N cases, for example in the case of swine manure is feasible, but with the risk of increased odor nuisance (Huang et al., 2004). In com-post preparations formulated at a C/N of about 13, the amount

Fluorescence characteristics of dissolved organic matter during composting at low carbon/nitrogen ratios

Lixia Wang1, Duian Lv2, Baixing Yan1 and Yubin Zhang3

AbstractWe investigated the composting of swine manure at low carbon/nitrogen (C/N) ratios (about 13). The purpose was to elucidate organic matter transformation during composting by means of chemical and spectral methods. Swine manure was composted with two bulking agents (rice straw and leaves) at a ratio of 2:1 (manure:bulking agent; v:v) respectively. Low initial C/N ratios (about 13) did not prevent the swine manure from composting, which would greatly decrease the usage of bulking agent. A high organic matter mineralization rate was observed in the co-composting of straw and manure paired with a high maximum temperature and long thermophilic phase. Fluorescence excitation-emission matrix spectra were also used to monitor the component changes in the dissolved organic matter. Fluorescence parameters, including peak location, peak intensity, the ratio of peak intensity and fluorescence regional integration, were displayed and discussed as the maturity index. The fluorescence regional integration, showing higher correlation coefficient than the fluorescence intensity peaks, could be used as a valuable tool for assessing compost maturity.

KeywordsCompost, organic matter, C/N ratio, fluorescence excitation-emission matrix, swine manure, regional integration analysis

1 Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, People’s Republic of China

2Graduate University of Chinese Academy of Sciences, Beijing, People’s Republic of China3Division of Agriculture, Jilin University, Changchun, People’s Republic of China

Corresponding author:Baixing Yan, Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, 3195 Gaoxin Road, Changchun, 130012, People’s Republic of China. Email: yanbx@neigae.ac.cn

468195WMR31210.1177/0734242X12468195Waste Management & ResearchWang et al.2013

Original Article

204 Waste Management & Research 31(2)

of treated manure increases at least once compared with com-post with a C/N of 30. Understanding OM transformation, and the proper evaluation of compost stability and maturity are critical for successful composting (Bustamante et al., 2008; Huang et al., 2004; Kabore et al., 2010), but those with OM transformation at low C/N ratios are limited. The cur-rent experiment aims to study OM transformation at low C/N ratios during composting using both chemical and spectro-scopic methods, which could provide more information for OM transformation and the operational parameters for effec-tive composting at low C/N ratios.

Materials and methodsComposting apparatus

The composting apparatuses were constructed using high-density polyethylene with volumes of about 0.64 m3 (0.8 m × 0.8 m × 1 m). Small holes were made at the bottom of each reactor grid, which supported the composting bed and facilitated the inflow of ambient air. The Chinese Technical Specifications for Static Aerobic Composting (CJJ/T52-93) suggests that the optimum aeration rate during composting should be about 0.05-0.2 m3·min−1·m−3. In order that composting was carried out under aerobic conditions, the ventilation of compost was provided by fans at an aerating rate of 3 l/s. The fans worked intermittently at cycles of 30 min (stop):10 min (on) at 0-30 d and 30 min (Stop):30 min (on) during 56d.

Experimental details

Composting was carried out on August and September, 2010. The bulking agents were rice straw from a nearby paddy field, and leaves from garden waste cut using a disintegrator to obtain pieces with dimensions smaller than 4 cm. Manure solids col-lected from a nearby swine farm were blended with both bulking agents at a ratio of 2:1 (manure: bulking agent, v:v). Four reac-tors were used and each treatment had two replicates. The raw compost characteristics are displayed in Table 1.

Three sampling holes at different heights (0.25 m, 0.50 m and 0.75 m from the bottom) were placed in the reactors. The samples were taken from different heights and mixed thoroughly on days 1, 2, 4, 6, 8, 12, 16, 21, 27, 33, 41, 56. These samples were sub-sequently transported to the laboratory and stored immediately at 4 °C for further analysis.

Analytical methods

The temperature was recorded using a temperature probe (LTM8861, Lance Technologies Inc., Beijing, China) set at the 50 cm depth of the piles. Another sensor was left in the air to record air temperature. The water content was determined after drying to a constant weight at 105°C for 24 h in a hot air oven.

All chemical analyses were carried out in triplicate and used chemicals of analytical grade. OM content was assessed by deter-mining the loss-on ignition at 430 °C for 24 h (Bustamante et al., 2008), and total carbon content was calculated with OM content divided by 1.72. The total nitrogen (TN) content was determined on dried 200 µm ground samples through elementary analysis and used to calculate the C:N ratio (Kabore et al., 2010). The pH and electrical conductivity (EC) were measured in the extracts (1:5 manure:water ratio, w/v). The percentage of decomposition (DEC) was calculated using the following formula (Haugh, 1993):

DEC% = [100 ×(OMi– OMf) /(100 – OMf) × OMi] × 100

OMi and OMf are the initial and final OM percentage respectively.

TN loss was calculated from the initial (Xi) and final (Xf) ash contents, according to the equation of Paredes (2000) :

TN loss (%) =100 – 100 [(XiNf) ÷ (XfNi)]

where Ni and Nf are the initial and final TN concentrations respectively.

Germination index (GI) was used to assess the phytotoxicity of the compost. Twenty Chinese cabbage seeds (Brassica camp-estris L.) were distributed on filter papers in Petri dishes (diam-eter = 10 cm) and moistened with 8 ml of the compost extract (1:5 manure:water ratio, w/v). Three replicate dishes for each sample were incubated at 25°C for 72 h, and 8 ml of distilled water was used as the control. The number of germinated seeds and length of root were measured. GI was calculated using the following formula (Sellami et al., 2008):

GI = × ×Seed germination% Root length of the treatment 100

Seed ggermination% Root length of the control×

Fluorescence determination and analysis

The DOC content in the mixtures was measured using a non-dispersive infrared detector to quantify carbon dioxide (CO2) lev-els (Shimadzu TOC – V CPH, Otsu, Japan) after water extracts

Table 1. Physicochemical properties of raw materials

TC(g·kg−1)

TN(g·kg−1)

WC(%)

pH EC(ms·cm−1)

Swine manure 363(7.82) 46.6(1.77) 77.1(2.13) 7.68(0.19) 2.89(0.09)Manure + leaves 343(8.65) 27.5(3.29) 64.3(2.03) 8.58(0.69) 2.51(0.42)Manure + rice straw 372(9.28) 29.00(5.16) 60.2(1.68) 7.89(0.35) 2.30(0.37)

Values in parentheses are standard error (n = 6).EC: Electrical conductivity; TC: total carbon; TN: total nitrogen; WC: water content.

Wang et al. 205

(1:5 manure:water ratio, w/v) were filtered using a 0.45 µm membrane from the composting mixtures. The extractant was diluted with water to the final DOC value of approximately 10 mg·l−1. The fluorescence EEM spectra of 3-ml diluted samples in a 1-cm path length fused silica cell was measured using a fluores-cence spectrophotometer (Varian CaryElipse, San Francisco, USA). The Em wavelength range was fixed from 250 to 400 nm in 5-nm steps, whereas the Ex wavelength was increased from 260 to 600 nm in 5-nm steps emissions. The slit widths were both 10 nm, and the voltage of the photomultiplier tube was set at 750 mV for low-level light detection.

Fluorescence intensity (Pi) was calibrated in quinine sulfate units (QSU), where 1 QSU is the maximum fluorescence inten-sity of 0.01 mg l−1 of quinine in 1 M H2SO4 at the Ex/Em of 350/450 nm (Tang et al., 2011). In order to quantify the relative changes in the EEM spectra, percent fluorescence response (Pi,n) was calculated using the integration method proposed by Chen et al. (2003).

Statistical analyses

Data were analyzed by analysis of variance (ANOVA) using the software SPSS 17.0 for Windows (SPSS, Chicago, IL, USA). A one-sample Kolmogorov–Smirnov test was used to assess whether the indices of different compost products belonged to a normal distribution. Pearson’s correlation coefficient was used to evaluate the linear correlation between two parameters. The cor-relations were considered statistically significant at a 95% confi-dence interval (P <0.05).

Results and discussionEvolution of temperature and water content

Different exogenous carbon sources contributed to the different pat-terns of heating (including peak heating temperature and the length of peak heating). The temperature of the leaf compost was lower

than that of the straw compost during composting (Figure 1). The temperature in the two treatments quickly increased and reached the thermophilic phase (45°C) (Unmar and Mohee et al., 2008) on day 5. The two treatments’ thermophilic phases lasted for 12 d and 28 d with maximum temperatures of 53°C and 60°C, which is particu-larly important for successful composting because pathogen micro-organisms are killed, thereby resulting in hygienized compost (Sundberg et al., 2004). The straw compost reached the thermo-philic temperature more quickly and had a longer thermophilic phase than did the leaf compost. Given the different components and decomposition rates of the OM in the raw materials used, the OM in the leaves was more resistant to microbial attack than that in the straw (Francou et al., 2008; Petric et al., 2009; Said-Pullicino et al., 2007). The secondary temperature peaks as the result of recovered thermophilic microbial population occurring in leaf com-post, indicating the degradation of cellulose after all readily degra-dable matter was consumed (Shin and Jeong, 1996).

Optimum water content (40-60%) represents a trade-off between the water requirements of the microorganisms and ade-quate oxygen supply. Higher initial water content influences the maximum temperatures reached during composting. In this study the maximum temperatures were 53°C and 60°C, which were slightly lower than those in other reports (Shao et al., 2009). During the first 4 d, the OM decomposed quickly, resulting in an increased water content exceeding 60%. However, the high water content (>60%) influenced the gaseous exchange by limiting the diffusion and oxygen utilization of the microorganisms, resulting in decreased microbial activity (Kabore et al., 2010). The decreased water content was verified by the lower OM decompo-sition rate (Figure 2). Another water content peak was seen from d 15 to d 23 because the OM had a higher decomposition rate during the thermophilic phase (Zmora-Nahum et al., 2005).

Degradation of organic matter

The initial OM content of the straw compost was higher than that of the leaf compost owing to the straw’s greater OM content in

Figure 1. The evolution of temperature and water content during composting.

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comparison with the leaves. OM contents tended to decrease from 64.2% and 59.2% to 50.0% and 52.3%, respectively, when OM was oxidized and converted into CO2, water, ammonia and new microbial biomass during composting (Francou et al., 2008). The DEC in the straw compost was significantly higher than that in the leaf compost (P <0.05). The DEC change in different stages varied, mostly appear-ing during the bio-oxidative phase (d 0 to d 40) and corresponding to the highest temperature, indicating marked microbial activity (Liang et al., 2003). Lower OM mineralization was observed during the maturation phase (d 40 to d 56), indicating product stability. OM decomposition not only provides a source of carbon for microorgan-isms, but also produces a large amount of heat, which kills various pathogens (Paillat et al,. 2005). United States Environmental Protection Agency 40 CFR (Code of Federal Regulations) 503 sug-gests a minimum temperature of 55°C for 3 d in aerated static piles or in vessel systems or for 15 d in windrow systems (Martin et al., 1993). Microorganisms may delay the decomposition of OM because of scarce C sources, while the heat produced by OM decomposition increases the temperature of the pile to meet the requirements for kill-ing pathogens even at initial C/N ratio of about 13.

The change of DOC during composting depends on the pro-cess and on the source material (Zmora-Nahum et al., 2005). In addition, to provide the optimum free air space, bulking agent in

compost regulates the water contents and C/N ratio (Iqbal et al., 2010). Owing to the different bulking agent, the profile of DOC in leaf compost decreased continuously while the DOC concen-tration increased in the first 30 d and then decreased over the remaining days in straw compost. The DOC concentration decreased as a result of the rapid degradation of labile OM, par-ticularly carbohydrates, amino sugars and low-molecular weight organic acids (Francou et al., 2008). The DOC concentration in the piles increased owing to the formation of simple organic compounds (soluble) from the hydrolysis of polymers such as cellulose or proteins (Liang et al., 2003).

The profile of the C/N ratio and TN loss are shown in Figure 2. The TN losses in both piles were below the range usually observed (15-69%) during composting (Barrington et al., 2002; Bernal et al., 2009; Bustamante et al., 2008). Significant TN losses were found from d 5 to d 14 owing to the volatilization of ammonia, which was affected by high temperatures and pH val-ues (>8.5). The TN content was as a consequence of a loss of mass, the N immobilization by the microbial biomass and ammo-nia volatilization (Paillat et al., 2005). The TN losses decreased from 25% to 5% over the following 30 d, while the TN loss showed a slight increase owing to higher air supply in the matu-rity phase. The straw compost showed slightly higher TN loss

Figure 2. The change of pH, dissolved organic carbon (DOC), organic matter (OM), decomposition (DEC), carbon/nitrogen (C/N) and total nitrogen (TN) loss during composting.

Wang et al. 207

than the leaf compost because bulking agents with high ligno-cellulose content have lower microbial degradability, which then leads to higher N losses. In a previous study examining aerobic swine manure static compost piles, piles with lower initial C/N (15) exhibited a slower increase in temperature than the piles with higher initial C/N (30) because of insufficient available car-bon sources (Moral et al., 2009). The C/N ratio showed an acute increase of up to 15 owing to amino acid decomposition, which often happens in the first stage of composting (Bernal et al.,

2009), then decreasing to less than 10 as a result of the degrada-tion of the greater total C relative to N losses.

The EEM spectra of DOC

The contour EEM and three-dimensional spectra of DOC dur-ing composting are shown in Figure 3. Most of the spectra indicate the presence of different fluorophores, characterized by Ex/Em wavelength pairs, and the specific fluorescence

Figure 3. Evolution of excitation-emission matrix (EEM) spectra during biostabilization of composting. L: leaves+manure; S: straw + manure.

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intensities of those peaks. The evolution of the EEM spectra from the different mixtures in piles was similar. Four peaks, namely peak 1, peak 2, peak 3 and peak 4 with Ex/Em wave-length pairs of 228 nm /345 nm, 280 nm/375 nm, 316 nm/435 nm and 235 nm/444 nm were identified during the compost-ing. Peak 1 fell in the region defined by shorter excitation wavelengths (<250 nm) and shorter emission wavelengths (<350 nm) related to the aromatic protein region, such as tryp-tophan. Peak 2 fell in the region related to soluble microbial byproduct-like materials. Peak 3 fell in the region with longer excitation wavelengths (>280 nm) and longer emission wave-lengths (>400 nm) related to humic acid-like compounds (peak 3). Fulvic acid-like materials are related to peaks at shorter excitation wavelengths (<250 nm) and longer emission wavelengths (>350 nm) (peak 4) (Antízar-Ladislao et al., 2006; McKnight et al., 2001).

Compared with the other peaks, peak 1 and peak 2 showed higher intensities in the immature compost and the similar trends which proved to have the same bacterial origin for the similar intensity ratio suggests that fluorophores have a bacte-rial origin (Coble, 1996). As the composting went on, protein-like substances (peak 1) and soluble microbial byproduct-like materials (peak 2) disappeared, and humic acid-like materials with an EEM of peak 3 formed subsequently. The presence of peak 3 indicates the formation of humic acids during the

composting process (Senesi et al., 1991). Peak 4 coincided with peaks typical of fulvic acid compounds (Tang et al., 2011) appeared in the middle of composting.

To quantify the fluorescence parameters of the spectra, peak locations and peak intensity (expressed by QSUs), different peak intensity ratios are summarized in Table 2. The QSU of peaks 1-4 in both composts were in the range of 97-991, 87-652, 151-464 and 101-307 respectively. The QSU of peaks 1 and 2 showed serrated fluctuations (Figure 4). During the first eight days, the QSU showed acute decrease, revealing that protein-like, microbial byproduct-like substances degraded quickly. In the following days, the QSU of both peaks showed a slight increase at d 21 and then decreased at the end of composting. However, the QSU of peaks 3 and 4 in both composts showed a variation. In leaf compost, the QSU of peaks 3 and 4 showed similar trends to peaks 1 and 2, while the QSU in straw com-post showed a significant increase at the first eight days and a slow decrease thereafter. It is possible that the different bulk-ing agent accounted for the different changes in QSU, and the trends of the peaks are in agreement with another study (Tang et al., 2011). By comparing fluorescence characteristics of mature and immature composts, some researchers have pointed out that the appearance of two peaks at Ex/Ems of 230nm/240nm and 330nm/420nm is an indication of mature compost (Yu et al., 2011).

The ratio of P1/P4 and P1/P3 in leaf compost showed a con-tinuous decrease, while there was an acute decrease over the first eight days and then a slight increase in straw compost thereafter, revealing that the humification process occurred in the varia-tions owing to an increase in the humic- and fulvic-like materi-als and a decrease of protein-like materials (Table 2). Owing to the different degradation of raw materials as a result of micro-bial activity (Marhuenda-Egea et al., 2007), the fluorescence intensity did not show similar trends. However, the P1/P3 and P1/P4 in the mature compost was significantly lower than that in

initial raw, which was consistent with the results of other research (Tang et al., 2011; Yu et al., 2011).

The two piles both showed similar trends of Pi,n as a function of the composting time (Figure 4). PI,n and PII,n decreased mark-edly over the first 21 d and then reached plateau values of 8-12 and 19-24 respectively. PIII,n, PIV,n and PV,n increased during the initial 21 d and then maintained plateau values of 33-38, 15-19 and 10-20 respectively. These trends also support the formation of humic substance by microorganism (Marhuenda-Egea et al., 2007).

Table 2. The change of fluorescence spectra parameters during composting

Peak 1 Peak 2 Peak 3 Peak 4 Peak intensity ratio

Ex/Em(nm)

QSU Ex/Em(nm)

QSU Ex/Em(nm)

QSU Ex/Em(nm)

QSU P1/P2 P1/P4 P1/P3 P2/P4 P2/P3 P4/P3

L-1 234/342 441 282/344 342 333/417 374 238/410 307 1.29 1.44 1.18 1.11 0.91 0.82L-8 234/367 150 292/364 125 341/442 333 247/448 210 1.20 0.71 0.45 0.60 0.38 0.63L-21 232/353 181 288/344 146 332/418 425 236/435 293 1.24 0.62 0.43 0.50 0.34 0.69L-33 232/353 121 288/344 119 332/418 417 236/435 219 1.02 0.55 0.29 0.54 0.29 0.53L-56 232/353 98 288/344 87 343/439 393 247/452 162 1.13 0.60 0.25 0.54 0.22 0.41S-1 232/328 991 282/331 652 339/421 325 238/410 101 1.52 9.81 3.05 6.46 2.01 0.31S-8 245/367 160 284/364 125 344/420 464 249/421 298 1.28 0.54 0.34 0.42 0.27 0.64S-21 232/364 189 288/345 168 334/411 387 243/424 229 1.13 0.83 0.49 0.73 0.43 0.59S-33 235/366 137 290/355 129 334/419 211 247/430 169 1.06 0.81 0.65 0.76 0.6 0.80S-56 236/368 97 290/360 92 344/421 151 253/434 102 1.05 0.95 0.64 0.90 0.61 0.68

Ex/Em: excitation/emission; L: manure+leaves; QSU: quinine sulfate units; S: manure+straw.

Wang et al. 209

Change of OM and maturity

Some OM indices for assessing compost maturity have been rec-ommended. For the C/N ratio, a threshold below 10 at the end of composting should be used (Wang et al., 2004). In the current research, the composting process for the different bulking agents-leaves and straw-ended after 21 d and 27 d respectively. Many reports have suggested a threshold DOC value of 4 g·kg−1 for mature compost (Zmora-Nahum et al., 2005). However, the leaf compost met this criterion after almost 56 d, whereas the DOC concentrations in the straw did not decrease below 4 g·kg−1. Composting involves the formation of some humic-like sub-stances, which occur predominantly in the water-soluble phase (Huang et al., 2004); hence, the formation of humic acid-like substances is often the indicator of maturity. However, in the pre-sent study, those substances appeared early, on the first day in leaf compost. The GI, representing the plant response to the manure, is believed to be a good indictor of maturity. Huang et al. (2004) researched a co-compost of manure and sawdust with a C/N ratio at 15. A low initial C/N ratio is found to need a longer composting time, as assessed by GI. However, in the present study, the GI of the manure and straw compost reached 90% after 25 d, whereas the manure and leaf compost required 32 d.

The compost maturity indices and fluorescence parameters were normally distributed, according to the one sample Kolmogorov–Smirnov test. The Pearson correlation between maturity indices and fluorescence spectra parameters is listed in Table 3. The QSUs of peaks P1 and P2 were significantly correlated (P <0.05) with OM and the C/N ratio, whereas P3

Figure 4. Pi,n of the five regions for piles 1 (, manure+leaves) and pile 2 (, manure+straw) during composting.

Figure 5. Changes of germination index (GI) during composting.

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correlated significantly with OM, C/N and DOC. The Pearson correlation coefficients between Pi,n and maturity indices were larger than those between the QSUs of peaks and maturity. OM showed significant correlation with PI,n, PII,n, PIII,n, PV,n and the PV,n / PIII,n ratio. However, no significant correlation was found between the DOC and Pi,n. The difference may be attributable to the fact that the compost in this study was at low C/N ratio. Some researchers recommend the PV,n / PIII,n ratio to be used to present the maturity of compost (Ko et al., 2008; Sellami et al., 2008; Yu et al., 2011). In this study, the PV,n / PIII,n ratio showed greater correlation coefficients with chemical and biological indices, including OM, DOC, C/N and GI. Therefore, it is con-cluded that the PV,n / PIII,n ratio is more suitable to assess the maturity of compost.

Conclusion

Using straw and leaves as C amendment, swine manure can com-post successfully, even at lower initial C/N ratios (about 13). The straw compost provides higher temperatures and a higher decom-position rate. Changes in OM at a low C/N ratio were similar to those in other composts with a C/N of 20-30. The composting

process was characterized by decreasing percent fluorescence response of the original protein-like materials (peaks 1 and 2), as well as increasing the percentage fluorescence response of humic- and fulvic-like materials (peaks 3 and 4). Compared with other OM indices, the fluorescence EEM combined with a regional integration analysis was more suitable to assess the degree of humification that further determines compost maturity.

AcknowledgementsThe authors are grateful to Wen-xin Li and Dian Dai from Jilin University for their help during sampling.

FundingThis work was supported financially by Frontier of Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences (KZCX3 - SW- NA09 -06). Jilin Provincial Research Foundation for Basic Research, China (201105033).

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Table 4. Pearson correlation between fluorescence regional integration and maturity indices (n = 10).

pH OM DOC C/N GI PI,n PII,n PIII,n PIV,n PV,n PV,n / PIII,n

pH 1 −0.135 −0.153 0.155 0.047 0.116 0.134 −0.033 −0.215 −0.192 −201OM 1 0.747* 0.763* −0.669* 0.835* 0.648* −0.699* −0.534 −0.719* −657*DOC 1 0.527 −0.703* 0.548 0.328 −0.264 0.493 −0.503 −0.538C/N 1 −0.669* 0.686* 0.525 −0.629 −0.397 −0.527 −0.385GI 1 −0.548 −0.461 0.516 0.467 0.408 0.290PI,n 1 0.904** −0.873** −0.792* −0.956** −0.894**PII,n 1 −0.955** −0.757* −0.931** −0.821**PIII,n 1 0.594 0.840** 0.682*PIV,n 1 0.789** 0.788**PV,n 1 0.967**PV,n / PIII,n 1

*Correlation is significant at the 0.05 level (2-tailed).**Correlation is significant at the 0.01 level (2-tailed).C/N: carbon/nitrogen; DOC: dissolved organic carbon; GI: germination index; OM: organic matter.

Table 3. Pearson correlation between fluorescence intensity and maturity indices (n = 10).

pH OM DOC C/N GI P1 P2 P3 P4

pH 1 −0.135 −0.153 0.155 0.047 0.172 0.175 0.000 −0.215OM 1 0.747* 0.763* −0.669* 0.757* 0.664* 0.718* −0.118DOC 1 0.527 −0.703* 0.452 0.342 −0.248 0.190C/N 1 −0.669* 0.671* 0.593* −0.656* −0.310GI 1 −0.449 −0.371 0.415 0.152P1 1 0.967** −0.885** −0.630P2 1 −0.919** −0.702*P3 1 0.639*P4 1

*Correlation is significant at the 0.05 level (2-tailed).**Correlation is significant at the 0.01 level (2-tailed).C/N: carbon/nitrogen; DOC: dissolved organic carbon; GI: germination index; OM: organic matter.

Wang et al. 211

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