Title: Characterization of Canadian Backyard Composts: Chemical and Spectroscopic Analyses. By: Preston[1], Caroline M., Cade-Menun[2], Barbara J., Sayer[3], Brian G., Compost Science & Utilization, 1065657X, Summer98, Vol. 6, Issue 3

Database: Academic Search Premier

CHARACTERIZATION OF CANADIAN BACKYARD COMPOSTS: CHEMICAL AND SPECTROSCOPIC ANALYSES

Contents

1. Introduction 2. Materials & Methods 3. Sample Origins 4. Sample Processing and Chemical Analysis 5. 31P NMR Spectroscopy 6. 13C CPMAS NMR Spectroscopy 7. Results and Discussion 8. Chemical Analysis 9. 31P NMR Spectra 10. 13C CPMAS NMR 11. The Backyard Composting Process 12. Conclusions 13. Acknowledgements 14. TABLE 1. Some chemical properties of the composts 15. TABLE 2. Chemical and NMR data for P in the composts 16. TABLE 3. Total metal content of compost samples 17. TABLE 4. Relative areas (percent of total area) of chemical shift regions of

compost 13C CPMAS NMR spectra 18. References

Despite the growing interest in backyard composting as a means to reduce residential refuse at source, there has been little study of its chemical nature and state of maturity. We obtained samples of mature compost from backyard sources in Newfoundland, Ontario and British Columbia, Canada, as well as raw input and immature compost from one BC municipal source. Chemical analysis indicated that composting was effective, proceeding with loss of C, decrease in

C:N ratio, increase in pH to near neutrality, and high available N and P. Contents of heavy metals were low. Solution [31]p nuclear magnetic resonance (NMR) spectroscopy of extracts showed a high proportion of orthophosphate P, indicating vigorous microbial activity and high P availability. Solid state 133C NMR with cross-polarization and magic angle spinning (CPMAS NMR) of whole composts showed that decomposition proceeds to some extent with increasing ratio of alkyl to O-alkyl C, as observed in many studies of organic soils, forest floor and composts of low substrate quality. However, the backyard operations also produced much more peak broadening, and a marked tendency for increase of carboxyl C. These also indicate vigorous biological activity. The chemical and spectroscopic analyses confirm traditional knowledge of the efficacy of backyard composting, and suggest that it is a worthwhile object of research. Introduction Many gardeners undertake small-scale backyard composting and apply the product to flower and vegetable beds. Recently this practice has been actively promoted by many municipalities to reduce residential refuse at the source. For example, almost 1.2 million backyard composters were distributed by Canadian municipalities to the end of 1995 (Gies 1997). Studies in Canada and the USA have shown reductions of around 70 percent of food and yard waste, or 25 percent of total household refuse (Amiran and Sherman 1992; Anonymous 1995; Gies 1996; Vossen and Rilla 1997). This corresponds to diversions of around 250 kg annually with ranges reported from 132 to 450 kg. While hard data were lacking, United States Environmental Protection Agency (USEPA) projections of the amount of yard trimming to be composted off site in 1995 and 2000 were less than 1990 levels because of the increased practices of home composting and leaving grass clippings on the lawn (Kashmanian 1993). Composts from municipal solid waste, leaves and plant waste have been shown to be good sources of N and P (Hue et al. 1994; Iglesias-Jiminez and Alvarez 1993; Iglesias-Jiminez et al. 1993), to increase the yield of vegetables (Kostov et al. 1996; Maynard 1996; 1997) and to improve soil physical properties (Giusquiani et al. 1995). In addition to source waste reduction, backyard

composts should provide similar benefits in maintaining soil fertility, soil organic matter quality and the biodiversity of the soil microbial and faunal communities in a mosaic of small urban sites. However, there has been little study of composts under conditions similar to those in backyard systems (Engelstad 1991; Illmer and Schinner 1997; Razvi and Kramer 1996), and there appear to be no reported studies of samples of typical product. Solid-state [13]C nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (CPMAS NMR) is well suited for characterization of complex materials such as plants, organic soils and soil organic matter fractions (de Montigny et al. 1993; Preston 1996; Preston et al. 1989; 1997; Zech et al. 1992). There have been a few applications of NMR to whole composts, including those derived from sewage sludge (Pfeffer et al. 1984; Piotrowski et al. 1984), cattle manure (Inbar et al. 1989), grape marc (Inbar et al. 1991), fish waste/peat mixtures (Preston et al. 1986), municipal solid waste (Chefetz et al. 1996), as well as studies of decomposition of straw (Skene et al. 1996), Eucalyptus litter (Skene et al. 1997), and 15N-labelled plants (Knicker and Ltidemann 1995). There has also been some application of 31p solution NMR to extracts of composted sewage sludge (Hinedi et al. 1988; 1989) and of peat/fish waste composts (Preston et al. 1986). We used [13]C CPMAS NMR of whole composts, [31]p solution NMR of NaOH-EDTA extracts, and chemical analysis to characterize backyard composts generated in a variety of management practices and a range of climate zones in Canada, from Victoria, British Columbia, to St. John's, Newfoundland. An additional sample was obtained from the Greater Victoria municipal yard waste composting operation. Materials & Methods Sample Origins Samples were donated by home composters who were asked to collect a representative sample of well-decomposed compost at the stage where they would consider it ready for use. They also provided some information on their compost management system. Unless otherwise indicated, kitchen waste was mainly uncooked fruit and vegetable scraps, and garden waste a variable mixture

of grass clippings, annual plants, fallen leaves, and small diameter woody material (< 1 cm). SJ (St. John's, Newfoundland), sampled 10/93. Slatted bin, approx. 0.5 m3. Kitchen and garden waste left for one year. A "handful" of 20-20-20 fertilizer added two to three times per year. HAM-1 (Hamilton, Ontario), sampled 10/93. Mainly garden waste in plastic composter 0.75 x 0.75 x 1m tall. Compost removed from door in bottom. A compost starter used (Compost Maker, Judd Ringer Corporation, 6860 Flying Cloud Drive, Eden Prairie, Minn 55343). HAM-2 (Hamilton, Ontario), sampled 6/93. Cedar box, layers of soil and leaves together with other plant matter and fruit waste. PG (Prince George, British Columbia), started fall 1991; 1/3 poplar leaves, 1/3 birch leaves, then 1/3 grass clippings added spring 1992. Last addition June 1992, sampled 4/93. VIC-1 (Victoria, British Columbia), sampled 2/93. Cedar box approx. 0.5 m3, kitchen and garden waste, turned once or twice per year, some food waste taken by crows and raccoons. VIC-2 (Victoria, British Columbia), sampled 5/93. Kitchen and garden waste. Three bins of approximately 0.5 m3. Collection bin turned into second bin with approximately 1 kg of urea mixed with contents in September (six months). Second bin left to overwinter covered (six months) and then turned into third bin in early spring. Left to age for one year in third bin prior to use. VIC-3 (Victoria, British Columbia), sampled 10/93. Two boxes, each about 120 by 120 cm, open front and top. New heap started early to mid October. Layers in fall heap bin start with about 15 cm of fine to medium branches (1-3cm diameter), 15 cm leaves, sprinkling of Rot-it, 2-3 cm layer of raw compost from the summer heap in adjacent bin, repeating layers of leaves and raw compost to height of about 100 - 120 cm. Remainder of summer compost used as mulch in flower and vegetable beds. Some leaves then placed in the empty bin. Through the late fall and winter kitchen waste (no meat or fish scraps) is placed on top of the fall heap

and leaves or green plant material from winter storms is used to cover and layer with the kitchen waste. In late April to early May, the spring heap is started in the empty bin, with branches in bottom, the fall heap turned over into the spring heap bin, and fine to medium materials from the fall heap separated out and used primarily in the vegetable garden. Through the spring and summer, kitchen waste is added to the top of the heap with garden clippings, weedings, senescent plants from vegetable garden and a few grass sods used to cover and layer with the kitchen waste. Lawn clippings are left on the lawn. Heap will be watered about every two to three weeks in a dry spell. Heap has lots of invertebrates including red wiggler worms used commonly for enclosed indoor kitchen waste composting. Residence time of material in heap depends upon nature of material and if in spring or fall heap. Fresh leaves and kitchen waste are in the fall heap for seven to eight months, spring heap four to five months, but probably well decayed before then. Senescent leaves and woodier material remain for a year. The fine to medium branches go through two to three years before becoming sufficiently decayed to be used in the garden. Corn cobs put in early September are usually decayed enough to go onto the garden the following spring. VIC-4 (Victoria, British Columbia), sampled 12/92. Two wood boxes, approx. 0.5 m3 each, kitchen and garden waste, turned once or twice per year. Each spring, contents of second box removed and contents of first box moved to second. In May 1994, samples were also taken of raw input (RAW), and of immature compost (IMM) when it was moved from the first to the second box. MUN From Greater Victoria Regional District large-scale composting of yard trimmings. Sample Processing and Chemical Analysis Samples were stored at 4C if they could not be processed immediately. They were sieved to <2 mm and then air-dried and ground in a Wiley mill to 20 mesh (850 mum). The raw and incompletely composted samples were air-dried, then ground without sieving. Samples were analyzed for total C by automatic combustion using a Leco model CR12 carbon analyzer. Nitrogen was determined by the semimicro Kjeldahl

method essentially as described by Bremner and Mulvaney (1982) except that mercuric oxide was used as the catalyst. Ash was determined by combustion at 600 degrees C for 4 h. The pH was determined on a slurry of 2 g compost and 0.01 M CaCl2. Cation exchange capacity (CEC) was determined after leaching with ammonium acetate as in Kalra and Maynard (1991), and ammonium in the leachate determined by distillation and titration as for total N. Elemental analysis for total metals was carried out by CanTech Laboratories (Calgary, Alberta) by atomic absorption after digestion by a nitric-perchloric acid mixture. To determine inorganic N, air-dry samples (1 or 2 g) were extracted with 50 ml of 0.1 M K2SO4 solution containing 5 mg L-1 phenylmercuric acetate and vacuum-filtered through #41 Whatman filter paper, followed by analysis with specific ion electrodes (Orion model 95-12 ammonia gas-sensing electrode and Orion 93-07 nitrate electrode using model 90-02 double-junction reference electrode with 0.5 M K2SO4 as the outer filling solution). Available P was determined with Bray P1 extraction (Olsen and Sommers 1982), followed by colorimetric analysis (Murphy and Riley 1962) on a Lachat Flow Injection Analyzer. Total P was determined by perchloric acid digest (Olsen and Sommers 1982) followed by ICP analysis. Organic P was measured using the ignition procedure (Olsen and Sommers 1982), followed by colorimetric analysis. 31P NMR Spectroscopy Air-dried samples (5-10g) were extracted in 100 ml of a 1:1 mix of 0.5 M NaOH and 0.1 M Na2EDTA (Cade-Menun and Preston 1996). A subsample was digested with persulphate (Bowman 1989) and was read using the Watanabe and Olsen (1965) method to determine the extracted P concentration. The remainder of the filtrate was freeze-dried. To prepare samples for NMR, approximately 0.5 g of the freeze-dried extract was weighed into a 50-ml plastic centrifuge tube with 2.5 mL of D2O. Samples were vortexed for two minutes, left to stand for 2 h, and then centrifuged at 10,000 rpm for 10 minutes. The supernatants were decanted into NMR tubes of 10 mm outside diameter and refrigerated until they could be run.

Phosphorus-31 NMR spectra were obtained at 101.27 MHz on a Bruker WM 250 high resolution NMR spectrometer using a 45 degrees pulse, 0.51 s acquisition time, 1.5s relaxation delay and accumulation times of approximately 24 h. The [31]P spectra were proton decoupled using an inverse-gated pulse sequence to overcome the nuclear Overhauser enhancement in order to achieve quantitative results (Newman and Tate 1980). Relative peak areas were determined by integration. 13C CPMAS NMR Spectroscopy Solid-state 13C NMR spectra were obtained on a Bruker MSL 100 spectrometer operating at 25.18 MHz for [13]C at 2.35 Tesla. Samples were spun at 4 kHz in an aluminum oxide rotor of 7 mm outside diameter. Spectra were acquired with 1 ms contact time, 1.5 s recycle time, and 12,000-50,000 scans, and were processed using 15 Hz line-broadening and baseline correction. Dipolar dephased spectra were generated by inserting a delay of 50 mus without [1]H decoupling between the cross-polarization and acquisition portions of the pulse sequence. Chemical shifts are reported relative to tetramethylsilane (TMS) at 0 ppm. Spectra were divided into chemical shift regions corresponding to chemical types of carbon as follows: 0-45 ppm alkyl C; 45-93 ppm O-alkyl C; 93-115 ppm di-O-alkyl C and some aromatic; 115-140 aromatic C; 140-163 pm phenolic C and 163-200 ppm carboxyl C. Areas of the chemical shift regions were determined by cutting and weighing, and were expressed as percentages of total area ("relative intensity"). Results and Discussion Chemical Analysis The physical state of the composts showed great variation. Most were a mixture of fine, dark, crumbly material, mixed with larger fragments of recognizable plant parts. The compost from the coldest setting (St. John's, Newfoundland) had the highest proportion of plant fragments, and the material from the plastic composter (HAM-1) the lowest. The municipal yard waste compost was the darkest in color, and was mainly a mixture of fine particles and woody plant fragments.

Some chemical properties of the mature composts (i.e., < 2mm fraction) are summarized in Tables 1 to 3. Carbon contents ranged from 9.5 to 26 percent, and nitrogen from 0.55 to 1.78 percent, with C:N ratios from 11.9 to 23.7. The highest total N values were found for composts to which some fertilizer had been added (SJ and VIC-2).Values of pH were between 6.1 and 7.0. Alt et al. (1994) reported that composts prepared from household refuse or other plant residues normally have a high pH, while Avinmelich et al. (1996) suggest that mature compost should have a pH near neutral. The cation exchange capacities ranged between 34 to 83 cmol+/kg. The values for total P of 1613-5322 mg/kg (Table 2) are within reported ranges for compost of 800 to 9000 mg/kg (Cabrera et al. 1991; Giusquiani et al. 1995; Li et al. 1997). Available P was high in all samples. Results of the metal analyses (Table 3) are consistent with those reported elsewhere, which show lowest heavy metal contents for composts prepared from plant material separated at source. Lustenhouwer and Hin (1993) analyzed composts prepared in municipal facilities in the Netherlands. Composts prepared from household fruit, vegetable and yard waste separated at source had lower metal contents than composts prepared from household waste after mechanical and magnetic separation. Similarly, Heckman and Kluchinski (1996) found that heavy metal content was lower in hand-collected leaf litter than in municipal leaf waste which becomes contaminated by soil and dust during collection and transport. Cole (1994) also found low metal content in compost prepared in windrows of grass clippings and brush. Our values tend to fall within this group, consistent with addition of varying amounts of soil to the compost, and lower than those found for composted municipal solid waste, which in turn is lower than composted sewage sludge (He et al. 1995; Tisdell and Breslin 1995). Our values are totals and levels of leachable or bioavailable metals would be much lower (Cole 1994; Lustenhouwer and Hin 1996). Therefore, the heavy metal content of backyard composts should not be a cause for concern, unless the surrounding soil was highly contaminated.

Extractable N values were variable. Zucconi and de Bertoldi (1986) recommend that two good indicators of compost maturity are a low ratio of ammonium N to nitrate N, and >90 percent of N in organic forms. The latter condition was met by all of the samples in this study. Ratios of ammonium to nitrate N were <0.2 for 8 of the samples, but one was 0.35, and one was nearly unity. The variations seen here may not be a good indicator of the state of maturity, because many backyard heaps are uncovered, and are therefore susceptible to leaching as well as supporting some plant growth. While attesting to the nutrient-supplying power and lack of phytotoxicity of the compost, this weed growth would also remove nitrate. Avinmelich et al. (1996) suggest that mature composts should have a pH near neutral and less than 50 ppm NH4+-N, conditions met in this study. In the progression from raw material to mature compost (RAW, IMM, VIC-4), C and N contents decreased, and the C:N ratio decreased then increased slightly. The CEC increased from 52 to 58 to 68 cmol+/kg in the mature product. The raw material sampled in the spring was largely fresh plant material and vegetable waste, so that the C:N ratio was lower than it would be in the fall when senescent leaves are a higher proportion of the input. These samples were also processed differently from the mature composts, in that the whole sample, not just the <2 mm fraction was analyzed. In general, the chemical properties of the composts were comparable to those reported elsewhere for mature composts from plant materials and municipal solid waste, and so should have comparable performance as nutrient sources when used to amend garden soil. 31P NMR Spectra Phosphorus extracted with 0.5 M NaOH/0.1 M Na2EDTA was 30 to 55 percent of total P for the backyard samples, and 86 percent for the municipal compost (Table 2). Except for the municipal compost, these are low recoveries for the NaOH/EDTA combination which extracted 60-99 percent of P in forest soils (Cade-Menun and Preston 1996; Dai et at. 1996). Solution 31p spectra of NaOH extracts (Figure 1 and Table 2) were assigned according to Newman and Tate (1980) and show that a high proportion of the NaOH-extractable P is in the form of orthophosphate, from 66 to 96 percent of that extracted. In this respect the

composts are more like fertilized soil than organic soil or forest floor, where typically, a higher proportion of P extractable by NaOH is in organic forms (mono- and di-esters, pyrophosphate, polyphosphate and phosphonate) (CadeMenun and Preston 1996; Dai et al. 1996; Gressel et al. 1996; Preston et al. 1986). The relatively high proportion of orthophosphate P and the lack of detectable polyphosphate or phosphonate indicate high levels of microbial activity and P availability, consistent with reports by Hue et al. (1994) and Iglesias-Jiminez et al. (1993). Alt et al. (1994) report that composts prepared from household refuse probably contain P mainly as sparingly soluble calcium phosphates. However, at the neutral to slightly acidic pH values found in our samples, calcium phosphates are unlikely to be the dominant P form. Table 2 also shows discrepancies in most cases between the proportion of organic P determined by chemical methods on the whole sample and by NMR on the extract. This is not surprising because in most cases the extract only represents one-third to one-half of the total P, some P forms may have been altered during the extraction, and the chemical method may overestimate the organic P content. 13C CPMAS NMR Figure 2 shows [13]C CPMAS NMR spectra of the composts, and Figure 3 the progression from fresh material to mature compost for VIC-4. The relative areas of the chemical-shift regions are shown in Table 4. The peak assignments and interpretations are based on many previous studies of composts (see Introduction), organic matter (de Montigny et al. 1993; Gressel et al. 1996; Preston 1996; Preston et al. 1989; Zech et al. 1992) and plant materials (Maciel et al. 1985; Preston et al. 1997). The alkyl region (0-50 ppm) is broad, with maxima found at approximately 15, 20, 23 and 30 ppm. The lack of a sharp signal at 30 ppm from -CH2-in long chains indicates that alkyl chains are short and/or highly branched, and may include large contributions from amino acids and the -CH3 of acetate. The peak for O-alkyl C occurs at 72-74 ppm and most spectra have shoulders or poorly resolved features at approximately 50-65 ppm. Part of this intensity comes from C-6 of carbohydrates at 62-65 ppm. Based on

the dipolar-dephased spectra (see next paragraph), the remainder arises from both N-bonded carbons of amino acids and methoxyl C of lignin both of which occur around 55 ppm. The region for di-O-alkyl C, including the anomeric C of carbohydrates has its maximum around 104 ppm. In the aromatic region, the maximum for C with C or H substitution occurs at 128-135 ppm, and for O- and N-substituted aromatics from 144 to 153 ppm. The latter includes the phenolic carbons of lignins and tannins. The maximum for carboxyl, amide and ester C is found at 174-176 ppm. Dipolar-dephased spectra were obtained for two samples (Figure 4). This experiment reveals carbons without directly bonded hydrogens, and also those with some motional freedom at the molecular level in the solid state. These two classes of carbon lose intensity much more slowly during the 50mus dephasing delay. Thus the large Oalkyl C-H signal at 72-74 ppm is completely eliminated and we see peaks for carboxyl, phenolic, and C-substituted aromatic C, although the latter is reduced to a shoulder for the VIC-4 compost. Some intensity is also retained in the alkyl region due to long alkyl chains and methyl groups which retain some motion in the solid state. The weak feature retained around 55 ppm is due to methoxyl groups of lignin, while the intensity due to carbons in proteins has been lost. The SJ compost also retains some intensity at 102-104 ppm, an indicator of condensed tannins (Preston et al. 1997). This is consistent with its lower extent of decomposition. While the general features are similar to those widely observed in studies of forest floor and organic soils (de Montigny et al. 1993; Gressel et al. 1996; Preston et al. 1996; Zech et al. 1992), the compost spectra generally show broader peaks, poorer resolution and in particular, the lack of a sharp feature at 30 ppm. Also noteworthy is the prominence of the carboxyl peak in several of the spectra. For organic soils and forest floor, decomposition is often limited by low quality of the plant inputs (high C:N ratios, or high proportions of lignin, tannin and cutin) or unfavorable conditions such as low temperature, moisture extremes and low earthworm activity. Decomposition generally progresses with a decrease

of O-alkyl C, and an increase of alkyl C. The alkyl C may derive both from plant biopolymers such as suberin and cutin, and from microbial biomass generated during decomposition. The relative proportion of aromatic and phenolic C may undergo little change, or accumulate if conditions limit lignin decomposition (Baldock and Preston 1995; Preston et al. 1989). With this selective preservation of plant biopolymers, the spectra retain to a large extent, the well-defined features found in spectra of the plant inputs; in particular there is often a relatively sharp peak at 30 ppm. Similar patterns have been found in NMR composting studies of substrates such as straw (Skene et al. 1996), eucalyptus litter (Skene et al. 1997), the fibrous fraction of cattle manure (Inbar et al. 1989), grape marc (Inbar et al. 1991), and young plants of Lolium perenne (rye grass) and Triticum sativum (winter wheat) (Knicker and Ltidemann 1995). The progression is less clear in the present study. From raw input to immature compost (Figure 3), the main change is a loss of O-alkyl C and increase in aromatic and phenolic C. From immature to mature compost, we see small decreases in alkyl, Oalkyl and di-O-alkyl C, and an increase in carboxyl C. The final products have a wide range for the ratio of alkyl to O-alkyl C, from 0.36 to 1.1. The proportion of carboxyl C is also high, especially for the HAM-2, PG and VIC-4. Several points should be considered in the interpretation of the NMR spectra. First, the relative intensities must be interpreted with caution, and only used as a general guide to the composition of the product and the pathways of decomposition. It is even possible that intensities may be distorted by iron which was present up to 2.92 percent by weight, if enough of the iron were in paramagnetic forms in close association with hydrophilic groups of the organic matter, especially carbohydrate (Pfeffer et al. 1984; Preston 1996). Only a small number of samples could be analyzed, and the progression shown in Figure 3 is not a true time series following a single cohort of plant input. The Backyard Composting Process There has been little study of composting under conditions similar to those in the backyard heap (Engelstad 1991; Illmer and Schinner 1997; Razvi and Kramer

1996). Our study of operating systems confirms that backyard composting is effective, with substantial carbon loss and transformation of the plant inputs. It does take longer than most municipal and industrial-scale composting and the time scale was generally one to two years for the samples in this study. Illmer and Schinner (1997) point out that two other important differences between backyard and large-scale composting are the lower temperatures, and the continuous addition of fresh material, compared to largescale batch processes. Another important point about backyard composting is that considerable amounts of soil may be added with root inputs, and also sometimes added as an inoculum. Satisfactory results were obtained with a variety of enclosures and management systems. A compost starter was used with two composts (HAM-1 and VIC-3) consistent with the finding by Razvi and Kramer (1996) that they are not necessary. Illmer and Schinner (1997) studied home composters fitted with a hand-operated crank to speed up composting and reduce problems with odors and flies. However, in our study, most operators turned their composts occasionally (one to two times per year) or not at all, and did not report problems with odors, rats or flies. Again, this may be a result of the substrate mix, with high-N materials such as grass diluted with leaves and woody materials. Studies have shown that leaves provide an excellent match for grass clipping (Barnes and Heimlich 1992; Michel et al. 1993; Razvi and Kramer 1996); a combination typical of backyard composting. To the nonexpert at least, the activities of earthworms and other soil fauna appear to be very high, which should enhance decomposition and N availability (Engelstad 1991; Willems et al. 1996). These conditions result in effective decomposition reflected in the chemical properties (low C:N ratio, high available P, high mineral content) and the broad NMR peaks which indicate substantial transformation of the original plant material. Composting proceeds to some extent with a relative increase of alkyl and decrease of O-alkyl C and little or no increase in aromatic/phenolic C, but there is also a tendency for carboxyl C to be high. This may be associated with high levels of protein, possibly originating from microbial biomass (Pfeffer et al.

1984; Piotrowski et al. 1984; Preston et al. 1986), consistent with the N content and loss of most of the intensity around 55 ppm upon dipolar-dephasing. Conclusions While this was an exploratory study of necessity limited to a few samples, it confirms the effectiveness of backyard composting with a variety of simple management regimes. The mature composts had chemical properties similar to those produced on a larger scale from a variety of sources. The results of chemical and spectroscopic analysis are consistent with the anecdotal evidence that the product should function as a source of nutrients and stabilized organic matter for the soil. Acknowledgements We would like to thank those who contributed samples of compost for this study, and Ann van Niekerk and Kevin McCullough for chemical analysis. TABLE 1. Some chemical properties of the composts Legend for Chart: A - C % (w/w) B - N % (w/w) C - C/N D - Ash % (w/w) E - pH F - NO3-N (mg/kg) G - NH4+-N (mg/kg) H - CEC (cmol+/kg) A B C D E F G H SJ 25.5 1.78 14.3 47.0 6.77 1048 165 82.5 HAM-1 12.1 0.82 14.8 76.9 6.39 147 21 36.3 HAM-2 13.1 0.59 22.2 77.6

ND 48 17 35.4 PG 15.9 0.90 17.7 70.9 6.93 299 18 44.3 MUN 26.2 1.39 18.8 57.7 7.04 207 6 51.9 VIC-1 9.5 0.55 17.2 82.4 6.14 113 16 34.2 VIC-2 19.5 1.63 11.9 63.8 6.72 265 41 52.8 VIC-3 12.9 0.86 14.9 75.1 6.78 333 21 39.7 VIC-4(RAW) 46.2 1.95 23.7 16.9 5.62 ND[a] ND 52.4 VIC4(IMM) 30.7 1.76 17.5 48.2 6.15 ND ND 59.5 VIC-4(MAT) 26.9 1.35 19.9 54.1 6.56 46 43 68.3

a ND, not determined TABLE 2. Chemical and NMR data for P in the composts Legend for Chart: A - Total (mg/kg) B - Avail (mg/kg) C - Organic (mg/kg) D - Organic (%[a]) E - NaOH Extracted (mg/kg) F - NaOH Extracted (%[a]) G - % of NMR area, Ortho H - % of NMR area, Mono

I - % of NMR area, Diest J - % of NMR area, Pyro K - Organic (%[b]) A B C D E F G H I J K SJ 3575 479 1109 31.0 1338 37.4 77.4 18.2 1.8 2.6 22.6 HAM-1 2197 272 603 27.5 665 30.3 65.9 26.1 4.9 3.1 34.1 HAM-2 1613 126 517 32.1 577 35.8 70.9 23.6 3.0 2.5 29.1 PG 2863 461 574 20.1 1500 52.4 80.5 16.9 1.1 1.5 19.5 MUN 2896 ND[c] ND ND 2500 86.3 96.3 3.7 0 0 3.7 VIC-1 2796 699 769 27.5 1019 36.4 84.7 12.5 1.6 1.2 15.3 VIC-2 5322 1103 946 17.8 2583 48.5 91.4 6.8 0.9 0.9 8.6 VIC-3 2668 482 738

27.7 1469 55.1 86.1 9.5 1.8 2.6 13.9 VIC4(MAT) 2084 225 541 26.0 918 44.0 67.4 20.8 6.7 5.1 32.6

a as percent of total P b organic P as percent of total P in NMR spectrum c not determined TABLE 3. Total metal content of compost samples Legend for Chart: A - SJ B - HAM-1 C - HAM-2 D - PG E - MUN F - VIC-1 G - VIC-2 H - VIC-3 I - VIC-4(R) J - VIC-4(I) K - VIC-4(M) A B C D E F G H I J K % (w/w) Al 3.69 4.05 3.68 3.88 3.71 5.11 3.27 4.78 0.56 2.82 3.90 Ca 2.29 2.32 3.97 2.49 2.98 2.26 3.29

2.79 1.32 2.72 3.05 Fe 2.34 2.21 2.00 1.88 2.44 2.92 1.73 2.64 0.37 1.62 2.51 Mg 0.67 0.81 1.31 0.68 1.19 1.13 0.77 0.98 0.26 0.60 0.62 Na 1.19 1.20 1.02 1.48 1.31 1.74 1.14 1.65 0.29 1.01 1.12 mug/g As 31 29 27 26 29 28 28 52 11 23 29 Cd 2.4 2.3 3.2 2.1 2.9 2.6 2.4 2.5 1.1 2.1 1.7 Co 2 2 2 2 2 8 2 9 2 2 2 Cr 36 51 90 66 59 106 59 109 13 44 49 Cu 86 43 48 49 65 65 58 77 37 45 98 Mn 674 705 552

429 674 889 613 736 245 521 705 Ni 17 23 17 23 38 33 20 33 5 17 19 Pb 134 64 280 93 88 201 112 60 23 40 71 Zn 372 169 394 190 161 248 249 233 83 111 270 TABLE 4. Relative areas (percent of total area) of chemical shift regions of compost 13C CPMAS NMR spectra Legend for Chart: A - Area of ppm range, 0-48 B - Area of ppm range, 42-95 C - Area of ppm range, 95-115 D - Area of ppm range, 115-141 E - Area of ppm range, 141-163 F - Area of ppm range, 163-190 A B C D E F SJ 28.4 40.2 5.4 7.4 4.6 14.0 HAM-1 25.4 45.0 3.6 9.8 4.8 11.4 HAM-2 30.3 28.7 3.8 11.1 6.3 19.8

PG 32.4 33.3 4.9 7.9 4.9 16.6 MUN 19.2 44.4 8.6 12.8 8.2 6.8 VIC-1 25.5 37.4 3.4 12.6 6.6 14.5 VIC-2 27.4 36.8 6.0 11.3 6.3 12.2 VIC-3 26.7 36.5 6.1 9.0 7.9 13.8 VIC-4(RAW) 16.8 54.3 10.2 4.7 3.7 10.3 VIC-4(IMM) 17.8 42.3 11.3 9.9 8.3 10.4 VIC-4(MAT) 14.1 39.5 4.1 8.1 12.0 22.2

S: Figure 1. Solution 31p NMR spectra of NaOH/EDTA extracts of two composts.

S: Figure 2: Solid-state 13C CPMAS NMR spectra of composts except VIC-4.

S: Figure 3: Solid-state 13C CPMAS NMR spectra of typical raw material, immature and mature composts' from VIC-4 site.

S: Figure 4: Normal and dipolar-dephased (DD) solid-state 13C CPMAS NMR spectra of two composts. References

Alt, D., I. Peters and H. Fokken. 1994. Estimation of phosphorus availability in composts and compost/peat mixtures by different extraction methods. Commun. Soil Sci. Plant Anal., 25:2063-2080. Amiran, O. and S. E. Sherman. 1992. Source reduction through home composting. BioCycle, 33(4):97-99. Anonymous. 1995. Measuring diversion through home composting. BioCycle, 36(3):74-76. Avnimelich, Y., M. Bruner, I. Ezrony, R. Sela and M. Kochba. 1996. Stability indexes for municipal solid waste compost. Compost Sci. and Util., 4:13-20. Baldock, J. A. and C. M. Preston. 1995. Chemistry of carbon decomposition processes in forests as revealed by solid-state 13C NMR. In: McFee, W. W. and J. M. Kelly (eds.). Carbon Forms and Functions in Forest Soils, SSSA, Madison, Wisconsin. pp. 89-117. Barnes, J. and J. Heimlich. 1992. Leaves prove best bulking agent for grass clippings. BioCycle, 33(5):38-39. Bowman, R. A. 1989. A sequential extraction procedure with concentrated sulfuric acid and dilute base for soil organic phosphorus. Soil Sci. Soc. Am. J., 53:362-366. Bremner, J. M. and C. S. Mulvaney. 1982. Nitrogen - total. In: Page, A. L., R. H. Miller and D. R. Keeney (eds.). Methods of Soil Analysis. Part 2-Chemical and Microbiological Properties. 2nd edition, ASA, CSSA, SSSA. Madison, Wisconsin. pp. 595-624. Cabrera, F., E. Diaz and L. Madrid. 1989. Effect of using urban compost as a manure on soil contents of some nutrients and heavy metals. J. Sci. Food Agric., 47:159-169. Cade-Menun, B. J. and C. M. Preston. 1996. A comparison of soil extraction procedures for 31p NMR spectroscopy. Soil Sci., 161:770-785. Chefetz, B., P. G. Hatcher, Y. Hadar and Y. Chen. 1996. Chemical and biological characterization of organic matter during composting of municipal solid waste. J. Environ. Qual., 25:776-785.

Cole, M. A. 1994. Assessing the impact of composting yard trimmings. BioCycle, 35(4):92-96. Dai, K. H., M.D. David, G. F. Vance and A. Krzyszowska. 1996. Characterization of phosphorus in a spruce-fir Spodosol by phosphorus-31 nuclear magnetic resonance spectroscopy. Soil Sci. Soc. Am. J., 60:1943-1950. de Montigny, L. E., C. M. Preston, P. G. Hatcher and I. Kogel-Knabner. 1993. Comparison of humus horizons from two ecosystem phases on northern Vancouver Island using 13C CPMAS NMR spectroscopy and CuO oxidation. Can. J. Soil Sci., 73:9-25. Engelstad, F. 1991. Impact of earthworms on decomposition of garden refuse. Biol. Fert. Soils, 12:13 7-140. Gies, G. 1996. Backyard composting plus recycling yields high diversion. BioCycle, 37(6):39-44. Gies, G. 1997. The state of garbage in Canada. BioCycle, 38(3):78-82. Giusquiani, P. L., M. Pagliai, G. Gigliotti, D. Businelli and A. Benetti. 1995. Urban waste compost: effects on physical, chemical, and biochemical soil properties. J. Environ. Qual., 24:175-182. Gressel, N., J. G. McColl, C. M. Preston, R. H. Newman and R. F. Powers. 1996. Linkages between phosphorus transformations and carbon decomposition in a forest soil. Biogeochemistry, 33:97-123. He, X.-T., T. J. Logan and S. J. Traina. 1995. Physical and chemical characteristics of selected U.S. municipal solid waste composts. J. Environ. Qual,. 24:543-552. Heckman, J. R. and D. Kluchinski. 1996. Chemical composition of municipal leaf waste and hand-collected urban leaf litter. J. Environ. Qual., 25:355-362 Hinedi, Z.R., A. C. Chang and R. W. K. Lee. 1988. Mineralization of phosphorus in sludge-amended soils monitored by phosphorus-31-nuclear magnetic resonance spectroscopy. Soil Sci. Soc. Am. J., 52:1593-1596.

Hinedi, Z.R., A. C. Chang and R. W. K. Lee. 1989. Characterization of phosphorus in sludge extracts using phosphorus-31 nuclear magnetic resonance spectroscopy. J. Environ. Qual., 18:323-329. Hue, N. V., H. Ikawa and J. A. Silva. 1994. Increasing plant-available phosphorus in an Ultisol with a yard-waste compost. Commun. Soil Sci. Plant Anal., 25:3291-3303. Illmer, P. and F. Schinner. 1997. Compost turning - a central factor for a rapid and high-quality degradation in household composting. Bioresource Tech., 59:157-162. Inbar, Y., Y. Chen and Y. Hadar. 1989. Solid-state carbon-13 nuclear magnetic resonance and infrared spectroscopy of composted organic matter. Soil Sci. Soc. Am. J., 53:1695-1701. Inbar, Y., Y. Chen. and Y. Hadar. 1991. Carbon-13 CPMAS NMR and FTIR spectroscopic analysis of organic matter transformations during composting of solid wastes from wineries. Soil Sci., 152:272-282. Iglesias-Jiminez, E. and C. E. Alvarez. 1993. Apparent availability of nitrogen in composted municipal refuse. Biol. Fert. Soils, 16:313-318. Iglesias-Jimenez, E., V. P. Garcia, M. Espino and J. M. Hernandez. 1993. City refuse compost as a phosphorus source to overcome the P-fixation capacity of sesquioxide-rich soils. Plant Soil, 148:115-127. Kalra, Y. P. and D. G. Maynard. 1991. Methods Manual for Forest Soil and Plant Analysis. Info. Rep. NOR-X-319. For. Can., Nor. For. Cen., Edmonton, Alberta, 116 pp. Kashmanian, R. M. 1993. Quantifying the amount of yard trimmings to be composted in the United States in 1996. Compost Sci. and Util,. 1:22-29. Knicker, H. and H.-D. Ludemann. 1995. N-15 and C-13 CPMAS and solution NMR studies of N-15 enriched plant material during 600 days of microbial degradation. Org. Geochem., 23:329-341.

Kostov, O., Y. Tzvetkov, G. Petkova, and J. M. Lynch. 1996. Aerobic composting of plant wastes and their effect on the yield of ryegrass and tomatoes. Biol. Fert. Soils, 23:20-25. Li, Y. C., P. J. Stoffella, A. K. Alva, D. V. Calvert and D. A. Graetz. 1997. Leaching of nitrate, ammonium and phosphate from compost-amended soil columns. Compost Sci. and Util., 5:63-67. Lustenhouwer, H. and J. Hin. 1993. Biosignificant content of heavy metals in compost. Sci. Tot. Environ., 128: 269-278. Maciel, G.E., J. F. Haw, D. H. Smith, B.C. Gabrielsen and G. R. Hatfield. 1985. Carbon-13 nuclear magnetic resonance of herbaceous plants and their components, using cross polarization and magic angle spinning. J. Agric. Food Chem., 33:185-191. Maynard, A. A. 1996. Cumulative effect of annual additions of undecomposed leaves and compost on the yield of field-grown peppers. Compost Sci. and Util., 4:81-88. Maynard, A. A. 1997. Cumulative effect of annual additions of undecomposed leaves and compost on the yield of eggplants and tomatoes. Compost Sci. and Util., 5:38-48. Michel, F. C., Jr., C A. Reddy and L. J. Forney. 1993. Yard waste composting: studies using different mixes of leaves and grass in a laboratory scale system. Compost Sci. and Util., 1:85-96. Murphy, J. and J.P. Riley. 1962. A modified single solution method for determination of phosphate in natural waters. Anal. Chim. Acta, 27:31-36. Newman, R. H. and K. R. Tate. 1980. Soil phosphorus characterization by [31]p nuclear magnetic resonance. Commun. Soil Sci. Plant Anal., 11:835-842. Olsen, S. R. and L. E. Sommers. 1982. Phosphorus. In: Page, A. L., R. H. Miller and D. R. Keeney (eds.) Methods of Soil Analysis. Second edition. Agronomy Series Part 9, Part 2., SSSA, Madison, Wisconsin. pp. 403-430. Pfeffer, P.E., W. V. Gerasimowicz and E.G. Piotrowski. 1984. Effect of paramagnetic iron on quantitation in carbon-13 cross polarization magic angle

spinning nuclear magnetic resonance spectrometry of heterogeneous environmental matrices. Anal. Chem., 56:734-741. Piotrowski, E.G., K. M. Valentine and P. E. Pfeifer. 1984. Solid-state, [13]C, cross-polarization, "magic-angle" spinning, NMR spectroscopy studies of sewage sludge. Soil Sci., 137:194-203. Preston, C. M. 1996. Applications of NMR to soil organic matter analysis: history and prospects. Soil Sci., 161:144-166. Preston, C.M., J. A. Ripmeester, S. P. Mathur and M. Levesque. 1986. Application of solution and solid-state multinuclear NMR to a peat-based composting system for fish and crab scrap. Can. J. Spectrosc., 31:63-69. Preston, C. M., D. E. Axelson, M. Levesque, S. P. Mathur, H. Dinel and R. L. Dudley. 1989. Carbon-13 NMR and chemical characterization of particle-size separates of peats differing in degree of decomposition. Org. Geochem., 14:393-403. Preston, C. M., J. A. Trofymow, B. G. Sayer and J. Niu. 1997. [13]C nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning investigation of the proximate analysis fractions used to assess litter quality in decomposition studies. Can. J. Bot., 75:1601-1613. Razvi A. S. and D. W. Kramer. 1996. Evaluation of compost activators for composting grass clippings. Compost Sci. and Util., 4:72-80. Skene, T. M., J. O. Skemstad, J. M. Oades and P. J. Clark. 1996. The influence of inorganic matrices on the decomposition of straw. Aust. J. Soil Res., 34:413-426. Skene, T. M., J. O. Skjemstad, J. M. Oades and P. J. Clark. 1997. The influence of inorganic matrices on the decomposition of Eucalyptus litter. Aust. J. Soil Res., 35:73-87. Tisdell, S. E. and V. T. Breslin. 1995. Characterization and leaching of elements from municipal solid waste compost. J. Environ. Qual., 24:827-833. Vossen, P. and E. Rilla. 1997. Home composters make a difference to diversion. BioCycle, 38(1):34-36.

Watanabe, F. S. and S. R. Olsen. 1965. Test of an ascorbic acid method for determining phosphorus in water and NaHCO3 extracts from soil. Soil Sci. Soc. Am. Proc., 29:677-678. Willems, J. J. G. M., J. C. Y. Marinissen and J. Blair. 1996. Effects of earthworms on nitrogen mineralization. Biol. Fert. Soils, 23:57-63. Zech, W., F. Ziegler, I. Kogel-Knabner and L. Haumaier. 1992. Humic substances distribution and transformation in forest soils. Sci. Total Environ., 117/118:155-174. Zucconi, F. and de Bertoldi, M. 1986. Compost specifications for the production and characterization of compost from municipal solid waste. In: de Bertoldi, M., Ferranti, M.P., L'Hermite, P. and Zucconi, F. (eds.). Compost: Production, Quality and Use, Elsevier, London. pp. 30-50. ~~~~~~~~ By Caroline M. Preston[1]; Barbara J. Cade-Menun[2] and Brian G. Sayer[3] 1. Pacific Forestry Centre, Natural Resources Canada, Victoria, British Columbia, Canada 2. Department of Environmental Science, Policy and Management, University of California Berkeley, California 3. Department of Chemistry, McMaster University, Hamilton, Ontario, Canada

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Characterization of Canadian Backyard Composts: Chemical and Spectroscopic Analyses

lowest. The municipal yard waste compost was the darkest in color, and was mainly a mixture of fine particles and woody plant fragments.

Some chemical properties of the mature composts (Le., < 2mm fraction) are sum- marized in Tables 1 to 3. Carbon contents ranged from 9.5 to 26 percent, and nitrogen from 0.55 to 1.78 percent, with C:N ratios from 11.9 to 23.7. The highest total N values were found for composts to which some fertilizer had been added (SJ and VIC-2).Values of pH were between 6.1 and 7.0. Alt et al. (1994) reported that composts prepared from household refuse or other plant residues normally have a high pH, while Avinmelich et 01. (1996) suggest that mature compost should have a pH near neutral. The cation ex- change capacities ranged between 34 to 83 cmol+/kg. The values for total P of 1613-5322 mg/kg (Table 2) are within reported ranges for compost of 800 to 9000 mg/kg (Cabrera et 01.1991; Giusquiani ef al. 1995; Li et al. 1997). Available P was high in all samples.

Results of the metal analyses (Table 3) are consistent with those reported elsewhere,

TABLE 1. Some chemical properties of the composts

C N Ash N 0 3 - N NH4+-N CEC ‘X,(w/w) ‘X,(w/w) C/N ‘%(w/w) pH (mg/kg) (mg/kg) (cmol+/kg)

SI 25 5 1 78 14 3 47 0 6 77 1048 165 82 5 HAM-I 12 1 0 82 I4 8 76 9 6 39 147 21 36.3 t IAIM-2 13 1 0 59 22 2 77 6 ND 48 17 35 4 I’G 159 0 90 177 70 9 6 93 299 18 44.3 M U N 26 2 1 3Y 18 8 57 7 7 OM 207 6 51.9 VIC-1 9 5 0 55 172 82 4 6 14 113 16 34 2 VIC-2 19 5 163 1 I 9 63 8 6 72 265 41 52.8 VIC-3 12 9 0 86 14 9 75 I 6 78 333 21 3Y 7 VlC-4(I<AW) 46 2 195 23 7 169 5 62 ND‘ NU 52 4 VK4( IMM) 30 7 1 76 17 5 48 2 6 15 NU ND 59 5 VIC-4( MAT) 2h 9 I35 19 Y 54 I 6 56 46 43 68 3

AD, not detc.rmincd

TABLE 2. Chemical and NMR data for P in the composts

Total Avail Orgenic (mg/kg) (mg/kg) (mg/kg) (‘V)

SJ 3575 479 1 tw 31 0 HAM-1 21g7 272 603 275 HAM-2 1613 126 517 321 r c 2863 461 574 201 MLiN ‘.?U% N D ND N D VlC-I 27% 6YY 76Y 275 V1C-2 5322 1103 946 178 VIC-3 2668 482 738 277 VIC--I(MAT) 2084 225 541 260

a as percent of total P organic Pas percent of total P in NMR spectrum not determined

N d W i Extracted (mg/kg) ( W )

1338 374 665 303 577 358 1500 524 2500 8 6 3 1019 364 2583 485 1469 551 918 440

Ortho

77 4 65 Y

70.9 80.5 96.3 84.7 91.4 86 1

67.4

Mono Diest Pyro Orgnnic % of NMR area (‘LP)

182 1 8 2 6 226 26 1 4.Y 3 i 34.1 236 3 0 2 5 291 169 1 1 I S 195 3 7 0 0 3 7 125 1 6 1 2 153 6 8 0.9 0.9 8 6 Y 5 1 8 2.6 139 208 6.7 5 1 326

which show lowest heavy metal contents for composts prepared from plant material separated at source. Lustenhouwer and Hin (1993) analyzed composts prepared in mu- nicipal facilities in the MetherIands. Composts prepared from household fruit, veg-

Characterization of Canadian Backyard Composts: Chemical and Spectroscopic Analyses

VIC-4

Raw Input

PPM 200 100 0

Figure 3 Solid-state '?C CPMAS NMR spectra of typical raw material, immaturc and mature composts from VIC-4 site.

TABLE 4. Relative areas (percent of total area) of chemical shift regions of compost

'3C CPMAS NMR spectra

Area of ppm range -

0-48 42-95 95-115 115-141 141-163 163-190 __

SI 28 4 40 2 5 4 7 4 4 6 14 0 HAM-1 25 4 45 0 3 6 9 8 4 8 11 4 HAM-2 30 3 28.7 38 11.1 6 3 19.8 PG 32.4 33 3 4 9 7 9 4 9 16 6 MUN 19 2 44 4 8 6 12 8 8 2 6 8 VIC-1 25.5 37 4 3 4 12 6 6 6 14 5 VIC-2 27.4 36 8 6 0 11 3 6 3 12 2 VIC-3 26 7 36 5 6.1 9 0 7 9 13.8 VICd(RAW) 16 8 5 4 3 10.2 4 7 3 7 10 3 VIC-4(IMM) 17 8 42 3 11.3 9 9 8 3 10 4 VIC-4(MAT) 14 1 39 5 4 1 8 1 12 0 222

ter includes the phenolic carbons of lignins and tannins. The maximum for carboxyl, amide and ester C is found at 174-176 ppm.

Dipolar-dephased spectra were obtained for two samples (Figure 4). This experi- ment reveals carbons without directly bonded hydrogens, and also those with some motional freedom at the molecular level in the solid state. These two classes of carbon lose intensity much more slowly during the 50ps dephasing delay. Thus the large 0- alkyl C-H signal at 72-74 ppm is completely eliminated and we see peaks for carboxyl, phenolic, and C-substituted aromatic C, although the latter is reduced to a shoulder for the VIC-4 compost. Some intensity is also retained in the alkyl region due to long alkyl chains and methyl groups which retain some motion in the solid state. The weak feature retained around 55 ppm is due to methoxyl groups of lignin, while the inten-

Compost Science a Utilizatii smmertgw 61

Caroline M . Preston, Barbara 1. Cade-Menun and Brian G. Sayer

P determined by chemical methods on the whole sample and by NMR on the extract. This is not surprising because in most cases the extract only represents one-third to one-half of the total P, some P forms may have been altered during the extraction, and the chemical method may overestimate the organic P content.

13C CPMAS N M R

Figure 2 shows I3C CPMAS NMR spectra of the composts, and Figure 3 the pro- gression from fresh material to mature compost for VIC-4. The relative areas of the chemical-shift regions are shown in Table 4. The peak assignments and interpretations are based on many previous studies of composts (see Introduction), organic matter (de Montigny et al. 1993; Gressel et al. 1996; Preston 1996; Pfeston et al. 1989; Zech et al. 1992) and plant materials (Maciel et al. 1985; Preston et al. 1997). The alkyl region (0-50 ppm) is broad, with maxima found at approximately 15,20,23 and 30 ppm. The lack of a sharp signal at 30 ppm from -CH,- in long chains indicates that alkyl chains are short and/or highly branched, and may include large contributions from amino acids and the -CH, of acetate. The peak for 0-alkyl C occurs at 72-74 ppm and most spectra have shoulders or poorly resolved features at approximately 50-65 ppm. Part of this inten- sity comes from C-6 of carbohydrates at 62-65 ppm. Based on the dipolar-dephased spectra (see next paragraph), the remainder arises from both N-bonded carbons of amino acids and methoxyl C of lignin both of which occur around 55 ppm. The region for di-0-alkyl C, including the anomeric C of carbohydrates has its maximum around 104 ppm. In the aromatic region, the maximum for C with C or H substitution occurs at 128-135 ppm, and for 0- and N-substituted aromatics from 144 to 153 ppm. The lat-

HAM-2 + PPM 200 100 0

MUN I L , " I

PPM 200 1M) 0

Figure 2 Solid-state 1% CPMAS NMR spectra of composts except VIC-4.

60 compost Science & Utilization Summer 1998

Chnracterization of Canadian Backyard Composts: Cheiizicnl a n d Spectroscopic Aiznlyses

the input. These samples were also processed differently from the mature composts, in that the whole sample, not just the <2 mm fraction was analyzed. In general, the chem- ical properties of the composts were comparable to those reported elsewhere for mature composts from plant materials and municipal solid waste, and so should have compa- rable performance as nutrient sources when used to amend garden soil.

37P N M R Spectra

Phosphorus extracted with 0.5 M NaOH/O.l M Na,EDTA was 30 to 55 percent of total P for the backyard samples, and 86 percent for the municipal compost (Table 2). Ex- cept for the municipal compost, these are low recoveries for the NaOH/EDTA combi- nation which extracted 60-99 percent of P in forest soils (Cade-Menun and Preston 1996; Dai et al. 1996). Solution 31P spectra of NaOH extracts (Figure 1 and Table 2) were as- signed according to Newman and Tate (1980) and show that a high proportion of the NaOH-extractable P is in the form of orthophosphate, from 66 to 96 percent of that ex- tracted. In this respect the composts are more like fertilized soil than organic soil or for- est floor, where typically, a higher proportion of P extractable by NaOH is in organic forms (mono- and di-esters, pyrophosphate, polyphosphate and phosphonate) (Cade- Menun and Preston 1996; Dai et nl. 1996; Gressel et al. 1996; Preston ef nl. 1986). The rela- tively high proportion of orthophosphate P and the lack of detectable polyphosphate or phosphonate indicate high levels of microbial activity and P availability, consistent with reports by Hue et a/. (1994) and Iglesias-Jiminez et al. (19931, Alt et aJ. (1994) report that composts prepared from household refuse probably contain P mainly as sparingly sol- uble calcium phosphates. However, at the neutral to slightly acidic pH values found in our samples, calcium phosphates are unlikely to be the dominant P form.

Table 2 also shows discrepancies in most cases between the proportion of organic

St. John's

Newfoundland

x 4 wl.il

orthophosphate Victoria

Municipal

phosphate monoester

pyrophosphate phosphate diester

x5

I I I I 1 I 1 I I I

5 0 - 5 5 0 - 5 15 10 PPM 15 10

Figure 1. Solution 3'P NMR spectra of NaOH/EDTA extracts of two composts.

Compost Science & Utilization Summer1998 59

Caroline M . Preston, Barbara J. Cade-Mentln and Brian G. Sayer

etable and yard waste separated at source had lower metal contents than composts pre- pared from household waste after mechanical and magnetic separation. Similarly, Heck- man and Kluchinski (1996) found that heavy metal content was lower in hand-collect- ed leaf litter than in municipal leaf waste which becomes contaminated by soil and dust during collection and transport. Cole (1994) also found low metal content in compost prepared in windrows of grass clippings and brush. Our values tend to fall within this group, consistent with addition of varying amounts of soil to the compost, and lower than those found for composted municipal solid waste, which in turn is lower than com- posted sewage sludge (Heet a/. 1995; Tisdell and Breslin 1995). Our values are totals and levels of leachable or bioavailable metals would be much lower (Cole 1994; Lusten- houwer and Hin 1996). Therefore, the heavy metal content of backyard composts should not be a cause for concern, unless the surrounding soil was highly contaminated.

Extractable N values were variable. Zucconi and de Bertoldi (1986) recommend that

TABLE 3. Total metal content of compost samples

SJ HAM-1 HAM-2 I'C: MUN VIC-1 VIC-2 VIC-3 VIC-4(K) VK-4(l) VIC-J(M)

,S,(W/\\')

AI 3.69 4.M 3.68 3.88 3.71 5.11 0.27 4.78 0.56 2.82 3.90 Cn 2.29 2.32 3.97 2.49 2.98 2.26 3.29 2.79 1.32 2.72 3.05 Fe 2.34 2.21 2.00 i.8n 2.44 2.92 1.73 2.64 0.37 1.62 2.51

M g 0.67 0.81 1.31 0.68 1.19 1.13 0.77 0.98 0.26 0.60 0.62 Na 1.19 1.20 1.02 1.48 1.31 1.74 1.14 1.65 0.20 1.01 1.12

As 31 29 Cd 2 4 2 3 CO 2 2 Cr 36 51 cu 8h 43 Mn 674 705 NI 17 23 Pb 1.24 64 Zn 372 I69

27 3.2 2

'10 48 552 17

280 3'14

26 2') 2. I 2.9 2 2

66 59 49 65 429 674 23 38 93 88 190 161

28 2.6 8 I 06 65 ntw 33 201 248

28 52 I I 23 20 24 2 5 1 1 2 1 1 7 7 9 2 2 2

59 109 13 44 49 38 77 37 45 98 h13 736 245 521 705 20 33 5 17 19 112 60 23 40 71 240 233 83 Ill 270

two good indicators of compost maturity are a low ratio of ammonium N to nitrate N, and >90 percent of N in organic forms. The latter condition was met by all of the samples in this study. Ratios of ammonium to nitrate N were ~ 0 . 2 for 8 of the samples, but one was 0.35, and one was nearly unity. The variations seen here may not be a good indica-

fore susceptible to leaching as well as supporting some plant growth. While attesting to the nutrient-supplying power and lack of phytotoxicity of the compost, this weed growth would also remove nitrate. Avinmelich et al. (1996) suggest that mature composts should have a pH near neutral and less than 50 ppm NH,+-N, conditions met in this study.

In the progression from raw material to mature compost (RAW, IMM, VIC-4), C and N contents decreased, and the C:N ratio decreased then increased slightly. The CEC in- creased from 52 to 58 to 68 cmol+/kg in the mature product. The raw material sampled in the spring was largely fresh plant material and vegetable waste, so that the C:N ratio was lower than it would be in the fall when senescent leaves are a higher proportion of

tor of the state of maturity, because many backyard heaps are uncovered, and are there- t

58 ~omposi Science utilization Summer 1998

tkn t h ic:

ra Cc:

t c

n4# D) Sii

hr tIr et: fa Ib tii P' rtt

CE

C(C u1 0)

Caroline M . Preston, Barbara J. Cade-Menun and Brian G. Sayer

PPM 200 100 0

VIC-4 Compost n

I I ~

PPM 200 100 0

Figure 4. Normal end dipolar-dephased (DD) solid-state CPMAS NMR spectra of two composts

sity due to carbons in proteins has been lost. The SJ compost also retains some inten- sity at 102-104 ppm, an indicator of condensed tannins (Preston et ai. 1997). This is con- sistent with its lower extent of decomposition.

While the general features are similar to those widely observed in studies of forest floor and organic soils (de Montigny et nl. 1993; Gressel et al. 1996; Preston et a[. 1996; Zech et al. 1992), the compost spectra generally show broader peaks, poorer resolution and in particular, the lack of a sharp feature at 30 ppm. Also noteworthy is the prominence of the carboxyl peak in several of the spectra. For organic soils and forest floor, decompo- sition is often limited by low quality of the plant inputs (high C:N ratios, or high pro- portions of lignin, tannin and cutin) or unfavorable conditions such as low temperature, moisture extremes and low earthworm activity. Decomposition generally progresses with a decrease of 0-alkyl C, and an increase of alkyl C. The alkyl C may derive both from plant biopolymers such as suberin and cutin, and from microbial biomass gener- ated during decomposition. The relative proportion of aromatic and phenolic C may un- dergo little change, or accumulate if conditions limit lignin decomposition (Baldock and Preston 1995; Preston et al. 1989). With this selective preservation of plant biopolymers, the spectra retain to a large extent, the well-defined features found in spectra of the plant inputs; in particular there is often a relatively sharp peak at 30 ppm.

Similar pattems have been found in NMR composting studies of substrates such as straw (Skene et al. 1996), eucalyptus litter (Skene et al. 1997), the fibrous fraction of cattle manure (Inbar et al. 1989), grape marc (Inbar et al. 1991), and young plants of Loli-

02 c ~ m ~ o s t science L Wlizetion Summer 1998

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