Relationship between compost stability and extractable organic carbon

Establishing a simple yet reliable compost stability test is essential for a better compost quality control and utilization efficiency. The objective of this study was to examine the relationship between extractable organic carbon (OC) and compost stability based on 18 compost samples from five composting facilities. The compost samples were extracted sequentially with water for 2 h [water(2h)] and 0.1 M NaOH for 2 and 24 h [NaOH(2h) and NaOH(24h), respectively]. The extractable OC was further separated into fulvic acid (FA) and humic acid (HA) fractions by adjusting the pH to <2. The mass specific absorbance (MSA) of OC in the six fractions was measured. Compost stability was estimated with a CO2 evolution method. The extractable OC concentration was influenced by the total volatile solids and decreased with curing time for compost with a high level of extractable OC. The OC levels in each fraction were significantly correlated (p < 0.05) to each other except for the water(2h)-extractable HA. In addition, all the FA and HA fractions except for water(2h)-extractable HA were highly (P < 0.01) and linearly correlated to CO2 evolution, but multiple regression showed that NaOH(24h)-extractable OC was insignificant for CO2 evolution. The relatively high slope of NaOH(2h)-extractable FA versus CO2 evolution suggests that this fraction may contribute the most to compost CO2 evolution. The water(2h)- and/or NaOH(2h)-extractable FA tests are recommended for measuring compost stability because of their high correlation with CO2 evolution. This estimation can be obtained through a simple photometric method covering a wide range of carbon concentrations up to 4,000 mg L(-1).     

川牛膝种子保存技术初探

对川牛膝种子开展室温常规贮藏、室温湿沙贮藏、室温超干燥贮藏、4℃低温贮藏、冷冻贮藏等5种贮藏试验,结果表明：①室温湿沙贮藏是川牛膝种子短期保存的最优方法,能显著提高种子发芽率,其值较常规保存高14.5％;其次为4℃低温贮藏.②冷冻贮藏是川牛膝种子长期保存的最佳方法,保存3年后当其他保存方式的种子寿命几乎丧失时,其生活力及发芽率仍保持在较高水平,分别为60.3％和49.9％;其次为超干燥贮藏,种子生活力和发芽率分别为51.3％和41.2％.     

Carbon monoxide from composting due to thermal oxidation of biomass

Emissions of carbon monoxide (CO) were observed from decomposing organic wastes and litter under laboratory, pilot composting plant, and natural conditions. Field studies included air from inside a compost heap of about 200 m3, emissions from composting of livestock wastes at a biologically operating farm, and leaf litter pile air samples. The concentration of CO was up to 120 micromol mol(-1) in the compost piles of green waste, and up to 10 micromol mol(-1) in flux chambers above livestock waste windrow composts. The mean CO flux rates were approximately 20 mg CO m(-2) h(-1) for compost heaps of green waste, and varied from 30 to 100 mg CO m(-2) h(-1) for fresh dung windrows. Laboratory studies using a temperature and ventilation-controlled substrate container were performed to elucidate the origin of CO, and included hay samples of fixed moisture content at temperatures between 5 and 65 degrees C, including nonsterilized as well as sterilized samples. The concentration of CO was up to 160 micromol mol(-1) in these experiments, and Arrhenius-type plot analyses resulted in activation energies of 65 kJ mol(-1) for thermochemically produced CO from the nonsterilized compost substrate. Sterilized samples showed dramatically reduced CO2 but virtually unchanged CO emissions, albeit at a slightly lower activation energy, likely a result of the high-temperature sterilization. Though globally and regionally these CO emissions are only a minor source, thermochemically produced CO emissions might affect local air quality in and near composting facilities.     

不同腐熟度猪粪、奶牛粪在小白菜和香瓜上施用的农学效应研究

进行猪粪和奶牛粪自然高温堆肥发酵,分别在15、25、35、50 d取样,获得了不同腐熟程度堆肥产物,分别进行了小白菜和香瓜种子发芽与田间应用试验,以期获得不同腐熟堆肥在蔬菜上施用的农学效应,旨在从堆肥农田施用的农学效应角度,为制订堆肥腐熟度标准提供科学依据。结果表明：牛粪堆肥过程中的最高温度高于猪粪,且高温期也长于猪粪;两种处理在35d有机碳含量均显著降低,全氮含量为先降低后升高趋势;两种堆肥在35d后,均达到无害化标准。不同腐熟程度堆肥对小白菜株高和主根长及香瓜苗重和主根长均没有明显抑制作用,对小白菜和香瓜出苗率、根系活力及小白菜单株鲜重和生物产量影响较大,尤其是猪粪腐熟25d,奶牛粪腐熟15d的堆肥表现出显著抑制作用。将堆肥理化参数与小白菜、香瓜生长指标进行相关分析表明：pH值、全氮含量和C/N这3种指标均与小白菜和香瓜各项生物性状无显著相关性;有机碳和DOC与各项生物性状指标均表现出显著或极显著相关性;铵/硝与小白菜和香瓜的GI和根系活力均表现极显著或显著的相关性,其结果与现行的堆肥腐熟度指标并不一致。因此,在制订堆肥腐熟度标准时,应关注堆肥产物农田施用后不同作物所表现出的不同农学效应。     

Greenhouse gas emissions and soil indicators four years after manure and compost applications

Understanding how carbon, nitrogen, and key soil attributes affect gas emissions from soil is crucial for alleviating their undesirable residual effects that can linger for years after termination of manure and compost applications. This study was conducted to evaluate the emission of soil CO2, N2O, and CH4 and soil C and N indicators four years after manure and compost application had stopped. Experimental plots were treated with annual synthetic N fertilizer (FRT), annual and biennial manure (MN1 and MN2, respectively), and compost (CP1 and CP2, respectively) from 1992 to 1995 based on removal of 151 kg N ha(-1) yr(-1) by continuous corn (Zea mays L.). The control (CTL) plots received no input. After 1995, only the FRT plots received N fertilizer in the spring of 1999. In 1999, the emissions of CO2 were similar between control and other treatments. The average annual carbon input in the CTL and FRT plots were similar to soil CO2-C emission (4.4 and 5.1 Mg C ha(-1) yr(-1), respectively). Manure and compost resulted in positive C and N balances in the soil four years after application. Fluxes of CH4-C and N2O-N were nearly zero, which indicated that the residual effects of manure and compost four years after application had no negative influence on soil C and N storage and global warming. Residual effects of compost and manure resulted in 20 to 40% higher soil microbial biomass C, 42 to 74% higher potentially mineralizable N, and 0.5 unit higher pH compared with the FRT treatment. Residual effects of manure and compost on CO2, N20, and CH4 emissions were minimal and their benefits on soil C and N indicators were more favorable than that of N fertilizer.     

The effect of phosphogypsum on greenhouse gas emissions during cattle manure composting

Phosphogypsum (PG), a by-product of the phosphate fertilizer industry, reduces N losses when added to composting livestock manure, but its impact on greenhouse gas emissions is unclear. The objective of this research was to assess the effects of PG addition on greenhouse gas emissions during cattle feedlot manure composting. Sand was used as a filler material for comparison. The seven treatments were PG10, PG20, PG30, S10, S20, and S30, representing the rate of PG or sand addition at 10, 20, or 30% of manure dry weight and a check treatment (no PG or sand) with three replications. The manure treatments were composted in open windrows and turned five times during a 134-d period. Addition of PG significantly increased electrical conductivity (EC) and decreased pH in the final compost. Total carbon (TC), total nitrogen (TN), and mineral nitrogen contents in the final composted product were not affected by the addition of PG or sand. From 40 to 54% of initial TC was lost during composting, mostly as CO(2), with CH(4) accounting for <14%. The addition of PG significantly reduced CH(4) emissions, which decreased exponentially with the compost total sulfur (TS) content. The emission of N(2)O accounted for <0.2% of initial TN in the manure, increasing as compost pH decreased from alkaline to near neutral. Based on the total greenhouse gas budget, PG addition reduced greenhouse gas emissions (CO(2)-C equivalent) during composting of livestock manure by at least 58%, primarily due to reduced CH(4) emission.     

Carbon and nitrogen mineralization rates after application of organic amendments to soil

The objective of this study was to quantify C and N mineralization rates from a range of organic amendments that differed in their total C and N contents and C quality, to gain a better understanding of their influence on the soil N cycle. A pelletized poultry manure (PP), two green waste-based composts (GWCa, GWCb), a straw-based compost (SBC), and a vermi-cast (VER) were incubated in a coarse-textured soil at 15 degrees C for 142 d. The C quality of each amendment was determined by chemical analysis and by 13C nuclear magnetic resonance (NMR). Carbon dioxide (CO2-C) evolution was determined using alkali traps. Gross N mineralization rates were calculated by 15N isotopic pool dilution. The CO2-C evolution rates and gross N mineralization rates were generally higher in amended soils than in the control soil. With the exception of GWCb all amendments released inorganic N at concentrations that would be high enough to warrant a reduction in inorganic N fertilizer application rates. The amount of N released from PP was high indicating that application rates should be reduced, or alternative amendments used, to minimize leaching losses in regions where ground water quality is of concern. There was a highly significant relationship between CO2-C evolution and gross N mineralization (R2= 0.95). Some of the chemically determined C quality parameters had significant relationships (p < 0.05) with both the cumulative amounts of C and N evolved. However, we found no significant relationships between 13C NMR spectral groupings, or their ratios, and either the CO2-C evolved or gross N mineralized from the amendments.     

Phytostabilization potential of quailbush for mine tailings: growth, metal accumulation, and microbial community changes

Abandoned mine tailings sites in semiarid regions remain unvegetated for extended periods of time and are subject to eolian dispersion and water erosion. This study examines the potential phytostabilization of a lead-zinc mine tailings site using a native, drought-tolerant halophyte, quailbush [Atriplex lentiformis (Torr.) S. Wats.]. In a greenhouse study germination, growth, and metal uptake was evaluated in two compost-amended mine tailings samples, K4 (pH 3) and K6 (pH 6) at 75, 85, 90, 95, and 100% mine tailings, and two controls, off-site and compost. Microbial community changes were monitored by performing MPN analysis of iron- and sulfur-oxidizing bacteria as well as heterotrophic plate counts. Results demonstrate that germination is not a good indicator for phytostabilization since it was only inhibited in the unamended K4 treatment. Plant growth was significantly reduced in 95 and 100% mine tailings, while growth in 75, 85, and 90% treatments was similar to the off-site control. Quailbush accumulated elevated levels of the nutrient metals Na, K, Mn, and Zn in the shoot tissues; however, metal accumulation was generally below the domestic animal toxicity limit. Initially, autotrophic population estimates were four to six logs higher than heterotrophic counts, indicating extremely stressed conditions. However, post-harvest, heterotrophic bacterial counts increased to normal levels (approximately 10(6) CFU g-1 dry tailings) and dominated the rhizosphere. Therefore, with compost amendment, quailbush has good potential as a native species candidate for phytostabilization of mine tailings in semiarid environments.     

Biochar and hydrochar effects on greenhouse gas (carbon dioxide, nitrous oxide, and methane) fluxes from soils

With a growing world population and global warming, we are challenged to increase food production while reducing greenhouse gas (GHG) emissions. We studied the effects of biochar (BC) and hydrochar (HC) produced via pyrolysis or hydrothermal carbonization, respectively, on GHG fluxes in three laboratory incubation studies. In the first experiment, ryegrass was grown in sandy loam mixed with equal amounts of a nitrogen-rich peanut hull BC, compost, BC+compost, double compost, or no addition (control); wetting-drying cycles and N fertilization were applied. Biochar with or without compost significantly reduced NO emissions and did not change the CH uptake, whereas ryegrass yield was significantly increased. In the second experiment, 0% (control) or 8% (w/w) of BC (peanut hull, maize, wood chip, or charcoal) or 8% HC (beet chips or bark) was mixed into a soil and incubated at 65% water-holding capacity (WHC) for 140 d. Treatments included simulated plowing and N fertilization. All BCs reduced NO emissions by ～60%. Hydrochars reduced NO emissions only initially but significantly increased them after N fertilization to 302% (HC-beet) and 155% (HC-bark) of the control emissions, respectively. Large HC-associated CO emissions suggested that microbial activity was stimulated and that HC was less stable than BC. In the third experiment, nutrient-rich peanut hull BC addition and incubation over 1.5 yr at high WHCs did not promote NO emissions. However, NO emissions were significantly increased with BC after NHNO addition. In conclusion, BC reduced NO emissions and improved the GHG-to-yield ratio under field-relevant conditions. However, the risk of increased NO emissions with HC addition must be carefully evaluated.     

Free-air CO2 enrichment of sorghum: soil carbon and nitrogen dynamics

The positive impact of elevated atmospheric CO(2) concentration on crop biomass production suggests more carbon inputs to soil. Further study on the effect of elevated CO(2) on soil carbon and nitrogen dynamics is key to understanding the potential for long-term carbon storage in soil. Soil samples (0- to 5-, 5- to 10-, and 10- to 20-cm depths) were collected after 2 yr of grain sorghum [Sorghum bicolor (L.) Moench.] production under two atmospheric CO(2) levels: (370 [ambient] and 550 muL L(-1) [free-air CO(2) enrichment; FACE]) and two water treatments (ample water and limited water) on a Trix clay loam (fine, loamy, mixed [calcareous], hyperthermic Typic Torrifluvents) at Maricopa, AZ. In addition to assessing treatment effects on soil organic C and total N, potential C and N mineralization and C turnover were determined in a 60-d laboratory incubation study. After 2 yr of FACE, soil C and N were significantly increased at all soil depths. Water regime had no effect on these measures. Increased total N in the soil was associated with reduced N mineralization under FACE. Results indicated that potential C turnover was reduced under water deficit conditions at the top soil depth. Carbon turnover was not affected under FACE, implying that the observed increase in soil C with elevated CO(2) may be stable relative to ambient CO(2) conditions. Results suggest that, over the short-term, a small increase in soil C storage could occur under elevated atmospheric CO(2) conditions in sorghum production systems with differing water regimes.     

Emissions of ammonia, methane, carbon dioxide, and nitrous oxide from dairy cattle housing and manure management systems

Concentrated animal feeding operations emit trace gases such as ammonia (NH?), methane (CH?), carbon dioxide (CO?), and nitrous oxide (N?O). The implementation of air quality regulations in livestock-producing states increases the need for accurate on-farm determination of emission rates. The objective of this study was to determine the emission rates of NH?, CH?, CO?, and N?O from three source areas (open lots, wastewater pond, compost) on a commercial dairy located in southern Idaho. Gas concentrations and wind statistics were measured each month and used with an inverse dispersion model to calculate emission rates. Average emissions per cow per day from the open lots were 0.13 kg NH?, 0.49 kg CH?, 28.1 kg CO?, and 0.01 kg N?O. Average emissions from the wastewater pond (g m(-2) d(-1)) were 2.0 g NH?, 103 g CH?, 637 g CO?, and 0.49 g N?O. Average emissions from the compost facility (g m(-2) d(-1)) were 1.6 g NH?, 13.5 g CH?, 516 g CO?, and 0.90 g N?O. The combined emissions of NH?, CH?, CO?, and N?O from the lots, wastewater pond and compost averaged 0.15, 1.4, 30.0, and 0.02 kg cow(-1) d(-1), respectively. The open lot areas generated the greatest emissions of NH?, CO?, and N?O, contributing 78, 80, and 57%, respectively, to total farm emissions. Methane emissions were greatest from the lots in the spring (74% of total), after which the wastewater pond became the largest source of emissions (55% of total) for the remainder of the year. Data from this study can be used to develop trace gas emissions factors from open-lot dairies in southern Idaho and potentially other open-lot production systems in similar climatic regions.     

Effect of amendment of bauxite processing sand with organic materials on its chemical,physical and microbial properties

The effects of addition of a range of organic amendments (biosolids, spent mushroom compost, green waste compost and green waste-derived biochar), at two rates, on some key chemical, physical and microbial properties of bauxite-processing residue sand were studied in a laboratory incubation study. Levels of exchangeable cations were not greatly affected by additions of amendments but extractable P was increased significantly by mushroom and green waste composts and massively (i.e. from 11.8 to 966 mg P kg^?1) by biosolids applications. Levels of extractable NO₃^?–N were also greatly elevated by biosolids additions and there was a concomitant decrease in pH. Addition of all amendments decreased bulk density and increased mesoporosity, available water holding capacity and water retention at field capacity (?10 kPa), with the higher rate having a greater effect. Addition of biosolids, mushroom compost and green waste compost all increased soluble organic C, microbial biomass C, basal respiration and the activities of β-glucosidase, L-asparaginase and alkali phosphatase enzymes. The germination index of watercress grown in the materials was greatly reduced by biosolids application and this was attributed to the combined effects of a high EC and high concentrations of extractable P and NO₃^?. It was concluded that the increases in water storage and retention and microbial activity induced by additions of the composts is likely to improve the properties of bauxite-processing residue sand as a growth medium but that allowing time for soluble salts, originating from the organic amendments, to leach out may be an important consideration before sowing seeds.     

Greenhouse gas emissions during co-composting of calf mortalities with manure

Composting may be a viable on-farm option for disposal of cattle carcasses. This study investigated greenhouse gas emissions during co-composting of calf mortalities with manure. Windrows were constructed that contained manure + straw (control compost [CK]) or manure + straw + calf mortalities (CM) using two technologies: a tractor-mounted front-end loader or a shredder bucket. Composting lasted 289 d. The windrows were turned twice (on Days 72 and 190), using the same technology used in their creation. Turning technology had no effect on greenhouse gas emissions or the properties of the final compost. The CO2 (75.2 g d(-1) m(-2)), CH4 (2.503 g d(-1) m(-2)), and N2O (0.370 g d(-1) m(-2)) emissions were higher (p < 0.05) in CM than in CK (25.7, 0.094, and 0.076 g d(-1) m(-2) for CO2, CH4, and N2O, respectively), which reflected differences in materials used to construct the compost windrows and therefore their total C and total N contents. The final CM compost had higher (p < 0.05) total N, total C, and mineral N content (NO3*+ NO2* + NH4+) than did CK compost and therefore has greater agronomic value as a fertilizer.     

Tillage and crop residue effects on soil carbon and carbon dioxide emission in corn-soybean rotations

Soil C change and CO2 emission due to different tillage systems need to be evaluated to encourage the adoption of conservation practices to sustain soil productivity and protect the environment. We hypothesize that soil C storage and CO2 emission respond to conservation tillage differently from conventional tillage because of their differential effects on soil properties. This study was conducted from 1998 through 2001 to evaluate tillage effects on soil C storage and CO2 emission in Clarion-Nicollet-Webster soil association in a corn [Zea mays L.]-soybean [Glycine max (L.) Merr.] rotation in Iowa. Treatments included no-tillage with and without residue, strip-tillage, deep rip, chisel plow, and moldboard plow. No-tillage with residue and strip-tillage significantly increased total soil organic C (TC) and mineral fraction C (MFC) at the 0- to 5- and 5- to 10-cm soil depths compared with chisel plow after 3 yr of tillage practices. Soil CO2 emission was lower for less intensive tillage treatments compared with moldboard plow, with the greatest differences occurring immediately after tillage operations. Cumulative soil CO2 emission was 19 to 41% lower for less intensive tillage treatments than moldboard plow, and it was 24% less for no-tillage with residue than without residue during the 480-h measurement period. Estimated soil mineralizable C pool was reduced by 22 to 66% with less intensive tillage treatments compared with moldboard plow. Adopting less intensive tillage systems such as no-tillage, strip-tillage, deep rip, and chisel plow and better crop residue cover are effective in reducing CO2 emission and thus improving soil C sequestration in a corn-soybean rotation.     

Decrease in water-soluble 17beta-Estradiol and testosterone in composted poultry manure with time

Little attention has been paid to the environmental fate of the hormones 17beta-estradiol and testosterone excreted in animal waste. Land application of manure has a considerable potential to affect the environment with these endocrine disrupting compounds (EDCs). Composting is known to decompose organic matter to a stable, humus-like material. The goal of the present study was to quantitatively assess levels of water-soluble 17beta-estradiol and testosterone in composting chicken manure with time. Chicken layer manure was mixed with hay, straw, decomposed leaves, and starter compost, adjusted to approximately 60% moisture, and placed into a windrow. A clay-amended windrow was also prepared. Windrows were turned weekly, and temperature, oxygen, and CO(2) in the composting mass were monitored for either 133 or 139 d. Commercial enzyme immunoassay kits were used to quantitate the levels of 17beta-estradiol and testosterone in aqueous sample extracts. Water-soluble quantities of both hormones diminished during composting. The decrease in 17beta-estradiol followed first-order kinetics, with a rate constant k = -0.010/d. Testosterone levels declined at a slightly higher rate than 17beta-estradiol (i.e., k = -0.015/d). Both hormones could still be measured in aqueous extracts of compost sampled at the conclusion of composting. The decline in water-soluble 17beta-estradiol and testosterone in extracts of clay-amended compost was not statistically different from normal compost. These data suggest that composting may be an environmentally friendly technology suitable for reducing, but not eliminating, the concentrations of these endocrine disrupting hormones at concentrated animal operation facilities.     

Addition of an organic amendment and/or residue mud to bauxite residue sand in order to improve its properties as a growth medium

The effects of addition of carbonated residue mud (RMC) or seawater neutralized residue mud (RMS), at two rates, in the presence or absence of added green waste compost, on the chemical, physical and microbial properties of gypsum-treated bauxite residue sand were studied in a laboratory incubation study. The growth of two species commonly used in revegetation of residue sand (Lolium rigidum and Acacia saligna) in the treatments was then studied in a 18-week greenhouse study. Addition of green waste-based compost increased ammonium acetate-extractable (exchangeable) Mg, K and Na. Addition of residue mud at 5 and 10% w/w reduced exchangeable Ca but increased that of Mg and Na (and K for RMS). Concentrations of K, Na, Mg and level of EC in saturation paste extracts were increased by residue mud additions. Concentrations of cations in water extracts were considerably higher than those in saturation paste extracts but trends with treatment were broadly similar. Addition of both compost and residue mud caused a significant decrease in macroporosity with a concomitant increase in mesoporosity and microporosity, available water holding capacity and the quantity of water held at field capacity. Increasing rates of added residue mud reduced the percentage of sample present as discrete sand particles and increased that in aggregated form (particularly in the 1-2 and >10mm diameter ranges). Organic C content, C/N ratio, soluble organic C, microbial biomass C and basal respiration were increased by compost additions. Where compost was added, residue mud additions caused a substantial increase in microbial biomass and basal respiration. L.?rigidum grew satisfactorily in all treatments although yields tended to be reduced by additions of mud (especially RMC) particularly in the absence of added compost. Growth of A.?saligna was poor in sand alone and mud-amended sand and was greatly promoted by additions of compost. However, in the presence of compost, addition of carbonated mud had a marked depressive effect on both top and root growth. The significant positive effect of compost was attributed to substantial inputs of K and marked reductions in the Na/K ratio in soil solution while the depressive effect of RMC was attributed to its greater alkalinity and consequently higher concentrations of HCO(3)(-) in solution.     

Humic acid formation in artificial soils amended with compost at different stages of organic matter evolution

A composting process was conducted under optimal conditions for 150 d, obtaining three biomasses at different levels of maturity: raw material (RM), fresh compost obtained after 11 d of composting (FC), and evolved compost (EC) obtained after 150 d of composting. During the composting process, HAs were extracted and fully characterized by mass balance, DRIFT, and 1H and 13C-nuclear magnetic resonance spectroscopy. Each compost sample was incubated for 180 d in an artificial soil, after which HA extraction was repeated and characterized. To compare composts containing different amounts of labile organic matter (OM), an equal amount of unhydrolyzable OM was added to the soils. Our results indicated that compost HAs consist of a biologically and chemically stable fraction (i.e., the unhydrolyzable HA [U-HA]) and a labile fraction, whose relative contents depended on the composting duration. Humic acid from more EC contained a higher amount of recalcitrant fraction (aromatic carbon) and a lesser amount of labile fraction (aliphatic carbon) than HA from RM and FC. These results suggest that the humification process during composting preserves the more recalcitrant fraction of the compost-alkali soluble/acid insoluble fraction (HA-fraction). Incubation of composts in soil showed that due to the higher labile fraction content, HAs from raw material were more degraded than those from EC. The abundance of labile carbon of soil amended with less-evolved compost (RM and FC) allowed the more recalcitrant fractions of U-HA to be more preserved than in EC. These results suggest that less-evolved compost could contribute more than well evolved compost to the stable soil OM.     

Effects of cattle slurry acidification on ammonia and methane evolution during storage

Slurry acidification before storage is known to reduce NH(3) emissions, but recent observations have indicated that CH(4) emissions are also reduced. We investigated the evolution of CH(4) from fresh and aged cattle slurry during 3 mo of storage as influenced by pH adjustment to 5.5 with sulfuric acid. In a third storage experiment, cattle slurry acidified with commercial equipment on two farms was incubated. In the manipulation experiments, effects of acid and sulfate were distinguished by adding hydrochloric acid and potassium sulfate separately or in combination, rather than sulfuric acid. In one experiment sulfur was also added to slurry as the amino acid methionine in separate treatments. In each treatment 20-kg portions of slurry (n = 4) were stored for 95 d. All samples were subsampled nine to 10 times for determination of NH(3) and CH(4) evolution rates using a 2-L flow-through system. In all experiments, the pH of acidified cattle slurry increased gradually to between 6.5 and 7. Acidification of slurry reduced the evolution of CH(4) by 67 to 87%. The greatest reduction was observed with aged cattle slurry, which had a much higher potential for CH(4) production than fresh slurry. Sulfate and methionine amendment to cattle slurry without pH adjustment also significantly inhibited methanogenesis, probably as a result of sulfide production. The study suggests that complex microbial interactions involving sulfur transformations and pH determine the potential for CH(4) emission during storage of cattle slurry, and that slurry acidification may be a cost-effective greenhouse gas mitigation option.     

Household organic waste composting using bins with different types of passive aeration

The objective of this study was to study the performances of six 200-L polyethylene bins, each with different design for passive aeration to organic wastes composting. Food scraps and dry leaves (1.6 kg) were added to each bin once a day until the bin was full. Temperatures at the middle portion were measured daily. The compost from each bin was taken once a week for 120 days for analysis of C, N, volatile solids, and a germination index once a week for 120 days. After 120 days, the compost sample from each bin was taken to determine the mass reduction, size distribution, CEC, N, P and K values. The results showed that the temperatures inside the bins were in the ranges of 24 °C-57 °C. The composts in all bins were found to be stable at around 56-91 days. The wastes decayed fastest in bins with lateral and vertical systems of natural ventilation. It took about two months to stabilize the organic wastes, with a 59-62% decrease of mass. The C/N ratio, CEC, N, P, and K values of the final composts were 14.8-16.0, 66-68 cmol/kg, and 1.26-1.50% N, 0.52-0.56% P₂O₅ and 1.66-1.92% K₂O, respectively.     

Quality assessment of composts in the Greek market: the need for standards and quality assurance

An extensive data survey and study of the Greek market for composts or products marketed as such was carried out in order to acquire a comprehensive image of the local situation, in view of the proposed operation of large municipal solid waste (MSW) composting facilities and EU legislation changes. Physical and chemical parameters (moisture, organic matter, electrical conductivity, pH and heavy metals), stability indicators (self-heating potential, germination index) and biological indicators (microbial population, pathogen indicators and selected pathogens) were analyzed for the assessment of product quality. Results revealed wide variations even within the same group of products, which is particularly significant for parameters directly related to environmental protection and public health. The heavy metal content ranged from levels exceeding the fairly lenient Greek standards to below the stringent limits for A+ class compost in Austria. About 25% of the composts examined met the heavy metal limits for the EU eco-label award. Salmonella spp. was not detected in any of the composts but Staphylococcus aureus and Clostridium perfringens were found in 17 and 96% of the composts respectively. Pathogen indicator microorganisms were present at levels above suggested limits in all the composts. The high variability of such important parameters in composts available on the Greek market suggests an urgent need for establishing quality assurance procedures and mechanisms in the country. Moreover, the wide range of limit values within EU member states suggests the need for developing EU compost quality standards, in order to harmonize the compost markets.