Dairy Compost Research Articles

Inactivation of Escherichia coli O157:H7 in Dairy Manure Compost with Alkaline Walnut Hull Biochar.

Biochar has been used to accelerate heating profiles during composting by increasing oxygenation, which could also reduce microbial pathogens. However, the antimicrobial inactivation of foodborne pathogens in compost, by amending with biochar without increased heating profiles, has not been evaluated. In this study, we examined the ability of biochar to inactivate E. coli O157:H7 (EC) in fresh dairy manure compost by amending with one of four types of biochar. Two slow pyrolysis biochars (high temperature walnut hull biochar [HTWHB], and walnut hull cyclone biochar [WHCB]), and two fast pyrolysis biochars were examined. Compost with 8.1 log CFU/g of EC + 10% amended biochar was held at 22°C and analyzed for EC weekly. The control treatment sustained ca. 8.7 log CFU of EC through week 7; however, the bacterium was not detected by direct plating in WHCB compost (below the detection limit) by day 7, through the entire 49 days (which may be attributed to increased compost alkalinity [i.e., pH 10.76]). Populations of EC in compost supplemented with 10% of the three other biochars sustained EC populations ≥ 9.2 log through the balance of the study. The four biochars were further tested in soil at 17% moisture to determine if concentrations as low as 3.5% could inactivate EC. When 3.5% HTWHB was added to soil, populations were 5.1 log CFU lower than when 10% of the same biochar was amended into dairy compost by week 3. This may indicate that alkaline biochar, amended into lower moisture, soil may be more biocidal than when alkaline biochar is added to high moisture manure compost. The current study demonstrates that highly alkaline walnut hull cyclone biochar is capable of reducing up to 8 log of EC in high moisture fresh compost in only 7 days, while as little as 3.5% alkaline WHCB in 17% moisture soil can reduce 6.7 log of EC in only 14 days. These results may assist farmers in amending compost, manure, cattle feedlots, or soil with biochar to reduce EC, and potentially other pathogens (e.g., Salmonella enterica, Campylobacter jejuni, and Listeria monocytogenes), with the goal of reducing the dissemination of human bacterial pathogens to meat, poultry, and fresh produce.

Biological Control of Escherichia coli O157:H7 in Dairy Manure-Based Compost Using Competitive Exclusion Microorganisms.

Animal manure-based compost is a valuable organic fertilizer and biological soil amendment. To ensure the microbiological safety of compost products, the effectiveness of competitive exclusion microorganisms (CE) in reducing Escherichia coli O157:H7 in dairy manure-based compost was evaluated. A cocktail of E. coli O157:H7 strains were inoculated into dairy compost along with CE strains isolated from compost, and the reduction in E. coli O157:H7 by CE was determined in compost with 20%, 30%, and 40% moisture levels at 22 °C and 30 °C under laboratory conditions, as well as in fall, winter, and summer seasons under greenhouse settings. Under lab conditions, CE addition resulted in 1.1-3.36 log reductions in E. coli O157:H7 in compost, with enhanced pathogen reduction by higher moisture and lower temperature. In the greenhouse, >99% of the E. coli O157:H7 population in compost with ≥30% moisture due to cross-contamination can be effectively inactivated by CE within 2 days during colder seasons. However, it took ≥8 days to achieve the same level of reduction for heat-adapted E. coli O157:H7 cells. Our results demonstrated that the competitive exclusion of microorganisms can be an effective tool for controlling foodborne pathogens in compost and reducing the potential for soil and crop contamination.

Survival of Clostridioides difficile in finished dairy compost under controlled conditions.

The survival of Clostridioides difficile (previously Clostridium difficile) vegetative cells and endospores was compared at different levels of indigenous microflora using autoclaved and unautoclaved dairy composts with different moisture contents (MCs). Both types of composts adjusted to 20, 30 and 40% MCs were inoculated with a suspension of C. difficile that contained both vegetative cells (c.5-6 log CFU per gram) and endospores (c.5·0CFU per gram), and then stored aerobically inside a humidity-controlled chamber at room temperature 22·5±0·8°C for 1year. The level of indigenous microflora was very stable during the storage after day 7 in both types of compost. The greatest reductions of C. difficile vegetative cell counts occurred during the first 24h of storage in autoclaved and unautoclaved composts, which had 4·7 and 5·5 log CFU per gram with 20% MC, 1·8 and 2·1 log CFU per gram with 30% MC, and 2·3 and 1·3 log CFU per gram with 40% MC, respectively. Both MC and the duration of storage have significant (P<0·05) effects on the survival of vegetative cells for first 120days of storage. The slow inactivation of C. difficile vegetative cells at higher MCs during aerobic storage was confirmed by exponentially decaying modelling data during the early stage of aerobic exposure. The reduction of endospore counts (<1·0 log CFU per gram) during the storage for both types of compost at all MCs was not significant (P>0·05) except for the autoclaved compost with 30% MC. The highly resistant C. difficile endospores to the unfavourable environmental conditions survived for more than a year while vegetative cells died off exponentially upon the initial aerobic exposure. The long-term survival of C. difficile endospores in contaminated compost may transmit the pathogen to fresh produce, animals or water in pre-harvest conditions.

Bacterial Community Dynamics Distinguish Poultry Compost from Dairy Compost and Non-Amended Soils Planted with Spinach

The aim of this study was to determine whether and how poultry litter compost and dairy manure compost alter the microbial communities within field soils planted with spinach. In three successive years, separate experimental plots on two fields received randomly assigned compost treatments varying in animal origin: dairy manure (DMC), poultry litter (PLC), or neither (NoC). The composition and function of bacterial and fungal communities were characterized by the amplicon sequencing of marker genes and by the ecoenzyme activity, respectively. The temporal autocorrelation within and among years was adjusted by principal response curves (PRC) to analyze the effect of compost on community composition among treatments. Bacteria in the phylum Bacteriodetes, classes Flavobacteriia and Spingobacteriales (Fluviicola, Flavobacteriia, and Pedobacter), were two to four times more abundant in soils amended with PLC than DMC or NoC consistently among fields and years. Fungi in the phylum Ascomycota were relatively abundant, but their composition was field-specific and without treatment differences. The ecoenzyme data verify that the effects of PLC and DMC on soil communities are based on their microbial composition and not a response to the C source or nutrient content of the compost.

Production, morphology and chemical-bromatological characteristics of Urochloa brizantha cv. Marandu under doses of compost from dairy cows

Confinement of dairy cows in Brazil is significant, with the compost badded pack barn being the most used model, generating a large amount of good quality organic compost that can be used as a fertilizer in the pastures of the farms, reducing the use of industrialized fertilizers and mitigating the environmental impacts of dairy activity. An experiment was carried out in pots under greenhouse conditions to evaluate the effect of compost doses on the production, morphology and chemical-bromatological characteristics of Urochloa brizantha cv. Marandu A completely randomized design with 3 replications and 6 treatments consisting of 6 doses of the compost: 0; 50; 10; 20; 40 and 80 g.vaso-1. Increasing compost doses resulted in higher dry matter yield, higher tillers density and higher potassium and phosphorus contents in the forage. Dairy cow compost can be used for pasture fertilization, partially replacing industrialized fertilizers.

Impact of novel materials on alkalinity movement down acid soil profiles when combined with lime

Subsurface soil acidity in conjunction with aluminium (Al3+) toxicity is a major limitation to agricultural production globally. The conventional use of surface-applied lime is often insufficient at correcting subsurface acidity; therefore, new practices and ameliorants are required. This 3-month leaching experiment investigated whether animal wastes and other novel ameliorants in combination with lime could improve alkalinity movement, leading to greater amelioration of acid subsurface soil layers compared with lime alone. Five ameliorants (mature dairy compost, vegetable garden compost, poultry litter, potassium humate and gypsum) were added at a rate of 18 mg dry matter g−1 to the topsoil layer either without or with lime (target pH 5.5). All ameliorants with lime improved alkalinity movement below the amended layer (0–10 cm), with pH increases of 0.03–0.10 units at 1 month and 0.02–0.20 units at 3 months. In comparison, the Al3+ concentrations in 10–12-cm and 12–15-cm layers were significantly decreased by 2–5.5 μg g−1. With lime, the improvements in alkalinity movement with ameliorants were in the order of gypsum > vegetable garden compost > potassium humate > poultry litter > mature dairy compost. Without lime, each amendment increased soil pH in the subsoil, with their effectiveness decreasing in the order of poultry litter > vegetable garden compost > mature dairy compost > gypsum > potassium humate. Some organic amendments are effective in addressing subsoil acidity. When combined with lime, their additive effects are limited.

Soil organic matter, greenhouse gas emissions, and sorghum yield in semi‐arid drylands

AbstractSorghum [Sorghum bicolor (L.) Moench] serves as a low‐cost alternative to corn (Zea mays L.) in semi‐arid regions of the world because of its high N and water use efficiencies. However, there has been a concern regarding N loss to the atmosphere as nitrous oxide (N2O) from semi‐arid drylands. This study investigated various soil C and N components, including CO2 and N2O emissions, and crop yield with a dairy compost (13.5 Mg ha−1) and four rates of chemical N fertilizer (0, 22.4, 44.8, and 67.3 kg ha−1) in dryland sorghum. There was no significant difference in soil C and N fractions among N fertilizer rates, although compost addition numerically increased soil C storage and 67.3 kg ha−1 N rate resulted the highest yield in both years. Potential nitrogen mineralization (PNM) was negatively related to crop yield and positively related to grain N content. Soils with greater inorganic N and PNM had a lower carbon dioxide (CO2) emissions, while soils with greater potential C mineralization (PCM) had lower N2O emissions. The results of this study show no significant improvements in yield of dryland sorghum in the semi‐arid environment of southern Great Plains in the short term. However, compost and 44.8 kg N ha−1 applications appeared to be beneficial when both yield and quality were compared.

Linking Soil Health to Sustainable Crop Production: Dairy Compost Effects on Soil Properties and Sorghum Biomass

Dairy compost is utilized in agricultural fields to supplement nutrients, yet its role in optimizing nutrient supply and health of semiarid soils is not clear. A greenhouse study was conducted over two months to evaluate soil properties and forage sorghum production under various compost rates. The study had six treatments and four replications. Treatments included compost application rates at 6.7 (C1), 13.5 (C2), 20.2 (C3), 26.9 (C4), and 33.6 Mg ha−1 (C5) and a control (C0). Soil samples were analyzed for soil organic carbon (SOC), potentially mineralizable carbon (PMC), total nitrogen (N), inorganic N, potentially mineralizable N (PMN), available phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Plant biomass production and biomass C, N, and lignin contents were also estimated. High compost rates improved soil properties significantly (p &lt; 0.05) indicated by increased SOC, N, P, K, Ca, and cation exchange capacity (CEC). Sorghum biomass production did not increase significantly with compost rate, while shoot N content increased at higher rates of compost. A nutrient management plan that integrates dairy compost application has potential to improve soil health and support sustainable forage production in semiarid regions.

Improving culture media for the isolation of Clostridium difficile from compost

This study was to optimize the detection methods for Clostridium difficile from the animal manure-based composts. Both autoclaved and unautoclaved dairy composts were inoculated with a 12-h old suspension of a non-toxigenic C. difficile strain (ATCC 43593) and then plated on selected agar for vegetative cells and endospores. Six types of enrichment broths supplemented with taurocholate and l-cysteine were assessed for detecting a low level of artificially inoculated C. difficile (ca. 5 spores/g) from dairy composts. The efficacy of selected enrichment broths was further evaluated by isolating C. difficile from 29 commercial compost samples. Our results revealed that using heat-shock was more effective than using ethanol-shock for inducing endospore germination, and the highest endospore count (p < 0.05) was yielded at 60 °C for 25 min. C. difficile agar base, supplemented with 0.1% l-cysteine, 7% defibrinated horse blood, and cycloserine-cefoxitin (CDA-CYS-H-CC agar) was the best medium (p < 0.05) for recovering vegetative cells from compost. C. difficile endospore populations from both types of composts enumerated on both CDA-CYS-H-CC agar supplemented with 0.1% sodium taurocholate (CDA-CYS-H-CC-T agar) and brain heart infusion agar supplemented with 0.5% yeast extract, 0.1% l-cysteine, cycloserine-cefoxitin, and 0.1% sodium taurocholate (BHIA-YE-CYS-CC-T agar) media were not significantly different from each other (p > 0.05). Overall, enrichment of inoculated compost samples in broths containing moxalactam-norfloxacin (MN) produced significantly higher (p < 0.05) spore counts than in non-selective broths or broths supplemented with CC. Enrichment in BHIB-YE-CYS-MN-T broth followed by culturing on an agar containing 7% horse blood and 0.1% taurocholate provided a more sensitive and selective combination of media for detecting a low population of C. difficile from environmental samples with high background microflora.

Persistence of Non-O157 Shiga Toxin–Producing Escherichia coli in Dairy Compost during Storage

Dairy compost with 20, 30, or 40% moisture content (MC) was inoculated with a mixture of six non-O157 Shiga toxin-producing Escherichia coli (STEC) serovars at a final concentration of 5.1 log CFU/g and then stored at 22 and 4°C for 125 days. Six storage conditions-4°C and 20% MC, 4°C and 30% MC, 4°C and 40% MC, 22°C and 20% MC, 22°C and 30% MC, and 22°C and 40% MC-were investigated for the persistence of non-O157 STEC in the dairy compost. During the entire storage, fluctuations in indigenous mesophilic bacterial levels were observed within the first 28 days of storage. After inoculation, the non-O157 STEC population increased 0.69 and 0.79 log CFU/g in the dairy compost with 30 and 40% MC at 22°C within the first day, respectively; for all other storage conditions, the pathogen population decreased rapidly. After the 125-day storage, the reductions of non-O157 STEC for 4°C and 20% MC, 4°C and 30% MC, 4°C and 40% MC, 22°C and 20% MC, 22°C and 30% MC, and 22°C and 40% MC storage conditions were >4.52, >4.55, 3.89, >4.61, 3.60, and 3.17 log CFU/g, respectively. All the survival curves showed an extensive tail, indicating non-O157 STEC can survive at least for 125 days in the dairy compost. The survival data were analyzed with log-linear with tailing and Weibull models. Compared with the log-linear with tailing model, the Weibull model was found to be a better choice for predicting the survival of non-O157 STEC in dairy compost owing to a high overall R2 value (0.8738 to 0.9909). The decay rate of non-O157 STEC was higher in dairy compost stored at 4°C compared with at 22°C, and the same trend was found for the compost with 40% MC versus 20% MC. In addition, two non-O157 STEC serotypes (STEC O145 and O45) were detected on the last day of the longitudinal study and may deserve special attention in the Big 6 STEC group. Our results have provided scientific data for risk assessment of the microbiological safety of dairy compost to control non-O157 STEC during subsequent storage of dairy compost.

Improving the Enrichment and Plating Methods for Rapid Detection of Non-O157 Shiga Toxin–Producing Escherichia coli in Dairy Compost

A culture method to detect non-O157 Shiga toxin-producing Escherichia coli (STEC) was optimized in this study. The finished dairy compost with 30% moisture content was inoculated with a cocktail of six non-O157 STEC serovars at initial concentrations of 1 to 100 CFU/g. Afterward, non-O157 STEC cells in the inoculated dairy compost were enriched by four methods, followed by plating onto cefixime-tellurite sorbitol MacConkey agar supplemented with 5 mg/liter novobiocin (CTNSMAC) and modified Rainbow agar containing 5 mg/liter novobiocin, 0.05 mg/liter cefixime trihydrate, and 0.15 mg/liter potassium tellurite (mRBA). Immunomagnetic bead separation (IMS) was used to compare the cell concentration of individual non-O157 STEC serotypes after enrichment. There was no significant difference (P > 0.05) between CTN-SMAC and mRBA for non-O157 STEC enumeration. The single-step selective enrichment recovered ca. 0.54 log CFU/g more cells (ca. 0.41 log CFU/g for compost-adapted cells) (P < 0.05) compared with the two-step enrichment. Furthermore, the duration of the process to detect non-O157 STEC from dairy compost by selective enrichment, followed by IMS, was optimized. Among six non-O157 STEC serotypes, serotypes O111, O45, and O145 reached the highest cell density after enrichment in dairy compost, and the cell populations reached 7.3, 7.4, and 7.8 log CFU/g within 16 h of incubation, respectively. In contrast, without an enrichment step, the IMS detection limit of individual non-O157 STEC serovars ranged from 3.15 to 4.15 log CFU/g in dairy compost. These results demonstrate that low levels of non-O157 STEC can be detected within 2 days from dairy compost by using a culture method with an optimized enrichment procedure followed by IMS.

Factors Affecting Pathogen Survival in Finished Dairy Compost with Different Particle Sizes Under Greenhouse Conditions.

This study investigated the survival of Escherichia coli O157:H7 and Salmonella Typhimurium in finished dairy compost with different particle sizes during storage as affected by moisture content and temperature under greenhouse conditions. The mixture of E. coli O157:H7 and S. Typhimurium strains was inoculated into the finished composts with moisture contents of 20, 30, and 40%, separately. The finished compost samples were then sieved into 3 different particle sizes (>1000, 500-1000, and <500 μm) and stored under greenhouse conditions. For compost samples with moisture contents of 20 and 30%, the average Salmonella reductions in compost samples with particle sizes of >1000, 500-1000, and <500 μm were 2.15, 2.27, and 2.47 log colony-forming units (CFU) g(-1) within 5 days of storage in summer, respectively, as compared with 1.60, 2.03, and 2.26 log CFU g(-1) in late fall, respectively, and 2.61, 3.33, and 3.67 log CFU g(-1) in winter, respectively. The average E. coli O157:H7 reductions in compost samples with particle sizes of >1000, 500-1000, and <500 μm were 1.98, 2.30, and 2.54 log CFU g(-1) within 5 days of storage in summer, respectively, as compared with 1.70, 2.56, and 2.90 log CFU g(-1) in winter, respectively. Our results revealed that both Salmonella and E. coli O157:H7 in compost samples with larger particle size survived better than those with smaller particle sizes, and the initial rapid moisture loss in compost may contribute to the fast inactivation of pathogens in the finished compost. For the same season, the pathogens in the compost samples with the same particle size survived much better at the initial moisture content of 20% compared to 40%.

Expression of Stress and Virulence Genes in Escherichia coli O157:H7 Heat Shocked in Fresh Dairy Compost

The purpose of this study was to determine the gene expression of Escherichia coli O157:H7 heat shocked in dairy compost. A two-step real-time PCR assay was used to evaluate the expression of stress and virulence genes in E. coli O157:H7 heat shocked in compost at 47.5°C for 10 min. Heat-shocked E. coli O157:H7 in compost was isolated by using an immunomagnetic bead separation method, followed by total RNA extraction, which was then converted to cDNA by using a commercial kit. E. coli O157:H7 heat shocked in broth served as the media control. In compost, heat shock genes (clpB, dnaK, and groEL) and the alternative sigma factor (rpoH) of E. coli O157:H7 were upregulated (P < 0.05), whereas the expression of trehalose synthesis genes did not change. Virulence genes, such as stx1 and fliC, were upregulated, while genes stx2, eaeA, and hlyA were down-regulated. In the toxin-antitoxin (TA) system, toxin genes, mazF, hipA, and yafQ were upregulated, whereas among antitoxin genes, only dinJ was upregulated (P < 0.05). In tryptic soy broth, all heat shock genes (rpoH, clpB, dnaK, and groEL) were upregulated (P < 0.05), and most virulence genes (stx1, stx2, hlyA, and fliC) and TA genes (mazF-mazE, hipA-hipB, and yafQ-dinJ and toxin gene chpS) were down-regulated. Our results revealed various gene expression patterns when E. coli O157:H7 inoculated in compost was exposed to a sublethal temperature. Clearly, induction of the heat shock response is one of the important protective mechanisms that prolongs the survival of pathogens during the composting process. In addition, other possible mechanisms (such as the TA system) operating along with heat shock response may be responsible for the extended survival of pathogens in compost.

Cured Dairy Compost Influence on Weed Competition and on ‘Snowden' Potato Yield

Potatoes are an important global food crop typically produced in high-input systems in temperate zones. Growers that have access to compost may use it to improve soil health and increase tuber yields, but compost may also increase weed competition by increasing early-season water availability and weed growth. A field study at the Michigan State University Montcalm Research farm in 2010 and 2011 investigated the impact of compost on weed competition in potato. Potatoes were grown in field plots with 0, 4,000, or 8,000 kg carbon (C) ha−1of compost under weed-free conditions, and in competition with common lambsquarters, giant foxtail, and hairy nightshade. Compost did not increase biomass or seed production of any weed species. Giant foxtail and hairy nightshade at 5.3 plants per meter of row reduced potato yield by 20%; common lambsquarters reduced yield by 45%. The yield reduction by giant foxtail and hairy nightshade was due to a decrease in tuber bulking, whereas yield reductions from common lambsquarters were a result of lower tuber set and bulking. Potato yield increased 5 to 15% in compost compared to non-compost treatments; tuber specific gravity decreased by 0.3% in composted treatments. Across weed densities, elevated soil potassium levels in the 8,000 kg C ha−1composted treatment may have increased potato yield and decreased tuber specific gravity.

Thermal Inactivation of Acid-AdaptedEscherichia coliO157:H7 in Dairy Compost

It is well documented that stress-adapted microorganisms can develop cross-resistance to other unrelated stress. This study was designed to evaluate the thermal resistance of acid-adapted Escherichia coli O157:H7 in both fresh and finished dairy composts. A three-strain mixture of E. coli O157:H7, either acid-adapted or non-adapted (control), was inoculated into dairy compost to a final concentration of approximately 10(7) CFU/g. The inoculated compost was kept in an environmental chamber which was programmed to raise temperature from room to target temperatures (50°C, 55°C, and 60°C) in 2 days, simulating the early phase of composting. In fresh dairy compost with 2 days of come-up time, acid-adapted and control E. coli O157:H7 survived for 19 and 17 days at 50°C, respectively, and 6 and 4 days for both types of culture at 55°C and 60°C, respectively. Overall, pathogen survival was non-significant (p>0.05) between control and acid-adapted cultures at all tested temperatures. In finished compost, the same trend in pathogen survival between control and acid-adapted cultures was observed at 55°C. However, the duration of survival for both cultures was short in comparison to that in fresh compost. In fresh compost with short come-up time (15 min), acid-adaptation provided E. coli O157:H7 some cross-protection to heat at 55°C up to 30 min of exposure. The effect of heating medium on thermal resistance of acid-adapted E. coli O157:H7 revealed that in saline, acid-adapted E. coli O157:H7 was inactivated slower (p<0.05) with 0.5 and 1 h of heat exposure at 55°C as compared to control culture. Our results revealed that cross-protection against heat in E. coli O157:H7 due to acid-adaptation was demonstrated in saline but lost in fresh dairy compost with 2 days of come-up time during composting. Additionally, the type of compost and heating medium can influence the rate of pathogen inactivation at composting temperatures.

Residual Effects of Fresh and Composted Dairy Manure Applications on Potato Production

Potato growers in Idaho and other dairy producing regions often grow potatoes on fields that have had a history of fresh and composted manure applications. Growers remain uncertain of the impacts that previous manure applications will have on tuber yield and quality, as well as diseases, physiological disorders, and contamination by human pathogenic bacteria such as E. coli. The focus of this study was to determine the long term effects of manure, compost, and chemical phosphorus (P) fertilizer applications on tuber yields, tuber quality, nutrient uptake, tuber disorders and diseases, and soil nutrient concentrations. Russet Burbank potatoes were grown in 2008 and 2009 on plots that had received dairy manure, dairy compost, P fertilizer, or no P source (control) at the same target P rate in 2003, 2004, and 2005. Compared with the P fertilizer treatment, applications of manure and/or compost significantly increased total yields, soil potassium (K), soil nitrate (NO3-N), early season petiole P, and late season petiole K in at least one year of the two-year study. There were no significant differences between P fertilizer, manure, and compost treatments on soil test P, late season petiole P, early season petiole K, E. coli populations on tuber surfaces, common tuber diseases and disorders, and tuber quality. Based on our findings, tuber yields significantly increased three years after applications of fresh and composted dairy manure, while tuber diseases, disorders, and quality were not affected.

Microbial Profiling of Cultural Systems for Suppression of Phytophthora Root Rot in Fraser Fir.

Phytophthora root rot of Fraser fir, caused by several Phytophthora spp., is a severe problem in Christmas tree production. Since fungicides are not economically viable for disease management in field plantings and host resistance is not available, cultural control methods were investigated. Mulches, dairy compost, and soil pH adjustment were tested at five field sites in North Carolina. Treatments included wood chips, wood chips plus compost, or pine bark as raised beds, and compost or sulfur tilled into soil. Soil and mulch microbial populations were characterized by dilution plating and calculation of a log series diversity index, and by enzyme analyses at 5, 12, 17, and 24 months after planting. Bacterial and fungal counts, microbial activity, and cellulase activity were higher in mulch than in soil at all sites and times (P < 0.01), and generally did not differ among mulch types or among soils. Treatments significantly affected disease ratings and tree survival at three of five sites, with one or more mulch treatments yielding lower disease ratings and greater survival than controls. Tree mortality at each time point varied significantly with cellulase activity in the upper root zone (P = 0.005). Other biological variables did not show significant relationships with disease ratings or mortality.

Determining thermal inactivation of Escherichia coli O157:H7 in fresh compost by simulating early phases of the composting process.

A three-strain mixture of Escherichia coli O157:H7 was inoculated into fresh dairy compost (ca. 10(7) CFU/g) with 40 or 50% moisture and was placed in an environmental chamber (ca. 70% humidity) that was programmed to ramp from room temperature to selected composting temperatures in 2 and 5 days to simulate the early composting phase. The surviving E. coli O157:H7 population was analyzed by direct plating and enrichment. Optimal and suboptimal compost mixes, with carbon/nitrogen (C/N) ratios of 25:1 and 16:1, respectively, were compared in this study. In the optimal compost mix, E. coli O157:H7 survived for 72, 48, and 24 h in compost with 40% moisture and for 72, 24, and 24 h with 50% moisture at 50, 55, and 60°C, respectively, following 2 days of come-up time (rate of heating up). However, in the suboptimal compost mix, the pathogen survived for 288, 72, and 48 h in compost with 40% moisture and for 240, 72, 24 h in compost with 50% moisture at the same temperatures, respectively. Pathogen survival was longer, with 5 days of come-up time compared with 2 days of come-up. Overall, E. coli O157:H7 was inactivated faster in the compost with 50% moisture than in the compost with 40% at 55 and 60°C. Both moisture and come-up time were significant factors affecting Weibull model parameters. Our results suggest that slow come-up time at the beginning of composting can extend pathogen survival during composting. Additionally, both the C/N ratio and the initial moisture level in the compost mix affect the rate of pathogen inactivation as well.

Chrysanthemum Production in Composted and Noncomposted Organic Waste Substrates Fertilized with Nitrogen at Two Rates Using Surface and Subirrigation

As nursery and greenhouse growers adopt more sustainable production practices, interest has grown in local, recycled organic materials (ROM) as partial or complete substitutes for peat in container substrates. Chrysanthemum ×morifolium Ramat. ‘Shasta’ was grown in substrates formulated from ROM: 1) 100% Groco, an anaerobically digested biosolids composted with sawdust; 2) 100% Tagro, a thermophilically digested class A biosolid mixed with sawdust and sand; 3) 100% dairy compost, the solids screened from dairy manure slurry and then composted; 4) 100% dairy fiber, the solids fraction from an anaerobic dairy manure digester; 5) 50% Groco:50% douglas-fir bark (mixed by volume); 6) 50% Tagro:50% bark; 7) 50% dairy compost:50% bark; 8) 50% dairy fiber:50% bark; and 9) the control, a commercial peat–perlite mixture. Soluble fertilizer [200 mg·L−1 nitrogen (N)] was applied every second day (high N) or every fourth day (low N). Water was applied through capillary mat subirrigation or overhead sprinkler surface irrigation. Surface irrigation and high N produced shoot dry weight, shoot growth index (SGI), quality, and flower bud counts similar to controls in all ROMs but Groco. Groco SGI was similar to the control but the other parameters were lower. Surface-irrigated, low N shoot dry weight, SGI, and flower buds in all ROM equaled or exceeded the control and quality was similar to or better than controls in all but dairy compost:bark. Subirrigated and high N substrate comparisons indicated that growth, quality, and flower bud measurements were similar to the control except for Groco in which performance was reduced. Low N rate subirrigation produced dry weight, SGI, quality, and flower buds similar to or better than the control in all but the Groco and dairy compost:bark substrates. The generally inferior performance in Groco is likely the result of its low water-holding capacity. In substrates with higher available N (Groco, Tagro, Tagro:bark, and dairy fiber), plant growth parameters generally did not respond to doubling the applied N; in the other substrates, including the control, growth generally increased in response to additional N. Measured differences in leaf color across treatments were not large. Root growth of plants in the experimental substrates was similar to the control in both irrigation systems. Substrate effects on leachate nitrate-N were small and inconsistent. When properly constituted, biosolids and dairy manure can be used as substrates under reduced fertilization with both surface and subirrigation systems.

The growth potential of Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes in dairy manure-based compost in a greenhouse setting under different seasons

The pathogen growth in dairy compost was studied in a greenhouse setting under different seasons. The five-strain mixtures of each Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes were inoculated separately into dry compost to yield c.1 log CFU g(-1) . After acclimation at room temperature, the inoculated compost was initially adjusted to moisture levels of 10-50% and then kept in a greenhouse under different seasons. The populations of all three pathogens increased by 2·1-3·9log CFU g(-1) within 3 days in autoclaved compost with initial moisture content of at least 40%. Listeria monocytogenes multiplied up to 2·4 log CFU g(-1) in compost with initial moisture content of 30% and was detected up to 28 days for all seasons, whereas populations of both E. coli O157:H7 and Salmonella increased by c. 1 log in compost with initial moisture content of 30% during winter months only. No pathogen growth in nonautoclaved compost was detected. Bacterial species, temperature, light intensity and moisture content affected the growth potential and survival of pathogens in compost when the population of background microflora was low. Keeping compost as dry as possible and maintaining certain levels of background microflora may be critical to prevent the growth of pathogens.