Salmonella in animal slurry can be destroyed by aeration at low temperatures

Cattle and other animals infected by Salmonella can emit high numbers of these bacteria. To determine an effective means for reducing this bacterial group in animal slurry, samples were subjected to aeration in laboratory experiments and in farm-scale slurry tanks. A clear reduction in Salmonella levels was found in laboratory experiments at temperatures from 4 to 40 °C. Aeration in farm-scale slurry tanks increased the temperature above the ambient temperatures (often less than 0 °C) to maxima ranging between 19 and 40 °C. Farm-scale aeration resulted in similar reductions in Salmonella as those achieved in laboratory experiments. Thus, reductions, ranging from greater than 99% of the initial number to no detectable Salmonella , could be reached after 2–5 weeks using aeration processes with cattle slurries contaminated by Salm. infantis or pig slurry contaminated by Salm. typhimurium . These results suggest that farmers can control the spread of Salmonella from slurry to agricultural fields. The reduction mechanisms remain unknown, though the increase in pH (to 7·6–9·0) found in slurries after aeration might exert a decreasing effect on these bacteria.     

Solid-state fermentation for gluconic acid production from sugarcane molasses by Aspergillus niger ARNU-4 employing tea waste as the novel solid support

Solid-state fermentation (SSF) was evaluated to produce gluconic acid by metal resistant Aspergillus niger (ARNU-4) strain using tea waste as solid support and with molasses based fermentation medium. Various crucial parameters such as moisture content, temperature, aeration and inoculum size were derived; 70% moisture level, 30 degrees C temperature, 3% inoculum size and an aeration volume of 2.5l min(-1) was suited for maximal (76.3 gl(-1)) gluconic acid production. Non-clarified molasses based fermentation media was utilized by strain ARNU-4 and maximum gluconic acid production was observed following 8-12 days of fermentation cycle. Different concentrations of additives viz. oil cake, soya oil, jaggary, yeast extract, cheese whey and mustard oil were supplemented for further enhancement of the production ability of microorganism. Addition of yeast extract (0.5%) was observed inducive for enhanced (82.2 gl(-1)) gluconic acid production.     

Survival of Escherichia coli O157:H7 in the rhizosphere of maize grown in waste-amended soil

AIMS: To assess whether the persistence of Escherichia coli O157:H7 in soil amended with cattle slurry and ovine stomach content waste is affected by the presence of a maize rhizosphere. METHODS AND RESULTS: Cattle slurry and ovine stomach content waste were inoculated with E. coli O157:H7. Wastes were then applied to soil cores with and without established maize plants. The pathogen survived in soil for over 5 weeks, although at significantly greater numbers in soil receiving stomach content waste in comparison to cattle slurry. Persistence of the pathogen in soil was unaffected by the presence of a rhizosphere. CONCLUSIONS: Other factors may be more influential in regulating E. coli O157:H7 persistence in waste-amended soil than the presence or absence of a rhizosphere; however, waste type did have significant affect on the survival of E. coli O157:H7 in such soil. SIGNIFICANCE AND IMPACT OF THE STUDY: Escherichia coli O157:H7 can be present within animal-derived organic wastes that are routinely spread on land. Introduced measures with regards to such waste disposal may decrease exposure to the organism; however, the persistence of E. coli O157:H7 for considerable periods in waste-amended soil may still pose some risk for both human and animal infection. This study has shown that whilst survival of E. coli O157:H7 in waste-amended soil is not significantly affected by the presence or absence of a maize rhizosphere; it may vary significantly with waste type. This may have implications for land and waste management.     

Effect of aeration rate and waste load on evolution of volatile fatty acids and waste stabilization during thermophilic aerobic digestion of a model high strength agricultural waste

Thermophilic aerobic digestion (TAD) is a relatively new, dynamic and versatile low technology for the economic processing of high strength waste slurries. Waste so treated may be safely disposed of or reused. In this work a model high strength agricultural waste, potato peel, was subjected to TAD to study the effects of oxygen supply at 0.1, 0.25, 0.5 and 1.0 vvm (volume air per volume slurry per minute) under batch conditions at 55 degrees C for 156 h on the process. Process pH was controlled at 7.0 or left unregulated. Effects of waste load, as soluble chemical oxygen demand (COD), on TAD were studied at 4.0, 8.0, 12.0 and 16.0 gl(-1) (soluble COD) at pH 7.0, 0.5 vvm and 55 degrees C. Efficiency of treatment, as degradation of total solids, total suspended solids and soluble solid, as well as soluble COD significantly increased with aeration rate, while acetate production increased as the aeration rate decreased or waste load increased, signifying deterioration in treatment. Negligible acetate, and no other acids were produced at 1.0 vvm. Production of propionate and other acids increased after acetate concentration had started to decrease and, during unregulated reactions coincided with the drop in the pH of the slurry. Acetate production was more closely associated with periods of oxygen limitation than were other acids. Reduction in oxygen availability led to deterioration in treatment efficiency as did increase in waste load. These variables may be manipulated to control treated waste quality.     

Immobilisation, remineralisation and residual effects in subsequent crops of dairy cattle slurry nitrogen compared to mineral fertiliser nitrogen

About 50–60% of dairy cattle slurry nitrogen is ammonium N. Part of the ammonium N in cattle slurry is immobilised due to microbial decomposition of organic matter in the slurry after application to soil. The immobilisation and the remineralisation influence the fertiliser value of slurry N and the amount of organic N that is retained in soil. The immobilisation and the remineralisation of 15 N-labelled dairy cattle slurry NH₄-N were studied through three growing seasons after spring application under temperate conditions. Effects of slurry distribution (mixing, layer incorporation, injection, surface-banding) and extra litter straw in the slurry on the plant utilisation of labelled NH₄-N from slurry were studied and compared to the utilisation of ¹⁵N-labelled mineral fertiliser. The initial immobilisation of slurry N was influenced by the slurry distribution in soil. More N was immobilised when the slurry was mixed with soil. Surface-banding of slurry resulted in significant volatilisation losses and less residual ¹⁵N in soil. Much more N was immobilised after slurry incorporation than after mineral fertiliser application. After 2.5 years the recovery of labelled N in soil (0–25 cm) was 46% for slurry mixed with soil, 42% for injected slurry, 22% for surface-banded slurry and 24% for mineral fertiliser N. The total N uptake in a ryegrass cover crop was 5–10 kg N/ha higher in the autumn after spring-application of cattle slurry (100–120 kg NH₄-N/ha) compared to the mineral fertiliser N reference, but the immobilised slurry N (labelled N) only contributed little to the extra N uptake in the autumn. Even in the second autumn after slurry application there was an extra N uptake in the cover crop (0–10 kg N/ha). The residual effect of the cattle slurry on spring barley N uptake was insignificant in the year after slurry application (equivalent to 3% of total slurry N). Eighteen months after application, 13% of the residual ¹⁵N in soil was found in microbial biomass whether it derived from slurry or mineral fertiliser, but the remineralisation rate (% crop removal of residual ¹⁵N) was higher for fertiliser- than for slurry-derived N, except after surface-banding. Extra litter straw in the slurry had a negligible influence on the residual N effects in the year after application. It is concluded that a significant part of the organic N retained in soil after cattle slurry application is derived from immobilised ammonium N, but already a few months after application immobilised N is stabilised and only slowly released. The immobilised N has negligible influence on the residual N effect of cattle slurry in the first years after slurry application, and mainly contributes to the long-term accumulation of organic N in soil together with part of the organic slurry N. Under humid temperate conditions the residual N effects of the manure can only be optimally utilised when soil is also covered by plants in the autumn, because a significant part of the residual N is released in the autumn, and there is a higher risk of N leaching losses on soils that receive cattle slurry regularly compared to soils receiving only mineral N fertilisers.     

Enhancing the Potential for in situ Bioremediation of RDX Contaminated Soil from a Former Military Demolition Range

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a toxic, mobile groundwater contaminant common to military sites. Biodegradation of RDX is an alternative, cost effective and environmentally friendly remediation approach. The effects of carbon amendments (waste glycerol and cheese whey) used alone or with a potential electron shuttle (ammonium lignosulfonate) on RDX biodegradation were assessed. These substrates are readily available waste materials that can be used as nutrients to promote oxygen consumption, creating a more reducing environment. Nutrient amended batch assays were conducted using RDX spiked contaminated demolition range soil under anaerobic conditions. The amendments that improved RDX mineralization the most were subsequently tested in a scaled up repacked soil column study to verify if this strategy could be effectively implemented on-site. Microcosm results indicated that RDX mineralization by indigenous anaerobic microorganisms was enhanced the most by the low carbon amendment concentration. The use of ammonium lignosulfonate was not effective, exhibiting an inhibitory effect on RDX biodegradation that was stronger at higher concentrations. The soil column study showed that the low concentration of waste was the most promising treatment scenario. These results offer good prospects for the use of waste glycerol for in situ treatment of soils contaminated with energetic-materials, such as RDX.     

Nitrogen transformations during biological aerobic treatment of pig slurry: effect of intermittent aeration on nitrous oxide emissions

A laboratory scale aeration treatment system was built to study the fate of nitrogen during aeration of pig slurry. For each run evaluated, the nitrogen mass balance was determined including measurement of the nitrous oxide gas emissions. Intermittent aeration led to a nitrogen removal of about 53% of the total nitrogen content of the raw slurry. About 18% of the total nitrogen content of the raw slurry was emitted as N2O during aeration with an aerobic to anoxic ratio equal to 0.625. In contrast, the extension of the anoxic period (aerobic to anoxic ratio = 0.375) allowed complete denitrification and avoided N2O emissions.     

Inactivation of poliovirus type 1 in mixed human and swine wastes and by bacteria from swine manure.

The persistence of poliovirus type 1 (PO1) in mixed septic tank effluent and swine manure slurry was determined, and the antiviral effects of several bacterial cultures isolated from swine manure slurry were demonstrated. In two field experiments, PO1 was consistently inactivated more rapidly in the mixed waste than in the control Dulbecco's phosphate-buffered saline (D-PBS). D values (time [in days] for a 90% reduction of virus titer) were 18.7 and 29.9 for the mixed waste and 56.5 and 51.8 for the D-PBS control, respectively. The virus inactivation in the mixed waste was temperature dependent. A comparison of PO1 inactivation in raw mixed waste, autoclaved mixed waste, and bacterium-free filtrate of raw mixed waste at the same pH and temperatures provided an initial demonstration that the virus inactivation in the mixed waste is related, at least in part, to microbial activity. At 25 degrees C, the D value was 6.8 for the mixed waste, 11.2 for the autoclaved mixed waste, and 10.5 for the bacterium-free filtrate of raw mixed waste. At 37 degrees C, D values were 1.3, 3.9, and 3.1 for these three suspending media, respectively. Three bacterial isolates which had shown antiviral effects in a screening test each caused virus inactivation in autoclaved mixed waste, in which the effect of other microorganisms was excluded. Inhibition of PO1 inactivation by protease inhibitors suggests that the virus inactivation in the mixed waste was due in part to proteolytic enzymes produced by bacteria in the waste.     

Inactivation of poliovirus type 1 in mixed human and swine wastes and by bacteria from swine manure.

The persistence of poliovirus type 1 (PO1) in mixed septic tank effluent and swine manure slurry was determined, and the antiviral effects of several bacterial cultures isolated from swine manure slurry were demonstrated. In two field experiments, PO1 was consistently inactivated more rapidly in the mixed waste than in the control Dulbecco's phosphate-buffered saline (D-PBS). D values (time [in days] for a 90% reduction of virus titer) were 18.7 and 29.9 for the mixed waste and 56.5 and 51.8 for the D-PBS control, respectively. The virus inactivation in the mixed waste was temperature dependent. A comparison of PO1 inactivation in raw mixed waste, autoclaved mixed waste, and bacterium-free filtrate of raw mixed waste at the same pH and temperatures provided an initial demonstration that the virus inactivation in the mixed waste is related, at least in part, to microbial activity. At 25 degrees C, the D value was 6.8 for the mixed waste, 11.2 for the autoclaved mixed waste, and 10.5 for the bacterium-free filtrate of raw mixed waste. At 37 degrees C, D values were 1.3, 3.9, and 3.1 for these three suspending media, respectively. Three bacterial isolates which had shown antiviral effects in a screening test each caused virus inactivation in autoclaved mixed waste, in which the effect of other microorganisms was excluded. Inhibition of PO1 inactivation by protease inhibitors suggests that the virus inactivation in the mixed waste was due in part to proteolytic enzymes produced by bacteria in the waste.     

Genetic structure of a novel biofuel-producing microorganism community

Biofuels are an important alternative, renewable source of energy in the face of the ongoing depletion of fossil fuels. Cheese whey is a dairy industry waste characterized by high lactose concentration, which represents a significant environmental problem. Bio-ethanol production by cheese whey could be an effective nonvegetable source for renewable energy production. Here, we report the isolation of a mixed microbial population, able to produce ethanol as main fermentation product from fermenting whey. The microbial consortium has been used to perform a batch fermentation of crude whey in both anoxic and hypoxic conditions. Maximum ethanol concentrations achieved in this study was obtained using the mixed culture in hypoxic conditions, grown at pH 4 and 30°C, with ethanol production yield of 60 g/L. Our research has pointed out an alternative way to both dispose and valorize cheese whey, a dairy by-product that could cause water pollution and harm to the environment if not properly treated.     

Nitrogen accumulation in kaolin mining wastes in Cornwall III. Nitrogenous fertilisers

Summary In the establishment of a grass cover on china clay waste it is necessary, as in most land restoration, to supply fertiliser nitrogen in substantial amounts. However the objective of nitrogen accumulation is restricted in south west England by severe leaching. A series of experiments were devised to investigate the nitrogen retention from a range of fertiliser sources.When fertiliser-N was applied to established swards, three times as much nitrogen (about 90 per soil and vegetation at the end of the first season of establishment. Sodium nitrate was especially susceptible to leaching, in contrast to sources containing ammonium. Slow-release formulations and organic materials produced a lower sward growth throughout the first growing season but tended to give higher levels of residual-N in the sand waste.When fertiliser-N was applied at seeding less than 30 per cent of the nitrogen was retained in the cent of that applied) was retained. Most of this nitrogen was retained in the sand waste. There was little difference between different types of fertiliser: the main effect was to alter the amount of nitrogen in herbage tissues.Plant growth and a healthy grass sward could only be sustained in the absence of a legume component by repeated applications of fertiliser-N. When applications were discontinued sward degradation was shown by decreases in biomass. Losses in nitrogen from the sward biomass were more than accounted for by an increase in the nitrogen content of the sand waste. These results indicate that once fertiliser-N is retained by the sward ecosystem on sand waste, there are few further losses, presumably because of rapid microbial immobilisation of nitrogen in the sand waste.In view of the expense of land restoration using numerous maintenance applications of nitrogen, it is clear that legumes must be included in the seeds mixture for the reclamation of kaolin mining wastes in Cornwall. However, legumes are difficult to establish and more susceptible to drought than grass species. Results from these trials suggest that slow-release nitrogen fertilisers could enable a controlled level of grass growth, thereby avoiding competition between the legume and grass components. Alternatively grass swards could be rapidly established to stabilise the sand waste using soluble ammonium salts, and in the second season oversown with legumes.     

Denitrification and N2O emissions from a UK pasture soil following the early spring application of cattle slurry and mineral fertiliser

Total denitrification and nitrous oxide (N₂O) losses were measured from three contrasting dairy management systems representing good commercial practice (system 1), production maintained but with reduced N losses (system 2); and nitrate leaching less than 50 mg L^-1 but with reduced production (system 3). Measurements were made following mineral fertiliser application and from two plot experiments where four treatments were applied: control, NH₄NO₃ at 60 kg N ha^-1, cattle slurry applied to the surface (equivalent to 45 kg N ha^-1), and cattle slurry injected. Despite low soil temperatures (<6 °C) and low rainfall (<3 mm), total denitrification and N₂O losses peaked at 56 and 16 g N ha^-1 d^-1, respectively. Total denitrification losses decreased: system 1 system 2 > system 3, whereas N₂O losses decreased: system 2 > system 3 > system 1. Total denitrification losses tended to decrease with decreasing fertiliser application rate, whereas fertiliser application rate was not the sole determinant of the N₂O loss. The system 3 field was injected with cattle slurry for 2 yr, system 2 received some slurry by injection and system 1 received slurry to the surface. Thus, the amount, timing and method of previous cattle slurry application was important in determining the loss following subsequent fertiliser application. For the plot experiments, total denitrification and N₂O losses decreased in the order: slurry injected > mineral fertiliser > slurry applied to the surface > control for 5 days following application. However, 16 and 19 days after application, N₂O losses above the control were measured from plots that had received cattle slurry. It was inferred that the application of cattle slurry to the pasture soil stimulated greater N₂O production and increased losses over a longer time period compared with mineral fertiliser additions.     

The Impact of Using Alternative Forages on the Nutrient Value within Slurry and Its Implications for Forage Productivity in Agricultural Systems

Alternative forages can be used to provide valuable home-grown feed for ruminant livestock. Utilising these different forages could affect the manure value and the implications of incorporating these forages into farming systems, needs to be better understood. An experiment tested the hypothesis that applying slurries from ruminants, fed ensiled red clover (Trifolium pratense), lucerne (Medicago sativa) or kale (Brassica oleracea) would improve the yield of hybrid ryegrass (Lolium hybridicum), compared with applying slurries from ruminants fed ensiled hybrid ryegrass, or applying inorganic N alone. Slurries from sheep offered one of four silages were applied to ryegrass plots (at 35 t ha⁻¹) with 100 kg N ha⁻¹ inorganic fertiliser; dry matter (DM) yield was compared to plots only receiving ammonium nitrate at rates of 0, 100 and 250 kg N ha⁻¹ year⁻¹. The DM yield of plots treated with 250 kg N, lucerne or red clover slurry was significantly higher than other treatments (P<0.001). The estimated relative fertiliser N equivalence (FNE) (fertiliser-N needed to produce same yield as slurry N), was greatest for lucerne (114 kg) >red clover (81 kg) >kale (44 kg) >ryegrass (26 kg ha⁻¹ yr⁻¹). These FNE values represent relative efficiencies of 22% (ryegrass), 52% (kale), 47% (red clover) and 60% for lucerne slurry, with the ryegrass slurry efficiency being lowest (P = 0.005). Soil magnesium levels in plots treated with legume slurry were higher than other treatments (P<0.001). Overall, slurries from ruminants fed alternative ensiled forages increased soil nutrient status, forage productivity and better N efficiency than slurries from ruminants fed ryegrass silage. The efficiency of fertiliser use is one of the major factors influencing the sustainability of farming systems, these findings highlight the cascade in benefits from feeding ruminants alternative forages, and the need to ensure their value is effectively captured to reduce environmental risks.     

Effects of an organic manure on the transformations of ammonium nitrogen in planted and unplanted soil

Cattle slurry supplemented with ¹⁵N labelled ammonium sulphate was applied to unplanted soil and to soil planted with sprouted potato tubers. For comparison, there was a similar treatment with ¹⁵N labelled ammonium sulphate alone. The pots of soil were kept at 20°C and the plants were harvested after 21, 42, 70 and 98 days. Labelled and unlabelled nitrogen were measured in the plants and, after the same intervals, in the soil as mineral, organic and clay-fixed nitrogen. The recovery of labelled nitrogen in plants plus soil by the end of the experiment was 90% with ammonium sulphate alone and 77% with cattle slurry; the corresponding recoveries in unplanted soil were only 65% and 48%. The greater recoveries of the labelled nitrogen in the planted soil are attributed to its greater protection against gaseous loss when within the plants. Another effect of the plants was to decrease the amount of labelled nitrogen that had been initially fixed by the clay. During the first 21 days with cattle slurry almost half of the labelled nitrogen became immobilized in organic matter. In the same period there was mineralization of unlabelled nitrogen, but the overall reaction was net immobilization. In later periods, immobilized labelled nitrogen in the unplanted soil decreased indicating remineralization. Estimates are given of the rates of gross mineralization, but the periods between sampling occasions were too long to yield reliable values. ei]Section editor: R Merckx     

Production of compost from marine waste: evaluation of the product for use in ecological agriculture

The sea contains large amounts of resources that are sometimes considered as waste. Such material includes the waste generated by the fish-processing industry and seaweed that is washed up on shores. In this study, these waste products were windrow composted, along with pine bark as a source of carbon and aeration. The final mix proportions were 20 % seaweed, 20 % fish waste, and 60 % pine bark (v/v). After 10 weeks, stable, well-structured, hygienic compost, which was rich in organic matter and nutrients and had a low metal content, was obtained. Tests for maturity, hygiene, and phytotoxicity, along with a detailed physical and chemical characterization, showed that this compost can be used as an organic amendment and/or growth substrate for use in ecological agriculture. The only limiting feature was the high salinity, which could easily be lowered prior to composting the material.     

Protein enrichment of corn cob heteroxylan waste slurry by thermophilic aerobic digestion using Bacillus stearothermophilus

Thermophilic aerobic digestion (TAD) of heteroxylan waste was implemented at waste load of 30gL(-1) with mineral nitrogen supplementation to study effect of the process on waste degradation, protein accretion and quality. Digestions were carried out at 45 50, 55, 60 and 65 degrees C using Bacillusstearothermophilus in a CSTR under batch conditions at 1.0vvm aeration rate, pH 7.0 for a maximum of 120h. Amylase and xylanase activities appeared rapidly in the digest, while basal protease activity appeared early in the digestion and increased towards end of the processes. Highest degradation of volatile suspended solid, hemicellulose and fibre occurred at 55 degrees C while highest degradation of total suspended solid occurred at 60 degrees C. Highest protein accretion (258.8%) and assimilation of mineral nitrogen and soluble protein occurred at 55 degrees C. The % content of amino acids of digest crude protein increased relative to raw waste and with digestion temperature. Quality of digest protein was comparable to the FAO standard for feed use. TAD has potentials for use in the protein enrichment of waste.     

Persistence of inoculated hepatitis A virus in mixed human and animal wastes.

The persistence of hepatitis A virus (HAV) was determined both in mixtures of septic tank effluent (STE) with dairy cattle manure slurry (DCMS) and in mixtures of STE with swine manure slurry (SMS). HAV was consistently inactivated more rapidly in the two types of mixed wastes than in STE alone or in the control Dulbecco's phosphate-buffered saline (PBS). At 5 degrees C, the D values (time, in days, for a 90% reduction of virus titer) were 34.6 for the mixed STE and DCMS, 48.5 for the mixed STE and SMS, 58.5 for STE, and 217.4 for the Dulbecco's PBS control. At 22 degrees C, the D values were 23.0, 17.1, 35.1, and 90.1 for the four suspension media, respectively. A comparison of HAV inactivation in mixed wastes subjected to different treatments at the same pH and temperatures showed that the virus inactivation in the mixed wastes was related, at least in part, to microbial activity. In mixed STE and DCMS, the D values at 25 degrees C were 8.3 for raw mixed wastes, 15.1 for autoclaved mixed wastes, and 9.6 for bacterium-free filtrate of raw mixed wastes; D values at 37 degrees C were 6.8, 10.1, and 7.0 for these three suspension media, respectively. In mixed STE and SMS, the D values at 25 degrees C were 8.1 for raw mixed wastes, 14.3 for autoclaved mixed wastes, and 9.1 for bacterium-free filtrate of raw mixed wastes; the D values at 37 degrees C were 6.8, 9.4, and 6.9 for the three suspensions, respectively.     

The effect of time of fertiliser-soil contact,distance of phosphate movement and fertiliser solubility on phosphate availability to early growth of lowland rice

Summary The importance of time of fertiliser-soil contact, distance of phosphate movement from fertiliser and phosphate fertiliser solubility in determining the availability of phosphate to the early growth of lowland rice was investigated. Phosphate availability was measured by phosphate uptake in a glass-house experiment in which two week old rice seedlings were transferred to the surface of fertiliser-treated soils for three weeks before harvesting. The fertilisers used in the study were monoammonium phosphate (MAP), ammonium polyphospate (APP), superphosphate (SP) and rock phosphate (RP). Availability of all fertilisers was tested in this way after 2, 4 and 8 weeks of fertiliser-soil contact. In an associated laboratory experiment the distance of phosphate movement and fertiliser solubility (as measured by quantity of phosphate that had moved away from the fertilizer source) was determined at 2 and 4 weeks in glass tubes containing waterlogged soil. The results showed that at all times of measurement, the availability of the fertilisers could be ranked MAP>APP≥SP>RP. Of the 6 possible correlations between phosphate uptake and phosphate movement, only one was significant for the fertiliser-soil contact period of 2 weeks and phosphate movement at 4 weeks, (r=0.950, P<0.05). Of the 6 possible correlations between phosphate uptake and fertiliser solubility, none were significant. However, of the 6 possible correlations between phosphate uptake and the product of the two laboratory parameters (referred to as the availability index) four were significant (P<0.05 in all cases), and involved only the fertiliser-soil contact periods of 2 and 4 weeks. These results indicate that fertiliser solubility alone is not a satisfactory correlative determinant of availability of fertiliser phosphate to lowland rice. Phosphate movement alone is marginally better, but the best correlations are obtained when both parameters are taken into account. While their combined effects are evident only during the first four weeks after fertiliser application, this may still be important to the successful establishement of a rice crop.     

Guanine as a hygienic index for allergologically relevant mite infestations in mattress dust

Since guanine is not only an essential constituent of vital nucleic acids, but also the main end product of nitrogenous waste excretion in arachnids, it is a potential candidate for a hygienic index for mite activity in house dust. The public health significance of these mites is based on their production of allergen in the home environment.In 101 mattress-dust samples, total number of mites and guanine content were positively correlated. The hygienic standard of 10 mites per 0.1 g dust (as derived from Danish investigations) was met in all samples with less than 0.06% guanine in the dry dust. Where the guanine content was more than or equal to 0.25% in the dry dust, mite numbers were higher than 10 mites per 0.1 g dust in 43 of the 44 samples. The three different groups (negligible mite content, possibly allergologically relevant mite concentration and allergologically unhygienic mite situation) could be easily discriminated on the color scale.The guanine-AZO-dye reaction in vacuum cleaner dust is a strong and promising candidate for an allergologically relevant hygienic index in the home.     

Influence of temperature and pH on the nonenzymatic reduction of triphenyltetrazolium chloride

The effects of temperature and pH on the nonenzymatic (chemical) reduction of triphenyltetrazolium chloride (TTC) to triphenyl formazan (TF) in cheese whey and municipal solid waste compost samples were studied. Ten different incubation temperatures and 13 pH levels were tested. The study showed that the TTC could be reduced nonenzymatically at high temperatures and/or under alkaline pH conditions. The nonenzymatic TTC reduction was observed at pH values greater than 9.5 and 11.0 for the cheese whey and compost, respectively. The TTC chemical reduction rate followed the same trend in both media. The TF content increased with increasing the pH value, reaching its maximum at a pH of 12, then decreased and was not detected at a pH of 13. The TTC was also reduced nonenzymatically at temperatures higher than 70 and 85 degrees C for cheese whey and compost, respectively. Evaporation did not seem to have any significant effect on the TTC chemical reduction since less than 3% of water content was lost at a temperature of 100 degrees C. It was noticed that the TF yield in cheese whey samples was higher than that in compost samples. This was due to the higher moisture content of cheese whey and the presence of copper in the compost samples, which reacted chemically with the TF causing reduction in the red color. For a given incubation period, the effect of pH on the TTC chemical reduction was more significant than the effect of incubation temperature (at a 2 h incubation period, 57.5% and 17.9% of the TTC were chemically reduced at a pH of 12 compared to 10.9% and 7.7% at an incubation temperature of 100 degrees C, for cheese whey and compost, respectively). Among the six metals tested (Ca, Cu, K, Na, Ni, and Zn) only Cu affected the color intensity of the TF. The activation energy of the TTC chemical reduction was 168,808 and 239,102 J/mol in cheese whey and municipal solid compost, respectively. For dehydrogenase activity measurement, the pH of the samples and the incubation temperature should not be higher than 9 and 60 degrees C in order to ensure that the TTC reduction is caused only by the biochemical reaction. Measuring the color intensity of TF in waste samples that contain copper could give misleading results as a result of the formation of formazan copper complex, which reduces the red color.