An easy-to-perform, culture-free Campylobacter point-of-management assay for processing plant applications

Aims

Current culture‐based methods for detection and determination of Campylobacter levels on processed chickens takes at least 2 days. Here we sought to develop a new complete, low‐cost and rapid (approximately 2·5 h) detection system requiring minimal operator input.

Methods and Results

We observed a strong correlation between culture‐based cell counts and our ability to detect either Campylobacter jejuni or Campylobacter coli by loop‐mediated isothermal amplification from the same samples. This knowledge was used to develop a rapid and simple five‐step assay to quantify Campylobacter, which was subsequently assessed for its specificity, reproducibility and accuracy in quantifying Campylobacter levels from processed chickens. The assay was found to be highly specific for C. jejuni and C. coli and was capable of distinguishing between samples that are either within or exceeding the industry set target of 6000 Campylobacter colony forming units (CFU) per carcass (equivalent to 12 CFU per ml of chicken rinse) with >90% accuracy relative to culture‐based methods.

Conclusions

Our method can reliably quantify Campylobacter counts of processed chickens with an accuracy comparable to culture‐based assays but provides results within hours as opposed to days.

Significance and Impact of the Study

The research presented here will help improve food safety by providing fast Campylobacter detection that will enable the implementation of real‐time risk management strategies in poultry processing plants to rapidly test processed chickens and identify effective intervention strategies. This technology is a powerful tool that can be easily adapted for other organisms and thus could be highly beneficial for a broad range of industries.

Nitrogen dioxide oxidizes mitochondrial cytochrome c

We previously reported that high micromolar concentrations of nitric oxide were able to oxidize mitochondrial cytochrome c at physiological pH, producing nitroxyl anion (Sharpe and Cooper, 1998 Biochem. J. 332, 9-19). However, the subsequent re-evaluation of the redox potential of the NO/NO(-) couple suggests that this reaction is thermodynamically unfavored. We now show that the oxidation is oxygen-concentration dependent and non stoichiometric. We conclude that the effect is due to an oxidant species produced during the aerobic decay of nitric oxide to nitrite and nitrate. The species is most probably nitrogen dioxide, NO(2)(•) a well-known biologically active oxidant. A simple kinetic model of NO autoxidation is able to explain the extent of cytochrome c oxidation assuming a rate constant of 3×10(6)M(-1)s(-1) for the reaction of NO(2)(•) with ferrocytochrome c. The importance of NO(2)(•) was confirmed by the addition of scavengers such as urate and ferrocyanide. These convert NO(2)(•) into products (urate radical and ferricyanide) that rapidly oxidize cytochrome c and hence greatly enhance the extent of oxidation observed. The present study does not support the previous hypothesis that NO and cytochrome c can generate appreciable amounts of nitroxyl ions (NO(-) or HNO) or of peroxynitrite.

Cytochrome bd confers nitric oxide resistance to Escherichia coli

The aerobic respiratory chain of Escherichia coli has two terminal quinol oxidases: cytochrome bo and cytochrome bd. Cytochrome bd was thought to function solely to facilitate micro-aerobic respiration. However, it has recently been shown to be overexpressed under conditions of nitric oxide (NO) stress; we show here that cytochrome bd is crucial for protecting E. coli cells from NO-induced growth inhibition by virtue of its fast NO dissociation rate.

Nitric oxide inhibition of respiration involves both competitive (heme) and noncompetitive (copper) binding to cytochrome c oxidase

NO reversibly inhibits mitochondrial respiration via binding to cytochrome c oxidase (CCO). This inhibition has been proposed to be a physiological control mechanism and/or to contribute to pathophysiology. Oxygen reacts with CCO at a heme iron:copper binuclear center (a(3)/Cu(B)). Reports have variously suggested that during inhibition NO can interact with the binuclear center containing zero (fully oxidized), one (singly reduced), and two (fully reduced) additional electrons. It has also been suggested that two NO molecules can interact with the enzyme simultaneously. We used steady-state and kinetic modeling techniques to reevaluate NO inhibition of CCO. At high flux and low oxygen tensions NO interacts predominantly with the fully reduced (ferrous/cuprous) center in competition with oxygen. However, as the oxygen tension is raised (or the consumption rate is decreased) the reaction with the oxidized enzyme becomes increasingly important. There is no requirement for NO to bind to the singly reduced binuclear center. NO interacts with either ferrous heme iron or oxidized copper, but not both simultaneously. The affinity (K(D)) of NO for the oxygen-binding ferrous heme site is 0.2 nM. The noncompetitive interaction with oxidized copper results in oxidation of NO to nitrite and behaves kinetically as if it had an apparent affinity of 28 nM; at low levels of NO, significant binding to copper can occur without appreciable enzyme inhibition. The combination of competitive (heme) and noncompetitive (copper) modes of binding enables NO to interact with mitochondria across the full in vivo dynamic range of oxygen tension and consumption rates.

Rotting by radicals--the role of cellobiose oxidoreductase?

Cellobiose oxidoreductase is a flavocytochrome secreted by wood-rotting fungi. The structure and functional role of the enzyme are reviewed, and a mechanism through which the enzyme produces superoxide, ferrous iron and hydrogen peroxide is proposed. The reactions of hydroxyl radicals formed by Fenton chemistry are discussed in the context of lignocellulose biodegradation.

The heme domain of cellobiose oxidoreductase: a one-electron reducing system

Phanerochaete chrysosporium cellobiose oxidoreductase (CBOR) comprises two redox domains, one containing flavin adenine dinucleotide (FAD) and the other protoheme. It reduces both two-electron acceptors, including molecular oxygen, and one-electron acceptors, including transition metal complexes and cytochrome c. If the latter reacts with the flavin, the reduced heme b acts merely as a redox buffer, but if with the b heme, enzyme action involves a true electron transfer chain. Intact CBOR fully reduced with cellobiose, CBOR partially reduced by ascorbate, and isolated ascorbate-reduced heme domain, all transfer electrons at similar rates to cytochrome c. Reduction of cationic one-electron acceptors via the heme group supports an electron transfer chain model. Analogous reactions with natural one-electron acceptors can promote Fenton chemistry, which may explain evolutionary retention of the heme domain and the enzyme's unique character among secreted sugar dehydrogenases.

Oxygen reduction by cellobiose oxidoreductase: the role of the haem group

We have used optical and electron paramagnetic spectroscopy to study the flavohaem enzyme cellobiose oxidoreductase (CBOR) from Phanerochaete chrysosporium. We have examined redox cycles of the enzyme in which the oxidation of cellobiose to cellobionolactone is coupled to the reduction of oxygen. During turnover flavin can reduce oxygen with one electron to produce superoxide or two electrons to produce hydrogen peroxide. Addition of superoxide dismutase significantly extended the time courses of these cycles, slowing the re-oxidation rate of both cofactors. Addition of catalase also affected the haem time course, but to a lesser extent. Experiments in which superoxide was generated in the reaction mixture showed that this radical greatly enhanced the rate of haem re-oxidation. From these results we propose a mechanism in which reactive oxygen species generation by CBOR flavin subsequently re-oxidises CBOR haem. We discuss this mechanism in relationship to the biological function of this enzyme, namely lignocellulose degradation.

Extracellular heme peroxidases in actinomycetes: a case of mistaken identity

Actinomycetes secrete into their surroundings a suite of enzymes involved in the biodegradation of plant lignocellulose; these have been reported to include both hydrolytic and oxidative enzymes, including peroxidases. Reports of secreted peroxidases have been based upon observations of peroxidase-like activity associated with fractions that exhibit optical spectra reminiscent of heme peroxidases, such as the lignin peroxidases of wood-rotting fungi. Here we show that the appearance of the secreted pseudoperoxidase of the thermophilic actinomycete Thermomonospora fusca BD25 is also associated with the appearance of a heme-like spectrum. The species responsible for this spectrum is a metalloporphyrin; however, we show that this metalloporphyrin is not heme but zinc coproporphyrin. The same porphyrin was found in the growth medium of the actinomycete Streptomyces viridosporus T7A. We therefore propose that earlier reports of heme peroxidases secreted by actinomycetes were due to the incorrect assignment of optical spectra to heme groups rather than to non-iron-containing porphyrins and that lignin-degrading heme peroxidases are not secreted by actinomycetes. The porphyrin, an excretory product, is degraded during peroxidase assays. The low levels of secreted peroxidase activity are associated with a nonheme protein fraction previously shown to contain copper. We suggest that the role of the secreted copper-containing protein may be to bind and detoxify metals that can cause inhibition of heme biosynthesis and thus stimulate porphyrin excretion.

Isolation of a novel G-protein gamma-subunit from Arabidopsis thaliana and its interaction with Gbeta

There is increasing evidence that heterotrimeric G-proteins (G-proteins) are involved in many plant processes including phytohormone response, pathogen defence and stomatal control. In animal systems, each of the three G-protein subunits belong to large multigene families; however, few subunits have been isolated from plants. Here we report the cloning of a second plant G-protein gamma-subunit (AGG2) from Arabidopsis thaliana. The predicted AGG2 protein sequence shows 48% identity to the first identified Arabidopsis Ggamma-subunit, AGG1. Furthermore, AGG2 contains all of the conserved characteristics of gamma-subunits including a small size (100 amino acids, 11.1 kDa), C-terminal CAAX box and a N-terminal alpha-helix region capable of forming a coiled-coil interaction with the beta-subunit. A strong interaction between AGG2 and both the tobacco (TGB1) and Arabidopsis (AGB1) beta-subunits was observed in vivo using the yeast two-hybrid system. The strong association between AGG2 and AGB1 was confirmed in vitro. Southern and Northern analyses showed that AGG2 is a single copy gene in Arabidopsis producing two transcripts that are present in all tissues tested. The isolation of a second gamma-subunit from A. thaliana indicates that plant G-proteins, like their mammalian counterparts, may form different heterotrimer combinations that presumably regulate multiple signal transduction pathways.

Completing the heterotrimer: isolation and characterization of an Arabidopsis thaliana G protein gamma-subunit cDNA

Heterotrimeric G proteins consist of three subunits (alpha, beta, and gamma). alpha- and beta- subunits have been previously cloned in plants, but the gamma-subunit has remained elusive. To isolate the gamma-subunit of a plant heterotrimeric G protein an Arabidopsis thaliana yeast two-hybrid library was screened by using a tobacco G-beta-subunit as the bait protein. One positive clone (AGG1) was isolated several times; it displays significant homology to the conserved domains of mammalian gamma-subunits. The predicted AGG1 protein sequence contains all of the typical characteristics of mammalian gamma-subunits such as small size (98 amino acids, 10.8 kDa), presence of a C-terminal CAAX box to direct isoprenyl modification, and an N-terminal alpha-helix region capable of forming a coiled-coil interaction with the beta-subunit. Northern and Southern analyses showed that AGG1 is a single-copy gene in Arabidopsis with a similar expression pattern to the Arabidopsis beta-subunit, AGB1 [Weiss, C. A., Garnaat, C. W., Mukai, K., Hu, Y. & Ma, H. (1994) Proc. Natl. Acad. Sci. USA 91, 9554-9558]. By using the yeast two-hybrid system, we show that AGG1 strongly interacts with tobacco and Arabidopsis beta-subunits. The in vivo results have been confirmed by using in vitro methods to prove the interaction between AGG1 and the Arabidopsis beta-subunit. As previously observed in mammalian systems, both the coiled-coil domain and the WD repeat regions of the beta-subunit are essential for AGG1 interaction. Also in agreement with previous observations, the removal of the N-terminal alpha-helix of the AGG1 greatly reduces but does not completely block the interaction.

Effect of weeds and nitrogen fertiliser on yield and grain protein concentration of wheat

Field trials at Beverley (19911, Salmon Gums (1991; 2 sites) and Merredin (1992; 2 sites), each with 5 rates of nitrogen (N) and 3 levels of weed control, were used to investigate the effect of weeds and N on wheat grain yield and protein concentration during 1991 and 1992. Weeds in the study were grasses (G) and broadleaf (BL). Weeds reduced both vegetative dry matter yield and grain yield of wheat at all sites except for dry matter at Merredin (BL). Nitrogen fertiliser increased wheat dry matter yield at all sites. Nitrogen increased wheat grain yield at Beverley and Merredin (BL), but decreased yield at both Salmon Gums sites in 1991. Nitrogen fertiliser increased grain protein concentration at all 5 sites-at all rates for 3 sites [Salmon Gums (G) and (BL) and Merredin (G)] and at rates of 69 kg N/ha or more at the other 2 sites [Beverley and Merredin (BL)]. However, the effect of weeds on grain protein varied across sites. At Merredin (G) protein concentration was higher where there was no weed control, possibly due to competition for soil moisture by the greater weed burden. At Salmon Gums (G), grain protein concentration was greater when weeds were controlled than in the presence of weeds, probably due to competition for N between crop and weeds. In the other 3 trials, there was no effect of weeds on grain protein. The effect of weeds on grain protein appears complex and depends on competition between crop and weeds for N and for water at the end of the season, and the interaction between the two.

Alpha 1-blocker doxazosin improves peripheral insulin sensitivity in diabetic hypertensive patients

The antihypertensive doxazosin is a selective alpha 1-adrenoceptor-blocking drug whose favorable impact on lipid metabolism is well known. A single-blind placebo-controlled crossover study was designed to determine whether antihypertensive treatment with doxazosin affects insulin sensitivity in diabetic, mildly hypertensive, non-obese patients. Twelve subjects (diastolic blood pressure, 98 +/- 1.5 mm Hg; body mass index, 25 +/- 0.6 kg/m2; hemoglobin A1c [HbA1c], 7.6% +/- 0.4%) who were not taking drugs and were treating diabetes only by diet were randomly assigned to placebo treatment for 6 weeks and then to doxazosin for the same period, or vice versa. The doxazosin dose (maximum, 12 mg/d) was increased to achieve a normotensive blood pressure (final diastolic pressure, 85 +/- 2 mm Hg, P < .05). A euglycemic (100 +/- 4 mg/dL) hyperinsulinemic (61 +/- 6 microU/mL) glucose clamp was performed at baseline and at the end of both placebo and doxazosin administration. Hepatic glucose production was measured by the isotope dilution technique using 3H-glucose. Body weights and HbA1c did not vary during the entire study. The basal mean glucose uptake and the insulin sensitivity index (2.3 +/- 0.3 mg/kg/min and 4 +/- 0.5 mg/kg/min per U/L x 100) remained unchanged during placebo administration (2.5 +/- 0.4 and 4 +/- 0.6, NS), but significantly increased during doxazosin treatment (3.3 +/- 0.4 and 5.6 +/- 0.7, P < .05). Hepatic glucose production showed no modification during both placebo and doxazosin. These data provide evidence that doxazosin improves insulin sensitivity in diabetic hypertensive patients, mainly through peripheral effects.

Effect of an acidifying nitrogen fertiliser and lime on soil pH and wheat yields. 2. Plant response

This paper reports the effects of an acidifying fertiliser on wheat yields and mineral composition in the first 10 years of trials at Merredin, Wongan Hills, and Newdegate, described in the previous paper. There were grain yield increases from application (kg/ha.year) of 17.5 N + 7.6 P and 35 N + 15.2 P in all years except 1980 (Wongan Hills and Newdegate) and 1989 (Merredin). At Merredin, 3 t/ha of limestone increased grain yields in all years except 1982 and 1983. At Wongan Hills, limestone increased yields in the continuous cropping system, in the presence of high N + P, during 1986 and 1989. At Newdegate, grain yield responses to lime were recorded in 1980, 1981, 1982, 1986, 1988, and 1989; limestone resulted in decreased wheat yields in 1984 because of an increase in the severity of the root disease take-all (caused by Gaeumannomyces graminis var. tritici), and decreased lupin yields in 1987 because of manganese deficiency. There were a few responses at Merredin and Newdegate to low rates of limestone with each N + P application. Application of the magnesium (Mg) + potassium (K) + molybdenum (Mo) in addition to limestone gave isolated responses at all sites. Concentrations of calcium (Ca), Mg, and K at the 1989 plant sampling were highest at Wongan Hills and lowest at Merredin. Calcium concentrations were higher at Merredin and Newdegate following N + P application, but lower at Wongan Hills. Application of N + P reduced the concentration of Mg at Merredin and Wongan Hills, but increased Mg at Newdegate. The concentration of K was decreased at all sites by N + P. Limestone had no consistent effect on Ca concentrations but increased the concentrations of Mg and K at Merredin and K at Newdegate. Where Mg + K + Mo had been applied in 1980, concentrations of Ca decreased and K increased, while there was no consistent effect on Mg concentration. The Mo concentration in plant shoots was reduced at all sites by increasing rate of N + P and increased by application of lime and Mo in 1980. Grain Mo concentrations were very low at Merredin and Wongan Hills, even in the absence of N + P. Concentrations at Newdegate were reduced by increasing N + P rate. Application of limestone increased grain Mo concentrations at all sites, but these were still lowered by N + P application. Concentrations were also increased by the application of Mo in 1980, but fell with time, particularly with application of N + P.

Effect of field peas and wheat on the yield and protein content of subsequent wheat crops grown at several rates of applied nitrogen

The responses of wheat to various rates of N fertiliser were compared following field peas (PW) or wheat (WW) in the previous year. Seventeen trials were carried out at 5 sites between 1986 and 1991. The trials were on medium- and fine-textured soils (clay loams or shallow duplex soils). The overall grain yield of PW appeared greater than WW in 11 trials [was significantly greater in 9 (P<0.05)], and did not appear different in 6 trials. When no N was applied the yield advantage of PW was 41% (PW 1.91 t/ha cf. WW 1.37 t/ha). Quadratic response curves were fitted to all yield data. Rotation x N rate interaction was significant (P<0.05) in 10 comparisons. In 5 trials, while there was a yield increase to N fertiliser with WW, the yields decreased with PW. In 3 trials while there was an increase with WW there was no response with PW or a reduction at higher rates of N. In the remaining 2 trials there were responses with both PW and WW, but this was greater for WW. The response curves in these 10 trials either converged and met, indicating that the difference between rotations was due to N availability, or converged but did not meet, indicating that N was important but did not explain the whole difference. Where there was no interaction between rotation and N rate the response curves were parallel. The type of response could not be predicted. It was not profitable to apply N fertiliser to wheat in the PW rotation in 11 of the 17 trials. The average yield advantage of PW over WW, in the absence of N was 540 kg/ha, while there was an average increase of 1.7% grain protein.

Effect of nitrogen source and soil type on inorganic nitrogen concentrations and availability in field trials with wheat

Thirteen trials, each with 3 nitrogen (N) sources (urea, ammonium nitrate, and ammonium sulfate) and 2 N rates (25 and 75 kg N/ha), were carried out during 1987-89, to measure the rate of disappearance of ammonium-N on different soils. Six soil categories were examined, from very acid to calcareous light soils, and from medium to heavy textured soils. Plots were planted with wheat, and at the higher rate of N, fallow plots were included to distinguish plant uptake from other processes such as nitrification and immobilisation that cause the disappearance of ammonium N. Reduction in concentration of ammonium-N was rapid on high pH, light soils (2-3 weeks at Dongara 1988), and slower with decreasing soil pH (e.g. >19 weeks at Merredin 1987). Nitrate-N concentration increased on fertiliser-treated plots at all sites, indicating that nitrification was taking place. Ammonium-N decline was slower with ammonium sulfate supplied than with urea or ammonium nitrate, consistent with its greater acidifying effect in the soil. This difference did not occur on the alkaline light soils, where reduction in concentration of ammonium-N was rapid for all sources. In 1989, the rate of decline of ammonium-N was considerably slowed because the soil surface containing the ammonium-N was dried during a very dry spring with little effective rainfall in September and October.

Effect of management of previous cereal stubble on nitrogen fertiliser requirement of wheat

The effect of either burning stubble, or incorporating it in the soil, on the nitrogen (N) fertiliser requirement of the following wheat crop was examined over 10 years (1978-87) in a continuous wheat system at 2 sites (Wongan Hills and Nabawa), and in both continuous wheat and wheat-fallow systems at one site (Merredin). There were significant grain yield increases in response to N fertiliser in all years at Nabawa. At Wongan Hills there was no response in 1978 and 1985, a yield reduction in 1979, and a yield increase in all other years. At Merredin, there was no response in 1980, a yield decrease in 1984 and 1985, and an increase in all other years. In some years grain yield responses were small at Wongan Hills and Merredin. The only significant overall effects of stubble treatment were at Nabawa in 1978 (P<0.01) and 1985 (P<0.05). The interaction between stubble treatment and N rate was significant at Wongan Hills in 1980 and 1981 (P<0.05), and at Merredin in 1981 (P<0.001), 1983, and 1985 (both P<0.05). Response to N fertiliser was higher where the stubble was incorporated than where it was burnt. There was also a tendency for higher optimum economic rates of N fertiliser with stubble incorporated rather than burnt, but differences were not large. At Merredin, the overall yield increase with fallow was significant (P<0.001) in 1979 and 1983. The fallow x N fertiliser rate interaction was significant in all comparison years except 1987. Responses to N were greater in the non-fallow treatments. Soil organic carbon (C) levels were higher with stubble incorporation than where the stubble was burnt, and fallowing resulted in lower organic C. There was a downward trend with time, especially when fallowing was carried out. Effects on total N levels in the soil were similar to those for organic C but were less marked. The study indicates that at a level of stubble residues of 1-3 t/ha with continuous wheat in this winter rainfall environment in Western Australia, stubble treatment is unlikely to be a major factor in determining the rate of N fertiliser required for a wheat crop.

Nitrogen fertiliser response of wheat in lupin-wheat, subterranean clover-wheat and continuous wheat rotations

Response of wheat to 7 rates of nitrogen (N) fertiliser was compared in clover-wheat (CW), lupin-wheat (LW) and continuous wheat (WW) rotations, in 4 alternate years on a grey gravelly sand over ironstone gravel at Badgingarra, during the period 1980-87. Nitrogen fertilisers significantly increased wheat grain yields in all assessment years (1981, 1983, 1985 and 1987). There were significant (P<0.05) interactions between rotation and N fertiliser in all years except 1983, with response to N fertiliser on wheat least in the LW rotation. The apparent average increases in N available in wheat dry matter, without added N, were 10.9 kg/ha from clover and 13 kg/ha from lupins. The contributions from clover and lupins in grain N were 10 and 12.3 kg/ha respectively. Organic carbon and total N levels in the soil were similar in the LW and WW rotations but were less than in the CW rotation. The levels of organic carbon in the LW and WW rotations decreased with time. Despite the difference in soil organic carbon and total N, grain yields were similar for the CW and LW rotations in the absence of N fertiliser but were higher than in the WW rotation. It was concluded that a LW rotation (in this environment) would be as effective, at least over a 6-year period, as a CW rotation in maintaining wheat yields due to the contribution of N from readily decomposible residues from the lupin crop. However, highest yields overall where obtained when N fertiliser was added to the CW rotation.

Effect of lupins and wheat on the yield of subsequent wheat crops grown at several rates of applied nitrogen

The responses of wheat to various rates of application of nitrogen fertiliser were compared following lupins (WL) or wheat (WW) in the previous year. Results covered 10 sites and trials were carried out between 1979 and 1984. giving 26 site-year comparisons. The trials were on sandy or duplex (sand over clay) soils. The overall yield of WL was greater than WW on 21 occasions (significant in 10 cases, P < 0.05), less than WW on 2 occasions (both significantly) and there was no difference on 3 occasions. When no nitrogen was applied the advantage of WL was 41% (WL 1.20 t/ha and WW 0.85 t/ha). The response to nitrogen differed between trials; over all trials a quadratic model best described the responses. There were significant interactions between rotation and nitrogen rate in 10 comparisons. In 4 of these cases, response to nitrogen with WW was greater than with WL and these response curves approached I another but did not meet, indicating that both residual nitrogen from the lupins and some other benefit from the lupins were involved. In 5 cases the greater response on WW resulted in convergence with the WL response curve, suggesting that residual nitrogen explained all of the benefit of lupins. In these cases the amount ofnitrogen fertiliser required to bring the yield of WW to that of the WL without nitrogen ranged from 20 to 47 kg N/ha, with a mean of 37 kg N/ha. Parallel response curves were observed In 12 cases, indicating involvement of factors other than residual nitrogen in the response to lupins, e.g. disease cleaning effects or slow release of nitrogen throughout the season. The type of response could not be related to particular site characteristics. When quadratic coefficients were averaged to give 'average response curves', similar rates of applied nitrogen were required for maximum yields in both WW and WL, and the maximum yields were 1.23 t/ha for WW and 1.41 t/ha for WL. The average advantage of WL over WW, in the absence of nitrogen fertiliser. was 350 kg/ha.

Effects of dicyandiamide (a nitrification inhibitor) on leaching of nitrogen and growth of cereals

Dicyandiamide (DCD) was tested as a nitrification inhibitor with urea in 10 field experiments (ammonium nitrate was included in 2 of them) in 3 years on sites where leaching of nitrogen was a potential problem. The investigations included different rates and times of nitrogen application. At 1 site in 1982 and 2 in 1983 the soil was sampled to 30cm throughout the season. Nitrification of ammonium nitrogen was delayed by DCD (applied as a mixture with urea and supplying 10% ofthe nitrogen in the mixture) by up to 30 days compared with untreated urea and reduced the danger of nitrogen leaching. Early sampling at the 1982 site showed increased uptake of ammonium nitrogen and decreased nitrate nitrogen in wheat plants receiving DCD-treated urea compared with those receiving untreated urea. This confirmed that DCD inhibits nitrification. The only significant (P<0.05) grain yield increase from DCD was a 22% increase from an application of nitrogen at sowing on a particularly highly leaching soil. DCD significantly (P < 0.05, P < 0.01) reduced grain yield (7 and 8%) and vegetative yield (1 3 and 9%) at 2 sites. DCD increased vegetative yield by 16% at 1 site (not the same site as the grain yield increase). In 2 of 3 experiments plant dry matter production (up to 11 weeks after sowing) was significantly (P < 0.05 to P < 0.001) reduced (up to 30%) by DCD application. The final value of the use of DCD will depend on the balance between the benefit in preventing nitrogen losses by leaching at a particular site and the harm caused by suppressing early plant growth.

Sulfur-coated urea as a source of nitrogen for cereals in Western Australia

The effects of four grades of sulfurcoated urea (SCU1, 35.1% nitrogen (N) and dissolution rate in water at 38�C of 10.5%; SCU2, 36.3%N and 25.9% dissolution rate; SCU3, 36.2%N and 1 1.2% dissolution rate; SCU4, 36.8%N and 15.4% dissolution rate) were compared with those of uncoated urea as sources of nitrogen for cereals in nine field experiments in two years. In five experiments at five sites in 1978, and in two experiments at two sites in 1979, comparisons were made between fertilizers topdressed either after sowing (1978) or before sowing (1979). In two further experiments in 1979, comparisons were made between fertilizers banded with the seed or topdressed immediately before or after sowing. Supplementary data on the effect of banding were obtained from a glasshouse experiment. There were no differences between sources in three of the five 1978 experiments. At the other two sites urea was superior to SCU when 50 kg N/ha was applied 2 weeks after sowing. Applications of urea 4 or 6 weeks after sowing gave grain yields, at these sites, up to 69 and 57% higher, respectively, than earlier applications. Apparent recovery of fertilizer nitrogen in one experiment in which it was measured was greater for two SCUs (13.1 and 2l.6%, respectively) than for urea (6+9%), but this was true only for applications at sowing. Urea applied 4 and 6 weeks after sowing resulted in much higher recoveries of fertilizer nitrogen (33.9 and 49.3%, respectively) and was more effective in overcoming leaching losses than was the slow-release SCU. There were no effects of time of application before sowing in the two 1979 experiments, indicating little or no loss of ammonia through volatilization, which precluded a comparison of the effects of the three nitrogen sources used. However, uncoated urea outyielded two SCUs in these experiments, by 7.5 and 6.5% in the first experiment and 5 and 2% in the second, respectively. When uncoated urea was banded with the seed at the equivalent of 70 or 140 kg N/ha all plants in the glasshouse experiment died. SCU at the lower nitrogen rate did not affect wheat emergence or survival but a 30% reduction in plant numbers resulted at the higher rate of SCU2. In one field experiment, uncoated urea reduced plant numbers by 96% compared with 20 and 13% for SCU3 and SCU4, respectively, when applied at 75 kg N/ha. Overall, this study showed no reason to use these grades of SCU in preference to uncoated urea, except where there is a need to band urea-containing fertilizer with the seed.

An investigation of reduction in wheat yields after use of a high level of ammonium sulphate for a number of years

Investigations were carried out to determine reasons for reduced yields in two out of three multiple wheat cropping trials, where ammonium sulphate (S/A) was applied each year at 376 kg ha-1 (76 kg N ha-1). These included chemical analysis of soil and plant samples from the trials, and a pot trial on soil from the two affected sites at Merredin and Wongan Hills. At all three sites the SIAtreatment lowered soil pH and exchangeable bases and increased exchangeable H in the soil. Available Al was markedly increased at Merredin and Wongan Hills, the sites where yields were reduced, but to a much lesser degree on the third site at Beverley. Available Mn was increased at Beverley. The reductions in soil Mg and K were reflected in the contents of these nutrients in wheat tops from the sites, but Ca content was affected only at Merredin. Plant Mn levels were increased by S/A at Wongan Hills and Beverley, but Al levels did not show any consistent effects. The level of plant Mo was reduced by S/A at all sites. In pots, on soil from the high S/A plots at Merredin and Wongan Hills a large growth response to lime was obtained, but no growth responses to Ca, Mg or K. The response to lime was associated with a decrease in Al in the plants at both sites and an increase in P at Merredin. It was considered that Al toxicity was the most likely cause of the yield reductions, but that levels of K and Mo could also be marginal for healthy growth.

Effect of successive cropping with nitrogenous fertilizers on wheat yields

Wheat was grown for twelve successive years at three sites with five rates of nitrogen either as calcium ammonium nitrate, ammonium sulphate or urea applied each year to the same plots. There was a long term yield decline, with and without nitrogen, on the site at Wongan Hills, but not at Merredin or Beverley. At each of the three sites there was no indication of a need for higher rates of nitrogen fertilizers with time to maintain yields. At Wongan Hills and Merredin, yields were depressed in most years when the highest rate of ammonium sulphate was used each year. Grain protein contents were low and did not decrease with time.

Effects of urea, ammonium nitrate and superphosphate on establishment of cereals, linseed and rape

In pots filled with a loamy sand the degree of harm caused by urea banded with the seed or topdressed on the soil surface, varied with species. The order of susceptibility to germination damage was rape> linseed > > oats > wheat > barley. In addition the emergence of rape and linseed was reduced from about 90 per cent of possible germination to around 50 per cent when superphosphate was banded with the seed. The adverse effect on wheat was greater when the seed bed was moist rather than dry and the effect was reduced when the pots were watered immediately after seeding. On the same soil in the field urea reduced emergence of wheat much more than did ammonium nitrate when both were drilled in contact with the seed.