Atmospheric trends in methylchloroform and the global average for the hydroxyl radical

Frequent atmospheric measurements of the anthropogenic compound methylchloroform that were made between 1978 and 1985 indicate that this species is continuing to increase significantly around the world. Reaction with the major atmospheric oxidant, the hydroxyl radical (OH), is the principal sink for this species. The observed mean trends for methylchloroform are 4.8, 5.4, 6.4, and 6.9 percent per year at Aldrigole (Ireland) and Cape Meares (Oregon), Ragged Point (Barbados), Point Matatula (American Samoa), and Cape Grim (Tasmania), respectively, from July 1978 to June 1985. These measured trends, combined with knowledge of industrial emissions, were used in an optimal estimation inversion scheme to deduce a globally averaged methylchloroform atmospheric lifetime of 6.3 (+ 1.2, -0.9) years (1sigma uncertainty) and a globally averaged tropospheric hydroxyl radical concentration of (7.7 +/- 1.4) x 10(5) radicals per cubic centimeter (1sigma uncertainty). These 7 years of gas chromatographic measurements, which comprise about 60,000 individual calibrated real-time air analyses, provide the most accurate estimates yet of the trends and lifetime of methylchloroform and of the global average for tropospheric hydroxyl radical levels. Accurate determination of hydroxyl radical levels is crucial to understanding global atmospheric chemical cycles and trends in the levels of trace gases such as methane.     

Spin-dependent WIMP limits from a bubble chamber

Bubble chambers were the dominant technology used for particle detection in accelerator experiments for several decades, eventually falling into disuse with the advent of other techniques. We report here on a new application for these devices. We operated an ultraclean, room-temperature bubble chamber containing 1.5 kilograms of superheated CF3I, a target maximally sensitive to spin-dependent and -independent weakly interacting massive particle (WIMP) couplings. An extreme intrinsic insensitivity to the backgrounds that commonly limit direct searches for dark matter was measured in this device under operating conditions leading to the detection of low-energy nuclear recoils like those expected from WIMPs. Improved limits on the spin-dependent WIMP-proton scattering cross section were extracted during our experiments, excluding this type of coupling as a possible explanation for a recent claim of particle dark-matter detection.     

The effect of sowing date, stale seedbed, row width and mechanical weed control on weeds and yields of organic winter wheat

Three field experiments were carried out in organically grown winter wheat in Denmark. The treatments were sowing time (normal or late sowing) and false seedbed, row width (12 and 24 cm) and weed control method [untreated; mechanical weed control (weed harrowing at 12 cm supplemented with inter‐row hoeing at 24 cm); and herbicide weed control]. Weed biomass in midsummer was greatest on plots sown at the normal sowing time (compared with delayed sowing) and was reduced by mechanical or chemical weed control (compared with untreated plots). Row width alone had no influence on weed biomass, but in the experiment with high weed pressure, the more intensive mechanical weed control used at a row width of 24 cm reduced weed biomass. Normal sowing time tended to give higher yields, but this was only statistically significant in one of the three experiments. Wide rows gave a yield decrease in the experiment with low weed pressure. The effect of weed control on yield was dependent on the weed pressure. At low weed pressure, mechanical weed control caused a yield decrease compared with untreated or herbicide treated. At intermediate weed levels there were no differences, whereas at high weed pressure, mechanical weed control and herbicide treatment caused a yield increase compared with untreated. False seedbeds were shown to contribute to a decrease in the soil seed reserve.     

Spatial variability in the mineralisation of the phenylurea herbicide linuron within a Danish agricultural field: multivariate correlation to simple soil parameters

The spatial variability in the mineralisation rate of linuron [N-(3,4-dichlorophenyl)-N'-methoxy-N'-methylurea] was studied within a previously treated Danish agricultural field by sampling soils from eleven different plots randomly distributed across an area of 20 x 20 m. The soils were characterised with respect to different abiotic and biotic properties including moisture content, organic matter content, pH, nutrient content, bacterial biomass, potential for mineralisation of MCPA [(4-chloro-2-methylphenoxy)acetic acid] and linuron. Five soils had a potential for mineralisation of linuron, with 5-15% of the added [ring-U-14C]linuron metabolised to 14CO2 within 60 days at 10 degrees C, while no extensive mineralisation of linuron was observed in the six remaining soils within this period. A TLC analysis of the methanol-extractable residues showed no development of 14C-labelled metabolites from linuron in any of the samples. Multivariate analysis was conducted to elucidate relationships between the intrinsic properties of single soil samples and initial rate of linuron mineralisation. The analysis indicated that important soil parameters in determining the spatial heterogeneity included the C(total)/N(total) ratio, pH and the water-extractable potassium contents, with the first of these highly negatively correlated and the last two highly positively correlated to the initial linuron mineralisation rate. This study shows that enhanced biodegradation of linuron may develop with successive field treatments, but that considerable in-field spatial heterogeneity in the degradation rate still exists. Combined with a parallel enrichment study focused on the underlying microbial processes, the present results suggest that intrinsic soil properties affect the linuron-metabolising bacterial population and thereby determine the spatial variability in the linuron mineralisation activity.     

Reaction of Ptr ToxA-Insensitive Wheat Mutants to Pyrenophora tritici-repentis Race 1

ABSTRACT The host-selective toxin Ptr ToxA is produced by races 1 and 2 of Pyrenophora tritici-repentis, causal agent of tan spot of wheat. Ptr ToxA has been causally associated with pathogenicity by the race 2 phenotype in this system. However, the role of toxin in disease caused by race 1, the most prevalent form of the fungus in the central and northern Great Plains of North America, has not been rigorously investigated. Three independent wheat lines harboring mutations for insensitivity to Ptr ToxA were derived from ethylmethane sulfonate treatment of the hard red spring wheat cv. Kulm, possessing the single dominant gene for toxin sensitivity. Each of the three mutants was insensitive to Ptr ToxA in bioassays based on necrosis development and electrolyte leakage. Each mutant was crossed to each of the other mutants and to the wild-type Kulm. Segregation data indicate that each mutant line harbors a single recessive mutation for toxin insensitivity that maps to or near the same locus, possibly the toxin-sensitivity gene. Each toxin-insensitive mutant line was susceptible to two isolates of race 1 of P. tritici-repentis. F(2) and F(3) generations derived from crosses between Kulm and each mutant segregated for toxin reaction. However, segregation for fungal reaction was not evident, and all F(3) families were tan spot susceptible regardless of toxin reaction. Host insensitivity to Ptr ToxA is not necessarily equivalent to resistance to race 1. Ptr ToxA should not be used alone as a proxy for fungal inoculations by breeding programs aimed at developing tan spot-resistant wheat.     

Use of paclobutrazol sprays at mid-anthesis for increasing fruit size and yield of avocado (Persea americana Mill. cv. Hass)

Mid-anthesis foliar sprays of paclobutrazol (PB) at 2.5, 1.25 and 0.62 g a.i. I-1 reduced spring growth and altered dry-matter distribution in fruiting spring shoots of ‘Hass’ avocado.(Persea americana Mill.) trees. There was a decrease in dry matter allocation to vegetative components and an increase in allocation to fruit. The starch concentration in the wood of spring shoots on trees treated with 2.5 g a.i. I-1 foliar PB was increased by ca. 70% compared with spring shoots from trees of other treatments. The mid-anthesis foliar treatments also reduced summer growth by ca. 20%. Trunk injection of PB at 0.2 g a.i. m~2 of canopy silhouette area when the spring growth matured, in addition to a mid- anthesis foliar spray of 1.25 g a.i. I-1, reduced the length of summer shoots by 36% when compared with untreated trees. The spray treatments of 2.5 and 1.25 g a.i. T1 PB at mid- anthesis increased the mean fruit size at harvest by 16 and 11% respectively. Fruit yield was not significantly affected by PB applications on an annual basis. However, the PB spray treatments of 1.25 and 0.62 g a.i. I-1 significantly increased the two year cumulative yield by ca. 63%. There was no significant effect from the trunk injection treatment on fruit yield in either the season of treatment or the following season.     

Effect of temperature on growth,dry matter production and starch accumulation in ten mango (Mangifera indica L.) cultivars

Summary

Ten mango cultivars of tropical and subtropical origin (Carabao, Kensington, Nam Dok Mai, Alphonso, Dashehari, Florigon, Glenn, Irwin, Haden and Sensation) were grafted onto cv. Kensington seedling rootstock and held at four day/night temperatures for 20 weeks (15/10°C, 20/15°C, 25/20°C and 30/25°C). Vegetative growth increased with increasing temperatures. All grew vegetatively at 25/20°C and 30/25°C. Cultivars which did not grow at 20/15°C were Carabao, Kensington and Dashehari. Cultivars Kensington, Nam Dok Mai, Alphonso, Florigon, Glenn, Irwin, Haden and Sensation produced flower panicles at 15/10°C. The rise in temperature increased the average number of growth flushes (in responsive cultivars) from 0.48 at 15/10°C to 3.21 at 30/25°C, and the number of leaves per growth flush (1.22 at 15/10°C to 13.63 at 30/25°C). Distribution of dry matter from new growth was mostly to the roots at the lowest temperature (95% at 15/10°C) and to the leaves (58%) at 30/25°C. The mean daily temperature for zero vegetative growth was calculated to be 15°C. Temperature and related growth activity also affected the concentration of starch in the woody tissue of rootstock trunks at the end of 20 weeks (15.9% starch at 15/10°C v. 4.8% starch at 30/25°C). ‘Irwin’ had the highest starch concentration at the two higher temperatures (twice that of any other cultivar at 30/25°C) while ‘Kensington’ the lowest starch level at 25/20°C, ca. 50% of most other cultivars.     

Influence of different disease control pesticide strategies on multiple pesticide residue levels in apple

Summary

Seven pesticide application strategies were investigated to control apple scab (Venturia inaequalis) and powdery mildew (Podosphaera leucotricha) and, at the same time, fulfil the new quality standards implemented by some German retailers. These demand that pesticide residues should be below 80% of European Maximum Residue Levels (EU MRL) and that the number of residues present at levels above 0.01 mg kg^?1 should be limited to a maximum of four. The strategies fulfilled the requirement to use combinations of different active substances in order to prevent the emergence of resistance to pesticides. The trials were conducted at two sites in Switzerland, in 2007, and all strategies and applications were in accordance with actual practice. Four replicates of apple samples from each strategy were then analysed for pesticide residues. The incidence of infection with apple scab and powdery mildew were monitored during the season in order to evaluate the efficacy of the different strategies. The efficacies of the different strategies against apple scab and powdery mildew were between 84% and 100% successful. In general, the level of pesticide residues found correlated with application rate and time, and no measured residue level exceeded the EU–MRL. The numbers of residues present at > 0.01 mg kg^?1 were between two and five.     

The role of flower and leaves in cut flower water uptake

Removal of the cut rose flower of ‘Forever Yours’ decreased water uptake by 20.4%, leaf removal 78.5%, and both flower and leaf removal 95.2%. Cut carnation ‘White Sim’ water uptake declined 27.1, 37,3 and 59.6% after flower, leaf, or both were removed, respectively. A high rate of water uptake (40.4%) continued after both carnation flower and leaf removal.     

A novel approach to estimating the competitive ability of Cirsium arvense in cereals using unmanned aerial vehicle imagery

Eight experiments were carried out in Denmark to determine the yield loss of spring barley due to Cirsium arvense in farmers' fields and to suggest and evaluate a novel approach for quantifying C. arvense infestation in large plots. Literature about the competitive ability of C. arvense is old, scattered and inconclusive, and existing models for estimating crop yield loss are based on data from North America. This study showed that C. arvense coverage could be quantified from unmanned aerial vehicle imagery using a manual image analysis procedure. This gave similar results as scoring the coverage. Yield loss of spring barley due to C. arvense infestation assessed at harvest was given by Y = 100·(1−exp(−0.00170·X)) where Y is the percentage of crop yield loss and X is the percentage of C. arvense coverage. The yield loss was much lower than estimates from models that have been developed in North America. It is speculated that the main reason for this is the later emergence of C. arvense than the crop due to lower soil temperatures in spring. Grain moisture increased linearly with C. arvense coverage: M = 0.0310·X where M is the proportional (%) increase in grain moisture and X is the proportion (%) of C. arvense coverage. Automated image analysis procedures are needed to estimate C. arvense coverage on field scales, and further experiments are needed to reveal whether the low competitive ability of C. arvense found in this study is representative for Northern Europe.