Stratification requirements for seed dormancy alleviation in a wetland weed.

Echinochloaoryzicola(syn.E. phyllopogon) is an exotic weed of California rice paddies that has evolved resistance to multiple herbicides. Elimination of seedlingsthroughcertain weed control methods can limit the spread of this weed, but is contingent on accurate predictions of germination and emergence timing, which are influenced by seed dormancy levels.In summer annuals, dormancy can often be relieved through stratification, a period of prolonged exposure to cold and moist conditions.We used population-based threshold models to quantify the effects of stratification on seed germination of four E. Oryzicola populations at a range of water potential (Ψ) and oxygen levels. We also determined how stratification temperatures, moisture levels and durations contributed to dormancy release. Stratification released dormancy by decreasing base Ψ and hydrotimerequired for germination and by eliminating any germination sensitivity to oxygen. Stratification also increased average germination rates (GR), which were used as a proxy for relative dormancy levels. Alternating temperatures nearly doubled GR in all populations, indicating that seeds could be partially dormant despite achieving high final germination percentages. Stratification at Ψ = 0 MPa increased GR compared to stratification at lower water potentials, demonstrating that Ψ contributed to regulating dormancy release. Maximum GR occurred after 2-4 weeks of stratification at 0 MPa; GR were often more rapid for herbicide-resistant than for herbicide-susceptible seeds, implying greater dormancy in the latter. Manipulation of field conditions to promote dormancy alleviation of E. oryzicola seeds might improve the rate and uniformity of germination for seed bank depletion through seedling weed control. Our results suggest field soil saturation in winter would contribute towards E. oryzicola dormancy release and decrease the time to seedling emergence

Assessment of the potential of MERIS near-infrared water vapour products to correct ASAR interferometric measurements

Atmospheric water vapour is a major limitation for high precision Interferometric Synthetic Aperture Radar (InSAR) applications due to its significant impact on microwave signals. We propose a statistical criterion to test whether an independent water vapour product can reduce water vapour effects on InSAR interferograms, and assess the potential of the Medium Resolution Imaging Spectrometer (MERIS) near-infrared water vapour products for correcting Advanced SAR (ASAR) data. Spatio-temporal comparisons show c. 1.1mm agreement between MERIS and GPS/radiosonde water vapour products in terms of standard deviations. One major limitation with the use of MERIS water vapour products is the frequency of cloud free conditions. Our analysis indicates that in spite of the low global cloud free conditions (~25%), the frequency can be much higher for certain areas such as Eastern Tibet (~38%) and Southern California (~48%). This suggests that MERIS water vapour products show potential for correcting ASAR interferometric measurements in certain regions

Interference of annual weeds in seedling alfalfa

The interference of barnyardgrass (Echinochloa crusgalli), pigweed (Amaranthus retroflexus),downy brome (Bromus tectorum),and tumble mustard (Sisymbrium altissimum) with alfalfa was studied. Alfalfa was seeded with each of the four weeds on August 14 and September 15, 1981, and on April 13, 1982. Alfalfa also was seeded on August 27, 1981, with a mixture of the four weed species, and the weeds were allowed to grow with the crop during several intervals. The presence of weeds emerging with the crop in the fall reduced alfalfa yields in the first two cuttings in the spring. When alfalfa and each of the weeds were planted on August 14 (early seeding), barnyardgrass and downy brome were the most interfering weeds. In a later seeding (Sept. 15), the summer annual weeds (barnyardgrass and pigweed) were killed by frost in the fall and did not compete with the crop; downy brome and tumble mustard (winter annuals), however, became more aggressive than if allowed to emerge with the crop a month earlier. When alfalfa seeded on August 27 was kept weed free for approximately 65 days after emergence, no further weed control was needed for maximum forage yields in the spring. Conversely, the crop tolerated weeds that emerged with it if they were eliminated before the onset of winter. In the spring seedings, the four weeds interfered equally with the crop. Alfalfa needed to grow free of weeds from approximately the 17th to the 39th day after emergence to avoid forage yield and quality reductions. Weeds that emerged early with the crop reduced forage yields more than later-germinating weeds. Once the alfalfa developed a canopy capable of covering the soil, weeds emerging thereafter were suppressed by shading. The initial tolerance to the presence of weeds allows the farmer flexibility in the timing of the first weed control measure. This initial tolerance seems to indicate that interference is not significant until competition for light begins

Where to Find 1.5 Million Yr Old Ice for the IPICS Oldest Ice Ice Core

Abstract. The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this pro- gression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic distur- bance and should be able to be recovered after careful pre- site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that po- sitions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to pre- vious ice core drill site selections, however, we strongly sug- gest significantly reduced ice thickness to avoid bottom melt- ing. For example for the geothermal heat flux and accumu- lation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined be- forehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity com- mences to bring datable samples to the surface and to allow an age check of the oldest ice

Intra- and interspecific interference between sweet corn (Zea mays L.) and a living mulch of white clover (Trifolium repens L.)

Living mulches are vegetative covers that can grow in association with row crops and may prevent soil erosion and suppress weeds. Crop reduction from association with the living mulch is a frequent problem with this cultural practice. The interference between a white clover (Trifolium repens L. "New Zealand") living mulch and sweet corn (Zea mays L. "Golden Jubilee") was studied using an established clover sward, that was mowed and then sprayed with 1 to 1.5 kg al/ha of atrazine [6_chloro__ethyl--(1-methylethyl) 1,3,5,triazine-2,4-diamine]. Corn, at different densities and planting arrangements, was planted into a 10-to 15-cm-wide band tilled in the clover. Replacement-series experiments and systematic density experiments also were conducted in this study. The experiments were irrigated. Interference by clover reduced corn yields. However, when corn row width was reduced from 76 cm to 38 cm, intraspecific interference among corn plants was reduced, and corn plants became more productive and clover suppressive. Corn and clover competed for the same resources (mainly for light) when grown in mixture for 35 days after corn emergence. Clover appeared to be the superior competitor. However, the two species partially avoided competition. Nitrogen concentration in corn tissue (48 days after planting) was reduced when the corn was grown with clover, whereas the concentrations of P, K,and S were not altered by the presence of the legume. Twenty-four days after spraying clover with atrazine, up to 3]. kg N/ha had been released into the soil from the clover. Thirty-four days later, the N concentration in soil of sprayed and unsprayed plots was the same. Soil moisture (20 cm depth) was not affected by the presence of the clover mulch

Nova Geminorum 1912 and the Origin of the Idea of Gravitational Lensing

Einstein's early calculations of gravitational lensing, contained in a scratch notebook and dated to the spring of 1912, are reexamined. A hitherto unknown letter by Einstein suggests that he entertained the idea of explaining the phenomenon of new stars by gravitational lensing in the fall of 1915 much more seriously than was previously assumed. A reexamination of the relevant calculations by Einstein shows that, indeed, at least some of them most likely date from early October 1915. But in support of earlier historical interpretation of Einstein's notes, it is argued that the appearance of Nova Geminorum 1912 (DN Gem) in March 1912 may, in fact, provide a relevant context and motivation for Einstein's lensing calculations on the occasion of his first meeting with Erwin Freundlich during a visit in Berlin in April 1912. We also comment on the significance of Einstein's consideration of gravitational lensing in the fall of 1915 for the reconstruction of Einstein's final steps in his path towards general relativity.Comment: 31 p

A cost effectiveness and capacity analysis for the introduction of universal rotavirus vaccination in Kenya : comparison between Rotarix and RotaTeq vaccines

Background Diarrhoea is an important cause of death in the developing world, and rotavirus is the single most important cause of diarrhoea associated mortality. Two vaccines (Rotarix and RotaTeq) are available to prevent rotavirus disease. This analysis was undertaken to aid the decision in Kenya as to which vaccine to choose when introducing rotavirus vaccination. Methods Cost-effectiveness modelling, using national and sentinel surveillance data, and an impact assessment on the cold chain. Results The median estimated incidence of rotavirus disease in Kenya was 3015 outpatient visits, 279 hospitalisations and 65 deaths per 100,000 children under five years of age per year. Cumulated over the first five years of life vaccination was predicted to prevent 34% of the outpatient visits, 31% of the hospitalizations and 42% of the deaths. The estimated prevented costs accumulated over five years totalled US$1,782,761 (direct and indirect costs) with an associated 48,585 DALYs. From a societal perspective Rotarix had a cost-effectiveness ratio of US$142 per DALY (US$5 for the full course of two doses) and RotaTeq US$288 per DALY ($10.5 for the full course of three doses). RotaTeq will have a bigger impact on the cold chain compared to Rotarix. Conclusion Vaccination against rotavirus disease is cost-effective for Kenya irrespective of the vaccine. Of the two vaccines Rotarix was the preferred choice due to a better cost-effectiveness ratio, the presence of a vaccine vial monitor, the requirement of fewer doses and less storage space, and proven thermo-stability

A fast Monte Carlo algorithm for site or bond percolation

We describe in detail a new and highly efficient algorithm for studying site or bond percolation on any lattice. The algorithm can measure an observable quantity in a percolation system for all values of the site or bond occupation probability from zero to one in an amount of time which scales linearly with the size of the system. We demonstrate our algorithm by using it to investigate a number of issues in percolation theory, including the position of the percolation transition for site percolation on the square lattice, the stretched exponential behavior of spanning probabilities away from the critical point, and the size of the giant component for site percolation on random graphs.Comment: 17 pages, 13 figures. Corrections and some additional material in this version. Accompanying material can be found on the web at http://www.santafe.edu/~mark/percolation