Effect of soil treatment with cereal straw and method of crop establishment on field pea (Pisum sativum L.) N2 fixation

The effects of soil incorporation with cereal straw (nil, 2.5, 5 and 10 t straw ha^–1) and direct drilling on the proportion and amount of pea N derived from biological N fixation were investigated in three field experiments. Fixed N was determined by¹⁵N dilution using barley as a reference plant. The three sites were on acidic, red clay-loams in the cropping zone of southeastern Australia. Seasonal plant available soil N, as determined by the N accumulated in barley, was 31, 56 and 158 kg N ha^–1, for the three sites. Incorporated straw reduced soil nitrate at sowing by 10–50 kg N ha^–1 (0–30 cm), and 5 or 10 t straw ha^–1 reduced barley uptake of N by 10–38 kg N ha^–1. However, reducing plant available soil N was generally ineffective for increasing the N fixed by pea. Fixed N increased only at the site with the least plant-available N, and only one-third of the increase could be attributed to lower soil N uptake by pea. There was no evidence that direct drilling pea increased fixed N by decreasing crop uptake of soil N. It is proposed that a lower requirement for soil N by pea as compared to barley, and availability of mineral N beneath the soil layer treated with straw, minimise the effectiveness of straw incorporation for increasing the N fixed by pea.     

Frequency distributions for durations and volumes of rainfalls in the Eastern United States in relation to acidic precipitation

A significant percentage (between 17 and 40%) of all showers recorded on Long Island, NY, Urbana, IL, Franklin, NC, and Seaside Park, NJ, had durations less than 20 min. Similarly, a large percentage had durations less than 40 min (50, 46, and 32% for 3 yr at Urbana, IL, 65% at Coral Gables, FL, 50% at Franklin, NC, and 54% at Seaside Park, NJ). When all data from the six growing seasons were pooled, over 88% of all rainfalls were less than 160 min. Similar results were observed when volume measurements were made. Between 38 and 57% of all recorded showers had less than 1 mm at all five stations in the eastern United States. When all data were pooled, over 65% of all rainfalls were less than 3 mm. These data demonstrate that plant foliage is wetted during the growing season by numerous showers which are of short duration and low volume.     

Use of a trap garden to find additional genetically distinct isolates of the rust fungus <Emphasis Type="Italic">Phragmidium violaceum</Emphasis> to enhance biological control of European blackberry in Australia

Biological control agents can be more effective if their populations are genetically diverse, particularly when the target invasive plant comprises a range of genotypes with different susceptibilities and occurs across various microclimates. We report on the use of an efficient approach to find, in the native range, diverse isolates of a rust fungus for biological control. An outdoor trap garden containing various clones of invasive European blackberry (Rubus fruticosus agg.) collected in Australia, each with a different DNA phenotype, was established in France. Within 4 weeks of establishment, the leaf-rust fungus Phragmidium violaceum was recovered from all clones in the garden. Molecular analyses of eight recovered and purified isolates of the fungus from the garden revealed that they were genetically distinct from each other and from isolates already present in Australia. These garden isolates also represented a subset of the population existing in Europe, when compared to isolates collected about 30 years ago. Two pathogenicity phenotypes were observed among the garden isolates in bioassays consisting of representative blackberry clones from Australia, and together the isolates were capable of infecting all clones. Results from host-specificity tests on key non-target plant species closely related to European blackberry concurred with previous findings that the leaf-rust fungus does not pose a threat to commercial blackberry cultivars and Rubus species native to Australia. The release and establishment of the garden isolates in Australia has potential to increase the genetic diversity and evolutionary potential of the leaf-rust fungus for more effective biological control.     

Issues in equitable access to agricultural information

Economic pressures and information policy changes in the public and private sectors are influencing the kinds, amounts, and availability of information to agricultural producers. This analysis identifies some of the major changes, examines their effects, identifies some issues of equity, and poses questions for further study. The changes are found to have special negative effects on producers with smaller operations, fewer financial resources, lower levels of formal education, remote locations, specialized enterprises, and low input enterprises.James F. Evans is Professor of Agricultural Communications and Journalism at the University of Illinois.     

Experimental verification of designer surface plasmons

We studied the microwave reflectivity of a structured, near perfectly conducting substrate that was designed to verify the existence of a theoretically proposed new class of surface mode. Measurements of the mode's dispersion curve show that it correctly approaches the predicted asymptotic frequency; the curve also agrees well with that derived from a computer simulation. Modeling of the field distribution on resonance provides evidence of strong localization of the electric field at the interface and substantial power flow along the interface, thus verifying the surface plasmon-like nature of the mode.     

Multiple representations of pain in human cerebral cortex

The representation of pain in the cerebral cortex is less well understood than that of any other sensory system. However, with the use of magnetic resonance imaging and positron emission tomography in humans, it has now been demonstrated that painful heat causes significant activation of the contralateral anterior cingulate, secondary somatosensory, and primary somatosensory cortices. This contrasts with the predominant activation of primary somatosensory cortex caused by vibrotactile stimuli in similar experiments. Furthermore, the unilateral cingulate activation indicates that this forebrain area, thought to regulate emotions, contains an unexpectedly specific representation of pain.