For lentil production to expand further in Australia, adaptation to the less favourable soils of the low to medium rainfall zones is required. To improve adaptation to these regions, varieties are required with increased tolerance to soil constraints such as high concentrations of boron (B), salinity and sodicity. To evaluate the range of B tolerance in lentil germplasm, 310 lines were screened in soil with a high concentration of B and tolerance was assessed at the seedling stage. A wide range in response to high concentrations of soil B was observed in the germplasm tested. Current Australian varieties were generally very intolerant to high concentrations of soil B. High levels of B tolerance was identified in germplasm originating from Afghanistan and Ethiopia. A subsequent experiment comparing lentils with different levels of B tolerance found that tolerant accessions (ILL213A and ILL2024) produced greater above and below ground biomass than intolerant accessions. The tolerant accessions had no significant yield loss under a high B treatment (extractable B = 18.20 mg/kg) compared to the control treatment (extractable B = 1.55 mg/kg). The large improvement in B tolerance, at soil concentrations typical of those found in the target regions, suggests there is potential to improve the tolerance level of adapted varieties and expand lentil production areas to regions with higher concentrations of soil B.
The primer-plant concept was tested for wheat (Triticum aestivum) grown on an alkaline sodic soil taken from the southern Mallee of Victoria. This concept relates to use of species of plants with high natural adaptation to hostile subsoils, being able to modify the soil environment and leave biopores for the benefit of subsequent annual crops. For the experiment reported here, wheat was sown into large (0.3 m diam. by 1.0 m length) intact soil cores (collected from a cropping paddock near Birchip in the southern Mallee region of Victoria, Australia) following either birdsfoot trefoil (Lotus corniculatus), canola (Brassica napus), chicory (Cichorium intybus), lucerne (Medicago sativa), safflower (Carthamus tinctorius), sulla (Hedysarum coronarium), or tall wheatgrass (Thinopyrum ponticum). At the conclusion of the priming phase [270 days after sowing (DAS)], all the different crops extracted c. 145 mm of stored water, the exception being canola (120 mm). Lucerne and birdsfoot trefoil produced the least above-ground biomass (26 g/pot), and safflower the most (115 g/pot). Greater early vigour and water extraction (49 mm) occurred for subsequent wheat crops after birdsfoot trefoil than with wheat after all other species (39 mm). This translated to a 15% yield advantage for wheat after birdsfoot trefoil compared with lucerne. Wheat after sulla yielded 12% more due to increased grain number and kernel size compared with wheat after lucerne. It was proposed that the difference in yield related to the root systems of species tested. Birdsfoot trefoil and sulla were characterised by intensive branching, which potentially produced a fine mosaic of residual biopores. Lucerne, in contrast, which was assumed to have similar break-crop effects, had a large taproot with fewer branches leaving fewer, larger residual root channels than either of the other legumes. It is believed that the fine biopores allowed more rapid and thorough exploration of the bulk soil by the crop roots.
The deep-placement of nutrient-rich organic amendments in poorly-structured subsoils can improve subsoil structure and increase grain yields, but its widespread adoption by farmers is limited by the availability and cost of animal manures, the current choice of amendment. Three glasshouse experiments investigated the effectiveness of dried field pea (Pisum sativum L.) shoots (green chop), as green manure, on wheat growth in three subsoils with contrasting soil chemical and physical properties. The growth of wheat plants was greatly suppressed when the green chop was placed in Sodosol and Chromosol subsoils. In contrast, there was a 2-fold increase in shoot biomass in response to the addition of green chop to Vertosol. Three allelopathic compounds, pisatin, anhydropisatin, and maackian, were identified at higher concentrations in the extracts of remaining green chop residues in the Sodosol and Chromosol, compared to the Vertosol, directly supporting phytotoxicity as the cause of observed inhibitory effects of green chop in these soils. The persistence of the phytotoxicity in the Sodosol might be attributed to its poor aeration caused by poor structure or compaction. Nevertheless, pre-incubation led to microbial decomposition of the allelochemicals in the Sodosol, though at a much slower rate than in the Vertosol. Further studies are needed to determine the time period required for the disappearance of the phytotoxic effects in soils with different physico-chemical properties.
DISCUSSIONDr. C. M. @inn (Birmingham) said: As discussants are no doubt aware by this time, Lloyd, Richardson and I at Birmingham University have recently begun a study of angular dependence in p.e. of surfaces. I am very impressed by Willis's paper since it seems to go a considerable distance along the road to our understanding electron emission processes at surfaces. I would like to ask him one question and make one remark about the interpretation of off-normal angular resolved emission data.My remark concerns the influence of momentum broadening normal to the surface whenever an evanescent final state occurs in the photoelectric process. Under such conditions the surface photoelectric process applies and the degree of normalmomentum broadening reflects the localization in the normal direction into the crystal of the incoming scattering function. Thus it seems to me that a characteristic of surface photoelectric emission should be an " angular broadening " in which spectral features due to the surface effect occur over a range of angles in angularresolved spectra, a range reflecting the normal-momentum broadening. For copper single crystals, our results to date suggest that we may be observing this type of effect in certain instances.For a copper (001) surface and analyser tracking from (001) to (100) directions, one expects band-structure in the rWKWr section of the Brillouin-zone to be observable. We expected for identical photon angles that we should be able to monitor the TW band-structure at -26" and then again at -63" off-normal. However, the spectra for the analyser settings are different and this is also true over a range on either side of these positions. Can this be due to a large refraction effect? My question concerns the problem of refraction.
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