VEGETATION MANIPULATION WITH SELECTIVE HERBICIDES IN VINEYARDS

Cover crops are planted between vineyard rows to control erosion, maintain organic material and influence pest management. Planted cover crops are preferable to resident vegetation (weeds) because they can be selected for beneficial characteristic. Sethoxydim and fluazifop-butyl alone and in combination with 2,4-D were applied in December 1988 and 1989 to release Festuca megalura (Zorro fescue). Untreated plots were mowed to maintain vegetation. Frequency, percent cover and biomass of the vegetation was evaluated to determine species shift. The vegetation was composed mainly of: 1. Festuca megalura, Poa annua with other grasses in minor amounts; and 2. Stellaria media, Centaurea solstitialis, Erodium botrys and Erodium cicutarium Following sethoxydim or fluazifop-butyl treatments, annual grasses other than Festuca megalura and Poa annua were reduced but Centaurea sp. increased over the length of the experiment. Treatments containing 2,4-D Centaurea and Erodium spp. declined in both frequency and percent cover. The desirable cover crop species (Festuca megalura) increased in all treated plots. No species shift was observed in the mowed treatments. Two applications of selective post-emergence herbicides maintained shift of species over the 5 years of the study.

Selection by grazing sheep of pasture plants at low herbage availability and responses of the plants to grazing

Merino sheep grazing annual pasture at the beginning of the growing season when the amount of herbage on offer was small, preferred to graze Wimmera ryegrass Lolium rigidum or subterranean clover Trifolium subterraneum rather than capeweed Arctotheca calendula, and Erodium botrys was avoided completely. Behaviour observations showed that capeweed plants were usually avoided. When the plants were grasped they were sometimes pulled up by the roots and then dropped so that the number of capeweed plants in the pasture declined. Supplementation with oats reduced grass intake. Harvesting behaviour changed with pasture conditions: as grass height declined in the pasture, the rates of biting, stepping and head swinging increased. Pasture measurements showed that, whilst capeweed plants continued to increase in height during grazing, as did ungrazed controls, ryegrass and clover plants decreased or remained short. Herbage dry matter increased in all species, owing especially to basal growth. The proportion of shoots and petioles which were erect increased in ungrazed plants, but the proportion which were prostrate was much greater in grazed plants. Individual plants adapted their growth form in a way which counteracted the depredations of grazers. The ecological implications of these findings are important. Firstly, the sheep were not foraging optimally in terms of maximising rate of intake, since two abundant species were largely ignored even though food availability was low. Secondly, because of their selectivity the sheep were giving the capeweed and Erodium a competitive advantage which, in these pastures, will persist through the growing season.

A Quantitative Study of the Spores and Anatomy of Mycorrhizas Formed by a Species of Glomus, With Reference to Its Taxonomy

The development of spores and sporocarps was studied in two isolates of a species of Glomus collected in Western Australia. The isolates, which had been maintained in pot culture, differed slightly in the size range of spores and in the relationship between spore size and the development of the peridium. Anatomical characteristics of mycorrhizas of three pasture species (Trifolium subterraneum, Erodium botrys and Lolium rigidum) formed with this species of Glomus were essentially the same and were largely unaffected by nitrogen supply. The hyphae in nitrogen-deficient plants were slightly wider than those in nitrogen-adequate plants of T. subterraneum and E. botrys. The effect of phosphorus supply on the anatomy of mycorrhizas formed by this fungus and T. subterraneum was studied with time. Phosphorus supply had no effect on the formation of arbuscles, the density of hyphae within infected roots, or the morphology of the branching pattern of the endophyte hyphae within the root. However, phosphate added above that required for maximum plant yield eliminated vesicle formation. Anatomical characteristics of the mycorrhizas changed little with time except for arbuscle number, which decreased markedly between 29 and 50 days after sowing. We concluded that the anatomy of vesicular arbuscular mycorrhizas formed by a particular endophyte species grown under a range of conditions may not be as variable as has been generally assumed. There is scope for identification of species of endophyte within plant roots. Furthermore, some features of infection morphology could prove to be useful for taxonomic purposes.

Nitrogen in temperate crop and pasture plants

Nitrogen concentrations were determined in the tops of 24 annual crop and pasture varieties grown together in ungrazed plots on a lateritic gravelly sand at Gidgegannup, W.A., and sampled at three stages during growth and at maturity. All legumes had higher nitrogen concentrations in the tops than all non-legumes, but considerable variation was evident within each group. Among pasture legumes, Ornithopus compressus and O. sativus had the highest concentrations, especially towards maturity, and Trifolium subterraneum cv. Yarloop and Clare the lowest. Nitrogen concentrations in all Lupinus spp. fell rapidly towards maturity, and they were unique in suffering substantial net nitrogen losses from the tops. The herb Erodium botrys grew better and took up more nitrogen under conditions of deficiency than did the grasses. Its nitrogen concentration was nevertheless very low. Among the grasses, Bromus rigidus consistently had the highest nitrogen concentration and Lolium rigidum the lowest. There was some evidence among non-legumes of a correlation between high nitrogen concentrations and/or total uptake and observed adaptation to sandy soils. The superior adaptation of legumes in the experimental environment was demonstrated. It is suggested that crop legumes could make a more important agronomic contribution than hitherto in this and similar environments.

The mineral composition of lupins. 2. A comparison of the copper, manganese, molybdenum, and cobalt contents of lupins and other species at the one site

In a field experiment on an ironstone gravel soil, six lupin varieties from four lupin species were compared with oats, Wimmera ryegrass, Erodium botrys, and three varieties of subterranean clover in their copper contents at four rates of copper application. Manganese, molybdenum and cobalt contents of bulked variety samples were also determined. At rates of up to 20 lb copper sulphate per acre, only subterranean clover and Erodium botrys showed appreciable response in terms of higher copper concentrations in the plants. Lupins had moderate to high contents, but showed little or no response to treatment. Oats and Wimmeya ryegrass maintained very low contents at all rates of application. Among the lupins, the order of copper concentrations in the whole plants, over all treatments, was L. digitatus > L. luteus > L. angustifolius > L. albns. Within L. luteus, the bitter strain wed had a higher mean copper content than the sweet Weiko III variety. Differences were also demonstrated among subterranean clover varieties, Yarloop being higher than Dwalganup or Mt. Barker over all treatments. Subterranean clover had the lowest molybdenum content. Lupins were very substantially higher in manganese than all other species. The particularly high manganese content of L. albus, especially in the seeds, was confirmed. Cobalt levels varied little between species, and were well below the minimum requirement of grazing ruminants. I t was concluded that generalizations as to the relative mineral contents of broad plant groups must be treated with caution when applied to particular species or varieties.