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1995 - 199912000 - 20011

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Author: search.filters.author.Beskow, Wagner BrodHas files: Yes

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    A study of the factors influencing the emergence and establishment of ragwort (Senecio jacobaea L.) seedlings in pasture : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University
    (Massey University, 1995) Beskow, Wagner Brod
    This study was designed to help understand the factors determining the emergence and establishment of ragwort seedlings in pastures. To achieve this it was necessary to determine (a) whether the germination of seeds was affected by the presence of light; (b)the influence of herbage cover on the emergence of seedlings; (c) the seasonality of seedling emergence; (d) the impact of treading on the emergence of seedlings and (e) the behaviour of seedlings in a real farm situation. In the first experiment, soil containing ragwort seeds was collected from a dairy pasture and subjected to constant light or dark conditions in growth chambers. Seeds subjected to light produced significantly more seedlings (55.6% seedling emergence) than those left in darkness (13.8% seedling emergence). It was concluded that germination is positively affected by light. Apparently, seeds which germinated in the dark were those originally close to the soil surface. In the second experiment, a hill country pasture near Woodville was either denuded of herbage cover or left intact once every month. For one year, ragwort seedlings were counted to provide information on the seasonality of seedling emergence. Seedling emergence was constantly higher on bare soil than under the pasture canopy, except in summer when no germination was observed for lack of moisture. Peaks of seedling emergence occurred in September (bare soil and intact pasture) and in June (bare soil). Seedling emergence (bare soil) was high even at low temperatures in winter. Seed germination was strongly checked by either the lack of moisture over summer or the presence of herbage cover at any time of the year. The third experiment was carried out at the same site. A number of defoliation treatments were imposed involving combinations of the presence and absence of herbage cover, treading and grazing. Any form of disturbance to pasture caused a significant increase in seedling emergence. The greatest emergence was found where soil had been denuded of herbage cover, whether trodden or untrodden. Treading generally stimulated germination through damage to the vegetation cover, and some increase in emergence also resulted from soil movement by hooves. Seedling emergence was minimal where pasture was undisturbed. The fourth experiment was carried out on a commercial dairy farm near Palmerston North over a 12 month period. Without interfering with the normal management system, several pasture attributes were monitored every week at three different sites within the farm to help explain the emergence and mortality of ragwort seedlings. Seedlings were counted every week in permanent quadrats and mapped every fortnight. Seedling emergence and survival varied greatly both between sites and throughout the year. The major determinant of seedling emergence was found to be the proportion of bare soil. Bare soil was largely caused by treading in wet months and by drought during summer/early autumn. No emergence was observed over summer when soil moisture levels were low. Depending on the site, peak emergence occurred in June, August and November. The major causes of seedling mortality were water stress, earthworm casts, treading damage and competition from neighbouring plants. Although autumn emergence was small compared to the emergence observed in winter and in spring, it is apparently the most important period of emergence during the year, since seedlings which emerge in winter and in spring are prone to die over summer from water stress. Ragwort seedlings survived longer periods when the sward height was between 2 and 7 cm (approx.) and when herbage mass was between 500 and 2000 kg DM ha-1. Beskow, W.B. (1995). A Study of the Factors Influencing the Emergence and Establishment of Ragwort (Senecio jacobaea L.) Seedlings in Pastures. M. Agr. Sc. Thesis, Massey University: New Zealand.
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    Integration of goats into sheep and cattle grazing systems as a permanent weed control tool : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2001) Beskow, Wagner Brod
    This project evaluated the integration of goats into sheep and cattle grazing systems as a permanent herbaceous weed control tool. Foraging behaviour of goats grazing pasture with no access to browse was monitored in Experiment 1. A selection index was used to determine degrees of effort for selection or avoidance of plant species. Although most of the grazing time was spent on herbage species, no effort was made to select them, whereas moderate to strong efforts were made to select weeds. Selection index varied with season of the year. Goats preferred taller vegetation and grazed above 10 cm from the ground whenever possible, though they took 70% of their bites from below the top of the sward, regardless of organ selected. Experiment 2 consisted of feeding known numbers of weed and herbage seeds to goats and recovering them to assess destruction and viability. On average, 92% of the viable seeds were destroyed, with up to 72 hours for complete excretion. The effects of goat and cattle grazing on the structure and competitiveness of swards against weed invasions were studied in Experiment 3. A pasture competitiveness index (PCI) was calculated using structural attributes of a sward resulting from goat and cattle grazing alone and in combinations, under hard and lax grazing severities. The sward was denser, leafier, more uniform, and covered the soil more thoroughly (greater PCI) with increasing participation of goats in the treatments, especially because of severe treading damage caused by cattle contrasting with no damage from goats. The PCI explained 93% of the variation in weed seedling density. The effect of pasture surrounding thistle rosettes on their consumption by goats was investigated in Experiment 4. Thistle rosettes that were exposed by clipping the adjacent sward were severely defoliated by goats, while rosettes surrounded by the sward were only nibbled or not eaten at all. Grazing management, economics, and drawbacks of using goats for herbaceous weed control are discussed. Integration of goats into grazing systems can result in a more desirable botanical composition, more uniform and competitive sward, reduced weed control costs, greater herbage utilisation, and better pasture quality.