Browsing by Author "Seager, Nicola Gillian"
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- ItemThe relative influence of above and below ground competition on the growth and survival of ryegrass seedlings transplanted into a hill country pasture : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University(Massey University, 1987) Seager, Nicola GillianIn many pasture improvement programmes, for example oversowing in hill country, seedling survival is influenced by competition from the existing vegetation. Competition between pasture plants occurs when resources are limited and may be for factors above or below ground, or both. Technically, the effective separation of above and below ground competition is difficult and considerable problems have been associated with previous studies. A technique developed for field studies combined the treatments of clipping herbage surrounding the transplanted seedling to prevent above ground competition and inserting a metal cylinder (root tube) into the ground to prevent below ground competition, resulting in conditions of shoot, root, full or no competition. Ryegrass seedlings were transplanted in August 1986 into a pasture in summer dry hill country near Wanganui and subjected to shoot, root, full or no competition from the existing vegetation. The duration of the experiment was three months. The effect of competition on the growth of the ryegrass seedlings was assessed by non destructive measurements (plant height, tiller number) taken at approximately weekly intervals. On three occasions, destructive harvests were made and the dry weight of shoots and roots was recorded. Below ground competition occurred before, and was more severe than above ground competition, as exemplified by changes in plant size. Ryegrass plants in the treatments with below ground competition were 80 % lighter, 64 % smaller and had 60 % fewer tillers than plants with either shoot competition or no competition. The distribution of plant size was highly skewed, and indicated that the stress plants encountered when subjected to below ground competition was severe. The effect of above ground competition on ryegrass growth was small except when root competition was also present. Shaded plants were usually taller than those that were unshaded. In conclusion, below ground competition, possibly for soil nutrients, was shown to be the major influence on growth and development of transplanted seedlings at the hill country site studied. The survival of seedlings introduced into pasture was also dependent on environmental factors, especially soil moisture, and therefore important in summer dry hill country. In a second experiment during spring 1986, ryegrass seedlings were grown in tubes and transplanted into a hill pasture at Wanganui. The six treatments consisted of combinations of two planting dates, two tube lengths, two harvest dates and were arranged as a randomised complete block design Seedling survival was high over all treatments (98 %), probably because rainfall during the experimental period was high.
- ItemTemperature effects on kiwifruit maturation : thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University, Palmerston North, New Zealand(Massey University, 1993) Seager, Nicola GillianThe effect of temperature on rate of kiwifruit maturation was studied using container-grown vines placed in controlled environments and field-grown vines from four orchards (Kerikeri, Te Puke, Palmerston North and Riwaka) at the geographical extremes of the kiwifruit growing regions. Soluble solids concentration (SSC) and partitioning of carbohydrate between starch and total sugar concentrations were studied at different stages of maturation in both the controlled environment and field work. Flesh firmness, dry matter concentration and fruit growth changes during fruit maturation were also measured. The effect of carbohydrate status on fruit maturation was determined by manipulating it using girdling of field-grown vines. A model relating changes in SSC to temperature was derived using data collected from controlled environment treatments. This model was applied to field-grown vines using meteorological data from kiwifruit growing regions. Use of controlled environments quantified changes in kiwifruit during maturation. Increase in SSC and total sugar concentration, and decrease in starch concentration were faster at cooler than warmer mean temperatures, irrespective of minimum temperature per se or magnitude of the difference between maximum and minimum temperature. A temperature perturbation altered the partitioning of carbohydrate compared to treatments where a perturbation did not occur. In some years fruit were not responsive to any temperature treatments; these fruit had not reached the stage of development at which they were able to respond to temperature. Differences in rate of fruit maturation were found among orchard sites. Some of these differences, such as decrease in starch concentration and increase in total sugar and SSC could be attributed to the effect of temperature. Girdling kiwifruit laterals altered carbohydrate concentration and affected rate of fruit maturation. Carbohydrate concentration was higher in fruit from the 5:1 than 1:1 leaf:fruit ratio treatment. Fruit in the 5:1 treatment matured similarly to fruit from ungirdled vines, compared to delayed maturation in fruit from the 1:1 treatment. Carbohydrate concentration in this treatment may be insufficient to support fruit maturation. The model developed to predict the rate of change in SSC during kiwifruit maturation was made up of two components; a state-dependent physiological response function and a temperatu re-dependent rate function. The base + exponential model was chosen to represent the state-dependent physiological response function, based on SSC being separated into two components; basal SSC and maturation SSC. The temperature-dependent rate function from container-grown vines placed in controlled environments was successfully transported to fit SSC in field-grown vines at different orchard locations. The model was developed using continuous temperature records but was later modified to use daily maximum and minimum temperatures allowing greater practical application. The partial rate coefficient accounted for most of the physiological differences between years, orchards and experiments; it required fitting at each orchard location. Transportability of the partial rate coefficient was demonstrated between years for two orchard locations. The model, therefore, has great potential for prediction of harvest date of kiwifruit in different regions and seasons.