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    Leaf regrowth stage as a morpho-physiological indicator of Bromus valdivianus and Lolium perenne mixed pasture defoliation in New Zealand grazing system : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatū, New Zealand
    (Massey University, 2022) García Favre, Javier Horacio
    Bromus valdivianus Phill. is a perennial grass species native to the South of Chile. Its better fitness for growing under low water availabilities compared with Lolium perenne L. has been assessed in field and glasshouse studies. However, Bromus valdivianus morpho-physiological attributes, such as root development under field conditions, and competitive ability are likely to manifest differently under contrasting defoliation criteria based on leaf regrowth stage. In addition, Lolium perenne and B. valdivianus growth can be complementary throughout the year under rainfed conditions. Therefore, the objective of the present thesis was to determine defoliation criteria based on leaf regrowth stage of mixed pastures (50/50% L. perenne and B. valdivianus) and consequences for species succession and functional traits development of the species. Four studies were developed in the thesis, two glasshouse and two field studies. The first glasshouse study evaluated the growth response and water-soluble carbohydrate (WSC) accumulation of B. valdivianus at three different defoliation frequencies. The results suggested that B. valdivianus increased herbage mass production and root biomass at low defoliation frequency (i.e., at 3.5–4.0 leaf regrowth stage). This was related to a higher WSC accumulation in the tiller base. In addition, under low soil water availabilities (20–25% of field capacity) WSC increased by ~20%, which indicated a drought resistant strategy of this species. The second study proved the growth enhancement (mainly root length and biomass) of B. valdivianus under competition with L. perenne compared with intraspecific competition when soil water shifted from high to low availabilities. In field studies, B. valdivianus mixed with L. perenne increased ~15% accumulated herbage mass compared to the species monocultures, which supported higher production during dry periods. This was due to the niche complementarity and asynchrony in herbage growth between the species, with B. valdivianus capable to maintain a steady tiller population throughout the year and root biomass accumulation at depth. Whereas L. perenne grew more than B. valdivianus under low level of oxygen in the soil and under optimal growth conditions and presented a higher nutritive value than B. valdivianus during winter, spring and autumn. The latter supports the partial grazing preference for L. perenne shown by sheep during part of the year, as measured in the second field study. This lower nutritive value (less energy) of B. valdivianus monocultures was overcame in the mixture, with a good overall value for high animal production. Regarding the mixture defoliation criterion, it was shown that it can be based on the optimal leaf regrowth stage of either species, as herbage mass production was similar between defoliation frequencies based on optimal leaf regrowth stage of either of the species. However, under defoliation based on optimal leaf regrowth stage of B. valdivianus, root biomass accumulation at depth increased ~45%. Overall, the results of the present thesis evidenced that Bromus valdivianus can successfully grow alongside L. perenne and, therefore, the mixture can increase forage production of New Zealand farming system in the event of climate change.
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    Pursuing pasture tolerance and resilience through species with different functional traits and soil-plant-water interactions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatu, New Zealand
    (Massey University, 2020) Ordóñez Vásquez, Iván Pablo
    Higher stability, persistence and yield can be achieved through increasing the biodiversity of pasture plants. The combination of species with different functional traits confers niche differentiation (e.g. different root depth). Otherwise species compete for the same resources in the same location and time. In diverse pasture, agricultural needs should overlap between species, enhancing species survival during critical periods. Productive ecosystems with low complexity (low plant functional diversity) show more the negative impacts of climate change, being less stable through the stress periods. Bromus valdivianus Phil. is regarded as having high potential for grazing systems, due to its high yield and good nutritive quality. It also has high tolerance to periods of soil water restriction, maintaining a higher growth rate during summer in comparison to Lolium perenne L. Alongside L. perenne, B. valdivianus co-dominates permanent perennial pastures in the South of Chile, indicating that it is a good competitor in mixed cool-temperate pastures. However, key parameters associated with recovery from defoliation, such as watersoluble carbohydrate (WSC) reserves, growth rate, tiller number and persistence, are unknown for B. valdivianus. Therefore, the first step in this thesis was to determine these defoliation criteria in relation to similar defoliation criteria of other highly productive species, L. perenne and Plantago lanceolata, to determine if and when any overlap occurred. This thesis consisted of three main experiments, which cover the physiological, morphological and competitive traits of B. valdivianus. The first experiment was designed to determine a theoretical optimum defoliation interval for B. valdivianus, and it was concluded that defoliation at leaf stage 4 (LS-4) was the optimum defoliation in terms of highest shoot and root growth rates, and accumulation of WSC. The second experiment was designed to determine the resilience and tolerance between monocultures and mixtures of B. valdivianus, L. perenne and P. lanceolata. All three species were defoliated when B. valdivianus reached LS-4, which coincided with approximately 3.5 regrowth leaves/tiller for L. perenne, and over 6 leaves/plant for P. lanceolata. Measurements included biomass production across critical periods, botanical composition, physiological response against water stress (waterlogging and soil water restriction) and water uptake at different depths, and it was concluded that a more diverse pasture (B. valdivianus + L. perenne + P. lanceolata) maintained higher biomass under soil water restriction and also had a more effective water uptake from the soil profile. The third experiment was designed to determine the tiller population dynamics, photosynthetic carbon fixation capacity (PCFC) and competitive ability of B. valdivianus in relation to L. perenne. It was concluded that L. perenne was a better competitor than B. valdivianus, however, B. valdivianus was able to recover its tiller population during a period of soil water restriction and reached a full recovery at the end of the experimental period. Also, a B. valdivianus + L. perenne mixed pasture had the highest values for PCFC during the waterlogging and soil water restriction periods. Pasture plants such as B. valdivianus and P. lanceolata can access water from deeper in the soil than L. perenne, having a direct effect on their physiological traits. Water accessibility (root depth) plays a key role in maintaining their photosynthesis, production, and improving their survival, during periods of soil water restriction, relative to L. perenne. On the other hand, L. perenne tolerate waterlogging and maintain a relatively high growth rates during winter. Pasture establishment and performance, in a climate with dry and wet seasons and in soils with a high percentage of silt and/or clay (low gas permeability), is related to species tolerance to drought and waterlogging conditions. Thus, increasing species diversity is a good strategy that confers stability to the pastoral ecosystem, especially when global warming has enhanced droughts and unpredictable rain events. Mixtures of L. perenne + T. repens + P. lanceolata or L. perenne + T. repens + B. valdivianus can reach higher growth rates during water restriction periods, in comparison to L. perenne + T. repens pastures, along with relatively high growth rates during winter. Therefore, combining species with the aim of complementary resources uptake, and depending on the contribution of each species within the pasture, will change the seasonal herbage growth rate under the stress periods. However, to keep a great contribution of the desirables pasture species it is essential to use a defoliation criterion that allow them to replenish its water soluble carbohydrates, only then, the persistence, survival and yield of the pasture and the desirables species within it will be maximized.
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    A study of the reaction of several variables of top growth of a perennial ryegrass/white clover pasture to different defoliation treatments and measurements on soil moisture status : a thesis presented at Massey Agricultural College in part fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand
    (Massey Agricultural College, 1959) Kerr, James Patterson
    The agricultural research worker must on occasion adopt a broad view of farming purely as the management of plants and animals to produce human food. He has the task of outlining many of the principles to be used in farming practice, to increase world food production, in order to meet the challenge of a growing world population. He needs to consider the biological efficiency of the living processes and systems involved in food production; in much the same way as a businessman or farmer must consider the business efficiency of his factory or farm operations. Food production may be increased either by bringing more land under cultivation or by intensifying agriculture on the existing areas of cultivation, thereby increasing production per acre. Watson (1958) described the problem as fundamentally one of increasing the total annual photosynthesis per unit area of crop, for it is the net product of photosynthesis which the farmer harvests. Photosynthesis requires light, moisture and nutrients, and as light is the only one of these factors which can not be readily supplied artificially, Donald and Black (1958) have suggested that the ultimate measure of agricultural efficiency could well be expressed in terms of the proportion of light energy utilised by the crops or pastures. The size and activity of the photosynthetic system then becomes one of the determinants of crop yield. The potential rate of photosynthetic activity is controlled by the genetic make-up of the plant. The same is true to a certain degree of the size of the photosynthetic system, but the farmer too, through various cultural and management methods, exerts considerable control over the size of the system. [FROM INTRODUCTION]
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    A study of the effects of different frequencies of defoliation on the recovery growth of two varieties of lucerne (Medicago sativa L.) : a thesis ... for the degree of Master of Agricultural Science at Massey University.
    (Massey University, 1971) Abbott, John Munro
    In recent years there has been increasing interest in the use of lucerne in the farming systems in localities other than those which have "traditionally" grown lucerne. Much of the North Island, including the Manawatu is involved with this developing interest. To contribute to the information needed to support this, a field experiment studying the effects of different frequencies of grazing lucerne was established in 1965 at Massey University. Pure sowings of two varieties were used. These were New Zealand certified Chanticleer and New Zealand certified Wairau, with treatments ranging from continuous grazing through to hay stage defoliation. This experiment is discussed in more detail in appendix 1A. By the spring of 1969 at the commencement of the author's study, treatment differences were apparent. The author's study continued selected treatments and measured their differences of spring growth. The initial interest was in the treatment yield differences, volunteer species ingress, lucerne persistence and the associated interaction, if any, between the defoliation treatments and the spring climatic parameters. [From Introduction]
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    Physiological and morphological responses of tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) to defoliation : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (Ph. D.) in Plant Ecology and Physiology, Department of Plant Science, Massey University
    (Massey University, 1993) Tavakoli, Hossein
    Tall fescue (Festuca arundinacea Schreb.) has been suggested as an alternative to perennial ryegrass, particularly in conditions of moisture limitation, but there is little comparative information on the plant characteristics influencing regrowth in the two species, particularly under continuous stocking. The objectives of this study were to :i) examine the response of tall fescue to continuous stocking in terms of tillering activity, leaf growth and competition, and ii) determine which physiological or morphological factors are important in influencing regrowth after defoliation, using perennial ryegrass as a reference standard. Experiments were undertaken in field, glasshouse and controlled environment conditions. In the field sown swards of tall fescue (Festuca arundinacea Schreb. cv. 'Grassland Roa') and white clover (Trifolium repens L. cv. 'Grassland Tahora'), with volunteer grasses mainly consisting of perennial ryegrass (Lolium perenne L. cv. 'Grassland Nui') were continuously stocked with varying numbers of sheep to maintain sward surface heights 90-100 mm (Lax, L), 50-60 mm (Medium, M) and 30-4 0 mm (Hard, H). Measurements were made on areas with and without clover by removal of white clover with clopyralid. Tiller population density, tiller weight, and leaf growth and productivity of tall fescue were all reduced under hard grazing. Tall fescue was susceptible to competition from companion species, particularly perennial ryegrass, and tended to be replaced by other species under hard grazing. Under glasshouse conditions individual plants of tall fescue and perennial ryegrass were defoliated to stubble heights of 100 mm (Lax, L), 60 mm (Medium, M), 30 mm (Hard1, H1) and 30 mm (Hard2, H2) 9 times with 5 day intervals over a period of 4 5 days. Treatments L, M, and H1 were initiated at an average of 1 1 tillers per plant for each species; treatment H2 commenced at 6 tillers per plant. Both species showed sensitivity to severe cutting treatments by reduction in tiller number, tiller weight, leaf growth and less shoot and root growth. Tall fescue showed lower leaf growth, tillering activity and herbage harvested per plant than perennial regress, but it produced larger tillers. The comparative response of tall fescue and perennial ryegrass to leaf defoliation was studied under controlled environment conditions at both the vegetative and reproductive stages of growth. The oldest leaf lamina was defoliated regularly to maintain four, three, two or only one live leaf per tiller for six or seven leaf appearance intervals. In both species repeated removal of older leaves had little effect on tiller production, tiller weight, leaf growth rate and consequently total accumulated shoot and root weight, and mean shoot and root relative growth rates. Removal of all fully expanded leaves resulted in significant reduction in the above components, though leaf elongation rate was little affected. Leaves were shorter, narrower and lighter under hard defoliation, but leaf appearance rate was not affected. Hard defoliation affected tall fescue tiller weight more than perennial ryegrass. Water soluble carbohydrate concentrations in stem bases of plants decreased with increasing severity of defoliation especially for tall fescue. Leaf photosynthetic capacity per unit area was not influenced by defoliation intensity, but photosynthetic capacity per unit leaf weight increased under hard defoliation. Hard defoliation decreased the proportion of root mass to shoot mass, and increased the proportion of leaf mass to shoot mass. Plants showed relatively similar sensitivity to defoliation at vegetative and reproductive phases of growth. At both phases tall fescue again produced larger tillers with longer leaves and had a longer leaf life-span than perennial ryegrass, but it had lower leaf growth and appearance, and produced fewer tillers per plant. Photosynthetic activity per unit leaf area was similar for the two species, but tall fescue often had lower photosynthetic rate per unit leaf weight than perennial ryegrass. In conclusion, hard defoliation intensity reduced both tiller population density and tiller weight and consequently decreased pasture regrowth through a reduction in LAI, life-span of leaf area, photosynthetic efficiency, and shortage of carbohydrate reserves. The factors that resulted in the regrowth of tall fescue being less responsive to hard defoliation than perennial ryegrass were slower leaf turnover, slower leaf appearance rate, lower tillering capacity and longer leaf lifespan. These resulted in lack of plasticity in tiller population density of tall fescue in response to hard defoliation.
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    Studies on duration and defoliation in lucerne : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, New Zealand
    (Massey University, 1978) Janson, Carroll Garth
    A project was conducted to study the influence of grazing duration (GD) on lucerne Medicago sativa L. 'Wairau'. GD was defined as the period of defoliation or grazing before regrowth to the early flowering stage was again permitted. A field trial conducted for eight months from spring to autumn examined three grazing durations (GDs), 2-4, 15 and 30 days, using sheep as the grazing animal. Following this, three studies in controlled environment rooms using simulated grazing techniques allowed a more detailed study of the influence of GD and also provided an insight into the interaction of GD with climate. In both the field and the controlled environments, total herbage production for the full duration of each of the studies was always greatest under the shortest GD (0-3 days) and least under the longest GD (30 days). In the field, total herbage production was reduced by 14% under the 15 day GD system and 29% under the 30 day GD system. However in all the studies the differences in total herbage production were generated almost entirely by differences in stem yield - there were generally no treatment differences in the total production of non-stem (leaf and new shoot) material. The studies in the controlled environment rooms indicated that GD had less effect on lucerne herbage production under dry conditions than under moist conditions favouring rapid growth. Detailed shoot population studies in which large numbers of shoots were individually tagged as they arose, demonstrated the impact of shoot decapitation, the relative contributions of the different shoot types and the importance of the time of shoot appearance in relation to grazing. Differences in the immediate growth rate of the herbage following the different GDs were noted. Maximum herbage growth rates in this period followed the intermediate GDs (10-15 days) with lower growth rates after both the very short (0-3 days) and the very long (30 day) GDs. The initial regrowth inertia following the very short GD was attributed to the low number of basal shoots on this treatment at the start of the regrowth period. However the initially reduced herbage growth rates following the 30 day GDs seemed to result from an 'earlier' partitioning of assimilate to the roots in the first half of the regrowth period following this treatment. It was postulated that this partitioning effect was generated by the 'sink' effect of the depleted root system (lowest root weight, and root TNC and starch concentrations) measured at the end of a 30 day GD. The project has indicated that under active growth conditions, while GDs of 2-4 days will give maximum herbage production, GDs of 10-15 days will have little significant effect on the performance of mature sheep. Under dry conditions, or when grazing young lambs, even longer GDs of up to 30 days are unlikely to seriously affect stock production.
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    Studies of late spring grazing management in perennial ryegrass dominant pasture : a thesis presented in partial fulfilment of the requirements for the degree of PhD in Agronomy at Massey University
    (Massey University, 1981) Korte, Christopher John
    Two grazing experiments and a mowing experiment were conducted to obtain information on the patterns of herbage accumulation and the tiller dynamics of "Grasslands Nui" perennial ryegrass (Lolium perenne) dominant pasture under a range of defoliation regimes during late spring/early summer. Defoliation intensity and defoliation interval were defined in terms of plant physiological criteria, that is, light interception and stage of reproductive growth. The effect of four late spring/early summer grazing intensity treatments, based on residual leaf area index (LAI), and two grazing interval treatments, based on light interception, were compared in the first grazing experiment. Net herbage accumulation was greatest when grazing was hard (LAI = 0.1-0.6) and least when grazing was lax (LAI = 1.5-2.5) in late spring (16.5 and 13.6 t DM/ha respectively). Grazing at 95% light interception reduced green herbage accumulation compared with grazing two weeks after 95% light interception (14.0 an 15.8 t DM/ha respectively). With lax grazing stemmy rank herbage developed, whereas with hard grazing dense leafy pasture with a higher ryegrass tiller density developed. The grazing interval treatments did not significantly affect ryegrass tiller density. The second grazing experiment compared the effects of the timing and intensity of spring grazings on herbage accumulation and ryegrass tiller dynamics. Interrupting reproductive growth of ryegrass at the head emergence stage, compared with at the start of culm elongation, did not increase herbage accumulation significantly although it resulted in a higher proportion of stem and a lower proportion of lamina accumulating. As in the first experiment, hard grazing in late spring increased herbage accumulation compared with lax grazing. Hard grazing appeared to increase herbage accumulation by reducing herbage death and decay, not by increasing herbage growth. Ryegrass tiller density was greater in hard grazed swards than lax grazed swards in summer. This difference was mainly due to a higher tiller appearance rate in hard grazed swards. The difference was still apparent in winter although all treatments were grazed similarly during late summer and autumn. Herbage accumulation was greater in autumn where grazing had been hard the previous spring/summer, partly due to the higher tiller density. Interrupting reproductive growth at the head emergence stage markedly reduced the density of vegetative tillers compared to interrupting reproductive growth at the start of culm elongation. Due to rapid tillering after interruption of reproductive growth this difference quickly disappeared. The effects of the time of cutting to control reproductive development and the subsequent cutting interval on herbage accumulation and tiller dynamics of ryegrass pasture were examined in the mowing experiment. Herbage accumulation was reduced by more frequent mowing and where reproductive growth was prevented. Tillers present at the start of each rest period contributed most herbage because new tillers were relatively small. After the first mowing, new tillers were generally of similar weight to older tillers at the end of rest periods. It appeared that during summer, under conditions of adequate moisture and nutrients, the tiller dynamics of perennial ryegrass swards were little influenced by mowing frequency. It was concluded that the objective for late spring grazing management should be to encourage leafy vegetative pastures and to prevent rank stemmy pasture developing. Dead culms in rank pasture reduced the digestibility of herbage and shaded photosynthetic tissue. Leafy swards had higher accumulation rates and a higher tiller density than stemmy swards. Methods of achieving leafy pasture on farms by combinations of hard grazing, forage conservation and mechanical topping are discussed.
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    The effects of defoliation and shading in root growth of Lolium perenne L. : a thesis submitted for the degree of Doctor of Philosophy to Massey University
    (Massey University, 1971) Evans, P. S.
    The effects of defoliation, shading and dark on the growth and morphology of roots of Lolium perenne L. plants have been examined using glass fronted containers and a technique developed for measuring root lengths and numbers of apices. A single defoliation caused a rapid drop in root elongation followed by a more gradual recovery with the most severe defoliation treatment having the greatest effect. Repeated defoliation caused a prolonged depression of root elongation but some recovery occurred. The most severe treatment resulted in considerable root death. With shading, root elongation fell over the first 8 - 10 days and then recovered to near the control level. Both defoliation and shading caused an increase in the length per unit weight of the root systems. Root elongation of plants placed in the dark fell rapidly to near zero, the effect being comparable with that of defoliating plants to 2.5 cm or less. Defoliation of plants placed in the dark caused a more rapid fall in elongation. Supplying glucose or sucrose to the roots of plants defoliated to the extent that root elongation would otherwise have ceased maintained elongation at up to two-thirds of the level of undefoliated plants. Sucrose was marginally more effective than glucose with little difference between concentrations 1-6%. Benzyladenine and indole-acetic-acid marginally increased elongation in the presence of sucrose. Dark-treated plants responded in a similar manner to defoliated plants to sucrose. The level of soluble carbohydrates in the roots of plants defoliated or placed in the dark was seen to be low after root elongation ceased and recovered as root elongation recovered. However the level at the time most roots ceased elongating was higher than in other experiments where root elongation was near optimum. That under these conditions the addition of sucrose or glucose maintains elongation at up to two-thirds of the control level suggests that translocation of soluble carbohydrates to the root apex may be the limiting factor. This possibility is supported by the difference in levels of soluble carbohydrates in various parts of the plant following defoliation at two different times of the day. The technique used to measure soluble carbohydrates was not sensitive enough to permit analysis of the root tips and thus check the hypothesis. Apart from the requirement for soluble carbohydrates and the apparent associated translocation factor there is evidently some other factor (s) limiting root elongation of defoliated and dark-treated plants. The nature of this factor was not determined.
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    Ecology of Paropsis charybdis Stål (Coleoptera : Chrysomelidae) : a Eucalyptus defoliator in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Zoology at Massey University
    (Massey University, 1989) McGregor, Peter Gerard
    Paropsis charybdis Stål (Coleoptera: Chrysomelidae), misidentified as P.dilatata Er. before 1963, seriously defoliates some Eucalyptus species in New Zealand. This study investigated the life history and phenology, behaviour, growth and development, population dynamics and host-plant interactions of P.charybdis, emphasising those aspects likely to affect biological control programmes. P.charybdis in the central North Island had a bivoltine life history. Adults diapaused during winter. Low temperatures and probably changes in foliage characteristics were sufficient for induction of diapause but no single factor was necessary. Adults emerged in spring to lay eggs. Young Eucalyptus foliage was necessary for oviposition. Activity of adults was increased in the presence of volatiles from E.viminalis leaves but did not differ significantly between mature and young leaf treatments. Egg-laying ceased in midsummer but this was not caused by lack of new growth, nor by high defoliation. The pattern of abundance in summer was driven by oviposition and temperature and enhanced by intra-specific competition among early instars. Density-dependent mortality occurred between eggs and 4th instars during the second generation and appeared to result from intra-specific competition for new growth. This was also the key stage that caused variation in summer morality. Egg survival rates were 93-99%. Survival between eclosion and establishment of 1st instars on new foliage averaged 45% and was independent of density in an experiment where food was in excess. Mortality of the pre-pupal to teneral adult stages in die soil was 90%, but was independent of density in both generations. Development rate-temperature relationships were described for larvae fed E.viminalis young adult foliage, and for eggs and pupae. A method was developed for minimising differences in duration among larvae grown at different temperatures, so that the effects of changes in food quality were obviated. The method appears widely applicable for development-rate studies. Defoliation in a five-year old plantation of Eucalyptus nitens was almost twice as severe in the second P.charybdis generation as in the first. Shoot growth was significantly correlated with rainfall and defoliation intensity. There was a strong inverse relationship between defoliation intensity and deviations from the seasonal trend in rainfall.