Seed Rain of a Native Pasture under a Range of Grazing and Fertiliser Regimes

In recent years, deferred grazing (no defoliation of pastures for a period generally from spring to late summer or autumn) has been widely adopted to rejuvenate degraded native pastures in marginal land classes such as steep hill country in western Victoria, Australia. One of the important features of deferred grazing is the increase of seed production over summer and autumn, which could potentially lead to natural regeneration and improved groundcover by pasture plants (Nie et al. 1999). While increasing seed numbers in the soil seed bank following deferred grazing were reported (Nie and Mitchell 2006), there has been little research on seed production during deferred grazing in this environment. This study aimed to investigate the seed rain (the fall to the ground of wind-dispersed seeds) of native pastures under various deferred grazing and fertiliser regimes. Seed population and composition in the soil seed bank are important contributors to the productivity, botanical composition and persistence of permanent pastures

Impacts of Strategic Grazing on Density and Ground Cover of Naturalised Hill Pasture

Low ground cover by perennial species is a major problem in naturalised pasture on steep hill country in southern Australia. This leads to water and nutrient runoff, recharge to groundwater, and soil erosion, all of which impact on the environmental sustainability and profitability of grazing enterprises. Restoration of perennial components, particularly the native grasses for these marginal land classes, is of great importance for improving water balance, halting land degradation (Ridley et al. 1997), extending growing season, and increasing pasture production. The objective of this study was to use strategic grazing management to increase the ground cover and plant population density of perennial species in steep hill country

Comparative Seed Strike of Temperate, Sub-Tropical and Native Grasses and Herb Species Under Contrasting Environments in Southern Australia

The role of deep-rooted perennials in reducing recharge to mitigate dryland salinity has been recognised widely in Australia recently. Poor seedling establishment is a key limiting factor for the expression of genetic merit for some perennial pasture species. Nie et al. (2004) investigated seedling establishment, and its relationship with rainfall and temperature, of a range of perennial grass and herb species in southern Australia. This paper reports seed strike of a range of perennial pasture species in 2 contrasting environments. There was significant interaction between species and site on seed strike. Environmental conditions caused different establishment outcomes within a diverse set of perennial forage species

Modelling of lucerne (Medicago sativa L.) for livestock production in diverse environments

Several models exist to predict lucerne (Medicago sativa L.) dry matter production; however, most do not adequately represent the ecophysiology of the species to predict daily growth rates across the range of environments in which it is grown. Since it was developed in the late 1990s, the GRAZPLAN pasture growth model has not been updated to reflect modern genotypes and has not been widely validated across the range of climates and farming systems in which lucerne is grown in modern times. Therefore, the capacity of GRAZPLAN to predict lucerne growth and development was assessed. This was done by re-estimating values for some key parameters based on information in the scientific literature. The improved GRAZPLANmodel was also assessed for its capacity to reflect differences in the growth and physiology of lucerne genotypes with different winter activity. Modifications were made to GRAZPLAN to improve its capacity to reflect changes in phenology due to environmental triggers such as short photoperiods, declining low temperatures, defoliation and water stress. Changes were also made to the parameter governing the effect of vapour pressure on the biomass-transpiration ratio and therefore biomass accumulation. Other developments included the representation of root development and partitioning of canopy structure, notably the ratio leaf : stem dry matter. Data from replicated field experiments across Australia were identified for model validation. These data were broadly representative of the range of climate zones, soil types and farming systems in which lucerne is used for livestock grazing. Validation of predicted lucerne growth rates was comprehensive owing to plentiful data. Across a range of climate zones, soils and farming systems, there was an overall improvement in the capacity to simulate pasture dry matter production, with a reduction in the mean prediction error of 0.33 and the root-meansquare deviation of 9.6 kg/ha.day. Validation of other parts of the model was restricted because information relating to plant roots, soil water, plant morphology and phenology was limited. This study has highlighted the predictive power, versatility and robust nature of GRAZPLAN to predict the growth, development and nutritive value of perennial species such as lucerne

Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films

Doped HfO2 thin films exhibit robust ferroelectric properties even for nanometric thicknesses, are compatible with current Si technology and thus have great potential for the revival of integrated ferroelectrics. Phase control and reliability are core issues for their applications. Here we show that, in (111)-oriented 5%La:HfO2 (HLO) epitaxial thin films deposited on (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates, the flexoelectric effect, arising from the strain gradient along the films normal, induces a rhombohedral distortion in the otherwise Pca21 orthorhombic structure. Density functional calculations reveal that the distorted structure is indeed more stable than the pure Pca21 structure, when applying an electric field mimicking the flexoelectric field. This rhombohedral distortion greatly improves the fatigue endurance of HLO thin films by further stabilizing the metastable ferroelectric phase against the transition to the thermodynamically stable non-polar monoclinic phase during repetitive cycling. Our results demonstrate that the flexoelectric effect, though negligibly weak in bulk, is crucial to optimize the structure and properties of doped HfO2 thin films with nanometric thicknesses for integrated ferroelectric applications

The influence of pastoral fallow on hill country pastures, emphasising white clover growth behaviour : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, New Zealand

Appropriate pre-sowing methods for oversowing new plant germplasm and the presence of productive legume are of key importance to development of New Zealand hill country. A pastoral fallow, which involves not defoliating pasture for a period generally from spring to autumn, has profound influence on plant and soil, and creates a potentially favourable environment for introducing improved germplasm. A series of field and glasshouse experiments examined the response of pasture structure, soil properties and natural reseeding to pastoral fallow, and the post-fallowing effects on white clover (Trifolium repens L.) and pasture growth in moist North Island hill country, New Zealand. Pastoral fallowing effectively reduced the plant population density and altered the structure of a hill sward. A seven-month (October - May) pastoral fallow dramatically decreased the densities of grass tillers by 72%, white clover growing points by 87% and other species by 87%. The decline in tiller density by pastoral fallow was enhanced on a shady, south facing aspect. Root growth and distribution was altered by pastoral fallowing and there was significantly less root biomass at 0 - 50 mm depth of soil in the fallowed than the grazed sward. Decreased plant density during pastoral fallowing was attributed to above-ground biomass accumulation which altered sward structure, leading to inter-plant competition and mortality by self-thinning and completion of the life circle of some matured plants. Pastoral fallowing significantly improved soil physical properties. Compared with the grazed treatment, pastoral fallow increased soil air permeability at 500 mm tension by 38%, saturated hydraulic conductivity by 26%, unsaturated hydraulic conductivity at 20 mm tension by 56% and soil moisture by 10 - 15%, and reduced soil bulk density by 11% at the end of an October - May pastoral fallow. Pastoral fallow had little effect on the concentration of most nutrients in soil both at the end of fallowing and two to three years after fallowing. A spring - autumn pastoral fallow increased the viable grass, legume and weed seed population by 51-160%, compared with the grazed control. The variation in viable seed population during the fallow followed a predictable pattern, which could be used to manipulate natural reseeding in practice. Regression analysis revealed that the patterns of cumulative seedling appearance followed a modified negative exponential function. Partial differentiation of this function derived a germination rate curve on which a two-pool (rapidly germinable pool and base pool) model was developed to quantitatively describe the seed dynamics of soil viable seed reserves. Short-duration (partial) pastoral fallow had a marked effect on plant population density and natural reseeding. Pastoral fallows starting from December, January and February or March with nitrogen addition and ending in June considerably reduced plant population density. Most partial pastoral fallows also considerably reduced viable seed population of all plant species, except for December to June fallow which had a higher viable grass seed population than the grazed sward. Pastoral fallowing increased dispersion of white clover stolons by internode elongation. At the conclusion of a pastoral fallow, the clover stolons initiated branching, and grasses initiated tillering. Their growth and competition resulted in a greater grass growth rate in the first two years after fallowing, and a greater white clover yield and content with an increase in clover patch density and size 3 - 4 years post-fallowing, compared with the grazed pastures