P. M. Dowling

Sustainable grazing systems for the Central Tablelands of New South Wales. 3. Animal production response to pasture type and management

The main limitations for prime lamb production in the Central Tablelands of New South Wales are low availability of forage early in the growing season (late autumn–early winter) and low nutritive value in the summer. This paper describes the performance of a first-cross lamb breeding enterprise on 4 pasture types and 2 management systems over 4 years for the Central Tablelands region. The pastures studied comprised a traditional unfertilised naturalised pasture, a similar pasture fertilised with superphosphate, a sod-sown fertilised introduced perennial grass pasture and a sod-sown summer growing perennial, chicory (Cichorium intybus L.) pasture. Grazing management involved either continuous grazing or tactical grazing that combined a lower annual stocking rate with an optional summer rest to maintain perennial grass content above 50%. An additional area of chicory pasture was set aside for finishing lambs. Over the experiment stocking rates were increased each year as the pasture became established, with increases ranging from 1.5 ewes/ha for tactically grazed unfertilised natural pasture to 3.6 ewes/ha, for chicory and clover pasture. The feed quality v. quantity problem of summer and autumn was reaffirmed for each pasture type except chicory and the lamb enterprise appeared to be sufficiently adaptable to be promising. Ewes lambed in September and produced satisfactory lamb growth rates (about 280 g/day for twins) on the various pastures until weaning in late December. Thereafter, lamb growth rates declined as the pastures senesced, except chicory, reaffirming the feed quality v. quantity problem in summer and autumn of naturalised and sown grass pastures for producing lamb to heavyweight market specifications. Weaning liveweights (in the range of 32–40 kg) from grass-based pastures were high enough for only about 45% of the lambs to be sold as domestic trade lambs with the remainder as unfinished lambs. In contrast, the chicory and clover finishing pasture produced lamb growth rates of 125 g/day and quality large, lean lambs suitable for the export market. Vegetable matter in the late January shorn wool was insignificant and there was no significant effect of pasture on fleece weight, fibre diameter or staple strength. Position of break in staples of wool from chicory pastures differed from that of the other pasture types and warrants further study on time of shearing. It was concluded that a first cross lamb producing enterprise of suitable genetics was effective in producing trade and store lambs before pasture senescence, but the inclusion of a specialised pasture of summer growing chicory would create greater opportunities. In the unreliable summer rainfall region of the Central Tablelands, the area of chicory pasture needed to maintain lamb growth rates of >125 g/day, estimated from these results, is around 10 lamb/ha of chicory.

Sustainable grazing systems for the Central Tablelands of New South Wales. 1. Agronomic implications of vegetation–environment associations within a naturalised temperate perennial grassland

Temperate perennial grass-based pastures dominate the high rainfall zone of south-eastern Australia and support a major livestock production industry. This area has experienced a recent change in overall pasture condition, however, typified by a reduction in the abundance of perennial grasses and an increasingly prominent winter-annual grass weed component. Improving the condition and productivity of these pastures can be achieved by improved management but this requires better knowledge of the interactions between management options and pasture species composition and of the interaction between pasture vegetation and the complex effects of a heterogeneous landscape. This paper reports the results of an intensive survey of a 60-ha paddock that was designed to identify the species present, determine their patterns of distribution and examine the relationships between pasture vegetation and the environment. The survey of species present in late summer was supplemented by the identification of seedlings that later emerged from extracted soil cores and by soil physical and chemical analyses. Data were analysed using ordination and interpreted with GIS software so that topographic features could be considered. The most frequently identified taxa were Hypochaeris radicata, Austrodanthonia spp. and Bothriochloa spp. (in late summer) and Vulpia spp., Bromus molliformis and Trifolium subterraneum (winter-annual species). Austrodanthonia spp. were commonly found on the drier ridges and more acid soils with lower phosphate levels. These were also the areas dominated in spring by Vulpia spp. and were generally lower in plant species richness overall. The most species-rich areas occurred downslope where soil fertility was higher and less moisture stress was presumably experienced. The measured environmental factors explained a substantial proportion of the variation in the vegetation dataset, which underlined the importance of considering landscape effects in the management of typical tablelands pastures.

Tall wheat grass (Thinopyrum ponticum) and puccinellia (Puccinellia ciliata) may not be the answer for all saline sites : a case study from the Central Western Slopes of New South Wales

Emergence and survival of Thinopyrum ponticum cv. Dundas, Puccinellia ciliata cv. Meneman, and Trifolium fragiferum cv. Palestine were observed over three seasons (2004–06) on part of a salinised area in Central Western New South Wales. Grid sampling of topsoils in August 2003 indicated that the site was acidic (mean pHwater 6.05), sodic (exchangeable sodium percentage 29), and saline (estimated ECe 18 dS/m). The site comprised a mosaic of low-salinity (ECe ~6 dS/m) vegetated patches and high-salinity (ECe ~30 dS/m) bare patches where EC was highly variable seasonally (exceeding 100 dS/m) and spatially. Despite suboptimal rainfall, emergence of the grasses was satisfactory on bare patches in all seasons but T. fragiferum failed to emerge in 2004 and was omitted from subsequent sowings. Various methods of ‘engineering’ the bare patches, viz. ditching, mounding, straw mulching, liming, or hand weeding, failed to promote optimum growth of the grasses, although survival was generally enhanced in treatments that included a shallow ditch. Results of the experiments, and observations elsewhere on the salinised area (where some patches supported optimal performance of the three species), suggested that high salinity was the main reason for poor performance on the bare patches. It was concluded that comprehensive site definition, both spatial and temporal, is important before attempting revegetation. Nevertheless the response of T. ponticum and P. ciliata in ditches will be limited on high-salinity sites. In addition, it was observed that surface disturbance and reduced grazing promoted establishment and growth of pre-existing species, particularly Cynodon dactylon and Lolium rigidum. There are many salinised sites in the Central West of NSW where neither P. ciliata nor T. ponticum has performed well, nor would be expected to do so, and where management of native and naturalised species already present may provide the best option for enhancing ground cover and herbage production.

Effects of perennial species on the demography of annual grass weeds in pastures subject to seasonal drought and grazing

A field experiment was established in a southern Australian temperate pasture to investigate the effects of identity and proximity of perennial grasses on the demography of the annual grasses Vulpia spp. (V. myuros, V. bromoides) and Hordeum leporinum (barley grass). Annual grasses were grown either alone or in mixtures, at different distances from rows of Dactylis glomerata (cocksfoot) and Phalaris aquatica (phalaris). Dactylis had a greater suppressive effect than Phalaris on Vulpia and Hordeum. Biomass, tiller production, and panicle production of annual grasses increased linearly with increasing distance from the perennial row. Tiller and panicle production were greater for Vulpia than Hordeum. The estimated rate of population growth (λ) for annual grasses was greater in Phalaris than in Dactylis and in Vulpia than in Hordeum, and increased with sowing distance from perennial grass rows. It was estimated that λ, when seeds were sown directly adjacent to a row of perennial grasses, was 1 and 0.4 for Vulpia and Hordeum, respectively, within Dactylis stands, and 7 and 3, respectively, within Phalaris stands. However, 15 cm from the row, λ reached 50 and 39 for Vulpia and Hordeum, respectively, within Phalaris stands, and 39 and 16, respectively, within Dactylis stands. In grazed, dryland pastures, perennial competition alone is therefore unlikely to prevent population growth of annual grasses, especially in systems heavily disturbed by grazing or drought. However, Dactylis showed more promise than Phalaris in limiting the abundance of these weeds.

Effect of grazing, gap dynamics, and inter-specific seedling competition on growth and survival of Vulpia spp. and Hordeum murinum ssp. leporinum.

Vulpia (Vulpia spp.) and barley grass (Hordeum murinum ssp. leporinum Link) are invasive annual grass weeds of agricultural and natural ecosystems. Understanding how gap dynamics influence their growth and survival can improve management of these species in permanent pastures and minimise their negative effect on these ecosystems. We investigated the effects of gap size, timing of gap appearance, grazing method (continuous or rotational grazing), and species sown in the gap (vulpia and/or barley grass) on vulpia and barley grass establishment, growth, and survival. Total establishment of vulpia and barley grass increased with gap size, but grazing method and inter-specific seedling competition had little effect on their establishment. Survival and tiller production were generally greater in larger gaps, under continuous grazing, and for barley grass than for vulpia, but were not affected by sowing the weed species in mixtures. Timing of gap appearance had little effect on survival or tiller production. Individual plant biomass of the weed species was generally greater in larger gaps and for barley grass, but was not affected by grazing method or timing of gap appearance. There was little difference between grazing method or gap size in surface soil moisture and temperature. Photosynthetically active radiation recorded in gaps at the soil surface in rotationally grazed pastures was less than 20% of that in continuously grazed pastures and less in medium than in large gaps. Pasture height was also less under continuous grazing. From this study we concluded that these annual grass weeds can readily establish throughout autumn and winter in gaps, regardless of the grazing regime imposed. However, minimising bare ground during this time can significantly reduce their establishment. Post-establishment, rotational grazing was more effective than continuous grazing in suppressing their growth and survival throughout the growing season, most likely because of greater vegetation height, perennial grass content, and competition for light under rotational grazing. If annual grass weed populations are to be suppressed, it is necessary to use appropriate grazing management throughout the growing season, rather than focussing on the seedling establishment phase alone.

Improved Procedures for Adjusting Soil pH for Pot Experiments

Abstract Liming is an effective method of correcting soil acidity, but the cost and other factors, such as sub-soil acidity, topography, and nutrient availability may limit its benefits. An alternative option is to grow acid tolerant plants. Pot experiments are an effective way of identifying plants with the genetic potential to grow in acidic soils. These experiments require a range of acidity levels. The soil used in this study was a sandy loam. Increments of aluminum sulfate [Al2(SO4)3.18H2O] and calcium carbonate (CaCO3) were added to derive dose-pH response relationships. The derived relationships were used to estimate the quantity of aluminum sulfate and lime required to change the pHCa (1:5, w:v, soil:10 mM CaCl2) of the soil from 4.4 to 3.89 and 4.4 to 5.2, respectively. The estimated quantities of aluminum sulfate (380 g) and calcium carbonate (48 g) were thoroughly mixed through 100 kg batches of the soil, which was potted (2 kg/pot). Then the acidified soils were leached to remove excess salts. The initial pHCa achieved was 3.86 and rose to 3.94 after leaching. A wide range of soluble aluminum (Al) concentrations (1:5, w:v, soil:10 mM CaCl2) was obtained from this study, e.g., 52 mg Al/kg soil in acidified soil and 1.8 mg Al/kg soil in limed soil. The variation in pH and EC between replicate pots was negligible (range 0.05 pH and 0.02 dS/m) and these remained relatively unchanged after six months. During the next six months some pots were held in the laboratory with 3 wetting/drying cycles; however, most were placed outdoors where they were sown with seed of Austrodanthonia spp. During this time, the pHCa of the acidified soils increased slightly to: 4.10 (laboratory), 4.18 (outdoors without plants), and 4.20 (outdoors with plants). A similar increasing trend was also observed in limed soils. It was concluded that adding aluminum sulfate and calcium carbonate followed by washing with water are quick and convenient methods for adjusting soil pH for pot experiments.

Integrated management of vulpia in dryland perennial pastures of southern Australia.

Vulpia (Vulpia species C.C. Gmel.) are annual grass weeds that can reduce pasture quality and stock-carrying capacity of perennial pastures throughout southern Australia. To develop more effective strategies to control vulpia, an experiment was established in western Victoria (average annual rainfall 565 mm) in phalaris (Phalaris aquatica L.) pastures comparing the effects of control methods [comprising combinations of fertiliser addition (Fert), a single herbicide (simazine) application (Sim), and pasture rest from grazing (Rest)] on vulpia populations. A further herbicide treatment [paraquat-diquat (SpraySeed®)] was imposed on some of these treatments. Measurements included botanical composition, phalaris and vulpia tiller density, seed production, and number of residual seeds in the soil. Vulpia content remained unchanged in the Sim-Rest treatment but increased in all other management treatments over the duration of the 3 year study and especially where paraquat-diquat was applied, despite paraquat-diquat causing an initial reduction in vulpia content. Vulpia content was lowest in the Fert-Sim-Rest treatment. The Fert-Sim treatment and in some cases paraquat-diquat application reduced vulpia tiller production. Vulpia seed production and the residual seed population were not influenced by any of the management treatments, while the single paraquat-diquat application increased vulpia seed production 18 months after application. Phalaris content was enhanced by the Sim-Rest and Fert-Sim-Rest treatments and initially by paraquat-diquat. No treatment affected phalaris tiller production and basal cover. The subterranean clover (Trifolium subterraneum L.) content declined during the experiment, but to a lesser extent where paraquat-diquat was applied. Volunteer species content was initially suppressed in the year following paraquat-application, although populations recovered after this time. Of the two Vulpia spp. present (V. bromoides (L.) S.F. Gray and V. myuros (L.) C.C. Gmelin), V. bromoides was the most prevalent. Results show how a double herbicide application can increase vulpia fecundity and rate of re-infestation of herbicide-treated sites. Pasture rest shows some promise, but to a lesser extent than in the New South Wales tablelands, where summer rainfall may increase the growth of perennial species. In lower rainfall, summer dry areas, responses to pasture rest may be slower. Despite this, integrated management (which combines strategies such as pasture rest, herbicide application, and fertiliser application) increases the perennial content and reduces vulpia seed production, thus improving vulpia control.

Effect of grazing strategy, ryegrass overdrilling and herbicide application on vulpia content, tiller density and seed production in perennial pastures

Vulpia species C.C. Gmel. are annual grass weeds that can reduce the productivity of perennial pastures throughout southern Australia. To develop more effective strategies to manage vulpia, a 3-year experiment was established in western Victoria (average annual rainfall: 625 mm) comparing different methods currently used to control this weed. Overdrilling perennial ryegrass (Lolium perenne L.) seed and simazine application treatments were applied to phalaris (Phalaris aquatica L.) pastures that were set-stocked or rotationally grazed (either as a four-paddock or strategic rotation) with Merino ewes. The content of vulpia, subterranean clover (Trifolium subterraneum L.) and other annual grasses as a proportion of total dry matter increased, and the proportion of phalaris decreased in most grazing treatments throughout the experiment. The mean vulpia content was lowest and the phalaris content was highest in the four-paddock rotation, whereas vulpia content was greatest and phalaris content was lowest under set-stocking. Simazine application in June with or without ryegrass overdrilling reduced the number of vulpia tillers/m2 in 2000 and 2001 and vulpia panicle production in 2000, although vulpia populations increased to pretreatment levels in herbicide-treated swards by 2002. The number of vulpia seeds in the soil seed bank was not affected by any of the treatments. The most effective treatment was a combination of ryegrass overdrilling and herbicide application in the four-paddock, rotationally grazed pastures. This experiment highlights the need for an integrated approach to manage vulpia since relying on herbicide application alone is ineffective. This is particularly the case when competitive pasture species are unable to adequately utilise available resources and prevent a recovery in vulpia populations.