Spatial and temporal effects of grazing management and rainfall on the vertebrate fauna of a tropical savanna

Grazing by domestic livestock is one of the most widespread uses of the rangelands of Australia. There is limited information on the effects of grazing by domestic livestock on the vertebrate fauna of Australia and the establishment of a long-term grazing experiment in north-eastern Queensland at Wambiana provided an opportunity to attempt an examination of the changes in vertebrate fauna as a consequence of the manipulation of stocking rates. The aim was to identify what the relative effects of vegetation type, stocking rate and other landscape-scale environmental factors were on the patterns recorded. Sixteen 1-ha sites were established within three replicated treatments (moderate, heavy and variable stocking rates). The sites were sampled in the wet and dry seasons in 1999-2000 (T-0) and again in 2003-04 (T-1). All paddocks of the treatments were burnt in 1999. Average annual rainfall declined markedly between the two sampling periods, which made interpretation of the data difficult. A total of 127 species of vertebrate fauna comprising five amphibian, 83 bird, 27 reptile and 12 mammal species were recorded. There was strong separation in faunal composition from T-0 to T-1 although changes in mean compositional dissimilarity between the grazing stocking rate treatments were less well defined. There was a relative change in abundance of 24 bird, four mammal and five reptile species from T-0 to T-1. The generalised linear modelling identified that, in the T-1 data, there was significant variation in the abundance of 16 species explained by the grazing and vegetation factors. This study demonstrated that vertebrate fauna assemblage did change and that these changes were attributable to the interplay between the stocking rates, the vegetation types on the sites surveyed, the burning of the experimental paddocks and the decrease in rainfall over the course of the two surveys. It is recommended that the experiment is sampled again but that the focus should be on a rapid survey of abundant taxa (i.e. birds and reptiles) to allow an increase in the frequency of sampling and replication of the data. This would help to articulate more clearly the trajectory of vertebrate change due to the relative effects of stocking rates compared with wider landscape environmental changes. Given the increasing focus on pastoral development in northern Australia, any opportunity to incorporate the collection of data on biodiversity into grazing manipulation experiments should be taken for the assessment of the effects of land management on faunal species

Increasing seeding rate does not improve legume establishment in undisturbed buffel grass pasture

Although good establishment is recognised as critical to the long term persistence of legumes, many producers don’t think they can afford to use more expensive seedbed preparation to allow establishment. Several producers and advisors in the pasture seed industry have suggested that increasing seeding rates, but still sowing with no seed bed preparation, will improve the reliability of establishing legumes into sown grass pastures. This paper reports the results of a legume seeding rate trial

Better agronomy improves the reliability of establishing legumes into existing grass pastures

Commercially, small seeded legumes have not established reliably in sown grass pastures. Although good establishment is recognised as critical to the long term productivity and persistence of legumes, most producers use low-cost and low-reliability establishment techniques such as broadcasting after either no or minimal pasture disturbance (e.g. fire) or severe soil disturbance and a rough seed bed behind a blade plough. This paper reports results from 6 legume establishment trials

Phosphorus fertiliser boosts grass-legume pasture yields up to 4 years after application.

Legumes can significantly boost animal diet quality and supply nitrogen for companion grasses. However sufficient numbers of well grown legumes are needed to obtain these benefits. A moderate to high soil phosphorus (P) supply is required to obtain the productivity potential of legumes suitable for clay soils (e.g. desmanthus and Caatinga stylo) (Peck et al 2015). However there is a lack of experimental data on the biomass responses of these legumes to fertiliser on low P soils

On-farm demonstrations of low-input methods for establishing legumes in central Queensland

In 2010 a three year Meat and Livestock Australia funded Producer Demonstration Site (PDS) was established to demonstrate low-input sowing strategies for achieving legume establishment in buffel grass (Pennisetum ciliare) pastures in central Queensland. Butterfly pea (Clitoria ternatea), burgundy bean (Macroptillium bracteatum) and siratro (Macroptillium atropurpureum cv. siratro and cv. Aztec atro) were sown by broadcast, direct drill and crocodile seeder methods. Intensive herd impact applied immediately post sowing was trialled to determine if seed germination and establishment would benefit from animal induced soil disturbance. Treatments with soil disturbance at sowing (direct drill and crocodile seeder) recorded higher first year legume numbers than broadcasting. Despite excellent rainfall in the first two years of the trial, strong population declines across all treatments were recorded in subsequent years, with similar plant populations per hectare recorded between treatments at the conclusion of the trial. The results from the application of herd impact were inconclusive. Siratro was the only species to persist within the buffel grass dominated pastures. This trial demonstrated that low-input sowing methods with little or no removal of grass competition achieved poor plant populations. Industry needs to adopt longer fallow management for moisture storage and control of grass when establishing legumes into existing grass pastures

Improving the reliability of establishing legumes into grass pastures in the sub-tropics

Poor establishment is the most common reason for failure of pasture legumes sown into existing grass pastures on commercial farms in the sub-tropics. Although good establishment is recognised as critical to the long term productivity and persistence of legumes, most producers use low-cost and low-reliability establishment techniques such as broadcasting after either no or minimal pasture disturbance; one-pass cultivation with seed spread at the same time; or severe soil disturbance and a rough seed bed behind a blade plough. This paper reports the results of a study designed to test the impact of different fallow periods (medium – 4 months; short – 2 months; disturb at sowing and no disturbance); seedbed preparation cultivation or zero tillage); drilling or broadcasting seed and post emergence herbicides when establishing legumes into existing grass pastures. The most common, commercially used establishment techniques of sowing legume seed into grass pastures with no disturbance or single pass cultivation treatments at sowing all resulted in establishment failure. Spraying at sowing resulted in adequate numbers of legumes. Short or medium fallows resulted in similar densities of legumes between all treatments, however treatments with greater control of the grass and post emergence weed control grew better which resulted in more seedling recruitment in the subsequent year. At 25 months after sowing only fallowed treatments with Spinnaker® post-emergence weed control achieved legume numbers above benchmark figures for establishment success. The study demonstrates that agronomic practices commonly used for grain cropping (such as fallowing to store soil moisture) can improve the reliability of establishing legumes into existing grass pastures

Scaling results up from a plot and paddock scale to a property - a case study from a long-term grazing experiment in northern Australia

Grazing experiments are usually used to quantify and demonstrate the biophysical impact of grazing strategies, with the Wambiana grazing experiment being one of the longest running such experiments in northern Australia. Previous economic analyses of this experiment suggest that there is a major advantage in stocking at a fixed, moderate stocking rate or in using decision rules allowing flexible stocking to match available feed supply. The present study developed and applied a modelling procedure to use data collected at the small plot, land type and paddock scales at the experimental site to simulate the property-level implications of a range of stocking rates for a breeding-finishing cattle enterprise. The greatest economic performance was achieved at a moderate stocking rate of 10.5 adult equivalents 100 ha(-1). For the same stocking rate over time, the fixed stocking strategy gave a greater economic performance than strategies that involved moderate changes to stocking rates each year in response to feed supply. Model outcomes were consistent with previous economic analyses using experimental data. Further modelling of the experimental data is warranted and similar analyses could be applied to other major grazing experiments to allow the scaling of results to greater scales

Foraging strategies on rangelands: Effects on intake and animal performance

Rangelands exhibit extreme spatial and temporal variability in forage quality and availability. The animals that utilise these rangelands have consequently evolved a range of foraging strategies in an attempt to cope with this variability and maintain nutrient intake. In general, animals respond to and exploit spatial variability at all scales by selecting those items or units which optimise the intake of digestible nutrients and hence animal production. Animals similarly employ a variety of strategies to cope with temporal variability on rangelands. These strategies may include adjusting foraging behaviour and/or exploiting critical resources or resource areas to buffer temporal variability in feed quality or supply. While current understanding of short term foraging processes operating in small scale, relatively simple environments is acceptable, our understanding and ability to predict longer term processes operating at the larger scale in more complex rangeland environments is poor. Consequently, our ability to predict foraging behaviour on rangelands and hence animal intake and production or the impact of animals on specific areas is severely limited. The major challenge therefor, is to advance our current information, theory and models upwards from the small scale to accommodate and realistically simulate, the larger, more complex systems operating on rangelands