Influence of storage conditions on survival and sowing value of seed of tropical pasture grasses. 2. Sowing value and storage strategies

Evaluation of effects of storage conditions of seed of 5 tropical pasture grass seeds (Panicum maximum, Brachiaria decumbens, Brachiaria humidicola, Setaria sphacelata and Chloris gayana) was extended from laboratory tests (Part 1) to seedling emergence and establishment tests in greenhouse and field in north Queensland. Seed cool-stored in woven bags at 10°C and 50% RH mostly had higher field sowing value than comparable open-stored seed, because the superior preservation of viability and vigour tended to outweigh the disadvantages of dormancy retention. Exceptions occurred when dormancy persisted, as it did inconsistently across seed lots, even within a single cultivar. Reduction in storage moisture content of seed sealed in moisture-proof packs helped to preserve viability and vigour, particularly with seed stored at ambient temperature. However, very low moisture content (7.2%) prolonged dormancy, with adverse effects on sowing value. Dormancy delayed germination even when not wholly preventing it. The benefits of retained vigour and the restrictions of dormancy were displayed in the field, but were masked in the more benign environment of the greenhouse. Cold storage at −12°C intensified dormancy of Gatton panic, delaying germination of seed in the greenhouse until the second and third seasons after sowing. The shortcomings of conventional storage and means of mitigating them are discussed, with emphasis on the need to vary strategies depending on the duration of storage required

Influence of storage conditions on survival and sowing value of seed of tropical pasture grasses. 1. Longevity

To find ways of improving the sowing value of seed of tropical pasture grasses through attention to the storage environment used commercially, fresh seed lots of Panicum maximum, Brachiaria decumbens, Brachiaria humidicola, Setaria sphacelata and Chloris gayana were stored under different conditions and sampled periodically for laboratory, greenhouse and field testing. Comparisons were made between seed lots stored in bags of open weave in a cool-room at 10°C and 50% RH and in an open store-room at ambient temperature. Seed lots of P. maximum in moisture-proof packets at 5 different moisture contents between 7.3 and 12.9% were compared. One seed lot was also freezer-stored at −12°C. Part 1 reports their viability and dormancy loss. Viability loss of seed in woven bags in open storage was complete within 3 years while barely detectable in similar cool-stored seed. Rates of loss in sealed packets increased with moisture content at ambient temperatures. They were much higher in seed in woven bags at comparable average moisture contents, an effect attributed largely to spatial moisture content gradients. Cool storage temperatures and low seed moisture contents appeared to prolong dormancy, while freezer storage retained and even intensified it

Effects of severity of threshing damage on seed quality of Gatton panic (Panicum maximum)

Different degrees of severity of threshing were imposed during combine-harvesting of seed of Gatton panic, a cultivar of Panicum maximum , to determine effects of degree of threshing damage on subsequent properties of seed. Threshing cylinder peripheral speeds and concave clearances covering the normal range employed commercially were varied experimentally in the harvest of 2 crops grown in north Queensland. Harvested seed was dried and cleaned, then stored under ambient conditions. The extent of physical damage was measured, and samples were tested at intervals for viability, germination, dormancy and seedling emergence from soil in a glasshouse and in the field over the 2 seasons following harvest. Physical damage increased as peripheral rotor speed rose and (though less markedly) as concave clearance was reduced. As the level of damage increased, viability was progressively reduced, life expectancy was shortened, and dormancy was broken. When the consequences were measured as seedling emergence from soil, the adverse effects on viability tended to cancel out the benefits of dormancy-breaking, leaving few net differences attributable to the degree of threshing severity. We concluded that there would be no value in trying to manipulate the quality of seed produced for normal commercial use through choice of cylinder settings, but that deliberate light or heavy threshing could benefit special-purpose seed, destined, respectively, for long-term storage or immediate use

Germination and hardseededness in desmanthus

The mechanisms and control of hardseededness in the 3 Australian cultivars of the genus Desmanthus were investigated in a series of experiments in which the effects of various seedsoftening treatments, particularly boiling water, were measured. Desmanthus seed is predominantly hard, only defective seeds being normally otherwise. As it has only very brief, early embryo dormancy, hardseededness is the only serious barrier to germination. Seed is most readily softened through rupture of the palisade at the lens (strophiole). The lens is of a typically mimosaceous type which is readily ruptured by immersion in boiling water or less readily by application of pressure to adjacent parts of the testa. Ruptures may consist only of separation of the palisade from underlying tissue, which alone does not confer permeability; mostly they also result in fractures to the palisade that then render seeds irreversibly permeable. The palisade becomes reflective as it separates, which allows the event to be witnessed at the moment of separation if suitable pressure is applied to the testa of an individual seed while it is viewed under magnification. Brief (4–10 seconds) immersion of highquality seed in boiling water consistently softened a high proportion of seeds without causing serious damage. Extending the duration of immersion led to a progressive increase in the proportion of seed deaths. Neither previous boiling water treatment nor scarification damage to the testa materially affected results of treatment, but immature and small seeds behaved differently, being more vulnerable to damage than mature seed, and less likely to undergo lens rupture. Adaptation of boiling water treatment to farm-scale seed handling was simple and reliable. Commercial treatment of seed by an alternative method suitable for greater bulks and consisting of passage through a rice-whitener was checked and found to be successful through a combination of gentle scarification and lens rupture, both attributable to the numerous minor impacts of the process. Percentage emergence of seedlings from soil in the greenhouse closely followed percentage laboratory germination, except when inferior seed grades were included in the comparison, when emergence was poor. Very little seed softened in soil. Already-permeable seed either germinated rapidly or died, while buried hard seed mostly remained hard and viable even more than a year after sowing

Liveweight performance of cattle grazing Redlands and Wondergraze leucaena north Queensland

Leucaena is a rapid-growing, perennial legume which has potential to intensify beef production in the northern rangelands of Australia. Adoption of leucaena in north Queensland has been limited, in-part by the prevalence of the leucaena psyllid (Heteropsylla cubana). Psyllid infestations cause yield losses (Bray and Woodroffe 1991) and all cultivars previously used by industry are susceptible. Leucaena leucocephala 'Redlands' (R) released in 2018 has genetic resistance to psyllids with potential to increase leucaena productivity in psyllid prone regions and increase adoption. However, the performance of R under commercial grazing was untested and cattle grazing a leucaena palatability trial at Whitewater Station in north Queensland, initially grazed other leucaena varieties in preference to R (Keating 2019)

A contemporary assessment of land condition in the Northern Gulf region of Queensland

A framework using assessments of soil condition, pasture composition and woodland density was applied to describe 14 grazing land types as being in A (100% of original carrying capacity), B (75%), C (45%) or D (20%) condition. We assessed the condition of 260 sites, principally along public and some station roads, to provide a benchmark for current land condition. Land types were also assigned relative grazing values between 10 (best) and 0, reflecting soil fertility and potential biomass production. The method identifies particular, 'at-risk' land types for priority investment of resources, while the rationale behind assessments might point to management interventions to improve the condition of those land types. Across all land types, 47% of sites were in A condition, 34% in B condition, 17% in C condition and only 2% in D condition. Seventy-five percent of land types with grazing values >5 were in A or B condition, compared with 88% for those with grazing values ?5. For Georgetown granites, only 27% of sites were in A or B condition, with values for other land types being: alluvials 59%, black soils 64% and red duplex soils 57%, suggesting that improving management of these land types is a priority issue. On land types with high grazing value, the major discounting factor was pasture composition (72% of sites discounted), while increasing woodland density was the main discount (73% of sites discounted) on low grazing value land types

Adoption, profitability and future of leucaena feeding systems in Australia

Leucaena (Leucaena leucocephala ssp. glabrata) is a highly palatable and productive forage used mainly by beef producers on extensive properties in northern Australia. When sown into native or sown grass pastures, leucaena provides significant production, economic, environmental and social benefits. Adoption of leucaena was slow initially due to a range of technical, agronomic and landscape factors. These have now been largely overcome through extensive research, development, producer experience and other advances, resulting in around 130,000 ha of cultivated leucaena being utilized across northern Australia. A range of aspects will need to be addressed if the adoption of leucaena is to be accelerated into the future. These include environmental concerns, especially potential weediness, and a range of technological needs, including soil nutritional requirements, grazing and toxicity management, opportunities for companion fodder systems and conservation options. Advances in technology and the ongoing need for a high-quality, profitable and sustainable perennial forage will ensure the continued adoption of leucaena across northern Australia for the foreseeable future. © 2019, Centro Internacional de Agricultura Tropical (CIAT)

Adoption, profitability and future of leucaena feeding systems in Australia

Leucaena (Leucaena leucocephala ssp. glabrata) is a highly palatable and productive forage used mainly by beef producers on extensive properties in northern Australia. When sown into native or sown grass pastures, leucaena provides significant production, economic, environmental and social benefits. Adoption of leucaena was slow initially due to a range of technical, agronomic and landscape factors. These have now been largely overcome through extensive research, development, producer experience and other advances, resulting in around 130,000 ha of cultivated leucaena being utilized across northern Australia. A range of aspects will need to be addressed if the adoption of leucaena is to be accelerated into the future. These include environmental concerns, especially potential weediness, and a range of technological needs, including soil nutritional requirements, grazing and toxicity management, opportunities for companion fodder systems and conservation options. Advances in technology and the ongoing need for a high-quality, profitable and sustainable perennial forage will ensure the continued adoption of leucaena across northern Australia for the foreseeable future. © 2019, Centro Internacional de Agricultura Tropical (CIAT)

Phosphorus nutrition and management – overcoming constraints to wider adoption

The importance of phosphorus nutrition for cattle grazing northern Australian rangelands has been well documented and demonstrated. Phosphorus is clearly one of the most important nutritional deficiencies, within the limitations of potential metabolizable energy intakes, of grazing cattle in the seasonally dry tropics. Nevertheless it appears that only a small proportion of cattle grazing phosphorus deficient pastures are supplemented or otherwise managed to alleviate phosphorus deficiency. Estimated requirements for dietary phosphorus by various classes of cattle grazing tropical pastures have recently been revised (CSIRO 2007). The development of faecal near infrared spectroscopy (F.NIRS) allows the routine estimation of metabolizable energy and nitrogen concentrations in the diet, and thus the potential productivity, of cattle grazing northern rangelands. The concentration of phosphorus in the diet of grazing cattle can be estimated from the concentration of phosphorus in the faeces, at least in cattle not fed phosphorus supplements. Combining estimates of diet metabolizable energy, nitrogen and phosphorus allows estimation whether current needs of the animal are supplied by the diet. Phosphorus-replete cattle have substantial body reserves of phosphorus which can be mobilized, especially in late pregnancy and lactation, to alleviate a dietary deficiency. However, these body reserves need to be replenished in late lactation or post-lactation if mobilization occurs each year. Diagnosis of subclinical phosphorus deficiency in grazing cattle, and prediction of animal responses to phosphorus supplements is difficult. In growing cattle the concentration of inorganic phosphorus in blood (Pi), in the late wet or early dry season, combined with information on diet metabolizable energy and nitrogen concentrations obtained by F.NIRS, provides the most reliable test. In pregnant or lactating cows measurements of faecal phosphorus concentration and F.NIRS provide the best estimate of whether phosphorus intake meets the current needs of the animal. However, estimates of adequacy of phosphorus supply need to also consider possible mobilization of body phosphorus reserves. Indicative responses to provision of phosphorus supplements by cattle grazing pastures ranging from marginal to acute deficiency are summarized. Economic evaluation of benchmark enterprises where cattle are expected to be phosphorus deficient indicate that phosphorus supplementation is highly cost-effective. Major obstacles to more widespread adoption of phosphorus supplementation appear to be lack of knowledge and appreciation by managers of the phosphorus status of their cattle, lack of appreciation of the cost-effectiveness of a phosphorus supplementation particularly for some classes of cattle, and the practical difficulties in implementing phosphorus supplementation during the wet season

Northern Gulf beef production systems : Preparing for, responding to, and recovering from drought

This report details the analysis of the economic implications of management decisions that can be applied to prepare for, respond to, or recover from drought in the Northern Gulf Natural Resource Management (NRM) region of Queensland. Accompanying reports in this series present results for other regions across Queensland's grazing lands. It is intended that the results of these analyses will support the implementation of resilient grazing, herd and business practices necessary in managing seasonal variability. The property-level, regionally-specific herd and business models which we have developed can be used by consultants, advisors and producers to assess both strategic and tactical management decisions for their own properties. We have applied scenario analysis to examine a range of management strategies and technologies that may contribute to building both more profitable and more drought resilient beef properties in the Northern Gulf region. In doing this, we developed property-level, regionally-specific herd and business models for a representative, constructed beef cattle property which was based on the median herd data from relevant industry surveys and research. The starting base property was 30,000 ha of native pastures on representative land types and was considered to be in ca. B- land condition on average (scale A-D) with a carrying capacity ca. 65% of the safe, long term carrying capacity of these land types when in A condition. The property initially carried ca. 2,500 adult equivalents (AE) with estimated ratio of AE to safe carrying capacity of 1.54 given the B- land condition status. It was assumed that under this sustained stocking rate the land condition would continue to decline at a rate of 0.5% decrease in safe carrying capacity per year over the next 30 years resulting in a decrease in herd performance. The management features of the self-replacing Brahman breeding herd included continuous mating and minimal (inadequate) phosphorus (P) supplementation. The average mortality rate of the base herd was 7.5% and the average weaning rate from all cows mated was 47.4%. The average annual post-weaning weight gain for steers was ca. 86 kg/head. The starting herd size, herd performance and approach to pasture management was assumed to represent the current status of local properties that have largely not adopted a sustainable approach to pasture management. Production systems that can be applied to improve the profitability and resilience of a beef property to drought are generally of a strategic nature. The Breedcow and Dynama herd budgeting software was used to develop integrated herd models and discounted cash flow budgets for each alternative management strategy. The economic and financial effect of implementing each strategy was assessed by comparison to a base production system for the representative property. Property level productivity and profitability was assessed over a 30-year investment period and incorporated the change in profit and risk generated by alternative operating systems, the changes in unpaid labour, herd structure and capital, and included the implementation phase. Management decisions which are considered in response to, or recovery from, drought tend to need consideration of both short term and long term implications and were examined using herd models in conjunction with spreadsheets designed to assess tactical decisions