H. Max Shelton

Soil organic carbon and total nitrogen under Leucaena leucocephala pastures in Queensland

Soil organic carbon (OC) and total nitrogen (TN) accumulation in the top 00.15m of leucaenagrass pastures were compared with native pastures and with continuously cropped land. OC and TN levels were highest under long-term leucaenagrass pasture (P0.05). For leucaenagrass pastures that had been established for 20, 31, and 38 years, OC accumulated at rates that exceeded those of the adjacent native grass pasture by 267, 140, and 79kg/ha.year, respectively, while TN accumulated at rates that exceeded those of the native grass pastures by 16.7, 10.8, and 14.0kg/ha.year, respectively. At a site where 14-year-old leucaenagrass pasture was adjacent to continuously cropped land, there were benefits in OC accumulation of 762kg/ha.year and in TN accumulation of 61.9kg/ha.year associated with the establishment of leucaenagrass pastures. Similar C:N ratios (range 12.714.5) of soil OC in leucaena and grass-only pastures indicated that plant-available N limited soil OC accumulation in pure grass swards. Higher OC accumulation occurred near leucaena hedgerows than in the middle of the inter-row in most leucaenagrass pastures. Rates of C sequestration were compared with simple models of greenhouse gas (GHG) emissions from the grazed pastures. The amount of carbon dioxide equivalent (CO 2-e) accumulated in additional topsoil OC of leucaenagrass pastures ≤20 years old offset estimates of the amount of CO2-e emitted in methane and nitrous oxide from beef cattle grazing these pastures, thus giving positive GHG balances. Less productive, aging leucaena pastures 20 years old had negative GHG balances; lower additional topsoil OC accumulation rates compared with native grass pastures failed to offset animal emissions.

Response of Leucaena leucocephala pastures to phosphorus and sulfur application in Queensland

A series of fertiliser trials were conducted on leucaena (Leucaena leucocephala subsp. glabrata) pastures growing on a range of soil types in south-east and central Queensland. The primary objective was to determine the extent of phosphorus (P) and sulfur (S) deficiencies in leucaena-grass pastures established on either virgin soils or previously cropped soils. Two experiments were conducted across nine sites and confirmed that, for many soils in Queensland, leucaena growth was restricted by P and S nutrient deficiencies, which limited plant growth directly and suppressed symbiotic N2 fixation. The major factors contributing to the P and S deficiencies and thus affecting leucaena response were: (i) inherent low soil fertility, (ii) nutrient removal by cropping and grazing, (iii) shallow soils, (iv) soil acidity, and (v) grass competition for available water and nutrients. A secondary treatment, inter-row cultivation, had little effect on leucaena growth but significantly increased grass growth in some soils. In all these experiments, leaf S concentrations and N : S ratios in index tissue were inconsistent indicators of adequacy of S. Similarly, leaf P concentrations were not useful indicators of P deficiency due to inappropriate (drought) leaf sampling conditions experienced in these experiments. The experiments demonstrate that the productivity of leucaena-grass pastures, especially in older leucaena plantations, will be limited by nutrient deficiencies on many soils in Queensland. While leucaena yield was suppressed, no foliar symptoms of nutrient deficiency were observed. Growers need to monitor the nutrient status of their leucaena-grass pastures by leaf tissue analysis using a new sampling protocol. Strategic fertiliser application has the potential to increase rainfall use efficiency by 50% with an expected parallel increase in cattle liveweight gain.

Leucaena toxicity: a new perspective on the most widely used forage tree legume.

The tree legume Leucaena leucocephala (leucaena) is a high quality ruminant feed, vitally important for livestock production in the tropics, despite the presence of mimosine in the leaves. This toxic non-protein amino acid has the potential to limit productivity and adversely affect the health of animals. In the 1980s, the ruminal bacterium Synergistes jonesii was discovered and subsequently distributed in Australia as an oral inoculum to overcome these toxic effects. However, in recent times, a number of factors, including: surveys of the status of toxicity worldwide; improved understanding of the chemistry and mode of action of the toxins; new techniques for molecular sequencing; and concerns about the efficacy of the in vitro inoculum; have cast doubt on some past understanding of leucaena toxicity and provide new insights into the geographical spread of S. jonesii . There is also confusion and ignorance regarding the occurrence and significance of toxicity in many countries worldwide. Ongoing research into the taxonomy and ecology of the Synergistetes phylum, improved methods of inoculation, and improved management solutions, along with aware-ness-raising extension activities, are vital for the future success of leucaena feeding systems.

Survey of long-term productivity and nutritional status of Leucaena leucocephala-grass pastures in subtropical Queensland

A survey of the productivity and nutritional status of leucaena (Leucaena leucocephala subsp. glabrata) pastures of different ages was conducted in subtropical Queensland from 2006 to 2008. Four leucaena stands (aged 8, 20, 31 and 38 years) growing on the same Vertosol soil type at Brian Pastures Research Station were surveyed. In the higher rainfall season of 2007-2008, leucaena yields and rainfall-use efficiency were highest in 8-year-old stands [2128 kg total dry matter (DM)/ha or 4.0 kg DM/ha.mm] and lowest in 38-year-old stands (978 kg total DM/ha or 1.9 kg DM/ha.mm). The reduced productivity in the 38-year-old leucaena pasture was associated with a decline in stem number/plant and leucaena plant density due to observed plant mortality. The reduced yield and vigour of aging leucaena was associated with nitrogen deficiency related to declining phosphorus and sulfur availability for adequate symbiotic N2 fixation and leucaena plant growth. Nutrient deficiencies of phosphorus and sulfur in leaf tissue were related to low to medium initial soil fertility (7-27 mg/kg of bicarbonate extractable phosphorus in the top 20 cm), coupled with inherent subsoil constraints (shallow soils, sodicity and high pH), and exacerbated by both long-term removal of nutrients by grazing animals and a reduction in soil phosphorus and sulfur availability over time. To maintain the productivity of leucaena pastures, plant nutritional status needs to be monitored in order to determine strategic fertiliser application.

Effect of environment and plant phenology on prediction of plant nutrient deficiency using leaf analysis in Leucaena leucocephala

Plant analysis is an important tool for predicting plant nutrient imbalances associated with variable soil fertility and it is usually based on analysis of index plant parts such as the youngest fully expanded leaf (YFEL). Recent use of the YFEL to diagnose plant nutrient status of Leucaena leucocephala subsp. glabrata (leucaena) pastures has given unreliable results. Two field trials, one irrigated and one dryland, were conducted in subtropical Queensland to investigate the effect of index leaf selection, plant phenology and environmental factors (ambient temperature and water stress) on leaf nutrient concentrations. The YFEL was identified as the best plant part to sample because it was readily identifiable and had consistent concentrations of most nutrients compared to older and younger leaves provided specific conditions were met when sampling. At both sites there was significant (P  0.75% DM were likely to be >21 days in age and should not be used for the diagnosis of plant nutrient status. It was concluded that leaf analysis could be used to confidently assess leucaena plant nutrient status provided the YFEL were sampled from actively growing plants in vegetative development that had received rainfall/irrigation in the preceding 28 days and were <21 days of age.

Potential of Australian bermudagrasses (Cynodon spp.) for pasture in subtropical Australia

In Australia, little work has been carried out on the improvement of tropical or subtropical pastures in recent years. There seems to be an increasing demand for pastures that can withstand heavy grazing, while producing high yields of high quality forage in the humid subtropical regions of Australia. Most graziers, who live in these areas, have small acreages, which they graze intensively. Cynodon spp. represent a potential source of grasses with these attributes. This study will evaluate the pasture potential of a large number of bermudagrass (Cynodon spp.) ecotypes collected from across Australia.

Effect of tree density on competition between Leucaena leucocephala and Chloris gayana using a Nelder Wheel trial. I. Aboveground interactions

Abstract. Silvopastoral systems with the tree legume leucaena (Leucaena leucocephala (Lam.) de Wit) and grass pastures are widely used for ruminant feeding in subtropical and tropical regions. Different densities and planting configurations of leucaena will influence relative yields of both species because of intra- and interspecific competition. With the aim to describe the effects of competition between leucaena and Rhodes grass (Chloris gayana Kunth), a Nelder Wheel trial with 10 different leucaena tree densities (100–80 000 trees ha–1) growing with and without Rhodes grass was established in a subtropical environment at Gatton, south-east Queensland, in November 2013. From 2014 to 2016, the biomass of leucaena (six harvests) and Rhodes grass (seven harvests) was measured by using allometric equations and the BOTANAL sampling procedure over 742 and 721 days, respectively. No complementary or facilitative aboveground interactions were observed between the leucaena and Rhodes grass components of the pasture system. Increasing leucaena tree density resulted in greater aboveground intra- and interspecific competition. Average maximum individual tree yield (38.9 kg DM tree–1 year–1) was reached at 100 trees ha–1 without grass competition and was reduced by 60% with grass competition. Rhodes grass biomass yield was negatively affected by shading from the leucaena canopy, with negligible grass yield at tree densities ≥8618 trees ha–1. Therefore, there was effectively no grass competition on individual tree yield at higher leucaena densities. Accordingly, edible leucaena biomass per unit area was positively related to log10 leucaena density (R2 = 0.99) regardless of grass competition, reaching 21.7 t DM ha–1 year–1 (2014–15) and 27 t DM ha–1 year–1 (2015–16) at the highest leucaena density of 80 000 trees ha–1. By contrast, the yield of Rhodes grass was linearly and inversely correlated with log10 tree density (R2 = 0.99). Practical implications for the design and management of commercial leucaena–grass pastures are discussed.

The efficacy of a cultured Synergistes jonesii inoculum to control hydroxypyridone toxicity in Bos indicus steers fed leucaena/grass diets

An experiment was conducted to investigate the efficacy of a cultured Synergistes jonesii inoculum in degrading the Leucaena leucocephala (leucaena) toxins: 3-hydroxy-4(1H)-pyridone and 3-hydroxy-2(1H)-pyridone (3,4- and 2,3-DHP). Sixteen stall-housed Bos indicus steers naive to leucaena were fed varying combinations of forage-harvested leucaena and Chloris gayana (Rhodes grass). Dietary treatments, offered at 25 g dry matter/kg LW.day, were: 25% leucaena; 50% leucaena; 100% leucaena; and 50% leucaena, switched to 50% Medicago sativa (lucerne) after 6 weeks at time of inoculation. The experiment was 10 weeks in duration, consisting of a 6-week pre-inoculation period, followed by inoculation with cultured S. jonesii, and a 4-week post-inoculation period. Mean daily dry matter intake was recorded. Twenty-four-hour urine collections and rumen fluid samples were obtained weekly for estimation of total urinary DHP, and detection of S. jonesii using nested polymerase chain reaction analysis including presence of single nucleotide polymorphisms (SNP), respectively. In the pre-inoculation period, total urinary DHP increased quickly to high levels, then gradually declined after Week 3 with 2,3-DHP the dominant isomer through to Week 6. Indigenous strains of S. jonesii were sporadically detected by PCR analysis, indicating S. jonesii was present before inoculation but at the lower limits of detection. After inoculation there was no change in the rate of total DHP degradation or the frequency of detection of S. jonesii, although there was increased rate of degradation of 2,3-DHP. SNP indicated the presence of different strains of S. jonesii in both indigenous and cultured S. jonesii. DMI was low, especially in the 100% treatment, due in part to the high stem content of the forage-harvested leucaena and probable DHP toxicosis. It was concluded that the cultured S. jonesii inoculum did not fully protect animals against leucaena toxicity.

Survey of Bali bull fattening practices in central Lombok, eastern Indonesia, based on feeding of Sesbania grandiflora

A longitudinal survey was conducted in 2013 to document the productivity of the Sesbania grandiflora feeding system for cattle fattening in central Lombok. Sesbania is integrated into the intensive rice-growing region by planting it along the rice bunds surrounding the rice fields. The hamlet of Nyerot in the subdistrict of Jonggat was chosen for the study as it had a long history of successful use of sesbania for fattening Bali bulls. Parameters measured included: area of rice paddy where sesbania could be planted; forage establishment, harvesting and feeding practices; cattle purchases and sales; and monthly liveweight gain. Farmers planted an average of 406 sesbania trees on bunds surrounding 0.6 ha of rice paddy. The median values for the main forages fed (dry matter offered) were harvested elephant grass (78% of diet), sesbania (12% of diet) and other feeds (mainly rice bran) (5% of diet). Sesbania was harvested by lopping the lower side branches of ~6 trees per bull per day and never completely defoliating single trees. The farmers fattened an average of 1.6 bulls at a time achieving a yearly mean liveweight gain of 0.41 kg/bull.day. New bulls were purchased with an average liveweight of 203 kg while the average sale weight was 260 kg. Purchase and sale prices were high at A

Growth of Bali bulls fattened with Leucaena leucocephala in Sumbawa, Eastern Indonesia

3.27 and A