Leucaena leucocephala subsp. glabrata (leucaena)-grass pastures are productive, perennial and long-lived (>40 years). However, little is known about changes in the productivity of these pastures as they age even though they are grazed intensively and are rarely fertilised. A postal survey of beef cattle producers in Queensland who grow leucaena pastures was conducted. The questionnaire gathered information regarding: property location; extent and age of leucaena pastures; soil type; leucaena and grass establishment methodology; grazing and fertiliser management; and grazier perceptions of changes over time in leucaena productivity, grass growth and ground cover, prevalence of undesirable grasses and weeds, and livestock productivity. Graziers were asked to report on both young (≤10 years old) and aging (>10 years old) pastures under their management. Eighty-eight graziers responded describing 124 leucaena paddocks covering 11 750 ha. The survey results described the typical physical and management characteristics of leucaena pastures in Queensland. Graziers reported a decline in leucaena productivity in 58% of aging pastures, and declines in grass growth (32%) and livestock productivity (42%) associated with declining leucaena growth. Leucaena decline was greater in soil types of marginal initial fertility, particularly brigalow clay, soft wood scrub, downs and duplex soils. Maintenance fertiliser was not applied to most (98%) leucaena pastures surveyed despite significant amounts of nutrient removal, particularly phosphorus and sulphur, occurring over prolonged periods of moderate to high grazing pressure. It is predicted that large areas of leucaena pasture will continue to suffer soil nutrient depletion under current management practices. Research is needed to develop ameliorative actions to reinvigorate pasture productivity.

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Impacts of cattle production vary among different production systems, but data on their distribution is scarce for most world regions. In this work, we combine datasets on cattle vaccination locations and land cover in a regression framework to define and map major cattle production systems in the Argentinean Dry Chaco. We also explore how cattle occurrence relates to spatial determinants. Results indicate that the region harbors about 5.5 million heads. Cattle density was mainly described by the share of pasture (69.9%), cropland (28.1%) and aridity (23.8%). We identified 12-major cattle production systems: six cow-calf, three whole-cycle, and three fattening systems. Of these, four systems had high woodland cover (>85%). Data generated is available in a website. Understanding the distribution of cattle production systems is important to assess the environmental impacts of beef production at broad scales. Integrating vaccination data with land-cover information provides a promising avenue to identify livestock systems.

Soil organic carbon (OC) and total nitrogen (TN) accumulation in the top 0–0.15 m of leucaena–grass pastures were compared with native pastures and with continuously cropped land. OC and TN levels were highest under long-term leucaena–grass pasture (P < 0.05). For leucaena–grass 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 79 kg/ha.year, respectively, while TN accumulated at rates that exceeded those of the native grass pastures by 16.7, 10.8, and 14.0 kg/ha.year, respectively. At a site where 14-year-old leucaena–grass pasture was adjacent to continuously cropped land, there were benefits in OC accumulation of 762 kg/ha.year and in TN accumulation of 61.9 kg/ha.year associated with the establishment of leucaena–grass pastures. Similar C : N ratios (range 12.7–14.5) 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 leucaena–grass 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 (CO2-e) accumulated in additional topsoil OC of leucaena–grass 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.

Keynote paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.This paper presents the current status of Leucaena leucocephala (leucaena) feeding systems and proposes research priorities for leucaena development in Argentina. Although research on leucaena as forage for cattle production began in the late 1960s, it was not widely adopted until 2010 (5 decades later). The recent adoption is related to the incorporation of the ‘Australian technology package’, previously adapted for use by farmers in the neighboring region of the Paraguayan Chaco. In June 2018, we surveyed 8 properties with about 2,400 ha of leucaena in silvopastoral systems for beef cattle production in the Argentinean Chaco region, as well as 10 smallholder farms with about 10 ha of leucaena protein banks for dairy cattle in the northeast of Argentina. In the silvopastoral systems, leucaena condition was excellent on most properties in the 750‒1,350 mm/year rainfall zone and low/poor on only 1 farm due to low rainfall (600 mm/year). In protein banks, leucaena condition was excellent or good on 6 of the properties and low/poor on the remaining 4, attributed to ingress of weeds and/or overgrazing. Grass condition was good in most of the systems but was low/poor in 2 silvopastoral systems due to very high stocking rates imposed to restrict leucaena height. Although there is high potential for leucaena development in Argentina, expansion should take place carefully with leucaena planted only on areas suitable for successful establishment, and using appropriate management practices to reduce establishment failures and costs, restrict leucaena height, enhance grass persistence, improve grazing strategies and manage mimosine toxicity problems.

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 < 0.05) seasonal variation in nutrient concentrations in leucaena YFEL, which was poorly correlated with ambient temperature but strongly correlated with rainfall in the preceding 28 days and chronological age of YFEL. Advancing plant phenological stage of development increased the chronological age of YFEL from 12 to 73 days under irrigation since no new leaves were produced for prolonged periods during pod filling and maturation. Similarly, YFEL could be 146 days old on plants in vegetative stages of growth under prolonged drought in dryland conditions. YFEL of ~21 days of age or less were found to be optimal for analysis. Furthermore, as the calcium (Ca) concentration of YFEL was strongly correlated with leaf chronological age, this parameter could be used to determine the age of the leaves sampled. YFEL with Ca concentrations >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.

Keynote paper presented at the International Leucaena Conference, 1‒3 November 2018, Brisbane, Queensland, Australia.This review describes the history of research in Leucaena leucocephala (leucaena) feeding systems carried out by the National Institute of Agricultural Technology (INTA) over the last 5 decades and discusses the main limitations resulting in poor adoption in Argentina. Leucaena was introduced in the subtropical region of the north of the country in the late 1960s and early 1970s. Since then, INTA has conducted research to evaluate forage and animal productivity, leucaena accessions, rhizobial strains, contribution to soil carbon and total nitrogen and density effects on competition and other ecosystem interactions in silvopastoral systems. In spite of the convincing research results showing the excellent potential of leucaena to increase forage quality and animal production in suitable areas, there has been poor adoption of this forage tree legume on a broad scale.

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.