Search

Trifolium subterraneum L. subsp. yanninicum is a pasture legume that is widely grown in medium and high rainfall areas of southern Australia and shows waterlogging tolerance. This study investigated diversity within subsp. yanninicum corresponding to eco-geographic variables, which may help to identify adapted parents with new traits for genetic improvement. Diversity for 10 morphological traits, flowering time and leaf isoflavone content was investigated using 108 ecotypes derived from wild Mediterranean populations and 10 cultivars, grown as spaced plants. Among the ecotypes, the range of flowering time was 94–149 days after sowing, and contents of formononetin, genistein and biochanin A were 0.05–1.38%, 0.73–2.33% and 0.15–2.10% of dry matter, respectively. Leaf markings also varied considerably. Leaf size and petiole length were correlated at each growth stage. Later flowering genotypes had larger leaves, longer petioles, longer internodes and thicker stems at flowering, but smaller leaves and shorter petioles at both 63 and 88 days after sowing. Contents of genistein and biochanin A were unrelated, but both were negatively associated with formononetin. Flowering time had a weak positive influence on genistein and biochanin A, but a weak negative influence on formononetin. All traits among the ecotypes (except stem diameter and leaf mark crescent size) were significantly correlated with at least one of 22 eco-geographic variables from their collection sites. Precipitation and altitude were more influential than temperature. The study found sufficient diversity to broaden the narrow genetic base of current subsp. yanninicum cultivars; however, other agronomically important traits also need to be considered. Further diversity may result from targeted collection, particularly in areas not represented in annual legume genebanks.

Context The use of dual-purpose crops (for grazing and grain) has increased in the high-rainfall zone in southern Australia. Aim A systems experiment examined the impact on livestock production and supplementary feeding when dual-purpose crops were incorporated into a production system based on Merino ewes producing yearling lambs for sale. Methods The experimental site near Canberra, ACT, was subdivided into nine experimental units (‘farmlets’) with three replicate farmlets for each of three production-system treatments. Each farmlet was managed as a self-contained unit with six Merino ewes and their progeny during 2013–16 (4 years). Ewes were joined in February, lambed in July and shorn in spring; the original cohort of ewes (born 2009) was replaced by a new cohort (born 2012) at the midpoint of the experiment. Six weaners were retained after weaning in each farmlet and sold as yearlings. Control farmlets were sown to pasture based on phalaris (Phalaris aquatica L.) and subterranean clover (Trifolium subterraneum L.) and comprised sub-paddocks to allow rotational grazing. Farmlets in treatments that included dual-purpose crops comprised six sub-paddocks (0.231 ha), with two sown to permanent pasture, and four supporting a rotation of pasture–pasture–dual-purpose canola (Brassica napus L.)–dual-purpose wheat (Triticum aestivum L.). In one of the crop–pasture production system treatments, crop-grazing was prioritised for ewes (ECG treatment); in the other, crop-grazing was prioritised for their progeny weaners (WCG treatment). Key results Greasy fleece weight from ECG (5.3 kg) and WCG (5.1 kg) ewes was higher (P < 0.001) than from control ewes (4.7 kg) averaged over the 4 years. The final sale weight of yearling weaners from the WCG system (44.3 kg) was higher (P < 0.001) than from the control (39.2 kg) or ECG (39.1 kg) systems when averaged over the 4 years. The benefit was predominantly due to greater weight gain during the period when weaners grazed the crop during late autumn and winter. Sale weight of lamb per hectare was higher (P = 0.003) in the WCG treatment (216 kg) compared with the ECG treatment (186 kg) when averaged over the 4 years of the experiment but did not differ (P > 0.05) to the control (201 kg). Meat production over the 4 years was higher (P < 0.001) in the WCG system (226 kg/ha) than other treatments when weight gain from wethers in 2014 was included. The impact of including dual-purpose crops on supplementary feeding was variable and depended on seasonal conditions. Conclusions Incorporation of dual-purpose crops into the high-rainfall production system can increase meat and wool production, with the highest meat production being obtained when crop grazing was prioritised for young carry-over livestock. Implications Prioritising dual-purpose crops for young growing livestock can increase meat production from the system while allowing other livestock classes (wethers or ewes) to graze the crops in better seasons when there was excess forage that would otherwise have been under-utilised.

Subterranean clover (Trifolium subterraneum L.) is Australia’s most widely sown annual pasture legume. Its widespread use as a pasture plant requires a well-functioning seed production industry, and Australia is the only significant producer of subterranean clover seed globally. However, the sustainability of this industry is under threat due to its reliance on ageing harvest equipment and the resultant environmental impacts. In order to evaluate seed harvesting practices, technology, and issues, we report on case studies, workshops, and a survey of seed producers across southern Australia. The Horwood Bagshaw Clover Harvester, designed in the 1950s, remains the most popular subterranean clover seed harvester. We discuss its use and modifications, and document several contemporary issues facing the seed production industry. Issues are primarily soil erosion and degradation; the expensive, slow and labour-intensive harvest process; and poor reliability and maintainability of harvesters that are now at least 30 years old. We conclude the root cause of these issues is the suction harvest technology utilised by the Horwood Bagshaw Clover Harvester. Analysis of the current harvest system is provided to support the development of new approaches to harvest subterranean clover seeds.

Context Biserrula (Biserrula pelecinus L.) is a relatively new legume species in Australia that has been shown to maintain higher quality forage late in the season than subterranean clover (Trifolium subterraneum L.). Aim This study investigated the suitability of lucerne (Medicago sativa L.), subterranean clover and biserrula, or a choice of both biserrula and subterranean clover, for finishing White Dorper and White Suffolk × Merino lambs during spring. Methods An experiment was established near Wagga Wagga, NSW, in 2013 in a randomised complete block design with three replicates and four pasture treatments grazed by lambs during late spring and early summer. Liveweight, carcass weight and GR fat depth of White Dorper and White Suffolk × Merino lambs grazing lucerne, subterranean clover, biserrula or a choice of subterranean clover plus biserrula were compared. Key results Lambs grazing lucerne had significantly (P < 0.05) higher final liveweight, carcass weight and GR fat depth than lambs grazing other pasture treatments. After 61 days of grazing, mean liveweight of lambs grazing lucerne, subterranean clover and subterranean clover plus biserrula was higher than of lambs grazing biserrula monoculture. In vitro digestible organic matter digestibility and crude protein content indicated that lambs grazing biserrula should have achieved growth rates at least as high as lambs grazing subterranean clover. Sheep genotype and pasture type affected final liveweight. Final liveweight was higher for White Dorper lambs when grazing the subterranean clover plus biserrula treatment than the subterranean clover monoculture (45.6 vs 44.5 kg; P < 0.05) but was similar for White Suffolk × Merino lambs grazing these treatments (47.3 vs 47.2 kg; P > 0.05). Conclusions Provision of a companion species or mixture of species when lambs graze biserrula during late spring to summer appears to offer benefits for lamb growth rate over this period.

To examine the legacy of pasture drill rows sown to various configurations of subterranean clover (Trifolium subterraneum L.), lucerne (Medicago sativa L.) and phalaris (Phalaris aquatica L.), on soil chemical characteristics and wheat (Triticum aestivum L.) production in the year following pasture removal. A field experiment comparing 10 pasture species combination treatments conducted on a Red Kandosol soil in a semi-arid environment in south-eastern Australia was monitored from the end of the pasture phase until harvest of the first wheat crop. Quadrats were fixed to the soil surface to mark previous pasture drill rows. Soil within and between rows was sampled to 0.6 m at three times and analysed for mineral nitrogen (N), pH, total carbon (C) and available macro-nutrients, and related to wheat growth rate and yield. Significantly higher total C, mineral N and plant-available potassium (K), and lower sulphur (S) concentrations, were still evident in the original pasture drill row after grain harvest compared to the inter-row area, four years after pastures were sown. Grain yield was 11% greater in wheat growing on the original pasture drill row compared to between rows. Pure lucerne swards had less mineralised N than mixed lucerne swards associated with reduced water in the soil profile. This study establishes the enduring legacy of pasture drill rows observed up to 14 months post-removal and highlights the opportunity to improve soil fertility through manipulation of pasture sowing configurations in a cropping field in south-eastern Australia.

Changed spatial configurations at sowing have been investigated as a strategy to minimize interspecific competition and improve the establishment and persistence of multi-species plantings in pastures, but the impact of this practice on the soil microbiome has received almost no previous research attention. Differences in populations of bacteria and fungi in the surface 10 cm of soil in the third year following pasture establishment were quantified using quantitative polymerase chain reaction and terminal restriction fragment length polymorphism methods. Populations were compared on, and between, drill rows sown to either the perennial grass phalaris (Phalaris aquatica L.), perennial legume lucerne (alfalfa; Medicago sativa L.) or the annual legume subterranean clover (Trifolium subterraneum L.). Results showed that soil microbial abundance and diversity were related to plant distribution across the field at the time of sampling and to soil chemical parameters including total carbon (C), mineral nitrogen (N), pH, and available phosphorus (P), potassium (K) and sulfur (S). Despite the 27-month lag since sowing, pasture species remained concentrated around the original drill row with very little colonization of the inter-row area. The abundance and diversity of bacterial and fungal populations were consistently greater under drill rows associated with higher total C concentrations in the surface soil compared with the inter-row areas. Our results showed that the pH and available nutrients were similar between the subterranean clover drill row and the inter-row, suggesting that soil microbial populations were not impacted directly by these soil fertility parameters, but rather were related to the presence or absence of plants. The abundance of bacteria and fungi were numerically lower under phalaris rows compared to rows sown to legumes. The richness and diversity of fungal populations were lowest between rows where lucerne was planted. Possible explanations for this observation include a lower C:N ratio of lucerne roots and/or a lack of fibrous roots at the soil surface compared to the other species, illustrating the influence of contrasting plant types on the soil microflora community. This study highlights the enduring legacy of the drill row on the spatial distribution of plants well into the pasture phase of a cropping rotation and discusses the opportunity to enhance the microbiome of cropping soils on a large scale during the pasture phase by increasing plant distribution across the landscape.

Phosphorus (P) is usually stratified in the topsoil layer under pasture, due to the broadcast application of fertiliser, excreta and leaf-litter deposition on the soil surface, and minimal soil disturbance. The objective of this study was to investigate root proliferation and P acquisition in response to P stratification by comparing two Trifolium subterraneum cultivars with contrasting root morphologies. Clover micro-swards were grown with deficient, constrained and sufficient P supplied in a topsoil layer overlying a P-deficient subsoil that mimicked the stratification of P that occurs under pasture. Phosphorus labelled with 33P- and 32P-radioisotope tracer was mixed throughout the topsoil and subsoil layers, respectively. The shoot yield and total plant P uptake of the cultivars increased in response to increased topsoil P supply. The length of roots produced by the cultivars was equivalent in each of the P treatments, although the specific root length achieved by the cultivars was substantially different. In the P-constrained and P-sufficient treatments, ~91% and ~ 99% of total plant P was acquired by topsoil roots, respectively. In contrast, subsoil roots acquired 60–74% of total plant P in the P-deficient treatment. Topsoil roots were most important for P acquisition when P was highly stratified, whereas subsoil roots contributed to P acquisition when P was uniformly distributed throughout the P-deficient soil profile. Selection for prolific nutrient-foraging roots, in conjunction with plasticity for subsoil exploration, may improve the P-acquisition efficiency of T. subterraneum genotypes and confer adaptability across a range of soil-P environments.

Tedera, (Bituminaria bituminosa C.H. Stirt var. albomarginata) a herbaceous deep rooted perennial legume is being evaluated as a summer-autumn feed for sheep production in South Western Australia (...

Dry matter yield and botanical composition of four grazed dryland pasture types were compared over 8 years in summer-dry conditions at Ashley Dene, Canterbury, New Zealand. The experiment was sown in March 2013 to evaluate cocksfoot (CF)- or meadow fescue/ryegrass hybrid (RG)-based pastures established with either subterranean (Sub) or subterranean and balansa (S+B) clovers. Plantain was included in all pasture types. Perennial ryegrass established poorly on the low soil moisture holding capacity Lismore soil and in Year 2 was re-broadcast into the RG pastures. Despite this, plantain was the main sown species in RG pastures beyond Year 3. Total spring yield was greatest in Year 5 at 6720 kg DM/ha and varied with spring rainfall. Cocksfoot-based pastures had 60% of sown species present in the spring of Year 8, compared with 28% in RG-based pastures. Balansa clover was only present up to Year 5 after a managed seeding event in the first spring. White clover did not persist in the dryland environment past Year 2. Sub clover yield depended on the time and amount of autumn rainfall but contributed up to 45% of the spring yield. Cocksfoot-sub clover pastures appear to be most resilient in this summer-dry environment with variable spring rainfall.

International audience; Mycorrhizal fungi are ubiquitous in agroecosystems and form symbiotic associations that contribute to the phosphorus (P) acquisition of many plants. The impact of mycorrhizas is most pronounced in P-deficient soil and commonly involves modifications to the root morphology of colonised plants. However, the consequences of mycorrhizal colonisation on root acclimation responses to P stress are not well described. Five annual pasture legumes, with differing root morphologies, were grown to determine the effect of mycorrhizal colonisation on shoot yield, root morphology and P uptake. Micro-swards of each legume were established in pots filled with a topsoil layer that had been amended with five rates of P fertiliser. The topsoil overlaid a low-P subsoil that mimicked the stratification of P that occurs under pasture. Mycorrhizal colonisation improved P acquisition and shoot yield in the low-P soil treatments, but did not reduce the critical external P requirement of the legumes for near-maximum yield. The yield responses of the mycorrhizal plants were associated with reduced dry matter allocation to topsoil roots, which meant that the P acquisition benefit associated with mycorrhizal colonisation was not additive in the P-deficient soil. The contribution of the mycorrhizal association to P acquisition was consistent among the legumes when they were compared at an equivalent level of plant P stress, and was most pronounced below a P stress index of ~0.5. The intrinsic root morphology of the legumes determined their differences in P-acquisition efficiency irrespective of mycorrhizal colonisation.

In the summer-dominant rainfall zone of inland northern New South Wales and southern Queensland, tropical grass-temperate legume mixed pastures can provide forage for grazing livestock for most of ...

Annual pasture legumes with a superior ability to acquire soil phosphorus (P) and a low external critical P requirement could reduce the need for P fertiliser. Roots of pasture legumes grown in field soil will commonly be colonised by arbuscular mycorrhizal fungi (AMF). However, recent research suggests a second community of arbuscule-forming root-colonising fungi may be present: fine root endophytes (FRE). AMF are known to enhance P acquisition by plants under certain conditions, whereas very little is known about FRE and their impact on plant P status. We, therefore, grew plants at seven levels of P supply to determine and compare the external critical P requirements of two species of Ornithopus and two cultivars of Trifolium subterraneum when colonised predominantly by FRE (FRE-dominant treatment) or both FRE and AMF (mixed treatment). As expected from previous studies, the Ornithopus species had a lower critical P requirement than the T. subterraneum cultivars. However, for the Ornithopus species only, the FRE-dominant community had a significantly lower external critical P requirement (24–31 mg P kg−1 soil) than the mixed community (50–58 mg P kg−1 soil). Moreover, at low-P supply (≤15 mg applied P kg−1 soil), Ornithopus species in the FRE-dominant treatment had longer specific root length, smaller average root diameter, 45–128% greater total root length, and lower shoot and root P concentration than in the mixed treatment. We concluded that comparisons among experiments of root morphological traits and external critical P requirements can be affected by the presence of different communities of arbuscule-forming root-colonising fungi and that these effects may vary among plant species.

CONTEXT The nutritive value of annual pasture legumes changes with phenology during each season, with a progressive decrease in feeding value as plants accumulate structural carbohydrates and nutrients are diluted. However, these changes differ widely among annual legume species, affecting the pattern of nutrient availability and production in a grazing enterprise. OBJECTIVE This paper set out to examine the implications of differences in the nutritive value of annual pasture legumes in relation to their economic value for mixed farming systems of southern Australia. METHODS Calibrated GrassGro™ plant models with data generated from field experiments to represent Dry Matter Digestibility (DMD) profiles of six annual legume species; Medicago truncatula Gaertn. (barrel medic), B. pelecinus L. (biserrula), Trifolium spumosum L. (bladder clover), Ornithopus sativus Brot. (French serradella), Medicago littoralis Rhode ex Loisel. (strand medic) and Trifolium subterraneum L. (subterranean clover). The plant models were used in a modelling study to support a self-replacing Merino sheep enterprise, which was simulated at seven locations across southern Australia, where annual pasture species are heavily relied on for livestock production. RESULTS AND CONCLUSIONS Modelled values of DMD of green material, averaged across all phenological stages, ranged from approximately 62% (French serradella) to 73% (bladder clover), with little variation due to location. Pastures with higher nutritive value had a reduced requirement for supplementary feeding of sheep. Variation in nutritive value had a greater effect on supplementary feeding costs and gross margins than differences in biomass production among the annual legume species. Differences in the levels of supplementary feeding required in systems with the different legumes was most pronounced during the period from May to July (late autumn to winter). For sheep enterprises compared at the same stocking rate, the total supplementary feed required was 18% lower with bladder clover pastures, and 9% lower in subterranean clover pastures, compared with an average of the remaining four pasture species. SIGNIFICANCE This is the first study to compare the effects of variation in nutritive value among the annual pasture legumes developed for the soils and climatic conditions of southern Australia. Our results demonstrated that the magnitude of differences in nutritive value among annual pasture legumes are economically important and that the establishment of higher nutritive value legumes will reduce supplementary feeding costs in extensive grazing systems, in some cases even where their biomass production is lower.

It is widely claimed that common mycorrhizal networks (CMN) play significant roles in facilitated transfer of nutrients between plants. This experiment investigated the role of a common mycorrhizal network with a C3 legume and a C4 grass under drought-stressed conditions, and assessed whether there was an interaction between water and plant species on rhizosphere bacterial DNA community profile. Shoot biomass of Trifolium subterraneum increased by almost 150% when grown in close proximity to Panicum clandestinum when the only possible connection between their roots was via a common mycorrhizal network. Inter-species competition between T. subterraneum and P. clandestinum was observed in low-nutrient soil. The soil bacterial communities in rhizospheres of both T. subterraneum and P. clandestinum were similar. Drought-stress increased the relative abundance of Firmicutes and Actinobacteria and decreased the relative abundance of Proteobacteria, especially when plants were likely connected by a CMN. Drought-stress decreased the abundance of N-cycling genes under P. clandestinum but not under T. subterraneum. The competitiveness of T. subterraneum when grown adjacent to P. clandestinum corresponded with enhanced P acquisition and depletion of soil P under P. clandestinum for both water treatments at different times. Thus, T. subterraneum may have been more competitive due to enhanced direct P acquisition from soil under P. clandestinum rather than by direct P transfer from P. clandestinum to T. subterraneum via a common mycorrhizal network.

Grazing systems are a major producer of food and fibre across the world. These systems often require the addition of fertiliser phosphorus (P) for maximum pasture growth, and it is now estimated that a four-fold increase in the use of P fertiliser in grasslands is needed to meet increased food demand by the year 2050. However, the recovery of P from fertiliser is often inefficient and global issues associated with P scarcity will continue to worsen. Knowledge on the uptake of fertiliser P by grasslands, including the effect of agronomic management, remains incomplete under field conditions. The aim of this study was to quantify the effects of soil P fertility (across three levels of soil P fertility), time of fertiliser application (at one level of soil P fertility), and placement of fertiliser (at one level of soil P fertility) on the growth and uptake of fertiliser P by clover pastures during a growing season. Subterranean clover (Trifolium subterraneum L.) monocultures established at two field sites in Australia were used to test the growth response to, and recovery of: (i) early-season (autumn) additions of fertiliser P to the soil surface at three levels of soil P fertility; (ii) mid-season (late winter) additions of fertiliser P to the soil surface; and (iii) early-season additions of fertiliser P placed 6 cm below the soil surface. Fertiliser P was applied to the pastures as single superphosphate that was labelled with a 33P radiotracer to supply ∼20 kg P ha−1. Total herbage yield and recovery of fertiliser P by the clover pastures was generally highest when fertiliser P was applied to the soil surface early in the growing season and to soils maintained at the optimum level of soil P fertility for maximum pasture growth. An audit of the 33P recovery of fertiliser P in the clover pasture revealed that up to 50% of the fertiliser P was recovered by the clover plant (shoots and roots), 5–15% remained in the fertiliser granule, and 20–25% was recovered in the 0–4 cm soil layer (largely as inorganic P) by the end of the growing season. We demonstrate that clover pastures are able to recover a relatively large proportion of surface applied fertiliser P during a growing season. Surface application is the simplest and most cost-effective strategy for management of fertiliser P in pastures.

In alkaline soils in arid and semi-arid areas toxic concentrations of the micronutrient boron (B) are problematic for many cereal and legume crops. Molecular markers have been developed for B toxicity in cereals and Medicago. There is a need for such tools in clovers—Trifolium. To this end, we undertook a genome-wide association study (GWAS) with a diversity panel of subterranean clover (Trifolium subterraneum L.), an established model pasture legume for genetic and genomic analyses for the genus. The panel comprised 124 T. subterraneum genotypes (97 core collection accessions and 27 Australian cultivars). Substantial and useful diversity in B toxicity tolerance was found in T. subterraneum. Such variation was continuously distributed and exhibited a high broad sense heritability H2 = 0.92. Among the subspecies of T. subterraneum, ssp. brachycalycinum was most susceptible to B toxicity (P < 0.05). From the GWAS, the most important discoveries were single-nucleotide polymorphisms (SNPs) located on Chr 1, 2, and 3, which mapped to haplotype blocks providing potential genes for a B toxicity tolerance assay and meriting further investigation. A SNP identified on Chr 1 aligned with Medicago truncatula respiratory burst oxidase-like protein (TSub_ g2235). This protein is known to respond to abiotic and biotic stimuli. The identification of these novel potential genes and their use to design markers for marker-assisted selection offer a pathway in pasture legumes to manage B toxicity by exploiting B tolerance.

Many epidemics involve plants infected with more than one pathogen, but few experiments address climate change scenarios that influence mixed infections. This study addresses the interactive effects of co-infection and temperature on disease development in plants of the annual pasture species subterranean clover (Trifolium subterraneum), which is widely sown in different world regions. Bean yellow mosaic virus (BYMV) and the fungus Kabatiella caulivora are two important pathogens causing considerable production losses in pastures containing this species. Both occur together in such pastures causing a severe necrotic disease when mixed infection occurs. Effects of temperature on symptom expression were investigated in subterranean clover plants infected singly or in mixed infection with these pathogens. Plants were maintained in controlled environment rooms at 18°C, 20°C or 22.5°C after sap inoculation with BYMV. K. caulivora conidia suspensions were inoculated to plants once systemic BYMV symptoms developed. Plants were assessed for three disease assessment parameters, dead petioles numbers, marginal leaflet necrosis and overall plant damage. In general, mixed infection caused most severe symptoms, K. caulivora least severe symptoms, and BYMV symptoms of intermediate severity. In single infections, effects of temperature on disease severity differed between pathogens: BYMV symptoms were most pronounced at 18°C, but K. caulivora induced more severe symptoms at 20°C and 22.5°C. In mixed infections, disease severity generally followed the pattern developed with BYMV alone as temperature increased. Also, synergistic increase in disease severity sometimes occurred at 18°C, but increases were only additive at 20°C and 22.5°C. These results reflected the greater BYMV multiplication detected in infected leaves at 18°C compared with 20°C or 22.5°C. Our findings indicate that in rainfed subterranean clover pastures, as global warming progresses disease severity from infection with BYMV and K. caulivora alone may decline or increase, respectively, and mixed infection with them may become less damaging.

Trifolium subterraneum L. is the predominant annual pasture legume in southern Australia. Cultivars with improved phosphorus (P) foraging ability would improve the P-use efficiency of agricultural systems. We therefore investigated variation in root traits related to P-uptake among six cultivars. Micro-swards were grown at six levels of P in field soil with indigenous arbuscular mycorrhizal (AM) fungi for six weeks. Dry matter yield, tissue P concentration, rhizosphere carboxylates, AM fungal colonisation and root morphological traits were measured. The cultivars showed similar shoot and root yield responses to P supply. Average root diameter did not change, specific root length (SRL) increased and root tissue density (RTD) decreased with increased P supply. Amounts of total rhizosphere carboxylates were low (

This work aimed to quantify the critical external requirement for phosphorus (P) (i.e. extractable-P concentration required for 90 % of maximum yield) for a number of temperate legume species and understand differences in dry matter allocation, P distribution and P acquisition efficiency among these species. Shoot and root growth of five legume and one grass species was assessed in response to six rates of P mixed into the top 45 mm of soil in a pot experiment. Dactylis glomerata and Trifolium subterraneum were used as benchmark species; they are commonly grown together in mixed temperate pastures and have low and high critical external requirements for P, respectively. Growth was compared with four alternative legume species: Ornithopus compressus, Ornithopus sativus, Biserrula pelecinus and Trifolium hirtum, that have root morphologies better suited to soil exploration and nutrient acquisition than that of Trifolium subterraneum. Dactylis glomerata, Ornithopus compressus and Ornithopus sativus had maximum yields equal to or greater than Trifolium subterraneum but achieved this at rates of P less than half that of Trifolium subterraneum. Biserrula pelecinus and Trifolium hirtum had critical P requirements between that of Trifolium subterraneum and the Ornithopus species, but also had lower yields. Root dry matter of Dactylis glomerata and the Ornithopus species in the fertilised soil layer was only marginally changed in response to low P supply. In contrast, Trifolium subterraneum, Trifolium hirtum and to a lesser extent Biserrula pelecinus markedly increased root dry matter allocation to this soil layer. Species with lower critical P requirements were able to take up more P per unit root dry mass than those with higher critical P requirements, particularly at lower levels of P addition. The high P acquisition efficiencies of the Ornithopus species and Dactylis glomerata were likely to have contributed to their low critical external P requirements. It was surmised that differences in root morphology traits underpin the differences in acclimation to low P stress and P acquisition efficiency among the species.

Development of more phosphorus (P)-efficient pasture legumes could improve the P balance of pasture systems. Trifolium subterraneum (subterranean clover) is the most widely-grown annual pasture legume in southern Australia and is host to arbuscular mycorrhizal fungi (AMF). To examine the potential to alter colonisation level through breeding, 97 lines from the core collection of subterranean clover (core lines) and 42 cultivars (cultivar lines) were grown in a glasshouse in a low-P sandy acid field soil with indigenous AMF (Experiment 1). To examine the robustness of rankings, two cultivars (Riverina and Woogenellup) were also grown in 11 field soils (Experiment 2). To examine whether the presence of AMF changed other root traits important for P uptake, cultivars Riverina and Woogenellup were grown in two low-P field soils (sand, sandy loam), either pasteurised to remove indigenous AMF or unpasteurised, and with and without addition of inoculum of AMF (Experiment 3). The range of colonisation for core lines and cultivar lines was similar (∼12–68% of root length), however, the core lines had higher mean colonisation (37% vs 33%) and a greater proportion of lines with >40% of root length colonised (41% vs 24% of lines). Woogenellup was more heavily colonised than Riverina in eight soils and had a similar level of colonisation in three soils. In the sand, pasteurisation resulted in shoot DM increasing by up to 100% (possibly due to reduction in root diseases). Inoculation, in pasteurised and unpasteurised soil, resulted in an increase in shoot DM, shoot P concentration and shoot P content of ∼100%, increased average root diameter by up to 13%, decreased specific root length by up 30% and decreased root mass ratio; effects on average root hair length were variable. In the unpasteurised sandy loam, shoot P concentrations were higher than in the sand, and inoculation slightly increased shoot P concentration, but not shoot DM; the effects of inoculation on root traits were mostly small. We conclude that potential may exist to select subterranean clover for higher or lower colonisation by AMF using cultivar lines. Also, indigenous AMF may be less effective at enhancing plant P uptake and growth than inoculants. Finally, key root traits for enhancing plant P-uptake may change in the presence of AMF, but not sufficiently so to warrant deliberate inclusion or exclusion of AMF when screening germplasm for such traits.

New Zealand hill and high country are marginal environments for perennial ryegrass and white clover. Other pasture species, particularly legumes, provide more productive and persistent options for the range of soil climate and topography found in these environments. On cultivatable hill country, lucerne (alfalfa) has been successfully introduced to dryland areas with imported seed increasing five-fold to 210 t per annum over the last decade. This has led to the first release of a New Zealand selected cultivar in 20 years. For subterranean clover reliance on hardseeded Australian cultivars that frequently fail to meet New Zealand biosecurity standards means seed supply is inconsistent. The potential exists to create a niche seed market through selection of locally adapted material grown for seed in New Zealand. Lotus pedunculatus is available commercially but seed often fails to meet certification standards and is predominantly used in forestry. Lotus corniculatus requires agronomic research to overcome some management constraints and the re-establishment of seed supply before it would be a viable option for drier hill country. Seed production for perennial lupins in New Zealand is predominantly for an export ornamental market, with some direct relationships with growers allowing onfarm use. Caucasian clover seed production has ceased in New Zealand and the demand for seed particularly from high country farmers is no longer met. The smallseeded annual balansa clover is being integrated into farm systems and its prolific seeding has enabled some on-farm production of seed for personal use. For it and arrowleaf and Persian clovers, imported cultivars are available and a local market is unlikely to thrive until agronomic and hard seed issues are addressed. Seed supply of forage legumes to satisfy demand for hill country is problematic and will require development of different models including grower co-ops, regional seed retailers, and on-farm production for niche markets. Keywords: alfalfa, Lolium perenne, Lupinus polyphyllus, Medicago sativa, perennial ryegrass, Sitona lepidus, Trifolium ambiguum, Trifolium michelianum, Trifolium repens, Trifolium resupinatum, Trifolium subterraneum, Trifolium tumens, Trifolium vesiculosum, white clover

The legumes most often used in temperate pastures such as Trifolium subterraneum have relatively high external P requirements for maximum growth. We investigated root traits associated with P acquisition in current and novel pasture legumes, as well as temperate grasses which have lower P requirements. Thirteen legume species, two pasture grasses, and three high carboxylate-exuding crop species (Lupinus albus, L. angustifolius, Cicer arietinum) were grown in a glasshouse for six weeks. Rhizosphere carboxylates and root morphological traits were measured. Ornithopus spp. had rhizosphere carboxylates in similar quantities to the Lupinus spp. (> 40 μmol g−1 root dry mass). Trifolium subterraneum lines had relatively large average root diameter, reduced specific root length and very short average root hair length resulting in specific root hair cylinder volumes (RHCVs) only 14–20 % of the grasses. However, O. sativus, O. compressus and Biserrula pelecinus had specific RHCVs more comparable to the grasses. Novel pasture legume species with root morphology more comparable to that of grasses than T. subterraneum were identified. Of these, Ornithopus spp. were notable as they also had high rhizosphere carboxylates relative to root dry mass.

Subterranean clover (Trifolium subterraneum L.) is a diploid self-pollinated annual pasture legume native to the Mediterranean region and widely sown in southern Australia and other countries with Mediterranean-type climates. This study utilised a core collection of 97 lines, representing around 80% of the genetic diversity of the species, to examine morphological diversity within subterranean clover. A total of 23 quantitative agro-morphological and 13 semi-quantitative morphological marker traits were assayed on the core collection and 28 diverse Australian cultivars as spaced plants in a replicated common garden experiment. Relationships between these traits and 24 climatic and edaphic parameters at their sites of origin were also examined within the core collection. Significant diversity was present for all traits. The Australian cultivars had similar levels of diversity to the core collection for several traits. Among the agro-morphological traits, time to flowering, leaf size and petiole diameter in mid-winter, plant area in late winter, maximum stem length, content of the oestogenic isoflavone biochanin A and total isoflavone content, were correlated with seven or more environmental variables. These can be considered highly adaptive, being the result of strong environmental selection pressure over time. For the first time in a clover species, morphological markers, including leaf mark, anthocyanin pigmentation and pubescence traits, have been associated with rainfall and soil parameters. This suggests they either have an adaptive role or the genes controlling them may be linked to other genes controlling adaptive traits. This study demonstrated the value of core collections to examine diversity within much larger global collections. It also identified adaptive traits from wild plants that can be utilised to develop more productive and persistent subterranean clover cultivars. The high heritability of these traits indicates that selection gains can be readily made.

Sheep production systems in south-west Victoria are based predominantly on perennial ryegrass pastures, resulting in highly seasonal growth and declining feed quantity and nutritive value in late spring and summer. These changes result in reduced animal performance and increased CH4 emissions per kg DM intake. A potential alternative to the feedbase used in south-west Victoria that provides high quality and quantity of feed in late spring and early summer are legume-based pastures, such as clovers and lucerne. This experiment examined the impact of legume-based pastures on the growth rates and CH4 emissions of Maternal Composite ewes during late spring and early summer. In 2014, 240 Maternal Composite ewes grazed either perennial ryegrass (Lolium perenne L.), lucerne (Medicago sativa L.), subterranean clover (Trifolium subterraneum L.) or arrowleaf clover (Trifolium vesiculosum Savi.) pastures for 6 weeks during late spring and early summer (November and December). Sheep grazing subterranean clover were heavier at the end of the experiment than sheep grazing perennial ryegrass. Methane measurements using portable accumulation chambers indicated lower daily CH4 emissions (g/day) from sheep grazing subterranean clover (23.5 g/day) than from sheep grazing lucerne (27.3 g/day) and perennial ryegrass (32.3 g/day) pastures. Methane emissions and liveweight changes appeared to be associated with the nutritive characteristics of the forage offered. Legume-based pastures provide sheep producers in south-west Victoria an option to increase growth rates and decrease CH4 emissions during a period when perennial ryegrass pastures are declining in nutritive value.

Temperate pasture legumes (e.g. Trifolium and Medicago spp.) often have a higher phosphorus (P) requirement for maximum productivity than pasture grasses. This is partly attributed to differences between legumes and grasses in their ability to acquire P from soil. We are the first to report differences in root morphology traits important for soil P acquisition in a range of novel pasture legumes being developed for use in temperate pastures of southern Australia. Up to a 3·6-fold range in specific root length (SRL) (79–281 m root g−1 root) and 6·1-fold range in root hair length (RHL) (0·12–0·75 mm) was found between the pasture species. The commonly used Trifolium subterraneum and Medicago sativa had relatively low SRLs and short root hairs, while Ornithopus compressus, O. sativus and Biserrula pelecinus had RHLs and SRLs more similar to those of two grass species that were also assessed. Specific root length was highly correlated with average root diameter, and root traits were relatively stable at different plant ages. We surmise that large differences among pasture legume species in the effective volume of soil explored could translate into significant differences in their critical P requirements (i.e. soil P concentration to achieve 90% of maximum shoot yield).

Single superphosphate (SSP) is a major source of phosphorus (P) used in grazing systems to improve pasture production. The aim of this experiment was to determine the fate of fertiliser P in clover pastures under field conditions. A procedure was developed to radiolabel SSP granules with a 33P radiotracer, which was then applied to the soil surface (equivalent to ~12 kg P ha−1) of a clover pasture. Recovery of fertiliser P was determined in clover shoots, fertiliser granules and soil fractions (surface layer: 0–4 cm and sub-surface layer: 4–8 cm). The P diffusion patterns of the 33P-labelled SSP granules were not significantly different to those of commercial SSP granules (P > 0.05). Recovery of fertiliser P in clover shoots was 30–35 %. A considerable proportion of the fertiliser P (~28 %) was recovered in the surface soil layer and was largely inorganic P. Recovery of fertiliser P by clover plants was up to 35 % in the year of application. Much of the fertiliser P in soil fractions was inorganic P, which highlights the importance of inorganic P forms and dynamics in soils under clover pasture on a single season timeframe at these sites.

Pasture legumes are important components of both mixed farming rotations and permanent pastures in temperate climates. Breeding of two widely sown pasture legumes, subterranean clover (Trifolium subterraneum L.) and French serradella (Ornithopus sativus Brot.), is constrained by the long generation cycle, typically enabling only one generation per year. We hypothesized manipulation of culture medium and conditions would enable the development of a laboratory-based protocol for in vitro reproduction in subterranean clover and French serradella. In vitro flowering and viable seed set was induced from both species. For subterranean clover, the most effective treatment was culturing on modified MS medium with 1 μm kinetin and 0·1 m sucrose under a 100 μmol m−2 s−1 light intensity and continuous photoperiod. For French serradella, culture on a hormone-free B5 medium with 5 mm NH4Cl and 0·1 m sucrose under a 100 μmol m−2 s−1 light intensity and 20 h photoperiod was optimum. It is expected this technique will have application in accelerating generation turnover within breeding programs, for the study of factors influencing flowering in pasture legumes, and for the propagation of valuable yet enfeebled plants such as embryo-rescued hybrids.

Mitigating methane production by ruminants is a significant challenge to global livestock production. This research offers a new paradigm to reduce methane emissions from ruminants by breeding climate-clever clovers. We demonstrate wide genetic diversity for the trait methanogenic potential in Australia’s key pasture legume, subterranean clover (Trifolium subterraneum L.). In a bi-parental population the broadsense heritability in methanogenic potential was moderate (H2 = 0.4) and allelic variation in a region of Chr 8 accounted for 7.8% of phenotypic variation. In a genome-wide association study we identified four loci controlling methanogenic potential assessed by an in vitro fermentation system. Significantly, the discovery of a single nucleotide polymorphism (SNP) on Chr 5 in a defined haplotype block with an upstream putative candidate gene from a plant peroxidase-like superfamily (TSub_g18548) and a downstream lectin receptor protein kinase (TSub_g18549) provides valuable candidates for an assay for this complex trait. In this way haplotype variation can be tracked to breed pastures with reduced methanogenic potential. Of the quantitative trait loci candidates, the DNA-damage-repair/toleration DRT100-like protein (TSub_g26967), linked to avoid the severity of DNA damage induced by secondary metabolites, is considered central to enteric methane production, as are disease resistance (TSub_g26971, TSub_g26972, and TSub_g18549) and ribonuclease proteins (TSub_g26974, TSub_g26975). These proteins are good pointers to elucidate the genetic basis of in vitro microbial fermentability and enteric methanogenic potential in subterranean clover. The genes identified allow the design of a suite of markers for marker-assisted selection to reduce rumen methane emission in selected pasture legumes. We demonstrate the feasibility of a plant breeding approach without compromising animal productivity to mitigate enteric methane emissions, which is one of the most significant challenges to global livestock production.

Growth and physiological parameters of intercropped subterranean clover (Trifolium subterraneum L.) and cocksfoot (Dactylis glomerata L.) were investigated under controlled and field conditions. Nitrogen nutrition was accomplished in symbiotic and heterotrophic form in both studied species under controlled concentration of mineral elements in the media and by inoculation with appropriate rhizobial strain. Intercropped variants were also grown in sand culture as follows: subterranean clover - 100%, cocksfoot - 100%, subterranean clover:cocksfoot - 75:25(%), subterranean clover:cocksfoot 50:50(%) and subterranean clover:cocksfoot - 25:75(%). In hydroponic cultures subterranean clover to cocksfoot proportion was always 50:50(%). Subterranean clover reacted positively with growth up to 1.25 mM nitrate concentration in the medium with stimulation of number of nodules formed and their nitrogenase activity. When separately grown both subclover and cocksfoot reacted with higher plant biomass formation under higher nitrate nutrition. When intercropped the process of growth stimulation in subclover was more prominent than in cocksfoot.

A farm systems experiment comparing five pasture-based dairy systems was conducted in south-western Australia over 4 years on an annual ryegrass:subterranean clover sward. Fertiliser N inputs (0, 0.5, 1, 1.5 and 2 kg N ha−1 day−1) and stocking rate (SR; 1.25, 1.50, 1.75, 2.0 and 2.25 milking cows ha−1) increased concurrently for each treatment (F1–F5, respectively). By design, milk yield per cow did not differ between treatments; therefore, the response was measured in terms of changes in herbage dry matter (DM) utilisation and nutritive characteristics, as well as differences in feed input and imported forage required. Total annual pasture utilisation (t DM ha−1) increased from treatment F1–F3 (5.1, 5.9 and 7.3 t DM−1 ha−1, respectively), but responses beyond treatment F3 were not significant. Mean total N response efficiency was 9, 13, 8 and 7 kg DM per kg applied N for F2–F5, respectively, while mean marginal N response efficiency was 9, 17, −2 and 3 kg DM per kg applied N for F2–F5, respectively. The most efficient use of N fertiliser was achieved on treatment F3, where annual pasture utilisation levels in excess of 7 t DM ha−1 yr−1 were consistently demonstrated under the management strategies outlined, substantially greater than the local industry average.

SUMMARYSubterranean clover (Trifolium subterraneum L.) is the most important annual pasture legume in the winter-dominant rainfall areas of Southern Australia. Systematic germplasm collections of subterranean clover from its centre of origin have been made since the 1950s, particularly by Australian scientists, in order to broaden the genetic base of the species. The present study reports on a meta-analysis of the distribution of the world collection of subterranean clovers and their relationships to eco-geographic variables of the collection sites in their native habitat. Diversity hotspots (areas rich in number of accessions and containing a high diversity of sub-species) and also gaps (areas with particular traits un- or under-represented in collections) were identified. This was achieved using a stratified data system to evaluate eco-geographical and agro-morphological data which incorporated three tiers of information for the subterranean clover collection: (1) information from each collection site, including ecological data; (2) information on the phenotypic diversity within each collection site; and (3) plant agro-morphological data from each sample grown under controlled conditions. Correlations were found between some eco-geographic conditions and agronomic performance. These included correlations between latitude and flowering time, mean temperature in winter and winter productivity and precipitation in summer and seed dormancy. The present study concluded that subterranean clover versatility is greater than suggested in the past. The results of the current analysis provide a guide for future collecting missions to specific regions towards areas of maximum diversity (hotspots) and unknown diversity (gaps).

This review examines the prospect of improving perennial legume adaptation to grazed mixed pasture swards across the higher-altitude regions of south-eastern Australia through improved management, particularly as it relates to soil fertility. The range of adapted perennial species available to farmers often remains limited to only one perennial forage legume species, white clover (Trifolium repens L.). Despite recent advances in cultivars for increased persistence in dryland environments, white clover remains sensitive to drought with its inherently shallow root system and limited capacity to restrict water loss from herbage. With few alternative species likely to become widely available in the foreseeable future, prospects for extending the boundaries of perennial legume adaptation likely rely on a dual approach of improving soil fertility and further genetic improvement in white clover. Improved soil fertility would focus on overcoming soil acidity and addressing nutrient deficiencies, particularly of phosphorus, potassium, boron and molybdenum, which tend to be more widespread in the target region. Addressing these soil constraints would alleviate periodic moisture stress by: (1) increased water availability through improved infiltration and soil hydraulic properties; (2) increased root growth to maximise exploration of the soil volume; and (3) better maintenance of plant cell structures to foster improved osmotic regulation. However, the extent to which white clover adaption may be extended remains an issue of further research. This review highlights an opportunity for further genetic improvement of white clover by focusing on improving the capacity to recover from periodic droughts through seedling regeneration. Further breeding efforts in white clover should examine the feasibility of selecting for hard seed characteristics more similar to the best-adapted subterranean clover (Trifolium subterraneum L.) cultivars across this region to promote ongoing seedling regeneration.

Mixed farming systems have traditionally incorporated subterranean clover (Trifolium subterraneum L.) and lucerne (Medicago sativa L.) as key components of the pasture phase across south-eastern Australia. However, poor adaptation of subterranean clover to acidic soils, insufficient and inconsistent rainfall, high input costs, soil acidification and the emergence of herbicide-resistant weeds have reduced efficacy of some traditional clover species in recent years. To overcome these challenges, numerous novel pasture species have been selectively improved and released for establishment in Australia. Despite their suitability to Australian climate and soils, limited knowledge exists regarding their weed-suppressive ability in relation to establishment and regeneration. Field trials were therefore conducted over 3 years in New South Wales to evaluate the suppressive potential of selected pasture legume species and cultivars as monocultures and in mixed stands against dominant annual pasture weeds. Pasture and weed biomass varied significantly between pasture species when sown as monocultures, but mixtures of several species did not differ with regard to establishment and subsequent weed infestation. Arrowleaf clover (T. vesiculosum Savi.) and biserrula (Biserrula pelecinus L.) cv. Casbah showed improved stand establishment, with higher biomass and reduced weed infestation compared with other pasture species. Generally, weed suppression was positively correlated with pasture biomass; however, yellow serradella (Ornithopus compressus L.) cv. Santorini exhibited greater weed suppression than other pasture legumes while producing lower biomass, thereby suggesting a mechanism other than competition for resources affecting weed-suppressive ability. Over the period 2015–17, arrowleaf clover and biserrula cv. Casbah were generally the most consistent annual pasture legumes with respect to yearly regeneration and suppression of annual pasture weed species.

In recent decades several pasture legumes have been available in southern Australia as potential alternatives to the most widely used annual pasture legume Trifolium subterraneum. Little is known about their soil phosphorus (P) requirements, but controlled environment experiments indicate that at least some may differ in their P fertiliser requirements. In this study, pasture legume varieties, including T. subterraneum as the reference species, were grown at up to four sites in any one year over a 3-year period (in total, seven site × year experiments) to measure herbage growth responses in spring to increased soil P availability. A critical soil test P concentration (corresponding to 95% maximum yield) was estimated for 15 legumes and two pasture grasses. The critical soil P requirements of most of the legumes did not differ consistently from that of T. subterraneum, indicating their soil fertility management should follow the current soil test P guidelines for temperate Australian pastures. However, the critical P requirement of Medicago sativa was higher than that of T. subterraneum, but remains ill-defined because extractable soil P concentrations in these experiments were often not high enough to permit a critical P estimate. Three forage crop legumes (Trifolium incarnatum, Trifolium purpureum, Trifolium vesiculosum) and two pasture legumes (Ornithopus compressus, Ornithopus sativus) had lower critical soil test P concentrations. It may be feasible to manage pastures based on these species to a lower soil test P benchmark without compromising yield.

Trifolium subterraneum L. is widely grown in the phosphorus (P) deficient soils of southern Australia. However, this pasture legume has a high critical external P requirement and requires frequent applications of P fertiliser to achieve high productivity. Twenty-six genotypes of T. subterraneum were grown to determine: (i) differences in shoot growth and P acquisition under low-P supply; (ii) the root morphological traits important for P acquisition; and (iii) the feasibility of selection among genotypes for these root morphological traits. Micro-swards of each genotype were grown with a topsoil layer that was either moderately P-deficient or had P supplied in excess of the critical requirement for maximum yield; the subsoil layer was P-deficient. Yield and P content of shoots and roots were determined after 5 weeks’ growth, and root samples were assessed for diameter, length and root hair length. All genotypes were equally highly productive when excess P was supplied. However, relative shoot yield in the moderately P-deficient soil ranged from 38–71%. Total root length ranged from 63–129 m pot–1, and was correlated with total plant P uptake (R2 = 0.78, P < 0.001). Variation was also observed in average root diameter (0.29–0.36 mm) and root hair length (0.19–0.33 mm). These traits were combined with root length to calculate the total surface area of the root hair cylinder, which was also correlated with total plant P uptake (R2 = 0.69, P < 0.001). The results demonstrated that there was significant variation in P acquisition efficiency and shoot yield among genotypes of T. subterraneum when grown in P-deficient soil, and that root length was important for improved P uptake. The results indicate potential to identify superior genotypes that achieve improved P acquisition and higher shoot yields in low-P soil.

The annual forage legume biserrula (Biserrula pelecinus L.) offers a promising opportunity as a low-methanogenic, bioactive pasture for southern Australian grazing systems where subterranean clover (Trifolium subterraneum L.) is the dominant annual pasture legume. This in vitro study to assess methanogenic potential examined how growth stage and cutting of biserrula affect biomass, nutritive value and fermentative parameters including methanogenic potential compared with subterranean clover. Both species were grown in a glasshouse, where three growth-stage treatments comprised plant collection at vegetative, reproductive or maturity growth stages. Three cutting (simulated grazing) treatments included cutting at the vegetative or reproductive stage and an uncut control, with herbage collection at maturity. Methane production in biserrula was unaffected by the stage of growth. Other nutritive value and fermentative parameters varied significantly with growth stage, the highest fibre content and lowest crude protein (CP) being found at maturity. Regrowth from herbage cut at the reproductive stage had higher CP and lower biomass than other cut treatments. In biserrula, this regrowth also showed the highest fermentability of the three cutting treatments including elevated methane yield. Notwithstanding these treatment effects on fermentability, biserrula maintained its strong anti-methanogenic advantage over subterranean clover across all treatments, confirming its potential as an anti-methanogenic bioactive pasture.

The soil phosphorus (P) requirements of 18 species that included native grasses and naturalised legumes were compared with the predominant sown species (Trifolium subterraneum, Lolium perenne and Phalaris aquatica) in a series of glasshouse and field experiments based on the Long-term Phosphate Experiment at Hamilton, Victoria. The native grasses Austrostipa scabra and Rytidosperma caespitosum had the lowest external P requirements, as measured by the Olsen P at which 90% of maximal dry matter (DM) production was obtained, but were of low nutrient value as livestock feed. The naturalised legume Lotus corniculatus had the lowest external P requirement of the legumes, but had low DM production. The highest legume DM production under low-P conditions in the field and one glasshouse experiment was obtained for T. subterraneum. This was attributed to its large seed, which enables rapid initial growth and thus captures light and nutrient resources early in the growing season. However, it forms a relatively low proportion of the pasture sward in low-P soil under grazed mixed pasture conditions in the field. This was attributed to its relatively high nutritive value, which leads to it being preferentially grazed, leaving species that are either less palatable or less accessible to grazing livestock. This work suggests that, in low-P environments, there is a much stronger selection pressure favouring low relative palatability over P efficiency. In conclusion, to maintain desirable species in temperate low-input pastures, sufficient P needs to be applied to maintain fertility above a threshold at which the less-palatable species begin to invade.

Barley grass (Hordeum spp.) is a relatively short lived annual that provides high quality grazing early in the season, but its seed heads cause contamination of wool and carcasses, and may irritate the mouth, eyes and nose of sheep. Treatments were imposed on established subterranean clover (Trifolium subterraneum L.) annual pasture in the same plots for three consecutive years (2015 to 2017) to evaluate changes in barley grass content. Treatments included: grazing alone (G), herbicide followed by grazing (HG), or a forage conservation harvest in early October, late October or early November consistent with an early silage harvest (ES), late silage harvest (LS) or hay cut (H). Grazing plus herbicide markedly reduced (P < 0.05) barley grass numbers compared with all other treatments, but increased (P < 0.05) the growth of annual ryegrass (Lolium rigidum L.). ES reduced (P < 0.05) barley grass and increased (P < 0.05) subterranean clover compared with H, but broadleaf weed content benefitted by LS in contrast to either ES or H. Although herbicide application was the most effective method for barley grass control, forage harvest timing could be used to beneficially manipulate pasture composition.

We investigated the role of arbuscular mycorrhizal fungi (AMF) and heterotrophic soil microbes in the uptake of phosphorus (P) by Trifolium subterraneum from a pulse. Plants were grown in sterilised pasture field soil with a realistic level of available P. There were five treatments, two of which involved AMF: 1) unsterilised field soil containing a community of AMF and heterotrophic organisms; 2) Scutellospora calospora inoculum (AMF); 3) microbes added as filtrate from the field soil; 4) microbes added as filtrate from the S. calospora inoculum; 5) no additions, i.e. sterilised field soil. After 11 weeks, plants were harvested: 1 day before (day 0), 1 day after (day 2) and 7 days after (day 8) the pulse of P (10 mg kg−1). There was no difference among treatments in shoot and root dry weight, which increased from day 0 to day 8. At day 0, shoots and roots of plants in the colonised treatments had higher P and lower Mn concentrations. After the pulse, the rate of increase in P concentration in the shoots was slower for the colonised plants, and the root Mn concentration declined by up to 50 % by day 2. Plants colonised by AMF had a lower rate of increase in shoot P concentration after a pulse, perhaps because intraradical hyphae accumulated P and thus reduced its transport to the shoots.

Soil testing was conducted during 1985–2005 in 11 paddocks on sandy duplex soils on Newdegate Research Station, average annual rainfall of 377 mm, with about 70% falling in the May–October growing season, in the Mediterranean-type climate of southwestern Australia. The study was undertaken to determine lime and fertilizer requirements of eight crop species grown in rotation with one another (one crop each year in the typical May–October growing season, comprising wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; oats, Avena sativa L.; lupin, Lupinus angustifolius L.; canola, Brassica napus L.; chickpea, Cicer arietinum L.; field pea, Pisum sativum L.; and subterranean clover-based pasture, Trifolium subterraneum L. All crops were sown using no-till. The study demonstrated that plant testing was required in conjunction with soil testing to confirm decisions based on soil testing and to assess management decisions for elements not covered by soil testing. Pasture dry-matter production seldom exceeds ...

We investigated commensalism of water use among annual shallow-rooted and perennial deep-rooted pasture legumes by examining the effect of hydraulic lift by Cullen pallidum (N.T.Burb.) J.W.Grimes and Medicago sativa on growth, survival and nutrient uptake of Trifolium subterraneum L. A vertically split-root design allowed separate control of soil water in top and bottom soil. Thirty-five days after watering ceased in the top tube, but soil remained at field capacity in the bottom tube, an increase in shallow soil water content by hydraulic lift was 5.6 and 5.9 g kg(-1) soil overnight for C. pallidum and M. sativa, respectively. Trifolium subterraneum in this treatment maintained higher leaf water potentials (with M. sativa) or exhibited a slower decline (with C. pallidum) than without companion perennial plants; and shoot biomass of T. subterraneum was 56% (with C. pallidum) and 67% (with M. sativa) of that when both top and bottom tubes were at field capacity. Uptake of rubidium (a potassium analog) and phosphorus by T. subterraneum was not facilitated by hydraulic lift. Interestingly, phosphorus content was threefold greater, and shoot biomass 1.5-3.3-fold greater when T. subterraneum was interplanted with C. pallidum compared with M. sativa, although dry weight of C. pallidum was much greater than that of M. sativa. This study showed that interplanting with deep-rooted perennial legumes has benefited the survival of T. subterraneum.

R. J. Simpson, A. E. Richardson, I. T. Riley, A. C. McKay, S. F. McKay, R. A. Ballard, K. Ophel-Keller, D. Hartley, T. A. O’Rourke, H. Li, K. Sivasithamparam, M. H. Ryan and M. J. Barbetti

Intensively grazed, rain-fed dairy pastures on the predominantly sandy soils in the high rainfall (>800 mm annual average) Mediterranean-type climate of south-western Australia comprise >90% ryegrass (annual ryegrass, Lolium rigidum Gaud. and Italian ryegrass, L. multiflorum Lam.). To maximise pasture use for milk production, the pastures are rotationally grazed by starting grazing when ryegrass plants have 3 leaves per tiller, and fertiliser nitrogen (N) and sulfur (S), in the ratio of 3–4 N and 1S, need to be applied after each grazing for profitable pasture dry matter (DM) production. In addition, farmers usually also apply low levels of phosphorus (P) and potassium (K) fertiliser to these pastures after each grazing, despite Colwell soil test P usually being well above critical values for pasture production, and fertilizer K being only required for clover in the traditional clover (Trifolium subterraneum L.) ryegrass pastures of the region. In field experiments undertaken May 2006–June 2010 on intensively grazed ryegrass dairy pastures in the region, no significant ryegrass DM responses to applied fertiliser P or K were obtained, regardless of level or method of P or K application. When no P was applied, soil test P declined gradually, by between 4.4 and 7.1 mg/kg per year, and remained above the critical value for the soils at 2 sites, but declined below the critical value for soil at a third site. Critical soil test P is located near the maximum yield plateau in the flat part of the relationship between yield and soil test P, particularly when, as appropriate for dairy production, the critical value is for 95% of the maximum pasture DM yield. Consequently, when no P is applied and soil test P decreases, significant pasture DM yield decreases will only occur when soil test P approaches the steeper part of the relationship, which can take some time. In addition, as occurs on farms, faeces deposited by cows while grazing supplied P to pasture even when no fertiliser P was applied. Soil K testing proved unreliable for indicating the need for fertiliser K applications to pasture in the next growing season because many soil samples collected within and between urine patches contained elevated levels of K deposited by cows while grazing. We conclude fertiliser P should only be applied to intensively grazed ryegrass dairy pastures when soil testing indicates it is required. Further research is required to assess if plant K testing is an alternative, but urine patches may also pose a problem for plant testing.

Despite annual legume pasture are of great importance for dryland agricultural systems in Mediterranean environments, there are few studies of N2 biological fixation (NBF) reported in Chile. In this study the NBF of four annual legume species: subterranean clover (Trifolium subterraneum L.), yellow serradella (Ornithopus compressus L.), arrow-leaf clover (T. vesiculosum L.), and crimson clover (T. incarnatum L.) (Experiment 1), as well as seven mixtures of these species (Experiment 2) were assessed. The NBF was measured by the 15 N natural abundance technique. The objective was to determine NBF in the legume species and in distinct mixtures used. The study was carried out in an Andisol of the Andean Precordillera located in the humid Mediterranean zone of Chile. Pasture was evaluated for biomass; and total N and natural abundance of 15 N were analyzed in plant material samples. In Experiment 1 (monospecific legume species pasture), N derived from fixation ranged between 43 and 147 kg N ha -1 and where T. vesiculosum and T. subterraneum presented statistical differences (P ≤ 0.05) in connection with the other species. In the legume mixtures (Experiment 2), N derived by fixation varied between 97 and 214 kg N ha -1 where the 50-50 mixtures (T. subterraneum and O. compressus, or T. subterraneum and T. vesiculosum, respectively) had the highest N fixation. Fixed N ranged between 12 and 25 kg N t -1 DM, showing significant differences among mono and polyspecific legume species.

Native perennial grass and sown grass-legume pastures are an important agricultural and environmental resource. We investigated the impact of rising carbon dioxide concentration ((CO2)) and projected climate changes on these pasture ecosystems in southeastern Tasmania, Aus- tralia, using a biophysical simulation model, EcoMod. The model consists of interdependent modules that describe soil physicochemical and hydrological characteristics, and pasture growth and senes- cence, with fluxes described by empirical and mechanistic equations. Our simulations showed that in native pastures, projected climate change increased the biomass of C4 grasses, with limited impact upon C3 grasses, a trend reversed by rising (CO2). In sown pastures, projected climate change decreased the biomass of perennial rye grass Lolium perenne and total biomass markedly by 2070, whilst subterranean clover Trifolium subterraneum biomass increased. Subterranean clover biomass changed little with increased (CO2) alone, whereas perennial rye grass biomass increased. Responses across pastures reflected species' tolerances to environmental factors, with projected climate change generally having more of an impact on biomass than rising (CO2). Changes in both (CO2) and climate led to a reduction in protein content and digestibility. Soil inorganic nutrient concentrations decreased with increasing (CO2) and increased with projected climate change. Further simulations should investigate whether these patterns are robust for different sites and alternative environmen- tal futures. Our results reinforce the need to pursue adaptation strategies in response to environ- mental change in order to maintain productive pasture ecosystems.

The mainstream pasture legume species such as Trifolium subterraneum, T. repens and annual Medicago spp. used in the temperate pasture systems of southern Australia have high critical external requirements for phosphorus (P) (i.e. P required to achieve 90% of maximum yield). This work aimed to identify alternative pasture legume species that could be used in systems with lower P input. Shoot and root biomass of 12 species of pasture legume was measured in response to seven rates of P applied to the top 48 mm of soil in a pot experiment. Most species had maximum yields similar to T. subterraneum, but some required only one-third of the applied P to achieve this. The critical external P requirement of the species, ranked from lowest to highest, was as follows: Ornithopus compressus = O. sativus

The abundance of four naturalised annual clovers (striated, cluster, suckling, haresfoot) and two sown clovers (subterranean and white clover) was investigated in relation to topographical, soil fertility and management factors on two contrasting hill/high country stations in the South Island: Glenfalloch in inland Canterbury (1 665 mm annual rainfall), and Mt Grand in Central Otago (703 mm annual rainfall).

Mechanisms for tolerance and avoidance of salinity at germination were examined in five self-regenerating annual pasture legumes of Mediterranean origin (Medicago polymorpha, Melilotus siculus, Trifolium subterraneum, T. michelianum and T. tomentosum). The maximum NaCl concentrations, for which no reduction in germination percentage occurred, were 300 mM for M. siculus, 240 mM for M. polymorpha and 120 mM for T. michelianum, T. subterraneum and T. tomentosum. Following 21 days exposure to 300 mM NaCl, imbibed seeds of T. subterraneum showed reduced germinability upon transfer to non-saline solution, whereas those of the four other species recovered full germinability. Following exposure to 600 mM NaCl, however, only T. michelianum and Melilotus siculus had some degree of recovery, with 38% and 31% germinability, respectively. Na+ in imbibed seed tissues of all species increased markedly with increasing NaCl concentration, while K+ decreased in all but Melilotus siculus. Seed coat impermeability (‘hard seeds’) acted as protection against the toxic effects of salinity. Melilotus siculus, Medicago polymorpha and T. tomentosum showed a delay in hard-seed breakdown (‘seed softening’) over the summer–autumn period, compared to T. subterraneum and T. michelianum, which acts to defer germination until soil surface salinity levels are likely to be lower. These three species also had higher levels of residual hard seeds. The results from this study support field observations that Melilotus siculus and Medicago polymorpha are the best adapted annual pasture legumes for highly saline soils in southern Australia, T. tomentosum and T. michelianum have some adaptation to moderately and mildly saline soils, respectively, whereas T. subterraneum has no adaptive traits for even mildly saline environments. A model for annual legume germination on saline land in southern Australia is also presented.

Annual dry matter (DM) production and botanical composition of six dryland pasture combinations, grown under sheep grazing at Lincoln University for 5 years, are presented. In 4 years, lucerne produced the highest DM yields (13.1-18.5 t/ha/yr) through higher daily growth rates, compared with grass based pastures, particularly during periods of water stress in summer and autumn.