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Context: Using forage grass species with complementary growth and resource-use strategies to enhance forage plant diversity in pastures may be an alternative to traditional monocultures in tropical regions. Aims: This study aimed to determine whether a mixture of three perennial tropical forage grasses (Andropogon gayanus cv. Planaltina, Panicum maximum cv. Massai, and Brachiaria brizantha cv. BRS Piatã) could be an alternative to enhance herbage intake rates relative to their respective monocultures. Methods: The treatments corresponded to three perennial tropical forage grasses cultivated as monocultures and as a mixture composed of all three species. Defoliation management corresponded to a pre-cutting height of 35 cm and post-cutting height of 17.5 cm. Key results: The botanical composition of the mixture was dynamic throughout the experimental period, with variations in the proportion of species across seasons. The upper half of the canopy predominantly comprised leaves for all treatments. The canopy structure of the mixture allowed for greater herbage intake rates than monocultures during winter/early spring. Andropogon gambagrass showed lower herbage intake rates than the other treatments. Conclusions: The findings of this study indicate that it is possible to combine tropical forage grass species without compromising canopy structure and grazing animal responses, compared with single-species grass pastures. Implications: The selection of forage species for mixed pastures should consider their phenological cycle, growth, and resource-use strategies to achieve temporal complementarity and provide an optimal grazing environment for animals throughout the year. Increasing pasture biodiversity using forage grass species with complementary traits may be an alternative to traditional monocultures in tropical regions. This study investigated the relationship between pasture characteristics and herbage intake, indicating that combining tropical forage grass species is possible without compromising pasture dynamics and grazing animal responses. By optimizing forage diversity, we highlight the importance of species selection and seasonal complementarity for maintaining pasture structure and providing an optimal grazing environment for animals throughout the year. [ABSTRACT FROM AUTHOR]

Context: Plant secondary metabolites are of increasing interest for agriculture due to their diverse beneficial ecological functions. The forage crop white clover (Trifolim repens L.) has been intensively studied for its heritable polymorphism in the production of hydrogen cyanide (HCN), a toxic defense phytochemical. In fodder production, white clover accessions are selected for biomass production, whereby HCN production is an unwanted trait. Aim: Although white clover is a legume crop species of global importance, little is known about the linkage between cyanogenesis and growth traits, in particular in combination with resistance-related phytochemicals, such as flavonoids. We aimed to identify differences in biomass production, estimated leaf flavonoid content, and trait correlations in cyanogenic (HCN-producing) and acyanogenic (not HCN-producing) individuals and accessions of white clover. Methods: We analysed 51 white clover accessions from a German germplasm collection for variability in selected traits: cyanogenesis as equivalent electrode potential, estimated leaf flavonoid content, root and shoot production, leaf area, specific leaf area, and number of leaves produced. Key results: Most accessions considered as cyanogenic were heterogeneous for HCN production. Chemical–morphological trait correlations differed between cyanogenic and acyanogenic plants. Acyanogenic individuals and accessions produced more and larger leaves compared to cyanogenic ones. Within cyanogenic accessions, the higher the HCN level of a plant, the fewer but larger leaves were produced. Conclusions: Our results highlight the variation in HCN production within the selected accessions, which calls for a consistent approach for cyanogenesis-based categorisation. Implication: This study demonstrates the potential of combining phytochemical traits with biomass production in white clover when selecting material in a breeding program. White clover is a widely grown legume and of particular interest as a forage and pasture crop due to its high nutritional value. Besides this, the ability to produce hydrogen cyanide, a toxic chemical compound involved in herbivore defence, represents a trait which entails advantages and disadvantages for agricultural practice. Plants producing this compound differ in growth from those not producing it, indicating the potential to integrate the linkage of this chemical trait with plant growth into future selection for breeding. [ABSTRACT FROM AUTHOR]

This foreword provides a summary of papers included in this special issue on biochar and fertiliser interactions for crop and pastures productivity. This special issue includes published papers on how biochar and fertiliser affect soil health and crop yields and overcome soil constraints such as acidity, salinity, low fertility and remediation of metal and pesticides contaminated soils. [ABSTRACT FROM AUTHOR]

Rotations and associated management practices in rainfed farming systems of southwest Australia have shifted towards intensified cropping. Survey data from 184 fields spanning 14 Mha of southwest Australia were used to document water use efficiency (WUE) and water-limited yield potential (WLYP) of commercial crops and crop sequences and identify biophysical variables influencing WUE. WUE achieved in commercial wheat crops was 10.7 kg grain/ha.mm. Using a boundary function Ywl = 25 × (WU − 45), farmers achieved 54% of WLYP. Climate variables affected WUE more than management and biotic variates, the highest latitude region having WUE of 9.0 kg grain/ha.mm, compared to 11.8 kg grain/ha.mm for regions further south. Increased soil nitrogen and nitrogen fertiliser increased WUE, as did sowing earlier; in keeping with farmers in southern Australia sowing crops earlier and trebling fertiliser nitrogen usage since 1990. Wheat yield and WUE increased a small amount after break crop or pasture (12.5 kg grain/ha.mm) compared to wheat grown after wheat (11.2 kg grain/ha.mm), due to good weed and root pathogen control, and high fertiliser nitrogen application. However, WUE of wheat declined to 8.4 kg grain/ha.mm when more than three wheat crops were grown in succession. Farmers continue to improve WUE with increased inputs and new technologies replacing some traditional functions of break crops and pasture. However, break crops and pastures are still required within the rotation to maintain WUE and break effects need to be measured over several years. High water use efficiency was associated with low levels of weed, disease and high fertliser nitrogen inputs in Western Australia's rainfed cropping systems. The yield benefit to wheat sown immediately after break crops or pasture was low, because of low levels of biophysical constraints. However, water use efficiency of wheat declined when three wheat crops were grown in succession. This highlights the need for continued research into the integration of break crops and pastures into wheat dominated rotations. [ABSTRACT FROM AUTHOR]

Spatial separation of species at sowing has been proposed as a means of managing interspecific competition in mixed swards. This study examined the effect of row configuration on persistence of lucerne (Medicago sativa L.) in pastures and pasture–cover crop mixtures at three sites in the Central West, and in pasture mixtures at three sites in the Riverina, New South Wales, Australia. Lucerne density, taproot diameter, groundcover, and spatial distribution relative to the original drill row were measured at all sites, and plant-available soil water and light interception during spring were assessed at some sites. Row configuration (alternate or mixed drill rows) did not affect lucerne persistence; however, where lucerne seed was concentrated in every third drill row, intraspecific competition led to increased lucerne mortality. This was estimated to occur at densities >28 plants/m drill row. A lucerne density of ~55 plants/m2 in every or alternate drill rows (at row spacings of 250 mm) would likely achieve maximum lucerne production in the semi-arid environments tested, subject to the chance event of favourable conditions in the period after sowing that would maintain that density (e.g. cumulative summer rainfall >100 mm and summer day degrees <2160°C in 2 years at Cowra). The presence of a cover crop in the establishment year reduced lucerne density by 39% compared with pasture only, regardless of row configuration. Changed row configuration did not reduce competition for light under a cover crop, but there was a small increase in available soil water of up to 4.9 mm in the 0–1.15 m depth, mainly during the first summer, where pasture was sown in alternate compared with mixed drill rows with a cover crop. Soil was drier in pasture-only treatments than those with a cover crop, attributable to increased lucerne density and lower levels of litter cover on the soil surface. Pasture species remained largely confined to the original drill row, especially in drier environments, highlighting the importance of narrower row spacings for pasture establishment. In addition, we determined a mathematical relationship between lucerne density and the non-destructive measure of basal frequency; this relationship could be applied in mature lucerne stands with densities ≤80 plants/m2. This study examined whether separating species in drill rows at sowing improved lucerne survival over a short pasture phase compared with multiple species being sown in the same row. Persistence was reduced only where lucerne was confined to every third drill row, indicating the effect of intraspecific competition on lucerne density; furthermore, interspecific competition from cover crops in the first year consistently reduced lucerne density. The study highlights the importance of narrower rather than wider row spacings in drier environments where pastures remained concentrated around the drill row, and shows that winter-active forage species are important for improving productivity of lucerne-based swards. [ABSTRACT FROM AUTHOR]

Perennial legumes have potential to increase pasture productivity in the high rainfall zone (600–850 mm) of south-eastern Australia through their ability to use summer rainfall and fix nitrogen (N2). Various perennial legumes are being evaluated for this environment; however, little information exists on legume–rhizobia cross-host compatibility and its consequences for biological N2 fixation. This is especially important when legumes are sown into fields with a background of competitive rhizobia such as WSM1325 or sown as a pasture mix with different host–symbiont pairs. We studied the effectiveness and cross-host compatibility of five commercial rhizobial strains for a range of pasture legumes (nine species, 18 cultivars) under controlled environment conditions, and further evaluated nodule occupancy and competitiveness of a newly established pasture (13 species, 20 cultivars) in the field, by determining nodulation and production (biomass and N2 fixation). Three of the commercial inoculant strains formed root nodules with multiple legume species; commonly however, less N2 was fixed in cases where the inoculant was not the recommended strain for the legume species. Within a legume species, cultivars could differ in their ability to form effective root nodules with multiple rhizobial strains. White clover cvv. Trophy, Haifa and Storm, strawberry clover cv. Palestine, and Talish clover cv. Permatas formed effective nodules with both TA1 and WSM1325 rhizobial strains. White clover cultivars that could not form an effective symbiosis with the common background strain WSM1325 fixed less N2. The white clover × Caucasian clover hybrid formed effective symbiosis with strain TA1 but not with other commercial strains. Some species such as birdsfoot trefoil, Talish clover, sulfur clover and tetraploid Caucasian clover formed ineffective symbiosis in the field. Until resolved, this will likely inhibit their further development as pasture plants for similar permanent pasture environments. Effectiveness and the consequence of cross–host compatibility of commercial rhizobial strains in forming root nodules with pasture legumes for N2 fixation is poorly understood. We screened current commercial rhizobial strains for their capacity to form effective nodules on pasture legume hosts and found that some rhizobial strains formed root nodules on multiple species and/or cultivars of legumes, whereas certain strains were more effective at increasing shoot biomass. The data can be used to guide rhizobial inoculant selection where multiple pasture legume species are sown in a mixture. [ABSTRACT FROM AUTHOR]

Balancing nutrient inputs and exports is essential to maintaining soil fertility in rainfed crop and pasture farming systems. Soil nutrient balances of land used for crop and pasture production in the south-west of Western Australia were assessed through survey data comprising biophysical measurements and farm management records (2010–15) across 184 fields spanning 14 Mha. Key findings were that nitrogen (N) inputs via fertiliser or biological N2 fixation in 60% of fields, and potassium (K) inputs in 90% of fields, were inadequate to balance exports despite increases in fertiliser usage and adjustments to fertiliser inputs based on rotations. Phosphorus (P) and sulfur (S) balances were positive in most fields, with only 5% returning losses >5 kg P or 7 kg S/ha. Within each of the three agroecological zones of the survey, fields that had two legume crops (or pastures) in 5 years (i.e. 40% legumes) maintained a positive N balance. At the mean legume inclusion rate observed of 20% a positive partial N budget was still observed for the Northern Agricultural Region (NAR) of 2.8 kg N/ha.year, whereas balances were negative within the Central Agricultural Region (CAR) by 7.0 kg N/ha.year, and the Southern Agricultural Region (SAR) by 15.5 kg N/ha.year. Hence, N budgets in the CAR and SAR were negative by the amount of N removed in ~0.5 t wheat grain, and continuation of current practices in CAR and SAR fields will lead to declining soil fertility. Maintenance of N in the NAR was achieved by using amounts of fertiliser N similar to other regions while harvesting less grain. The ratio of fertiliser N to legume-fixed N added to the soil in the NAR was twice that of the other regions. Across all regions, the ratio of fertiliser N to legume-fixed N added to the soil averaged ~4.0:1, a major change from earlier estimates in this region of 1:20 under ley farming systems. The low contribution of legume N was due to the decline in legume inclusion rate (now 20%), the low legume content in pastures, particularly in the NAR, and improved harvest index of lupin (Lupinus angustifolius), the most frequently grown grain legume species. Further quantifications of the effects of changing farming systems on nutrient balances are required to assess the balances more accurately, thereby ensuring that soil fertility is maintained, especially because systems have altered towards more intensive cropping with reduced legume production. Balancing nutrient inputs and exports is essential to maintain soil fertility in Western Australia's rainfed crop and pasture farming systems. Despite increases in fertiliser usage in recent decades, we found that nitrogen inputs in 60% of paddocks and potassium inputs in 90% of paddocks were inadequate to balance exports, whereas phosphorus and sulfur balances were positive most paddocks. Further quantifications of nutrient balances are required because crop and pasture rotations in Western Australia have altered towards more intensive cropping with reduced legume production. [ABSTRACT FROM AUTHOR]

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. Subterranean clover is the backbone of sheep and beef pastures in southern Australia. However, harvesting subterranean clover seed is slow, difficult, and causes environmental issues, which we determined is due to the industry's reliance on 60-year-old vacuum harvesters (which suck seed up from the ground). We evaluate current harvesting practices and machinery to support the development of new harvest systems that are urgently needed for the advancement of this important Australian industry. [ABSTRACT FROM AUTHOR]

Soil organic matter (SOM) in agricultural soils is generally lower in cultivated and intensively managed cropping soils than in pasture soils. Cultivation during the transition from pasture to crop leads to a loss of SOM, which may affect soil functionality and subsequent agricultural productivity. However, it is unclear how management practices influence SOM dynamics following this transition. We investigated the impact of initial soil fertility and application of lime and nutrients (nitrogen (N), phosphorus (P) and sulfur (S)) on changes in soil carbon (C) during the transition from a permanent pasture to a crop. The pasture was managed over 20 years with fertiliser to generate soils with initial high and low fertility (referred to as P2 and P0, respectively), based on soil C, N, P and S concentrations. Prior to sowing, pasture residue was incorporated with three treatments applied: control, lime, and lime + nutrient. Two successive crops of triticale (Triticale (x Triticosecale)) were then grown. The P0 and P2 soils were again cultivated in March 2018 with incorporation of the triticale stubble residue (9 Mg ha-1) in each of the three soil treatments. After the two successive cereal crops, higher whole-soil C stocks were retained in the P2 than the P0 soils (difference of 2.1 Mg C ha-1 compared with an initial difference in stocks of 2.4 Mg C ha-1), with smaller loss of whole-soil C in P2 soils receiving the lime and lime + nutrient treatments than in the P2 control (average 10.3%, 10.0% and 20.2% loss of total C, respectively, relative to initial levels of soil C). Loss of C from the more active >0.4-mm fraction as a proportion of total C loss was higher in the first year with incorporation of legume-based pasture residue than in the second year with incorporation of C-rich, nutrient-poor crop residue (56% and 18% of the loss of C from the whole soil was from the >0.4-mm fraction in the first and second year, respectively). In P2 soil, loss of C was smaller in the more stable <0.4-mm fraction in the lime and lime + nutrient treatments than in the control (average loss of 9.6%, 11.2% and 17.6%, respectively). By contrast, in the low-fertility (P0) soil, loss of C was greater in the <0.4-mm fraction in the lime treatment than in the control (12.3% and 3.4% loss, respectively) unless supplementary nutrients were added at the time of cultivation (7.0% loss). Narrowing of nutrient ratios (C : N and C : S) in the P0 whole soil over time suggested that the loss of soil C was associated with increased microbial processing of C in the coarse-fraction soil. Taken together, the results demonstrate that loss of C from the pasture soils after cultivation was lower for soil with initially higher soil fertility when lime was applied, and that for soils with lower initial fertility, application of nutrients in addition to those for crop growth reduced C mineralisation induced by lime application. [ABSTRACT FROM AUTHOR]

Low levels of plant-available micronutrients were an inherent feature of many agricultural soils in Australia, mostly due to the prevalence of highly weathered soil parent materials. The diagnosis and correction of the widespread deficiencies of micronutrients, especially copper (Cu), molybdenum (Mo) and zinc (Zn), were prerequisites for the development of productive, legume-based pastures in southern Australia. In subtropical and tropical regions, Mo deficiency commonly limited pasture-legume production. Soil treatments involving micronutrient fertiliser incorporated in soils, or applied as additives to superphosphate, were generally effective in alleviating micronutrient deficiencies. In the low-output dryland pasture systems, the annual removal of micronutrients in wool and meat is small compared with rates added in fertiliser. Hence, in general, the residues of soil-applied micronutrient fertilisers remain effective for many years, for example, up to 30 years for Cu. By contrast, shorter residual values occur for manganese (Mn) fertiliser on highly calcareous soils, and for Zn in high-output pasture systems such as intensive dairy production. In the last two decades since the recommendations for micronutrient management of pastures were developed, there have been many changes to farming systems, with likely implications for micronutrient status in pastures. First, increased cropping intensity and low prices for wool and meat have meant lower nutrient inputs to pastures or to the pasture phase of rotations with crops. However, when pastures have been rotated with crops, ongoing small additions of Cu, Zn and Mo have been common. In cropping phases of farming systems, lime application and no-till may have altered the chemical and positional availability of micronutrients in soils to pastures. However, there has been little study of the impacts of these farming-systems changes on micronutrient status of pastures or profitability of the production system. The intensification of dairy production systems may also have altered the demand for, and removal rates of, micronutrients. Soil tests are not very reliable for Mn or Mo deficiencies, and well-calibrated soil tests for boron, Cu and Zn have been developed only for limited areas of pasture production and for a limited range of species. There is limited use of plant tests for nutrient management of pastures. In conclusion, there is limited knowledge of the current micronutrient status of pastures and their effects on animal health. Pasture production would benefit from targeted investigation of micronutrients status of pasture soils, pasture plants and micronutrient-linked animal-health issues. Low levels of plant-available micronutrients were an inherent feature of many agricultural soils in Australia. Recommendations developed for management of micronutrients in pastures have not been systematically updated to keep pace with the ongoing farming-system changes affecting micronutrient status in pastures. Pasture production would benefit from targeted investigation of the current micronutrient status of pasture soils and plants and of micronutrient-linked animal-production issues. [ABSTRACT FROM AUTHOR]

Pasture legumes must be adequately and effectively nodulated in order to reach nitrogen-fixation targets. Of 225 pasture paddocks sampled across the Central Tablelands, Central West, Monaro and Riverina regions of New South Wales, 93% had inadequate legume nodulation. Legume content was significantly higher in the mixed faming zone (>50%, Central West and Riverina) than the permanent pasture zone (26%, Central Tablelands; 28% Monaro). Available phosphorus (P) was below critical levels in 40% of paddocks sampled and sulfur (S) in 73% of paddocks; >35% of all paddocks had soil pHCa <5.0. Deficiency of P was more prevalent in the Central Tablelands (63% of paddocks), whereas S deficiency occurred more frequently in the Central West (95% of paddocks). Legume nodule scores were associated with host legume species, soil pH, available P and/or S, and cation exchange capacity, which collectively accounted for 73% of variation. For Trifolium spp., at soil pHCa >5.55, nodulation was predicted to be near adequate (score 3.95, where adequate = 4). At pHCa <5.55, higher available S resulted in a higher nodulation score (2.42) than in paddocks where S was deficient (score 0–1.97). These results suggest that improving the capacity of legumes to supply nitrogen should focus on addressing soil acidity and plant nutrition, specifically P and S. There has been no assessment of nodulation status of pasture legumes or how it is affected by soil conditions and management across the permanent pasture and mixed farming zones of New South Wales. This study found poor legume nodulation in >90% of paddocks sampled, related to host plant–symbiont associations, soil pH, and availability of phosphorus and sulfur. The data can inform appropriate legume–symbiont associations depending on soil conditions and drive remediation to address soil pH issues and nutrient needs for improved pasture and crop productivity in the permanent pasture and mixed farming zones. [ABSTRACT FROM AUTHOR]

In Australia, ruminants rely on introduced pastures or native vegetation for most or all of their nutritional requirements. Recent pasture selection and breeding programs have focused on improving or facilitating the establishment, persistence and growth of plants, with little emphasis on nutritive value or mineral composition. In some cases, such as selection for phosphorus (P) utilisation efficiency, mineral supply from plants may even decrease. Currently, a significant proportion of pasture plants contain less calcium (Ca), P, magnesium (Mg), sodium (Na), sulfur, copper, iodine, zinc, selenium or cobalt than is required for growth and reproduction, with significant genetic variation among and within legumes and grasses. Young crops and shrubs are now also an integral part of grazing systems. Many young crops contain concentrations of Ca, Mg, Na and potassium (K) that are low or imbalanced for ruminants. Conversely, many shrubs contain minerals at levels higher than required by livestock. Livestock requirements may have changed in recent years with animals selected for more efficient feed conversion, and flock and herd structures changed to increase productivity. New studies have indicated that higher mineral supply may be beneficial during periods of oxidative stress related to growth, reproduction, and external stresses such as heat and parasites. These results indicate that mineral supply from pastures is not sufficient to support high levels of production for at least part of the year and that designing grazing system to incorporate the complementary benefits of grasses, legumes, crop forage and shrubs may improve the mineral status of grazing ruminants. The low mineral content of many Australian soils means that improvements in pasture and livestock production potential may increase the risk of mineral deficiencies. There is evidence to support this, but there is also wide variation in the mineral concentrations among forage types. This means that innovative grazing-system design using forage diversity offers an opportunity to avoid deficiency or imbalance. [ABSTRACT FROM AUTHOR]

The Australian Grassland Association (AGA) research symposium "Resilience in the Face of Change - Pastures for the Future" was held as a weekly series of virtual sessions in March 2021. Pasture-based animal production systems must continue to evolve to meet the challenges of the future, including feeding a growing global population and maintaining or improving environmental outcomes while adapting to a changing climate. This was the fifth in a series of AGA research symposia following on from the "Australian Legume Symposium" (2012), "Perennial Grasses in Pasture Production Systems" (2014), "Livestock Productivity from Pastures" (2017) and "Soil constraints to Pasture Productivity" (2019). [Extracted from the article]