Take home message

• Pasture legumes used in rotation with crops can significantly reduce expenditure on nitrogen fertilisers for following crops, but their capacity to do this is not a given
• Recent surveys have found a need to address fundamental issues with regard to issues including site preparation, sowing rates, sowing timing, inoculation and inoculation forms and nutrient provision if potential nitrogen fixation benchmarks and other legacy benefits are to be realised
• Second generation hard seeded legumes (G₂HSLs) such as biserrula, serradella and hardseeded annual clovers (arrowleaf, bladder and gland) and emerging methods of incorporating them into farming systems is offering scope to further increase nitrogen, soil carbon and other legacy benefits from pastures while increasing system flexibility.

Introduction

High and fluctuating input costs along with increasing weed and disease threats are squeezing profitability of cropping enterprises. A fifteen-year review of nitrogen fertiliser costs (based on urea) exemplify the volatility growers deal with where monthly prices have ranged from $218-1250/t (Anon 2023). Similarly, growers continue to face increasing issues with herbicide resistance impacting the efficacy with which they can control current and emerging weed issues in crops. Pests and disease also continue to be problematic.

Pastures, and particularly pasture legumes have traditionally been pivotal in supporting crop production through provision of nitrogen to following crops, offering alternative mechanisms for weed control and providing a pest and disease break. However, changes in farming system management, particularly increases in cropping area and cropping intensification, have and continue to change how pastures are used in rotations. In terms of pasture legumes being able to sustain the traditional roles of supporting crop production, broadly, it could be argued that R&D with respect to pasture breeding and system development, with some notable exceptions, has failed to keep pace with the evolution of cropping systems. This paper will provide a brief review on pasture use in cropping systems, how changes in cropping systems over time have affected pasture legume legacies for following crops, and the potential for emerging R&D on pasture breeding and crop-pasture rotation system development to complement contemporary cropping systems.

Use of pastures in cropping rotations – changes over time

A recent survey of 150 farming businesses in southern Australia found that pastures were only successful in meeting farming system goals (cropping and livestock production aspirations) 50% of the time (Hackney et al. 2021). Despite this, growers were looking to expand the role of pastures in their farming systems for the purposes of increasing nitrogen supply for crops and/or to support an increase in livestock enterprises on the back of rising prices for livestock and their products. That expansion of pasture area was being considered, despite what could be considered marginal pasture performance, makes it clear that attention needs to be given to how pastures are integrated with cropping systems and whether the pasture species used are suited to the role they are expected to fulfil.

It is worth remembering the thoughts of Professor John Howieson, who has led the domestication and breeding efforts of second generation hard seeded legumes (G₂HSLs), that ‘all legumes are niche species, which means that they require their correct growing environment to be highly productive’. If legume needs are met with regard to adaptation AND the legume forms and maintains an effective symbiosis with suitable rhizobia, then they are capable of fixing 20-30 kg N/t shoot DM produced. Thus, IF an effective symbiosis is formed, the quantity of nitrogen it can fix is simply a function of how much biomass the legume can produce (we will get to things that can go wrong with the AND and IF functions later in the paper).Beginning in the 1930s, ley farming systems (Figure 1) utilising either subterranean clover or annual medics, became the dominant rotation system used in southern Australian agriculture. Pasture legumes, which could regenerate spontaneously between crops, supplied nitrogen requirements for the following crop and high value feed for livestock. However, in the 1980s farming systems started to shift as livestock enterprises (apart from the brief wool boom of the late 1980s) entered a 30-year period of relatively low returns. Consequently, the need for pastures to support livestock production declined and the area of farms cropped in the mixed farming zone increased along with the intensity of the cropping phase. The ley system began to break down with less reliable regeneration of the legumes after the cropping phase and hence increasing reliance on fertiliser N for crop production (Puckridge and French 1983).

Both subterranean clover and annual medics are considered hard seeded, and indeed both have very high levels of hard seed immediately following formation. However, they differ considerably in how quickly hard seed breaks down between the late spring and early summer when they are formed and mid to late autumn when they need to regenerate to form a pasture the following season. With a couple of exceptions of new subterranean cultivars, the remainder rarely have more than 30% hard seed in the autumn following formation. Relatively rapid breakdown of hard seed means the seed bank is prone to depletion from false breaks. Further, the shallow root system means it is also subject to reductions in seed set and seed bank replenishment if spring rainfall is unreliable. Combine these attributes with a longer cropping interval and it can be seen that the seedbank can be exhausted relatively quickly. The annual medics generally retain higher levels of hard seed in the autumn following formation (60-90%) but are similarly shallow-rooted and subject to reduced seed production in dry spring conditions and have become increasingly challenged in terms of adaptation and capacity to fix nitrogen due to ongoing soil acidification. Many periods of extended drought and/or unreliable autumn breaks or spring finishes have further impacted seed bank reserves of these species. Additionally, both annual medics and subterranean clover have poor survival following ingestion, which can again significantly reduce seedbank replenishment.

Figure 1. The main legumes used and mechanisms of pasture system incorporation over time for southern Australian farming systems. Note G₂HSL refers to second generation pasture legumes

In south-eastern Australia, where pastures are integrated with contemporary cropping systems, it is primarily through use of a phase system where pastures are grown generally for 3-7 years between cropping phases. Phase pastures initially tended to be based on use of perennial grass-annual legume mixes, but over time, lucerne-based phase pastures have become more prominent. Pasture phases offer increased periods of time to build soil nitrogen (and carbon) provided the legume can form and maintain and effective symbiosis (lucerne) or consistently regenerate at adequate density and maintain an effective symbiosis seasonally (annual legumes).

Key issues with phase pastures include having to resow the pasture after each cropping phase, difficultly in maintaining the legume component in pastures over time. Annual legume regeneration can be compromised by competition for moisture, space and light with perennial pasture components. To maintain adequate lucerne density in lucerne-based or perennial grass-lucerne pastures requires careful grazing management due to the relatively high growing point of lucerne. In many areas, perennial grasses as a component of the phase pasture have fallen out of favour due to a number of factors including capacity for becoming too dominant in the pasture over time (higher rainfall areas), not being persistent enough (lower rainfall areas), cost and availability of seed of suitable cultivars, slow establishment, lack of opportunity to control annual grass weeds in the pasture phase and/or capacity of perennial grasses to harbour pests and disease.

The phase system is also relatively inflexible with areas of the farm sown either to crop or pasture for extended periods meaning capacity to flex and take advantage of opportunities in crop or livestock markets is limited. Phase systems also tend to rely largely on traditional annual legumes, and hence are subject to the same problems of adaptation and seedbank maintenance (i.e., false break and short springs) or on the perennial lucerne, which has limitations on adaptation with soil pH (and associated aluminium toxicity in some but not all acidic soils) and waterlogging.

Additionally, running successive years of pasture does not necessarily guarantee high levels of available nitrogen at the end of the pasture phase. High levels of nitrogen create a negative feedback signal for nodulation of legumes. Fixing nitrogen is an energy expensive process and hence if plants can readily access nitrogen from the soil pool instead of fixing it, they will. The variability in nitrogen availability after longer term pasture phases can be seen in a number of field experiments that have reported significant variation in crop nitrogen needs following the pasture, particularly where the long-term pasture was lucerne-based (e.g., Holford and Crocker 1997, McCallum et al. 2000, Armstrong et al.2019). Management of water availability for following crops also needs to be considered as significant profile dry-down by deep-rooted pasture species (particularly lucerne over summer) can be a confounding factor leading to lower than expected post-pasture crop yields.

An emerging option for integration of pasture legumes into farming systems is the use of second-generation pasture legumes (G₂HSLs) such as arrowleaf, biserrula, bladder clover, gland clover, serradella (French and yellow) and trigonella as on-demand break options in a cropping rotation. The G₂HSLs have the added advantage of being seed-retaining, aerial seeders that can be harvested using a header. The unprocessed seed of suitable species/varieties captured by the header can then be used to establish pastures using techniques developed over the last decade such as summer sowing (Nutt et al. 2021). Summer sowing, with appropriate inoculation, can be completed well ahead of the winter cropping program with a proportion of seed softening and emerging on opening autumn rainfall. Research over the last 10 years has shown significant increases in herbage production and hence nitrogen fixation compared to conventionally late autumn-established pastures (Hackney et al. 2021). The G₂HSLs have residual hard seed levels (seed remaining hard in the autumn following seed set) of 50->90%. Hence, there are options to run cropping phases of 1-4 years over an established seedbank of G₂HSLs and have them regenerate after the cropping phase without the need for resowing. Research in NSW and WA has shown that significant savings can be made on nitrogen fertiliser for following crops with the use of these legumes in rotations (Hackney et al. 2021; Loi et al. 2022). The smaller seeded G2HSLs (e.g., arrowleaf, biserrula, gland clover) also retain high viability (>50%) post-ingestion and hence the impact of grazing legume residues over summer on seedbank replenishment is less than for subterranean clover and annual medics.

A significant advantage of on-demand rotation systems is the capacity, once a seedbank of the legume is established, to alter the crop to pasture and therefore crop to livestock ratio on farm quickly in response to anticipated seasonal conditions and commodity prices. For example, if a dry year is anticipated, then a decision may be to leave a paddock out with the knowledge that the legumes can regenerate and offer useful feed to livestock, build soil carbon, and protect soil from erosion.

Research using G₂HSLs in cropping systems has a relatively short history compared to traditional legumes. Gaps exist in adaptation of G₂HSLs across southern Australian farming systems. With the exception of gland clover, most are not tolerant of waterlogging. All have performed well across soils with pH_Ca 4.8-7.0, with serradella and biserrula (and their symbionts) also performing well on more acidic soils. The impending commercial release of trigonella (Trigonella balansae) gives scope to move on-demand rotations to more neutral to alkaline soils.

Recent investment (e.g., Dryland Legume Pasture System project 2018-2022) was the first substantial investment in G₂HSLs in 15 years and has identified a range of new species and cultivars of existing G₂HSLs for ongoing development for commercial release, though this will require additional investment to bring them to market. A key component of research that brought G₂HSLs to commercial fruition was parallel symbiont development. Excellent case studies of this research are provided by Howieson et al. (1995), Yates et al. (2005 and Loi et al. (2014) with respect to biserrula (Group BS) and the broadening in host specificity and effectiveness of the Group C symbiont strain to ensure coverage of new annual clovers; gland and bladder. Such co-alignment of legume and symbiont development ensured that G₂HSLs came to market as a ready-to-go nitrogen fixation package. Research is also ongoing to better understand herbicide tolerances of the G₂HSLs and advice should be sought on herbicides that can be safely applied and are registered for use.

Achieving nitrogen legacy benchmarks

Numerous prior research efforts (e.g., Bolger et al. 1995; Peoples & Baldock 2001) have shown that a legume which has formed and maintained an effective symbiosis with suitable rhizobia can supply 20-30 kg N/t shoot biomass via nitrogen fixation. However, there are many factors that can impact achievement of these benchmarks, most of which can be controlled, at least to some degree, by making smart management decisions. These include:

A weed management phase prior to sowing new pasture

Weeds are the leading cause of establishment failure or sub-optimal establishment. It is far better to have a concerted weed clean-up effort in the 2-3 years leading up to establishing a new pasture rather than relying solely on use of selective herbicides to control weeds post-sowing.

Herbicide residues

Be sure to observe all plant back requirements for herbicides used leading up to sowing pasture. These requirements can include, but are not limited to:

• time elapsed since application
• variation in requirements for breakdown based on application rate
• specific minimum rainfall and/or soil moisture requirements for breakdown, and
• impacts of soil characteristics such as texture and pH on breakdown requirements.

Thoroughly read and abide by herbicide label requirements and seek advice if unsure. Remember for pastures established via summer sowing, sowing occurs 2-4 months earlier than conventional sowing and this must be kept in mind when assessing whether plant-back requirements have been met. Recent industry surveys have found that there is potential for damage to more than 40% of newly sown legume pastures due to inadequate meeting of plant back requirements based on herbicides used in the final year of crop and in the interval between crop harvest and pasture sowing (Hackney et al. 2020).

Species choice

Thoroughly consider the tolerances of legume species and cultivars within species to specific challenges that might be encountered in your farming system. This can include appreciation of the tolerance of legumes and their rhizobia (remembering that a legume that fails to form an effective symbiosis can utilise more nitrogen than it contributes) to factors such as soil pH, nutrient requirements, capacity to survive false breaks, incidence of and capacity to reliably set seed under sub-optimal spring rainfall conditions, capacity to be utilised for purposes other than grazing (e.g. fodder conservation), spectrum of selective herbicides available and suitability for use in rotation system used on-farm (i.e. ley, phase and/or on-demand).

Effective inoculation Effective inoculation

Legume species differ in the inoculant group required, for example most annual clovers require Group C, lucerne requires Group AL, serradella Group G/S and biserrula Group Biserrula Special. If the wrong inoculant group is used legumes will either fail to nodulate or form a sub-optimal symbiosis. Up to date advice on which inoculant should be used can be accessed from the Australian Inoculants Research Group. Traditionally, most pastures have been sown using a wet inoculant delivery system such as peat or freeze-dried inoculant applied to the seed prior to sowing. These methods have the potential to deliver very high numbers of rhizobia with the seed, but rhizobia numbers decline quickly due to desiccation. When using these methods only treat enough seed that can be sown within 24 hours of inoculation and make sure there is adequate moisture in the soil to allow rhizobia survival post-sowing and until the legume germinates and can form a symbiosis.

Liquid injection can also be used to supply appropriate rhizobia at sowing and this technique also relies on adequate soil moisture for survival. For any of the wet inoculant delivery systems, do not apply additional seed treatments that may cause death of rhizobia, only use clean tanks and non-chlorinated water (Farquharson et al. 2022).

A range of granular inoculants are also available and vary in terms of formulation and moisture content of the granules. Good results have been achieved sowing into dry soils (i.e., for summer sowing or prior to the autumn break) with low moisture clay-based granular inoculants (Nutt et al. 2021).

In eastern Australia, pre-coated seed that contains rhizobia are relatively common. Rhizobia numbers in precoated seed can decline to suboptimal levels within weeks (Farquharson et al. 2022) so if using this form of inoculant check expiration dates and closely follow storage guidelines.

Plant population

Past research has established suitable sowing rates for pasture legumes to establish a dense pasture capable of fixing adequate nitrogen for following crops. As an example, the foundational research of Quinlivan et al. (1973) used minimum sowing rates of 8 kg/ha for subterranean clover in ley farming systems with increases in productivity and seed production at sowing rates up to 24 kg/ha. Research on use of subterranean clover in mixtures with lucerne or phalaris used rates of 3 kg/ha (Wolfe and Southwood 1980) to 7 kg/ha (Dear et al. 2001). Recent industry survey found where subterranean clover was sown in monoculture and mixtures, the average sowing rates used were 4.8 kg/ha and 2.2 kg/ha respectively (Hackney et al. 2021) which may contribute to perception that pastures are only fulfilling farming system goals 50% of the time.

Sow on time

Just as with crops, there are optimum sowing windows for pasture legumes to optimise growth, nitrogen fixation and seed production. Research with traditional annual legumes found sward production and seed yield declined significantly when sowing dates were delayed from April to June for subterranean clover (Quinlivan et al. 1973) and from May to June for barrel medic (Carter et al. 1992). Similarly, more recent research with G₂HSLs has found significantly higher herbage and seed production where the legume was established via summer sowing compared to conventional late autumn sowing, with late sown legumes frequently not meeting seed yield targets required for reliable future regeneration (Nutt et al. 2021; Hackney et al. 2022).

Legumes are capable of germinating at low temperatures, but as temperature decreases the time taken for emergence increases. Legumes require cumulatively more heat units for leaf expansion than grasses; meaning light interception and therefore growth can be severely restricted for late sown legumes. Additionally, late sown legumes are more susceptible to competition from weeds. Further, late sowing and low temperatures can delay the formation of an effective symbiosis between the legume and its rhizobia meaning nitrogen fixation potential is also compromised. Small, poorly developed plants are more susceptible to spring moisture stress which can limit seed production potential. Recent industry survey has found that more than 65% of legume-based pastures were sown after mid-May.

Some slippage in sowing time due to changes in climatic conditions, specifically timing of the autumn break is understandable. Both subterranean clover and annual medics require good moisture conditions for reliable establishment, a consequence of relatively poor capacity to regulate transpiration losses. Conventional pasture sowing also generally has to compete with the winter sowing program, frequently leading to the sowing of pastures after the cropping program is completed. The capacity for G₂HSLs to emerge early and survive what would be high mortality conditions for traditional legumes offers alternative establishment options. Specifically, summer sowing and the ability to have pastures sown ahead of the winter cropping program so legumes emerge and commence growth in a window that can optimise production, nitrogen fixation and the formation of a seedbank for future regeneration.

Establish to optimise legume performance

All plants have four basic requirements for successful establishment, growth and seed production: space, light, moisture and nutrients. In south-eastern Australia, the dominant form of pasture establishment has been to undersow pasture with the final crop in the rotation with the rationale that the crop (sown at a much-reduced rate), can partially offset the cost of sowing the pasture. A survey of more than 200 farmers in 2008 found more than 80% of farmers used undersowing to establish pasture, but only 30% considered it to be a highly effective method (Hackney et al. 2009). More recent surveys have shown the use of undersowing is being used by less than 50% of farmers (Hackney et al. 2021).

Undersowing places extreme pressure on the establishing pasture in satisfying all four of the essential requirements for plant growth. Interestingly, undersowing was the dominant form of pasture establishment used in Western Australia up until the late 1960s when a series of field experiments (n=44) reported legume seed yield was significantly reduced compared to the stand alone sowing. Seed yield was reduced by more than 50% at 70% of field sites and by more than 75% at 30% of sites (Poole and Gartell 1970). Mention of undersowing in the literature for Western Australia is virtually absent from that time forward. Similar results have been reported in eastern Australia for both annual and perennial legumes (e.g., Dear et al. 2001, Li et al. 2014) with negative implications for seed size (Hackney et al. 2012) also reported and indeed modelling has shown that the upfront cost of sowing pastures stand alone is recouped by increased production and persistence in the long term (Nordblom et al. 2016). The potential negative consequences of undersowing are further exacerbated under conditions of spring moisture stress and drought (Dear et al. 2001).

Anecdotally, farmers wanting to persist with undersowing are having increased success where they practice some spatial separation of the crop and pasture, for example by skip-row sowing where sowing machinery is already set up with wide (i.e., 12 inch) row spacing. Stand-alone sowing either by conventional establishment using species with suitable capacity to establish and survive an early to mid-autumn sowing or by summer sowing of G₂HSLs give greater capacity to meet production, nitrogen fixation and seed yield benchmarks.

Manage annual legumes in the first year to optimise seed production

Building of seed bank (for annual pastures) and setting up perennial legumes to optimise persistence is paramount to maximising potential for pasture potential. Choose the right species for your purposes, prepare the site correctly, sow on time and at an appropriate rate ensuring that the required inoculant is used and in a form that is suitable for the time of sowing and moisture available. For conventionally sown legumes, it is unlikely that there will be potential for grazing. For summer sown legumes, it might be necessary to graze depending on biomass present at the end of winter. In average to above average rainfall years, stands established via summer sowing can benefit from strategic grazing to manage the herbage overburden and for species such as biserrula, increase airflow through the sward and minimise botrytis incidence. In short, manage your annual legumes like a crop. For perennial legumes such as lucerne, manage swards to optimise plant survival through the first summer and hence maintenance of density potential over the life of the stand.

Managing annual legume regeneration when grown in association with perennial species

If sowing annual legumes with a perennial grass or lucerne, manage the perennial to enable adequate seed set of the annual and its regeneration – the space, light, moisture, nutrient theme comes back into focus when managing annual legume regeneration. Established lucerne and perennial grasses can become dominant quickly in a sward and minimise opportunity for annual legume regeneration. Where annual legume regeneration is required, it is important to open up the canopy in late summer and early autumn to provide opportunity for regeneration.

A note for G₂HSLs – some of them hold seed quite tightly above ground in the flowerhead (e.g., arrowleaf clover) or in pods on the ground (e.g. biserrula). Where residues of these species are left undisturbed over summer, there can be minimal hard seed breakdown. It is important to graze or mulch residues to get seed on the ground and in contact with the soil.

Manage weeds in established pastures

A key thing to remember in terms of soil nitrogen is the ‘use it or lose it’ philosophy. Weeds are extremely opportunistic and can rapidly deplete soil nitrogen pools. While in a longer-term pasture, the nitrogen taken up by weeds may ultimately be recycled to the pasture by grazing livestock, the redistribution will be uneven, by virtue of camping behaviour, and further significant losses can be incurred via deep drainage and volatilisation from urine patches. For legume dominant annual pastures (ley and on-demand pastures) there is often temptation to allow year on year pasture regeneration. In the case of G₂HSL pastures, this is often because they regenerate successfully early in the season and can provide very useful stock feed early in the growing season. However, it is important to keep in mind that previous research has shown these legumes, if established via summer sowing in the year prior, have capacity to fix 100 to >300 kg N/ha. Thus, the value of nitrogen fixed for subsequent crop production needs to be balanced against the potential for weed incursion if the pasture is left to regenerate. Also, remember that high soil nitrogen levels are a negative feedback signal for nodulation and nitrogen fixation in legumes, so running successive years of legume dominant pasture does not necessarily confer sequential increases in soil nitrogen levels.

Don’t neglect nutrition for pastures

Paddock surveys (n=300) undertaken in central and southern NSW have shown considerable disparity in most regions in nutrient availability in crop and pasture paddocks, with availability of key nutrients generally lower in pasture paddocks (Hackney et al. 2020). Pasture legumes and rhizobia generally have similar threshold levels to common crops to optimise production.

Use fertilisers appropriate for legumes. Recent surveys indicate when pastures are fertilised, nitrogen-based fertilisers such as MAP and DAP are the most commonly used (Hackney et al. 2020). These fertilisers lack adequate sulphur to support legume and rhizobia function and to support the development and maintenance of the symbiosis. The same paddock surveys showed widespread soil sulphur deficiency so carefully consider fertilisers used during establishment and maintenance of legume-based pastures.

Other legacies of legumes used in rotation with crops

Fodder conservation – pastures can be purpose sown or used opportunistically for fodder conservation. Conserved fodders can be used on farm to fill feed gaps or sold to generate additional cashflow. Fodder conservation can also be a useful tactic to manage problematic weeds by consideration of cutting time (silage vs. hay) and management of regrowth (Piltz et al. 2017, Piltz et al. 2021). Additionally, choosing to cut excess pastures growth for silage offers opportunity to considerably reduce the viability of seeds of a range of problematic crop weeds (Table 1)

Grazing for weed control – grazing livestock can be very valuable as an additional weed control strategy. There can be significant differences in palatability between some problem cropping weeds (e.g. annual ryegrass) and particular legumes (e.g. biserrula) that mean that sheep in particular will target these weeds in preference to grazing the legumes (Hackney et al. in prep). Additionally, ingestion by livestock of seed of a range of problematic crop weed species can greatly reduce their viability. Where conserved fodders (particularly silage) are fed to livestock, the weed seed viability is further reduced (Table 1).

Options for other weed control strategies – aside from fodder conservation and grazing, the incorporation of pastures into cropping rotations also offers opportunity to utilise a different suite of weed control strategies which may range from utilising herbicides with a different mode of action to those used in crops, incorporating strategies such as spray-grazing of some broadleaf weeds where sufficient livestock are available and paddocks are an appropriate size, through to combining grazing with strategies such as weed wiping.

Table 1. The germination of a range of weed seeds that were ensiled or subject to digestion by cattle or to both ensilage and digestion compared to non-ensiled, non-ingested seed.

Source: Piltz et al. (2017)

Reducing pest burdens – pasture breaks in the cropping rotation are frequently quoted as providing opportunity for pest and disease breaks. One example of this is the impact legume species selection may have on the population of nematodes in cropped paddocks (Collins et al. 201818). Initial glasshouse screening showed consistently high resistance of French serradella to root lesion nematode with variable resistance shown by yellow serradella, biserrula and subterranean clover. Both arrowleaf clover and gland clover were consistently susceptible (Table 2). Subsequent field evaluation pre- and post a French serradella pasture showed significant decline in nematode populations (Figure 2). Thus, in situations where particular legume species are well suited to be grown and they have known capacity to reduce pest pressures, their incorporation into rotation systems may be highly advantageous.

Table 2. Root lesion nematode (Pratylenchus neglectus) resistance profiles for pasture species in glass house experiments in WA

R=resistant, MR=moderately resistant, S=susceptible, SVS-susceptible to very susceptible.
Source: Collins et al. (201818).

Figure 2. Root lesion nematode (Pratylenchus quasitereoides) levels (RLN/g soil) in paddocks before and after a French serradella pasture. Adapted from Collins et al. (2018)

Pastures have been variously shown to have both positive and negative impacts on the population of other pests. In terms of legumes, species differ in their tolerances to these pests (Table 3). Smart choices made in legume selection can assist in reducing the build-up of pest numbers for following crops (Table 3).

Table 3. The susceptibility of hard seeded legume species to a range of pests.

¹Plants are most susceptible to attack at the cotyledon stage of development. Black shading indicates resistance/tolerance, grey shading indicates moderate susceptibility, hatched shading indicates susceptibility. Note for subclover, some newer cultivars have improved tolerance to RLEM at the cotyledon stage.

Disease- legumes differ in their tolerance to disease and smart decisions can be made in terms of selection to assist in prevention of disease build up in pastures that may impact following crops (Table 4).

Table 4. The tolerance of a range of annual legumes to various common diseases

Black shading indicates resistance/tolerance, grey shading indicates moderate susceptibility, hatched shading indicates susceptibility. Note: For subterranean clover, there can be significant variation in tolerance between cultivars to the diseases shown and the shading indicates the susceptibility averaged across all cultivars, advice should be sought regarding individual cultivar susceptibility.

Conclusion

Pasture legumes used in rotation with crops can offer significant nitrogen and other legacy benefits, including the build-up of soil carbon. However, achieving the expected contributions of nitrogen from use of legume-based pastures in rotations requires attention to selection of appropriate legume species and cultivars for soil and climatic challenges as well as consideration of production aspirations. Opportunities for incorporating legume-based pastures into cropping rotations has expanded over time and notably over the last decade with the development of on-demand pasture break systems. Proper attention to fundamental agronomic issues regarding site preparation, sowing techniques, sowing rates, inoculation, nutrient provision and weed control should see the perception of success of pastures in supporting cropping production increase over time.

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Contact details

Belinda Hackney
Select Carbon
425 David St, Albury, NSW 2640
Email: belinda.hackney@selectcarbon.com

Date published: February 2023

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