Better pastures for better production

Subterranean clover (sub clover) warrants special mention on account of the fact that so many cultivars of this species are currently available. This speaks to the importance of this species in Australian agriculture. There are three sub-species of sub clover; subterraneum (subs), yanninicum (yans), or brachycalicinum (brachys). The subs are the most common varieties and include cultivars such as Goulburn, Seaton Park and Dalkeith. The yans are the white-seeded varieties and are better suited to waterlogged soils, including cultivars such as Gosse and Riverina. The brachys are best adapted to cracking clay soils as they ‘hide’ their seed amongst the soil cracks rather than bury it as the subs and yans do. Examples of brachy cultivars include Clare and Antas. Cultivars of sub clover are divided further on the basis of maturity. Earlier maturing cultivars are better suited to drier environments, with later maturing varieties better suited to higher rainfall environments. However, as drought can occur in any environment in which sub clover is grown, it is suggested to include a mix of three different cultivars of sub clover when it is sown. The three cultivars might include one from a different sub species, and include a narrow range of maturity groups suited to the target environment. For example, a paddock east of Wagga (average annual rainfall, 550 mm) which has several drainage lines across it might be sown to Riverina (a mid-season yan) plus two subs such as Coolamon (mid-season) and Goulburn (mid-late season). In this example, the Riverina is included to account for periodic waterlogging that may occur on parts of the paddock. The Goulburn might be expected to dominate over the remainder of the paddock if a series of wetter seasons is experienced, or under drier conditions the earlier Coolamon might be the more dominant cultivar. The inclusion of multiple cultivars of this species helps ensure broad adaptation of the species to variable soils and seasons.

Perennial legumes

Perennial legumes also have the capacity to fix N, but as opposed to annual legumes which regenerate from one year to the next from seed, perennial legumes survive year round and rely upon longevity for persistence. It is noted that some perennial legumes, such as white clover, use both strategies for persistence; seedling regeneration and longevity. Lucerne is the most broadly adapted perennial legume available. It is highly productive, drought tolerant and has a deep root system which can explore a large depth of soil volume for water and mitigate the risk of soil degradation attributable to deep drainage. Lucerne is less well suited to shallower soil types, to acidic soils particularly those prone to Al and Mn toxicity, or to waterlogging. There are dozens of cultivars of lucerne currently available with much confusion in the marketplace as to which cultivars are superior in a given environment. Australian lucerne fields were decimated in the 1970s by incursions of insect pests and disease. Farmers should ensure that the cultivars they purchase have genetic resistance to common pests. Lists comparing cultivars are published from time to time by NSW DPI and can be found on the internet. Lucerne cultivars are also distinguished on the basis of winter activity groups; with highly winter active cultivars assigned a score of 9-10, while semi-winter dormant types are assigned scores of 4-5. Highly winter dormant types are generally not marketed in Australia due to our milder winters compared to many northern hemisphere environments. A recent field study showed little difference in persistence of different winter activity groups of lucerne under a phased farming regime near Ariah Park, NSW (RC Hayes unpublished data), although anecdotal evidence suggests that under intensive grazing the highly winter active lucernes are less persistent. Similar to subterranean clover, it perhaps makes sense for farmers to sow several cultivars of lucerne to mitigate the risk of establishment failure, and to increase sward resilience in the face of soil and seasonal variability.

Few other perennial legumes can be recommended for use in cropping environments. In recent evaluations, strawberry clover performed as well as or better than lucerne at particular sites, reflecting the superior adaptation of this species to heavy soils and waterlogged conditions. White clover is also a productive species, but tends to have insufficient drought tolerance for most cropping environments. Aside from specific niches where these alternative species might play a role, farmers have little option but to plant lucerne or opt for non-leguminous perennial options.

Temperate perennial non-legumes

A small range of alternative perennial pasture species exist which are broadly adapted across the cropping environments of south-eastern Australia. These include the perennial grasses phalaris, cocksfoot and tall fescue, as well as the perennial herb, chicory. Other species, such as plantain or perennial veldt grass, may have a role in some niche environments, but previous evaluation experiments suggest that their adaptation is far more limiting than the initial species mentioned. For all non-legume pasture species, it is assumed that they would be grown in mixtures with lucerne and/or an annual legume species to ensure adequate N supply for the pasture and for the subsequent cropping phase.

Many cultivars of chicory and the three grass species are available, and so it is important that appropriate cultivars are selected for the target environment. A recent research initiative has evaluated the three grass species in cropping environments from Inverell in northern New South Wales (NSW) to Eversley in western Victoria, and several new cultivars suited to cropping environments may become available from that research initiative. Sirolan phalaris, an old cultivar of Mediterranean origin is perhaps the best phalaris option for environments with an average annual rainfall of 550mm or less. Few other phalaris cultivars currently available have been developed for cropping environments with most of Australia’s phalaris found in the high rainfall permanent pasture zone. The Hispanic cocksfoots were the most persistent group of that species and are probably better suited to lower rainfall environments than Sirolan phalaris. Kasbah cocksfoot is perhaps the best available Hispanic cultivar for very hot and dry environments. In higher rainfall environments (e.g. 550-700mm), intermediate types such as cultivar Currie may be suitable. The new tall fescue cultivar, Barnaby, was released as a result of the recent evaluation in south-eastern Australia. Bred from Sardinian material this continental type is suited to regions which receive an average annual rainfall greater than 500mm. The Mediterranean cultivar, Flecha, also performed well in those trials and may be more suitable in environments which expect a reduced incidence of summer rainfall.

A recent cross-site evaluation of seven chicory cultivars, including Chico, Choice, Commander, Puna, Puna II, Grouse, and La Certa was unable to identify a single superior cultivar. Chicory is perhaps the most similar species to lucerne due to its high quality forage, summer growing growth habit and deep tap root, but is less drought tolerant than lucerne and is of course not a legume. Chicory is better suited to shorter pasture phases; perhaps two years in drier environments or up to 4 years under more favourable conditions. Chicory is a far more vigorous seedling than lucerne so lends itself to a shorter establishment phase. A study near Cowra, NSW, showed that sub clover, arrowleaf clover and balansa clover were better companions with chicory than lucerne, most likely due to the reduced competition for water from the annual species (Li et al. 2012).

Tropical and native species

Figure 1: Poor establishment of green panic following a spring sowing at Cowra, 2015. (Photo: Matt Newell, NSW DPI).

Other pasture options that might be considered by farmers include native or tropical grasses. This group of species is unlikely to provide viable options for the target region. Tropical species, such as rhodes grass or paspalum, are species that have evolved with a modified pathway of photosynthesis and are referred to as C₄ plants in contrast to the temperate C₃ species. The modified pathway of photosynthesis provides a number of adaptation advantages over temperate species, such as increased tolerance of drought stress or nutrient deficiency, and is therefore seen as a promising option for farmers looking to adapt to more variable weather conditions. However, significant practical limitations exist, mainly associated with establishment, which severely restricts the increased use of tropical grasses in farming systems of south-eastern Australia. Tropical species require warm soil temperatures to germinate. In southern Australia where rainfall patterns are typically winter-dominant, it is relatively uncommon for soil temperatures to be adequate for seedling establishment at the same time moisture conditions are favourable. This mis-match in soil temperature and water makes the establishment of tropical grasses notoriously unreliable, and generally an unviable practice for farmers wishing to establish pastures reliably, despite the fact that many tropical grass species proliferate in lawns and on roadsides across south-eastern Australia.

Many native grasses, such as kangaroo grass, are also C₄ species although others, such as wallaby grass, are C₃. The primary limitation for the use of native species as pastures in cropping sequences is also their poor reliability of establishment. For many of the native grasses, this relates to poor seed production resulting in low and unreliable supply of quality seed through the supply chain. Native species, and for that matter, many exotic C₄ grasses, have evolved to be opportunistic; to respond when conditions are favourable. Many of their adaptive characteristics make cultivating them as reliable plants firstly for seed production, and more generally for pasture production, extremely challenging. Because of this, native species are commonly restricted to parts of the landscape where they already exist as a viable stand, and this frequently rules out their use in many cropping regimes.

Reliable pasture establishment

One of the key aims when establishing a pasture is to limit the incidence of pasture establishment failure. Pasture establishment is an expensive exercise when input costs and foregone production from the land under establishment are considered. Failure to establish a productive pasture reduces returns on sunk costs, reduces whole-farm productivity, and can disrupt the cropping rotation leading to other costs and limitations on the business. The following provides some tips to reducing the risk of establishment failure and increasing the productivity of sown pastures.

Pasture mixtures

There is a long-standing debate as to whether pastures should be sown as diverse species mixtures or as monocultures. Generally speaking, the weight of evidence supports the sowing of multi-species pasture swards, however, some consideration needs to be given to the species that are included. Where non-legume species are sown, such as a perennial grass or chicory, it is essential that at least one legume species is sown alongside to provide N for the pasture components, if nothing else. It could be argued that lucerne could be sown as a monoculture as it is capable of fixing its own N. After all, reduced species diversity leads to increased management simplicity in terms of increasing the herbicide options available to control weeds or for easier grazing management. However, as a recent sampling of an EverCrop field experiment at Mirool illustrates, the inclusion of a perennial grass into a lucerne pasture can substantially increase total productivity. The EverCrop experience over five sites was that lucerne monocultures were generally not as productive as mixed swards, had a high level of bare ground in the sward and were vulnerable to weed invasion.

Figure 2: Cumulative production of pastures grown at Mirool 2012-2014 which included lucerne or subclover in monocultures (mono), or in mixtures with each other and/or phalaris. (Source: Sandral et al. 2015).

Mixed swards typically fail where unsuitable species are included in the mix. Only species that are adequately persistent in the target environment should be included. For example, perennial ryegrass was often included in traditional pasture mixtures to increase early pasture growth. However, perennial ryegrass is poorly adapted to many cropping environments across south-east Australia due to its poor drought tolerance. The inclusion of that species in these environments therefore represented a poor investment in seed which was never going to persist in the sward, and moreover, out-competed less vigorous pasture seedlings reducing the establishment of other sward components. Always limit species in a mixture to those expected to persist for the life of the pasture. In addition, as with the example of sub clover used above, always try to include several adapted cultivars of the one species to enhance performance in variable soils and seasons.

Cover cropping

Many pastures sown in crop rotations are established under a cereal cover crop. That is, the crop (usually wheat or barley) and pasture seed is sown together, the crop grows and dominates the sward in year one before being harvested for grain, after which the pasture is spelled before grazing commences. Cover-cropping can be a useful way to obtain an income in the establishment year of a pasture. On the other hand, a vigorous cover crop can represent substantial competition for resources during the establishment phase and lead to reduced pasture production. The EverCrop experience showed that it was common to reduce production of sown pasture species by more than 50 per cent by including a cover crop at establishment (Table 2).

Table 2: Difference in cumulative biomass production of perennial species (t/ha) in the year following sowing between swards sown with or without a cover-crop, and the reduction (%) in perennial species biomass in year two due to the presence of a cover-crop at sowing.

Doubling the lucerne sowing rate in the EverCrop experiments increased initial lucerne density in year one and basal frequency following the first summer, leading to an increased proportion of lucerne in the pasture sward and decreased weed biomass, but had no effect on crop density or yield (Table 3). Halving the cover-crop sowing rate from the standard farmer rate of 20kg/ha, had no effect on lucerne performance, initial wheat density or final wheat yield. This result was observed at Ariah Park in 2010 where annual rainfall was 733mm, well above the long term average of 501mm for that location.

Table 3: Initial seedling density (plants/m2), wheat grain yield (t/ha) and lucerne basal frequency in year two (%) following sowing in 2010 at Ariah Park. Values in columns followed by the same letter are not significantly different at P=0.05; ns – not significant.

If a cereal cover crop is to be sown with an establishing pasture, the following guidelines may help to reduce pasture establishment failure:

• Crop sowing rate should be reduced to quarter normal sowing rate to reduce the competition with the pasture in a dry year. That is, if wheat is usually sown at 40kg/ha in your environment, the sowing rate should be reduced to 10kg/ha where it is used as a cover crop.
• Maintain pasture sowing rates at their normal level, to give the pasture every chance of surviving the competition of the crop. That is, if lucerne is normally sown at 2.5kg/ha in your environment, ensure it is still sown at 2.5kg/ha under a cover crop.
• Only sow a cover crop where a lucerne pasture is to be sown. If alternative species, such as phalaris or chicory are to be sown, do not sow a cover crop. Pasture species other than lucerne are much less tolerant of competition from a cover crop, and therefore much more likely to fail at establishment.

Pre-coated pasture seed

1. Farmers are commonly unaware of how much seed coat they are purchasing with their seed making it very difficult to determine actual pasture sowing rates, or adjust sowing rates accurately to account for the seed coating.
2. The survival of N-fixing bacteria on pre-coated seed is variable and often poor, reducing the N-fixation potential of legumes.
3. The very short shelf-life of seed coats limits the capacity to sow unused pasture seed at a later date, potentially adding to wastage costs.
4. Independent surveys show a significant percentage of coated legume seed that is within the advised shelf-life still fails to meet quality standards for inoculant.
5. A lack of information about the other components of seed coats, such as insecticides and fungicides, makes it difficult for a grower to assess whether the seed coat offers additional advantages in a particular situation and whether other approaches, such as ground application of insecticides post-sowing, would be a more cost-effective approach to improving pasture seedling growth.

It is very likely that in many situations, coating on pasture seed serves to reduce the effective sowing rate of pastures. The 2kg/ha lucerne sowing rate in Table 3 was chosen by the farmer and has been a common sowing rate used in that region for several decades. However, to get the equivalent of 2kg/ha of seed into the ground using pre-coated seed, a farmer may need to double or triple sowing rates. Table 3 shows the benefit to lucerne performance of doubling the sowing rate of coated lucerne seed. This serves to increase the unit cost of pasture seed which is yet to be demonstrated to represent a sound value-proposition in most broadacre situations. There may be instances where a coating on seed is justified, for example, to improve the flow of tropical grass seed through a seeder or where local data exists quantifying the production gains due to seed coats. Otherwise, in general we recommend that farmers avoid the use of pre-coated seed due to the significant risks associated with it. Where possible, the traditional approach of sourcing bare legume seed and freshly inoculating prior to sowing should be used. If coated seed is used, farmers should ensure that every seed lot they purchase complies with the industry code of practice and is labelled to specify the content of seed coat on the seed. Further information is available on the Australian Seed Federation website.

Herbicide residues

There is increasing suspicion that the use of residual herbicides in the cropping phase is having a negative impact on sown pastures. Little research has been done on this aspect to date, and the issue is complicated by variable seasons and soil types impacting the life and effectiveness of herbicide residues in soils. Growers need to be mindful of herbicide application in the years leading up to pasture establishment and select herbicides that are unlikely to impact negatively on the pastures they sow. Very few pasture cultivars have been developed specifically for their tolerance to residual herbicides; the annual medics (such as Angel) tolerant of sulfonyurea herbicides is perhaps the best example. Herbicide residues may lead to a complete failure of the pasture phase, or may simply lead to pastures of ill-thrift, the cause of which may be difficult to identify.

Conclusion

Pastures are a key part of the mixed farming business. They underpin the livestock enterprise, and their positive impacts on soil health and nutrition yields benefits well into the cropping phase. It is important that farmers and advisers seek to establish a resilient pasture stand, appropriate to the environment and the farming enterprise. This is achieved by first selecting the appropriate species, which in most cropping environments in south-eastern Australia will include annual legumes, lucerne, a perennial grass or chicory. In species such as sub clover where a large range of cultivars is available, the pasture mix might include two or three cultivars suited to the target environment to help increase adaptation to variable soils and seasons. Sowing of a lucerne pasture may occur under a cover crop to increase returns during the establishment year, although it is acknowledged that under unfavourable seasonal conditions, this can increase the risk of establishment failure. Reducing the cover crop sowing rate to quarter of normal crop will help to reduce the competition from a cover crop. All other pasture species should be sown without a cover crop to maximise establishment, and sown at appropriate sowing rates. Caution should be used when sowing pre-coated seed as this serves to reduce the effective sowing rate of the pasture, or to increase the unit cost of seed. Care should also be taken to avoid the use of potentially damaging residual herbicides late in the cropping phase which may be detrimental to pasture performance. Both the cropping and livestock enterprise of a farm business benefit greatly from a resilient pasture sward.

Acknowledgements

Funding for this work was provided through the GRDC Project CSA00044 and their support is gratefully acknowledged.

Useful resources

NSW DPI Pastures and Rangelands

Li G, Hayes R, Gardner M, McCormick J, Newell M, Sandral G, Lowrie R, Zhang H (2012) Companion legume species maximise productivity of chicory (Cichorium intybus). In ‘Capturing opportunities and Overcoming Obstacles in Australian Agronomy’ Proceedings of the 16th Australian Agronomy Conference, 15-18 October, Armidale, NSW. Australian Society of Agronomy.

Nichols PGH, Loi A, Nutt BJ, Evans PM, Craig AD, Pengelly BC, Dear BS, Lloyd DL, Revell CK, Nair RM, Ewing MA, Howieson JG, Auricht GA, Howie JH, Sandral GA, Carr SJ, de Koning CT, Hackney BF, Crocker GJ, Snowball R, Hughes SJ, Hall EJ, Foster KJ, Skinner PW, Barbetti MJ & You MP (2007). New annual and short-lived perennial pasture legumes for Australian agriculture - 15 years of revolution. Field Crops Research 104 (1-3): 10-23.

Sandral GA, Swan TD, Li GD, Goward L, Peoples MB, Hayes RC (2015). Alternate row sowing: a novel approach to maintain sown species in mixed pasture swards. In ‘Building Productive, Diverse and Sustainable Landscapes’ Proceedings of the 17th ASA Conference, 20-24 September, Hobart, Australia. Australian Society of Agronomy

Contact details

Richard Hayes
Wagga Agricultural Institute
Pine Gully Rd, Wagga Wagga NSW 2650
0448 231 704
richard.hayes@dpi.nsw.gov.au