Pastures are important to most farmers who grow crops in Australia. About 60% of all producers of cereal grain and oilseeds have livestock enterprises. On the south western slopes this relationship approaches 100%. Crops are grown as part of a crop/pasture-ley rotation. In most situations the growth and use of the pasture influences the yield and productivity of rotating crops. This paper explores four aspects of pasture-ley farming:

(i) the role and potential of the pasture ley;

(ii) characteristics required by pastures to maximise their utility;

(iii) strategies for more effective use of pasture leys; and

(iv) species and varieties for ley farming.

PASTURE LEYS - WHAT ARE THEY?

Traditionally, pasture leys were concerned with the replenishment of soil fertility and provision of forage for livestock. The definition of Cornish and Pratley (1987) is typical:

"......A rotation in land use that specifically includes a legume-based pasture to improve soil fertility as well as provide grazing for stock in the farm system....."

Recently there has been a realisation that the pasture ley plays a more varied and important role, a role which is often not compared to an individual farm but is part of a much more complex agroecosystem. These functions and how they are changing are now explored.

THE FUNCTIONS OF A PASTURE LEY

Nitrogen (N) Fixation

Nitrogen is an important limiting factor to crop growth over much of Australia (Hamblin and Kyneur, 1993). The ability of pasture legumes to fix nitrogen is the main mechanism by which most dryland crops and pasture grasses are supplied with their N requirements.

The amount of nitrogen fixed by a pasture is determined by:

(i) the amount of dry matter produced by the pasture;

(ii) the proportion of legume in the pasture; and

(iii) the dependence of the pasture legume on symbiotic nitrogen fixation.

Although N available to subsequent crops is strongly influenced by symbiotic N fixation other sources of N addition and loss, particularly

leaching and volatilisation, can determine what is finally available.

Nitrogen fixation can be approximated from the quantity of legume pasture grown throughout the year. For example, Kleinig (1974) proposed that:

N (fixed) kg/ha = legume dry matter (kg/ha)

x 0.18

N fixation is therefore largely dependent on how well the legume grows. Low yields are reflected in low N fixation and high legume dry matter yields with high levels of N fixation. A critical factor is thus, the pasture legume yield potential and the extent to which farmers are able to realise this potential. Given adequate nutrition and suitable species, the pasture legume yield potential is set by available soil water and, in turn, growing season rainfall. The relationship between growing season rainfall and grain yield is well established for winter grain crops, particularly wheat (French and Schultz, 1984; Cornish and Murray, 1989). However, there are few estimates for pasture (Whittaker, 1970; French, 1991) and none which effectively describe the potential for southern NSW. The

data in Table 1 is a first attempt to establish the water-limiting yield potential of subterranean clover and to relate these to nitrogen fixation. The water-limited yield potential for wheat crops and their N requirements at two protein levels have also been estimated.

These guidelines are for legume only pastures, dry matter yield can be increased by up to 25% by inclusion of a suitable grass in the pasture (Hochman et al., 1990). Where grasses are part of the pasture mixture an adjustment down of the N fixation potential proportional to the percentage of non-legume components is required. Those estimates are for annual pastures, the nitrogen fixation from perennial legume pastures, e.g. white clover/lucerne should be slightly higher (Ellington, 1986).

Improvements in Soil Organic Matter and Structure

In parallel with the increases in soil N that occur with the growth of a legume pasture ley are the additions of organic matter (OM) to the soil. Improved OM levels confer many physical benefits to the soil. They include increased porosity; water retention and available water; levels of water stable aggregates; biological activity; and cation exchange capacity (Greenland, 1971; White et al., 1978; and Heenan and Chan, 1992).

Table 1. Annual Pastures and Wheat Crops - Growth potential, nitrogen addition from legume pastures and the nitrogen requirements for wheat of various protein levels.

Seasonal Growing Season(1) Yield potential(2) N required for(3) Potential(4) N addition(5)

characteristic available water of wheat 9% and 12% pasture yield from pasture

(mm) (t/ha) protein (kg/ha) (t/ha) (kg/ha)

Half seasonal mean 194 1.68 53 71 3100 56

70% seasonal mean 272 3.20 101 134 5050 91

25 year mean 388 5.56 176 234 7950 143

120% seasonal mean 504 7.78 246 327 10850 195

* Values are all based on adequate nutrition especially P

1. Growing season available water = 1/4 x January to April rainfall + May to November (inclusive)

2. Yield potential for wheat = growing season available water - 110 mm x 20 (French, 1991)

3. N required for grain yield of various protein levels = yield (t/ha) x wheat protein ÷ 5.7 x 20

4. Yield potential of subterranean clover = growing season available rainfall - 70 mm x 25

5. N addition from pasture = clover yield (kg DM) x 0.018 (Kleinig, 1974)

Although legume-only leys have been widely demonstrated to be beneficial to soil structure and other physical characteristics, there is general agreement that grasses, particularly ryegrass, have a more profound and longer lasting positive effect (Payne, 1988).

Disease Break

Farmers are now realising the importance of rotations with effective disease breaks that control take-all (Gaeumannomyces graminis var. tritici) to achieving high wheat yields. Paddock histories of the best district wheat crops over the past four years reveal that these top wheat paddocks always precede canola, a grain legume or a grass-free pasture. The importance of effective rotations was highlighted by Mead (1992). He concluded that:

"....the ideal crop rotation would involve spraying the grasses out of the pasture phase and growing canola....followed by wheat....".

The use of a grass-free pasture followed by canola ensures that there is an effective break to the take-all disease cycle. Work by Kidd et al. (1992) is helping to define the period free of host grasses that is necessary to minimise disease carry-over to the wheat crop in the following year. Preliminary results indicate that winter cleaning early in winter (June) is much more effective than late winter cleaning (late July) or spraytopping. However, the additional disease break provided by a year of canola, as suggested by Mead (1992), is likely to be even more effective.

Pastures and Weed Control

Good pastures that are dense with a high potential for growth will help suppress weeds in the pasture and, in turn, the ley/cropping system. Perennial pastures that are well adapted are more competitive against weeds than annual pastures and pastures which have a sown grass component are usually better than pure legume pastures. Pastures can also provide a unique opportunity for the control of specific weeds which are more difficult to control in-crop. For

example, silvergrass (Vulpia spp), Bromus spp and annual ryegrass (Lolium rigidum) can all be easily removed from a pasture by winter-cleaning.

With broadleaf weeds spray grazing is a cheap and effective in-pasture method for broadleaf control.

In addition, the pasture phase can help in managing the development of herbicide resistance. Fodder conservation, particularly silage making, is an efficient non-selective weed reduction practice. Such non-selective controls are the best way to slow the buildup of herbicide resistant plants.

When considering the use of the pasture ley in the management of herbicide resistance in annual ryegrass, thought should be given to the sowing of herbicide susceptible annual ryegrass. Annual ryegrass is a valuable forage species which will suppress the growth of the less desirable and harder to control annual grasses such as Vulpia spp and Bromus spp. However, you should ensure the seed that you buy is tested as herbicide susceptible. A random sample of annual ryegrass seed sold by seed merchants in NSW in 1992 found that 58% of all seed samples were resistant to one or more common grass herbicides (Pratley et al., 1993).

Stock Carrying Capacity and Water Use

Best district stocking rates from a legume ley pasture are about 16 DSE/ha from a lucerne/subclover mix pasture. This contrasts with a district average stocking rate on an annual grass/legume mix of about 8 DSE/ha. Those stocking rates should not be simply thought of as DSE per unit area but rather in terms of DSE in relation to the growth limiting resource (which cannot be controlled) water. From this viewpoint the previously mentioned stocking rates might be expressed as 35-70 mm average annual rainfall/DSE. When it is considered that plant growth is linearly and positively correlated to plant water use it can be quickly realised that plants that grow better and can carry more stock also use more water. Making sure that pastures use as much available water as possible is important, not only for ensuring large amounts of pasture growth but also to minimise the deep drainage of unused water and dissolved nutrients through the soil profile. This unused water is a major contributor to acidification, rising water tables and dryland salinity. A good pasture ley therefore is one where all rainfall is used for productive growth. Perennial pastures are better able to utilise rainfall throughout the season and thus on a yearly basis tend to be higher and more efficient users of water. They also minimise erosion risks and compete strongly with weeds. Good pasture leys thus have a role not only in increasing production but in minimising environmental problems.

High Quality Fodder

The role pasture leys play in providing feed for animals from pasture grazed in the paddock is well documented. What, however, is less well appreciated is how valuable and productive well made fodder (conserved from a pasture ley) can be. Table 2 provides some estimates of the common nutritional values of well made hay and silage and contrasts those with values for oaten grain.

Table 2. Some estimates of the value for animal producton of a legume pasture ley when conserved as fodder.

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Fodder type

Good clover/ Clover Oat

lucerne hay silage grain

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Energy value

(Mj/kg DM) 9.5 - 11 10 - 11 9.5 - 11.5

Protein % 15 - 18 17 - 21 8 - 10

Animal weight gain with ad lib. feeding

250 kg steer

(kg/hd/day) 0.7 - 1.0 0.8 - 1.1 0.6 - 0.8

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Note: From a good pasture conserved as silage (4 t/ha) you can produce up to 460 kg of beef/ha.

Acknowledgement: Dr Alan Kaiser, NSW Agriculture.

ROLE OF THE PASTURE LEY PAST AND PRESENT

From the preceding discussion it can be understood that the pasture ley plays an integral role in the management of the mixed farm. The nature of that role has in recent years become increasingly complex and varied. The changing perceptions of the pasture ley are summarised in Table 3. Most of the new emphasis is concerned with the role pastures can play in improving the farm environment and its surrounding agroecosystem.

Table 3. Changing perceptions of pasture leys

In the past	Now
Add nitrogen	Add nitrogen
Add organic matter	Add organic matter
Provide livestock feed	Provide livestock feed
Pasture hay opportunity	Pasture hay opportunity
	* Year round sink for water
	- reduces water tables
	- reduces salinity
	- reduces acidification
	* Effective disease break
	* Slow development of herbicide resistance
	* High quality fodder suitable for production feeding

PASTURE CHARACTERISTICS FOR THE IDEAL LEY PASTURE

Since the pasture needs to fulfil a variety of roles and at the same time fit comfortably into a complex rotational sequence, there are certain characteristics that a pasture should possess to maximise its usefulness. No species will satisfy all criteria but most commonly used species have sufficient attributes to make their use worthwhile. The ideal pasture-ley species mixture should:

be easy to establish under a cover crop;

fix large amounts of nitrogen;

improve soil structure;

be competitive with weeds;

be easy to manage;

persist for a minimum of 3 years;

yield well and have high water use;

be an effective year round sink for soil nitrates;

not host crop diseases;

be easy to kill prior to cropping; and

be deep rooting.

Some possible pasture species for inclusion in the pasture ley and their characteristics are summarised in Table 4.

SPECIES, VARIETIES AND STRATEGIES FOR MORE EFFECTIVE PASTURE LEYS

Use of Perennials

These should be considered for all pasture leys. Perennials have the potential to use rainfall in all seasons more fully than annuals. At Wagga Wagga, 40% of the annual rainfall on average falls in the summer semester (October to March), a time when most annuals have little capacity to grow.

In recent times there has been much discusison on the place of perennial grasses in mixed farming pasture leys. In favour of them are the benefits of having high yield potential, an ability to minimise the wastage of soil nitrates (thus minimising acidification (Cregan and Helyar, 1986) and the capacity to maintain pasture species stability with little weed invasion provided the pasture species are well adapted to the environment in which they are grown (Medd et al., 1987). Opposed to this are concerns about the impact on nitrogen fixation rates, the carryover of cereal diseases and, with Phalaris

(Phalaris aquatica), the ability of the farmer to kill the pasture at the end of the pasture phase. These are important considerations and require careful planning and management to overcome.

Where short-term leys are planned (3 years or less) the use of less persistent perennial species (with a life-span in this environment of 2-4 years) such as perennial ryegrass may have a useful role.

Where possible and practicable lucerne is a preferred species. Its benefits are well documented (Cregan, 1987). The only limitations to the success of this species in a pasture ley are acid soils and the need for rotational grazing management. In most situations both can be overcome.

The Use of Species and Varietal Mixtures

Compared to monocultures pasture mixtures offer more diversity in their ability to adapt to climatic and soil variations and pest and disease attacks. A blending of grasses and legumes provide the opportunity for higher yields and water use, more stable growth, a sink for excess nitrogen and less animal health problems. Within species, mixtures of varieties can help stabilise production and increase persistence. For example, with subterranean clover (Trifolium subterraneum), a three-way mix which (in addition to the standard variety for the district) includes a shorter season variety and a Yanninicum type (T.yanninicum) such as Trikkala will result in more consistent clover growth in areas that are subject to the occasional dry season and waterlogging. Table 4 shows the characteristics of some of the pasture species mixes.

NEW DEVELOPMENTS WITH KEY PASTURE SPECIES

Here we are not reviewing all new varieties of current pasture species but, rather, highlighting important developments in a few key species.

Subterranean Clover

This is still the most important pasture legume for pasture leys in south eastern Australia. Four new varieties have recently been registered and will become available over the next two years. Their important characteristics are summarised.

T. yanninicum - adapted to poorly drained soils and waterlogging, has a brown or creamy coloured seed.

Gosse (available 1994)

A mid-season variety suited to >650 mm average annual rainfall or irrigation until early November.

Higher yielding than Trikkala in late spring.

More hard seeded than Trikkala but generally a lower seed yield.

Better resistance to Phytophthora root rot than Trikkala.

Superior clover scorch tolerance to Trikkala

76Y51-31 (Riverina) (available 1997)

Developed as a replacement for Trikkala, it is similar in maturity and adaptation.

Phytophthora root rot resistance better than Trikkala and is the best of all current varieties.

Higher hard-seed levels than Trikkala.

Better winter growth than Trikkala.

Better seed production than Trikkala.

Better clover scorch tolerance than Trikkala.

T. subterraneum - most common type of subterranean clover, adapted to acid to slightly acid soils with fair to good drainage.

York (available 1996-97)

A Seaton Park alternative.

Better (30%) scorch tolerance.

More hard seed (2x).

Resistant to powdery mildew.

Susceptible to virulent strain of Phytophthora root rot.

Seaton Park LF (available 1994)

A selection of Seaton Park which has low formononetin and will not cause clover disease in sheep.

Better Phytophthora root rot resistance than Seaton Park.

Better tolerance to clover scorch.

For all subterranean clover types recent research has indicated that root disease caused by the fungus Phytophthora clandestina is an important and widespread limitation to successful growth and persistence (Dear et al., 1993; Taylor and Greenhalgh, 1987). The susceptibility to this disease is quantified in Figure 1 (Dear et al., 1994). These data can be used to help select suitable varieties for situations where root rots are known to be active.

Lucerne

There is much information which clearly demonstrates that the inclusion of lucerne in a pasture mix can increase animal production, on average about 10% for wool and 20-40% for meat (Cregan, 1987). The reason for this is simple - lucerne is a perennial which has the potential to grow over the summer/autumn when annuals produce little. Also over this period its feed is of higher digestibility than the dead residue of annual species. Remember, on the south west slopes about 40% of the rainfall falls during the summer semester (October to March) and lucerne can take full advantage of this rain. Experience indicates that lucerne is of particular benefit during drought when the rainfall often falls as summer storms. Also, due to its high growth potential, it can use large amounts of water (Lolicato and Cook, 1993) and has proven successful in lowering watertables and reducing induced salinity.

Figure 1. Cultivar susceptibility to Phytophthora clandestina.

Based on data from S. Flett.

Two new varieties of outstanding merit have recently been registered by NSW Agriculture. They are:

Aquarius A highly winter-active variety with exceptionally high resistance to Phytophthora root rot and high yield potential. It is best suited to flood irrigation and to heavy or poorly drained locations where lucerne can be grown. Aquarius is less suited to districts where crown rot is a major problem such as coastal and northern NSW and under sprinkler irrigation.

Gemini A winter-active variety with high levels of pest and disease resistance and generally superior persistence in a wide range of environments.

Phalaris

Holdfast This variety is similar to Sirosa but has the added advantages of being more tolerant to acid soils and having higher seed yields.

CONCLUSION

The nature of dryland pasture-ley farming is changing in response to the need to increase productivity, to make farming more resilient and to maintain the resource base for future generations. Farmers need to be constantly monitoring the performance of their crops and pastures so they can make the necessary adjustments not only in the cropping component but to the pastures which are so important to the functioning of their farming system.

REFERENCES

1. Cornish, P.S. and Murray, G.M. (1989). Low rainfall rarely limits wheat yields in southern New South Wales. Australian Journal of Experimental Agriculture 29:77-83.

2. Cregan, P.D. and Helyar, K.R. (1986). Non-acidifying farming systems. Proceedings 15th Riverina Outlook Conference - Acid Soils Revisited. Riverina Institute of Higher Education, Wagga Wagga: 49-62.

3. Cregan, P.D. (1987). Lucerne agronomy - a review of important aspects. Proceedings 16th Riverina Outlook Conference - Realising the potential of pastures. Riverina-Murray Institute of Higher Education: 47-56.

4. Dear, B.S., Murray, G.M., Gregan, P.D. and Taylor, P.A. (1993). Comparison of the performance of subterranean clover cultivars in southern New South Wales. 2. Effects of Phytophthora clandestina and bromoxynil on seedling survival, growth and seed set. Australian Journal of Experimental Agriculture 33:591-596.

5. Dear, B.S., Murray, G.M. and Flett, S.P. (1994). Phytophthora root rot in subterranean clover. Agnote DPI 92, NSW Agriculture.

6. Ellington, A. (1986). Nitrogen inputs and utilisation in leguminous pasture: a review of recent Australian literature. Technical Report No. 128 (Victorian Department of Agriculture and Rural Affairs, Melbourne).

7. French, R.J. and Schultz, J.E. (1984). Water use of wheat in a Mediterranean-type environment. I. The relationship between yield, water use and climate. Australian Journal of Agricultural Research 35:743-764.

8. French, R.J. (1991). Monitoring the functioning of dryland farming systems. Chapter 17. In: Dryland Farming - A Systems Approach. Eds. V. Squires and P. Tow (Sydney University Press, South Melbourne).

9. Greenland, D.J. (1971). Changes in nitrogen status and physical condition of soils under pasture with special reference to the maintenance of the fertility of Australian soils use for growing wheat. Soil and Fertilizers 34:237-251.

10. Hamblin, A.P. and Kyneur, G.W. (1993). Is Australian wheat productivity under threat? Proceedings 7th Australian Agronomy Conference, Adelaide: 272-275.

11. Heenan, D.P. and Chan, K.Y. (1992). The long-term effects of rotation, tillage, and stubble management on soil mineral nitrogen supply to wheat. Australian Journal of Soil Research 30:977-988.

12. Hochman, Z., Osborne, G.J., Taylor, P.A. and Cullis, B. (1990). Factors contributing to reduced productivity of subterranean clover (Trifolium subterraneum L.) pastures on acid soils. Australian Journal of Agricultural Research 41:669-682.

13. Kidd, C.R., Leys, A.R., Pratley, J.E. and Murray, G.M. (1992). Controlling annual grasses to minimise the significance of take-all to following wheat crops. In: Rotations and Farming Systems. Eds. G.M. Murray and D.P. Heenan. (NSW Agriculture, Wagga Wagga).

14. Kleinig, C.R., Noble, J.C. and Rixon, A.J. (1974). Herbage production and the accumulation of soil N under irrigated pastures on the Riverine Plain. Australian Journal of Experimental Agriculture and Animal Husbandry 14:49-56.

15. Lolicato, S.J. and Cook. A.M. (1993). Potential water use of phalaris, cocksfoot, lucerne, and birdsfoot trefoil cultivars with varying seasonal growth patterns. Proceedings 7th Australian Agronomy Conference, Adelaide: 389.

16. Mead, J.A. (1992). Rotation systems and farming systems: the current situation. In: Rotations and Farming Systems. Eds. G.M. Murray and D.P. Heenan (NSW Agriculture, Wagga Wagga).

17. Medd, R.W., Kemp, D.R. and Auld, B.A. (1987). Management of weeds in perennial pastures. Chapter 12. In: "Temperate Pastures - their production, use and management". Eds. J.L. Wheeler, C.J. Pearson and G.E. Robards. (AWC/CSIRO, Melbourne).

18. Payne, D. (1988). Soil structure, tilth and mechanical behaviour. Chapter 12. In: Russell's Soil Conditions and Plant Growth. Ed. A. Wild (Longmans, Burnt Mill, Harlow).

19. Pratley, J.E., Ingrey, J.D. and Graham, R.J. (1993). Spread of herbicide resistance through seed retail outlets. Proceedings 7th Australian Agronomy Conference, Adelaide: 151-153.

20. Taylor, P.A. and Greenhalgh, F.C. (1987). Significance, causes and control of root rots of subterranean clover. Chapter 11, pp 149-151. In: "Temperate Pastures - their production, use and management". Eds. J.L. Wheeler, C.J. Pearson and G.E. Robards (AWC/CSIRO, Melbourne).

21. White, D.H., Elliot, B.R., Sharkey, M.J. and Reeves, T.G. (1978). Efficiency of land-use systems involving crops and pastures. Journal Australian Institute of Agricultural Science 44:21-27.

22. Whittaker, R.H. (1970). Communities and Ecosystems (Macmillan, London).

Table 4. The characteristics of possible pasture species and their suitability for including in pasture leys in southern NSW.

Species	Characteristics
	Potential summer growth	Ease of establishment	Acidity Tolerance	Carrying/ yield potential	Waterlogging tolerance	Persistence	Perennial or Annual	Ease of management	Competitive ability	Ease of removal prior to cropping
Lucerne	üüüü	üü	VS	üüüü	VS	üü	P	ü	üüü	üü
Phalaris	ü	üü	S	üüü	T	üüü	P	üü	üüüü	ü
Cocksfoot	üü	üüü	T	üüü	T	üü	P	üüü	üü	üü
Perennial ryegrass	üü	üüüü	T	üüü	T	ü	P	üüü	üü	üüü
Annual ryegrass	0	üüüü	T	üüü	T	üü	A	üüü	üü	üüü
Subclover	0	üüüü	T	üü	T	üüüü	A	üüüü	üü	üüüü
White clover	üüü	üü	T	ü	T	ü	P	üü	ü	üüüü
Balansa	0	üü	T	ü	VT	ü	A	üü	ü	üüü
Barrel medic	0	üüüü	VS	üü	VS	üüüü	A	üüü	üü	üüüü
(Murex)	0	üüüü	T	üüü (FYO)	VS	ü	A	üü	üüü	üüü
Danthonia	üü	üüü	T	üü	S	üüü	P	üüü	ü	üüü

Key:	0	=	none		üüüü	=	very high	VT	=	very tolerant
	ü	=	little		P	=	perennial	T	=	tolerant
	üü	=	moderate		A	=	annual	S	=	susceptible
	üüü	=	high		FYO	=	first year only	VS	=	very susceptible