Introduction

Lucerne (Medicago sativa) persists and produces well on the freely drained less acidic soils of southern New South Wales. Its use can result in consistent and substantial increases in animal production. In addition, lucerne can be an effective competitor with summer growing weeds and fixes nitrogen (N) for subsequent crops, in a ley - farming system. Sufficient technology is available for farmers to reliably establish and grow good lucerne pastures. The challenge is now the farmers: can they successfully use the potential?

Benefits Of Using Lucerne

Animal Production

The benefits of lucerne or lucerne - based pastures have been exhaustively documented and are summarised in Table 1. Most of the increases in animal production are attributed to the additional quantity and quality of forage produced by lucerne during summer and autumn (Mulholland, 1987).

Table 1. Animal production increases obtained in experiments from animals grazing lucerne - based pastures when compared with non - lucerne pastures (FitzGerald et al., 1980)

Experiment	Livestock	Product	Increase from Lucerne (%) *
Canberra 1967/68	Lambs and	Wool (per fleece)	+10
	Weaners	Lamb (growth per head)	+46
Wagga 1969/72	Ewes and	Wool	+10
	Lambs	Lamb growth	+43
Wagga 1969/73	Dry ewes	Wool	+12
Temora 1969/73	Ewes and	Wool	+21
	Lambs	Lamb growth	+15
Canberra 1972	Steers	Steer (growth per head)	+103
Canberra 1973/75	Steers	Steer (growth per head)	+9
Wagga 1975	Steers	Steer growth	+11
Wagga 1976		Steer growth	+128
Wagga 1977	Steers	Steer growth	+11

* In these experiments the production from animals grazing combinations of lucerne and subterranean clover or phalaris was compared with animals grazing subterranean clover with annual grass and/or phalaris.

Nitrogen Fixation

A healthy, well nodulated lucerne pasture is capable of converting soil - air nitrogen to plant available forms (nitrogen fixation). Data on the amount of N fixed by lucerne is scarce. However, that which is available (Wells, 1970 - from the Mallee in Western Victoria; and Holford, 1980 - in northern New South Wales) shows that in two contrasting environments annual N accretion is high and of importance to the nutrition of the following wheat crops. Wells (1970) found that wheat crops following lucerne were less responsive to added nitrogen than crops following either volunteer or medic pasture; the soil also had generally higher soil nitrate levels (0 - 15 cm) of 140 kg N/ha/yr for black soil and 110 kg NAla/yr for red soil. At a current value of $0.70/kg for bag N the purchase of a similar amount of N would cost $98 to $77. From the limited evidence available it appears likely that the N fixation from lucerne is greater than that from an annual legume pasture. Holford (1981) also suggests that the effects of lucerne on soil nitrogen may extend deeper into the soil profile than those from subclover.

Weed Control

Once established, lucerne competes strongly for light and water. This competitive ability and its perennial growth with a summer peak in production potential makes lucerne a successful competitor with many problem weeds, e.g. skeleton weed (Chondrilla juncea) (Cuthbertson, 1967; Wells, 1969), variegated thistle (Heliotropium europaeum) (Noble, 1970). Lucerne is particularly effective in controlling summer growing weeds that are often difficult to control in annual pastures, particularly in years with significant summer rain.

Lucerne Varieties

Prior to 1977 when the spotted alfalfa aphid (SAA) (Therioaphis trifolii f. macutala (Monell)) and the blue - green aphid (BGA) (Acyrthosiphon kondoi Shinji) were first detected on Australian lucerne stands, there was one main variety grown in Australia: Hunter River. In response to these pests, which initially caused severe losses, many varieties were imported from NorthAmerica. From 1979 onwards new Australian - bred varieties were also released. With these new varieties came a wide range of different agronomic characteristics. Choices could now be made between varieties with contrasting seasonal growth patterns, insect resistance and disease resistance.

However, little was known of the performance of these varieties under Australian conditions, particularly their reaction to grazing. An initial study (1977 - 1981) by Brownlee et al. (1984) showed that many of the imported varieties performed well in contrast to Hunter River. Where SAA was active or phytophthora root rot (PRR) (Phytophthora megasperma) was present, the performance of Hunter River, which is susceptible to both of these pests, was often poor. These situations were most common where lucerne was irrigated. Varietal evaluations with more recently released lines show that varieties have improved over the past 10 years

(W. McDonald, pers. comm.), although choosing a variety for best performance is a matter of matching the variety with the intended use of the paddock and the pest and disease spectrum that is known, or likely to exist within the paddock (McDonald et al., 1987). In addition, in New South Wales environments, the pronounced winter dormancy of many of the North American varieties is not required and the presence of dormancy (LAWG classes <5) severely restricts yield potential. Most of the advances that have been made in lucerne variety development over the past 10 years have been related to improved insect and disease resistance. (Table 2).

Table 2 Characteristics of some lucerne varieties. (Adapted from McDonald et al., 1987)

Variety	Origin	Year Released	Pest Resistance
			LAWG+	SAA	BGA	PRR	CCR
Hunter River	NSW	naturalised	5	5	5	5	5
		early G19
Falkiner	NSW	1976	5	LR	S	MR	S
Nova	NSW	1979	5	HR	S	MR	S
Hunterfield	SA	1983	6	HR	LR	S	S
Aurora	NSW	1986	6	HR	MR	R	MR
Trifecta	QId	1983	7	MR	LR	MR	R
Siriver	NSW	1980	9	HR	MR	S	S
Guf	USA	1977	9	HR	LR	MR	S
Sequel	Qld	1985	9	R	LR	MR	R

Pest disease resistance ratings:

HR Highly resistant - most plants will be unaffected by a severe attack.

R Resistant - light damage will occur under a severe attack but there will be little effect on the long - term performance.

MR Moderate resistance - moderate damage will occur under severe attack but with satisfactory long - term performance.

LR Low resistance - heavy damage will occur under severe attack which may affect long - term performance.

S Susceptible - heavy damage will occur under moderate attack and long - term performance will be affected.

LAWG Late autumn winter growth: 2 = very slow; 6 = moderate; 9 = very active

However, where insect and disease factors have not appeared to be major limitations to production, data from the Southwest Slopes of NSW indicate that the long - term persistence of the Australian - derived variety Falkiner is superior to the North American varieties introduced in 1977 (Table 3). These data contrast with that of Brownlee et al. (1984) where short - term evaluations indicated that there was generally no difference in the rate of density decline between varieties.

Table 3. Changes in plant density of lucerne varieties at Teinora, 1978 - 1986 (P. Cregan and L. Jenkins, unpublished data).

Variety	Plant Density (Plants /M )
	1978	1981*	1985	1986
Falkiner	70	25	9	9
Hunter River	73	27	8	6
Pioneer brand 581	70	22	6	6
WL318	54	25	6	5
Pioneer brand 572	99	27	4	3
Cuf 101	83	17	6	2

* 1981 results are reported in Brownlee et al., 1984

Note: In a similar experiment sown at Wagga Wagga in 1977 the persistence of Falkiner and Hunter River is superior to other varieties (P. Cregan and B. Scott, unpublished data).

The reasons for the superior long - term persistence of Falkiner at these sites is not known and is currently being investigated. At the Wagga Wagga site in 1987 Phomopsis spp. fungi were associated with the death of many plants (G. Stouold, pers. comm.). However, this is only one of many factors that may be of importance.

Long - term evaluations are very time - consuming and most of the varieties are obsolete at the completion of the evaluation. Thus their usefulness is confined to better defining the factors affecting long - term survival and identifying the germplasm that contains the desired characteristics. For example, the variety Falkiner may be a parent that confers attributes for persistence under grazing in southern New South Wales. The recently released variety Aurora has Falkiner as its major parent (72.5% of parentage) thus its persistence will be of considerable interest.

Grazing Management And Establishment

Farmer success with the use of lucerne is strongly dependent upon being able to establish it reliably and then upon its management. These two aspects of establishment are considered in detail. Regardless of how good the variety is, production will be low unless the establishment and management are adequate.

Grazing Management

Unlike most other sown temperate pasture species used in southern Australia lucerne will not persist when set stocked with sheep. A high rate of set stocking will result in an accelerated decline in plant density. Southwood and Robards (1975) found that with set stocking at a high rate (10 Merino ewes/ha), lucerne plants survived only four months whereas at a low stocking rate (5 Merino ewes/ha) a density comparable with rotationally grazed paddocks persisted for three years, until an extended period of moisture stress occurred. In addition, high stocking rates generally increase the rate of lucerne plant density decline.

Similar results have been achieved in northern New South Wales (Peart, 1968; Thompson et al., 1976), central New South Wales (Brownlee, 1973) and in South Australia (Smith, 1970).

The duration of the grazing/spelling periods can also influence persistence. Generally the grazing period (when grazing to ground level) should not exceed about 21 days while the regrowth time needs to be about 42 days. These constraints have led to the development of a three paddock rotational system for the higher rainfall area, i.e. three weeks grazing is followed by a six weeks rest. Such a system is practical and easy to manage and requires little additional fencing. For the drier environments (less than 500 mm average annual rainfall) a shorter grazing period is required for the survival of lucerne plants (Peart, 1968; Smith, 1970; Southwood and Robards, 1975). In these areas a grazing period as short as one week, i.e. a seven paddock system, may be necessary if long - term persistence is required.

For new stands, grazing can start once the plants first reach flowering, but the duration of grazing in the first season should be no longer than one week.

Stocking rates are best regulated to ensure that all top growth, including stems, is removed by the end of the grazing period. Regrowth from the crown of the plant is superior to that from old stems (Sheridan, 1964). However, damage to the crown from over - grazing should be avoided as it reduces regrowth and allows the entry of crown rot diseases.

Establishment

Lucerne establishment failure is common and is caused by the same range of factors that affect pasture establishment generally. However, lucerne is much more susceptible to soil acidity than other pastures sown in the high rainfall (>500 mm average annual rainfall) zone. Lucerne is also a perennial with little ability to increase its density with time, therefore a failure to obtain sufficient density in the year of establishment results in a stand with a lower production potential for the life of the stand.

Soil Acidity

Both the lucerne plant and its Rhizobium are highly susceptible to acid soil factors, particularly aluminium toxicity. Lucerne cannot be grown successfully where the whole soil profile has a pH* of.<5.0.

However, many apparently lower pH soils can grow lucerne successfully. These are soils where the surface (top 10 cm) is of low pH but this acid layer overlies soil of higher pH. On soils where only the surface is of low pH the plant initially grows very slowly and can be severely stressed, but once the roots extend to the higher pH of the subsurface soil growth quickens.Provided adequate moisture is available, the plant loses its stressed, unhealthy, often nitrogen deficient symptoms, and grows vigorously.

* pH in 0.01 in CaCl₂ (1:5)

Low surface soil pH can be an important limitation to establishment when the plant experiences moisture stress. The young plant with a slow growing and poorly developed root system may not be capable of extracting sufficient moisture from the soil to survive. Such moisture stresses often occur when the lucerne plant is subjected to competition from a cover crop or weeds.

The problems of surface soil acidity can be overcome by the use of lime incorporated into the soil. Sufficient lime should be applied to ensure that the soil pH does not fall below pH 5.5 during the life of the lucerne stand.

Farmers considering sowing lucerne must have their soil tested for pH prior to sowing. Soil samples to be tested should be taken from the surface (0 - 10 cm) and from deeper down the profile (30 - 40 cm). If the deeper soil sample is less than pH 5.5 the soil is not suitable for growing lucerne as the effects of the lime (raising pH) are mainly confined to the depth of soil to which the lime has been incorporated. Alteration of pH down the profile following liming is extremely slow (Bromfield et al., 1987).

Sowing Depth

Like many pasture seeds, lucerne seeds are small (approximately 450,000 seeds/kg) and are incapable of emerging well from depths greater than 15 mm, particularly in heavy soils (Sund et al., 1966) (Table 4). Sowing should therefore be aimed at placing the seed near the surface (5 - 15 mm) on a firm moist base. Unfortunately, most commonly used sowing equipment is poorly suited to sowing pastures and modifications are necessary to ensure the correct placement (Allen, 1987; Gollasch, 1987).

Table 4. Effect of sowing depth on % emergence of lucerne (Sund et al., 1966)

Depth	Sand	Loam	Clay
(cm)
1.25	71	59	52
2.50	73	55	48
3.75	55	31	28
5.00	40	16	13

Cover Crops

Undersowing cereal crops with lucerne is a common practice in the wheat/ sheep belt. Unfortunately, these so - called cover crops compete strongly for moisture and light and frequently result in establishment failure (Table 5). The effect of cover crops is the same as that of weeds;

they both provide severe competition. The only difference is that the cover crop grain is saleable. Undersown lucerne usually emerges and grows satisfactorily until mid/late spring when the cover crop, particularly if conditions are dry, has priority use of available water because of its larger and stronger root system. From this time onwards, unless there is unseasonal summer rain, e.g. as in 1983, the young lucerne seedling becomes progressively more moisture stressed and dies before the season breaks in the following autumn. Generally the greater the dry matter production of the crop the greater the water use and light competition and the poorer the lucerne survival. If cover crops are to be used successfully, practices must be adopted to reduce competition to a level that the lucerne plant can tolerate; that is, a compromise needs to be reached. Two approaches can be followed, and often both need to be combined for best results. Firstly, a less competitive cover crop can be used. Cover crops can be ranked in order of competitiveness: oats > wheat/triticale > barley > linseed. Secondly, the sowing rate can be reduced (Table 5).

Table 5. The effect of sowing rate of wheat on the establishment of lucerne (Cregan, 1985)

Location/Yr	Wheat Variety	Sowing Rate (Kg/Ha)	Lucerne Establishment (Plants/in2)
Junee Reefs 1980	Egret	nil	22
		6	16
		11	16
		17	11
		22	11
		28	5
Ardlethan 1979	Condor	nil	22
		25	3.5
		45	0.3
		70	nil

Other Factors

There are many influences that determine the success of lucerne establishment and these are summarised in Table 6. For a farmer to maximise his chance of establishing lucerne he needs to pay attention to every detail. The task of successfully establishing lucerne is a much more difficult and demanding one than growing a cereal crop or a subclover (Trifolium subterraneum) pasture. However, by understanding the problems, planning ahead, adopting the necessary practices then regularly monitoring the growth of the young pasture, reliable establishment can be achieved.

Table 6. Lucerne Establishment Checklist

Check	Action
Rainfall	Limit of 350 mm average annual rainfall in southern NSW to 400 mm in northern NSW
Soil suitability
- acidity	Subsoil pH <5.0 is not suitable for lucerne; use some other species. Surface pH <5.0 - lime to pH 5.5.
- drainage	Poorly drained soils are not suitable for lucerne.
Variety	Consider growth pattern and resistance to diseases and insects
Seed quality	Use certified seed with a high germination level. If germination level is low or the level of hard seed is high, adjust sowing rates.
Inoculation	Routine for all new paddocks. Use group A inoculum.
Fertiliser	Test soil, apply adequate phosphorus. Assess the need for molybdenum.
Sowing time	With cover crop, sow early. Without cover crop, sow April to September but for spring sowings the soil profile should have adequate moisture. Avoid mid - winter sowings on tablelands.
Sowing depth	0 to 15 mm on a firm base. Use furrow sowing for dry environments and where the moisture is below the surface.
Insects	Earth mites: control as soon as observed on young seedlings. Cover crops If cover crops are used, reduce sowing rate.
Weed control	1. Use trifluralin before sowing to control grasses and some broadleaf weeds.
	2. Post - emergence - 2,4 ID - B or bromoxynil useful for broadleaf weed control.
Early management	Start rotational grazing/cutting when plants first flower. Graze leniently during establishment year.

References

1. Allen, P. (1987). A lucerne farmer’s viewpoint. Proceedings 16th Riverina Outlook Conference, Wagga Wagga.

2. Bromfield, S.M., Cumming, R.W., David, D.J. and Williams, C.H. (1987). Long - term effects of incorporated lime and topdressed lime on the pH in the surface and subsurface of pasture soils. Australian Journal of Experimental Agriculture 27:533 - 538.

3. Brownlee, H. (1973). Effects of four grazing management systems on the production and persistence of dryland lucerne in Central Western NSW. Australian Journal of Experimental Agriculture and Animal Husbandry 17:259.

4. Brownlee, H., Cregan, P.D., Lodge, G.M. and Munson, R.D.. (1984). The evaluation of aphid - resistant lucerne varieties in New South Wales 1977 - 81. Technical Bulletin 29 (Department of Agriculture, New South Wales).

5. Cregan, P.D.(1985). Managing the seedling for establishment. Proceedings Grasslands Society of Victoria 26th Annual Conference: 4 1 - 46.

6. FitzGerald, R.D., Simmons, K.V. and Southwood, O.R. (1980). Lucerne. Division of Plant Industry Bulletin (Department of Agriculture, New South Wales).

7. Gollasch, P. (1987). Pasture management - a farmer viewpoint. Proceedings l6th Riverina Outlook Conference, Wagga Wagga.

8. Holford, I.C.R. (1981). Changes in nitrogen and organic carbon of wheat - growing soils after various periods of grazed lucerne, extended fallowing and continuous wheat. Australian Journal of Agricultural Research 19:239 - 249.

9. McDonald, W.J., Waterhouse, D.B., Read, J.W. and Falconer, G.W. (1987). Lucerne varieties 1987 Agfact (Department of Agriculture, New South Wales).

10. Michael, P.W. (1968).Perennial and annual pasture species in the control of Silybum marianum. Australian Journal of Experimental Agriculture and Animal Husbandry 8:101.

11. Mulholland, J.G. (1987). Animal production from lucerne - based pastures. Proceedings 16th Riverina Outlook Conference, Wagga Wagga.

12. Noble, J.C. (1970). Competition between Heliotropium and dryland lucerne. Proceedings Australian Weeds Conference, Hobart.

13. Peart, G.R. (1968). A comparison of rotational grazing and set stocking of dryland lucerne. Proceedings Australian Society of Animal Production 7:110.

14. Sheridan, K.P.(1964). Management of lucerne. Agricultural Gazette of New South Wales 75:751 - 753.

15. Smith, M.V. (1970). Effects of stocking rate and grazing management on the persistence and production of dryland lucerne on deep sands. Proceedings 11th International Grasslands Congress, Surfers Paradise: 624.

16. Southwood, O.R. and Robards, G.E. (1975). Lucerne persistence and the productivity of ewes and lambs grazed at two stocking rates within different management systems. Australian Journal of Experimental Agriculture and Animal Husbandry 15:747 - 752.

17. Sund, J.M., Barrington, G.P. and Scholl, J.M. (1968). Methods and depths of sowing grasses and legumes. Proceedings 10th International Grassland Congress, Helsinki: 319.

18. Wells, G.J. (1969). Skeleton weed (Chondrilla juncea) in the Victorian Mallee. 1. Competition with legumes. Australian Journal of Experimental Agriculture and Animal Husbandry 9:521.

19. Wells, G.J. (1970). Skeleton weed (Chondrilla juncea) in the Victorian Mallee. 2. Effect of legumes on soil fertility, subsequent wheat crop and weed population. Australian Journal of Experimental Agriculture and Animal Husbandry 10:622.