M.F. Quirk
Introduction
Suitable Sites for Leucaena
Agronomy of Leucaena
Grazing Systems and Cattle Production
Commercial Adoption of Leucaena
References
The tree legume, leucaena (Leucaena leucocephala cv. Peru) initially attracted attention in the Burnett region in the 1960s. Its major attraction was its ability to persist on the clay soils of the region. Prior to leucaena, lucerne (Medicago sativa) was the only suitable legume for clay soils, but it rarely persisted for more than 3-5 years. Subsequent experiments confirmed the high beef production potential from leucaena-based pastures. Seed treatment, establishment methods, weed control, planting density, fertiliser requirements, grazing management and cattle production were all studied in subsequent experiments at the Brian Pastures Research Station. The synthesis of this work into possible production systems for the Burnett region will be described in this section. Problems encountered in the transfer of this technology to commercial enterprises will also be discussed.
The inland Burnett (latitude 26°S) is not an ideal environment for growing leucaena. Soil moisture is often limiting during the growing season as the mean annual rainfall of 700 mm is quite variable. Cold temperatures prevent growth from April to September, frosts cause leaf-drop and most soils are shallow and infertile. Hence, good site selection is crucial for successful leucaena production in this environment.
Availability of soil moisture is the major determinant of leucaena growth. Hence, growth is markedly influenced by soil characteristics, especially the water holding capacity and depth of rooting. Cooksley et al. (1988) found that production of edible leucaena was much greater on deep, fertile alluvial/colluvial plains than on shallower soils located on low to medium slopes (Table 7.4.1). This occurred despite the greater frost damage to leucaena plants on the plain, suggesting that in such situations, the advantages of a deep and fertile soil outweigh the disadvantage of frosting.
Table 7.4.1. Effect of soil type on growth and height of leucaena at Brian Pastures (from Cooksley et al. 1988).
|
|
Alluvium |
Colluvium |
Andesite |
Basalt |
|
Growth (including leaf fall) (kg/ha) |
1,515 |
2,375 |
1,215 |
1,145 |
|
Height (cm) |
165 |
235 |
155 |
145 |
For sites where leucaena grows well (1,500 - 3,000 kg edible material/ ha/year), leucaena-based pastures are likely to give much higher and more persistent benefits to cattle growth than other pasture improvement options. However, on sites of lower growth potential, leucaena-based pastures may not give greater benefits than other development options (e.g. sowing stylos). As sowing leucaena is usually more risky and more costly than other development options, using leucaena on such sites is unlikely to confer advantage. Thus, for the Burnett region, only fertile soils with good drainage and at least 60 cm in depth, are considered suitable for leucaena.
Reliable and rapid establishment of legumes in the inland Burnett is often difficult due to the unreliability of summer rainfall. With leucaena, good sowing methods are even more crucial than for other legumes, for two reasons. Firstly, leucaena seedlings are slow-growing, making them susceptible to both moisture stress and weed competition. For example, Cooksley (1981) found that vigorous weed competition reduced the growth of leucaena seedlings by 87% in the first 40 days after emergence. Clearly, such slow growth will greatly increase the time before leucaena is able to provide useful grazing.
Secondly, the early productivity of leucaena in this environment is dependent on achieving an adequate plant population in the first year. Improvement in the population of mature leucaena plants with time may occur but will be slow.
Essential practices
To help overcome these problems special emphasis should be placed on the following:
· seedbed preparation,
· storage of soil moisture prior to sowing,
· seed scarification and inoculation,
· fertiliser use (N,P),
· weed control, and
· control of marsupials, rabbits and hares.
Given attention to the above, leucaena can be expected to reach a height of 0.5-1.5 m at the end of the first growing season.
Plant density and row spacing
As with any crop, yield of leucaena per hectare increases with plant density. Cooksley and Goward (1988) found that leucaena yield increased from 640 kg/ha at 6,000 plants/ha, to 2,260 kg/ha at 62,500 plants/ha. In practice, leucaena is grown in rows, with a distance between rows of at least 3 m. This facilitates cultural practices such as fertilising, sowing and weed control. When grown in rows 3 m apart, plant populations stabilise at around 10,000 plants/ha (3-4 plants/m of row) (Addison et al. 1984).
Varieties
The cultivars Peru and Cunningham are used in the region although there is little difference in yield of edible material between the two (Cooksley 1979). However, Cunningham flowers 1 month later than Peru, which may limit its seed production in years with early frosts.
Fertiliser requirements
Leucaena is considered only for the higher fertility soils in the Burnett. Hence, maintenance fertiliser is generally not required to maintain good production (Cooksley et al. 1984). Sulphur deficiency, however, has been detected in older stands of leucaena growing on clay soils (Prinsen et al. 1992). For example, from January to May 1990, leucaena yields increased from 450 to 1,100 kg/ha of edible herbage when it was fertilised with 15 kg S/ha.
Pests and diseases
Prior to the arrival of the leucaena psyllid in 1986, there were no major insect pests or disease problems on leucaena in Queensland. Minor pests include long soft scale (Coccus longclus), which lives on the stem, and Ithome larvae, which can reduce seed set. Leucaena plants in the Burnett are often covered by sooty mould growing on an exudate from the scale insects.
The effects of the leucaena psyllid in the Burnett have been far less dramatic than in more humid areas. Occasional outbreaks have occurred which may have reduced growth but it is not considered a major problem. Control would be considered only for young, establishing stands and for seed crops.
Using leucaena as a protein supplement for cattle grazing native pasture
In most paddocks of native pasture, only a portion of the total area may be suitable for leucaena. One option is to grow leucaena on the better soil, fence it off from the rest of the paddock and allow cattle access to it only when the native pasture is deficient in protein. The use of leucaena as a protein bank in this way formed the basis for all of the early work with leucaena in the region. As native pasture suffers its greatest protein deficiency in the cool dry season (April to October), most studies combined year-round grazing of native pasture with cool season grazing of leucaena.
Addison et al. (1984) grazed steers on paddocks with 25% of the area sown to leucaena (in rows 3 m apart) and the remainder as native pasture. The growth of these steers during autumn and winter was compared with those of steers grazing native pasture only, steers grazing native pasture and supplemented with protein meal (690 g/head/day of peanut meal) and steers grazing native pasture plus leucaena that were also supplemented with peanut meal. The leucaena was grazed rotationally (four plots, 1 week grazing, 3 weeks rest) in an attempt to ration the leucaena. Steers with access to leucaena were 57 kg heavier than steers on native pasture alone (Table 7.4.2). This response was better than the response obtained from feeding protein meal. When steers had access to both leucaena and protein meal, there was an additional response in weight gain, particularly during winter (Table 7.4.2). The autumn grazing depleted the amount of leucaena available in winter. As a result, steers with access to leucaena responded to additional dietary protein at this time. There was little or no compensatory gain during the subsequent spring-summer grazing. These results demonstrate the value of leucaena as a protein supplement for cattle grazing native pasture.
Table 7.4.2. Liveweight changes of weaner steers in autumn and winter when grazing native pasture only, and when grazing native pasture supplemented with either leucaena, peanut meal, or leucaena plus peanut meal (from Addison et al. 1984).
|
|
Liveweight change (kg/head) |
||
|
Autumn |
Winter |
Total |
|
|
Native pasture (NP) only |
-5 |
-23 |
-28 |
|
NP + leucaena |
27 |
2 |
29 |
|
NP + peanut meal |
16 |
6 |
22 |
|
NP + leucaena + peanut meal |
36 |
20 |
56 |
Foster and Blight (1982) compared weight gains from year-round grazing of native pasture with year-round grazing of native pasture combined with winter-spring grazing of leucaena. In the latter paddocks, leucaena pasture (rows 3 m apart) made up 25% of the area, and was divided into four blocks so that it could be rotationally grazed during the winter/spring. Cattle grazing the native pasture plus leucaena paddocks gained 226 kg/head from 9 to 30 months of age, compared with only 142 kg/head for cattle grazing only native pasture.
Mimosine toxicity
When leucaena was used for seasonal grazing with native pasture, there were rarely signs of mimosine toxicity. Apparently, the cattle were not eating enough leucaena to suffer any side-effects from either mimosine or its ruminal break-down product, 3-hydroxy-4(IH)-pyridone (DHP). This was confirmed when cattle dosed with DHP degrading rumen bacteria did not gain more weight than unclosed cattle when leucaena was used as a supplement (Quirk et al. 1988).
The emphasis in the early work in the Burnett was on integrating relatively small areas of leucaena with larger areas of native pasture. This gave a boost in growth rate of 20-40 kg/head/year to all the cattle in the paddock. However, another option is to use leucaena pasture by itself, since a good leucaena pasture produces 1,500-3,000 kg/ha of edible foliage and also 4,000-6,000 kg/ha of inter-row grass annually. How should leucaena be managed in such a role, and what productivity would it give? Also would this intensive grazing of leucaena lead to problems with mimosine toxicity?
A grazing trial was designed to assess the need for DHP degrading rumen bacteria when cattle grazed leucaena pasture only (Quirk et al. 1988). Steers were grazed on either native pasture (year-round), native pasture (year-round) with seasonal access to leucaena, or year-round on just leucaena pasture. Within each pasture type, there were paddocks grazed by cattle dosed with the DHP degrading bacteria and paddocks with unclosed cattle.
Results showed that dosing with bacteria had no effect on liveweight gain of steers grazing native pasture and leucaena together, but doubled weight gain in steers grazing leucaena-only pasture (Table 7.4.3). In the latter case, unclosed steers were consuming sufficient mimosine to cause a DHP-induced depression in serum thyroxine concentrations. However, with dosed steers, DHP was broken down in the rumen and serum thyroxine levels were normal.
Table 7.4.3. Average daily gains (kg/head) of unclosed and dosed (with DHP degrading bacteria) steers grazing either native pasture with seasonal access to leucaena pasture, or leucaena pasture only for the 0-6 and 6-19 week periods following treatment (from Quirk et al. 1988).
|
Treatment
|
Liveweight gain (kg/head/day) |
||
|
0-6 weeks |
6-19 weeks |
||
|
Native pasture + leucaena |
|||
|
|
Untreated steers |
0.95 |
0.62 |
|
|
Dosed steers |
0.80 |
0.63 |
|
Leucaena pasture |
|||
|
|
Untreated steers |
1.06 |
0.52 |
|
|
Dosed steers |
1.19 |
1.03 |
The annual production from the three pasture systems was also measured (Table 7.4.4) (Quirk et al. 1990). Steers on native pasture with access to a small area of leucaena gained an extra 37 kg/head/year, while steers grazing only leucaena pasture (same total area as other systems) gained twice as much weight as those on native pasture alone (205 versus 90 kg/head/year). Clearly, the more leucaena available, the better the liveweight gain, provided the DHP degrading bacteria are present.
Using leucaena to finish cattle for market
Notwithstanding the above results, year-round grazing of leucaena is not recommended in this region, as the trees need an opportunity to regrow. Best production is obtained when periods of intensive grazing are combined with periods of rest, the latter occurring when growing conditions are favourable.
Table 7.4.4. Seasonal and annual liveweight gains of steers grazing either native pasture, native pasture with seasonal access to leucaena, or leucaena pasture (from Quirk et al. 1990).
|
|
Liveweight change (kg/head) |
||||
|
Spring |
Summer |
Autumn |
Winter |
Annual |
|
|
Native pasture |
53 |
39 |
26 |
-27 |
90 |
|
Native pasture + leucaena |
73 |
34 |
42 |
-21 |
127 |
|
Leucaena pasture |
107 |
64 |
47 |
-11 |
205 |
This management system is now used on Brian Pastures to finish cattle for market. The leucaena pasture is used as a permanent forage crop. Leucaena pastures are not grazed for several months during the growing season, to allow accumulation of a large amount of foliage, and then grazed for short periods (about 80 days) by forward store steers (about 500 kg liveweight, 2.5 years old) during the late summer/autumn/early winter months. Stocking rates vary from 1.5 to 3 steers/ha, depending on the amount of leucaena pasture on offer. Steers gain weight quickly (0.75-1.3 kg/head/day) and most are then ready for sale (Table 7.4.5) at the end of the grazing period.
Which system is best?
The choice between using leucaena pasture in conjunction with native pasture and using leucaena pasture as the sole feed source will depend on the desired level of liveweight gain. For example, allowing breeding animals limited access to leucaena (i.e. using leucaena as a seasonal protein supplement) may give sufficient boost in liveweight to ensure high conception rates. On the other hand, quick finishing of sale cattle may require grazing solely on leucaena pasture.
There has been a very low level of adoption of leucaena by cattle producers in the Burnett. Lesleighter and Shelton (1986) found that the three major barriers to increased use of leucaena in Queensland were: low level of awareness, lack of information and high failure rate among leucaena growers. The latter problem appeared to be linked to the low level of use of essential cultural practices such as seed scarification and inoculation. The small size (<4 ha) of most first plantings would also have increased their vulnerability to damage by wildlife (e.g. marsupials, rabbits and ducks).
Table 7.4.5. Productivity of a 5 ha block of leucaena pasture used for finishing steers for market (J.D. Mullaly, unpublished data).
|
Period |
Number of steers |
Age of steers |
Length of grazing |
Average steer weight at start |
Stocking rate |
Average LWG |
No. sold off leucaena |
|
1987 summer/autumn |
15 |
2 |
146 |
428 |
2.6 |
0.73 |
7 |
|
1988 autumn/winter |
11 |
2 |
78 |
434 |
1.9 |
1.30 |
9 |
|
spring/summer |
7 |
2.6 |
82 |
525 |
1.5 |
0.74 |
7 |
|
1989 summer/autumn |
12 |
2.5 |
74 |
513 |
2.5 |
0.82 |
12 |
|
1990 autumn |
15 |
2.6 |
57 |
541 |
3.1 |
0.82 |
13 |
AE = animal equivalent = 400 kg liveweight
LWG = liveweight gain
Other factors which also limit the potential for leucaena pasture in the Burnett region are:
· Limited areas suitable for leucaena - i.e. sites with arable soils that are sufficiently deep and fertile to compensate for erratic summer rainfall and frost damage. Such sites are also open to other options e.g. cropping.· Unreliable and slow establishment - to overcome erratic summer rains and weed growth requires an intensive approach to establishment. Producers may not be able to afford or risk the costs associated with such development.
Despite these problems, leucaena remains an option for pasture development on some properties in the Burnett. The successful use of leucaena on Brian Pastures over the past 20 years provides good evidence of its potential.
Addison, K.B., Cameron, D.G. and Blight, G.W. (1984) Effect of leucaena and peanut meal supplements fed to steers grazing native pasture in subcoastal south-east Queensland. Tropical Grasslands 18, 121-130.
Cooksley, D.G. (1979) A field plant comparison of Leucaena leucocephala cv. Cunningham against cv. Peru at Brian Pastures, Gayndah. Queensland Department of Primary Industries Agriculture Branch Project Report, pp. 4-79.
Cooksley, D.G. (1981) Chemical control of weeds in seedling leucaena (Leucaena leucocephala) - post emergence applications. Queensland Journal of Agricultural and Animal Sciences 38, 110-115.
Cooksley, D.G. and Goward, E.A. (1988) Effect of plant density and spatial arrangements on the yield of Leucaena leucocephala cv. Peru in subcoastal south-eastern Queensland. Australian Journal of Experimental Agriculture 28, 577-585.
Cooksley, D.G., Paton, C.J. and Whitehouse, M.J. (1984) Response of Leucaena leucocephala to a range of fertilizers on "Brian Pastures". Queensland Department of Primary Industries, Bulletin Series QB84008, 15 pp.
Cooksley, D.G., Prinsen, J.H. and Paton, C.J. (1988) Leucaena leucocephala production in subcoastal, south-east Queensland. Tropical Grasslands 22, 21-26.
Foster, A.H. and Blight, G.W. (1982) Comparative use of the browse legume Leucaena leucocephala and urea-molasses to supplement beef cattle grazing native pasture in south-east Queensland. Proceedings of Australian Society of Animal Production 14, 285-288.
Lesleighter, L.C. and Shelton, H.M. (1986) Adoption of the shrub legume Leucaena leucocephala in central and south-east Queensland. Tropical Grasslands 20, 97-106.
Prinsen, J.H., Mullaly, J.D. and Robbins, G.B. (1992) Responses to fertilizer sulphur applied to old stands of leucaena. Tropical Grasslands 26, 25-29.
Quirk, M.F., Bushell, J.J., Jones, R.J., Megarrity, R.G. and Butler, K.L. (1988) Liveweight gains on leucaena and native grass pastures after dosing cattle with rumen bacteria capable of degrading DHP, a ruminal metabolite from leucaena. Journal of Agricultural Science (Cambridge) 111, 165-170.
Quirk, M.F., Paton, C.J. and Bushell, J.J. (1990) Increasing the amount of leucaena on offer gives faster growth rates of grazing cattle in south-east Queensland. Australian Journal of Experimental Agriculture 30, 51-54.
