Lucerne is the main pasture legume used for dairy, prime lamb and beef production in subtropical southern Queensland. It makes a major contribution to the total quantity and quality of feed on offer to grazing animals. It is one of the most palatable legumes, has high crude protein, and high energy and protein digestibility. It is used frequently in irrigated grazing systems, predominantly to provide high quality forage for dairy cattle throughout the year.
Lucerne is also used in dryland grazing systems for growing and finishing beef cattle and prime lambs. In both grass/lucerne pastures and in swards, it can be managed to provide a more even supply of feed and a high quality protein supplement throughout the year. This is especially significant in the variable subtropical climate where the feed supply from grass pasture is erratic and its quality diminishes from mid-summer onwards.
In particular, some roles of lucerne in grazed pasture systems include:
• As a perennial sward, providing high protein feed all the year round. It is the most adapted and widely grown temperate legume in subtropical Queensland and will provide high quality, green forage after rain at any time of the year.
• As a protein supplement in both native and introduced tropical grass pastures which are productive in spring and early summer but whose feed value falls rapidly in the autumn - winter period. Lucerne will grow in both winter and summer and supplements the protein-deficient summer grasses in the colder months.
• As an alternative to forage sorghum and millet for summer feed. Lucerne provides less feed, but it holds its feed value better.
In dryland grazing systems, lucerne has two significant limitations:
• During extended dry periods, lucerne plants will cease growing and lose their leaves. Thus, additional feed in the form of grass, hay, silage or some other forage must be available to fill the feed gap during dry times. The losses associated with leaf drop can be minimised if hay is made from the forage that is in excess of the needs of stock at the stocking rate applied (see the section ‘Management’ below).
• Lucerne can cause bloat. This issue is dealt with in detail later in this chapter.
Dry matter production
Lucerne does not convert soil water into dry matter as efficiently as perennial grasses or annual forage crops. When given the same amount of water, lucerne will not produce as much feed as those crops. However, it produces dry matter of exceptional nutritive value throughout the year. Established lucerne plants also tap into subsoil water that is not available to shallower rooted pastures, and continue to produce dry matter from this source during the first season of growth.
The rainfall received, or the irrigation applied, determines the dry matter production. In the first season after sowing under dryland conditions, yields vary from about 3 t/ha in a dry season to 12 t/ha in a wetter season. These yields are usually less in the second and subsequent season, after lucerne has exhausted the soil water at depth in the profile. Under irrigation, lucerne can produce up to 25 t/ha. Not all of the dry matter produced is utilised by the grazing animal. Generally, between 40-500/0 is utilised, but this will vary, depending on the grazing system. As seen from the growth patterns outlined in Figure 1.1, at least 700/0 of this production occurs in the summer months.
Production varies between locations and cultivar activity types. The extremes in carrying capacity are presented in Table 9.1. These have been calculated for a highly winter-active lucerne in central Queensland and a winter-dormant lucerne in south-east Queensland, based on growth rates derived under irrigation (Figure 1.1).
Table 9.1 Monthly beef cattle carrying capacities
*Expressed in Adult Beef Cattle Equivalents (440 kg LW animal)/day. Feed consumption 10 kg/AE/day.
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