Legumes for fodder crops and short-term pastures on clay soils in Queensland
There are a number of tropical legumes suited for planting on the more fertile, heavier clay soils, providing high quality forage. These soils, which have more water holding capacity than the light textured soils, will often have been used for cropping, and now be depleted in nitrogen and organic matter.
Legumes for grazing can be grown on these soils as fodder crops or short-term pastures between other crops (leys), or in permanent pasture, providing higher levels of protein for grazing stock.
Including legumes into pastures also provides long-term benefits by adding nitrogen to the soil. An example of the benefits was observed at Brian Pastures Research Station near Gayndah (Queensland), when sorghum was grown following lablab. Sorghum crop yields ranged from 3.5 to 5t/ha in the first crop after lablab, and were more than 3t/ha in the fourth crop following lablab. This compares with the district average of 2.3t/ha.
Annual fodder crops
Legumes as fodder (or forage) crops can be planted into cultivation each year in the same way as annual summer crops. The main summer legume fodder crops in south-east Queensland are the annual cowpeas and lablab.
Cowpea (Vigna unguiculata)
Easily established annual legume, produces high forage yields in a short growing season.
Cowpea is suited to a wider range of soils than lablab, including more acid soils. Grows well on clay soils provided they are well drained.
Unfortunately, cowpea is susceptible to root and stem rots. Red Caloona and Ebony varieties have some resistance to phytophthora stem rot.
Planting rates vary from 20 to 40kg/ha.
Lablab (Lablab purpureus, formerly known as Dolichos lablab)
Lablab has a longer growing season than cowpea, is more tolerant of frost, and very drought tolerant once established.
It can provide high quality forage for grazing over late summer, autumn and early winter. At stocking rates of 2 to 2.5 steers/ha (1 steer/acre), growth rates are consistently between 0.6 and 0.8 kg/head/day for 80 to 100 days grazing.
Lablab is less susceptible to root diseases than cowpea, and can be planted to a depth of 10 cm.
Forage varieties are Rongai, Highworth and Endurance. Rongai (white flowers, brown seeds) is a late flowering type with high forage yields. Highworth (purple flowers, larger black seeds) flowers earlier and produces similar forage yields. Endurance, a perennial variety (although its success as a perennial is variable), has a smaller seed than Highworth and can be planted at a lower rate (about 15 instead of 20 kg/ha).
Ley pastures or short-term pasture
As soil fertility declines on old crop lands, ley farming is being more widely considered. Ley pastures with a grass or legume mix are planted for two to four years in rotation with crop. The legumes used in these systems need to establish readily, grow quickly and produce high forage yields to maximise their forage value and the amount of nitrogen that can be returned to the soil. Two legumes being used in this capacity are burgundy bean and butterfly pea.
Burgundy bean (Macroptilium bracteatum)
Burgundy bean is a perennial species with a relatively large seed. It can regenerate from seed but rarely lasts for more than two to three years in a grazed pasture because it is so palatable.
It establishes easily in prepared seedbeds when planted at a depth of two to four centimetres and grows rapidly, producing high forage yields in the first year.
An advantage of burgundy bean is its ease of establishment. This allows for a rapid improvement in soil nitrogen which is highly desirable for a ley pasture.
Planting rates are 2–5 kg/ha.
Varieties, Cadarga (an erect form) and Juanita (lower growing but can be more persistent and less affected by bean mosaic virus), are usually sold as a composite.
Burgundy bean grows on a wider range of soils and is better adapted to cooler sub-tropical climates than butterfly pea.
Butterfly pea (Clitoria ternatea)
A strong perennial twining legume, butterfly pea is well suited to clay soils. It is identifiable by the flower colour, which ranges from white to dark blue.
Butterfly pea tolerates some water inundation but does not withstand prolonged waterlogging. It is also not suited to areas with severe or frequent frost but will recover from some frost by regrowing from the base or the woody stems.
Forage production is highest in summer and is limited when average daily temperatures drop below 15°C.
Large seed establishes easily when planted at depths to 5 cm. Planting rates of about 6 kg/ha on ley pastures will achieve a good plant density of 5–10 plants/m². Often producing higher yields in the second and subsequent years, after a good framework of woody stems has developed.
For butterfly pea to persist in pastures for many years, it must not be continuously grazed, as it will need to set seed. Seedling recruitment is sporadic but can be very successful under favourable weather conditions.
It is palatable at most stages of growth, although there have been some reports that it is not always well eaten.
Milgarra, the Australian cultivar, is a composite of six main lines and a number of minor lines.
Research comparing density changes between butterfly pea and burgundy bean over five years demonstrated the superior persistence of butterfly pea (see Table).
Table 1. Changes in legume density (plants/m2) of Milgarra butterfly pea and burgundy bean over four years at Brian Pastures Research Station, Gayndah
|Legume density (plants/m2)|
|Milgarra butterfly pea||13||9 (1)||8 (1)||7 (6)||12 (3)|
|Burgundy bean||18||12 (5)||8 (5)||1 (9)||6 (2)|
At Brian Pastures Research Station, growth rates (kg/head/day) of steers grazing burgundy bean were higher (0.55 kg/h/d) in the first year than for butterfly pea (0.4 kg/h/d), which was probably due to the higher amount of forage available. In subsequent years (1998–2002) growth rates were similar with a range of 0.5 to 0.65 kg/h/d.
Combined with grasses
These legumes can be used in pure legume swards. However, there are advantages in planting grasses with them, particularly if the grasses are not so aggressive in the establishment phase that they severely reduce legume forage yields. The grasses can take advantage of increased soil nitrogen and reduce the likelihood of weeds becoming dominant, especially in winter when the tropical legumes are not actively growing. Grasses also provide more forage for grazing and, because grasses degrade more slowly than legumes, the release of nitrogen to subsequent crops can be spread over a longer period.
Written by Bob Clem, formerly Queensland Government.