The scene is of Mount Dromedary across Horseshoe Bay, Bermagui, on the New South Wales South Coast
By Graham Andrews
This article was published in the science journal Australian Biologist Volume 11 Number 2, June 1998.
The overseas experience
No grass grows in the Atacama Desert in Chile. It is a desert covered with a salt crust up to one metre thick. The meagre rainfall, just a few millimetres a year, does not promote the growth of grasses anyway. Yet the carrying capacity of a part of the Atacama Desert is twenty sheep or goats per hectare (Felker 1981).
In that part of Chile, Prosopis tamarugo trees have been planted as a sole source of fodder for livestock, and these trees provide about six tonnes of leaves and pods per hectare each year. Holes about a metre or so across, and a couple of metres deep, are excavated through the salt crust for the trees. Despite the almost total absence of rain, the trees receive abundant water from the water table below the surface (Felker 1981, Felker et al. 1984).
In Peru, thousands of hectares of another species of prosopis, Prosopis juliflora, have been cultivated for livestock. On maturity, the trees provide six or seven tonnes of high protein pods per hectare in a year (Felker 1981).
And in Africa, trees have been used for centuries as a source of feed for animals. One which is valued is the acacia, Acacia albida. Acacias, being legumes, are able to convert, by means of rhizobium bacteria, atmospheric nitrogen into usable nitrates. These trees can thus grow on nitrogen-deficient soils.
The use of trees and shrubs as a source of feed for livestock is not new. Plato, in his Critias and Timaeus, cites
...there were also many other lofty cultivated trees which provided unlimited fodder for beasts.
Some countries have been using trees for livestock for centuries. Even in recent decades, South Africa has been developing trees of the species Prosopis and Gleditsia, with reported yields of edible beans of up to twenty tonnes per hectare per year, and also varieties of the Australian saltbush, Atriplex spp., to suit conditions there.
New Zealand scientists have researched the potential, and farmers there have adopted one or more of the varieties of trees or shrubs that are suitable for that country, for example tagasaste, saltbush and willow (MacFarlane 1985; Bell 1985; Sheppard 1985; Radcliffe 1985).
In England and parts of northern Europe, elms were used as a source of fodder until the mid-1800s. They formed an integral part of the farming system (Lamb 1979). The elm's large volume of canopy contains much needed proteins, carbohydrates and minerals sought by livestock.
Since Biblical times, the carob has been recognised as a source of food, mainly for humans, but it is well recognised in parts of the world as a source of fodder for animals. The pods of the carob, not the leaves, are consumed. And the habitat of the carob tree? It grows on rocky or stony outcrops, or clefts of rocks where no grasses could ever get a hold (Duke 1981).
The Australian experience
In Australia, in some parts of the semi-arid regions of the continent, there are vast tracts of chenopods-plants that grow in soil that is too infertile, and too saline to permit almost any other type of vegetation. Rainfall can be as little as 120 millimetres of winter fall per year, yet production there can be as high as several tonnes of dry matter per hectare. Nevertheless saltbushes can be grown over a wide range of climatic conditions, and on good soils.
Australia, it has sometimes been claimed, has an efficient agricultural system. But if this means converting forests to grazing lands for them to become vast erosion gullies, or converting grazing lands to irrigation fields then to become huge salt plains, then this is a recipe for disaster. Yet, this is what has happened with much of Australia. Grazing lands in most parts of the world have suffered in a similar way.
Each year, soils become less productive. Yet each year those depleted soils require more and more input of labour, and capital, and fertilisers, to maintain the production levels of previous years (Douglas & Hart 1978).
Agriculture is an ongoing process. Yields not only have to be maintained, they should, ideally, be increased, to provide food for our increasing population (Douglas & Hart 1978).
Are present-day livestock farming methods lucrative? Are large profits made from the land? Yes, they are - sometimes. But this depends on the input, and the rainfall, and soil fertility, and prices set for livestock, and numerous other factors. Sometimes it is because of good management and good luck.
The potential for agroforestry
Agroforestry is, in my opinion, the only alternative to pastures and grasses. It involves the use of fodder trees and shrubs - trees that are permanent, and which will replace annual grasses; trees which will provide their own nitrogenous fertilisers; trees which will extend their roots deep beneath the ground to the water table. Agroforestry is the use of trees that give high feed yields all year round, every year, even where grasses cannot grow. How many grasses (apart from those native grasses that grow only after heavy rains) prefer depleted, impoverished, deficient soils? Introduced pastures are dependent on a good reserve of water, minerals and nutrients in the soil, and the addition of fertilisers before they will grow (Douglas & Hart 1978).
The answer is not to eke out the most from every millimetre of rain, but to allow trees to tap the vast reserves of water deep below the surface. Many of the trees and shrubs that are suitable for fodder are far less affected by drought (Douglas & Hart 1978). The feed yield from fodder trees - even grown under adverse conditions and in poor soils - can match, and often exceed, that from pastures grown under good conditions (Lamb 1979). The potential of some of the semi-arid regions could match the productivity of many more fertile, moister land.
Australia has a range of indigenous trees and shrubs that are of value to livestock. Many of these are dry country species able to endure drought and saline soils, such as the chenopods (saltbush and bluebush). Acacias and casuarinas too are suitable for supplementary fodder (Oates & Clarke 1987).
The limitations of agroforestry
Is there a limit, then, to where trees for fodder can be grown? Perhaps not. Hill tops that cannot be ploughed or planted to grasses, can carry trees (Douglas & Hart 1978; Lamb 1979). Steep slopes that are unsuited to ploughing will grow trees. Low rainfall areas with annual, irregular rainfall of less than 200 millimetres per year can grow some of the chenopods, or carobs, which will yield several tonnes of dry matter per hectare every year. Unlike pastures, there are few limits for growing at least some species of trees or shrubs for fodder.
So why shouldn't countries like Australia make those barren soils productive within only a few years. And why shouldn't we provide a plentiful supply of fresh, highly nutritious and palatable feed for the animals, to take some of the burden out of farming?
Fodder trees can improve the output from existing properties and make them viable once again. Many of the trees that are planted as sources of fodder make ideal windbreaks; they modify the microclimates beneath their canopies; they reduce water loss from the soil, and reduce evaporation from nearby fields, and from dams; they reduce soil erosion; they lower the temperatures the animals must endure. Trees might cost a few dollars, but the increased profits to farmers might be thousands of dollars. Many can be propagated from seed, or from cuttings, a process which minimises establishment costs considerably (Felker 1978).
Fodder trees take from two or three years to about seven or eight years before they will provide sufficient high protein pods, seeds or foliage. It takes about the same time to improve pastures on moderately fertile soils.
Certainly, it may not be practical, nor wise, to plant thickets of fodder trees to the exclusion of all else on a paddock. Livestock will need a variety of feed. Tagasaste, for example, although high in protein, is low in carbohydrate (Oates and Clarke 1987).
The ideal fodder tree
Criteria should apply to those trees that will replace pastures, so a comparison of their worth can be evaluated (Felker & Bandurski 1979). Trees and shrubs with potential should:
Some of the species that fulfill these minimum requirements include:
Tagasaste: Chamaecytisus proliferus
Carob: Ceratonia siliqua
Honey Locust: Gleditsia triacanthos
Willows: Salix spp, especially the weeping willow, Salix babylonica, and the hybrid Salix matsudana x alba
Poplars: Populus spp
Leucaena: Leucaena leucocephala
Chenopods: particularly Atriplex nummularia.
And of course, there are numerous native species that are edible, such as some of the acacias (Sheppard 1985), the brachychitons, cassias, the casuarinas and other chenopods. Minimum tillage livestock agriculture holds promise in Australia as well as the rest of the world as the future way livestock farming must go. Such measures are essential to prolong the life of livestock production, and of the soils themselves. Edible species of trees and shrubs will make the difference between survival and disaster, for the farm, the farmer, the farming community and the economy of the country.
The way ahead in Australia
An argument sometimes used for not planting trees for fodder is that the cost of seedlings is prohibitive. The cost of planting seedlings too is high. Anyone can find an argument not to do something. But tagasaste, for example, is grown from seed (Race 1993).
The same people who see no value in planting saltbushes should remember the use made last century and in the first half of this century by graziers who depended on such trees and shrubs. Has the New Zealand experience with tagasaste been a complete disappointment to the farmers who have taken the initiative and planted such trees? And have farmers forgotten their predecessors who, during times of drought, relied on the foliage from the cut branches of the introduced weeping willows growing along river banks to feed their stock? Oates and Clarke (1987) suggest that early settlers found that lopping the scrub for emergency feed was often all that kept them going during especially dry seasons. The green and fresh foliage of acacias, casuarinas, tamarisk, kurrajong and saltbush are well known examples from last century.
Did Plato get it wrong? Have the South African graziers got it all wrong? Looking at the overseas experience, it appears there is great potential in Australia for the use of fodder trees for livestock production. But ... where are the trees?
Race (1993) claims that the greatest potential value of tagasaste to agriculture lies in its ability to produce large amounts of leaf and stem that are palatable and nutritious as fodder for livestock. Another claim (Race 1993) is that tagasaste is not known to cause bloat.
Trials at the Ellinbank Dairy Research Institute in Victoria have shown that, under good conditions and in a good rainfall area, tagasaste can grow up to three times as much fodder as pasture on the same site (Race 1993). Because tagasaste can tap the water deep in the soil, the relative yield from tagasaste compared with pasture will generally be higher under low rainfall conditions. In trials in Western Australia, in deep sand and with 530 mm rainfall, tagasaste planted at 900 trees per hectare produced three tonnes of dry matter per hectare. This compared with less than one tonne per hectare from annual pasture.
Although there may be wild claims about the potential and yields from some fodder trees (Oates and Clarke 1987), there is no doubt that, because trees are deep rooting compared with grasses, they will tap minerals and water deep in the soil.
There is a small movement in Australia interested in the use of trees for fodder. That is encouraging. Perhaps another long drought will persuade more farmers that there is value in growing trees for livestock production. Or, perhaps it will convince even more graziers that, in the years following the current drought, and the next, and the next, that really, after such bad conditions on the land, there is no money to invest in this form of fodder.
Vital statistics of some important fodder trees and shrubs
Tagasaste: Chamaecytisus proliferus: Evergreen tree; fast growing under most conditions, reaches its full potential in three to four years. Long-lived species - expected life of about 50 years. Propagated from seed or from cutting. Mature trees are tolerant of frosts to -10 degrees C. Renowned for soil stabilisation work. Yield about 15 tonnes dry matter per hectare per year on one-third tree cover to two-thirds grass cover; recovers quickly from complete defoliation and heavy grazing. Legumes, producing their own nitrogen - ideal for impoverished soils, but require free-draining soils. Foliage contains about 23% protein (Davies 1982; Davies 1985; Rumball & Cooper 1985). Tagasaste has more productive potential than lucerne (Oates and Clarke 1987). As tagasaste roots more deeply than lucerne, it may have a greater tolerance to drought.
Carob: Ceratonia siliqua: Slow growing, producing pods in 5-8 years; long-lived, about 100 years. Grows in a variety of soils. This tree is a legume, but it is not known to fix nitrogen, although this is highly likely. Prefers hot, dry climate, but is suited to wide variety of climates. Prefers well-drained, deep soils, but quality is immaterial. Susceptible to more than 3-4 degrees C of frost. Propagated from grafted stock. Trees are dioecious. Require about 5% male trees for pollination. Trees need to be well spaced for best growth. Pods are consumed - seeds contain 21% protein; yield can be 400 kgs per tree or 50 tonnes of pods per hectare per year (Douglas & Hart 1978; Duke 1981).
Honey locust: Gleditsia triacanthos: Grown for high yield of pods. Tolerant of frosts. Pods contain 16% protein. Suited to drier and even semi-arid conditions, but rapid growth with 500 mm rainfall or more. Needs reasonable soils. Propagated from seeds or from suckers. Yields of 50 tonnes per hectare per year after five years have been reported (Lamb 1979).
Willows: Salix spp, especially the weeping willow, Salix babylonica, and the hybrid Salix matsudana x alba: Valued for their spring and summer foliage. Fast growing and long-lived. Propagated from cuttings, yielding copious foliage after two or three years; yields of 200 kgs per tree per year; foliage contains 17% protein. Willows coppice readily, even when cut right back. Trees are kept low, and grazed directly. Drought tolerant and frost resistant. Ideal for soil stabilisation work (Batten 1985; Douglas & Hart 1978; McLeod 1985).
Poplars: Populus spp: Grown under conditions similar to willows. Deciduous, providing foliage in spring and summer. Fast growing, maximum yield if kept well grazed and small, but trees should be well spaced. They can tolerate dry periods. Propagation from cuttings or suckers. Yields of five to seven tonnes dry matter per hectare per year on first cutting, second browsing should double this. Can be grazed within their first two or three years (Batten 1985).
Leucaena: Leucaena leucocephala: Tall shrubs, prolific growth in warm regions; sensitive to frosts. Tolerate wide variety of soils. Legumes, growing well in impoverished soils. Drought resistant, these grow in low rainfall areas, although an even rainfall of 100 mm per month provides best growth. Foliage contains 18% protein. Recovers rapidly from complete defoliation or heavy grazing. Yields of up to 50 tonnes per hectare per year can be expected under a variety of conditions. Propagated from seed or cuttings. Valuable in soil stabilisation work (Duke 1981; Felker & Bandurski 1979).
Varieties of Leucaena have been developed that do not contain the previously high levels of mimosine, a depilatory when fed in excess to cattle.
Saltbush: Atriplex nummularia: Able to survive conditions that prohibit the growth of most other plants, such as low rainfall, saline, and poor soils. Can be grazed in moderation, but not completely defoliated. Propagated from seed or cuttings. Foliage contains 22% protein; yields of three tonnes dry matter per hectare per year in semi-arid areas in low rainfall and poor soil, much higher yields under better conditions. Can be grazed within two to three years of establishment; very palatable (Douglas & Hart 1978).
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