Drought resistant fodder shrub crops in South Africa*

G.C. De Kock

Grootfontein College of Agriculture, Middleburg, Cape Province 5900, South Africa

1. Introduction

2. Requirements of a drought-resistant fodder crop

3. Spineless cactus

3.1. Introduction

3.2. Description of the crop

3.3. Establishment of spineless cactus

3.4. Spineless cactus cultivars

3.5. Reclamation and conservation of the veld

3.6. The establishment of spineless cactus under limited irrigation

3.7. The feeding value of spineless cactus

3.8. Utilization of spineless cactus as stock feed

3.9. The production of spineless cactus fruit

3.10. Control of insect pests of spineless cactus

4. Drought resistant shrubs

4.1. Introduction

4.2. Description of these crops

3. Climatic requirements

4. Soil requirements

5. Irrigation

6. Yield

7. The establishment of oldman saltbush

8. Establishment of Australian bluebush

9. The establishment of Australian creeping saltbush

10. Feed value

11. Grazing

12. Shrubs and spineless cactus in mixed stands

13. Reclamation of bare patches

14. American aloe

14.1. Introduction

14.2. Description of the crop

14.3. Establishment of American aloes

14.4. Feeding value and utilisation

14.5. Use as a reclamation crop

1. Introduction

Approximately ninety percent of the total area of the Republic of South Africa consists of natural pasture. Approximately sixty-five percent of this area is semi-arid. Owing to the inconsistency of the rainfall in this area moderate and severe droughts are the rule rather than the exception.

The South African stock industry regularly suffers exceptionally large losses as a result of a scarcity of food during droughts. There is thus a shortage of low cost fodder, especially during droughts.

The most important single factor limiting plant production in the Republic of South Africa is the lack of moisture. Increased plant production in these areas is thus coupled to factors which will either increase the amount of moisture or make better use of it. Irrigation water is limited in these areas and practical methods of increasing the rainfall are not available, with the result that the establishment of drought-resistant fodder crops, which make better use of the available moisture, remains the most important possibility.

Due to the low relative water requirements of spineless cactus (Opuntia spp.), oldman saltbush (Atriplex nummularia) and American aloe (Agave americana), as shown in Table 1, these crops are at present the most important drought-resistant fodder crops.

Table 1. The relative consumption of water by crops.

With the exception of the higher mountain areas where the minimum temperatures drop to lower than–12°C, rainfall is the most important limiting climatic factor in the establishment of drought-resistant fodder crops. The rainfall areas which can be regarded as drought-resistant fodder crop areas can be indicated on the map of the average annual rainfall of the Republic of South Africa as follows:

1. The 375 to 500 mm rainfall area can be regarded as the area where drought-resistant fodder crops are cultivated chiefly for fodder reserves in times of seasonal and catastrophic droughts, as the general dryland cultivation of the known fodder crops does not produce sufficient fodder.
2. The 250 to 375 mm rainfall areas are the natural drought-resistant crops areas. The main purpose in these areas must be to strive for higher production per unit of area by the improvement of the natural vegetation by means of planting drought-resistant fodder crops in the veld, or supplementing the veld with drought-resistant fodder crop plantations.
3. The 100 to 250 mm rainfall area is the area where, due to the limited amount of irrigation water available, preference should be given to the propagation of drought-resistant fodder crops under limited irrigation because of their better water irrigation.

The planting of drought-resistant fodder crops not only assures the building up of fodder reserves, but they can also be grazed annually, or in times of drought, and can play an important part in the conservation and improvement of the natural vegetation. After good rains, stock can be removed from the veld and maintained on these crops for a period of from four to six weeks. The veld is thus given a chance to recover and seedlings can become established before grazing recommences.

To achieve his purpose, it is desirable to establish paddocks of these crops in strategic places in the veld. If the soil is suitable, these plantations can be established to advantage near dams or other water sources in the veld.

The control of soil erosion, efficient grazing control and fodder conservation (the making of hay and silage where possible) contribute considerably to the strengthening of the farmer's position in times of drought, but the establishment of drought-resistant fodder crops is a very important factor that is often disregarded.

In the arid and semi-arid areas of the Republic the establishment of drought-resistant fodder crops should form an important part of the farming enterprise. There are various plants which can be used as drought-resistant fodder crops. The most important are spineless cactus (Opuntia spp.), drought-resistant shrubs, such as oldman saltbush (Atriplex nummularia), and American aloe (Agave americana).

2. Requirements of a drought-resistant fodder crop

b) Drought-resistant fodder crops must have a high carrying capacity.

c) It must be able to supply succulent fodder to animals during droughts.

d) It must not have an adverse effect on the health of the animals utilising it.

e) Severe utilisation must not have an adverse effect on the plants. In other words, the plants must have a high recovery ability after severe utilisation.

f) The establishment must have as few problems as possible.

g) The establishment and maintenance of the plantations must be economical. It must thus have a low initial cost.

h) The plants must be relatively not very fastidious regarding soil and climatic requirements. They must thus be adapted to a wide series of soil and climatic conditions, so that they can be planted where the cultivation of ordinary fodder crops is an uncertain undertaking.

3. Spineless cactus

3.1. Introduction

Spineless cacti have on occasions been referred to as "camels of the plant world", "Nature's fodder bank" and "Living fodder banks". These apt references to spineless cactus are also very descriptive of the crop.

Spineless cacti possess the exceptional characteristics of begin able to store large quantities of water in their succulent leaves in a relatively short period. A shower of rain measuring a few millimetres which would normally be of no value to the ordinary fodder crop, can be efficiently utilised by spineless cacti. This is made possible by their relatively shallow spreading root system and their ability to absorb water from the soil at a stage when other crops can no longer do so.

3.2. Description of the crop

The family Cactaceae is one of the newest plant families which possibly originated in the West Indian Islands. The spineless cactus and the prickly pear belong to the genus Opuntia. These cactus plants are indigenous to the Americas. They occur from Patagonia in South America to the Peace River in Canada. Some species even occur in tropical forests. The Optuntias are usually limited to the arid and semi-arid regions. Because of their different appearance these plants are spread over the whole world today. Due to the absence of their natural enemies, some species are problem weeds, for example, Opuntia aurantiaca (jointed cactus) in South Africa and Opuntia ficus-indica (prickly pear) in South Africa and Australia.

Table 1.2. A comparison between the fodder yield and the amount of digestible nutrients produced by spineless cactus, oldman saltbush and lucerne per unit of water (25 mm) received.

The spineless cactus is a recessive mutant of Opuntia ficusindica which is normally spiny. It is chiefly descended from selections from natural spineless populations and is also known as Burbank cactus as a result of the selection work which Luther Burbank, a well known plant breeder, carried out in North America. The spineless cacti which are planted as a fodder crop in South Africa, of which there are a few cultivars, have descended chiefly from the Burbank selections which were imported as fodder plants in about 1914.

The spineless cactus is a dicotyledonous perennial, with pads which are modified stems. The spines are modified leaves and are a good example of xerophytism. The plant is thus leafless. The pads are covered by a layer of wax and thick epidermis which limit evaporation. The stomata are sunken and close when the temperature or the light intensity rises; they are usually closed for the largest portion of the day.

Spineless cacti absorb water through their roots and combine it immediately with a hydrophilic mucus compound from which the water evaporates very slowly. This compound is stored in the fleshy mesophyll in the cells of the pads. Photosynthesis takes in a thin surface layer of cells in the pads or stems. The plants also possess a closed oxalic acid metabolism, due to respiration during the night and morning, the pad contents are acid and free acid is present in the plant. Photosynthesis takes place during the day with the consequent formation of carbohydrates which recombine with the acid, resulting in a reduction of the acid-content of the pad.

Spineless cacti form taproots, which anchor the plant, with a horizontal basal root system which spreads horizontally. These basal horizontal roots are fleshy, very shallow and appear just below the soil surface for water absorption. The surface of the root system is suberised to prevent dessication. A spineless cactus pad can lose as much as 60% of its total water-content before the cells collapse. The pads are well provided with a fibrous network of veins through which the movement of nutrients takes place. This fibrous network also serves as a mechanical reinforcement to stiffen the plant when it dries out or wilts.

The flower is round with bright coloured petals. The ovary is thick and fleshy and situated in a connate calyx with a large number of detached stamens with anthers on their tips. It is usually pollinated by insects and the stigma usually opens a few days after the flower opens.

Various polypoid forms occur. The normal blue-leafed cultivars which are propagated for fodder have 44 chromosomes per somatic cell while the green-leafed types which are propagated for fruit production have 88 chromosomes per somatic cell. The fruit contains a large number of seeds. The seed is hard-coated and because of cross-pollination and reversion (atavism) the seed is not used for the establishment of spineless cactus.

3.3. Establishment of spineless cactus

Although spineless cacti are reasonably resistant to cold and can withstand temperatures as low as–10°C, it is desirable to establish plantations when possible on the northern or northeastern slopes (in the southern hemisphere).

Spineless cacti do well on a variety of soils types, but for optimum growth and production it is better to plant them in good soil unless they are being used entirely for reclamation. Fertilisation is only necessary at planting time if the soil is low in phosphates and potash. These deficiencies can be supplemented with 50 to 100 kg, superphosphate and 50 to 100 kg potassium chloride per hectare. If the soil is poor in nitrogen 50 kg of ammonium sulphate per hectare can be applied. Fertilisation should be based on soil analyses.

The best planting time is spring: from September to October. The pads are well developed and ready to sprout at this stage and the plants should then be well established before the first frost and well able to withstand the winter. Only pads which are more than a year old are used for planting. The pads need not be allowed to wilt before planting. As soon as the wounds where they were cut off are healed (calloused) they can be planted.

When spineless cacti are to be established in areas which are predominantly grass-land, it is desirable to cultivate the soil with a plough or disc to eliminate the initial competition between the grass and the newly-established spineless cactus. 

There are various methods of planting the pads:

b) Pads can be planted on their edges in loose soil or against the side of a furrow made by a single furrow plough or a subsoiler. It is desirable to keep the point where the pad was cut off above the surface of the soil, as this is where fungi, which cause rotting, tend to enter the pad. With this method a strong plant is obtained and this plant also develops quicker. Rain is also utilised more efficiently as the water collects in the furrows and can be utilised by the plants. This method however requires more labour and than the first method.

c) The quickest growth and development is obtained when double pads are planted. Although more pads, time, and labour are required for this method, the plants are ready for utilisation much sooner.

The general spacing for spineless cactus established in plantations is in rows 3.0 to 4.5 m apart and the plants 1.5. m apart in the rows. The distance between the rows and also between the plants in the rows can however vary according to circumstances. In order to establish the largest possible number of pads per hectare the rows can be spaced alternatively, 3.0 and 1.5 m apart. The number of pads necessary for the different spacing are given in Table 3.1.

Table 3.1. The number of pads required for the different spacing of spineless cactus.

3.4. Spineless cactus cultivars

For fodder production a distinction can be made between the so-called blue-leafed cactus and the green-leafed cactus. As far as possible only the blue-leafed types should be planted for fodder production. These blue-leafed types have the following advantages over the green-leafed types: they are resistant to cochineal; less susceptible to cactoblastis infection; more drought resistant. The disadvantages of the blue-leafed types are that they are less palatable and usually yield less than the green-leafed spineless cactus.

There are three recognised cultivars of the blue-leafed type namely, Robusta, Monterey and Chico. The cultivars Robusta and Monterey produce the highest yields while Chico is more cold resistant. Preference should be given to the cultivars Robusta and Monterey.

3.5. Reclamation and conservation of the veld

Spineless cactus is not only of value as a source of succulent fodder during droughts but can also be of use in the reclamation of bare patches and in the conservation of the veld. The ability of spineless cactus to grow even under extremely unfavourable conditions, makes it possible to establish these plants on bare patches in the veld, where they assist natural revegetation on these exposed areas.

As the natural grazing remains the most economical source of stock-feed, the farmer must do everything in his power to conserve and to improve this source. In this aspect spineless cactus can be of great value as a reserve fodder source for stock which can then be withdrawn from the veld after rain in order to allow the veld to recover.

3.6. The establishment of spineless cactus under limited irrigation

Spineless cactus only requires 267 kg of water to produce 1 kg of DM compared to lucerne the most important fodder crop in the arid regions, which requires 750 kg of water to produce 1 kg of DM. Lucerne thus requires nearly three times as much water as spineless cactus to produce 1 kg of DM. In terms of area and available water, three hectares of spineless cactus can be planted to every hectare of lucerne.

The question thus arises whether it would not be better for the stock farmer in the arid regions to use his limited supply of water to irrigate spineless cactus rather than to irrigate a small area of lucerne, insufficiently, with small amounts of water. It has been found that spineless cactus reacts exceptionally well to single irrigations during the summer months. The plants not only grow faster but the yield of succulent, fodder material is also considerably increased under limited irrigations.

Table 3.2. Increase in the production of green material of different spineless cactus cultivars over season

^a Plants too young

The yields in Table 3.3 were obtained from spineless cactus in rows. 2.7 m apart with a spacing of 1.2 m between the plants in the rows. The irrigation was applied to the rows by means of furrows. The material was harvested when the plants were three years old.

Table 3.3. The yield of spineless cactus under irrigation (1965/66 to 1967/68), 1820 plants per hectare

It appears that even one irrigation at the beginning of the growing season (September) increases, the yield noticeably, while two irrigations (September and November) more than doubled the yield of GM, and the DM produced was also almost doubled. Taking all factors into consideration it appears that two or three irrigations give the most efficient use of the irrigation water.

This data was obtained in an area with an average rainfall of only 178 mm per year. On rainfall alone a yield of nearly 25 tonnes of green material was obtained. Although spineless cacti are hardy it is thus obvious that they also require sufficient water for optimum production under normal veld conditions with a rainfall of from 250 to 300 mm per year; they can thus produce good yields of green succulent fodder without additional irrigation.

3.7. The feeding value of spineless cactus

A fresh spineless cactus pad contains approximately 90 percent moisture. The composition of the 10% DM is as follows:

Crude protein                                                         4%
Total digestible nutrients (TDN)                           65%
Calcium                                                                  1.4%
Phosphorus                                                            0.2%
Sodium                                                                   0.1%

A 35 kg sheep requires approximately 350 of total digestible nutrients to supply its energy needs for maintenance. Such a sheep would thus have to ingest 538 g of dry spineless cactus pads to obtain sufficient energy. This means that 5 to 6 kg of fresh spineless cactus must be ingested. However, a sheep only eats on an average 4 kg of fresh cactus leaves per day.

One reason why a sheep cannot ingest sufficient spineless cactus pads to supply its needs, is the high moisture content of the pads. It has been found that sheep fed on fresh, chaffed, spineless cactus pads hardly drink any water. Actually they take in more water from the cactus leaves than a sheep on a dry ration would normally drink. The high moisture content is thus the factor limiting the amount of cactus they can eat.

Although the high moisture content of the succulent spineless cactus pad has disadvantages, spineless cacti can be of inestimable value during dry periods when drinking water becomes scarce. The succulent pads can then serve as a source of drinking water for stock. Experiments have shown that sheep kept in pens can do without water for more than 500 days if they have daily access to sufficient quantities of spineless cactus.

It is also important to take the fact that spineless cacti are exceptionally low in crude protein into consideration. It is accepted that a ration for non-producing sheep should contain at least 7% crude protein. Spineless cacti only contain an average 4% crude protein. Rations with a low crude protein content are not usually ravished by sheep. A sheep with a mass of 35 kg requires approximately 50 g of crude protein per day. The 500 g of average dried spineless cactus which a sheep eats in a day only contains 20 g of crude protein. It is thus clear that spineless cacti must be supplemented with one or other form of protein. Other noticeable deficiencies of spineless cactus are the exceptionally low phosphorus and sodium contents.

It is thus clear that spineless cacti cannot be regarded as a balanced fodder crop. It should be regarded chiefly as a good, cheap, source of energy and be utilised as such.

3.8. Utilization of spineless cactus as stock feed

The method of utilization of spineless cactus will differ from farm to farm according to circumstances such as available labour, facilities, quantity of spineless cactus, etc.

It is best to utilize spineless cactus in rotation so that a plantation is utilized every three to five years. In this way a plantation can be chopped or grazed each time to the height of one pad higher than the original planting. When spineless cacti are utilized in this manner, the plants recover well, the material available for use is of good quality and the plants are kept within a usable size.

3.8.1. Grazing

The easiest way to utilize spineless cactus is by grazing. It requires very little labour and is thus also the cheapest method. Overgrazing of the plantation must, however, be guarded against. Young plants are especially susceptible to overgrazing and can be killed by sheep. Even older plants can be so badly damaged that the subsequent production will be considerably lower. The best method of grazing is to divide the plantation into small paddocks and to graze each of these intensively for a short period. Large losses may occur during grazing due to wastage, if great care and discipline is not exerted. Plants must also not be grazed during the first growing season.

3.8.2. Chaffing

A large intake, and thus better utilization, can be obtained by chaffing the pads. The ideal size of cubes is approximately 30 mm × 31) mm. It is in fact sufficient if the pads are chaffed in strips approximately 20 to 30 mm wide. In this form the material dries fairly quickly and wastage is reduced to a minimum. The method which requires the least time and labour is to chaff pads with a mobile chaff-cutter which is transported between the rows in the plantation, and spreads the chaffed material in strips between the rows where the sheep pick it up. To limit wastage to a minimum it is preferable to feed the chaffed material in troughs.

3.8.3. Meal

As already mentioned the high moisture content of spineless cactus has a limiting effect on the voluntary intake and thus on the utilization of this crop. Chaffed spineless cactus pads can be dried on any suitable surface and then ground in a hammer-mill through a 6 mm sieve. In the form of meal, the spineless cactus material is not only ingested better, but is also easier to store. A supply of spineless cactus meal can thus be stored for use during droughts.

3.8.4. Silage

Good quality silage can be made from spineless cactus by chaffing the pad together with oat straw, low grade lucerne hay or any roughage on the basis of 84 parts mass by spineless cactus and 16 parts by mass of roughage with the addition of two per cent molasses meal. When pads with fruit are used for silage, the addition of molasses is not necessary. The silage is then made and utilized in the conventional manner.

3.8.5. Supplementary feeding

In an emergency where nothing else is available, spineless cactus can be fed alone in any form and sheep can actually survive on it for months. For optimal utilization, however, this should be supplemented. As protein is the most important deficiency of spineless cactus, a protein-rich supplement should be supplied. A like comprising one third bonemeal, one third salt and one third buiret can be used with spineless cactus meal. A ration consisting of spineless cactus meal and 6.5 per cent fishmeal will supply all the needs of sheep.

The most suitable supplement for spineless cactus meal, however, appears to be lucerne meal or lucerne hay. 100g of lucerne in summer and 200 g in winter per sheep with spineless cactus meal ad lib is recommended. Any other legume hay with a reasonably high protein content can be used instead of lucerne. Spineless cactus pads can also be used as supplementary feed on dry Karoo veld. Provided reasonable quantities of dry veld fodder are still available with the spineless cactus leaves, no additional fodder need be given.

3.8.6. Laxative action

A problem experienced when spineless cactus pads are fed to sheep in any form is their severe laxative action. This laxative effect is, however, not a disease symptom and has, as far as is known, no direct detrimental effect on the animal. It does however have the disadvantage that the food passes through the animal's digestive system faster with the result that digestion is poorer. It appears that hay, as a supplement, retards this laxative effect to a certain extent. This is another reason why lucerne hay is regarded as an exceptionally suitable supplement to spineless cactus pads in any form.

3.9. The production of spineless cactus fruit

The green-leafed spineless cactus can also be established for fruit production. The control of insect pests is, however, essential for fruit production.

There is a good local market for spineless cactus fruit in some areas and this can be a source of income in the arid and semi-arid regions of the Republic.

3.10. Control of insect pests of spineless cactus

There are at present two insects, namely (a) the larvae of the prickly pear moth Cactoblastis cactorum and (b) cochenille Dactylopius (spp) which cause considerable damage in spineless cactus plantations. The mechanical control of C. cactorum, namely the removal of the eggs and pupae and the burning of infected leaves, especially in large plantations, is not very practical or efficient. These insects can actually be efficiently controlled by two insecticides. For the efficient use of these insecticides and the control of these insects knowledge of their life cycles is necessary.

Prickly pear moth (Cactoblastis cactorum). The adult insect is an inconspicuous grey moth with a wingspan of about 35 mm. A characteristic feature of the insect is the way the eggs are laid. These are stuck together in a long chain called an "eggstick". The eggsticks resemble yellowish, curved thorns without a sharp point. The eggstick is attached either to a thorn, or directly to the exterior of the pad and can easily be seen when the plants are inspected.

As the larva develops in the eggs the eggsticks become darker and later become black just before the larvae hatch. The number of eggs laid varies but each eggstick contains on an average from 60 to 100 eggs. The eggs are slow to hatch and incubation takes about three weeks under favourable conditions During colder weather the incubation period can be considerably longer. Temperature is thus the most important factor.

On hatching, the larvae congregate at the base of a thorn and feed there for about three weeks. After this they bore into the pad and feed on the succulent pulp. The larvae are of a bright orange colour with dark bands or rows of bluish-black dots across the body. Their activities cause the pads to decay and a whole plant can collapse within about two months.

The larvae feed for about two months in summer and about fifteen weeks during winter. When fully grown they spin cocoons under old decayed pads and debris that may be found in and under the plants. The duration of the pupae stage is about twenty-four days in summer and about eight to nine weeks in winter. There are only two generations per year. The one generation lays eggs during autumn (usually the first two weeks in March) and the other generation in spring (usually the first two weeks in November).

Cochenille (Dactylopius spp)

As with the case of the cactoblastis this insect was improved to control the wild prickly pear which had made valuable grazing useless in certain areas. It unfortunately later attacked certain spineless cactus cultivars. Cochenille is related to the scale insects but has a thick protective layer of wax instead of the scale insects, armour. When conditions are favourable these insects multiply very quickly and millions of small insects known as creepers, can be spread by wind from plant to plant. As soon as a host plant is found, the insect pushes its mouth parts into the plant cells and sucks the sap. Apart from the sucking of the sap, the saliva of the insect also has a toxic effect on the plant. Soon after they start feeding, the females form a layer of wax around their bodies which impedes the penetration of insecticides.

The so-called blue-leafed spineless cacti are not attacked by the cochineal, or only to a lesser extent. However it can happen that these cultivars become infested with cochineal, especially when the pads are very young or when the growth has been retarded by drought or other causes. Secondary rotting sometimes occurs in pads which have been damaged by cochineal.

Control measures

Apart from the use of insecticides to control these two pests, the following practical measures can be applied:

b) The pads for fodder should be regularly harvested every three to four years depending on the amount of growth. This will prevent the plants becoming too dense. Excessive growth provides ideal shelter for the pupae.

c) Harvesting of pads and the removal of old decaying pads from in and under the plants can be done simultaneously. All these old rotten pads should be burned.

d) More spineless cactus than required for the farming unit should not be planted.

Spraying

Two insecticides are registered for use in spineless cactus against both cochinea and cactoblastis. They are (a) larbary 85% wettable powder available commercially under the names Dicarbam, Sevin, Carbaspray and Capex 7, and (b) Methidathion 40% known commercially as Ultracide. Both insecticides must be applied as a coarse spray. A knapsack sprayer fitted with a no. D5 nozzle is suitable for this purpose.

Method

Spray the whole plant to the point of runoff. Excessive runoff must be prevented to avoid wastage of the spray. All cactoblastis eggsticks and all cochineal must be wetted. It is essential to use a coarse spray to penetrate the wax layer of the cochineal. It is important to spray at the correct time so that spraying of the cactoblastis eggsticks is assured. The best times are usually during the first two weeks of March and November. Carbaryl 85% wettable powder is used at the rate of 32 g dissolved in 18 litres of water. Methidathion 40% wettable powder is applied at the rate of 9 g dissolved in 18 litres of water.

Safety precautions

All insecticides are dangerous to warm-blooded animals. Special care must therefore be taken when mixing and spraying these insecticides, especially in the case of Methidathion. Protective clothing such as a suitable respirator, overalls, gumboots and rubber gloves should be worn when handling and applying these insecticides. Provided the insecticides are applied at the recommended dosages and in the recommended manner the safety period is only one day. The plants can thus be harvested and fed to stock the day after spraying. The label on the container must be carefully studied and the instructions on the label strictly adhered to.

4. Drought resistant shrubs

4.1. Introduction

Drought resistant shrubs do well in areas where the rainfall is low and variable, where the cultivation of fodder crops such as Lucerne and annual crops is uncertain. Due to their well developed root system, low transpiration and physiological adaptation (such as high mineral content) these plants can make efficient use of water. The two best known drought resistant shrubs are old man saltbush (Atriplex nummularia) and Australian blue bush (Kochia brevifolia). Australian creeping saltbush can also be used for grazing.

4.2. Description of these crops

4.2.1. Oldman saltbush (Atriplex nummularia)

Oldman saltbush is a perennial shrub, indigenous to Australia, and has been found in South Africa for the past hundred years. It can grow to a height of 3 m and can also form bushes with a diameter of 3 m. It possesses a well-developed taproot system together with horizontal basal root development. The root system is suberous. The leaves are a bluish-grey colour, covered with a white layer and small salt cells. The leaves are more or less round but broader than they are long. The male and female flowers are normally borne on separate plants, but may exceptionally be borne on the same plant. The small round yellowish-brown male flowers are borne in clusters of from 75 to 100 mm long on the tips of the branches. The female flowers are the same colour as the leaves and are borne in dense clusters, the weight of which bends the branches over towards the ground. The plant is wind-pollinated. The seed consists of two leathery or papery scale leaves which have grown together around the small round reddish-brown seed. These scale leaves contain a high sodium chloride concentration which serves as a germination inhibitor. The sodium chloride first has to be leached out before the seed will germinate. This is a mechanism which prevents seed from germinating after a light rain and only allows germination when there is sufficient moisture for the plant to become established.

Oldman saltbush is a halophyte, or salt-loving plant. Due to the high concentration of salt in the roots and leaves the plant maintains a high osmotic value in the cellsap which is a physiological adaptation of the plant to moisture stress, thus making it drought-resistant. The plant also possess a C4 carbon metabolism which means that photosynthesis is very effective especially at high temperatures and high light intensity. 

4.2.2. Australian creeping saltbush (Atriplex semibaccata)

Australian creeping saltbush is a procumbent shrub seldom growing higher than 300 mm but spreading horizontally to 1200 mm. The upper surfaces of the leaves are green, and the undersides white. They are sometimes serrated and up to 25 mm long. The male flowers are borne in clusters at the base of the upper leaves. The female flowers are borne singly at the base of the lower leaves. The fruits are diamond-shaped and vary in colour from red to orange and are approximately six mm long.

4.2.3. Australian bluebush (Kochia brevifolia)

Australian bluebush is a perennial shrub with branched stems and grows to a height of 1.5 m. The plants are dark green in colour. The leaves are soft, succulent, virtually without veins, cylindrical in shape, approximately 2.5 mm in diameter and 12 mm long. The round, veined seeds from 6 to 12 mm in diameter are borne on the tips of the stems in the leaf axils. The actual seed is encircled by a thin light-brown wing. These shrubs flower from August to May. The seeds germinate at temperatures of from 10°C and will germinate as soon as sufficient rain has fallen. The plant immediately develops a strong taproot system as well as horizontal fibrous feeding roots which are discarded when the soil dries out.

3. Climatic requirements

These crops have the advantage that they are well adapted to a large variety of climatic conditions. Oldman saltbush and Australian creeping saltbush are entirely resistant to cold and frost. Although the top growth of Australian blue bush is killed by severe frost, this dry material can be utilised by stock and the plant quickly shoots when warmer conditions are experienced. Australian bluebush, however, is not recommended for the higher, cold areas.

4. Soil requirements

The drought-resistant shrubs possess a wide adaptation regarding soil and even grow on bare, alkaline patches. Australian bluebush prefers soils rich in lime for normal growth and production. On brackish soils preference must be given to oldman saltbush and Australian creeping saltbush. These two crops will also grow on heavy clay soils even if they are poorly drained. Acid and leached sandy soils usually contain too little sodium and potassium salts for good production from these halophytes. The germination of Australian bluebush is poor on alkaline or alkaline brackish soils. .

5. Irrigation

Irrigation now and again can be of advantage in areas with an average annual rainfall of 180 mm or less. Water of poor quality for irrigation can be used to advantage for these crops. Irrigation, especially during the first year or two after establishment, causes the plants to develop faster with the result that they are ready for grazing sooner. For this reason and to make planting easier, it is desirable to plant these crops in paddocks near windmills or dams in the veld, where possible. This will also simplify the utilisation of the efficient use of water by these plants.

6. Yield

Apart from the drought resistance, a noteworthy characteristic of these plants is their high production of green, succulent feed under relatively poor moisture conditions. An indication of the amount of edible material per hectare produced by oldman saltbush is given in Table 6.1.

Table 6.1. The yield of leaves of oldman saltbush

The results in Table 6.1 also illustrate the ability of oldman saltbush to recover after defoliation each year. This is one of the reasons which make this crop exceptionally suitable as a grazing crop. The grazing value of oldman saltbush is further illustrated by the figures in Table 6.2.

Table 6.2. The carrying capacity of various fodder crops for 4 months of the year.

See under "Grazing" for the yields of the other shrubs.

7. The establishment of oldman saltbush

The establishment of oldman saltbush requires a fair amount of attention. It is advisable to soak the seed in water for 2 to 3 days prior to sowing to get rid of the excess salt in the seed coat. Change the water 2 to 3 times daily. If running water is available (e.g. windmill), very good results are obtained. The seed should be sown immediately after this treatment. It is advisable to sow the seed in seedbeds, tins, plastic bags or trays and to transplant the seedlings at a later stage.

The optimum temperature for germination is from 15°C to 20°C. The seed is sown in August or September and covered lightly with soil (approximately 5 mm). The soil must be kept moist by regular watering. The advantage of sowing seed in tins or plastic bags, is that the seedlings may then be transported in containers. The roots of the seed are thus less subject to damage during the lifting of the plants, and drying out of the roots is kept at a minimum.

As soon as the seedlings are 150 to 200 mm high they should be transplanted. This usually takes place during late summer and autumn (February to March). Most rains occur during this time of the year and the plants are thus able to establish themselves better. If the rainfall is sufficient, or where irrigation is possible, the plants can be transplanted at a younger stage.

The soil should be well ploughed in advance. If this is not possible, furrows may be drawn or even holes dug. When it is not desired to disturb the soil, furrows can be drawn with a ripper. The furrows are made 2 m apart and the plants are planted 1 to 2 m apart in the furrows. The plants are cut back prior to planting to about 150 to 200 mm. Depending on the spacing, between 2500 and 5000 plants are required per hectare. With a good germination, about 500 g of seed, should yield approxi the roots must be well covered with soil and the soil pressed down well around the plants. The furrows should be irrigated before and immediately after transplanting. An irrigation 3 to 4 weeks after planting followed by one irrigation during winter, will encourage the plants to establish paddocks near windmills or other water sources in the veld. A few further irrigations during the first summer will encourage the plants to develop quicker. Good establishment can also be obtained by the application of one litre of water per plant at the time of transplanting followed by 2 litres ten days later and a further 2 litres 20 days later.

Modified tobacco planters have been used to plant saltbush plants, which apply the water directly to the plants. Otherwise the water is transported in tankers. If the plants are well established, seed may be harvested during the second season for further plantings. Saltbush should not be grazed during the first year. Oldman saltbush seed which is properly dry and is stored under dry conditions in a tin or plastic bag will retain its viability for approximately three years after which the germination gradually decreases.

Oldman saltbush can also be multiplied by means of cuttings. Cut lengths of young stems which are not thinner than 6 mm and approximately 250 mm long, between two leaf axils. Leave a leaf or twig on the top and lay about half the stem in sandy soil during early spring or autumn. Keep the cuttings moist. The cuttings usually root within six weeks and are ready for planting ten weeks after cutting.

8. Establishment of Australian bluebush

The optimum germination temperature for Australian bluebush seed is 15° to 20°C. Seed should thus be sown from August to May in seed boxes, plastic planting bags, tins or a sheltered seedbed. For germination a sandy loam soil is preferred. Avoid brackish soils. Sow the seed shallow, i.e. 3-5 mm deep, and keep the soil moist until the seeds have germinated (usually 7 to 14 days depending on the temperature). The seedling, when first seen after germination, has two thin almost grass-like leaves and the real woolly leaves develop subsequently.

The plants are ready for transplanting when they are about 100 to 150 mm high. When older plants are transplanted, about a third of their growth should be cut back. The transplanting of older plants is difficult as the top roots of the seedlings develop very quickly. When plants are transplanted, it is essential that they should be well watered on transplantation followed by one or two irrigations 7 to 14 days later. The plants are spaced one metre apart in the rows and the rows are spaced 1.5 to 2 m apart. Grazing should not take place until the plants are one year old or have grown for one season.

Australian bluebush usually flowers from August to May and the seed is borne in a wind-pollinated flower. The seed is very light and is spread by the wind. Seed production is high and the plants often commence to produce seed from 6 weeks under favourable conditions. After the plant has been grazed, it may take up to 3 months before seed is again produced. The seed is easily harvested by shaking it off the bush. Seed harvested in this manner has a germination rate of 60 to 80 per cent. Seed falls from the bush when it is ripe. By controlling weeds between the plants thus keeping the soil in a loose condition, a natural seed bed is created and large numbers of seedlings may develop which can be transplanted later.

The seed is ripe when the kernel of the flower is dark brown to almost black. Seed which is collected under the bushes is usually not so viable as those harvested, as this seed is easily damaged by moisture. When the bush is shaken, leaves, ripe and unripe seed, can be gathered. These must then be well dried in the sun as soon as possible. The viability of seed is easily affected by moist conditions. Consequently seed should not be kept in knotted plastic bags, but preferably in tightly-screwed fruit jars or other dry containers.

9. The establishment of Australian creeping saltbush

The optimum germination temperature for Australian creeping saltbush is 15° to 20°C. Seed should thus be sown from August to April. Seed of Australian creeping saltbush is usually sown directly at a rate of from 3 to 6 kg per ha. Normal seedbed preparation is followed where old lands are seeded. Where this crop is sown for the reclamation of bare patches it is sown in plough furrows or roughly worked soil. The seed is usually sown 5 to 10 mm deep.

The seed germinates easily and should preferably be sown at the beginning of the rainy season. Seed production is high and is easily harvested by shaking the seed off the plants. The seed is ripe when it changes from orange or red to a shade of brown. Harvested seed must be dried as soon as possible. Dry seed can be stored for up to three years under dry conditions without a loss of viability.

10. Feed value

The mean composition of oldman saltbush, Australian bluebush and Australian creeping saltbush is given in Table 10.1

Table 10.1. The mean composition of oldman saltbush, Australian bluebush and Australian creeping saltbush on a dry basis.

Nutrient	Oldman saltbush %	Australian bluebush %	Australian creeping saltbush %
Dry material	25.29	33.40	31.8
Moisture	74.71	66.60	68.2
Protein	22.93	15.72	13.3
Fat	3.05	2.67	2.1
Minerals	19.77	19.45	28.7
Carbohydrates	40.58	38.63	40.8
Fibre	13.77	23.53	15.1

Although it appears from an analysis of these crops that they do not supply a balanced ration in all respects, grazing experiments have shown that they supply the maintenance requirements of sheep. Even a slight increase in mass has been observed, although the purpose is not to fatten stock but only to prevent losses during dry periods. Grazing experiments with saltbush have also shown that these crops can maintain ewes during late pregnancy, and thereafter the ewes and lambs until the lambs are 42 days old. Withers were kept on bluebush for 180 days and during this period they showed a slight increase in body mass while the wool production was normal.

11. Grazing

Oldman saltbush can be grazed from the second season so that the plants can develop a bushy growth habit. Plants which are not grazed are inclined to develop beyond the reach of sheep so that only the older material can be reached by the stock. If the plants develop beyond the reach of sheep they should be cutback to a height of about 1.5 metres. When saltbush is grazed, sufficient drinking water must be supplied as the sheep become thirsty from the salt in the plants. The drinking water should contain as few brackish salts as possible as brackish water inhibits the intake of saltbush.

Australian bluebush can be grazed when it is one year old or after it has been established for one growing season. Australian bluebush should preferably be grazed off quickly and it is thus best to concentrate a large number of animals on a small area for a relatively short period. With this method provision for the recovery of grazed paddocks can be made by means of a planned rotational grazing system. Australian bluebush must be regarded exclusively as a fodder crop to bridge periods of grazing shortages and cannot be recommended for planting in the veld with the aim of improving the natural grazing in the Karoo. It can however be recommended for the improvement of fine bushveld in certain winter rainfall areas. It can also be established in paddocks, to relieve grazing pressure on the natural velds just after rains or during dry periods. The stock can thus be removed from the veld to encourage recovery of the grazing.

These crops cannot be regarded as very palatable, and stock often have to learn to eat them. This may take three or four days. However it has been found that stock which have learned to eat them, make good use of this grazing even, if returned to it after a period of absence. The palatability is also influenced by the type of soil on which these plants are grown. These plants are less palatable if grown on very brackish soils and the amount of brackish salts in the drinking water also influences the intake by the grazing animals.

These crops should be established in pure stands and should not be mixed in the same paddocks. This simplifies the management of these grazing as the recovery rate of the different crops differs. They can be grazed at any time of the year. It is, however, essential to allow sufficient time between grazing for the plants to recover. It is thus advisable to divide the plantations into paddocks of from one to two hectares in size for efficient utilisation and to ensure sufficient rest for the plants to recover. Temporary electric fencing is very suitable for this purpose. A practical method is to graze each paddock with a large number of animals for the shortest possible time.

The carrying capacity of oldman saltbush is given in Table 6.2. The average sheep grazing days for the different drought resistant shrubs is given in Table 11.1.

Table 11.1. The average number of sheep grazing days per ha provided by drought resistant fodder crops at the Grootfontein College of Agriculture.

12. Shrubs and spineless cactus in mixed stands

These carrying capacity figures are the average obtained over 5 years at the Grootfontein College of Agriculture. This shows that these plants can be grazed every year after the second year from establishment without any noticeable influence on the vigour and recovery of the plants.

Where drought-resistant shrubs and spineless cactus were established in the same plantation for grazing, it was found in general that due to the higher palatability of the spineless cactus, the sheep showed a tendency to overgraze the spineless cactus before the shrubs were made full use of. This method of establishing plantations is thus, in general, not recommended. In exceptional cases it has however been found that sheep have utilised both crops efficiently. Practical experience on each particular farm will thus indicate whether this is possible. However, if there is any doubt, these crops should preferably be planted in separate paddocks. Where the shrubs and spineless cactus are established in adjoining paddocks, a rotational system of grazing between the paddocks can be practised with good results.

Chaffed spineless cactus can be supplied to the sheep in the drought-resistant shrub paddocks. It is not usually necessary to supply the chaffed cactus more than once a week, as the sheep make good use of the cactus even in a dried form.

13. Reclamation of bare patches

Drought-resistant shrubs are particularly suitable for the reclamation of bare patches in the veld. These areas should be fenced off if these shrubs are to be used for their improvement. Furrows are drawn, usually with a ripper, from two to ten metres apart. It is essential that the plants are watered directly after planting and possibly two weeks later to ensure a good rate of establishment. It is advisable to establish these plants during the autumn, during which period the possibility of rain is usually better in the arid areas.

The use of seedlings established in plastic planting packets or other suitable containers is recommended for this purpose, as the shock to the plants during transplanting is less. Australian creeping saltbush is usually sown directly after the soil surface has been ripped. Seed can also be sown in the furrows, but this is not as successful as when seedlings are planted, especially when the rainfall is insufficient. The most arid zones of the farm can thus be converted into living fodder banks which will not only relieve the grazing pressure in times of drought, but also help to improve .the natural grazing.

14. American aloe

14.1. Introduction

American aloe (Agave americana) is one of the hardiest plants which can be established for the production of fodder in the arid and semi-arid regions. It can be of value in the control of erosion when established on the periphery or on eroded patches. This crop uses exceptionally little water for the production of dry material. (See Table 1.1)

14.2. Description of the crop

The American aloe (Agave americana) is related to the sisal plant, but its fibre has no commercial value. The plant requires 93 kg of water to produce one kg of dry material. The American aloe leaf is covered by a waxy layer and a very thick epidermis. The stomata are deeply sunken in the leaf. The stomata close when exposed to strong light and this is one of the reasons for the drought-resistance of this plant.

The American aloe has a taproot system as well as a horizontal shallow root-system from which suckers develop. The plant grows slowly and an inflorescence develops from the centre of the plant after from six to ten years, and takes approximately a year to mature. As soon as the flowers mature, the original plant dies. The seed germinates easily and a number of young seedlings develop around the original plant.

14.3. Establishment of American aloes

Two year old suckers or seedlings are used to establish this plant. The plants are planted in furrows 3 to 5 metres apart and 1 to 2 metres apart in the furrows. American aloe is often planted on the periphery or alongside fences.

14.4. Feeding value and utilisation

The average composition of American aloe leaves is given in Table 14.1.

Table 14.1. The average composition of American aloe leaves on a dry basis.

American aloe leaves alone are not sufficient for a maintenance ration. Although American aloe is palatable and can form a portion of the daily ration, it must be supplemented by sufficient Lucerne hay, meal, etc. to prevent paralysis, which can be experienced if American aloe leaves alone are fed continuously. It has however been shown that American aloe leaves can, to a large extent, take the place of silage, mangels etc, as the succulent portion of the ration.

For fodder the leaves are chopped against the stem so that as much as possible of the thick fleshy portion is used, as this is the most palatable part. The fibrous points and edges of the leaves are removed and the leaves are chaffed in pieces not larger than 50 × 100 mm. A hand chaff-cutter or chopping knives are suitable for this purpose. Leaves are usually harvested from 4 - to 6 -year old plants. A yield of from 120 tons of leaves per hectare can be expected annually from America alone and that on relatively poor soils.

14.5. Use as a reclamation crop

When planted on the contour the American aloe can fulfill an important function in the control of soil erosion; it allows water to pass through while much of the soil and debris is kept back with the result that a contour wall is built up in time. The biggest disadvantage is that it provides shelter for vermin such as rock rabbits, polecats and wildcats. The flower stalks can also be used for fencing.