THE USE OF OPUNTIA AS A FODDER SOURCE IN ARID AREAS OF SOUTHERN AFRICA

Gerhard C. DE KOCK

INTRODUCTION

Drought is a natural and normal attribute of the arid lands of arid and semiarid climates. Agricultural drought may be defined as a deficiency of rainfall with respect to the median or to the mean, that seriously impairs agricultural production for a period of several months to several years, extending over a large geographical area. Drought should not be confused with aridity, which rather refers to the average long-term relationship between rainfall and potential evapotranspiration, although it may occur in non-arid zones as well.

Southern Africa, with its variable and limited rainfall, is arid, and seasonal and severe droughts normally occur. During droughts, considerable stock and stock-product losses occur due to the lack of fodder.

CLIMATE

Southern Africa is subject to the most complex bio-climatic conditions on the African continent (Le Houérou et al., 1993). This complexity results from a combination of various geographic conditions, among which are the following:

* Large variation in latitude between Messina in Northern Transvaal (22°30’ S) and Cape Agulhas (34°50’ S), a distance of approximately 1350 km north-south.

* Large variation in elevation, from sea level to about 3 500 m, with a direct effect on rainfall and temperature.

* The presence of the oceans to the east and west. These are associated with the influences of warm currents (Mozambique and Agulhas) in the east, and a cold current (Benguela) to the southwest.

* Mean annual precipitation varies from 40 mm at the mouth of the Orange River, to over 2500 mm on the eastern slopes of the Drakensberg and the upper and western slopes of the Cape mountains.

The rainfall regime may be tropical summer mono-modal; Mediterranean winter mono-modal; spring and autumn bimodal; or completely amodal (without a regular dry season). The mean potential evaporation may vary from a little less than 1000 mm along the Cape and Natal, to over 2 500 mm in the Upington-Pofader-Pella area on the southwest border with Namibia.

OPUNTIA CULTIVATION

Cacti perform well on deep, light textured soils, including coarse sands, but clay should be avoided. Shallow soils tend to give low yields. Cacti are tolerant of pH up to 8.5, and maximum electrical conductivity at soil saturation should not exceed 5-6 mS/cm (Le Houérou, 1992).

Cacti respond to application of nitrogen and phosphorus fertilizer. A production increase of 200 to 300% has often been observed following moderate nitrogen and phosphorus application. Manuring also increases yield even with very low precipitation of 150-200 mm (Monjauze and Le Houérou, 1965; Le Houérou, 1992; De Kock, 1980). Cacti cannot withstand waterlogging.

WATER REQUIREMENT AND USE

Cacti and other drought tolerant fodder crops use water more efficiently than conventional fodder crops. According to De Kock (1980), opuntia uses 267 kg H₂O/kg DM, or 3.7 mg DM/g; Atriplex sp. uses 304 kg H₂O/kg DM, or 3.3 mg DM/g; and Agave sp. uses 93 kg H₂O/kg DM, or 10.7 mg DM/g.

The productivity of opuntia is also very high if compared to most native vegetation under similar conditions. Opuntia produces up to 10 t of aboveground DM/ha/yr in arid zones, 10-20 t in semi-arid zones and 20-30 t in sub-humid areas under appropriate or close to optimum management (Monjauze and Le Houérou, 1965; De Kock and Aucamp 1970; Steynberg and De Kock 1987; Nobel 1988; Le Houérou 1991b, 1992).

Such high yields, however, demand careful crop management and good deep soils. Under such conditions, productivity is about ten times that of standard rangelands under common management conditions. With neither cultivation nor fertilization, yield is still three to five times that of rangeland (De Kock, 1980; Le Houérou, et al., 1988). The rain use efficiency (RUE) and water use efficiency (WUE) under rainfed and irrigated conditions are summarized in Table 47.

Table 47. Rain use efficiency (RUE) and water use efficiency (WUE) under rainfed and irrigated conditions for several crops

Using the WUE characteristic of an opuntia in an area with 200 mm mean annual precipitation, the yields of cactus material presented in Table 48 were produced under various systems of limited irrigation (De Kock and Aucamp, 1970). In arid and semi-arid areas with limited supply of irrigation, irrigating spineless opuntia is more efficient than irrigating a small area of alfalfa.

Table 49 summarizes the fodder yield and the amount of digestible nutrients produced by spineless cactus (Opuntia robusta), oldman saltbush (Atriplex nummularia) and alfalfa per unit of water received (25 mm).

Table 48. Yield of spineless opuntia (2920 plants/ha) under limited irrigation at the Carnarvon Station (average rainfall: 200 mm/yr) (Two seasons: 1965-66; 1967-68)

Table 49. Comparison between fodder yield and digestible nutrients (kg/ha) produced by three fodder crops per unit of water received

PRODUCTION

In South Africa, there are three species of spineless cacti utilized for fodder production:

(ix) O. robusta. This cactus has large, circular, bluish cladodes, almost spineless. It was first introduced into South Africa in 1911 from the selection programme of Luther Burbank in California. This tetraploid is tolerant to Dactilopius opuntia. It does not produce marketable fruit and so is mainly used as fodder.

(x) O. fusicaulis has narrow, lanceolate, green cladodes with an upright growth habit.

(xi) O. ficus-indica f. inermis is a green, oblong type, with dense growth habit.

O. fusicaulis and O. ficus-indica cannot produce both fodder and fruit in the same stand in fruit orchards (unless pruning waste is considered). Fodder plantations are harvested every two to three years, before they produce fruits.

In South Africa, opuntia cactus is propagated vegetatively by placing pads flat on the ground with a shovelfull of soil or a stone on top, to improve contact with the soil. Alternatively, double joints can be planted in a furrow, burying the lower end with soil drawn from an adjacent furrow. Roots will develop from the areolas within a few weeks.

Rows are laid out following contour lines. Deep furrows or trenches are made with a heavy ripper and partially filled with manure, which in turn will be covered by soil, planting cladodes on top. The method is more expensive than simple planting, but it yields better growth in the first two to four years, implying earlier production and higher productivity. Rows are usually established 2 to 6 m apart with 1 to 2 m between plants. Planting density may vary from 850 to 5000 plants/ha. The best time for planting in South Africa is September and October, when the pads are fully-grown and ready to sprout. The resulting plants will be well established before the first frost of the following winter. It is preferable to use one-year-old cuttings as planting material.

The selection of a planting layout depends on the type of use envisaged. For direct browsing, dense stands (3 000 to 5 000 plants/ha) with short plants are used. In contrast, the cut-and-carry system requires a wider space to allow a tractor and a trailer to collect the harvest. In this case, a 1 m × 6 m layout is preferred, giving a mean planting density of about 1 666 plants/ha.

CROP MANAGEMENT

Under rainfed condition, yield may vary from 2 to 10 t DM/ha/yr, if harvested every 2 to 3 years. Yield rates from irrigated opuntia are presented in Table 48. Yield is increased if weed competition is reduced. Contour planting to reduce rainfall runoff can also improve yield. The protein content of fodder opuntia can be raised from 3.5 to 4.5% crude protein to 8 to 10% through application of nitrogenous fertilizer.

UTILIZATION

Fresh spineless cladodes contain approximately 90% moisture. The energy requirement for the survival of a 35-kg sheep is approximately 350 g of TDN per day; therefore, the ingestion of 538 g of dry cactus is enough to obtain sufficient energy. This means that 5 to 6 kg of fresh cactus must be ingested daily. However, a sheep eats an average of 4 kg a day.

For cattle, to provide the daily energy requirements for the survival of a 400 kg beast, 2 850 g of TDN are required per day. Therefore, such an animal will require approximately 4 385 g of dry cactus to meet its requirements. That means a daily ingestion of 44 to 45 kg of fresh cladodes. However, an animal only eats an average of 40 kg of cactus per day.

One of the reasons why animals (especially sheep) do not eat sufficient amount of fresh cactus cladodes is the high moisture content. Although the high water content limits consumption by animals, this moisture can be valuable during droughts, to reduce the need for drinking water. Penned sheep could be kept alive for 500 days without drinking water, provided they had free access to fresh cactus cladodes. The intake of TDN can be increased if the fresh cladodes are wilted or dried before feeding.

Cactus cladodes are very low in crude protein in general, but any ration for non-reproductive sheep and cattle should contain at least 8% of crude protein. Rations or feeds with low protein content are poorly ingested by animals. A sheep with a liveweight of 35 kg requires approximately 50 g of crude protein per day. The average 500 g of dry material from the daily ration of cactus cladodes contains only 20 g of crude protein, so cactus cladodes must be supplemented with some form of crude protein. Cactus cladodes are low in phosphorus and sodium, requiring supplementation of these elements as well. In general, cactus cladodes are not a balanced feed but rather a good, inexpensive source of energy.

Grazing

The easiest way to utilize cactus is by direct grazing, which requires little labour and therefore is cheaper. There is a risk of overbrowsing and destruction of the plantation if strict control of stock and grazing is absent. Grazing or harvesting should take place every two to three years. The pads reduce in feeding value after the third year (Walters, 1951). For efficient grazing, the plantation can be divided into small paddocks, which are then used intensively for a short period each. Large loses can occur during grazing due to wastage.

Chaffing

Increased intake by animals and better utilization can be obtained by chopping the cladodes. To limit waste, it is preferable to feed the chaffed material directly in the trough.

Meal

Chaffed cactus cladodes can be dried on any suitable surface, and then milled. A supply of cactus meal can thus be stored for use during droughts and/or for supplementing fresh cactus pads to increase dry matter intake.

Silage

Good silage can be made from cactus cladodes by chaffing them with oat straw, low grade alfalfa or any other dry roughage on the basis of 84 parts mass of cactus cladodes and 16 parts of roughage, with the addition of molasses meal. When cladodes bearing fruit are used for silage, the addition of molasses is not necessary. The silage is then made and used in a conventional manner.

Opuntia fruit and cladodes - even the spiny types - can be made into silage with low quality hay, cereal straw or veldt hay, and supplemented with protein feed (cotton or sunflower seed meal, and urea) and a mineral supplement of phosphorus and sodium (bone meal, salt and lime) and this can sustain dairy production in arid and semi-arid rural areas during dry seasons and drought periods.

Supplementary feeding

In an emergency, where nothing else is available, cactus cladodes can be fed alone in any form, and sheep and cattle can survive on it for many months. Wool sheep were kept for 500 days on cactus cladodes alone and survived.

For optimal utilization, however, cactus cladodes should be supplemented. As protein is the most important deficiency of cactus, a protein-rich supplement should be supplied. A supplement comprising one-third bone meal, one-third common salt and one-third urea can be used. Another possibility is a ration consisting of cactus meal and 6.5% of fishmeal, which will supply the needs of sheep.

The most suitable supplement for cactus meal is alfalfa, either meal or hay. It is recommended to provide 100 g of alfalfa in summer and 200 g in winter, with cactus ad libitum. Any other hay legume with a reasonably high protein content could be used instead of alfalfa. Cactus cladodes are an excellent succulent supplement on dry Karoo range (shrub type veldt, high in protein), or in dry grass range during winter, with a protein-rich supplement.

LAXATIVE ACTION

A problem experienced when cactus cladodes are fed in any form to sheep and cattle is the severe laxative action. This laxative action is not a disease symptom and has no detrimental effect on the animal’s health. It is the result of a fast passage through the digestive system. The laxative effect can be curtailed by:

* Feeding fodder lime (approximately 3% of the total intake), to counteract acidosis. The high acid content of cactus cladodes is related to the Crassulacean Acid Metabolism of the plant.

* Limit access of the animals to drinking water.

* Feed hay with cactus cladodes. Hay as a supplement retards the laxative effect. Alfalfa hay is regarded as an exceptional supplement to spineless cactus cladodes in any form.