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CULTIVATION OF OPUNTIA FOR FODDER PRODUCTION: FROM RE-VEGETATION TO HYDROPONICS

Candelario MONDRAGÓN-JACOBO, Santiago de J. MÉNDEZ-GALLEGOS and Genaro OLMOS-OROPEZA

Candelario MONDRAGÓN-JACOBO

Santiago de J. MÉNDEZ-GALLEGOS


and Genaro OLMOS-OROPEZA



Instituto Nacional de Investigaciones


Agropecuarias y Forestales

Centro Regional de Zonas Aridas

Guanajuato

San Luis Potosí

México

México

INTRODUCTION

Opuntia or nopal is cultivated for fresh fruit production in Chile, Italy, Mexico and the USA, and interest is also growing in many other countries. The main physiological advantage of opuntia is its high water use efficiency, with production of 1 kg DM per 162 kg water intake in Opuntia ellisiana (Han and Felker, 1997). However, adoption of fruit production in countries without a tradition of consumption or with no immediate access to export markets is slow and difficult. The experience of Brazil has demonstrated that utilization of opuntia as a forage is easier to integrate into the farming systems of semi-arid regions, where the cultivation of cactus for forage dates back to the early 1900s, and at present there are more than 300 000 ha planted (Russell, 1990). No appreciable use of fruits is reported.

Plantations of opuntia for specialized forage production are not widespread in Mexico, as wild populations provide reservoirs of forage for livestock. However, these wild stands are endangered due to intensive exploitation and severe frosts. Plantations of opuntia for forage production could reduce the pressure on the natural stands while improving the profitability of dairy and meat operations.

Opuntia tolerates a variety of growing conditions, but productivity in its natural habitat is limited by drought and poor soils. When O. ficus-indica was irrigated in Chile, yields were reported of 1.3 kg DM/m2/yr, including 0.3 kg/m2/yr as fruit (Acevedo et al., 1983). Assuming 10% moisture content, the yield of fresh pads for animal consumption reaches 100 t/ha/yr.

Computer models indicate that productivity could be increased by 40% by modifying planting layouts (García de Cortázar and Nobel, 1986).

In this chapter, some of the physiological bases for forage production are reviewed. Three production systems differing in cultivation intensity are discussed:

(xii) extensive, low-cost plantations aimed at reducing desertification and producing forage;

(xiii) small, intensively managed orchards, demanding high labour and inputs; and finally

(xiv) hydroponic production.

These systems have been studied in Mexico for growing opuntia under rainfed or limited irrigation conditions for forage, fruit or vegetable production. For vegetable production, crop management practices have been adapted to produce mature cladodes for fodder. This information could be applicable with minor adaptation to other semi-arid regions of the world in which opuntia has shown promise.

FACTORS ASSOCIATED WITH OPUNTIA FODDER PRODUCTION

The cladode as a water reservoir

Anatomically, the opuntia plant has a jointed succulent pseudostem, with cladodes differing in water content according to age. Younger cladodes have the highest moisture content, with mean values of 90.8, 89.1 and 83.4% for young, mature and older cladodes, respectively (Flores et al., 1995). Minerals show a similar trend, with N, P, K, Mn, Zn and Na decreasing, and Mg increasing, in older cladodes of O. amyclaea Tenore (Lopez et al., 1988). Young cladodes are more palatable due to their low fibre content.

Cladode shape has evolved to store the maximum amount of water with minimum loss (Nobel, 1994). A cross section of this organ shows that the innermost tissue is spongy, with large cells adapted to store water. During drought, water is preferentially lost from the water-storage parenchyma rather than from the photosynthetic chlorenchyma (Nerd and Nobel, 1991). The chlorenchyma is also protected by a waxy epidermal layer that restricts water loss. Opuntia is a Crassulacean Acid Metabolism (CAM) plant (Gibson and Nobel, 1986), associated with built-in features to save water during the photosynthetic process, including, inter alia, nocturnal stomata opening for CO2 intake.

Length of growing season

Disregarding the planting season - early spring or late autumn - opuntia produces at least one flush of new cladodes arranged in layers. Rainfed conditions common in semi-arid central Mexico, with 300 to 450 mm of rainfall annually, induce the formation of a single layer of new shoots during early spring, which continues until the end of summer. Adequate water and nutrient supply combined with suitable temperatures may induce the formation of three new layers of cladodes per season, as observed by Mendéz et al. (1999) in the hydroponic cultivation of spineless varieties.

If the plant is not managed or disturbed, these cladodes will be mature at the end of the growing season. Lower temperatures in autumn and winter induce dormancy. Throughout the winter season the cactus loses some water as a result of drought and transpiration losses, and can be used advantageously as a forage. Cladodes can remain on the plant and be either browsed by the animals, or “harvested” according to needs (using the plant as in situ live storage), or collected and stored for latter use. Fibre and dry matter content increase with age, but, if properly cleaned and chopped, cladodes up to three years old can be utilized to feed livestock.

Propagation

The basic meristematic unit in opuntia (and the cacti in general) is the areole (Gibson and Nobel, 1986). They are helically positioned on the cladodes (Sudzuki Hills, 1995) and can develop either branches or flowers (Boke, 1980) or roots. The cladodes can initiate the rooting process soon after they come in contact with soil. Soil moisture is important - but not limiting - for rooting, because the root initials are supported by the water stored in the cladode.

If the cladodes are detached from the mother plant they undergo a healing and suberization process, which seals the potential sites of additional water loss. The immediate release of mucilage by wounded cells enhances and accelerates healing. Once suberized, each piece can act as an independent propagule. The water stored will support transpiration, and the formation of new shoots and root initials if placed in the ground. The cladode can sustain water loss for a long time: up to six months without losing viability if stored in a shaded location.

According to Nobel and Castañeda (1998), the unrooted cladodes of O. ficus-indica remain alive for at least 12 months. This feature is particularly useful for animal feeding, as cactus cladodes can supply and partially substitute the water needs of livestock for a long period. Any other traditional source of fodder available during the dry season in semi-arid zones (cereal straw, maize, sorghum or millet stubble) is stored dry, requiring additional water to be ingested. Consumption of 40 kg of opuntia per day by cattle provides 35 litre (85%) of water (Felker et al., 1977)

Initiation of new organs on cladodes of Opuntia ficus-indica maintained unrooted in a glasshouse was greatest when the cladodes were detached in winter (Nobel and Castañeda, 1998). The response to cladode excision is very rapid, and enables the cutting to establish rapidly a relationship with the soil. The stimulus to cell differentiation and multiplication may occur within the first 48 hours, and root primordia emergence may take as little as two weeks (Fabbri et al., 1996).

The size of the cladode does not affect the ability to form shoots or roots (Mondragón and Pimienta, 1995), but the size of the cladode is correlated positively to the number and size of the new shoots. Luo and Nobel (1993) found that, under greenhouse conditions, growth of new cladodes is markedly influenced by the dry weight of basal cladodes, which act as a carbon source for the new shoots. Whole cladodes are able to produce at least one layer of new shoots a year, depending on cultivar and the soil moisture available during the growing season. A new plant can be formed as long as there is an areole at the top and at the bottom of the cutting, and the first layer can have anywhere from 2 to 6 pads.

Better establishment and shorter time between planting and the first harvest are achieved with large cuttings composed of more than one cladode. However, the investment in handling and transportation of this type of material increases accordingly. This is a reasonable alternative only in those areas in which opuntia cultivation is traditional, and there is a continuous supply of planting material. Healthy, vigorous branches with two to three pads are the best choice.

New plantations can be undertaken even if there is no soil moisture available, using entire cladodes or fractions according to availability of planting stock. In extensive, low maintenance plantations this is a unique feature that confers advantage to opuntia over some trees and shrubs commonly used against desertification (e.g. Eucalyptus spp., Casuarina spp. and Atriplex spp.), which rely on soil moisture at planting for successful establishment.

The succulence of the propagule is a disadvantage when establishing large plantations, due to its weight compared to ordinary budwood or stem cuttings in other species (Fabbri et al., 1996).

Response to pruning

Opuntias can endure heavy and continuous pruning. In frost-free locations, pruning can be performed at any season. Orchards devoted to fruit production are pruned after harvest, at the end of the growing season. Bud emergence is heavier if plants are pruned during the growing season. In most cultivars, the vegetative growth overwhelms the reproductive growth. The plant can be maintained in the juvenile stage indefinitely by continuous pruning, which is the basic crop management tool for vegetable opuntia production. If not pruned, the cladodes will continue growing until autumn, giving rise to flowers at the beginning of spring. Development of floral buds is mostly observed in mature cladodes that are at least six months old (Pimienta, 1990).

Disregarding the planting system, plants can be pruned down to the initial cladode if needed. However, pruning intensity should be adjusted in the light of rate of recovery, future plant productivity and fodder quality. Efficiency of animal utilization of pruning waste of different ages and quality should also be balanced against fodder needs.

The number of buds available to form new cladodes depends on the number of pads. Planting systems using bushy plants at low planting densities are more productive (on a per-plant basis) than high-density (using short plants) systems. High density planting systems therefore can withstand heavier pruning.

In locations with mild winter temperatures, the plants can be induced to continuously bud if winter protection of some sort is provided, along with irrigation and fertilization. This interesting feature is the basis of out-of-season production of vegetable opuntia across central Mexico and southern Texas. Application of high manure rates to soil and pruning are responsible for the high yields observed in vegetable production in Milpa Alta, Mexico, which can reach 400 ton/ha/year (Nobel, 1994). In general for cladode production, either tender or mature, the productivity of the crop should be tightly regulated by pruning practices.

Growing opuntia for forage production needs careful timing of pruning practices. Cladodes stored “on the plant” maintain a higher water content than the detached ones, while labour and storage needs are reduced. However, it is advisable to remove them just before the start of the next growing season, to avoid sprouting of new buds.

Response to fertilization

Cacti in general present low productivity due in part to the limitations imposed by the natural environment in which they grow. Wild opuntia stands are usually found in poor soils with low contents of dry matter, in regions with a short growing season that does not allow the full expression of their growth potential.

Fertilization trials conducted in Mexico and other countries (Mondragón, 1994; Karim et al., 1996) showed that fertilizers induce higher yields of fruits and cladodes. Combining manures with synthetic fertilizers gave the best results in fruit orchards. The reactivation of buds and the increase in size of the cladodes are immediate effects of fertilization, which can be advantageously manipulated for forage production. Higher N application (from 0 to 160 kg/ha) increased the number of new cladodes of O. engelmannii in Texas. The individual cladodes were slightly thicker, leading to 12% dry weight enhancement per cladode at the high-N level (Nobel et al., 1987).

Fertilization increases yield as well as nutrient content, according to González (1989). O. lindheimeri (Engelm) fertilized in the spring for three consecutive years showed increased protein levels of 3.1, 4.2 and 4.4 percentage units in response to applications of 67, 135 and 224 kg N/ha, respectively.

The efficiency of fertilizers and manures in semi-arid environments, however is strongly influenced by soil moisture. Therefore, fertilization should be spared for those years and seasons in which the amount of rain can guarantee its efficacy.

Response to high planting densities

High inter-plant competition reduces the reproductive ability of opuntia plants, leading to extended juvenility and generation of new cladodes, which is the objective in forage production. This effect is enhanced in the broad-bed system, which allows minimum space for individual plants. The basis of productivity from high planting densities is the total biomass production, even though individual plants may have a small yield. In contrast, a row layout allows higher individual yields with a fairly low planting density and facilitates mechanization.

Opuntia is affected by shading at any stage of growth. The thickness of the cladodes as well as the plant architecture tends to reduce photosynthetic efficiency. The most important limiting factor in high density plantings is photosynthetic active radiation (PAR), as found by García de Cortázar and Nobel (1986) using computer simulation models validated with field studies conducted under irrigated conditions in Chile. Water and temperature were found to be of secondary importance for plant productivity. Increasing Stem Area Index (SAI) or cladode area per unit ground up to 4.0 for plants that are 5 cladodes tall, productivity could be increased by up to 40%. Orientation of initial cladodes had no significant effect.

Typical plantations for vegetable production in Milpa Alta Mexico are done in furrows, training the plant to obtain a compact low height (<1.5 m) bush, with around 40 000 plants per hectare (80 × 40 cm). Similar planting methods in rows are used in Brazil to grow opuntia for fodder. Empresa Pernambucana de Pesquisa Agropecuaria (undated) recommends two planting layouts: 100 × 25 cm (40 000 plants/ha), which are more intensive than the traditional planting method using 2 m between rows and 1 m between plants. Two years after planting, the reported yields were 246 ton/ha for the high density planting versus 100 ton/ha for the low density plantation. Both systems were supplemented with fertilizers or manures. These observations support the trend of using higher planting density in Brazil.

EXTENSIVE CULTIVATION OF OPUNTIA FOR FORAGE IN ECOLOGICALLY-ORIENTED PROGRAMMES

Opuntia has been the plant of choice for socio-ecological-oriented plantations in northern Mexico. It has been used as a government employment strategy in semi-arid areas, justified by the potential ecological impact in areas depleted of their natural opuntia vegetation. The extent of over-exploitation of opuntia for fodder in northern Mexico was highlighted by Lopez et al. (1997), indicating that in the 1970s, opuntia was collected from sites located within a radius of 20 km around the main cities, while in the 1990s the distance had increased to more than 120 km.

Flores and Aranda (1997) reported that there were 3 million ha of scattered wild opuntias in northern Mexico, with another 150 000 ha planted by ranchers with government support, with the aim of increasing the availability of forage, providing refuge for the local fauna, and countering desertification. Plantation sites occupy areas where wild opuntias formerly grew. Attempts to introduce selected genotypes have been unsuccessful, so native species are preferred. Cultivation of cuttings from frost-tolerant selections has been also reported (Borrego et al., 1990). Extensive plantations of wild O. engelmannii Salm-Dick and O. rastrera Weber were reported by Medina et al. (1987).

Soil and crop management are kept to a minimum; flat terrain is preferred, without removal of initial vegetation. The opuntia is planted in furrows following contour lines, laid out with a disk. Once cactus is established - after 2-3 years - undesirable vegetation is removed and pasture grasses are seeded.

MINIMUM REQUIREMENTS FOR EXTENSIVE PLANTATIONS

Opuntia plantation on an extensive scale (>1000 ha) should be undertaken applying the same technical criteria as for smaller, commercial orchards. However, due to the limitations of the criteria used for conservation and land reclamation projects, such projects usually suffer from careless planning, deficient operation and lack of basic horticultural principles. A few points to consider are listed in the sections below.

Site selection

Even though it is imperative to reclaim all areas affected by desertification, new projects should to be directed to the least affected spots, and then gradually move onto more problematic areas. This strategy allows users to obtain faster results, while the costs of reclamation are reduced.

Select sites with the least restrictions for implementation of simple water harvesting and soil conservation techniques, soil preparation of light-slope terrain (<4%) can be done with standard agricultural machinery. Contour planting is the simplest and cheapest technique, which can be enhanced by drawing furrows close to the plants to collect rainwater to the benefit of the opuntia.

Opuntia is a perennial plant, and so it deserves care to obtain fast and sustainable yield of either cladodes or fruits. Projects that include opuntia should regard at least three years as the minimum period to assess genotype adaptation and forage productivity. The final length of this period should be adjusted according to local climatic criteria, such as the precipitation recurrence period.

Site protection

During the establishment period (1 to 2 years), opuntia needs protection from predators, and controlled livestock consumption should not start until after this period. Protection of the site is required to avoid overgrazing and destruction of the newly planted cladodes.

Planting material

Native species are to be preferred. Species that have been extensively used represent a resource that is vanishing and needs the opportunity to recover. Its suitability as animal feed is already proven by depletion! Select plants that are indigenous to the region. Mature and old plants that have survived unusual frost and drought events should be multiplied and reintroduced. Spiny species are more resistant to herbivore predation.

Collection of planting material from wild stands

Even under limiting conditions there are spots where water and soil collect; abandoned anthills and rodent burrows also provide better growing conditions for cactus plants, promoting vigour and cladode production. These spots are the best for selection of planting material. Pre-conditioning of planting material (partial dehydration) can be eliminated when planting in dry soil.

Planting techniques

Using two cladodes per planting spot increased the success of plantation to 95% in a reforestation trial conducted at Coahuila, Mexico, using O. rastrera and O. lindheimeri (Tores et al., 1990). Manually building an individual micro-catchment around the plant improved utilization of the scarce rainwater available in the region (mean annual precipitation of 327 mm).

Fertilization

Save the application of synthetic fertilizers for those years with above-average rainfall. Utilization of manure from local sources is the best choice, due to its long-term effect. The rate of manuring is limited only by local availability; responses to extremely high doses of manure have been reported in Milpa Alta, Mexico, where rates exceeding 200 ton/ha every other year are common.

Utilization

Use rotational, controlled harvesting according to site productivity. Avoid methods that lead to total destruction of the plant, such as non-selective burning and uprooting. Leaving a high number of branches allows faster plant recovery.

INTENSIVE CULTIVATION OF OPUNTIA FOR FORAGE PRODUCTION

Some of the developments intended to improve nopalitos (tender cactus pads used as a vegetable) production can be adapted towards similar systems for forage production.

Opuntia is a plant that tolerates competition and heavy pruning. The entire aerial part can be utilized as a forage if needed. It also shows a notable response to manure and chemical fertilizers. Manipulation of planting densities and plant nutrition allow large yields of fresh pads. The broad-bed planting system takes advantage of all these features. It was proposed for use in small plots (<0.5 ha) in the backyard or near the household. These spots are usually more productive than the open fields (due to the accumulation of domestic waste), and in some places they have access to limited irrigation. Both these factors benefit plant productivity. The labour needed to maintain the plot is provided by the family.

The system can produce fresh tender pads (an advantage where there is a tradition of consumption) and/or mature pads for forage. Production is higher during the summer season (the rainy season in Mexico). Longer production periods are feasible in frost-free places or by providing some sort of frost protection.

Site selection

Planting sites are more convenient if located near to the household or in a backyard, which allows for continuous care and protection. If plantations are to be located in the open field, then select the plot with easiest access. Fresh opuntia pads are heavy feedstuff, therefore it is necessary to ensure quick access to roads in good condition at any season of the year.

The site should be preferably flat, but slopes up to 3% can be handled with simple soil and water conservation practices, such as contour planting, without increasing cost of site preparation.

Land preparation

Eliminate perennial weeds or shrubs. Till the soil to facilitate broad-bed formation. Depending on the soil type, it is advisable to plough it twice. Slight terrain imperfections can be reduced by grading. Levelling the planting site improves water distribution, ensuring more uniform growth.

Rainfall management is a key issue for effective plant growth. Simple techniques that improve rainfall management have been tried successfully, the aim being to reduce runoff and impound the water in situ to allow better infiltration and extended availability for the crop. Rainwater can be collected on the site prior to planting if the field is ploughed in advance. After planting, the furrows that separate the beds can be “tied up” every 2 to 3 m to distribute rainwater evenly.

Cultivars

Spineless cultivars are most preferred for forage production in this system because they are easier to handle and process. They also present fewer problems during feeding. In Mexico, the cultivars Pabellón and CPF1 are the most suitable. Both are highly productive and posses large spineless pads. Pabellón has ovoid, thick, dark green pads, and the adult plants produce red, tasty fruits. CPF1 produces long, thin, green pads, suitable for consumption as a vegetable when tender. The fruits of this cultivar are white, with thin pericarp and slight blush. Under rainfed conditions, at least one flush of pads per growing season is produced.

Irrigation and fertilization can induce more than one layer of pads per season and increase yield. Recorded yields of fresh mature pads without irrigation in central Mexico are 75 and 118 ton/ha for Pabellón and CPF1, respectively.

Propagation material

Planting material should be collected from robust, productive and healthy plants. The pads can be collected at the end of the growing season and subjected to slight dehydration to induce suberization of the joints. Collect pads of medium to large size, devoid of suspicious dark spots or discolorations. After collection, they are stored in a shaded dry place for 2 weeks. Pad portions can also be used when planting material is scarce, but the smaller the portion, the longer the time new shoots will require to reach full size. The smallest portion that can be planted should have at least two to three areoles in each face.

To reduce rotting, the pads are treated with Bordeaux mixture prepared on the same day as treatment. Mix 1 kg of copper sulphate in 5 litres of warm water until completely dissolved, then add 1 kg of lime, stirring until the mixture is homogeneous, and then dilute to 100 litres (enough to treat up to 2000 pads).

Plantation layout

The broad-bed system provides high planting density and productivity per unit area. Several options are possible, according to the machinery available. In the authors’ experience, the best dimensions of the broad-bed are 150 cm wide with a 120 cm top, and the length is adjusted as needed. Broad-beds are built using a small (120 HP) tractor or animal-drawn device. Three or four rows of pads are aligned on top of the broad-bed with a separation of 30 cm between rows and 40 cm between pads in the row. Eliminate any buds or roots that have sprouted during storage, which most likely will be misplaced as they can interfere with the planting operation. The pads are buried halfway into the ground. Using these dimensions, 20 pads are needed for each 2-m broad-bed length.

Planting date

Tender shoots are highly susceptible to frost damage, and they start emerging 2-3 weeks after planting. Therefore planting should be done after risk of frosts is over. A safe lower limit temperature would be 5°C for most cultivars.

Fertilization

To ensure high yields, it is convenient to apply manure prior to planting. Manure can be broadcast and ploughed in prior to planting. The best results are obtained when manure is supplemented with synthetic fertilizers. Chemical fertilizers are a quick source of nutrients, while manure represents a longer-term, steady supply. A minimum of 20 ton/ha of cow manure every other year, supplemented with 90-40 (kg of N-P205) supplied annually are suggested. These rates have to be adjusted according to the source. Chemical fertilizers can be applied during the rainy season, providing half of the nitrogen fertilizer early in the season and the rest 45 days later. The product is spread along the rows and lightly covered with soil (Mondragón, 1990).

Weed control

Once planted, opuntia can serve as a nurse plant for many weed species, so periodic weeding becomes an integral element in crop management. Maintain the plot free of perennial weeds and shrubs to eliminate competition with opuntia. Weed control between the beds can be accomplished either manually or by using herbicides. Felker (1988) reported the use of glyphosate at 20 g/litre of the commercial formulation (“Roundup”) used as a broadcast post-emergence spray to control Johnson grass (Sorghum halepense) and Bermuda grass (Cynodon dactylon).

Management of pests and diseases

Pests that thrive inside the pads are the most destructive and difficult to control. However selective pruning can help to maintain a healthy plantation. Some rotting problems can also be solved by pruning. Some pests that live on the surface of the pads, such as mealy bugs and thrips, can be controlled with contact insecticides. Effective control has been achieved by spraying with dithiocarbamate at 1 kg/200 litre of water.

Harvesting

Mature pads can be collected at the end of the growing season. They are detached from the plant using a sharp knife, with a clean stroke right in the joint. Avoid unnecessary chopping of the harvested pad or the plant, to reduce risk of rotting. The number of pads to be harvested varies with cultivar and age of the plant. During the first year, 2-4 pads per plant can be collected. In order to get steady yield, the plants are left with only two branches (“rabbit ears”) oriented along the broadbed. Cactus pads can be consumed directly on the plants, but uncontrolled browsing can cause damage. It is more efficient to collect and store them close to the livestock yard until needed.

Storage

Fresh pads should be stored in a shady dry spot. They can be either stacked or arranged in rows sitting on their sides. Avoid spots that collect runoff in order to minimize rotting or sprouting. Those pads in close contact to the ground need to be flipped over every 4 to 6 weeks to avoid rooting. Some relief from direct sunshine can be obtained with a thin layer of dry straw spread on top of the stored pads. Direct sunshine induces pad deformations and chlorophyll degradation on the exposed area, thus reducing nutritional quality. Under the semi-arid cool conditions of central Mexico, the authors have stored pads for up to six months without appreciable losses.

HYDROPONIC CULTIVATION

Although water has been considered to be a renewable resource in some areas, population growth and urbanization are changing the scenario. Initiatives to improve water management in urban as well as agricultural lands are increasingly required. Hydroponics is perhaps the last frontier for opuntia fodder production: it can be adapted to arid areas where the availability of water for irrigation is restricted and there is strong pressure on grasslands. Hydroponics also improves nutrient use efficiency.

Hydroponic modules could allow the efficient utilization of limited volumes of water to produce food or forage crops, improving rural income. Some systems are relatively easy to handle and could be quickly adopted. The size of the hydroponic operation can be adjusted to other farm operations, and farmers could consider it as a part-time occupation and self-employment strategy.

In Mexico, some of the most traditional growers are hesitant to use hydroponics, although commercial modules to produce export-quality vegetables are becoming fashionable in central and northwest Mexico.

Small-scale hydroponics possesses special significance for arid and semi-arid zones, where agricultural production is limited by low water availability. In many of these areas, there are shallow artesian wells and intermittent water sources that can provide enough water to irrigate plant species such as opuntia, characterized by its high water use efficiency and productivity. Opuntia can produce up to 47 t/ha/yr as irrigated high-density plantations in open fields, which is higher than C3 and some C4 plants (Nobel, 1998).

Exploratory trials conducted in central Mexico showed that hydroponics may play an important role in fodder production in extreme climates. The results of three of these trials are discussed below.

HYDROPONICS: ADVANTAGES AND DISADVANTAGES

Hydroponics literally means “waterworks,” and includes all methods and systems to grow plants without soil (Steiner, 1977; Douglas, 1985; Gómez 1995). According to Durany (1982), the most common hydroponic systems are:

Cultivation in liquid media. In this system, the plants have their roots immersed in the nutrient solution and the type of support depends on the crop.

(iii) Cultivation on solid, inert and porous substrates. In this case, the plant anchors to the substrate and acquires the nutrient solution by percolation.

Sub-irrigation belongs to the latter type: the nutrient solution is provided and drained through the same inlet (Steiner, 1977). The system is “closed” and recycles the nutrient solution every two to six weeks (Resh, 1987). Numerous variants of this type have been developed using the latest technological advances.

Hydroponics promotes efficient water and nutrient use. Compared to traditional agriculture, hydroponics uses only an insignificant fraction of the water. Hydroponics allows the use of poor quality water, either moderately saline or alkaline. Some disadvantages are: high energy input (gas, gasoline, oil and electricity) and initial investment. Basic water-quality analysis and some training are needed to prepare and maintain the nutrient solutions. The availability of simple instruments to determine pH and electro-conductivity should also be considered.

Hydroponics ensures better stand establishment, leading to higher densities, saves water and nutrients, and provides some protection against limiting climatic factors such as drought and light frosts. Well-fed plants tolerate cold temperatures better and recover faster from frost damage.

THE SYSTEM

The system utilized to grow opuntia was sub-irrigation, using lava as growing media. The system includes:

(xvii) Storage tank for the nutrient solution.

(xviii) Planting benches. Rectangular shaped and arranged in five pairs, they covered 18 m2 each (15 × 1.2 m) and were 30 cm deep.

(xix) Growing medium. Red volcanic gravel, with a granulometry between 5 and 20 mm. Gravel, crushed lava, basalt gravel, porous or non-porous or any other rocky inorganic material can also be used.

(vi) Distribution tanks. Built of mortar and bricks, they distribute and drain the nutrient solution.

(vii) Hydraulic network. A gasoline pump (4 HP) provides the power, and is connected to a network of 50 mm PVC pipes.

The nutrient solution is prepared from commercial sources (Table 50). Two methods of preparation can be used: stock solutions or a dry mix of commercial fertilizers. In both methods, the fertilizers of low solubility are dissolved in advance, then added first to the solution. The products with acid reaction are added next, followed by the micronutrients in solution.

The pH is maintained at around 6.5 by adding either phosphoric or nitric acid, according to the pH readings, with mean values of 3.5 dS/m electro-conductivity. The nutrient solution is replaced every 15 days, after plants have consumed about two-thirds of the initial volume.

Table 50. Composition of nutrient solution

Source

Concentration (g/m3)

Nutrient

Potassium nitrate

150 - 250

N

Phosphoric acid

40

P

Potassium sulphate

289.4 - 350

K

Calcium nitrate

210

Ca

Magnesium sulphate

40

Mg

Ferrous sulphate

12

Fe

Copper sulphate

0.1

Cu

Zinc sulphate

0.2

Zn

Boric acid

0.6

B

Source: Calderón, 1995

The nutrient solution moves out to the storage tank due to the suction exerted by the pump, then it is deposited in the check tanks to feed the distribution network and fed to the growing benches. The same negative pressure forces the solution up to the surface of the planting medium. Once the solution floods the medium, the pump stalls and drainage begins by gravity. The growing benches are fed in pairs. The nutrient solution is briefly in contact with the roots, reducing evaporation and potential rotting problems. The key mechanisms of the system are the recirculation and efficient drainage of the solution.

Planting material. Spineless accessions from central Mexico with previous records of high productivity under open field conditions were selected for the trials. They were provided by INIFAP (National Institute of Agricultural, Forestry and Husbandry Research). The plants were allowed to grow freely and a single yield evaluation was performed after six months. The variables included cladode length and width, plant diameter and number of shoots, and fresh and dry weights. The tissue was sampled and sent for nutrient analysis.

Effect of irrigation schedule and planting method. Two cladode orientations - NS and EW - as well as two planting positions - vertical buried vs. horizontal on top of the soil - were studied. Once the plants were established they were subjected to four irrigation schedules: twice a day every day; twice a day every other day; once a day every day; and once a day every other day. Recorded variables were establishment percentage; days to budding; number of shoots; and yield on a fresh (FW) and dry weight (DW) basis.

The tissues collected from the 15 most productive accessions were analysed for bromatological parameters, neutral and acid detergent fibre (according to Goering and Van Soest 1970), as well as in vitro digestibility.

GENOTYPE PERFORMANCE

All accessions responded well to cultivation in hydroponics and a positive correlation between number of shoots and weight was detected. No reduction was observed in dry weight associated with higher number of shoots. After six months, the average number of mature pads was 10.2 (ranging from 1 to 18 pads per plant), 97% of the accessions presented two or more layers of pads and cv. Valtierrilla yield was larger (Table 51). The morphological and phenotypic features did not change significantly in hydroponic cultivation. An interesting observation was that O. robusta initiated budding at the same time as in the wild. Average fresh weight per pad was 475 g, reaching a yield of 5 kg of fresh pads per plant in six months.

Considering the maximum values of number of cladodes per plant (18) and cladode weight (845 g), the experimental yields could reach 15 kg fresh weight per plant with cv. Selection 34 and cv. Milpa Alta. If a hydroponics module has a planting density of 30 000 plants/ha, the potential yield could reach 450 ton/ha on a fresh weight basis in six months: sufficient volume to be the sole feed source for a herd of 30 cows for 180 days, or 523 pregnant sheep for 3 months. The authors’ observations confirmed the findings of Calderón (1995).

The N content in cladode tissue ranged from 1.73 to 4.02% on dry basis (Table 52), supporting the report that N content in opuntia is higher than the best grass, Nobel (1998). According to the analysis, cv. Valtierrilla and cv. Tapón Hembra showed an N content above 4%. If this value is converted to protein content, then opuntia can be compared to other valuable forage crops, such as alfalfa (Table 52).

Considering plant productivity, absence of spines and early budding, 17 genotypes were out-standing. Some of the accessions qualify as dual use: vegetable and fodder; or fruit and fodder. They can and do represent an important fodder source for the driest part of the year (April-May).

Reports from Lopez et al. (1988) indicated a phosphorus range of 0.1 to 0.5 % on dry basis as influenced by cultivar, cladode age and planting site. Under hydroponics, the average content was 0.55 %, with a maximum of 0.84% for cv. Tapón Hembra. K was the nutrient that showed the highest accumulation (mean 3.89%). Six cultivars - Pabellón, #75, Redondo, RSR, RDR and #70 - showed above average K concentrations, with 5.96,5.75,5.72,5.50,5.37 and 5.24%, respectively.

Calcium is found mostly in the cell wall of cacti, providing mechanical support to the cell. It also participates in ATP and phospholipid hydrolysis. In cacti, Ca is mostly found as oxalate crystals and druses (Gibson and Nobel, 1986). The average content of calcium in opuntia tissue varies from 2 to 9.5%, depending on plant age and soil type. Cladodes produced in hydroponics had an average calcium content of 2.66% (Table 52), with a maximum of 6.4 in cv. #V-3. A study of the chemical form in which calcium is present in opuntia is needed in order to understand its significance for animal or human nutrition.

Ash content ranged from 18.68 to 30.31%, higher than any other regional forage. Reported values (NRC, 1984) are only 7.6,7.2 and 6.4 for oat hay, maize stover and sorghum stover, respectively. Fodder production with hydroponics could be an important source to cover maintenance and production levels of Ca, P, K and Zn.

Protein content is one of the most limiting factors for cattle raising in semi-arid rangelands (Fuentes, 1992). Wild opuntia has a range of 2.72 to 5.8% of crude protein, insufficient to provide for the needs of cattle and sheep (Table 53), leading to weight loss. Protein content in cactus fodder obtained with hydroponics ranged from 11.72 to 18.07% for cv. LCNF and cv. Pabellón Amarillo, respectively (Table 54).

These values cover the minimum requirements for grazing cattle, sheep and goats (McDonald et al., 1981). The nutrients content found in some of the accessions tested are similar to those reported for good quality fodder such as alfalfa, maize silage and orchard grass (12-20.8.4 and 15% CP, respectively (NRC, 1984)) and higher than maize stover and wild opuntia (Table 53).

Table 51. Growth features of opuntia accessions from central Mexico, cultivated in hydroponics

Accession

Cladode DW (g)

Number of cladodes/plant

DW
(g/plant)

1st layer

2nd layer

Total

Average

Redondo

16.6

8

10

18

6.0

99.6

ACNF

27.5

8

9

17

5.6

154.0

70

21.8

13

37

40

13.3

289.0

Milpa Alta

37.1

6

13

19

6.3

233.7

Tehuacán

22.4

11

9

20

6.6

147.8

44

29.7

9

18

28

9.3

276.1

Rosalito

22.3

9

21

30

10.0

223.0

RSA

26.8

13

33

46

15.3

410.0

40

14.9

16

34

50

16.6

247.3

Villanueva

20.9

15

17

32

10.6

221.5

RSR

33.2

7

26

35

11.6

385.1

RDR

12.6

7

17

24

8.0

100.8

34

17.5

15

40

55

18.3

320.2

LCNF

28.7

7

18

25

8.3

238.2

75

13.5

9

22

31

10.3

139.0

Italiano

12.9

10

23

33

11.0

141.9

V-3

13.2

7

6

13

4.3

56.7

T-L

10.6

10

35

45

15.0

159.0

Valtierrilla*

7.6

17

4

21

13.3

101.0

V-1

13.2

11

29

40

13.3

175.5

RSB

8.9

12

32

44

14.6

129.9

R-7

19.4

11

22

33

11.0

213.4

F-1

29.5

3

19

22

7.3

215.3

AGO

29.1

8

23

31

10.3

299.0

R-72

15.2

9

25

34

11.3

171.7

Pabellón

15.2

13

24

37

12.3

187.0

COPENA

13.0

9

21

30

10

130.0

Pabellón Amarillo

23.7

8

15

22

7.3

173.0

Tapón Hembra

10.4

7

9

16

5.3

55.1

Tapón macho

4.5

3

0

3

1.0

4.5

S-34

21.5

12

29

41

13.6

292.0

S-35

7.0

5

10

15

5.0

35.0

Tezontepec

5.4

10

7

17

5.6

30.20

Irapuato

8.0

11

5

16

5.3

42.0

Control

5

0


5

1.6

8.0

Note: * = Produced more than three layers of cladodes.

Table 52. Nutrient content of 30 accessions of opuntia from Central Mexico

Accession

N
%

P
%

K
%

Ca
%

Mg
%

Fe
ppm

Mn
ppm

Cu
ppm

Zn
ppm

B
ppm

Redondo

2.68

0.38

5.72

1.65

1.28

135

39

3

38

42

ACNR

3.39

0.32

4.79

1.16

0.93

54

26

0

23

32

70

2.60

0.53

5.24

2.07

1.84

177

206

3

45

44

Milpa Alta

3.31

0.36

4.18

2.06

1.24

305

14

0

32

57

Tehuacán

3.15

0.67

4.58

2.00

1.71

178

24

2

50

49

44

3.70

0.24

2.20

2.70

0.87

102

153

0

20

36

Rosalito

3.23

0.56

4.59

2.32

2.15

160

56

3

53

60

RSA

3.62

0.56

4.42

1.89

1.95

159

115

0.61

41

55

40

3.62

0.71

4.81

2.91

1.83

144

331

4

63

53

Villanueva

1.73

0.43

3.12

4.95

1.65

293

92

1

34

87

RSR

2.99

0.62

5.50

1.97

2.01

233

102

3

101

58

RDR

3.15

0.48

5.37

2.99

2.27

152

363

1.27

51

67

34

2.60

0.50

3.76

2.65

1.70

149

163

1.34

49

56

LCNF

3.23

0.54

4.30

2.36

1.55

168

366

2

48

56

75

3.15

0.74

5.75

2.12

1.78

126

304

3

48

61

Italiano

3.54

0.73

4.80

2.59

1.82

105

23

0

45

92

V-3

2.99

0.60

4.11

6.40

1.84

116

300

0

42

77

T-L

3.07

0.75

4.09

2.74

1.87

152

46

3

50

62

Valtierrilla

4.02

0.59

3.42

3.68

1.72

231

307

0.74

47

98

V-1

3.39

0.53

4.77

2.31

1.59

144

32

1.40

37

63

RSB

2.91

0.66

3.92

2.77

1.84

103

136

1.19

49

74

R-7

3.62

0.60

2.75

3.09

2.00

138

65

1.78

49

64

F-1

3.54

0.58

3.33

2.35

1.51

104

95

0

42

53

AGO

3.86

0.55

2.18

3.29

1.41

108

71

0

50

50

R-72

3.39

0.50

2.47

2.43

1.63

116

370

0.91

36

69

Pabellón

3.15

0.56

5.96

2.25

1.85

114

442

1.90

46

74

COPENA

2.76

0.37

3.01

2.59

2.03

91

29

0

47

69

Pabellón amarillo

3.15

0.62

4.87

2.31

1.70

133

37

0

42

72

Tapón hembra

4.02

0.84

2.78

3.08

2.05

103

60

0.06

53

83

Tapón macho

3.62

0.46

2.98

2.23

1.54

89

64

0

48

82

DM digestibility in vitro varied from 84.9 to 95.5% (Table 54), above values reported elsewhere (e.g. Flores and Aguillar, 1992; Lastra and Pérez, 1978; De Kock, 1998). NDF or cell wall values were below those reported for most of the forages used in the region to feed cattle (NRC, 1984). It means a higher potentially digestible rate of cell contents, which might explain the high in vitro digestibility observed in cv. Pabellón Amarillo and cv. Villanueva.

Table 53. Analysis of opuntia (Opuntia spp.) and some common feedstuffs used in semi-arid zones compared to nutritional requirements of cattle and sheep(1)


ME
(Kcal/kg DM)

Protein
(%)

Ca
(%)

P
(%)

Na
(%)

DMC(4)
kg

Alfalfa

2.10

17

1.41

0.24

0.12


Corn stover

1.81

6.6

0.57

0.10

0.07


Opuntia


4

1.4

0.2

0.1


Nutritional requirements(1)

Cow(2)

2.21

10.32

0.29

0.21

0.1

9.66

Sheep(3)

1.92

9.55

0.37

0.23

0.1

1.3

Notes: (1) Nutritional requirements based on NRC, 1984. (2) Cow of 450 kg liveweight producing 3 kg milk/day. (3) Sheep of 45 kg liveweight in the last third of pregnancy. (4) DMC = Dry matter consumption.

Table 54. Nutrient content and in vitro digestibility of opuntia grown in hydroponics

Accession

DM
(%)

Ash
(%)

Crude protein
(%)

ADF
(%)

NDF
(%)

Cellular content
(%)

Hemi- cellulose
(%)

DM in vitro digestibility
(%)

Italiano

94.61

24.01

17.78

18.67

29.42

70.58

10.75

88.4

40

92.90

25.44

16.25

23.01

35.71

64.29

12.70

87.2

34

92.79

26.37

15.28

19.66

27.63

72.37

7.97

89.9

RDR

93.17

26.28

15.21

23.6

26.71

73.29

3.11

86.7

LCNF

92.59

28.59

18.07

24.78

30.35

69.65

5.57

87.8

Villanueva

92.96

30.31

15.55

21.17

39.27

60.73

18.10

84.9

Tehuacán

93.75

22.35

15.77

14.45

32.26

67.74

17.81

91.3

75

92.65

27.37

15.25

16.20

32.23

67.77

16.03

87.2

70

92.94

22.51

13.67

20.08

37.42

62.58

17.34

84.8

RSR

93.19

23.52

15.91

20.21

37.23

62.77

17.02

91.5

Rosalito

92.75

28.40

15.58

20.78

34.98

65.02

14.20

92.4

AGD

92.32

26.01

16.41

21.97

33.97

66.03

12.00

90.6

44

93.17

28.07

15.86

21.00

33.36

66.64

12.36

22.6

COPENA

92.39

24.59

16.55

18.53

33.08

66.92

14.55

91.9

P. Amarillo

92.77

18.68

11.72

18.37

37.10

62.90

18.73

95.5

Key: ADF = acid detergent insoluble fibre. NDF = neutral detergent insoluble fibre.

Wild opuntia is an important source of water during the dry season; there are reports of cattle feeding on opuntia for 400 to 525 days using opuntia as the only source of water. However, moisture content of forage obtained in hydroponics ranged from 90-92%, which could limit usefulness. DM requirements would be difficult to meet because of the associated high volumes of consumption, as cattle would have to consume 90-100 kg/day of fresh opuntia fodder. An interesting possibility is the use of dehydrated opuntia, or its combination with other sources with low moisture content, like maize and sorghum stover, dry bean straw, etc. Considering agronomic as well as nutritional criteria, the best selections were “34”, “70”, “40” and “LCNF.”

Nutrient accumulation value is obtained by multiplying DW by the nutrient concentration and dividing into 100, which is the nutrient content in grams accumulated in the cladode during a specific period. In this study, it corresponds to six months (Table 55). The extraction order for the main elements was K, N, Ca and P, with mean values of 0.77, 0.60, 0.48 and 0.09 g, respectively. High extraction results from high DM production and high concentration. Regarding N accumulation in cvs Milpa Alta (1.22 g), AGO (1.12 g) and Selection 44 (1.09 g) had the highest values, while for P cvs RSR (0.20 g) and F-1 (0.17 g) had the highest values. In the case of K, the genotypes with the highest accumulation were Milpa Alta (1.55 g), LCNF (1.23 g) and Pabellón Amarillo (1.15 g). Significant Ca accumulation was recorded for cvs Villanueva (1.03 g) and AGO (0.95 g).

Effect of irrigation schedule and planting method

Plant survival varied from 70.2 to 88%; the failures were attributed to rotting, probably due to origin of propagules, as planting material was collected from a previous hydroponic unit and was more succulent than regular material collected from commercial orchards.

Bud emergence started in February, simultaneously with late frosts, but a second flush was observed in March, except for cv. Río Verde and cv. Tapón Hembra, which generated vegetative buds until April. There were large differences in FW and DW among irrigation schedules (p<0.05), irrigating twice a day every other day was significantly superior to the rest of the irrigation treatments: the yield differences were attributed only to cladode size (Table 56). Cladodes planted in the vertical position and N-S oriented presented a higher number of shoots and higher yield (Table 58).

It is feasible to produce high quality fodder under hydroponics during the dry season when other sources of fodder are scarce. The best results are obtained by irrigating twice a day every other day. We detected four outstanding genotypes, namely “34,” “70,” “40” and “LCNF,” which produce tender cladodes of good quality for consumption as vegetables, and mature cladodes for fodder. The system allowed an efficient use of water and nutrients, making it competitive with other, traditional

Table 55. NPK and Ca accumulation in 30 accessions of opuntia grown in hydroponics

Accession

DW
(g)

Accumulation (g)

N

P

K

Ca

1. Redondo

16.6

0.44

0.06

0.94

0.27

2. ACNF

27.5

0.93

0.08

1.31

0.31

3. 70

21.8

0.56

0.11

1.14

0.45

4. Milpa Alta

37.1

1.22

0.13

1.55

0.76

5. Tehuacán

22.4

0.70

0.15

1.02

0.44

6. 44

29.7

1.09

0.07

0.65

0.80

7. Rosalito

22.3

0.72

0.12

1.02

0.51

8. RSA

26.8

0.80

0.15

1.18

0.50

9. 40

14.9

0.53

0.10

0.71

0.43

10. Villanueva

20.9

0.36

0.08

0.65

1.03

11. RSR

33.2

0.99

0.20

1.82

0.65

12. RDR

12.6

0.39

0.06

0.67

0.37

13. 34

17.5

0.45

0.08

0.65

0.46

14. LCNF

28.7

0.92

0.15

1.23

0.67

15. 75

13.5

0.42

0.09

0.77

0.28

16. Italiano

12.9

0.45

0.09

0.61

0.33

17. V-3

13.2

0.39

0.07

0.54

0.84

18. T-L

10.6

0.32

0.07

0.43

0.29

19. Valtierrilla

7.6*

0.30

0.04

0.25

0.27

20. V-1

13.2

0.44

0.06

0.62

0.30

21. RSB

8.9

0.25

0.05

0.34

0.24

22. R-7

19.4

0.70

0.11

0.53

0.59

23. F-1

29.5

1.04

0.17

0.97

0.69

24. AGO

29.1

1.12

0.16

0.63

0.95

25. R-72

15.2

0.51

0.07

0.37

0.36

26. Pabellón

15.2

0.47

0.08

0.90

0.34

27. COPENA

13.0

0.35

0.04

0.39

0.33

28. Pabellón Amarillo

23.7

0.74

0.14

1.15

0.54

29. Tapón Hembra

10.4

0.08

0.06

0.35

0.38

30. Tapón Macho

4.5

0.16

0.02

0.13

0.10

Table 56. Effect of irrigation schedule on number of shoots, dry weight and yield of forage opuntia

Irrigation frequency

Shoots/plant

FW (g)

DW (g)

Once a day

4.65

875.85 b

65.73 b

Twice every other day

5.07

1401.4 a

84.20 a

Twice a day

4.1

1080.8 b

75.11 b

Once every other day

5.1

574.7 c

52.07 c

Note: Different letters in the same column indicate significantly (p<0.05) different means

Water use efficiency

All genotypes tested presented higher WUE compared to the control (Table 59). RSA, Villanueva and 43 appeared superior. The WUE values observed are lower than the data reported by de Kock (1998) for irrigated opuntia.


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