As part of the design of the farm these plants not only will act as windbreakers but also contribute to micro climate if planted along each plot border 4 sides, along roads, fence boundaries swale bunds on down stream side.
Multipurpose Exotic Species in Small Farm Agroforestry
Dr. J.N. Daniel
Traditional agroforestry systems in India have usually included native tree species as the perennial component. Fast-growing multipurpose tree species (MPTS) are preferred in intensive agroforestry models introduced in recent times. Most of these species are exotics of small to medium size, amenable to repeated pruning management and ideally suited for small farm conditions. BAIF Development Research Foundation has introduced several of these species in small farms through rural development programmes. Among them, Leucaena leucocephala (varieties K8 and K636) has succeeded as a preferred species for agroforestry and farm forestry interventions throughout the country. Improved genotypes of Gliricidia sepium and Sesbania sesban have shown promise for agroforestry, but their use in small farms is limited at present. The use of Casuarina cunninghamiana in social forestry programmes has been growing in Karnataka. Field experimentation with Jatropha curcas showed that seed yields under low fertility rainfed conditions are much lower than those reported in literature.
In agroforestry systems on small farms of less than 1.0 ha, the border is the most preferred site for MPTS. Therefore, it is the exotics suitable for live fencing that figure prominently in the development projects implemented by BAIF. Participants in these projects are mostly subsistence farmers owning less than 2.0 ha of low-fertility land in the semi-arid tropics and depend totally or predominantly on rain-fed agriculture. In the tree-based model introduced by BAIF, the live fence constitutes of at least five MPTS at the time of establishment, but the species diversity tends to come down with time.
Key words: agroforestry, live fencing, multipurpose trees, small farms
Exotic tree species have found their way into Indian farming systems since long. In dry tropical areas, the traditional practice of farmers has been to plant species like neem and mango within the cropping area, but include the exotics along the fence and on farm bunds. Hence, species such as Jatropha curcas and Prosopis juliflora are usually found on farm boundaries. Many of the exotic tree species probably entered the local farm scene through plantation agriculture. Because commercial plantations were mostly established in humid tropical areas, the species introduced were generally those adapted to high moisture regimes. In due course, small farmers brought some of these species with adaptation to a wider environmental range to semi-arid areas.
The common characteristics of exotic species preferred for agroforestry are fast growth, multiple uses and small to medium canopy size. A majority of these species also have the ability to fix atmospheric nitrogen and are amenable to repeated pruning management. Recognising the range of benefits, BAIF Development Research Foundation has been interested in multi-purpose tree species since the early 1970s. Initially, the focus was to produce fodder in hedges. The vigorous growth seen in some of them, particularly in Leucaena leucocephala, shifted the interest to fodder trees. Thereafter, elite germplasm of some multipurpose tree species was obtained, their performance tested under local conditions and promoted through the development projects implemented by BAIF. The experiences of the promotional efforts and information on some of the elite germplasm are discussed in this paper.
2. Production Systems with Multi-Purpose Tree Species
In the production system popularised by BAIF in its development projects, annual crops and horticultural perennials are planted in the cropping area of the land whereas the multi-purpose tree species (MPTS) are planted along the perimeter. Apprehensions about the suitability of MPTS for dry land agroforestry are expressed by many because of the substantial reduction in annual crop yields due to the competition from perennial species in the system. This is partially overcome in the BAIF-promoted model as the interface area between the MPTS and annual crops is minimised by restricting the trees to the perimeter as live fencing. The MPTS preferred for this purpose are mostly exotics like Leucaena leucocephala, Gliricidia sepium, Acacia species and Sesbania species.
The main reason for the instant acceptance of exotic MPTS by farming communities is their fast-growing nature. In L. leucocephala, for example, the slow-growing early introduction did not find favour with growers although it had become naturalised in the country. Fast-growing MPTS produce substantial quantities of biomass within a short period of time. This biomass in the form of fresh foliage, leaf litter and wood meets the fodder, fuel, timber and manure requirements of the rural population. The introduction of MPTS on farmlands enabled communities that had become dependent on nearby forests and common lands for their biomass to grow at least some of it on their own land.
There are some exotic species such as Eucalyptus tereticornis and Acacia auriculiformis that have gained popularity among farmers in semi-arid areas. BAIF’s strategy is to have diversity in the species planted as live fencing. For this reason, beneficiaries in development projects are encouraged to plant not more than 20% of a single species, necessitating the inclusion of at least five species. However, this is not an easy goal to achieve. Although species diversity is ensured at the time of planting, it is not maintained in the long run. Preferential selection of species by farmers during gap filling and harvesting ultimately results in a live fence dominated by 1-3 species.
3. Experiences with Exotics in Agroforestry
The experience of BAIF with exotic tree species includes obtaining germplasm, performance evaluation under local conditions, multiplication and promotion. The status of five key species in this regard is presented below.
3.1 Leucaena leucocephala
BAIF, known for its work on cattle development, received attention among the forestry community in the country with its work with Leucaena leucocephala (subabul). The Hawaiian Giant type of subabul made an immediate impact on its introduction because of its unusually high rates of growth and biomass accumulation. The value of this biomass as fodder, wood and manure appealed to small farmers throughout the country. The K-8 variety of subabul adapted extremely well to semi-arid conditions and soon became one of the most popular species for all types of forestry programmes in India.
Subabul did have certain shortcomings as an agroforestry species. Unlike Prosopis cineraria and Butea monosperma in the native agroforestry systems, in intensive systems such as alley cropping, subabul causes substantial yield losses of annual crops. This is undesirable in small farms where food production is the priority. These losses can be minimised by adopting plant arrangements that reduce the tree-crop interface. For example, in the model promoted by BAIF, subabul and other forestry species are confined to the farm boundary. Even such an arrangement does not overcome the second drawback of subabul, that of weediness.
Huge quantities of seed produced annually by subabul trees get dispersed over a large area of land. They germinate during the rainy season and establish easily. The seedlings make an excellent green manure when ploughed under after the kharif crop. In single cropped areas, however, this may not be possible. But the seedlings that survive the summer can still be ploughed under during the land preparation for the kharif crop. If a land remains uncultivated, the seedlings will be almost two years old by the next rainy season and they would have become woody and difficult to weed out. It is at this stage subabul becomes a weed.
A serious problem that subabul successfully overcame in the late 1980s was the psyllid pest. The initial devastation in most areas was acute, but the ability of the trees to recover after defoliation by the pest and the build up of natural enemies of the pest resulted in the continued use of K-8 variety of subabul. Globally, in most planting programmes K-8 was discontinued and was replaced by K-636. Under Indian conditions, the differences in the growth characteristics between the two varieties are not too evident, but growers have reported K-636 to be superior. In general, K-636 has a better tree foam, faster growth and greater tolerance to low temperature than K-8. In recent years, subabul has become popular in farm forestry systems of Andhra Pradesh that grow this species for the paper pulp industry.
3.2 Gliricidia sepium
In spite of its familiarity, the use of gliricidia by small farmers is limited. In Karnataka, it is referred to as the green manure plant and this is perhaps the main use of this species in India. In other countries, gliricidia is regarded as an excellent fodder. The Oxford Forestry Institute of United Kingdom conducted a long-term international provenance trial of gliricidia (OFI, 1996). Results of this trial showed three provenances of gliricidia from its native range of Guatamala to be more productive than other entries. These provenances – Retalhuleu, Belen Rivas and Monterrico - have been introduced in the development projects of BAIF. Their performance under local conditions does not appear to be drastically different from the local genotype. Some of the farmers in whose field boundaries these provenances have been planted use the foliage as green manure for rice. Because the usual fertiliser or manure application rates of these farmers are very small, they have been able to increase the rice yields by about 10% by green manuring with gliricidia alone.
3.3 Sesbania species
There are two Sesbania species of interest: S. sesban (sesban) and S. formosa. The commonly occurring S. sesban in India tends to have an upright growth with limited lateral spread. In contrast, a cultivar named Mount Cotton, obtained from Australia, has a bushy spreading habit. This cultivar produces more biomass than the erect-growing type (Gutteridge and Shelton, 1995). Whereas the earlier type is suitable for farm bunds and borders, Mount Cotton can be used for intensive fodder production systems and planting as hedgerows. Another Sesbania in BAIF’s collection is S. formosa. This native of Australia closely resembles S. grandiflora. Preliminary observations show a potential use of the wood of this species for pencil making.
3.4 Jatropha curcas
A species generating a great deal of interest in recent times is Jatropha curcas. Interest in this species stems from the biodiesel utility of its seed oil. Like gliricidia, it is also a species of Central American origin, but has become naturalised in India. This species shows wide variation in the natural stands found in different parts of the country. Most promotional literature on jatropha emphasise the hardiness of the species, low management requirement, starts bearing in the second year, more than 10 tons per ha of seed yield and 25-50% kernel oil content. BAIF conducted a field trial on jatropha in its Karnataka station to evaluate three genotypes planted in three plant densities. The genotypes were collections from Karnataka and Maharashtra and a variety from Nicaragua; the densities were 2500, 3300 and 4000 plants per ha. The nine treatments were replicated three times and arranged in a randomised complete block design. The average annual rainfall of the site is about 600 mm, and the experimental field was of marginal soil fertility. The seed yields obtained at 40 and 60 months after planting are shown in Figures 1 and 2.
The results showed that there are substantial differences among the genotypes in their seed production potential, with the local collection outperforming others. Another observation was that seed yield declined with increasing plant density. The maximum seed yield obtained was about 500 kg per ha from the fourth year onwards. The soil and input application rates in this study were at levels appropriate for small farmers. At such levels, it does appear that the very high yields often projected are unlikely to be achieved.
3.5 Other species
The commonly found Casuarina species in India is C. equisetifolia. In its Karnataka site, BAIF tried C. cunninghamiana and the results are very encouraging. The tree has a beautiful shape and it is an excellent candidate for agroforestry. There are some indications that it may be more susceptible to moisture stress than C. equisetifolia, but this needs to be verified through multi-locational trials. The Karnataka Forest Department has established block plantations of C. cunninghamiana while many small farmers have been planting it on bunds and as live fencing. BAIF also participated in an international provenance trial for C. equisetifolia that was coordinated by CSIRO in Australia. This trial was also carried out at the Karnataka location, but none of the genotypes appeared to be outstanding.
Calliandra calothyrsus is another species that BAIF tried in its research centres in Maharashtra and Karnataka. Although this is a species for humid tropical conditions, the genetic variation in adaptability to dry conditions was examined with five genotypes obtained from the Oxford Forestry Institute, United Kingdom. In both locations, the growth was not to the level of yielding high quantities of fodder, which is the main utility of the species. There was no seed production in the Maharashtra location, probably because of the absence of appropriate pollinators. There is seed production in the Karnataka location and farmers in humid areas of the state are including it in their farming system. Like subabul, this species also has the tendency to become a weed in humid areas.
4. Concluding Remarks
Small farmers in the country have benefited by the introduction of exotic species on small farms. In general, it appears that the benefits of exotics outweigh the problems. Ability to withstand harsh environmental conditions and produce enormous quantities of biomass are the major benefits of this group of species, but these same traits also make them to be potential weeds. Fast-growing species are likely to compete with annual crops and this has to be minimised by management and plant arrangement. Planned introduction of exotics in combination with natives and their regular management in the chosen agroforestry or farm forestry systems are necessary to realise their potential.
The author gratefully acknowledges the information provided by Dr. G. V. Hegde (BAIF Institute for Rural Development – Karnataka) and Mr. P. S. Takawale (BAIF Central Research Station, Urulikanchan, Pune).
Gutteridge, R. C. and H. M. Shelton (1995). New herbage plant cultivar: (a) Sesbania sesban (L.) Merrill (sesban) cv. Mount Cotton. Tropical Grasslands 29(3): 188-189. Dep. Agric., Univ. Queensland, Brisbane, QLD 4072, Australia.
Hughes, C. E. 1998. The Genus Leucaena: A Genetic Resources Handbook. Tropical Forestry Paper 37. Oxford Forestry Institute, Oxford, U.K.
Oxford Forestry Institute, 1996. Gliricidia sepium: Genetic Resources for Farmers. Tropical Forestry Paper 33. (J. L. Stewart, G. E. Allison and A. J. Simon, eds.), Oxford Forestry Institute, Oxford, U.K.