Major Contributor: F. Owino
2.0 Performance objectives
2.1 Suitable tree and shrub species for alley farming
2.2 Methods for MPT screening and evaluation
2.3 Sources of seeds and seedlings
2.4 MPTs germplasm documentation and improvement
2.5 Feedback exercises
2.6 Suggested reading/ references
Unit 2 is intended to enable you to:
1. Name the multipurpose tree species (MPTs) that have received the most attention in studies of alley farming.2. Recall the criteria for selecting suitable MPT species for alley farming, including special considerations for production of livestock forage and for acid soils.
3. Describe the most significant insect pest threat to Leucaena.
4. Recognize in the field the best-known alley farming MPT species.
5. Describe the three experimental stages in MPT evaluation.
6. Recall important guidelines for screening MPTs.
7. Describe nursery operations for raising vigorous and uniform seedlings for field experimentation.
8. Name organizations which can supply well documented propagules for experiments.
9. Discuss the importance of MPTs germplasm collection and documentation.
2.1.1 General Selection Criteria
2.1.2 Additional Criteria for Forage Production
2.1.3 Environmental Adaptation Selection Criteria
A number of multipurpose tree and shrub species (MPTs) are potentially suitable for alley farming, but only a handful have been tested. Woody species that have been most commonly studied in the system worldwide include Leucaena leucocephala, Gliricidia sepium, Cassia siamea, Calliandra callothyrsus, Flemingia macrophylla and Acacia auriculiformis. Some indigenous African tree species such as Alchornea cordifolia and Acioa barteri have also been studied in alley fanning trials.
Leguminous trees and shrubs that can fix atmospheric nitrogen are preferred over non-legumes. Multipurpose species that have additional uses are generally preferable because they give the alley farming system more flexibility. Ideally, trees and shrubs suitable for alley farming should meet the following criteria:
· establish easily,· grow rapidly,
· have a deep root system with few lateral branches near the surface,
· have a suitable branching pattern, including high branch and leaf productivity, both quantitatively (biomass production) and qualitatively (mulch quality and decomposition, etc.),
· regenerate readily after pruning,
· have good coppicing ability,
· provide useful by-products such as fuelwood, stakes, food,
· be free from pest and diseases, particularly those of crops grown in the alleys,
· the above qualities should not be impeded as the tree matures
Few tree species meet all of the above criteria and some have serious disadvantages that must be overcome. For example, Leucaena has slow early growth and its seedlings must be protected against weeds during early establishment; once established, however, the seedlings grow vigorously. Occasionally, it may be desirable to choose a species that is excellent for one specific purpose, for example, Acioa barteri, for its slow decomposing mulch, or the fast-growing Calliandra callothyrsus for its ability to produce large quantities of biomass within a short time.
When livestock production will be incorporated into an alley farming system, the tree or shrub must provide forage in addition to its other functions. Again, the legumes are preferred because of their high protein value. The following characteristics are desirable:
· high forage productivity that is unimpeded by maturity, (good juvenile - mature correlation),
· good feeding value and high palatability.
Again, the legumes are preferred because of their high protein value.
A species should grow well under the specific limitations of the site, such as drought, flooding, heavy winds, insect pests, or other hazards. Species should perform will in spite of a site's limiting climatic and soil factors. The ongoing AFNETA/NARS collaborative research program, and other research efforts, should eventually yield a good deal of information on the performance of numerous MPTs under alley farming management across a very broad spectrum of conditions in Africa. In the meantime, results of research to date permit several important generalizations to be made. These are presented in Table 2-1 and below.
Non-acid soils
· Leucaena leucocephala and Gliricidia sepium are the best performing hedgerow species for alley farming for the low altitude humid and subhumid tropics. Although optimum rainfall for good performance of these species has not been established, field observations have shown that a minimum annual rainfall of 1000 mm may be needed.· Other species with good potential for alley farming at low altitudes are Flemingia macrophylla, Cajanus cajan (pigeon pea), and Sesbania sesban. Cajanus and Sesbania hedgerows, however, may require frequent replanting.
· Woody species suited to lowland non-acid soils generally do not grow well in highland areas. Table 2-1 contains list of species tentatively identified for low, middle, and high altitudes.
Figure 2-1. Some characteristics of trees or shrubs suitable for alley farming.
Acid soils
· Acidic soils (pH lower than 5.0) may occur in areas with high rainfall. Results of observations at IITA's high rainfall station at Onne in southeastern Nigeria indicate that Acioa barteri, Flemingia macrophylla and Tephrosia candida do well on lowland acid soils. Additional research on acid-tolerant MPTs is needed. The value of indigenous species in this case cannot be overemphasized, indicating the need for natural forest explorations to find new and better-adapted species.
Table 2-1. Tentative list of suitable multipurpose tree and shrub species for alley farming systems in the humid and subhumid zone.
|
Environment |
Humid Zone |
Subhumid Zone |
|
Non-acid Soils |
|
|
|
Lowlands |
Leucaena leucocephala (1) |
Leucaena leucocephala (4) |
|
Middle Alt. |
Sesbania sesban |
Leucaena leucocephala (1) |
|
Highlands |
Albizia species |
Albizia species |
|
Acid Soils |
|
|
|
Lowlands |
Acioa barteri |
Cajanus cajan |
|
Middle Alt. |
Cassia floribunda (5) |
Cassia floribunda |
|
Highlands |
Albizia species |
Albizia species |
(1) Var. K8, K28, K636.
(2) Needs frequent replanting.
(3) Not a legume.
(4) Var. K636.
(5) Non-nodulating.
Figure 2-2. Pictorial guide to certain better known multipurpose tree and shrubs, showing goal potential for alley farming in tropical Africa. The appearance of most trees is altered under alley farming management.
HUMID ZONE
Leucaena leucocephala
Gliricidia sepium
Acioa barteri
SUBHUMID ZONE
Cajanus cajan
Acacia auriculiformis (Young plant)
Albizia lebbeck
SEMI-ARID ZONE
Acacia senegal
Acacia tortilis
Prosopis juliflora
HIGHLAND ZONE
Leucaena diversifolia
Cassia spectabilis (Young plant)
Erythrina poeppigiana
Insect Pest Threat to Leucaena
· The need for further selection and research on a wider spectrum of MPTs has taken on added importance with the threat posed to Leucaena by an insect pest. A sap-sucking psyllid, Heteropsylla cubana, has caused widespread devastation of the lowland Leucaena leucocephala in East Asia and the Pacific. The advance of this pest to the Indian continent has also been reported. It is thus essential that testing of tolerant or resistant Leucaena species such as Leucaena diversifolia and Leucaena pallida be taken up as a research priority.
2.2.1 Stages of Experimentation
2.2.2 Additional Guidelines for MPT Screening Experiments
In theory, the number of multipurpose tree and shrub species (MPTs) with potential for alley farming is high. For example, the number of potentially useful MPTs currently entered in the MPTs database at the International Council for Research in Agroforestry (ICRAF) stands at 1,600. Most of these MPTs have not been subjected to scientific study the world over. The task of comprehensive evaluation of MPTs for agroforestry development is large, presenting a major challenge to ICRAF and its partner institutions all over the world.
In practice, of course, alley farming researchers in Africa do not have to wait for the completion of such a comprehensive review. They are able to design manageable, effective MPT screening experiments by working with a limited number of promising species. The initial evaluation of MPTs should be carried out in three stages:
1. A list of promising MPTs is developed based on previous research worldwide experience with local MPTs, and local research priorities. The criteria for suitable alley farming MPTs should be applied (discussed in section 2.1). Both local and exotic species should be included on the list. In AFNETA/NARS research projects, a total of about 10 species and accessions is suggested as a manageable number.2. Field trials for continuous growth assessment are conducted. Continuous growth trials permit general evaluation of each species for adaptation to local conditions, relative growth performance, and freedom from pests and diseases.
3. In a separate set of field trials, each species is subjected to alley farming management. This permits evaluation of hedgerow establishment, biomass production, and pruning recovery.
The field trials (stages 2 and 3) may be conducted simultaneously for improved efficiency. In the AFNETA/NARS projects, experimental design is kept simple: the continuous growth and alley farming management trials both employ the Randomized Complete Block design with three or four replications. Details of the recommended AFNETA designs are given in a separate AFNETA manual.
The end result should be a short list of "best-bet" MPTs that are promising enough to merit further experimentation (e.g., spacing and fertilization trials, on-farm testing). If very few or no species perform satisfactorily, or if there is a need for MPT improvement, the experimentation process should be repeated with a new list of species and accessions.
The experimental design issues in species and provenance research are generally well known to researchers in agriculture and forestry. For example, comprehensive coverage is provided in Burley and Wood (1976). Six issues worth stressing in connection with screening MPTs for agroforestry development are:
1. In cases where the numbers of species and provenances are likely to be large, the simpler designs such as the Randomized Complete Block design may not be the most efficient. Incomplete Block Designs such as lattice designs could be more efficient in such experiments. Principles of experimental design are covered in Volume 2, Technical Paper 7.2. When screening mixtures of trees and shrubs, care should be taken to subdivide the species into near-homogenous sets with respect to their growth forms and rates. Such an arrangement will safeguard against undue competition for light in the later stages of field experiments.
3. The issues of plot size and shape should be given special consideration. Small rectangular plots (including single and two-row plots) are used in screening MPTs, instead of the traditional large, square plots. In extreme cases, experiments have five-tree, single-row plots.
4. As compared with the cultivars and provenances which are currently used in intensive forestry and agricultural production systems, the MPTs of potential value in agroforestry systems are at much lower levels of domestication. At these lower levels, great opportunities exist for exploiting within-species genetic variation. The traditional research path in forestry has been to screen for species and subsequently to screen for the best provenances within top priority species. This time-consuming path may not be necessary for MPT screening, because information on general growth performance of numerous species is now more readily available to researchers. Efforts should be made to combine both species and provenance screening in appropriately designed experiments.
5. For ease of comparison of data among scientists, it is important that measurements of trees and shrubs be standardized. A partial list of standard measurements is given in the Annex. Standardization becomes even more important in experiments which are established on a network basis.
6 . The Diagnosis and Design (D&D) methodology developed at ICRAF can assist in the selection and assessment of MPTs. D&D provide a rationalized approach for diagnosing land use system needs and designing suitable agroforestry interventions. See Volume 2, Paper 4, for information on D&D.
2.3.1 Nursery Operations
2.3.2 Acquisition of Seed from External Sources
Successful experimentation with MPT species depends on finding a reliable source for tree seeds and/or seedlings. Because MPT susceptibility to pests can be disastrous, it is always wise to use a wide genetic base. Where possible, use seeds from a variety of cultivars and parent trees.
In this section, brief mention is made of key factors affecting quality of seedlings obtained from nurseries and seeds obtained from external sources. Information on production of Leucaena and Gliricidia in on-station seed orchards is provided in the Appendices.
Not all alley farming research projects will need to establish their own nursery. In regions with more than 1000 mm rainfall, planting of trees can be timed such that establishment from direct seeding is satisfactory. In semi-arid regions, help to ensure adequate numbers of viable seedlings by protecting young trees from the relatively harsh environment . Another reason to establish nurseries would be to protect scarce germplasm; a nurseries can help to minimize wastage of seeds or cuttings.
For all seedlings raised for field experimentation, detailed information should be recorded on potting medium, fertilization, seed pre-treatment, use of inoculants, and use of fungicides and insecticides.
The overall goal of all nursery operations should be the production of vigorous seedlings raised as uniformly as possible for field experiments. Since MPT screening trails will be aimed at detecting small differences in growth performance at early stages, care must be taken to avoid differential treatment of seedlings in the nursery.
Unfortunately, this precaution is seldom observed. Instead, relatively large, healthy, vigorous stock of a particular species is outplanted with unhealthy, retarded, or spindly stock of another. It is no surprise that the species of good stock commonly shows superior initial development in the field. It is important to avoid this mistake in all AFNETA experiments involving screening and evaluation of MPT for continuous growth and/or alley farming studies.
As manuals and reports fully describe nursery operations, only important points are summarized briefly here. The recommendations are based on Briscoe (1990).
Nursery germination
The objectives of germination in the nursery phase include the following:
· evaluation of germination and seedling survival percentages on an operational scale,
· provision of suitable planting stock for field trials,
· evaluation of juvenile characteristics, and
· establishment of juvenile/mature correlations using mature characteristics acquired at a later date.
Seeds should be of known origin. Germination procedures should be kepts as uniform as possible for a particular species or provenance. Such procedures may include seed pre-treatment. Requirements and guidelines for pre-treatment are covered in Unit 3.
Containers and Beds
The date of sowing should be scheduled so as to allow the time necessary for the species to attain a suitable size by the planned date of planting. Most fast-growing species take three to six months to reach plantable size, but each nursery must determine its own rate of development for each species.
Various containers for sowing are commonly used. Currently, the most popular is a black polyethylene bag, approximately 10 × 15 cm when flat. The bag is perforated with 8 to 12 holes from the bottom up to half total depth. Plastic bags are popular because they are relatively cheap and convenient to use; however, the round shape encourages undesirable circling of the roots, and the drainage holes, although essential, permit the roots to emerge and enter the underlying soil.
To keep roots from penetrating into the soil, move the bags periodically to break off all escaped roots, set them on a sheet of plastic to prevent roots from entering the soil, or do both. Where rainfall and drainage conditions may cause saturation or flooding, avoid using such plastic sheets.
Beds and containers should be well-drained and usually kept above mean ground line to prevent waterlogging, improve aeration, and reduce root rot.
Seedling Care
Care of the seedlings (also called culture) is necessary from the time seed is sown until the planting stock is dispatched to the field. The small size of the plants and their concentration in a small area (10 to 400 per m2) makes care relatively economical and permits close supervision. Seedlings are most delicate during the first three months after germination.
It is important to ensure that only well documented seeds and other propagules are used in all experiments. Seeds obtained from commercial suppliers are often not good enough. While the ICRAF multipurpose trees and shrubs seed directory is very useful as a general guide, it is recommended that consultations be made with organizations which can supply well documented propagules for experiments. Such organizations include:
· National Tree Seed Centers
· National Gene Banks
· Regional Seed Centers
· CSIRO (Australia)
· DANIDA Forest Seed Center (Denmark)
· Oxford Forestry Institute (UK)
· Royal Botanic Gardens, Kew (UK)
· CAMCORE (USA and South America)
· CATIE (Costa Rica)
· NFTA (Hawaii)
The AFNETA secretariat, ICRAF, ILCA, and IITA can assist in the acquisition of seeds for alley farming trials in many cases.
When acquiring seeds, distinction must be made between unclassified seed, source-identified seed (seed stands), selected seed (known parents), and certified seed (seed orchards). In order to reduce storage requirements, every attempt should be made to synchronize time of seed acquisition with expected sowing dates. Furthermore, it must be emphasized that arrangements for seed and other propagule acquisition(s) should be made much in advance of the planned establishment of field experiments, often as much as one year in advance.
Many potentially useful MPTs are presently unknown to science. Valuable MPT germplasm remains to be collected and properly documented. This activity requires particularly urgent attention in tropical countries experiencing rapid rates of devegetation threatening total loss of some species and varieties. National, regional, and international research centers could accord high priority to this activity.
ICRAF and the International Board for Plant Genetic Resources (IBPGR) have recently initiated MPT germplasm collection and documentation projects in East and West Africa. Similar initiatives have been made in both francophone and anglophone West Africa. The International Livestock Centre for Africa (ILCA) maintains a germplasm collection of fodder trees and shrubs. IBPGR and the Royal Botanic Gardens, Kew, have published a valuable reference book on forage and browse plants for arid and semi-arid Africa (IBPGR, 1984).
However, much still remains to done in strengthening national institutions in the tropics for collection, documentation, and storage of MPT germplasm. Great gains could also be derived from breeding MPT for agroforestry development. This would required the initiation of well planned MPT germplasm improvement programs. ICRAF is currently developing cooperative breeding strategies with national research systems.
All answers can be found in the text and figures of Unit 2.
1. a.) List eight of the general criteria for selecting a suitable tree or shrub species for an alley farming system:
1. ________________________
2. ________________________
3. ________________________
4. ________________________
5. ________________________
6. ________________________
7. ________________________
8. ________________________
b.) List two additional criteria for species that will be used for livestock forage:
1. ________________________
2. ________________________
2. For the following MPT species, indicate the suitable environments. Use the coding: A for acid soils or NA for non-acid soils; H for humid zone or SH for sub-humid; L for low-altitudes, M for middle altitudes, or H for highlands. More than one environment may be possible for some species.
|
Species Name |
Soil Type(s) |
Climate(s) |
Altitude(s) |
|
Leucaena leucocephala |
NA |
H |
L, M |
|
Gliricidia sepium |
|
|
|
|
Sesbania sesban |
|
|
|
|
Cajanus cajan |
|
|
|
|
Albizia spp. |
|
|
|
|
Acacia auriculiformis |
|
|
|
|
Flemingia macrophylla |
|
|
|
|
Acioa barteri |
|
|
|
|
Cassia floribunda |
|
|
|
3. Provide a brief description of each of the following experimental steps in MPT evaluation:
i) Development of MPT list: _______________________
______________________________________________
______________________________________________ii) Continuous growth assessment: __________________
______________________________________________
______________________________________________iii) Alley farming management assessment: ___________
______________________________________________
______________________________________________
4. The following five concern experimental guidelines for MPT screening and evaluation. Circle T for true statements or F for false ones:
|
i) When the number of species to be screened is large, the Randomized Complete Block designs are always the most efficient. |
T |
F |
|
ii) Small rectangular plots are used in MPT screening. |
T |
F |
|
iii) MPT provenances are at a high level of domestication as compared to cultivars used in agricultural systems. |
T |
F |
|
iv) ICRAF's Diagnosis and Design (D&D) methodology is not relevant for MPT screening because it operates at a macro level. |
T |
F |
|
v) The evaluation of MPTs is not important for agroforestry research since ICRAF has already evaluated 1,600 MPTs. |
T |
F |
5. Provide brief answers to the following questions concerning nursery operations:
i) State the overall goal of nursery operations.
ii) Name several specific objectives of nursery operations.
iii) Describe the use of plastic bags as containers for sowing.
6. a.) List five organizations that you might wish to contact when acquiring seeds for MPT experiments.
1. ________________________
2. ________________________
3. ________________________
4. ________________________
5. ________________________
b.) The seed used for agroforestry interventions could be of four types. One type is mentioned below. Give the name of the other three types:
1. unclassified seed
2. ________________________
3. ________________________
4. ________________________
Briscoe, C.B. 1990. Field Trials Manual for Multipurpose Tree Species. Second edition. Winrock International Institute for Agricultural Development, Morrilton, Arkansas, USA.
Burley, J., and Wood P.J. 1976. A manual on species and provenance research with particular reference to the tropics. Oxford, England: Commonwealth Forestry Institute.
IBPGR (International Board for Plant Genetic Resources). 1984. Forage and browse plants for arid and semi-arid Africa. Rome: IBPGR.
International Development Research Centre. 1983. Leucaena Research in the Asia-Pacific Region: Proceedings of a workshop held Singapore, 23-26 November 1982. IDRC-211E. Ottawa, Canada: IDRC.
Kang, B.T., G.F. Wilson, and T.L. Lawson. 1984. Alley cropping: a stable alternative to shifting cultivation. Ibadan, Nigeria: IITA
Owino, F. 1990. Small-scale farmer oriented strategy for evaluation and improvement of multipurpose trees. In: C. Haugen, L. Medema and C. Lantican (eds.) Multipurpose Tree Species Research for Small Farms: Strategies and Methods. Proc. of International Conference held 20-23 November 1989, Jakarta, Indonesia. Forestry/Fuelwood Research and Development Project (F/FRED) and IDRC. pp. 167-170.
Reynolds, L., and A.N. Atta-Krah. 1989. Alley farming with Livestock. In B.T. Kang and L. Reynolds (eds). Alley farming in the humid and subhumid tropics. pp. 27-36. Ottawa, Canada: IDRC.
