multipurpose tree species research for small farms: strategies ... - part

taking into account possible effects on companion
crops. Such factors as tree-crop competition above
and below ground, weediness, etc. should be
considered. Finally, MPTS adaptation to the
intended management by the farmer deserves
special mention. Characteristics such as ready
coppicing, easy rooting and lack of thorns become
additionally beneficial when MPTS are grown on
farms.
Several comprehensive databases already exist
which can provide useful guidance on the selection
of MPTS for intensive screening in different parts
of the world. However, in order to derive
maximum benefit from such databases, the user
must clearly define the required adaptation
characteristics (von Carlowitz 1987).
Improvement of MPTS Yields
In all cases, large increases in MPTS yields can
be achieved relatively inexpensively through
improved husbandiy such as good nursery
practices including inoculation with appropriate
rhizobium/mycorrhiza, weeding, pruning, thinning,
coppicing, and rejuvenation. In the initial phases,
emphasis should be on such MPTS management
research. In cases where breeding programs are
justified, a sequential approach starting with
provenance screening and leading to individual
tree selection and subsequent breeding should be
adopted. It is important, however, to realize that
breeding research is both long-term and expensive
and should only be attempted with prior
justification and the design of technically sound
breeding plans.
Agroforestry Technology-Specific
Experimentation
Several recognized agroforestry technologies
are hedgerow intercropping (alley farming), trees
on contour/bund strips, fodder banks, scattered
trees on pasture/cropland, improved fallow,
multi-strata arrangements, taungya, windbreak, live
fencing, etc. While adaptation factors already
discussed will apply to MPTS intended for such
specific techno ogies, there may be a need to
consider additional technology-specific factors
such as the selection of appropriate crown
ideotypes; plasticity in crown morphology; and
possil)e use of MPTS species, variety and clone
mixtures.
MPTS Germplasm Supply and Exchange
It is important to ensure that only well
documented MPTS germplasm be used in all
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experiments and planting programs.
Distinctions between unclassified seed,
source-identified seed (seed stands), selected
seed (parents known) and certified seed (seed
orchards) should be maintained. Regulations of
the International Seed Testing Association
(ISTA 1976) should apply in all cases of seed
exchange and in some cases, the Organization
for Economic Cooperation and Development
regulations may also apply (OECD 1974).
Experimental Design Implications
It is to be expected that research on MPTS
evaluation and improvement would require
special experimentaldesign considerations. For
example, large numbers of entries of species
and provenances, widely replicated oh-farm
trials, and testing for response to soil
amendments may all call .for special designs.
The following experimental design suggestions
are worth considering for MPTS evaluation and
improvement research:
- for testing large numbers of species/
provenances the use of incomplete block
designs such as rectangular and cubic
lattices, or alpha-designs;
- for combiniii replicated and nonrepiLted
entries the use of designs such as
augmented design, or blocks in replication
designs;
- for testing the response of several
provenances to different fertilizer levels the
use of designs such as the split-plot design,
or the randomized complete block design;
- experiments which involve the estimation
of genetic parameters will call for the union
of mating designs and field designs, for
example: partial diallel mating design and
incomplete block field design, or test
cross-mating design and randomized block
field design; and
-with regard to plot size and shape,the need
will arise to move away from the traditional
large square plots to smaller rectangular
plots, towards double and single row plots and
even single tree plots.