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Areas where the practice is relevant

In most situations, it is feasible to have trees in cropland but it is
particularly relevant in areas with shade-tolerant crops like coffee or
beans. There are limited possibilities in irrigation schemes. The
benefits to be obtained from the trees, in terms of soil fertility and soil
structure, are normally more clearly seen in areas where little or no
inorganic fertilizer is used.

Establishment and spacing

Many methods of tree propagation are possible. Which one is chosen
will depend largely on which species are desired. Protection of wildings
is a good option which should always be considered before
recommending nursery production of seedlings. Direct sowing may be
feasible if trees are to be grown in lines, otherwise it is difficult to
know where the seeds will germinate.

A population of up to 100 trees per hectare, corresponding to a
spacing of 10 m x 10 m, is appropriate in high-potential areas if the
crop is light demanding, e.g. maize. If trees are to be planted, a better
option than square spacing may be to plant trees in lines with close
spacing in the rows and a wider between-row space resulting in a
similar overall density. A spacing of 5 m within rows and 20 m
between rows can be suggested. The tree and crop species and
management methods chosen are factors that will influence decisions
on spacing. With shade-tolerant crops a greater density of trees can be
tolerated, as can a certain loss in yield if the tree products are in high
demand. If the trees are of a species which has very light shade, e.g.
some Acacia, more trees can be grown per hectare, and the same
applies if the trees will be intensively pollarded. Root pruning can also
be done to minimize competition.

In ASAL areas, lower tree populations are recommended, e.g. 40-70
trees per hectare, corresponding to a square spacing of 12-15 m. If
trees in cropland are to be established from seedlings, a greater
number than that ultimately required need to be planted since there
will always be some mortality.

Management aspects

Tree-management practices will depend on the tree and crop species
concerned and the need for tree products. With a light-demanding
crop, pollarding or pruning is essential, but this does not apply to
shade-tolerant crops or to trees that naturally only have light shade.
Species that need and tolerate pollarding are Albizia spp.,Balanites
aegyptiaca, Bauhinia spp., Bridelia micrantha, Cassia siamea,
Commiphora eminii subsp. zimmermanni, Cordia abyssinica, Croton
macrostachyus, Ficus sycamorus, Grevillea robusta, Markhamia lutea,
Morus spp., Piliostigma thonningii, Spathodea nilotica, Syzygium spp.