Growing Food: A Guide to Food Production

Alley Cropping—Method
Rows of trees are planted 4–8 metres apart. During the main growing season, which
usually coincides with the main rainy season, they are pruned back, and often not
allowed to reach their normal full height. The prunings of branches, leaves and twigs
can be used as either fodder, mulch, or ploughed in.
When the trees reach the size required they are cut down, providing fuelwood, poles
and stakes.
The foliage makes a fairly good fertiliser. For example, 15–20 MT/ha per year of
leaves and twigs can be produced in warm, humid regions. This can be either fed to
animals, used as a surface mulch, or ploughed or dug back into the soil—in which case
providing up to about 160 kg nitrogen, 15 kg phosphate and 150 kg potash per hectare.
In more arid regions, more drought resistant or locally adapted tree species can be
used, planted at wider spacings.
Alley cropping can provide a useful alternative to a fallow period, allowing farmers
to continuously cultivate the same area of land. There is also the additional advantage of
reducing or eliminating the need for chemical fertilisers.

A green manure crop is grown to be ploughed under into the soil when the plants are
young and green ie succulent. Sometimes the green manure crop is cut down or pulled
up and then left on the soil surface as a mulch; after some time the plants rot and are
taken down into the soil by termites, earthworms etc. There are both positive and
negative aspects of green manure, described below.

Positive Aspects of Green Manure

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  systems such as alfalfa (lucerne);

  
  


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  diseases of the roots when grown after a green manure crop.

  
  

Negative Aspects of Green Manure

• Volunteer green plants can be a nuisance in the following crop, so must be
  effectively removed by either a stale-seed bed and/or cultivations;


• Land is occupied which is then not able to grow a cash crop or a food crop;


• Only a little nitrogen will be added to the soil if the plants are old and fibrous,
  although the soil’s organic matter content will still increase;


• The soil’s organic matter content will only increase a little if the plants are young,
  though the soil’s nitrogen content will be increased;


• Good ploughing techniques, which need a high investment in machinery, fuel
  and/or labour, are needed to thoroughly incorporate the plants into the soil.

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The soil is enriched with nitrogen and other plant nutrients;

The organic matter of the soil is increased;

Leaching of plant nutrients during periods between regular crops is reduced;

Soil erosion is reduced;

Sometimes crops such as sweet potato and cotton are less damaged by fungal

Nutrients are brought up from the subsoil by green manure crops with deep root

GROWING FOOD – THE FOOD PRODUCTION HANDBOOK

d Green Manure