a lesser role, include broad beans protecting lettuce, and sunflowers protecting green
peppers.
In hot climates a wide range of plant species are used, including pigeon peas,
bananas, Crotalaria spp., Tephrosia spp.(may also deter rodents, due to the rotenone it
contains), papaya, cassava and tree cassavas, tannias (Xanthosoma spp.), dasheens and
eddoes—the so-called “cocoyams” (Colocasia spp.) and Albizia spp.
H Farming Systems
Rotation is the name given to a cropping system in which different kinds of crops are
grown in more or less a fixed sequence on the same land. Rotations are of the greatest
benefit when crops are grown as pure stands and are rarely used when crops are
intercropped. One basic form of rotation is known as slash-and-burn (or swidden), used
in many simple agricultural systems.
The Benefits of Rotation
- reduces the accumulation of disease and insects, such as Club Root in brassicas,
Brown Streak virus in cassava, Take-all in cereals, Eelworm (nematodes) etc.; - reduces the accumulation of weeds;
- maintains or improves soil fertility;
- distributes labour requirements (for cultivations, planting, harvesting etc.) more
evenly through the year, reducing labour, financial (paying for everything at once)
and storage bottlenecks; - avoids creating a sub-surface pan by not cultivating the soil to the same depth every
year; - makes use of a greater depth of the topsoil because different crops occupy and use
different levels of the soil profile; - ensures that fertilisers are used to the best advantage.
called bare fallow when the soil is left unplanted, or grass fallow if grass is planted.
Provided that weed growth is controlled, a fallow period helps to naturally reconstitute
the soil’s fertility.
Rotations should be flexible so that new crops can be introduced and other small
changes made according to changes in needs, markets etc.
In many parts of the world cereals are grown almost continuously, with break crops
of, say, legumes or potatoes occasionally grown to rest the land. In these situations,
fertiliser has replaced crop rotations as the principal means of maintaining soil fertility.
This type of farming system depends heavily on chemicals, including fertilisers, in order
to maintain yields. The long term negative impact of such activity on a global scale is
clearly unsustainable and other means, which include sensible crop rotations, should be
adopted whenever practical.
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Sometimes a part of the farm or garden is left fallow as part of the crop rotation. This is